Electronic cigarette awareness and use has been increasing rapidly. E-cigarette brands have utilized social networking sites to promote their products, as the growth of the e-cigarette industry has paralleled that of Web 2.0. These online platforms are cost-effective and have unique technological features and user demographics that can be attractive for selective marketing. The popularity of multiple sites also poses a risk of exposure to social networks where e-cigarette brands might not have a presence.To examine the marketing strategies of leading e-cigarette brands on multiple social networking sites, and to identify how affordances of the digital media are used to their advantage. Secondary analyses include determining if any brands are benefitting from site demographics, and exploring cross-site diffusion of marketing content through multi-site users.We collected data from two e-cigarette brands from four social networking sites over approximately 2.5 years. Content analysis is used to search for themes, population targeting, marketing strategies, and cross-site spread of messages.Twitter appeared to be the most frequently used social networking site for interacting directly with product users. Facebook supported informational broadcasts, such as announcements regarding political legislation. E-cigarette brands also differed in their approaches to their users, from informal conversations to direct product marketing.E-cigarette makers use different strategies to market their product and engage their users. There was no evidence of direct targeting of vulnerable populations, but the affordances of the different sites are exploited to best broadcast context-specific messages. We developed a viable method to study cross-site diffusion, although additional refinement is needed to account for how different types of digital media are used. Electronic cigarettes, also known as e-cigs or e-cigarettes, are battery-operated products that deliver nicotine by turning it into an aerosol that is inhaled by the user . Today, The Internet represents a medium that offers an opportunity for e-cigarette brands to expand their audience reach. However, this unregulated domain can also be a cause for concern. Several studies have suggested that e-cigarettes can be a viable method to quit smoking ,8, althoThere are countless social networking sites with unique technological features and user demographics that can be attractive for selective marketing. The growth of e-cigarettes occurred as social media and other Web 2.0 sites became an important platform for commercial advertising. It is no surprise that e-cigarette brands, especially smaller ones that have no affiliation with larger tobacco companies and no sizable advertising budgets, took to social media to market their products. Recent e-cigarette studies have typically examined product health effects eg, ,11). Few. Few11])Social networking sites such as Facebook or Twitter are inherently built to support social networks. Whether posting messages to a Facebook wall or sending updates on Twitter, interactions between users are the foundation of all activity on these sites. The distinction in how users of different sites interact depends on the digital media affordances the sites focus on. Affordances are the actionable relationships between an actor and an aspect of the environment that offer the actor the potential for action . This coWeb 2.0 tools provide an abundance of ways to interact, and social networking sites use these tools to great advantage. Kietzmann and colleagues’ well-cited work  describeSocial networking sites also have varying user demographics. A Pew 2013 report on social media  revealedThe unique affordances and demographics of each social networking site, especially how they are used by online marketers, is the focus of this paper. In this study, we explore the possibility of e-cigarette brands potentially taking advantage of social networking site demographics and targeting vulnerable sub-populations, such as underage youth. We will also see if and how e-cigarette brands utilize different digital media in their marketing strategies. As such, we ask two primary research questions: (1) Are e-cigarette brands exploiting the affordances of each site in their marketing? And (2) Are e-cigarette brands targeting sub-populations  by taking advantage of the demographic differences of different social networking sites?We also study how different social networking sites potentially interact with one another, for example when posting a tweet to one’s Facebook wall. To our knowledge, no studies have examined the diffusion of information across multiple social networking sites. However, Pew’s latest 2014) survey indicates that 52% of online adults use two or more social media sites, rising from 42% in 2013 [14 surveyThis study examined four social networking sites and two e-cigarette brands that maintain a presence in each site for marketing and advertising. Data from each of the four sites were collected from October 20, 2012 through April 14, 2015. The sites were chosen based on popularity (from current eBizMBA.com rankings), differences in the affordances of the platform’s technologies, accessibility of data, and user demographics . The finData were collected by establishing connections to each social networking site via the platform’s Application Programming Interface (API). An API allows external software to make requests for data and post information and to perform tasks that are made allowable by the service. Custom software was written to communicate with the API of each of the four social networking sites. The 3 main objectives were to:Gather any available long-term historical data, primarily any content posted by Blu or V2 and related information, such as users who shared or commented on such posts. This process was conducted a single time.Gather recent data as it was being posted. This task was the same as objective 1 but only collected recent data (about 3-4 days old), as many social networking sites limit the amount of data that can be requested. This process was executed every 3-4 days.Gather related data unique to each site, as their methods of online interactions are different. For example, the data collection included retweets on Twitter, comments on Facebook, shares on Google+, likes on Instagram, and so on. Users who performed these actions were also recorded, along with any available demographic information. This process was executed every 3-4 days, in parallel to objective 2.All data collected were publicly available since any person with an Internet connection is able to view data that has been retrieved through this mining software. The primary data being collected were content posted on the social networking sites. Demographic information came from users’ self-reported data in the site and was only collected if the user had made it public. Personal information such as emails, phone numbers, or addresses was not collected. This study was reviewed by the University of Southern California Health Sciences Institutional Review Board, which found that it does not qualify as Human Subjects Research and thus is not subject to the requirements of 45 CFR 46.102.We analyzed the content posted on each of the social networking sites and parsed data according to e-cigarette brand and social networking site. Our primary method of analysis was Term Frequency-Inverse Document Frequency (TF-IDF) weighting a commonly used statistical method in information retrieval to calculate word relevance for a document across a large corpus . TF-IDF We conducted an exploratory network analysis of users who had posted content or interacted with one of the e-cigarette brands in one of the four social networking sites. To examine the possibility of cross-platform diffusion of e-cigarette messages, we ran the test in two steps. First, we identified usernames from each site that had an identical matching username in another site. While this tactic did not guarantee certainty that the different users are the same, it provided a starting approximation. We then analyzed content posted by the identified users in the different sites. Using the names that were found in multiple sites, we confirmed it was in fact the same person via identical profile pictures or personal descriptions, and then examined whether their activity on one site  resulted in sharing the content on another site .ecig is used by both companies in all four sites, and thus has a count of 8 for number of cases, also called an 8-case scenario. In another example, the term RT is used by both companies but only on Twitter, and thus has a count of 2 for number of cases.BLUCRM or PWD in In contrast, a 1-case scenario shows words that are only found in a single brand/site case , with the majority of interactions aimed at connecting followers to their home website. V2 did not have any notable 1-case discriminating content on Facebook, Google+, or Instagram. On Twitter, V2’s content remained focused on website advertisement, although interactions with users were also included. Blu had unique content in both Twitter (66%) and Facebook (28%). Unlike V2, Blu’s use of Twitter focused on interacting with users on a wide range of topics, from product support to general conversation. On Facebook, Blu’s posts centered on political activities . Blu had no significant unique activity on Google+ or Instagram. Here are content examples from several of the top categories:(Blu/Twitter/User interaction) @anonymized_username but that doesn't say, "I'm either really embarrassed or really proud to wear this at Christmas".(Blu/Twitter/Event info) We've seriously had Fun Fun Fun giving out these @funfunfunfest tix #FFFfest Did you see where a local Wisconsin legislature wants to pass a bill ensuring e-cigs are allowed to be used in public? Hit LIKE if you support this!(V2/Twitter/Website) If you want to try some NEW flavors on your V2 battery, check out our clearance section!(V2/Twitter/User interaction) @anonymized_username Nice V2 stash! Happy vaping! :)RT in Twitter or href in Google+) to focus on terms that are topic-specific . Without the IDF discriminator or site-specific terms, these data provide a broad view of all general-purpose terms that are used in each site, according to each brand. We were able to see what themes and concepts the e-cigarette brands were broadcasting to their followers, regardless of which site they were using. The results are shown in A second follow up was conducted to investigate the terms in each brand/site with the highest raw frequency by removing any discriminating factor based on IDF. In addition, we filtered out site-specific terms  likes/plusoners, which includes a single supporting action that is collectively aggregated, and 3) resharers/retweets, which are actions where users repost existing content. These actions were not fully inclusive, as we only collected those that were relevant to this study.RT has the highest TF-IDF score and is found in only two case scenarios (Blu/Twitter and V2/Twitter). However, this is not unexpected, as it is only used in Twitter as shorthand for “retweet”. Similarly, terms such as href or nofollow are webpage-coding syntax used only in Google+ to create links to external sites, usually to images or videos. Interestingly, Instagram is the only site where coding terms are not used, another artifact of the available technology. As an image-based platform, there would be no need for text to contain any additional image links for each Instagram post. Other types of links seen in Facebook or Google+ were not seen in Instagram captions. Overall, the n-case results suggest that properties inherent to specific platforms can dictate the types of discriminating content found.The 1-case data provides valuable information in determining some of the most