These ice records represent some of the longest climate observations directly collected by people. We highlight the importance of applying the same definition of ice-on and ice-off within a lake across the time-series, regardless of how the ice is observed, to broaden our understanding of ice loss across vast spatial and temporal scales.In recent decades, lakes have experienced unprecedented ice loss with widespread ramifications for winter ecological processes. The rapid loss of ice, resurgence of winter biology, and proliferation of remote sensing technologies, presents a unique opportunity to integrate disciplines to further understand the broad spatial and temporal patterns in ice loss and its consequences. Here, we summarize ice phenology records for 78 lakes in 12 countries across North America, Europe, and Asia to permit the inclusion and harmonization of   For example, one of the oldest ice and climate datasets directly collected by people was started in 1443 for Lake Suwa, Japan by Shinto priests because of the importance of ice formation to their Shinto traditions2. Moreover, long ice records increase our understanding of climatic changes since the Industrial Revolution as ice phenology (the timing of ice-on and ice-off) is a sensitive indicator of climate4.People have been recording the dates lakes freeze and thaw every winter from decades to centuries across hundreds of lakes because of the importance of ice to refrigeration, hydropower generation, winter transportation, and recreation6. The purpose of LIAG was to form a network of researchers so that they could discover patterns not visible in short time series as well as uncover similarities and differences at broader spatial scales than previously analyzed, such as a lake, province, state, or country. They used the ideas of “Invisible present”7 and the “Invisible place”8 to make clear the importance of expanding the time and the space scales of ecological research to understand the world around us6. The first LIAG group from North America, Europe, and Asia met at the Center for Limnology’s Trout Lake Station in Wisconsin, United States, to share the data amongst the group and more generally at the U.S. National Oceanic and Atmospheric Agency’s National Snow and Ice Data Center. The initial data set was developed by John Magnuson and Barbara Benson from the Center for Limnology, University of Wisconsin-Madison and Dale Robertson with the United States Geological Survey resulting in the first Hemisphere-wide comparisons4. The next major effort to update the data and expand the number of lakes was led by John Magnuson and Barbara Benson9. A new and expanded lake ice network with some old members and many new contributors has since been developed and led by Sapna Sharma11 to update and extend the lake ice seasonality data set; the present paper is part of that effort6. The ice seasonality data continue to be archived at the National Snow and Ice Data Center. Climate change was apparent in the earliest LIAG papers12 and trends in climate warming appear to be accelerating in recent decades. Today the United States Environmental Protection Agency considers changes in lake ice seasonality as one of the strong indicators of climate change (https://www.epa.gov/climate-indicators).In 1996, a network of lake ice researchers and their data from around the Northern Hemisphere was formed, called the Lake Ice Analysis Group (LIAG) led by John Magnuson from the University of Wisconsin-Madisonin situ observations do not exist or have not been updated13. Rapid losses in seasonal ice cover in recent decades14 highlight the urgency of integrating in situ and remote observations to obtain both a broad spatial and temporal understanding of ice loss, which is currently not possible with either of these approaches independently. However, the harmonization of data from both disciplines requires well-documented definitions and the historical context of the recorded observational data. Here, for the first time, we provide detailed records of in situ ice observations for some of the longest studied lakes, in addition to lakes from countries that have not been previously included in global synthesis studies10.In recent decades, the proliferation and advances in remote sensing technologies are enabling the collection of ice records from many regions of the world where 15. Regardless, the same definition for ice-on and ice-off should be applied for a lake over its time series to limit the uncertainty within the ice record and to assess long-term trends and patterns in ice phenology4. In some cases, lakes may have inconsistent standards of judging ice phenology information over time, and this is especially concerning when integrating in situ and remote sensing observations. For some lakes, additional information on freeze/thaw events within a season, ice thickness, and ice quality, may exist and are useful in understanding ecological under-ice dynamics17, such as water temperatures18, primary production16, and fish biodiversity19.Across lakes, a standard definition for ice phenology does not yet exist. For example, the timing of ice-on and ice-off data may be defined either based on a percentage of ice coverage or the ability of ships and boats to navigate across the lake20). In this study, in addition to the ice phenological records, we asked: i) What are the physical characteristics of the lakes?; ii) What were the definitions of ice-on and ice-off?; iii) How were ice observations made and recorded?; iv) Why was the ice record started historically?; and vi) Did the methodology change over the entire time series?Here, we provide ice phenology records and their corresponding meta-data for 78 lakes from 12 countries in North America, Europe, and Asia. These lakes comprise some of the longest ice phenology records collected around the Northern Hemisphere (>100 years) and also include lakes from countries such as Canada, Iceland, Norway, and Poland, that have typically not been included in global synthesis studies or within the National Snow and Ice Data Centre (NSIDC) Lake and River Ice Phenology Dataset  were recently incorporated to supplement two recent missing years in the spring of 2004 and fall of 2017. There is a limited uncertainty because of subjectivity of observers, inconsistent numbers of observers and observing locations during the data collecting period, and possible historical errors associated with the early start of the dataset in 1852.21 then updated in Hodgkins22. These comprehensive compilations systematically identified known observers, data sources, and some site-specific notes on methodology through 2008, relying substantially on an earlier compilation by C.B. Fobes23. As noted by the authors, original observation methodology was frequently not recorded or reported, and ice-off is generally defined as the date when winter ice disappears from the lake21. A more in-depth discussion of shoreline morphology and variability in reported ice-out dates in Hodgkins et al.24, states that the shape of some of the lakes in this compilation show increased variability between reporters if the lake had one particularly long axis. Ice on these long, narrow lakes might clear at one end but not the other, yielding a difference in reported ice out of several days while relatively round lakes had much smaller variability21.Ice-out data for New England, including Maine, New Hampshire, and Massachusetts, were compiled and reported by Hodgkins and JamesLake Auburn’s ice phenology record began in 1863. The local power company and Auburn water district started the ice record and publicly shared ice-off dates when the winter ice disappears in the spring in local newspapers. All of the information was based on visual observations of multiple observers including Erica Kidd of Auburn Water District who reported the date in 2020. A comparison between two data sources (the state Bureau of Parks and Lands and USGS) with 5 overlapping years differ by +/− 1 day in most years.China Lake’s ice record began in 1874 by the China Lake Association based on visual observations of Kennebec Water District staff. Dates were initially recorded for most years 1874–1883 then not recorded consistently until 193221. The lake ice off data is recorded when the lake is mostly free of visible ice and is navigable by boat. Observations were conducted eastward between 6:30 am and 3:00 pm at the East Vassalboro boat launch.Cobbosseecontee Lake’s ice phenology record began in 1840. The record started in 1840 with Sara Farr, Mary Oatway, Bill Schenck, and Nancy Schenck noted as visual observers of the date that lake ice completely disappears in the spring22. In 1974 and 1994, data were also recorded by a secondary observer. These ice-off dates were adjusted by the average difference between the primary and secondary observers.Damariscotta Lake’s ice observations were first recorded in 1837. Ice-off for most years was observed from the northern end of the lake21. The record was started based on visual observations made by three generations of Fred Jackson’s family, James Birkett, and the Maine Bureau of Parks and Lands21. A secondary observer recorded dates for 1959, 1962–68, 1970–78, and 1997–98; for these years, ice-off dates were adjusted by the average difference in the dates between the primary and secondary observers21.Kezar Lake’s earliest ice phenology record is 1901 by Arthur P. Stone (1901–1961) and kept at the Lovell town office. There are no missing years in the time series. According to the current observers, John Bacchiochi and Stan Tupaj, who have been conducting observations for about the past two decades, ice-off date is defined as the date when navigation is possible from one end to the other end of the lake. This also means that there might be ice in the coves and some other areas within the lake. Since Kezar Lake is 14.5 kilometres long and the Lower Bay is relatively shallow (~4.5 m) compared to the rest of the lake, the Lower Bay opens much earlier. Observations are made above the Lower Bay where observers look at the lake from both the eastern and western shores, as well as the North End. Each year, data are collected from various vantage points to obtain a more complete view of Kezar Lake. The same observation method has been applied since ~2000 in order to maintain consistency in the data. However the residents who recorded the ice phenology information before John Bacchiochi and Stan Tupaj (1962 - ~1999), would collect data from the north end of the lake where, at ~48 metres, it is the deepest part of the lake, when they could access different observation locations. For example, the data collected from different sources for overlapping years (2008–2018) show agreement between different observers in some years, and up to two days of disagreement for other years.Moosehead Lake’s ice phenology record extends back to 1848. Ice-off date is defined as “the earliest date of open navigation from Greenville to Northeast Carry21”. The ice-off record was started by observers for the Kennebec Water Power Company and continued by the Maine Department of Inland Fisheries and Wildlife using visual observations21. Recently, small aircraft have also been collecting ice-off data and the current observer is pilot Roger Currier.Pennesseewassee (Norway) Lake’s ice record began in 1874 by Woodman’s Sporting Goods, located near the southern end of the lake. Multiple observers have recorded ice data when annual winter ice cover disappears from the lake with the most recent reporter being the current lake association president, Sal Girifalco. Two residents on the lake are asked to report ice-out dates each year to make sure there is no bias because of observation location.Rangeley Lake’s earliest ice phenology information was started by employees of the Union Water Power Company in 1880 and continues to present-day each year based on visual observations of the date when ice completely disappears from the lake. More recent dates have been reported by employees for FPL (Florida Power & Light) Energy22.Richardson Lake’s ice record began in 1880 and Mooselookmeguntic Lake’s ice record began in 1884 by the Union Water Power company; these two lakes are located quite near each other and have similar ice-off reporting histories. The records are associated with data collection on water level management for electricity generation on dams. Ice-off dates are recorded when winter ice previously covering the lake disappears in spring21. Different observers are listed in both records.Sebago Lake’s ice record began in 1870 with the earliest reporter believed to be the Maine Sunday Telegram. Ice-off dates were recorded by the owners of Jordan’s Store in the town of Sebago who note the disappearance of the ice across the Big Bay on the west shore of the lake. If Big Bay does not completely freeze over, the data is recorded as “No complete ice cover” and assigned a day of year of 70 in the original data files. A Standard Operating Procedure (SOP) has been established by observers through the ice record, primarily the proprietor of Jordan’s Store in the town of Sebago, as well as Brie Holme of the Portland Water District, who reports the date.Sebec Lake’s ice record was started in 1897 by Bill Elliott22. The first day, when navigation from one end to another end of the lake is possible, is recorded as the lake ice-off date22. In the past, data were collected via visual observations. More recent information may be additionally gathered from webcam images along the lake.Thompson Lake’s ice record was started by Joseph Trebilcook in 190222. Since then, several different observers have been recording ice-off dates including Kathryn Cain and the Thompson Lake Environmental Association who are currently collecting these data. Ice-off date is recorded as the date a watercraft can navigate up and down the lake (north and south) without obstruction of ice sheets. However, ice may remain in the coves.West Grand Lake’s ice phenology record began in 1878 by Marion Staples’ family. Marion Staples’ grandmother started the record to inform sport fishermen at the family sporting camp. Ice-off dates are generally defined as the date when the annual winter ice previously covering the lake disappears in spring22.Wilson Lake’s ice record started in 1889. Several data collectors have been providing information throughout the time series, including Bruce Dyke (Wilton Fish & Game Association) and Robert Lively (Friends of Wilson Lake) who are currently recording ice-off dates. Ice-off is defined as when a boat can travel from the boat launch to the big island (southeast to northwest across lake). Different observers sometimes report dates that are one day apart for the same year.Houghton’s Pond, also called Lake Hoosic-Whisick, began in 1886 by the staff of Blue Hill Observatory who have been collecting weather and climate data daily for well over a century  based on visual observations. Ice cover is observed daily from the summit (where the observatory is located 145 m above the pond) with the assistance of binoculars if necessary. When the pond is not visible from the summit, observations are made at the shoreline. The pond is considered thawed when a trace amount (five percent or less) of ice remains after the last full freeze. Ice-on is also recorded at this site as the first date with complete ice coverage; intermittent ice coverage is tracked by the observers.The ice record in Grand Traverse Bay in Lake Michigan ice record started in 1850 which along with Bayfield Bay in Lake Superior15 is the longest ice phenology dataset for the Great Lakes. The ice-on date is recorded when the lake is covered with ice over West Bay from the southern shore to Power Island25. Data were collected to provide information for transportation, fishing, hunting during the winters and more recently to monitor climate change over the past several centuries25.Christmas Lake’s ice record started in 1887. For the past 22 years, Harley Feldman has visually observed ice cover several times per day from fall to spring facing south on his house deck. Before 1998, the data was documented in the Lake Association paper records and has been passed down from previous Christmas Lake Homeowners Association secretaries and treasurers. Ice-off date is defined as when there is no permanent visible ice on the lake in the spring. If the lake re-freezes, the ice-off date is moved out until the next date when there is no visible ice on the lake.Clear Lake’s ice record which is composed of ice-on and ice-off dates was started in 1874. Over the time series, records have been kept by local residents and newspapers including (i) Waseca Paper “Minnesota Radical” in 1874–1880; (ii) Mrs Orrin Smith and Mrs Herb Starr in 1894–1939; (iii) Marvin Johnson in 1940–1979; (iv) Edgar Johnson in 1980–1988, (v) Richard and Phyllis Fisher in 1990–2001, (vi) Don and Bob Lynch, Ron Fuchs, Dean Hagen, and Bill Severin in 1987–2008; (vii) University of MN SROC and the Waseca Lakes Association since 2001 until present. The ice-on date of the lake is defined as the first day in the winter season when the lake is completely frozen without temporal thaw. The ice-off date is defined as the day when 90% of the ice is melted. Data have been collected based on visual observations at multiple sites and directions as it is easy to drive around the perimeter of the lake.Detroit Lake was started in 1893 for ice-off and 1910 for ice-on. The earliest data were collected by unaided visual observations, while after 1993, data have been collected through a variety of methodologies including telescope, drive-by, and consultation with Dick Hecock. As Hecock resides on the north shore of Big Detroit near the sandbar dividing the lake into Big and Little Detroit bays, he can conduct observations of a large portion of Little Detroit and most of Big Detroit with a telescope or in close distance if the viewing weather is poor. Secondary observations for ice-out dates are also collected from two other residents on Big Detroit south shore. More daily observations, many of which are in the early morning, are made when the ice-off day is approaching. Ice-on date of Detroit Lake is defined as the date when the lake is frozen without substantial further openings because of thaws according to the MPCA (Minnesota Pollution Control Agency). Ice-off date is defined as the date the entire lake is “essentially ice-free”. The southwest shore is monitored more carefully since it is almost always the last portion of the lake to thaw. Hecock has been following guidance established by the MPCA since he took over the record in 1993. However, the uncertainty of the earlier data was in the order of about five days because of the lack of knowledge of former observers, inconsistency in data definitions, and an incomplete view of the lake. Before roads were built around Detroit Lake, the lake area that froze last was furthest away from the town where early observations were made so that ice coverage might have been overestimated. The ice-off date might also have been recorded earlier than the actual date because Little Detroit, which was closer to the town, typically thawed earlier than the deeper parts of Big Detroit found along the south shore of the lake.The ice record for Lake Minnetonka’s ice phenology record started in 1855. Observers, who are selected members of the Freshwater Society Board or Staff, along with deputies from the Hennepin County Sheriff’s Water Patrol, collect data in the watercraft three times per day including at night when ice-off date approaches. After 2014, web cameras located at certain yacht clubs and marinas were used to supplement visual ice observations. The ice-off date is currently defined as when a watercraft is able to travel from any shore to any other shore without being stopped by hard ice. Floating ice is allowed if the watercraft can drive through it. In some of the previous years, climatologists or weather forecasters recorded ice-off dates based on different criteria from the one that is currently used.Shields Lake began in 1894. Over the time series, the transfer of responsibility for recording has been passed down by different individuals living near the lake with Larry Smisek as the most current data contributor. Smisek started collecting ice phenology data in 2013 by visually observing the lake from the northeast side of the lake, which has often been the last location of the lake to thaw. Ice-off date is recorded when 95% of the lake is open water.The ice phenology record of Lake Sunapee’s ice record was started by the Osborne family in 1869 who have continued observing ice phenology across several generations. The ice-off dates are defined as the date it is possible to navigate on a boat from George’s Mills at the northern end of the lake to Newbury Harbor at the southern end. This path transects the long axis of the lake and is adjacent to the Lake Sunapee buoy26.Umbagog Lake’s ice record was likely started in association with water level management for power generation in 1880 by the Union Water Power Company. Ice-off dates are generally defined as the date when the annual winter ice previously covering the lake disappears in spring21.Lake Winnipesaukee’s earliest ice phenology data was recorded in 1887. Ice-off date is recorded as the date when all of the ports for the cruise boat Mount Washington including Alton Bay, Weirs Beach, Center Harbor, Meredith and Wolfeboro are free of ice. The record was first used to track the availability of commercial and passenger transport across the lake based on visual observations from multiple points and different directions around the lake. Modern data are collected by Dave Emerson who flies over the lake two to three times per day for ice coverage information.Cazenovia Lake’s ice record started in 1839. Ice-on date is defined as when the lake is covered with ice and ice-off date is defined as the date that most of the lake is open water. For Cazenovia Lake, freeze and thaw events are recorded as dates when ice breaks up and refreezes. The data on Cazenovia Lake was checked, corrected, and complemented through a review by P.G. Rudstam of available diaries at the Lorenzo Mansion State Historical Site on Cazenovia Lake, and information from Dr. Ken Stewart, University of Buffalo. The diaries were kept from 1839 by consecutive owners of the Lorenzo Mansion (members of the Ledyard family) and are kept at the library of the Lorenzo Mansion State Historical Site. Data after 2008 are from Mr. Phillip Hart, Cazenovia, and his father before him, kept track of these dates for some time and is the source of Ken Stewart’s earlier data. The original Ken Stewart dates were maintained when there was a discrepancy between records from the Hart family and Stewart's assessment. Mr. Hart states that he checks the ice by driving