discriminating terms used by each e-cigarette brand, for the different social networking sites. It also reveals early evidence of how the two e-cigarette brands differ in their social media marketing strategies, with V2 focusing on marketing products on their website and Blu using Twitter for user interactions and Facebook for political activity information. The 163 terms were able to show that specific combinations, specifically Blu/Twitter, Blu/Facebook, and V2/Twitter, were being utilized by each brand for a particular type of marketing. However, the limited data—only 163 terms—does not provide enough information for deeper investigations. Therefore, we viewed the data through several other lenses. First, we examined the n-case data to include all possible terms . In manythanks, customer, and help in Twitter were indicative of interactions with their followers. The only political term, ward , was found only in Facebook. Interestingly, we saw a theme across Blu’s social networking site presence, containing the terms blunation and blufreedom in Google+, Instagram, and Twitter. Blu’s social media strategy appears to focus more on community and lifestyle, contrasting sharply with V2’s efforts to market products and direct users to their website. Blu’s efforts are more engaging than V2, possibly leading to more conversations and additional activities across the sites. We continued to broaden our view by removing the discriminating IDF and also filtering out technology-specific terms . These rThe cross-platform network analysis found several meaningful results . First, The content analysis of cross-platform posts yielded no results where activity from a user on one site led to sharing that message on a different site. While our methods were sound, we found several limitations to consider. When we searched for identical content between Instagram and another site, either Twitter or Facebook, we found that an image-based post would be difficult to forward to another site; the user would need to save the image and repost it, otherwise the caption text would not make sense out of context. Conversely, a message on Twitter without an image would not be posted on Instagram. Also, it is important to consider that the nature of one’s network of friends on each site might be distinct. Different sites might be used to develop and maintain different relationships . People While not directly related to our research questions, we were also able to observe some of the consequences of each brand’s marketing strategy. We compared the available interactions that users could have with each e-cigarette brand for the four websites; these included Facebook’s comments and likes, Google+’s plusoners and resharers, Instagram’s comments and likes, and Twitter’s retweets. In every case, Blu’s followers always had higher percentages of interactions see . This suIn addressing the first research question—Are e-cigarette brands exploiting the affordances of each site in their marketing?—we found evidence that Blu and V2 were using the sites in different ways, likely utilizing the affordances made available. The methods by which each brand interacted with its audience, advertised products, or relayed information aligned with the affordances of each platform. We could see Blu’s usage of Twitter as a medium to interact with its followers, frequently mentioning users by name, and directly conversing with them. Twitter’s @user_mention function, and an interface that allows users to immediately see Blu’s interactions with them, all support an interactive environment. Facebook’s “wall” feature offers a different format, in which users immediately see all other posts connected to a single parent discussion message. This affords a system whereby mass broadcasting is effective, reflected in the high number of political announcements and news events posted, with almost no direct user interaction. Kietzmann et al’s  view of In addressing the second research question—Are e-cigarette brands targeting sub-populations  by taking advantage of the demographic differences of different social networking sites?—we found no data suggesting direct targeting of sub-populations based on social networking site. The results of the 1-case view found it was likely that some of the sites were being used in different ways, but not in a manner consistent with focusing on any specific demographics. We followed up by analyzing the data from each site during specific holidays that might show a favoring of announcements or advertisements for one site over another and combined this information with the trends in different demographics reported by Pew on each of the sites . For exaIn addressing the third research question—Are there identifiable instances of users and information crossing different social networking sites?—we found a small percentage of users that had identical screen names on multiple sites, with the highest percentage being from Instagram/Twitter (128). These numbers differed from Pew’s report that multi-site users tended to use Facebook with another platform , althougThe purpose of this study was to examine the marketing strategies of leading e-cigarette brands on multiple social networking sites. We found that the two brands, Blu and V2, utilize different methods in how they interact with their customers. While Blu tends to be more conversational, V2’s focus is to direct people to their website. We did not find any evidence that either brand targets vulnerable populations in their strategies. However, we are able to see that Blu harnesses the affordances of different sites to conduct different types of marketing to their customer base. Our results demonstrate that a content analysis of multiple social networking sites can serve to identify how companies or brands can vary their marketing strategies based on the available technologies. We plan on expanding the foundation of this methodology to further understand potential diffusion of information across multiple sites.There are several limitations in this study. Primarily, we focused on only two e-cigarette brands. While their dominant online presence made them attractive candidates, we are also interested in following up with additional brands. Similarly, we only chose four social networking sites. Other social networking sites such as Pinterest, Tumblr, and LinkedIn were considered but were not included due to various limitations. We also did not interview any of the users in the study for specific reactions to or comments on the messages by the e-cigarette brands. Presenting the user side and experience would help provide additional context to the media messages. However, two of the authors are involved in a parallel project that, informed by some of the results of this pilot, will involve such interviews. Relatedly, we limited our content to publicly available data. While this affords easy access since all of the text or images posted can be viewed by anyone online, we do not know the impact on the larger online audience, which includes users that restrict access to their accounts. Therefore, the ability to generalize the results should be limited to public user accounts. Lastly, our content analysis focused on individual terms and we did not develop a synonym set of conceptually equivalent themes prior to the analysis. While this allows for a cleaner analysis, it risks over-representation of certain concepts.We strongly believe cross-platform studies will be a vital area of research in the future. There are apps available that allow users to streamline their post activity by broadcasting content, whether text, image, or other media, to multiple social networking sites at once . New social networking sites are also continuing to be developed, especially as technology provides new opportunities in other hardware, such as mobile phones or wearable devices. A fast-paced arena makes single-platform studies very narrow and difficult to generalize, as more of the population continues using multiple social networking sites . Additio


We recently reported a relationship between plasma levels of cystatin C and incidence of the metabolic syndrome (MetS) among the first 2,369 subjects who participated in the re-examination study of the population-based Malmö and Diet Cancer Cardiovascular cohort (MDC-CC-re-exam). In this study we aimed to replicate these results and also investigate if cystatin C was causally associated with MetS and diabetes.We estimated the effect size of the strongest GWAS derived cystatin C SNP  on plasma cystatin C in the now completed MDC-CC-re-exam  and thereafter examined the association between plasma cystatin C (403 cases of diabetes and 2665 controls) as well as rs13038305 (235 cases and 2425 controls) with incident diabetes. The association of rs13038305 and incident MetS (511 cases of MetS and 1980 controls) was similarly investigated in the whole MDC-CC-re-exam. We also attempted to replicate our previously shown association of cystatin C with incident MetS in subjects from the MDC-CC-re-exam (147 cases and 711 controls) that were not included in our previous report.-28) in age and sex adjusted analysis. Cystatin C in plasma was not associated with incident diabetes after adjustment for known diabetes risk factors (OR per 1 SD increment 0.99 (0.86–1.13), p = 0.842). In the replication cohort of MDC-CC-re-exam, the OR (95% CI) for incident MetS in subjects belonging to quartiles 1, 2, 3 and 4 of plasma cystatin C levels was 1.00 (reference), 1.21 (0.70–2.07), 1.62 (0.95–2.78) and 1.72 (1.01–2.93) (ptrend = 0.026) in age and sex adjusted analysis. In the entire MDC-CC-re-exam the odds ratio for incident MetS and diabetes per copy of the major rs13038305 allele was 1.13, (0.95–1.34), p = 0.160 and 1.07, 95% CI 0.89–1.30, p = 0.478, respectively.In the entire MDC-CC-re-exam, each copy of the major allele of rs13038305 was associated with approximately 0.30 standard deviation (SD) higher plasma concentration of cystatin C (β = 0.33, p = 4.2EWe were able to replicate our previously shown association between high levels of cystatin C and increased risk of future development of MetS. However, a causal involvement of cystatin C in the etiology of MetS or diabetes seems unlikely since genetic elevation of plasma cystatin C was not significantly related to incidence of these diseases. Cystatin C, an established sensitive marker of glomerular filtration , has alsIn this study we performed a re-examination of the population-based Malmö Diet and Cancer (MDC) study cardiovascular cohort (MDC-CC) 17 years after the baseline examination (MDC-CC-re-exam), and tested the hypothesis that a high baseline plasma level of cystatin C was associated with the development of the MetS and diabetes during long-term follow-up. To test whether any association between cystatin C and the MetS was driven by any individual components of MetS, baseline plasma level of cystatin C was related to the incidence of each of the five different components. Furthermore, since genome-wide association studies (GWAS) for genetic determinants of cystatin C have identified the strongest signal of the genome associating with variation of plasma concentration of cystatin C at the cystatin C locus on chromosome 20, represented by the single nucleotide polymorphism (SNP) rs13038305 , we set The MDC study is a population-based study that enrolled 28,449 individuals between 1991 and 1996 . During Of the 967 subjects (MDC-CC-re-examination-replication-cohort), 109 subjects had prevalent MetS at the baseline examination, resulting in a total of 858 subjects (147 cases and 711 controls) for the analysis of incident MetS. In analyses of the incidence of the five subcomponents of the MetS, patients with of each of the five separate MetS criteria at the baseline examination were excluded separately, resulting in 878 subjects (285 cases and 593 controls) with complete data for the analysis of incident large waist circumference , 745 subjects (82 cases and 663 controls) for reduced HDL levels, 807 subjects (25 cases and 782 controls) for elevated TG levels, 927 subjects (295 cases and 632 controls) for elevated glucose levels and only 350 subjects (169 cases and 181 controls) for incidence of elevated blood pressure  criteria at the baseline examination). The mean follow-up time for all these subgroups was 18±1 years.The whole MDC-CC re-examination cohort (re-examined from January 2007 to January 2012) consisted of 3,734 subjects, (mean follow-up time was 17±1 years)  and, of Since we had not previously examined plasma cystatin C′s association with incident and prevalent diabetes, this cohort of 3,151 subjects was used for the study of such possible associations. Of the 3,151 subjects, 83 had prevalent diabetes at the baseline examination, resulting in a total of 3,068 subjects  for the analysis of incident diabetes. The mean follow-up time was 17±1 years. We also investigated plasma cystatin C association with incident MetS in the entire MDC-re-examination cohort excluding patients with prevalent MetS at baseline (n = 442), leaving subjects 2709 subjects (562 incident MetS cases and 2147 controls). The mean follow-up time was 17±1 years. rs13038305 was successfully genotyped in 2,900 of these subjects with full data of all covariates. Of these 409 had prevalent MetS at baseline leaving 2491 subjects (511 cases and 1980 controls) for the study of the major allele of rs13038305 association with incident MetS. The mean follow-up time was 17±1 years. Finally of the 2,900 successfully genotyped subjects with full data of all covariates, 79 had prevalent diabetes at baseline leaving 2821 subjects (366 cases and 2455 controls) for the study the major allele of rs13038305 association of incident diabetes with a mean follow up time of 17±1 years. All participants provided written informed consent, and the ethical committee at Lund University, Lund, Sweden approved the study.® automatic device. We calculated body mass index (BMI) as weight in kilograms divided by the square of the height in meters. Hypertension was defined as SBP ≥140 mmHg or diastolic blood pressure ≥90 mmHg, or use of AHT. The examination protocol performed by a trained research assistant included measurement of maximal waist circumference, fasting plasma glucose (FPG), fasting plasma insulin, fasting TGs, cholesterol, low density lipoprotein (LDL) cholesterol and high density lipoprotein (HDL). Medical history and current medication were retrieved by a self-administered questionnaire.Clinical characteristics of the MDC-CC-re-examination-replication-cohort at the baseline examination are shown in All analyses in plasma and whole blood were performed using overnight fasting samples. Analyses of fasting plasma lipids, FBG (baseline examination) and FPG (re-examination) were carried out at the Department of Clinical Chemistry, Skåne University Hospital in Malmö, which is part of a national standardization and quality control system. Levels of plasma cystatin C were measured using a particle-enhanced immunonephelometric assay  and presented in mg/L. The assay has an intraindividual coefficient of variation of 7.7% percent. The range of detection of the assay is 0.195 to 7.330 mg per liter, with the reference range for young, healthy persons reported as 0.53 to 0.95 mg per liter. eGFR was assessed with the formulae of Cockroft-Gault creatinine clearance (mL/min/1.73 m2) = (140-age) x weight in kg x 1.23 / P-creatinine  (CG) .® Assay by Design primers and probes, with a real-time PCR assay using the ViiA7 equipment  according to the manufacturer’s instructions ..14].In a recently published paper by Shlipak (senior author) in 2014, where genetically lowered cystatin C  was tested for possible associations with incident CVD in a population of 14,645 individuals, no significant associations were seen for incident CVD, OR, (95% CI), 0.98 (0.92–1.06), p = 0.7 nor total mortality 0.98 (0.92–1.03), p = 0.4 arguing against a direct cystatin C mediated effect on CVD/mortality-risk . In addiThere are however studies that indicates that rs13038305 elevate plasma cystatin C independetly of renal function and other CVD and diabetes risk factors  and one Our study is to the best of our knowledge the first to examine the effects of genetic elevated cystatin C  on incident diabetes and MetS. Here rs13038305 showed no significant associations with diabetes nor MetS development, and these data, together with the findings by Shlipak  and Sven2 = 0.142), which limits the causal estimations of cystatin C, however this is to be compared with the work by Shlipak (senior author) in which each copy of the minor T allele of rs13038305 was associated with 6% lower cystatin C levels (P = 4.1×10−113) [Strengths and limitations of this study should be considered. We included a large population sample and the definition of new-onset diabetes and MetS was based on clinical re-examination. Through clinical re-examination we were able to retrieve the great majority of incident cases of diabetes and MetS. However, we were limited because rs13038305 explained only about 14 percentage of cystatin C variation (r×10−113) . Of noteIn conclusion, our findings show that cystatin C measured in plasma might serve as a predictor of future MetS but not diabetes. A causal involvement of cystatin C in the etiology of MetS or diabetes seems unlikely since genetic elevation of plasma cystatin C was not significantly related to these diseases.S1 File(DOCX)Click here for additional data file.


Past fluctuations of the West Antarctic Ice Sheet (WAIS) are of fundamental interest because of the possibility of WAIS collapse in the future and a consequent rise in global sea level. However, the configuration and stability of the ice sheet during past interglacial periods remains uncertain. Here we present geomorphological evidence and multiple cosmogenic nuclide data from the southern Ellsworth Mountains to suggest that the divide of the WAIS has fluctuated only modestly in location and thickness for at least the last 1.4 million years. Fluctuations during glacial–interglacial cycles appear superimposed on a long-term trajectory of ice-surface lowering relative to the mountains. This implies that as a minimum, a regional ice sheet centred on the Ellsworth-Whitmore uplands may have survived Pleistocene warm periods. If so, it constrains the WAIS contribution to global sea level rise during interglacials to about 3.3 m above present. Predicting the West Antarctic Ice Sheet's response to future warming is hindered by a lack of historical evidence. Here, based on geomorphological evidence from and cosmogenic dating of Ellsworth Mountains' deposits, the authors show that at least a regional ice sheet survived Pleistocene interglacial cycles. Bryozoa between the Pacific and Atlantic sectors suggests that much of the ice sheet disappeared during interglacials, creating an open seaway between these sectors679311The West Antarctic Ice Sheet (WAIS) is pinned on an archipelago with its central dome situated over subglacial uplands and bedrock basins, the latter more than 1,500 m below sea level . For ove4The Heritage Range, situated in the heart of the Weddell Sea embayment, lies within 50 km of the interface between the grounded ice sheet and the floating Filchner-Ronne Ice Shelf in Hercules Inlet . Two com14The use of cosmogenic nuclide dating on bedrock and glacially transported material on nunataks in Antarctica has provided much quantitative data on the history of ice thickness changes over time161718192021222426Al/10Be, it takes several tens of thousands of years for the burial signal to become evident. By measuring multiple isotopes in three adjacent erratics at each specific sampling site, the degree of scatter and extent to which the erratics have shared the same history of exposure can be determined. Thus, one can gain information on the age of deposition and possible subsequent overriding and disturbance by ice.The combination of geomorphological analysis of landforms and measurement of multiple cosmogenic nuclides can provide rare insight into ice-sheet history. The advantage of measuring multiple cosmogenic nuclides in single samples is that both the age and exposure history can be constrainedin situ cosmogenic 26Al, 10Be and 21Ne from newly collected, quartz-bearing erratics to investigate elevated blue-ice moraines. Our evidence reveals several relict ice-marginal blue-ice moraine deposits as old as 1.4 Ma. The isotopic evidence indicates that the highest deposits have not been disturbed by ice since deposition, but lower deposits have experienced subsequent burial. All geomorphic and cosmogenic nuclide data are consistent with an ice sheet that thickened and thinned in response to quaternary glacial–interglacial cycles. We find no evidence to suggest a change in glaciological conditions that would accompany the loss of the entire ice sheet and the build-up of individual mountain glaciers. We interpret this consistency as evidence for continuous ice-sheet conditions in this part of the Weddell Sea sector. The minimum configuration that maintains strong katabatic winds is a regional ice sheet centred on the Ellsworth-Whitmore block. This interpretation, where the WAIS shows dynamic equilibrium about a continuous ice divide, supports numerical models that indicate a maximum WAIS contribution to sea level of about 3.3 m . A diff10Be ages because the production rate is better constrained; 26Al and 21Ne are used to constrain exposure histories. The measurement of 21Ne was completed because, as a stable isotope, it gives a measure of the total exposure time (assuming no erosion) irrespective of subsequent burial, and because it can potentially record longer periods of exposure than is generally possible with radioactive isotopes.The cosmogenic nuclide data are presented in 10Be and 26Al, implying that they were first exposed to cosmic rays when they emerged at the ice-surface. In view of the similar lithologies, and thus origin, of quartz-rich erratics at higher elevations, it is reasonable to argue that they too were deposited with no significant pre-exposure. This is reinforced by the clustering of multi-isotope exposure ages from each sampled site. Thus, we conclude that the cosmogenic nuclide concentration in the erratics accurately reflects their exposure history since deposition.The sampling strategy for cosmogenic nuclides was designed to reduce the chance of nuclide inheritance, and exclude the possibility of nuclide loss through erosion. We targeted subglacially derived clasts with striated surfaces and subangular to subrounded shapes. We sampled the freshest appearing, quartz-bearing, brick-sized clasts resting on flat bedrock to minimize problems of post-depositional movement and self-shielding. It is crucial to be convinced that the exposure ages reflect the time since deposition of a freshly exposed clast rather than a signal inherited from the past. To test whether clasts emerging on the glacier surface in blue-ice areas have no inherited cosmogenic nuclides, we analysed seven clasts on the present ice margin. All had negligible amounts of both 10Be/9Be and 26Al/27Al ratios were measured in 20–30 g of quartz at the Scottish Universities Environmental Research Centre Accelerator Mass Spectrometry (AMS) Laboratory in East Kilbride, UK. Measurements are normalized to the NIST SRM-4325 Be standard material with a revised10Be/9Be of 2.79 × 10−11 and half-life of 1.387 Ma  were spiked with 250 μg 9Be carrier  and 1.5 mg 27Al carrier . Samples were spiked with 250 μg 9Be carrier and up to 1.5 mg 27Al carrier . Blanks range from 3.3 to 9.3 × 10−15 [10Be/9Be] ; and 1.6–7.5 × 10−15 [26Al/27Al] . Concentrations