around the lake and that he does not count ice-on dates if the lake broke up again the same day . Over the course of the time-series, changes in data collection procedures were documented in the database.Mirror Lake is located in the Adirondacks with ice phenology information collected from 1903 onwards. Ice-on date is recorded when the lake is covered completely with ice. The ice-off date is the first day after winter ice cover when the lake is mostly free of ice, except possibly small pieces of ice near the shore. Freeze-thaw events, usually at the time of ice formation, are additionally noted. For example, the lake may freeze and melt a day later, then freeze for the rest of the season after two weeks. Lake Placid residents started collecting the data in 1903, most recently data collection has been in coordination with Judith Shea of the Lake Placid Volunteer Fire Department and Dr. Brendan Wiltse, Adirondack Watershed Institute Water Quality Director. Data were collected based on visual observations over the entire lake from the lake shore. Recently, data were supplemented with a 24/7 live feed from a webcam observing the main portion of the lake from the south looking north. When ice-on or ice-off dates near, the lake is further observed in person. Since the historical definition of ice-on and ice-off data have not been well documented, there may be an uncertainty corresponding to the time needed for ice-off to occur. Over the time series, there are no missing years in the ice-off dataset, but 11 years are missing from the ice-on record.Mohonk Lake in 1932. Both ice-on and ice-off dates have been collected since 1932-present. The Smiley Family began recording weather data in 1896 and Daniel Smiley began recording lake ice phenology dates in 1932 each year until his passing in 1989. Daniel Smiley Research Center staff assumed all data collection after Dan passed away and in 2014, a small group of citizen science volunteers named the “Climate Trackers” was trained to collect the data which has continued through 2020, with substitutions by Research Center staff. Ice-on date is defined as the first date of the season when lake ice coverage is 100% and ice-off date is defined as the first date after ice-on when lake ice coverage is completely absent . Further, the percent coverage of lake ice is recorded consistently throughout the season. For instance, if the lake is half frozen, 50% lake ice is recorded. Observers stand at the end of the Mohonk Lake Boat Dock and look toward the southernmost end of the lake from 4 pm to 6 pm to collect information on ice coverage. Additional information, such as ice thickness, was recorded from the center of the lake when it was safe for people to cross. The procedure for collecting data has remained consistent over the time series.The first observation of ice was recorded from Oneida Lake’s ice record began in 1827 with the earliest ice limnological data obtained from two diaries: (i) Asa Eastwood’s diary  interpreted by Jack Henke27 and (ii) James Bernard’s diary  interpreted by E. Mills and C. Hoffman of the Cornell Biological Field Station (CBFS). During the overlapping period of the two diaries (1846–1965), the Bernard diary data was used since that diary also included ice-on dates. The diary data replaces previous data from 1844 to 1900 that were found to be in error. Note that these problematic data were used by Magnuson et al.4, but corrected in subsequent papers from that group e.g.28. Data obtained from 1901 to 1974 were from seven different observers and were kept at the Oneida Fish Culture Station. After 1975, CBFS personnel have been observing ice conditions in the middle of the lake (Shackelton Point) due East, West, and North in both the mornings and afternoons. Further, the amount of open water is noted. For Oneida Lake, ice-on dates are more difficult to define as the ice usually temporarily forms and breaks up again before the final freeze over. This dataset follows the convention of the National Ice Database which states that the first date that the lake completely froze over is recorded as the ice-on date. Ice-off date is better defined as ice often leaves the lake in a few days. However, when the observations are questionable, ice-off date is defined (since 1975) as the date when it is possible to drive a boat from the south to the north shore at a mid-lake location by Shackelton Point at the CBFS. Freeze and thaw events between the first ice-on date and the ice-off date are also recorded. Ice duration is calculated from the day of first ice-on to the day of ice-off and subtracting the number of days the lake was open in between. In the winter of 2001–02, Oneida Lake did not freeze completely so there is no ice-on date. However, there was some ice on the lake and most of that ice had melted by the provided ice-off date. In 2006, half of the lake opened up on March 15th, 2006 and most ice disappeared on April 1st, 2006. For that year we used March 15th to calculate the duration of ice cover, but April 1st as the date when most ice was absent from the lake (ice-out date). When notes indicate the presence of short ice-on periods prior to the given first ice-on date, a three-day ice duration is added to those periods when calculating ice duration for that winter.Otsego Lake’s ice phenology record begins in 1849. Ice thickness data exists for the winters of 1970–71 to 1974–75. The dataset is currently maintained by the SUNY Oneonta Biological Field Station. Records from 1843–1972 were kept by a series of Weather Observers, beginning with George Pomeroy Keese (1843–1910), followed by Elizabeth Cooper Keese (1910–1930), and then staff of a local newspaper the Freeman’s Journal (1930–1972). Those data were compiled and described in a 1973 Climatological Summary29. Definitions of ice-on and ice-off were described for 1843–1930: ice-on date was recorded when the lake was “entirely closed by ice”, ice-off date recorded when “the last ice left the lake”. It has not been confirmed that data collected from 1930–1967 followed the same convention or that observations were made of the entire lake, which may increase the uncertainty of ice-on dates for those years. If observations were made from the Village of Cooperstown (at the southern end of the lake), the area of the lake that usually freezes last is not visible from that location. It is possible that freeze dates prior to ~1950 reflect the condition in the southern end of the lake, and thus may report earlier freeze than would be experienced mid-lake. According to local anecdotes, large sums of money and other commodities were gambled on the ice-out date, so the accuracy of these recorded dates would have been of high importance. The records would have served to inform and document many commercial and recreational activities in Cooperstown that relied on lake ice including commercial ice fishing for lake whitefish, ice harvesting for summer use, transporting over the ice for construction, and maintenance and repair of lake-side summer cottages. In 1967, a Biological Field Station was established in Cooperstown by the State University of New York (SUNY) College at Oneonta and Otsego Lake became a focus of research efforts30. Ice records are maintained by this institution to the present. Ice observations are made by the faculty and staff and occasionally by trained lakeshore residents who will drive around the lake to obtain an entire view of the lake. When observers suspect the lake is ready to freeze, observations of ice conditions are prioritized. Location and size of openings are further noted, but not consistently tracked. One freeze/thaw event was recorded for the winter of 2005–6 when the lake completely thawed and then completely froze again. Total duration of ice cover has been reported as the total number of days with complete ice cover, excluding the span during the thaw.Lake Champlain is located on the border between the United States and Canada and its ice record began in 1814. For Lake Champlain, ice-on dates are referred to as “closure” dates which can be interpreted as cessation of commercial shipping traffic or full ice coverage on the lake from Burlington, Vermont directly west/northwest of Port Kent, New York. The ice-on data were collected from local newspapers and multiple observers including: (i) U.S. Weather Bureau Climatological Record Book in Burlington, Vermont, and Burlington Free Press clipping (Data sources unknown) from 1816–1871; (ii) Charles E. Allen from 1872–1886; (iii) cooperative weather observer Mr. W. B. Gates from 1886–1906; (iv) U.S. Weather Bureau and National Weather Service from 1906-present. Throughout the period, historical records from Shoreham, Vermont, and Old Fort Ticonderoga provided additional information. It is noted that small stretches, or gaps of open water may still exist on portions of the lake which are too small to be observed by the satellite data.Green Lake’s earliest ice records began in 1939. Ice-on dates are defined when a complete line between Sandstone Point and Robin Hood Point is frozen; therefore, ice does not necessarily need to cover the entire lake. Ice-off dates are defined as the date when it is possible for a boat to navigate from the east end to the west end of the lake. The presence of ice chunks is acceptable at this time. Freeze/thaw events within winter are occasionally recorded for Green Lake. Since Carl Mapps started the ice record in 1939, several different observers who lived on Robin Hood Point have been collecting ice phenology data with no missing years. Citizen scientists visually observe the lake from Robin Hood camp point toward Sandstone point. Observers, of which Joseph Norton of Norton Boat Works and Paulette Janssen of the Green Lake Sanitary District are the most recent, try to follow earlier protocols so that the observation methodology remains consistent throughout the time series. Recently, a secondary record with the dates of complete ice cover has been started to complement the record using the original methodology.Geneva Lake’s ice record began in 1862. Theodore W. Peters has been recording the data for the last 25 years. Geneva Lake typically freezes from the east end to the west end. The deepest area of the lake is the last area to freeze. Peters observes the ice from the west end of the lake at the following points: Conference Point, Cedar Point, George Williams College, Brookwood Subdivision lakefront, Fontana, and Williams Bay lakefront while looking towards the lake and scanning for presence of ice with binoculars. Observations are sometimes made multiple times a day with the first observation at around 8 am if the conditions are appropriate. It is easier to detect open water if there is light snowfall. Ice-on date is recorded as the date the lake has been frozen for two days. However, waterfowl will often keep water open, so up to about five acres of open water full of waterfowl is acceptable for the lake to be categorized as frozen. The ice-off date is defined as when the lake is free of ice other than small ice plates that float around or are washed up on the leeward shore of the lake. Freeze/thaw events within a winter are additionally recorded in the database. Factors such as variation in observation point, weather, and ability to see last ice formation contribute to uncertainty in the recent data. The uncertainty of early data may be different because the collecting procedures may not be the same as the one currently applied. The lake has not completely frozen in five of the last 23 years.Lake Mendota’s ice record began in 1852 and Lake Monona’s ice record began in 1851. The earliest ice information for the two large lakes that border Wisconsin’s capital city of Madison, was gathered initially from newspapers. By the 1880s, the ice records were maintained by weather observers at Washburn Observatory and the U.S. Weather Bureau Office at North Hall on the University of Wisconsin-Madison campus. For the last six decades, staff from the Wisconsin State Climatology Office have maintained the ice record, which continues with Lyle Anderson and Ed Hopkins. Because of the irregular shapes of these two large lakes, each lake cannot be viewed in their entirety from one location. Thus, observations are conducted for Lake Mendota from multiple points including Maple Bluff Beach due west direction, Tenney Park due north and west of the locks directions, and Observatory Hill due north direction. For Lake Monona, observers view the lake from: boat launch at Olin Park due east-northeast; BB Clarke Beach due south; Few Street due south; along streets along the north shore of the lake to the east of the Yahara River due south and southeast; and Esther Beach due north. Observations for both lakes are made during the day by multiple observers and cross checked with each other afterward. Webcams on the Space Science and Engineering Building roof at the University of Wisconsin-Madison are consulted during the daylight when the observers are not near the lakes. For Lake Mendota, the date of ice-on is recorded when at least 50% of the lake is frozen and the line between Picnic Point and Maple Bluff is covered with ice, a tradition that goes back for probably a century. When at least 50% of Lake Mendota is ice free and the line between Picnic Point and Maple Bluff is open, the date is recorded as the ice-off date. Ice-on date for Lake Monona is defined as the date when at least 50% of the lake is frozen. Lake Monona ice-off date is defined when 50% of the lake is open water. Multiple freeze/thaw events that occur primarily at the start of the ice season are placed into the records; ice openings or closures of less than 24 hours are not considered. Variations in data collecting procedures undoubtedly occurred in the mid-19th century, but Anderson and Hopkins have strived to reduce current discrepancies as they observe the lakes more routinely and at more different angles than in the early years. Uncertainty may remain due to visual estimation of the percentage of the lake actually covered, foggy or low visibility, and low stability of thin ice sheets that break within 24 hours.Shell Lake’s ice phenology record was started in 1905 based on visual observations made by several individuals of the Washburn County Clerk’s Office, including O.J. Soholt (1931–1981), Jack Brown (1981–2006), Lynn Hoeppner (2007–2012), and Lolita Olson (2013 - present). Observations are conducted from Rolph’s Point where observers look in the northeast direction as described in the Standard Operating Procedure (SOP) which is passed among observers. The ice-on date is recorded when the lake is completely frozen, which is typically when the deepest area of the lake freezes. Ice-off date is defined as the date when the lake is completely thawed with no ice at the deepest area of the lake, although few ice sheets may be present along the shores. Weather conditions leading up to freeze events may additionally be noted.Lake Superior at Bayfield, Wisconsin goes back to 1857. Data collection was started by Neil Howk and his son Forrest for his high school science project15. Early data regarding the opening and closing of Bayfield harbor due to ice cover were gleaned from the Bayfield County Press from 1857 until 1963 and the Island Gazette newspaper from 1964 to 1970, after which they were obtained from the Madeline Island Ferry records. After 2008, a Standard Operating procedure was established for collecting data in which Howk observed ferry operations and verified the dates with the Madeline Island Ferry Line. The dates when the ferry boat ceases and begins operations due to ice conditions were noted. Observations were made at Bayfield, Wisconsin toward the channel between Bayfield and Madeline Island. The ice-on date is the date that the last boat of the season left Bayfield harbor, whereas the ice-off date is defined as the date that the first boat of the season arrives at Bayfield harbor.Ice phenology for Lakes Oulujärvi, Kallavesi, Näsijärvi, Vesijärvi, Päijänne, Pielavesi, Haukivesi, Lentua, Pielinen, Visuvesi, and Palovesi are all located in Finland. For these lakes , ice-on date is defined as the final freeze-up of the lake “within sight” at the observation site  after any possible thaw events31. Ice-off date is recorded when the ice breaks up and is not visible from the observation site. Within sight at a small lake often means the whole lake, but it is difficult for an observer to get information about the freezing of all the parts of a large and complex lake. Ice-on is observed at four stages according to the Finnish Environment Institute’s (SYKE) observation instructions32, depending on the extent of the ice cover within the horizon of the observation site. The four stages of freezing are: i) freezing of the shores, ii) freezing of the bays, iii) freeze-up of the lake within sight and iv) freeze-up of the whole lake. Only a few observation sites display a clear sequence of these four stages, whereas at other sites, it is difficult to distinguish among the four. In some years, severe cold conditions cause all four stages to occur during the same night. The four stages of ice melting are: i) thawing of the shores, ii) thaw areas out of the shore, iii) ice in movement and iv) no ice within sight. If there were several records for the same year from different data sources, the earlier date was used. The duration of ice cover in days was defined as the number of days between ice-on and ice-off32.th century to monitor hydrology, water level records, and waterways important for trading. The longest lake observations, such as in Näsijärvi and Kallavesi, began as lake harbour offices made notes of the open-water lake navigation season. Lake Oulujärvi observations from 1854–1885 were made by a local resident and they were published in a local newspaper in 1934. Since the late 1880s, lake water levels were monitored with ice phenology in many of these lakes. Typically, observations were made from the water level station towards all possible directions by a local observer who was engaged for the duty. Whole lake views were sometimes possible at some observation sites but not for the whole time series and it was not compulsory to take such observations. Observers used to take records at 8 am (the time of water level reading) but ice-on/ice-off stages were reported at any time if the observer was living nearby the station. Sometimes, the exact time is given in the paper reports by the observer, but these are not available in the database since only dates could be stored in the database. All other notes written by reporters were also kept on paper but not digitized. Remote sensing observations from MODIS and Sentinel-2 and web cameras supplement more recent observational data. However, they are not regularly used for screening because of cloudiness and the fact that many of these Finnish lakes are too small and fragmented for remote sensing. Ice data collection procedure instructions, including the different freezing and melting stages, have been written and published in Hydrological Yearbooks (1910–2010). There may have been unremarkable changes in the procedure, although there have been no changes since the 1960s according to the definitions in the yearbooks. It is estimated that the uncertainty associated with the observations was low during the 20th century when the water stations were not automated and observations were conducted daily by persons living by the station. However, over the last 5–10 years, the water level stations were automated on a wider scale, and therefore uncertainty may be larger, as not all observers live nearby, and they may visit a station only every two weeks. In some years, lakes were not visited and freezing/melting dates were estimated from ice records of other lakes. The subjective component of the observation (different observers are involved) is another factor that contributes to the uncertainty of the record32.Ice phenology records were started in the 19Lake Balaton has been on-going since 1925 from a site in Siófok, where the state of lake ice is recorded on a daily basis. These ice records were supplemented with historical ice observations from earlier studies, including “Fishing on the ice of the Lake Balaton33”, “The thermal regime of the Lake Balaton34”, and “The ice of the Lake Balaton35” from three different sites around the lake  to produce a consistent ice record from 1885 to 201636. The ice-on date we report is the start date of the continuous solid ice cover period. The ice-off date is the day the ice cracks, and returns to floating ice. In years where ice phenology data were collected at multiple sites, no significant differences were observed between dates among sites36.The ice record for Lake Þingvallavatn’s ice record started in 1922 by farmer Guðmann Ólafsson at Skálabrekka farm, located in the middle of the lake’s western shore. Ólafsson was keen on nature and enthusiastic about natural phenomena, thus kept diaries with detailed information on farm life, nature, and fishing logs. From 1987 and onwards, Árni B. Stefánsson, an ophthalmologist and owner of a summer house close to Skálbrekka farm, who knew Ólafsson began recording the observations. Visual observations generally took place between 10 am to 6 pm. Observations were conducted from a high location, mostly from hills on the west side of the lake, to obtain a view of the entire lake. A closer look is usually obtained with binoculars or by visiting one or two lake sites. Additional information may be collected from either residents around the lake or from lake photos available over the observation period. The ice-on date is recorded when Lake Þingvallavatn is covered throughout with land-fast ice, except for areas with spring-fed inlets mainly along the North and southwest coast . Ice-off date is defined as the date when the land-fast ice starts to break up resulting in open water and drifting ice-flakes. Although the procedure for collecting data has remained similar, there is large uncertainty during the period 1992–2000 due to some delays in observers’ visits. From 2001 onwards, Árni B. Stefánsson has been backing up his own observations by contacting farmers around the lake when he is away from his summer house37.Lake Atnsjøen in 1917 by directly observing the lake in the morning. Between 1917–1999, observers would stand at the northern shore of the lake  and face towards the north. After 1999, observations were made from the northern part of the lake  towards the south. Different staff of the NVE have been following the same procedure to collect this data. However, since the 1980s, the same observer has recorded the ice dates. In recent years, web-cameras and residents who live near the lake provide additional information to increase the data accuracy during critical periods. The ice-on date