in 27Al measurement inductively coupled plasma optical emission spectrometry uncertainty.Whole-rock samples were crushed and sieved to obtain the 250–710 μm fraction. Be and Al were selectively extracted from the quartz component of the whole-rock sample at the University of Edinburgh's Cosmogenic Nuclide Laboratory following established methods37 Ma refs , 41, and−8 torr for 48 h before analysis. Samples were successively heated for 20 min to 1,200 °C in a double-vacuum resistance furnace with a tungsten heating element and a molybdenum crucible. The extracted gas was cleaned on two hot SAES TiZr getters. The heavy noble gases  were absorbed onto a charcoal trap cooled with liquid nitrogen. Neon was then absorbed on to a charcoal trap at −228 °C for 20 min, and the residual He was removed by a turbomolecular pump. The Ne was released from the charcoal at −173 °C, and the isotopic composition analysed using a MAP 215–50 noble gas mass spectrometer. All Ne isotopes were measured in 11 peak jumping cycles using a Burle channeltron electron multiplier operated in pulse-counting mode. Neon abundances were determined by peak height comparison with Ne from 95.2±0.5 μcc STP air. The reproducibility of Ne abundances was better than ±1.5%, and isotopic ratios of replicate calibrations were better than ±0.5%. Interference corrections and detailed analytical procedure is presented elsewhere20Ne blank at 1,200 °C was typically ∼1 × 10−11 ccSTP and were indistinguishable from the atmospheric isotopic composition after correction for interfering species. Consequently no blank correction is made to the data in 21Ne concentration in replicate analyses of MH12–27  of 7.7±2.4 × 106 at g−1. This is the value estimated by Middleton et al.21Ne measured in Antarctic rocks . Samples were wrapped in aluminium foil and loaded into a Monax glass tree and evacuated to<10 MH12–27 . In all −1 a−1 for 10Be and 28.5±3.1 atoms g−1 a−1 for 26Al. However, the use of Lal/Stone2610Be and 26Al, respectively. Rock density is 2.7 g cm−3 and the attenuation length used is 153±10 g cm−2. No corrections are made for rock surface erosion or snow cover and thus exposure ages are minima. Finally, we make no attempt to account for production rate variations caused by elevation changes associated with glacial isostatic adjustment of the massif through timeFor exposure age calculations we used default settings in Version 2.0 of the CRONUScalc programme21Ne was modelled after the existing code for 3He and only includes spallation production. The 21Ne production rate is tied to the total CRONUScalc 10Be production rate : 14.5 . In our samples, the burial signal implied by the 21Ne/10Be ratios is greater than that implied by 26Al/10Be ratios. There are a few possible explanations. First, this may partly reflect the uncertainties on 21Ne production rates as discussed above. Second, it is possible that the samples contain additional nucleogenic 21Ne that has not been corrected for. A final explanation is that 21Ne, which is stable, is recording a period of exposure that is not evident in the 26Al/10Be system. At present it is not possible to discriminate between the above scenarios. In any case, our conclusions are not sensitive to these minor discrepancies.Scherer  examined four till samples from both current and elevated blue-ice moraines and found no evidence of diatoms or biogenic silica.How to cite this article: Hein, A. S. et al. Evidence for the stability of the West Antarctic Ice Sheet divide for 1.4 million years. Nat. Commun. 7:10325 doi: 10.1038/ncomms10325 (2016).Supplementary Figures 1-6, Supplementary Tables 1-3 and Supplementary References


The current standard of care for operative repair of scaphoid fractures involves reduction and internal fixation with a single headless compression screw. However, a compression screw in isolation does not necessarily control rotational stability at a fracture or nonunion site. The single screw provides rotational control through friction and bone interdigitation from compression at the fracture site. We hypothesize that osteosyntheses with novel bone screw sets (BSS) equipped with anti-rotational elements provide improved rotational stability.®mini, HCS®3.0 and Twinfix®. Biomechanical tests were performed on scaphoids from single donors in paired comparison and analyzed by balanced incomplete random block design. Loading was increased by 50 mNm increments with 1,000 cycles per torque level and repeated until a rotational clearance of 10°. Primary outcome measure was the number of cycles to 10° clearance, secondary outcome measure was the maximum rotational clearance for each torque level.Stability of osteosynthesis under increasing cyclic torsional loading was investigated on osteotomized cadaveric scaphoids. Two novel prototype BSS, oblique type (BSS-obl.) and longitudinal type (BSS-long.) were compared to three conventional screws: Acutrak2®mini and HCS® . BSS-long. performed significantly better than HCS® (p = 0.010). No significant difference in performance between BSS-obl. and BSS-long. (p = 0.361), between BSS obl. and Twinfix® (p = 0.50) and BSS long. and Twinfix® (p = 0.667) was detected. Within the torque range up to 200 mNm, four of 21 (19%) BSS-long. and four of 21 (19%) BSS-obl. preparations showed early failure. The same loading led to early failure in four (29%) Twinfix®, seven (50%) Acutrak2®mini and 10 (71%) HCS® of 14 screw samples, respectively.BSS-obl. performed significantly better than Acutrak2® , higher rotational stabilities were identified in comparison to single component headless compression screws.For both BSS and to a lesser extent for Twinfix The objective regarding the therapy of scaphoid fractures is to obtain osseous consolidation as rapidly as possible in order to restore function of the wrist .Even though surgical therapy by single screw osteosynthesis permits earlier return to work and exercise than conservative therapy, the difference in consolidation rate and speed of fracture healing itself is subject to controversial discussion ,3,4. Sim®) [It is not known if these shearing and torsion movements are possible causes of non union development and long consolidation times in conservative therapy. Compared to conservative treatment single screw osteosynthesis improved results in consolidation rate tremendously . It is o®) ,13; thes®) , rotatio®) ,16,17. T®) ,18. When®) ,19, whic®)  or throu®)  a singulAcute evaluation of rotational stability of three different headless standard screw types in comparison to the two stabilizing prototype bone screw sets was performed in a balanced incomplete random block design experimental setup. The primary measure was the total number of stress cycles for each screw until a defined failure condition of a maximum rotational clearance bigger than 10° was reached. The secondary outcome was the mean rotational clearance for each screw.Fresh frozen cadaveric human scaphoid bones were obtained from donors who had signed a written informed consent form and voluntarily donated their bodies to the Center of Anatomy and Cell Biology for research. A total of 84 ex vivo scaphoid bones were used for the study. Three clinically established screw models:® Mini Headless Compression Screw System, Acumed®, Hillsboro, OR, USA   , as wellPA, USA) . Both tyThe primary screw of both BSS is a cannulated small fragment central threadless shaft screw with different pitches of the proximal and distal threaded portions of the screw. At the proximal end, there is a cylindrical thread with a maximum outer diameter of 3.5 mm and a gradient of 0.5 mm, over a length of 3 mm. The screw tip bears an 8.5 mm long conical thread with a gradient of 1 mm and an outer diameter which decreases from 3.2 to 2.6 mm towards the tip in a linear manner. This primary screw has an inner thread which is intended to receive the smaller secondary screw  with a crosswise centered drill hole which progresses at an angle of 20° to the longitudinal axis. In a composite with the secondary screw, this forms an intersecting rigid construction which stabilizes the connected bone segments against traction and torsion loads .The second variant consists of an analogously designed compression screw, however—instead of the pass-through bore with a partly countersunk guiding channel —parallel to the longitudinal axis with a thread section near the base. The secondary torsion-stabilizing screw  can be screwed into the countersunk guiding channel of the primary screw .Each of the two novel BSS was directly compared as individual reference screws to each of the standard screws. Left and right cadaver hands from one individual were used alternatively for a reference screw and a directly compared standard screw. The balanced incomplete random block design was chosen to account for differences in bone quality. To reduce the potential impact of training effect of the surgeon concerning the screw insertions, the different standard screws were applied in sequentially changing order from test-sequence to test-sequence. Seven test sequences of each standard screw type were performed in comparison with each of the two BSS types. Overall, 14 pieces of each of the three standard screws and 21 of each of the two BSS underwent the test procedure, summing up to the 84 scaphoid bones processed. Cyclical torque loads were applied under continuous monitoring of displacement between the two bone fragments.® data) and then statistically evaluated and graphically displayed using the table calculation program MS Excel . Aside from the primary and secondary outcome measure, this tool was also used to obtain the continuous progressions of the measurement figures of torque against rotational clearance.The measuring procedure was defined in a manner that the osteotomized scaphoid bones which were being tested were stressed cyclically, with simultaneous measurement of the rotational clearance of the segments in relation to each other, each 1,000 times in twist-out direction at a torque level. Herein the base load equaled 50 mNm; stress was increased by 50 mNm for the further torque levels, with 1,000 cycles respectively. This process was continued until the termination criterion of 10° rotational clearance of the scaphoid bone fragments in relation to each other was reached. The testing time span, rotational clearance, torque and number of cycles were saved as a text file  scans were made of all ex vivo scaphoid bones which were used in the trial in order to verify the comparability of the bone density of the scaphoid bone pairs. Scan settings were 60 kVp energy, 1 mA current, 100 ms integration time, 1536x1536 pixels image matrix and 82 μm isotropic voxel size. The gray values of the voxels were converted to bone mineral density  units using the calibration phantom data of the instrument. The images were coarsened by rescaling to 164 μm voxel size and the subchondral bone contour of each scaphoid was identified automatically by means of a 3D fill algorithm [® (www.dr-pahr.at/software). The mean and standard deviation of BMD was finally evaluated from the values of the voxels within this bone domain. Cadaveric scaphoids were excluded from analysis when apparent; intraosseous cysts were detected by HR-pQCT.In order to design the test implementation for each ex vivo scaphoid bone in a standardized, reproducible manner, the following process protocol was specified for the orientation of clamping scaphoid bone fragments to the test array, the osteotomy and the osteosyntheses: High Resolution Peripheral Quantitative Computer Tomography  and 3D-Print , the surface models of each scaphoid bone were used to produce acrylic resin models as specific, precisely fitting negative forms of the scaphoid bones, which were glued to the defatted bone surface as a fixing base  and to connect them to the device for the osteotomy and osteosynthesis, as well as to the test array. This set up allowed to orient the test objects along the anatomical longitudinal axis of the scaphoid and clamp them in the sample holder in a defined manner to carry out the osteotomy and subsequent osteosynthesis  to guide the drill and screw was positioned using a centering sheath. A specifically manufactured drill was used for the newly developed 2-component screw sets.In particular the HR-pQCT data were used to digitally produce surface models via a surface reconstruction. Using the software Rhinocerosynthesis . Using aynthesis . A1 mm gThe drill depth was limited to 24mm by markings on all drills. For the osteotomy, the fixing connections of the collet chuck were rigidly fixed against each other; after osteotomy the stops at the collet chuck were released for the subsequent osteosynthesis, so that the scaphoid bone fragments were stabilized against rotation, but unlocked and mobile in the axial direction to equalize distance. Repositioning was performed without diastasis between the scaphoid bone fragments. The osteosyntheses were implemented according to the manufacturer’s specifications, resulting in standardized compression conditions. The prototype screws were placed analogously to the instructions for the standard screws so that the screw end was precisely flush with the cortical surface. The samples and the sample holders were then taken out of the holder system and clamped into the test array for testing the rotational stability see .