is recorded as when some ice first appears on the lake, whereas the ice-off date is when the lake is completely ice free. The dataset additionally contained information of daily weather conditions and water level.The Norwegian Water Resources and Energy Directorate (NVE) began recording ice data from Lake Aursunden’s ice phenology record began in 1902 by the regional hydropower company (Glommens og Laagens Brukseierforening). Between 1902–2012, the data were collected through weekly morning observations from the western shore of the lake  towards the east. As the observers lived nearby, sometimes additional information was obtained in between the weekly visits particularly during critical periods of ice formation and thaw. After 2002, remote sensing including Moderate Resolution Imaging Spectroradiometer (MODIS) from the National Aeronautics and Space Administration (NASA) (up to 2015) and Sentinel-2 from the European Space Agency (ESA) (2015 onward) have been additionally used to collect ice phenology data to increase the accuracy. The ice-on date is defined when the ice is first observed, whereas the ice-off date is the date there is no ice on the lake.Lake Tesse in 1908 with weekly observations in the morning from the northern shore  while looking southward. The ice-on date is the day when some lake ice appears for the first time and ice-off is recorded as the date that the lake is completely ice free.The regional hydropower company (Glommens og Laagens Brukseierforening) started the lake ice phenology dataset for Lake Tunhovdfjorden’s record began in 1920 by the NVE to provide information for the development of a hydropower reservoir. Weekly direct observations were made in the morning from the southern shore  towards the south of the lake from 1920 to 1994. There was a large gap in the ice record during 1994–2014 after which the ice data were collected using remote sensing observations from Sentinel-2 at the lake centre . The observers that lived near the lake sometimes provided additional information between weekly visits which increased the data accuracy during critical periods. The ice-on date is the day when some lake ice first appears, whereas the ice-off date is when the lake is completely free of ice.For all of the Norwegian lakes described in this study, additional features of the ice were recorded prior to and during the time of observation including: first ice in registration site, partial freeze-up at registration site, complete freeze-up at registration site, first ice near shore, ice freeze-up near shore, partial freeze and break up if there was open water in sight of several kilometers, breaks in data record, freeze-up across the entire lake, and ice-free across the entire lake.Serwy Lake’s ice phenology record began in 1888. The Russian Ministry of Road Information started the record to manage inland waterways and reported it annually from 1888 to 1918. After 1918, the ice record was conducted by Polish Hydrographic Service. Observations were made daily from piers about 20 m away from the southern shoreline of the lake towards the north at 06 GMT by employees of the Institute of Meteorology and Water Management - National Research Institute (IMWM – NRI) in Warsaw. Additional information such as the place of occurrence  and type of ice was also noted. Subsequently, web cameras were incorporated into the study as a complementary observation. The ice-on date is defined as the first day with ice cover in winter (but ice may melt later), when 100% of the lake area within a visible measurement sector was covered with ice. Ice-off date is defined as the last day with ice cover in winter (day before the date of disintegration of the ice cover).Lakes Orsasjön, Näckten, Kallsjön, Storuman, Göuta, Runn, and Jukkasjärvi are lakes located across Sweden. The systematic recording of lake ice began in the late 19th century and early 20th century, for example in 1859 for Runn, in 1870 for Orsasjön, Kallsjön and Göuta, and in 1908 for Näckten. For all of these lakes, ice-on dates are defined as the day when the main lake area is first covered by ice and the ice cover lasts for at least 3 days over at least two-thirds of the lake area. Ice-off date is defined as when the main lake area is ice free implying that some small bays may still have ice cover. If the lake freezes again, the last date when it opens is taken as the ice-off date38. Freeze-thaw events throughout the winter season are also recorded. The Swedish Meteorological Institute (SHMI) was founded in 1945 and started recording lake ice data for national monitoring using a Standard Operating Program established in the national ice monitoring program. The institute also collected older ice observations and homogenized them. They further used visual observations (including daily observations for larger lakes) as the primary means to collect data which were supplemented with satellite imagery in the last few years. Although the procedure for collecting data was consistently used throughout the study and the SHMI’s staff was highly experienced, there may be limited uncertainty associated with the variability in personal judgements and observations.Ice coverage information from ten lakes located on the Swiss plateau, an area in Switzerland with altitudes between 400–700 m, is included in the database. As the average winter air temperatures in this area of Switzerland are slightly above the freezing point, these relatively deep lakes no longer freeze each winter. For these lakes, a common definition was used for ice-on and ice-off dates. The ice-on date is defined when the lake is completely or almost completely (>90%) covered with ice for more than one day. On the other hand, the ice-off date is defined as the date when more than 10% of the lake has open water (this implies that less than 90% of the lake is still frozen). In years when the historical information is from newspapers, there may be uncertainty in the dataset of a few days. It is possible that freezing events were not reported by newspapers, and would be missed. We believe that this risk is in general small, as the freezing of larger lakes did not occur each winter, and had economical , and socio-cultural  implications. Visual observations might be especially affected in case of impaired visibility . For some of the lakes systematic registrations were made, which are expected to be associated with less uncertainty .Lake Aegeri’s ice phenology record began in 1914. Observers examined the lake from different locations around the shore. The information was gathered from several sources: i) the newspaper Zuger Zeitung (1914 - present), ii) systematic handwritten chronicle (1914–1964), iii) Livingstone’s scientific publication (1964–1988)39, iv) lake police’s systematic registration and some non-systematic registration of fishermen (1981–2006), and v) webcams and restaurant owner on the lake shore (2007 - present).Lake Baldegg are gathered from a local newspaper, diaries, and personal communication. In 1891, Naturforschenden Gesellschaft Luzern started the record and continued for the first ten years for scientific investigation purposes. After 1901, information was collected via newspapers  up to 1955. Family Hofer, in addition to fishermen on Lake Baldegg and Lake Sempach continued the record based on visual observations up to recently. Ice is observed on the lake at various locations visually.Freeze and thaw events in Lake Biel’s ice record was started by the fishermen Arnold Martin, out of his curiosity and for fishing purposes in 1923. From 1923 to 2006, ice phenology information was observed and systematically recorded each year into the family’s diary. Arnold Martin and family would observe the lake mostly in the morning in the southern direction from the shore or on boats while on the lake. Measurements of ice depth and percent ice coverage were also noted. Since 2007, data have been obtained unsystematically from newspapers with additional information provided by webcams. Limited visibility can lead to overestimation of ice coverage.Lake Greifen from 1901 to 1948. Between 1949 and 1980, data were gathered from von Eugen and Orn40. From 1963 onwards, data have also been obtained from the lake security service’s observations distributed around the lake, in addition to webcams, and information from boats used for daily passenger traffic over the lake. Webcams observe the lake from the eastside opposite of Maur in the northwest and south directions. Boats, on the other hand, collect data from Maur to Uster (middle of lake). Observations are done mostly in the morning. The uncertainty of the data before 1949 is larger than data more recently.Local newspapers were used to gather early ice records for Lake Hallwil’s ice phenology records began in 1901 and data were collected from the newspaper Luzerner Zeitung (1901–1954), the boat designer Urs Merz (1955–2010), and a webcam combined with social media afterwards. Web cameras provided observations for ice coverage information from high locations due east in the morning. Urs Merz made many of the observations for most of the time series before he passed away. Taking into consideration the diverse information sources from the observers and other villagers along the lake, the data is likely reliable.Lake Murten’s ice record began in 1901. Data were first obtained from the local newspaper Murtenbieter for the first 70 years (to 1970), after which it was based on observations of fishermen until 2006. After 2006, ice data have been obtained from webcam images and information from a boat service across the lake. The lake is observed in the northwest direction over the lake. Additionally, for Lake Murten, newspapers and fishermen reported information of freeze and thaw events, although the fishermen did not systematically record freeze-thaw events after 1971.Lake Pfäffikon’s ice record began in 1922. The earliest data were collected from newspapers. From 1942 to 1999, ice phenology information was supplemented with visual observations from Anton Hiestand (1942–1999) and von Eugen & Örn40 (data for 1948–1980). Observations were usually performed in the morning at multiple locations while observers were looking over the lake. Anton Hiestand and von Eugen & Örn40 also provided two time series of systematic registration for freeze-thaw events which were also reported in newspapers. In addition, webcam images (since 2003) and social media have provided additional ice records.Lake Sarnen began in 1901. Data were mostly obtained from the newspaper Obwaldner Volksfreund. In addition, the lake police and the fisher family Hofer have been providing scattered ice information based on their observations since 1971, and webcam images have been used since 2007. Observations were made due southwest and north while observers took notes of ice phenology information including ice depth and ice coverage. In the period between 1947 and 1954, more information was provided from personal diaries and systematic registration. Only from 1947 to 1954 freezing events were registered systematically by observers at site, while for other periods the information on ice cover was only written down in case of freezing events of interest.The ice record in Lake Sempach have been recorded since 1891. Data from 1891 to 1900 were recorded by Naturforschenden Gesellschaft Luzern, who started the scientific record. Ice phenology dates that occurred between 1901 