® with a connected planetary drive 23/1 . The utilized torque was recorded and controlled through a feedback loop using an axially installed isometric torque sensor TS70® and a measurement amplifier unit GSV3-LS® . The drive and sensor were axially coupled to a clamping device for the fitted sample holder. On the side facing the screw tip, the torque sensor was rigidly connected to a base plate and bore the fitted part for the sample segment held by the screw tip on its upper end. The drive unit was mounted above, axially oriented and hanging in the array, and carried the fitted part for the sample end which was held by the proximal screw end. The sample holder on the screw end side was rigidly connected to the drive axle; the sample holder in the screw tip region was guided via a square bar (20mm) which permitted tension-avoiding equalization movements in the axial direction. This construction ensured that only rotational loads and not traction or pressure loads were introduced into the sample.The technical array was powered by a multiphase motor Type AM2224®, Faulhaber, Germany).After the samples were mounted, the position of the unloaded sample holders with the osteosynthesized scaphoid bones which were fixed therein and the torque which was applied in the resting position were defined as the zero parameter via the test array control software. The multiphase motor was controlled via software controls and a serially connected motor driver  resolution. A specific control software was developed to operate the test array, carry out the automated control of the test processes and to record and visualize the measurement data. This software also continuously monitored rotational play and automatically stopped it when a maximum rotational clearance of 10° was reached see . The loaSince no data on the variability of the proposed endpoint in our setting were available, the sample size considerations were based on similar experiments ,16,22, wEven though various studies ,16 reporThe secondary outcome measure  was modeled by a linear mixed effects model that incorporates implant type as fixed-effect, body as random-effect and stress level (torque) as a repeated factor. This model was used to estimate the expected maximum rotational clearance for each implant at each torque level. Therefore least squares estimate for the expected maximal rotational clearance for each implant and each torque level were calculated. Measurements were performed incrementally until the termination criterion of 10° rotational clearance of the scaphoid bone fragments in relation to each other; however, depiction took place up to 200 mNm, since we assumed greater clinical relevance in this lower torque range. No significance tests were conducted for this analysis. Descriptive statistics  for the raw outcomes are presented as numbers and in graphical form (box and dot plots).This study was approved by the institutional ethics board of the Medical University of Vienna  than those on the left side (310.71±243.92 mg/cm3), wherein the observed minimum of the absolute parameters was at 119.46 mg/cm3 on the left and 74.94 mg/cm3 on the right, and its maximum was at 431.71 mg/cm3 on the left and 421.56 mg/cm3 on the right side . Right-hand scaphoid bones are denser on average (319.84±250.53 mg/cmThe results on the number of load cycles to the fault limit are shown in Further details by screw type and load stages are found in 3); another reached 11,397 at 650 mNm (BMD of the sample 431.71 mg/cm3). An individual BSS long. reached 12,388 at 700 mNm (BMD of the sample 380.51 mg/cm3). The best standard screw connection was reached by a single Twinfix® screw with 11,052 at 650 mNm (BMD of the sample 381.23 mg/cm3).For instance, an individual osteosynthesis with a BSS obl. reached 17,188 total cycles at 950 mNm . The implant BSS long. performed significantly better than HCS® 3.0 (p = 0.0090). There was no significant difference in performance between BSS-obl. and BSS-long. (p = 0.361), between BSS obl. and Twinfix® (p = 0.50) and BSS long and Twinfix® (p = 0.667). No difference could be observed between BSS long. and Acutrak® 2 Mini (p = 0.2959).The analysis shows a significant performance difference between implants regarding the primary outcome measure  [Based on the targeted design of the BSS, we assumed differences in their mode of action and were indeed able to prove significant differences in rotational stability. The selected study design furthermore showed differences between the conventional screw types. Isolated osteosyntheses with different screw types were able to resist torque stress for a particularly large number of cycles into very high levels on the one hand; on the other hand osteosyntheses with the same conventional screws were noted as a result of some early failures. Early failures were observed in osteoporotic scaphoid bones as well as in bones of average bone density. The feasibility and usability of dual-component osteosynthesis screw sets which possess greater stability of the osteosynthesis while almost maintaining the dimensions of conventional screws, without enlarging the implant cross-section in the osteotomy/fracture region, were confirmed. To our knowledge, this subject of rotational stability was thus far investigated in only three publications: According to in vitro tests, the recommended placement is as central as possible, orthogonally to the fracture line , using tawbone®) . In thisawbone®) ) and an In view of the clinical relevance, we did not wish to limit ourselves solely to the maximum number of cycles to the specified termination criterion of a 10° rotational clearance in order to systematically evaluate the screw-specific early failures as well. This assessment in the lower torque range up to 200 mNm  is partiIn fact, it was possible to stress a large share of the osteosyntheses in the range of up to 100mNm torque with a low failure rate. However, loads of up to 200 mNm then resulted in clearly visible differences in the stabilization capacity of the various screw types, wherein the BSS long. only showed first signs of weakness at 200 mNm, and the BSS obl. did not show noticeable signs of loosening across this entire load range .® screw, we assume rotational stability nearly solely based on friction adhesion due to bone fragment compression. Due to its construction which is uncoupled from the rotating shaft, the screw base, which rotates freely apart from a small amount of residual friction, prevents rotational instability in the twist-out direction by enlargement of the osteotomy gap, therefore the scaphoid bone fragments consequently remain in contact and continue to maintain friction between the fragments. Distancing of the fragments which is linked to displacement in the twist-out direction and therefore loosening of the screw-fragment connection is expected in all screw models wherein the screw body is rigid within itself. It is likely that this particularly affects the stabilization properties of the HCS screw, which, due to its uniform thread gradient, transforms twist-out movements into enlargements of the osteotomy gap. The initial compression force with which the Twinfix® screw and the HCS® screw compress the fragments depends on the discretion of the surgeon. In contrast to screws with a single, rigid screw body and variable pitches, the compression force is almost solely determined by the construction attributes of the screw itself as well as the bone density. The surgeon may influence the compression force only by the grade of initial fragment reduction and deeper insertion. Since a frictional connection is given only in the screw tip and head areas in central threadless shaft screws, screws with continuous thread were conceived, with the objective of a better development and consistency of the compression and pull out force within the bone [® 2 mini in the lower torque range is maybe due to compacting of cancellous bone between the flanks of the screw threads during the screw insertion process. The progressively changing gradient between the continuous threads causes the screw to clamp and dowel itself within the porous cancellous bone. If this clamping effect decreases due to rotation in the twist-out direction, the osteosynthesis promptly loses rotational stability. Since the extent of compression force [®2 screw), this specific stability attribute may play an important role in clinical application when stabilizing small fragments and scaphoid non unions by means of interpositional bonegrafting [in vitro human bone [Since the screw base with regard to the screw tip consists of a freely rotating part in the Twinfixthe bone . The conon force  is subjegrafting . Certainman bone ,19, as wBoth BSS were developed in order to block both fragments against rotation by a second screw which protrudes from the cross-section of the compression screw without significantly enlarging the dimensions of the standard headless screws used in the test.®). In the BSS long., the diameter of the secondary screw and its protrusion from the primary screw needed be increased, as stability against cyclical loading turned out not to be better than the most stable standard screw (primary outcome). BSS obl. clearly demonstrated improved stability of the osteosynthesis along the test sequence. Plastic deformation of both screw elements of the BSS obl. occurred, in the primary screw at the bore for penetration of the secondary screw, the secondary screw due to small shaft diameter. The stability of the BSS long. was superior to the BSS obl. We could not observe plastic deformation of the BSS long. after any test sequences.In spite of the technically immature and clinically not proven stage of prototypes both BSS achieved better measurements in comparison to all standard screws with respect to the secondary outcome but did not resist significantly more stress cycles until failure than the most stable standard screw .The actually early development stage of the novel screw models cannot be tested in vivo due to clear ethical limitations. Despite all limitations, a statistically elaborated in vitro study on cadaver specimens can provide more realistic data than one on polyurethane foam Click here for additional data file.S1 Table(XLS)Click here for additional data file.S2 Table(XLS)Click here for additional data file.