and 1955 were noted in the Luzerner Zeitung newspaper. From 1955 onward, they are recorded in the fishermen family Hofer’s diary. The family would stand at the northwestern part of the lake in Oberkirch and look over the lake in the southeastern direction to obtain information. In addition, the degree to which the lake is frozen is noted.Freeze and thaw events in Lower Lake Constance (Untersee)’s ice phenology record started in 1887 by the Iceclub Steckborn to manage outdoor ice-skating activities. The ice club also kept the record of most freeze and thaw events, in addition to ice depth measurements. After 1955 up to 2012, ice phenology records were obtained from newspapers such as Newspaper Bote vom Untersee and Rhein to complete the data set. Iceclub Steckborn continues to perform observations from 1955 until present, but with less systematic registration in diaries. Webcams have been incorporated into the study since 2006. Webcams were set up along the southern lake border in Steckborn, Switzerland and directed due north to obtain images of the lake in the morning. Other points of the southern border of Lower Lake Constance such as Ermatingen are also observation sites. Social media is an additional means of collecting data. It is believed that the ice club observations are very precise.Lej da San Murezzan is located in an alpine valley and not on the Swiss plateau. The ice dataset for Lej da San Murezzan was started in 1831. Both the ice-on and ice-off data were collected based on visual observations. The methodology for collecting data in years prior to 2016 was unavailable. However, after 2016, observations were conducted on an hourly basis with assistance of two webcams at the north shore (St Moritz) that provide images toward the south and east directions for most of the lake. Additional information was obtained from water temperature measurements performed at the center of the lake. Since temperature-based estimation is an indirect method, there is an uncertainty owing to the lag time between webcam and temperature monitoring.Lake Suwa’s ice-on record was officially started in 1443 by the The Ohori family of the Suwa Grand Shrine. The ice records were collected primarily for religious purposes based on the worship of nature. The appearance of the sinusoidal ice ridge, the omiwatari, is traditionally interpreted by the shintoist tradition as the mark of a god who walked across the frozen lake. The direction of the cracks of the omiwatari was used as a signal to forecast the agricultural harvest for the coming summer. Observers stand at the shoreline of the lake and look towards the lake centre. The observation is often conducted at a single point view at the mouth of the Funato River, but sometimes the observers may confirm the ice-on or omiwatari from multiple sites, especially since the advent of vehicles which allowed observations at multiple sites. During the era of the current Shinto priest, Mr. Kiyoshi Miyasaka, observations were conducted by the Chief Priest (Guji in Japanese) and some parishioners (Ujiko in Japanese) who live in Takashima (later Kowata) village at 6:30 AM every day from the start of January to the start of February. After 1897, people from Yatsurugi Shrine and Suwa Meteorological Observatory were trained to observe ice data of the lake. The ice-on date is recorded when the lake is completely covered with ice. For Lake Suwa, the date of the appearance of a sinusoidal ice ridge also called the “omiwatari” in Japanese is further noted. The data collection procedures may have slightly changed over the time-series because the principal reason for the observations was to forecast the agricultural harvest in the coming summer based on the direction of the omiwatari, so the ice-on dates did not need scientific accuracy. No one knows exactly how the procedures have changed. The information was reported annually, although ice-on dates are missing and uncertain during the middle of the record. For example, the years between 1682 and 1896 are uncertain because of changes in the calendar from lunar to Gregorian and confusion between recording the ice-on date, omiwatari date, or the omiwatari ceremony date2.Lake Baikal’s ice phenology record began in 1896 in Listvyanka  to control the goods transported across the lake between Russia and China. Data in the years prior to 1950 were collected from different historical records by head of department of Hydrology and Hydrophysics (1960–1971), Limnological Institute, Siberian Branch of Russian Academy of Sciences, Vladimir Sokolnikov. After 1950, ice data have been attained via visual observations by Anna Ponomareva, Matrena Alsaeva, and Ekaterina Fomina (1950–1990); in addition to Andry Zhdanov, Rita Zhdanova and Elena Salva (1991 - present). Observers would conduct observations during the afternoon at the pier of boats 30 m away from the shore in Listvyanka while facing south and looking from east to west. Percentages of open water and ice coverage are noted during the observation progress. The ice-on date is recorded when lake Baikal is completely covered with ice. When more than one percent of the lake is open water, the date is recorded as the ice-off date. Freeze/thaw events as well as a description of freezing and thawing processes are additionally documented at various locations across the lake.41. The datasets were split into three main files that include ice-on and ice-off dates (PhenologyData.csv), the physical characteristics of each lake including the geospatial coordinates (LakeCharacteristics.csv), and corresponding metadata for each lake, including the number of missing years and definitions of ice-on and ice-off (Definitions.csv). All datasets can be connected by the unique lake name (column name = lake) that is present in each. For those interested in examining patterns in ice phenology among lakes, the PhenologyData.csv would be all that is required. We also recommend downloading additional ice phenology data for hundreds of lakes and rivers around the Northern Hemisphere from the Lake and River Ice Phenology (LIAG) dataset stored at the National Snow and Ice Data Centre (NSIDC42) or within Canada specifically from the Canadian Ice Database housed at the Polar Data Catalogue43. Some of the lakes provided in this study are a subset of those found within LIAG, although unfortunately detailed data descriptors had not been previously collected. For others interested in using the data in combination with remotely sensed data or downscaled climate models, we recommend joining the LakeCharacteristics.csv to the PhenologyData.csv and the Definitions.csv by the “lake” column. Potential resources that could be relevant for testing changing patterns in lake ice include the HydroLAKES database for geomorphic data44, Moderate Resolution Imaging Spectroradiometer (MODIS) for spectral bands to be used in remote sensing, or Climatic Research Unit of East Anglia for monthly climate values45. We also recommend WorldClim for historical and future climate patterns under multiple general circulation models and four shared socio-economic pathways46.All data is open access and can be found on FigshareAlthough we could not precisely quantify uncertainty in ice-on and ice-off dates for these 100+ year long datasets, the uncertainty for many of the lakes may be in the order of magnitude of one day to several days. General factors contributing to uncertainty include: variability in personal judgement between lake ice observers, low visibility, or a lake freezing over the weekend or holidays. For example, in Wilson Lake, different observers sometimes report dates that are one day apart for the same year. Low visibility, including fog, incomplete views of lakes, and nightfall, such that a lake freezes overnight and has melted by the morning, can contribute additional uncertainty in ice-on and ice-off dates.We conducted quality assurance and quality control on the database to ensure each observation was accurate. The data were reviewed by multiple members of the team using similar methods to check for discrepancies. There were three components that required specific attention during review including: 1) lake names, 2) lake physical characteristics, 3) dates for ice-on or ice-off.Lake names were reviewed for consistency among observation records. In many instances, lakes had inconsistent names due to differences in locations surveyed, anglicization of lake names, or local synonyms. For instance, Lake Baikal was occasionally reported as Listvyanka, the town where the observations of the lake was reported. In another instance, Cobbossee Lake is often used for Cobbosseecontee Lake, presumably a local colloquialization of the name. We reviewed each of the lake names and created consistent labelling with each lake name being all lower case and multiple words separated with an underscore. For each lake name, we did not include any mention of the word “Lake” . Accented or non-ASCII characters were replaced with non-accented, similar alphabetic equivalents. We included within our database a column that represents identically the italicized names of the lakes reported within this manuscript (LakeCharacteristics.csv).We obtained geospatial coordinates from the Lake Ice Analysis Group (LIAG), part of the National Snow and Ice Data Center (NSIDC). There were twelve lakes that were not matched in the NSIDC database and were instead collected by contacting the original data providers. We reviewed these coordinates to ensure each occurred in the identified lake. In a few instances, we adjusted the coordinates of lakes that were slightly outside of the water to be located near the center of the lake. These discrepancies would occur because latitude and longitude from NSIDC were only reported to two decimal places, which often lacks the precision to accurately identify a point within the lake. Some observations had different geospatial coordinates but were located within the same lake. For consistency, we use the same latitude and longitude for all observations within the same lake. We collated characteristics and morphology of the lakes including elevation, surface area, mean lake depth, maximum lake depth, and shoreline length. We also provide columns for the data source that was used to obtain these data. For instance, in many lakes, we were able to acquire this information from the LIAG database, but in other instances, we used very specific resources such as the Norwegian Water Resources and Energy Directorate for the Norwegian Lakes. We were not able to obtain lake characteristics and morphology for all variables and all lakes.The dates of ice-on and ice-off were reviewed for consistencies among lakes and anomalies among years. The first verification step was to confirm the correct year, as the 2019–2020 ice season, for example, would alternately be reported as 2019 or 2020; the latter of these, sensibly, was used in cases where only ice-out is recorded. All dates were revised to follow the format of year-month-day with year being in a four-digit format (i.e. YYYY-MM-DD). When no data were available, a blank was reported. Most of the database provides information for the longest continuous ice presence, but in some cases there were intermittent freeze-thaw events. We provide a column specifying the freeze event that occurred when multiple freeze thaws would occur. Each additional freeze-thaw event would be labelled sequentially . This formatting allows for recording of a near infinite number of freeze-thaw events. However, lakes rarely had more than three ice on-off dates. For a given season, ice-on has to occur before an ice-off event. We reviewed observations where ice-off dates were reported to occur before ice-on dates. There is typically a linear relationship between ice-on and ice-off dates. Therefore, to check for anomalies in dates, we conducted regressions between ice-on and ice-off day-of-year. Dates that departed considerably from the linear pattern were reviewed to ensure accuracy. In some instances, the original observer or data collector from the lake was contacted to verify the date. We also checked the difference of the minimum and maximum date relative to the next closest value within the timeseries to determine if there were transcription errors. If the data provider included a “duration” column we added it to our dataset, but we found that these values were not consistent with the difference between ice-off date and ice-on date. Two of the most common reasons why the duration column had inconsistent estimates was because 1) some providers only subtracted ice-on date from ice-off date, while others added 1 to make it an inclusive duration, and 2) in years with multiple freeze-thaw events, some providers took the difference from the first ice-on and last ice-off, but others summed only the days when the lake was ice covered (i.e. only counted the ice frozen days).


Placement of the pedicle screw is technically challenging during C1-2 fusion surgery in children and different intraoperative image-guided systems have been developed to reduce the risk of screw malposition. The purpose of the present study was to compare surgical outcomes between C-arm fluoroscopy and O-arm navigated pedicle screw placement in the treatment of atlantoaxial rotatory fixation in children.We retrospectively evaluated charts of all consecutive children with atlantoaxial rotatory fixation who underwent C-arm fluoroscopy or O-arm navigated pedicle screw placement from April 2014 to December 2020. Outcomes including operative time, estimated blood loss (EBL), accuracy of screw placement (Neo's classification) and completed fusion time were evaluated.p < 0.05) was observed with respect to the median blood loss. There were no statistically significant difference  with respect to the median operative time.A total of 340 screws were placed in 85 patients. The accuracy of screw placement of the O-arm group was 97.4%, which was significantly higher than that of the C-arm group (91.8%). Both groups had satisfied bony fusion (100%). Statistical significance (230.0 ± 34.6 ml for the C-arm group and 150.6 ± 47.3 ml for the O-arm group, O-arm-assisted navigation allowed more accurate screw placement and less intraoperative blood loss. Both groups had satisfied bony fusion. O-arm navigation did not prolong the operative time despite the time required for setting and scanning. The atlantoaxial joint is the most mobile joint of the spine because of the horizontally oriented facet joints, the lax ligaments and the robust synovium that allow hypermobility . But theWith the development of modern techniques and instruments, the atlantoaxial posterior screw-rod technique has become the gold standard of the posterior fixation technique for AARF . This haThe O-arm navigation system , a three-dimensional intraoperative imaging device, has gained worldwide popularity since its first introduction in 2008 , 12. HowWe retrospectively reviewed the medical records of consecutive patients who underwent C1–C2 fusion between April 2014 and December 2020. The study was reviewed and approved by the Institutional Review Board of Second Affiliated Hospital of Naval Medical University. All patients were subjected to instrumentation utilizing the Resnick and Benzel's procedure . for C1–Each patient received preoperative cervical traction for an average of 3 days. Surgery was recommended for those who were resistant to closed reduction , 14. RadThe patients were placed in a prone position with a radiolucent plaster bed to secure the head under general anesthesia. Cranial traction (with a maximum of one sixth body weight) was performed to reduce the dislocation as much as possible. A posterior midline incision was made to expose the posterior region of the C1-2 complex. The surgical technique for the fluoroscopic guided group was previously described . RegardiVariables including operative time, estimated blood loss (EBL), screw placement accuracy, intra- and postoperative complications, length of stay, and complete fusion time were recorded.A CT scan at postoperative day 1 was taken to confirm the position of the screws. Screw accuracy was assessed using Neo's classification :. Grade Solid bone fusion was assessed on a 12-month CT-scan, and was defined as the presence of continuous bridging trabecular bone between the dorsal elements of C1 and C2.p value < 0.05 was considered as a statistical significance. Normalized data were compared using the unpaired t test, with data expressed as means ± standard deviation. Fisher's exact test and the Chi-square test were used to analyze categorical data.Statistical analyzes were performed with SPSS version 21.0  and the Eighty-five patients who underwent C1-2 fusion were included in the present study: 46 in the C-arm and 39 in the O-arm groups. Mean age at surgery was 9.67 years . The mean follow-up was 12 months (range 13–16) .p = 0.025), details shown in A total of 340 screws were inserted. On postoperative CT-scan, the screw accuracy rate of the O-arm group was 97.4%, which was significantly higher than that of the C-arm group  was observed regarding the median operative time between the two groups, details shown in EBL showed a statistical difference between C-arm and O-arm groups with 230.0 and 150.6 ml respectively, No serious complications such as vascular complications, spinal cord injury, or cerebrospinal leak occurred and, the postoperative course was uneventful for all patients. The average length of stay was 3.5 days (range 3–6). Both groups had satisfied bony fusion (100%) at 12 months of follow-up.In this study, we showed that the accuracy of pedicle screw placement in C1-2 fusion surgeries using the O-arm guidance was higher than those using C-arm. Ling et al. reported that 98% of their screws were placed in ideal positions in 21 patients treated with a Harm's construct or occipital cervical fusion using the O-arm . We achiAnother benefit of O-arm navigation was that it could reduce intraoperative blood loss. Hitti et al.  reportedMore importantly, as the pedicle size in children is small, repeated adjustment during screw placement could lead to screw loosening, which would seriously affect the pullout strength. Navigation with the O-arm provided the precision to insert all C1 and C2 screws in a single path, which technically also translated into greater bony purchase and biomechanical stability. Additionally, because of interference from the mandible and teeth that overlap, conventional fluoroscopic techniques cannot clearly assess the degree of reduction due to the relationship between the odontoid and the lateral mass. The advent of O-arm navigation has overcome this shortcoming by providing axial CT images during navigation, which clearly shows the position of the odontoid in relation to the lateral mass, as well as the foramen transversarium and spinal canal in relation to the pedicle screws. Another point, when navigated with fluoroscopy, interpretation of the screw trajectory requires constant switching between the lateral and antero–posterior views. O-arm navigation based on simultaneous guidance by axial, sagittal, and coronal views allowed the positions of the screws to be updated in real time as they advanced into the vertebrae. Therefore, we could check the trajectory and position of the screw to reduce the possibility of reoperation due to mispositioned screws.Prolonged operative time was another potential problem with O-arm navigation due to the time required to set up and scan. Hitti et al. reported that posterior fixation of C1–C2 with O-arm navigation (198.4 ± 13.56 min) takes longer than with the C arm fluoroscopy (156.9 ± 10.03 min) . HoweverThis study was limited by its retrospective design and the non-randomization of patients. Since the introduction of the O-arm in our institution, only a few C-arm surgeries have been performed. Furthermore, surgery for pediatric C1-2 fusion was relatively rare and required a steep learning curve, which was a limitation for large-scale studies. Further studies will be required to reach a more definitive conclusion.O-arm-assisted navigation allowed more accurate screw placement and less intraoperative blood loss in pediatric C1-2 fixation, compared to a conventional fluoroscopic guided device. Using O-arm navigation did not prolong the operative time despite the time required for setting and scanning.


Human cytochrome P450 CYP3A4 is involved in the processing of more than 35% of current pharmaceuticals and therefore is responsible for multiple drug-drug interactions (DDI). In order to develop a method for the detection and prediction of the possible involvement of new drug candidates in CYP3A4-mediated DDI, we evaluated the application of midazolam (MDZ) as a probe substrate. MDZ is hydroxylated by CYP3A4 in two positions: 1-hydroxy MDZ formed at lower substrate concentrations, and up to 35% of 4-hydroxy MDZ at high concentrations. The ratio of the formation rates of these two products  was used as a measure of allosteric heterotropic interactions caused by effector molecules using CYP3A4 incorporated in lipid nanodiscs. The extent of the changes in the SOM in the presence of effectors is determined by chemical structure and is concentration-dependent. MD simulations of CYP3A4 in the lipid bilayer suggest that experimental results can be explained by the movement of the F-F’ loop and concomitant changes in the shape and volume of the substrate-binding pocket. As a result of PGS binding at the allosteric site, several residues directly contacting MDZ move away from the substrate molecule, enabling the repositioning of the latter for minor product formation. CYP3A4 is the main drug metabolizing cytochrome P450 in humans. The simultaneous binding of two or three substrate molecules results in non-Michaelis behavior because of homotropic or heterotropic interactions between substrates ,7,8,9. IIn most cases, drug interactions are detected in vitro as the reversible or irreversible inhibition of CYP3A4, and as concomitant diminished clearance of the target substrate. The identification of such effects requires measurements of metabolism at various effector concentrations and the estimation of an IC50. In addition, subsequent in vivo studies may reveal other factors, such as the induction of P450 expression, which may invalidate in vitro conclusions. Understanding the molecular mechanisms of possible DDI mediated by cytochromes P450 would provide a useful conceptual basis for a systematic analysis of the most important factors. Importantly, experimental protocols for in vitro studies should provide quantitative and reproducible measurements of essential biochemical parameters, such as catalytic rates and binding constants. The incorporation of heterologously expressed CYP3A4 in lipid nanodiscs allows one to obtain an array of data supporting the