Antarctica contains some of the most productive regions on Earth for collecting meteorites. These small areas of glacial ice are known as meteorite stranding zones, where upward-flowing ice combines with high ablation rates to concentrate large numbers of englacially transported meteorites onto their surface. However, meteorite collection data shows that iron and stony-iron meteorites are significantly under-represented from these regions as compared with all other sites on Earth. Here we explain how this discrepancy may be due to englacial solar warming, whereby meteorites a few tens of centimetres below the ice surface can be warmed up enough to cause melting of their surrounding ice and sink downwards. We show that meteorites with a high-enough thermal conductivity  can sink at a rate sufficient to offset the total annual upward ice transport, which may therefore permanently trap them below the ice surface and explain their absence from collection data. Collection data suggest the proportion of iron-based meteorites recovered from Antarctica is significantly lower than the rest of the world. Here, the authors propose a mechanism to explain this discrepancy, showing that iron meteorites heated by solar energy can move down through the ice, not to re-emerge. When meteorites fall onto a large area of inland Antarctica, the subsequent ice flow dynamics direct many of them to localized surface regions called meteorite stranding zones (MSZs)24567It is our hypothesis that the under-representation of iron-based meteorites in Antarctic data is caused by solar energy penetrating the clear ice of the MSZs2Under our hypothesis, sinking (relative to the upwelling ice) of englacial meteorites in an Antarctic MSZ will be seasonally dependent. In the winter months, with little-to-no solar radiation, sinking will not be possible, and so all classes of englacial meteorites can be expected to rise with the speed of the ice , while allowing meteorites with lower conductivities to emerge from the ice. As a consequence of this filtering mechanism, the model suggests a few tens of centimetres beneath the ice surface of a MSZ, there are sub-layers of ice that potentially contain a (sparse) distribution of meteorites with high-thermal conductivities. With meteorites constantly being englacially transported towards many MSZs14Our experiments centred on subjecting a meteorite encased in a block of ice to the radiation from a solar-simulator lamp held directly above the ice surface, and focused onto the meteorite (see the Methods section). Two classes of meteorite were tested: an ordinary chondrite meteorite (North West Africa (NWA) 869 L3.9–L6), and an achondritic iron meteorite (Sikhote-Alin). Both samples were of near-prolate-spheroidal geometry, with the axis of symmetry horizontally aligned with diameter 15 mm, and width 10 mm. Under the laboratory conditions, both classes of meteorite proved able to warm up enough that they could melt their surrounding ice and sink down, as shown in −1 K−1  Frontier Mountain meteorite trapters see , resultsThe energy balance model is able to identify further meteorite parameters that might affect englacial trapping or release, for example, its broadband surface albedo and mass density. It is found that variations in meteorite surface albedo alter the predicted meteorite depths by only a modest amount: a significant ±50% change in meteorite surface albedo was found to alter the iron meteorite depth of αi . So far we have used a default mean value of 0.62 based on field measurements of blue iceαi is varied by ±7.5% : the higher albedo is now sufficient for the iron meteorite to emerge, whereas the lower albedo deepens the meteorite's resting depth by some 10 cm. As this result suggests, a light covering of snow  on a MSZ could allow iron-based meteorites to emerge, helping explain why a small number of iron-based meteorites are still found on the surface of Antarctica's MSZs, and trapped in glacial moraine fields. Conversely, it is possible to adjust the model parameters  so as to have the chondritic meteorites also permanently englacially trapped. Interestingly, blue-ice fields in Greenland of similar latitude and elevation, but with a higher average temperature profile than Antarctica, have not yielded any surface meteorites, consistent with our work and aligning with previous suggestions for their absenceA notable parameter that uniformly affects the dynamics within our modelling is the ice broadband albedo w, where iron meteorites of widths >22 cm emerged at the ice surface  terms in the various energy balance equations and so should be taken to offer generalized quantitative predictive results at this stage.We consider three distinct stages within our modelling. Chronologically, the evolution starts with the meteorite heating due to absorption of downwelling solar radiation through the ice; however, it remains fully encased in ice while temperatures remain below freezing throughout. Then, once the top surface of the meteorite is sufficiently heated it is able, through conduction, to induce melting of the overlying ice, allowing an upper water layer to form; this water layer can itself evolve through its interaction with both the overlying ice and the underlying meteorite. Next, if the meteorite continues to warm sufficiently, melting at its lower surface will also commence. When it does, we allow the sub-meteorite melt water to be squeezed upwards by the weight of the meteorite adding to the overlying water layer, thereby enabling the meteorite to sink downwards and fill the displaced volume. These three stages can stop at any time, and freezing reoccur, as the meteorological inputs vary, thus bringing the sinking process to a halt (this being the case for the Antarctic situation during the winter months).z: (i) an upper ice layer that is exposed to the atmosphere; (ii) a water layer ; (iii) the meteorite; and (iv) a lower ice layer. To model the Antarctic situation, one must incorporate the relative motion of the meteorite to the ice surface. With the MSZ surface in equilibrium at z=0, say, the upwelling ice velocity V must be matched by the ablation rate .To model this process in the simplest and most elucidating manner, we consider a one-dimensional representation to the physical problem, as sketched in z=a), and the water/meteorite interface (z=b). The time-varying solution to these two variables thus determines the dynamics of the meteorite within the ice. In solving for them, we must also solve for the other variables involved within the model, namely the temperatures Tj in regions j=1−4 (note that the air temperature is a model input).To frame the problem mathematically, we need to consider the energy balance at the five boundaries/interfaces of the four regions. It is of note that two of these interfaces are ‘free-boundaries', whose locations are variables that require solving as part of the problem: the upper ice/water interface (z=0), the energy balance is given byAt the atmosphere/ice interface ; the sensible heat flux; and sublimation, respectively. The right hand side is the heat flux into the ice, which is given by Fourier's heat-transfer law. All model parameters are defined in z=a; once it exists) the temperature must be at 0 °C. Further, the energy balance tells us that the energy flux for melting the ice (or its refreezing) plus the heat flux into the ice must equate with the heat flux from the water layer:At the ice/water interface  and kw becomes ki.where the overdot denotes differentiation with respect to time. Note that the inclusion of +z=b), we must consider the shortwave solar energy that is reaching the meteorite surface (the longwave flux having been absorbed at the surface), and how this flux decays with depth below the surface. To achieve this we make use of the Beer–Lambert's exponential decay law with extinction coefficient γi. The balance at this interface is given by the solar energy flux plus the heat flux from water layer equating with the heat flux into the meteorite:At the water/meteorite interface (1−αm)(1−sh)S, where S is the total incoming solar flux, αi is the ice surface broadband albedo, αm is the broadband meteorite albedo and sh is the percentage of incoming solar radiation that is shaded . Due to the inclination of the sun to the horizontal (solar elevation angle θ), we make use of an effective distance b′ that represents the distance travelled while being attenuated within the ice and melt water (where we neglect the tiny effect of refraction within the very-thin melt-water layer):Here z=b+w), where w is the meteorite width, one needs to compute whether the temperature is high enough to melt the ice. When the interface temperature is at 0 °C, melting is permitted, and the energy balance is given by the heat flux from the meteorite layer equating with the energy flux for melting plus the heat flux into the lower ice layer:At the lower meteorite/ice interface .Again, the +At the bottom of the lower ice region we shall prescribe a temperature-gradient condition of the formT∞ at z∞. Thus, the ‘far-field' temperature gradient isIn the laboratory, where the ice block is relatively warm and thin (5 cm), and the incoming heat fluxes held constant, we use a measured value of the ice temperature z∞, as the temperature profile within the ice varies with time . As an alternative, we note that the ice underneath the meteorite must tend to the temperature profile of the surrounding ice, and so we must prescribe a condition drawn from the meteorite-free situation, that is, we need to match the temprature flux at z∞ with that of the ice thermal boundary layer. To achieve this, we can utilize the fact that the magnitude of the (meteorite-free) annual ice-temperature variation in the boundary layer diminishes rapidly with depth, which means that in practice there is only a small average annual temperature gradient at z∞ , we are able to simplify matters by considering the time scales involved. By noting that the critical depth scale in the model is the annual ice uplift height H (H=V × 1 yr), it allows us to compute the associated time scale of sinking Λ1, as ∼10 days (for the Antarctic parameters given in 2 for which the full heat equation will relax to its steady-state version (Tzz≈0), can be shown to be the order of 1 h (Λ2=ρicH2/ki). With this large relative difference between time scales j=1–4 , namely:To prescribe the underlying equations within each region, we need to consider the conservation of heat energy. While one could use the full heat equation , one can compute the location of the ice/water interface, a, from the dynamic equationDuring the second stage, where melting of the lower ice has not yet commenced but the upper water layer is in existence  assuming that any scattered shortwave energy within the ice only affects the ice at the atmospheric interface, that is, the shortwave energy directly warms only the ice surface and the meteorite (which then heats up the remaining ice by conduction). This assumption, which greatly simplifies the analysis, is expected to lower very slightly the temperature of the ice near the meteorite compared with reality. This consequently reduces the rate of sinking, and thus is, by design, a slightly conservative estimate .This last term in z=b+w) has commenced, and thus the meteorite starts to sink, one must switch to computing the coupled pair of equations,Once melting of the lower meteorite/ice surface (b in (14) is positive: while it is positive, we solve for a and b from (13) and (14), and if its numerical value ever becomes negative (no melting), one takes b as fixed and reverts to determining the evolution of a from To determine whether or not melting of the lower surface has begun, one can simply check whether or not the velocity of S(t) from the libRadtran atmospheric radiative-transfer model323334352≈1 h . The computed maximum, minimum and mean daily values for the incoming shortwave solar flux S are shown in Ta and thus the incoming longwave energy flux Qlong, we allow these parameters to also be seasonally dependentThe final aspect to note in the Antarctic representation of the model is that the atmospheric energy fluxes are seasonally dependent. To account for this we calculated and used the six-hourly average shortwave flux θ=90° and the incoming energy fluxes are held constant).where in situ Antarctic parameter values are all in relation to the Frontier Mountain Meteorite Trap areaki  that was held at a constant 10 mm above the ice surface and focused onto the englacial meteorite. This was conducted in a  temperature-controlled room, with ambient temperature −1 °C. The meteorite movement was recorded over a 3-h period using an HD time-lapse camera positioned at the side of the ice block, from which the meteorite's progress could be measured (with an error of under ±1 mm), see Our experiments centred around subjecting a meteorite encased in a block of ice (400 × 400 × 50 mm) to the radiation from an Oriel Solar Simulator arc lamp .Supplementary Notes 1-3 and Supplementary References


Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site  and the long-hydroperiod site  fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (−11 to −110 g CO2 m−2 yr−1) compared to El Niño and neutral years (−5 to −43.5 g CO2 m−2 yr−1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m−2 yr−1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO Teleconnections from the El Niño Southern Oscillation (ENSO) are known to strongly affect climate patterns across North America 2) exchange rates have been linked to changes in surface hydrology in short-term studies 2 exchange rates respond to changes in surface hydrology 2 exchange. As a result, inter- and intra-annual fluctuations in CO2 exchange rates in the Everglades region may be significantly influenced by El Niño and La Niña phases.In the Florida Everglades, changes in the long-term hydrologic cycle have been linked to extreme ENSO phases (El Niño and La Niña phases) 2 and other greenhouse gases are expected to alter the frequency of El Niño and La Niña phases Increased atmospheric concentrations of CO2 dynamics in the Everglades. Because El Niño and La Niña phases are expected to alter the frequency and intensity of precipitation and temperature regimes, it is unknown how, when, and with what magnitude ecosystem CO2 exchange rates will respond to these fluctuations. However, this information is key to develop a prognostic understanding of how these ecosystems will behave in the future.Surface hydrology is managed differently among watersheds within Everglades National Park, which provides a unique opportunity to examine ecosystem function with differing hydroperiods, while still experiencing similar climate. Schedlbauer et al. 2 exchange rates .The goal of this research is to understand the relationship between extreme ENSO phases and intra- and inter-annual fluctuations in CO We hypothesize that El Niño and La Niña will amplify the site-specific seasonal responses in CO2 fluxes. At the short-hydroperiod site  it has been shown that enhanced net carbon uptake rates are associated with the dry season, while at the long-hydroperiod site  greater net carbon uptake rates are associated with wet season conditions 2 dynamics in the respective processes of uptake and efflux. For example, longer and wetter wet seasons will increase the capacity to uptake carbon at long hydroperiod sites, whereas longer and hotter dry seasons will increase the capacity for carbon uptake at short hydroperiod sites. In this study we used the eddy covariance method to estimate whole ecosystem exchanges in CO2, and a combination of linear, non-linear and time series modeling techniques to statistically address these hypotheses.The Florida Everglades are classified as subtropical wetlands with a year-long growing season and distinct wet and dry seasons that define annual variation http://fcelter.fiu.edu/research/sites/; The study sites are two oligotrophic freshwater marsh ecosystems that are within the Florida Coastal Everglades (FCE) long-term ecological research (LTER) program in Everglades National Park  and Muhlenbergia capillaris (Lam.) Cladium jamaicense, Eleocharis sp. and Panicum sp.) dominate ridge areas. Sloughs are dominated by short-statured (0.70 m), submerged species . Periphyton exists at both sites on submerged structures and as floating mats at SRS  and water vapor molar density , and a paired sonic anemometer  was employed to measure sonic temperature  and 3-dimensional wind speed . These paired sensors were 0.09 m apart and installed at 3.30 and 3.24 m above ground level (a.g.l.) at TS and SRS, respectively. Data were logged at 10 Hz on a datalogger  and stored on 2 GB CompactFlash cards. Both IRGAs were calibrated monthly using a trace gas standard for CO2 in air (+1.0%), dry N2 gas and a portable dewpoint generator . Footprint analyses air; °C) and relative humidity   mounted within an aspirated shield , and barometric pressure  . The Tair/Rh sensors were installed at the same height a.g.l. as the IRGA and CSAT.At each site, open-path infrared gas analyzers  were used to measure CO−2 s−1) , incident solar radiation  , and net radiation  . Precipitation measurements were made with tipping bucket rain gages (mm) . Soil volumetric water content  was calculated from equations developed for peat and marl soils using the methodology of Veldkamp & O'Brien s; °C) was measured at 5 cm, 10 cm, and 20 cm depths at two locations within each site using insulated thermocouples . When inundated at SRS, water temperature,  was measured using two pairs of insulated thermocouples , each pair located at a fixed height 5 cm above the soil surface and another attached to shielded floats that held the thermocouples 5 cm below the water surface. At TS, Tw was measured using insulated thermocouples  located at a fixed height 2 cm below the water surface. Water level (m) at both sites was recorded every half-hour with a water level logger .At each site, additional meteorological data was measured at 15-sec, and collected as 30-min averages through a multiplexer (AM16/32A Campbell Scientific Inc.) with another datalogger (CR10X Campbell Scientific Inc.). This included photosynthetically active radiation  w) was first estimated mean to streamline using a 2-d rotation in a Cartesian coordinate framework −2 s−1) was then estimated using the covariance of the turbulent fluctuations of the vertical rate of change of mean molar density of CO2 (c′), and the vertical scalar flux divergence (w′), where the turbulent fluctuations are the instantaneous deviation (at 10 Hz) from the mean block average (term I) over 30 min, and the storage flux (term II):−1 µmol C mol−1) of the molar density of CO2 measured at a fixed plane above the plant canopy (Z), z is the vertical dimension, and the overbar is the averaging period, in this case is 30-min. NEE was then divided by the molar volume of air, V, (m3 mol−1) to convert the units from density to molar fraction, i.e., µmol CO2 m−2 s−1, such that:R is the ideal gas constant (0.082 L atm K−1 mol−1), P is atmospheric pressure (1.10325 atm), and kT is the actual air temperature, estimated by:q is the molar fraction of water vapor calculated by unit conversion of vρ. Micrometeorological convention is used here, where negative NEE values indicate ecosystem uptake of CO2.Net ecosystem exchange (NEE) of COH; W m−2) was determined from the covariance of the turbulent fluctuations of w and sT, and w and q  and pC is the specific heat of air at constant pressure (J kg−1 °C−1). Corrections for the effect of water vapor on the speed of sound were applied Sensible heat  was calculated from the covariance of the turbulent fluctuations of w and vρ and averaged over 30-min,λ is the heat of vaporization (J g−1), and airM and wM are the molecular weights of air (28.965 g mol−1) and water (18.01 g mol−1), respectively. Corrections for thermal and pressure related expansion and/or contraction, and water dilution were applied Similarly, latent energy , LE (<−100 or >800 Wm−2), and NEE  values, stationarity criteria, and integral turbulent statistics n on a monthly basis. When R2 values were less than 70%, annual relationships between Rn and H or LE were used to gap fill data in that month.10 Hz raw flux data were processed with EdiRe , and when PAR was <10 W m-2, NEE data was gap-filled using an Arrhenius approach :α is the apparent quantum efficiency , and maxP is the maximum ecosystem CO2 uptake rate (µmol CO2 m−2 s−1).0R is the base respiration rate when air temperature is 0°C and b is an empirical coefficient. In ecoR is an estimated model parameter, whereas ecoR measurements are the dependent variable in n (with replacement) from the original dataset of size n for each estimated gap-filling model (Eq.6 and Eq.7) on a monthly or annual basis where appropriate were used NEE and ecoR data (Eq. 8).http://ameriflux.ornl.gov).Missing half hourly NEE data were gap-filled using separate functions for day and night. When PAR was ≥10 W mt denotes the tth daily value in the time series. Similar to methods used by Nuttle H and LE .As an indication of season intensity, the seasonal mean Palmer Drought Severity Index was used PDSI;  [41]. PDhttp://www.esrl.noaa.gov/psd/data/climateindices). The ONI is the running 3-month mean sea surface temperature (SST) anomaly from a 30-year mean SST for the Niño 3.4 region . Cold (warm) phases are defined as 5 consecutive months at or below (above) the -0.5° (+0.5°) anomaly.Long-term weather data were obtained from the nearest weather station, NCDC Royal Palm Ranger Station (25°23′N/80°36′W), where NOAA surface meteorological data was available from 1964 to 2013. The Oceanic Niño Index (ONI) was used to define extreme ENSO phases and was retrieved from the National Oceanic and Atmosphere Administrations Earth Physical System Research Laboratory  of order q, and if necessary, differencing of degree dtY) using its one period previous value (tY-1) and its associated error (εt-1):α1 is the first-order AR coefficient, θ is the first-order MA coefficient, εt is the current period error, and εt-1 is its one period previous error. “Memory” can be added to the model by adding lags and associated MA and/or AR components, and potential covariates can also be added as predictor variables, which may also have lagged components.An intervention time series approach was used To facilitate the inclusion of independent categorical variables for ENSO, El Niño and La Niña phases were coded as indicator variables, where a value 0 or 1 specified the absence or presence, respectively, of a categorical effect. We then determined if there were teleconnection lags between ENSO phase and precipitation and temperature.In developing time series models, first, all data series were tested for stationarity via the augmented Dickey-Fuller unit root test Because of the presence of autocorrelation in the explanatory series, input series were pre-whitened eco to light and temperature, respectively, non-linear To examine changes in the response of NEE and R2 dynamics  and a set of explanatory variables over a 5-year time series of daily data (2009 to 2013). These variables included: water level, season, ENSO phase , daily precipitation, drought condition, and average air temperature. The combined effect of ENSO phase and season (e.g. El Niño × wet season and El Niño × dry season) on CO2 fluxes were included in time series models as predictors with indicator variables. Indicator variables were also developed to identify sections of each season that directly followed an ENSO phase (post-La Niña and post-El Niño). Beckage et al. 2 exchange rates, indicator variables were used to identify the day of a precipitation event (Rain Day), the day after precipitation, and the quantity of precipitation . The indicator for the day after a precipitation event identified the first rain free day following a day with precipitation. Finally, drought conditions were defined as those days where PDSI<-2 and verified the drought extent with the National Oceanic and Atmospheric Administration's Drought Monitor (http://droughtmonitor.unl.edu/DataArchive.aspx).An intervention time series approach was used to identify and model the relationship between CO Monitor . Drought2 exchange rates in the Everglades freshwater ecosystems In addition, previous studies identified water level as one of the most important drivers for COecoNEE, GEE, R, and the Water Index) using pre-whitened explanatory series as predictor variables. Cross-correlation coefficient plots identified relationships at