general mechanistic understanding of homotropic and heterotropic cooperativity in CYP3A4 ,25,26,27CYP3A4 monomer in nanodiscs can bind up to three steroid molecules ,24, as wA functional importance of steroid binding at the remote site was shown by multiple spectroscopic and biochemical methods. For example, the binding of TST at this site inhibits the autoxidation of CYP3A4 ,33, incrSimilar results were obtained with larger substrates, atorvastatin (ARV) and dronedarone (DND) , where tOverall, most substrates can also appear as allosteric effectors for CYP3A4, when they bind to the peripheral site shown in In this work, we propose using midazolam (MDZ) as a probe substrate as a means for testing multiple compounds for potential drug-drug interactions.Midazolam has been commonly used as a specific substrate for CYP3A4 activity in vitro ,36,37,38Based on this information, MDZ can be considered as a sensitive probe for drug-drug interactions mediated by CYP3A4. To extend this understanding, we systematically probed the effects of several steroids and other drugs on MDZ metabolism and on the site of metabolism (SOM) ratio, determined as the ratio of 1OH and 4OH production rates. We found that mutations at residues 211–214 significantly perturb these allosteric interactions, again indicating the involvement of F-F’ loop as the part of CYP3A4 allosteric site in the regulation of the MDZ regiospecificity.Overall, these results strongly suggest that the 1OH/4OH SOM ratio in MDZ hydroxylation can serve as a sensitive probe for the ability of other drugs to interact with the allosteric site in CYP3A4 and to perturb the metabolism of CYP3A4 substrates. In order to study these interactions in a systematic manner, we first studied these allosteric interactions using MDZ as a substrate and PGS as a well-established effector with known affinity to the allosteric site . Then, wIn a previous paper , we demoAndrostenedione (9001311), corticosterone (16063), medroxyprogesterone (24908), progesterone (15876), testosterone (15645), gefitinib (13166), schisandrin A (19849), α-naphthoflavone (16924), and midazolam (16193) were purchased from Cayman Chemical Company. POPC lipids were purchased from Avanti Polar Lipids. All other chemicals were purchased from Sigma-Aldrich. Structures are shown in the The expression and purification of the membrane scaffold protein (MSP) used for nanodisc formation, cytochrome P450 CYP3A4, and rat P450 reductase, as well as the assembly of CYP3A4 into POPC nanodiscs (ND), were performed following previously described protocols ,33. BrieSubstrate titration experiments were performed using 1–2 μM CYP3A4 in nanodiscs with a Cary 300 spectrophotometer  at 37 °C. The final concentration of methanol used for substrate solubilization was always <1.5%.−1 cm−1.CYP3A4-incorporated nanodiscs with CPR added at a 1:4 molar ratio in the presence of a substrate were preincubated for 5 min at 37 °C in a 1 mL reaction volume in 100 mM HEPES buffer (pH 7.4) containing 10 mM MgCl2 and 0.1 mM dithiothreitol. The concentration of CYP3A4 was in the range of 60–100 nM. The reaction was initiated with the addition of 200 nmol of NADPH. NADPH consumption was monitored for 5 min and calculated from the absorption changes at 340 nm using an extinction coefficient of 6.22 mMg for 30 min, and 20–40 μL portions of supernatants were injected onto an Ace 3 C18 HPLC column  on a model LC-20LD chromatograph (Shimadzu). The mobile phase contained 22% acetonitrile and 28% methanol in water; products of PGS hydroxylation and MDZ hydroxylation were separated at a flow rate of 0.15 mL/min as follows: isocratic separation for 20 min, then a linear gradient for 5 min during which the concentrations of acetonitrile and methanol were increased to 50% and 32%, respectively, followed by a second isocratic separation for 12 min. The calibration and method validation were performed using commercially available metabolites of PGS and MDZ. The chromatograms were processed with Shimadzu software.For product analysis, the reactions were performed in volumes of 80–100 μL in microcentrifuge tubes. At the end of the incubation period, the reactions were quenched by the addition of 20 μL of acetonitrile containing an internal standard (37 μM nordiazepam). The samples were centrifuged at 3000× http://www.charmm-gui.org/ last accessed 15 May 2022) [We prepared conventional all-atom molecular dynamics simulations using the CHARMM-gui software (ay 2022) ,52 as deay 2022) . Each syay 2022)  (proteinay 2022) . For theay 2022) . We seleay 2022)  to incluay 2022) , the Ambay 2022)  to derivay 2022) . Parametay 2022) .−1 nm−1 and next equilibrated in six steps using a Berendsen thermostat while gradually decreasing restraints at T = 310 K. For minimization and equilibration, all bonds to hydrogen atoms were converted to constraints and the LINCS algorithm was employed [The systems were first energy minimized using a steepest descent algorithm if the maximum force did not exceed 1000 kJ molemployed . For proemployed .In order to explore the sensitivity of the SOM ratio of MDZ hydroxylation (the ratios of 1OH-MDZ and 4OH-MDZ formation) in the presence of various effectors, we measured the rates of MDZ hydroxylation at different substrate concentrations in the absence and in the presence of various effectors. As reported earlier , progestNext, we tested the sensitivity of the SOM ratio of MDZ hydroxylation in the presence of other steroids, using similar approach. We measured the rates of 1OH-MDZ and 4OH- MDZ production at various MDZ concentrations in the presence of several steroids, namely, androstenedione, corticosterone, testosterone, and medroxyprogesterone, The concentrations of steroids were 20 µM and 50 µM, except for medroxyprogesterone (2 µM and 8 µM), based on their apparent binding constants to CYP3A4, estimated from the spectral titration curves (data not shown). The binding of medroxyprogesterone was significantly tighter, and lower concentrations of this steroid were used to prevent the complete inhibition of MDZ hydroxylation.All steroids show the allosteric perturbation of MDZ metabolism, changing the SOM ratio (1OH/4OH). The strongest effect is from testosterone, and the weakest is from corticosterone. For all steroids, this effect is concentration-dependent, which may be the result of the different affinity of these steroids to the allosteric pocket and partly due to possible variations in the interaction mode and in the conformational changes of CYP3A4 caused by these interactions. The allosteric effect of steroids is concentration-dependent, indicating the binding of all the steroids to the remote allosteric site of CYP3A4 because the productive site is occupied by the substrate MDZ. At higher MDZ concentrations, the difference in the SOM caused by the presence of steroids becomes significantly weaker, similar to the tendency observed with PGS, suggesting that MDZ competes with steroids for the allosteric site.The same set of experiments was performed with several other non-steroid substrates. We used the well-known effector of CYP3A4 ANF ,44, the S, in order to avoid the significant inhibition of MDZ hydroxylation, similar to the experimental conditions with steroids as effectors. ANF concentrations were selected in a similar manner based on earlier titration results [In order to probe the possible binding of these drugs in the substrate-binding pocket, we performed the spectral titration of CYP3A4 in nanodiscs with Gefitinib and Schisandrin. The results shown in  results .The SOM ratios for MDZ hydroxylation measured in the presence of ANF, Gefininib, and Schisandrin are shown in 1, (FeO) intermediate. This choice of productive position of the substrate is based on the commonly accepted mechanism of P450 catalyzed hydroxylation as hydrogen atom abstraction followed by oxygen rebound. We scanned all eight simulations, 3.8 µs total, for these conformations of CYP3A4 and found 13,879 such structures for simulations without PGS and 14,238 structures with PGS present as an allosteric effector, or slightly more than 50% of all of them. This is consistent with the high uncoupling of MDZ hydroxylation, as measured for CYP3A4 in nanodiscs [CYP3A4 is highly dynamic, and its substrate-binding pocket undergoes substantial changes in size and shape during MD simulations. The substrate MDZ is also moving with respect to the heme, and rotating so that the orientation of the substrate with respect to the catalytic heme iron–oxygen intermediate changes significantly. Because our goal is to find the most important structural parameters responsible for the site-specific hydroxylation of MDZ, we selected for analysis only those frames in which MDZ was in a “productive” position. We defined the positions of MDZ as potentially productive, when C1  and C4 (minor site) from the virtual point corresponding to the oxygen atom of Cpd The statistical analysis of the number of close contacts of CYP3A4 residues with substrate MDZ is shown in In these simulations, the binding of PGS as an effector is seen to induce the significant loss of MDZ contacts with residues 106 and 108 in the B-C loop and residues 215, 218, and 220 in the F-F’ loop. In addition, contacts with residues 217 and 309 are also becoming rarer, but these numbers are relatively lower, i.e., they represent a decrease of less than 50%. On the other hand, contacts of MDZ with residue 214 occur significantly more often in the presence of PGS, and residues 304 and several others are also more often in contact with MDZ, although these increases are significantly less than 50%. Overall, these observations are consistent with experimentally observed the higher mobility of the substrate MDZ in the presence of effector PGS, as the total number of lost contacts with CYP3A4 residues decreases as a result of allosteric effector binding.A representative example of the conformational changes observed in the presence of PGS at the allosteric site is shown in Understanding the mechanism of allosteric interactions in CYP3A4 is important for the development of new drugs and for the prediction of drug-drug interactions. Although a complete picture of CYP3A4 allostery may not yet be available, the essential details schematically shown in The results obtained in this study, together with earlier publications, provide an experimental basis for simple and sensitive screening for potential heterotropic drug-drug interactions mediated by CYP3A4. Using MDZ as a probe substrate, allosteric interactions with the peripheral site at the protein–lipid interface can be detected by monitoring the SOM ratio, i.e., the ratio between the major C1-hydroxylated product and the minor C4-hydroxylated product. The effect of various compounds is concentration-dependent, indicating their competitive displacement of the probe substrate MDZ, which also acts as an effector. The latter observation provides a useful measure of the relative affinity of tested compound binding to the allosteric site. This method of detection of allosteric effectors for CYP3A4 as an alternative source of potential drug-drug interactions complements the commonly accepted monitoring of drug interactions caused by competitive inhibition, where the rate of the main product of MDZ hydroxylation is measured in the presence of alternative substrates or inhibitors.The position of the substrate and SOM preferences may be changed by mutations ,68,69 an