various lags, and autocorrelation plots were used to verify that the residuals had characteristics of random error. Model selection was based on minimum AIC, removing the least significant parameters. For each dependent variable, a single model form was selected with common predictor variables to aid site comparisons. Non-significant parameters remained in the model only if the parameter was significant at one site and it did not affect the final model of the other site. Multicollinearity between explanatory variables was also explored to ensure models did not contain input series that were highly correlated.As in the models of monthly weather data, all daily time series were tested for stationarity and non-stationary series were made stationary by differencing The long term ONI data ranged from 2.5 to −2.05 and indicated that the neutral phase occurred over about half (46%) of the period 1964–2013, while the El Niño and La Niña phases occurred 26 and 27% of this long-term study period, respectively. Neutral phases ranged in length from ∼1 month to>12 months and just 6 years contained no neutral phase . There were 14 different El Niño and 14 La Niña events, and the average ONI index was ∼1.1, −1, and −0.02 for all El Niño, La Niña and neutral phases, respectively. Although it is common for an El Niño event to be separated from a La Niña event by a short neutral phase (14 occurrences), a neutral phase occurring between consecutive El Niño (1 occurrence) or La Niña phases (4 occurrences) were less frequent. The majority (∼52%) of wet season months (May to October) were associated with a neutral phase while just ∼25% and ∼23% of wet season months occurred during El Niño and La Niña phases, respectively. Dry season months (September to April) were associated with the neutral phase ∼41% of the time, while El Niño and La Niña phases occurred 27 and 32% of time. Time series analysis of long-term monthly precipitation and minimum and maximum daily temperatures versus ENSO phase showed that rain increased the month after the start of El Niño phases  and declined the month following the start of La Niña (p = 0.7719), though not significantly ; S1 Fig.Throughout the study (2009–2013), 3 short La Niña phases , and an El Niño phase (2009–2010) occurred with shifts in precipitation patterns that resulted in both wetter than average (2010) and drier than average years , which corresponded to changes in season intensity. The ratio of GEE to Reco suggests that CO2 exchange rates at both sites were most similar in 2010  occurred during the La Niña phase at TS followed by the neutral phase. At SRS the greatest CO2 uptake rates were during the El Niño and neutral phase compared to seasons associated with a La Niña phase  and the dry season of 2013   .eco was often higher than wet season Reco, increasing CO2 release at SRS when the dry season was extended , GEE surpassed Reco and the site became a larger sink for CO2  was greatest during La Niña and directly following La Niña phases compared to rates during neutral and El Niño phases, although at higher PAR values (>1500 µmol m−2 s−1) curves for La Niña and the neutral phase converged (eco) were consistently higher at TS, for all ENSO phases as compared to SRS (−2 s−1).In addition to site differences, ENSO phase and season altered photosynthetic capacity and ecosystem respiration ; Fig. 6.onverged . Seasonad to SRS . At bothd to SRS ;. Overaleco differed between ENSO phases, and Reco showed distinct seasonal patterns in temperature sensitivity  but statistically significant autocorrelation remained in pre-whitened series; however, this sensitivity resulted from the large number of observations available and was judged to be biologically insignificant eratures , lagged −1; p<0.0001) had significant positive relationships with NEE, showing that as the change in water level and the quantity of daily rainfall increased, net CO2 uptake decreased  compared to neutral and El Niño phases at TS (p = 0.0039); however, post-La Niña phases in the dry season at SRS were associated with greater NEE . Moreover, there was a significant increase in NEE at TS (higher net CO2 uptake) the day after rain. At TS where hydroperiods were shorter, the effect of rain and post-La Niña phase during the dry season were significantly stronger than at SRS  were significantly linked to increased Reco ] and AR [AR(1)] component at both sites p<0.0001;. The dayModels for the water index had a significant 1-day lagged MA [MA(1)] and AR [AR(1)] component at both sites  in Everglades freshwater marsh ecosystems.The goal of this research was to understand the relationship between ENSO phases and CO The relationships between ENSO extremes, precipitation and hydrology in the Everglades region suggest that El Niño and La Niña phases could be important for C dynamics 2 dynamics, demonstrating that in addition to climate change and water management, ENSO is an additional source of variation in C cycling in Everglades freshwater ecosystems.Interannual variability in precipitation can be large in the Everglades region Abnormal precipitation and water level patterns over the study period coincided with El Niño and La Niña phases. Changes in ENSO phase have been associated with shifts in the position of the midlatitude jet, which is important for patterns in frontal precipitation. In the Everglades where frontal precipitation is the main source of dry season rainfall 2 exchange rates.Results found by Beckage et al. 2 exchange rates. Hydroperiods alter ecosystem production by interfering with exposed leaf area 2 fixation within the water column 2 exchange rates during and directly following El Niño and La Niña phases. The lag in El Niño and La Niña phase effect on CO2 exchange rates is the result of the effect of extreme ENSO phases on water levels during transition periods. El Niño (La Niña) phases increase (decrease) surface water levels during seasonal transitions and, major drainages often contain no water during transitions in a La Niña phase 2 exchange rates between ENSO and post-ENSO phases at TS and SRS.Hydroperiods have shaped soil conditions and species composition at each site in ways that have led to different seasonal patterns in CO2 exchange rates were sensitive to El Niño and La Niña phase in both the wet and dry seasons, while at SRS the effect of El Niño and La Niña phase on the wet season was not as strong as the effect in the dry season. La Niña phases resulted in higher photosynthetic capacity and greater seasonal net carbon uptake rates in both seasons at TS compared to neutral and El Niño phases. While La Niña increased photosynthetic capacity at SRS, the increase in Reco reduced net exchange rates compared to neutral and El Niño phases. As a result of changes in GEE relative to Reco, El Niño led to greater net CO2 uptake at SRS during the dry season compared to La Niña and neutral phases. As water levels and precipitation increased, NEE and GEE also increased at both sites (less CO2 and net CO2 uptake). At TS where hydroperiods were shorter, the effect of rain and the post-La Niña phase during the dry season were significantly stronger than at SRS  or dryer (-) than normal, which magnifies CO2 exchange rates at TS and SRS.The sites differed in their response to ENSO phases. At TS, COn at SRS . Rain waeco, and GEE. At TS where mean GEE surpassed Reco during the dry season, an increase in dry season length and intensity amplified the site's net CO2 uptake rates. Annually, SRS was usually a small source of CO2, although when wet season conditions intensified during El Niño, net CO2 uptake increased. The effect of ENSO phase also differed by site, showing that longer hydroperiods mute the effect of climate fluctuations on CO2 exchange rates, and as water levels decline the system becomes more vulnerable to climate. The ecosystem's sensitivity to climate fluctuations has important implications for water management and climate change 2 exchange rates.The results presented here show that the length and intensity of the wet and dry season varied annually with climate patterns. Considering the site-specific response to season, these results support our hypothesis that variations in season length would explain interannual fluctuations in NEE , Reco, a2 exchange rates. Shifts in water management and land use change  could also significantly alter both hydrology and CO2 dynamics in the Everglades region, making it important to develop a baseline understanding of how hydroperiod drives changes in CO2 dynamics and how climate alters hydrology. With water managers striving to adjust hydroperiods closer to natural values, in the future we might expect water levels in TS to increase, offsetting changes in climate by maintaining current patterns in hydrology. Alternatively, we might anticipate higher water levels to increase hydroperiods, making the system less sensitive to climate change altogether. With longer hydroperiods, SRS will likely remain less sensitive to changes in climate and land management. As a result, the two sites will likely behave more similarly in the future as SRS remains neutral or a very small source of CO2 to the atmosphere and TS becomes more neutral.In sub-tropical ecosystems, phenology is less sensitive to temperature and photoperiod, and more tuned to seasonal shifts in precipitation 2 dynamics Patterns observed in ENSO phases and the co-occurrence of extreme wet and dry seasons suggest changes in climate patterns can significantly alter ecosystem function. Equatorial Pacific SST during the past half century show a clear warming trend that is consistent with global warming 2 exchange rates showing that extreme ENSO phases magnify the site-specific seasonal response in freshwater marsh ecosystems. Although a longer time series is required to verify that this relationship is persistent, this research provides initial insights into an important driver of seasonal and inter-annual variation in CO2 exchange rates in Everglades ecosystems.This research shows that the length and intensity of the wet and dry season vary annually with ENSO phase in the subtropical Everglades region where dry season precipitation is dependent on frontal systems. Changes in season length and intensity are also correlated with COS1 FigARIMA model versus observed data of (a) precipitation, (b) maximum temperature and minimum temperature. Long-term weather data were obtained from NCDC Royal Palm Ranger Station (25°23′N/80°36′W), where NOAA surface meteorological data was available from 1964 to 2013.(TIF)Click here for additional data file.S2 Figeco at TS and SRS.The ratio of GEE to R Seasonal patterns in the ratio of GEE to Reco at (a) TS and (b) SRS shows that there is no clear pattern in wet season CO2 uptake rates and the (c) annual ratio of GEE to Reco were most similar during El Niño and neutral phases at TS and SRS.(TIF)Click here for additional data file.S3 FigSeasonal NEE at TS and SRS. At TS patterns in (a) wet and (b) dry season NEE shows that net CO2 uptake was greatest in years associated with La Niña phases (2011 and 2012). At SRS (a) wet and (b) dry season NEE suggests that the greatest net CO2 uptake occurred in years associated with El Niño (2010) and neutral phases (2013).(TIF)Click here for additional data file.S4 Figeco, (c) GEE, and (d) the water index for TS.ARIMA model versus observed data of (a) NEE, (b) R An intervention time series approach was used to identify and model the relationship between CO2 dynamics  and a set of explanatory variables over a 5-year time series of daily data (2009 to 2013).(TIF)Click here for additional data file.S5 Figeco, (c) GEE, and (d) the water index for SRS.ARIMA model versus observed data of (a) NEE, (b) R An intervention time series approach was used to identify and model the relationship between CO2 dynamics  and a set of explanatory variables over a 5-year time series of daily data (2009 to 2013).(TIF)Click here for additional data file.S6 FigThe relationship between season length and NEE at TS and SRS. NEE had a negative relationship with dry season length at (a) TS and a positive relationship with dry season length at (b) SRS. Annual NEE was positively correlated with wet season length at (c) TS and negatively correlated with wet season length at (d) SRS.(TIF)Click here for additional data file.