Interactive comment on “ Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident ” by M . A
The paper presents an interesting estimation of the offshore and vertical 134Cs fluxes from the Fukushima Nuclear Power Plant that followed the earthquake and resulting tsnunami of 11 March 2011. The radium-based methodology is appropriate to attain the objectives of the study, allowing to estimating water apparent ages as well. The manuscript is well written and structured and the covered issue is of undoubtedly relevance within the scope of BG. However, there are some general and specific comments that should be addressed before publication.
On the calculation of eddy diffusivity in the shelf water from radium isotopes: High sensitivity to advection
Abstract The concentrations of the radium isotopes have been used in previous studies to estimate eddy diffusivity on the continental shelf. These studies assume that the advective transport of the radium isotopes is negligible. A theoretical investigation using an analytic model with advection indicates, however, that the eddy diffusivity thus estimated is highly sensitive to the advection. It is shown that the error can be very large even for an advective velocity of the order of 1 mm/s–1 cm/s. The sensitivity increases with the increase of the half life of the isotope. For a 1 mm/s advective velocity, the estimated eddy diffusivity for the radium isotope with the shortest half life (i.e. 224Ra) is almost doubled. In addition, we also conclude that (1) advection has more important effects on smaller values of eddy diffusivity; (2) the effect of advection increases rapidly as advection increases; and (3) offshore advection tends to increase the apparent eddy diffusivity and inshore advection tends to decrease the apparent eddy diffusivity, if the advection is ignored. Based on these facts, an improved model is presented to calculate both advection and eddy diffusivity using the activities of two isotopes, which yields consistent diffusivity and advection from different isotope pairs.
Ocean predictive skill assessments in the South Atlantic: Crowd-sourcing of student-based discovery
Autonomous Underwater Gliders have over a decade long history of successful regional deployments serving scientific, societal and security needs in application areas ranging from pole to pole and including the full range of water depths from shallow coastal seas to the deep ocean. Glider deployments covering the basin scale are much fewer, but are a growing capacity as demonstrated by the Woods Hole to Bermuda line that crosses the Gulf Stream, the Atlantic Crossing line that follows the Gulf Stream, and the basin circling flights now being conducted as part of the Challenger Glider Mission. The next step in the evolution of the global Challenger mission is to enable an ensemble of modelers from different institutions and agencies to participate in a meaningful way. This process with be formalized in 2014 by leveraging the data management tools of the U.S. Integrated Ocean Observing System (IOOS) and the education tools of the U.S. National Science Foundation's (NSF) Ocean Observing Initiative (OOI). The Education Visualization (EV) tools developed by the OOI's Education and Public Engagement (EPE) Implementing Organization (IO) are currently being configured through the cyber OOI net to display real time OOI glider data with intuitive interactive browser-based tools, reducing the barriers for student participation in sea exploration and discovery. Through U.S. IOOS, forecast ocean data will be harvested from the ephemeral ocean snapshots produced by an ensemble of ocean models along the same glider tracks as Challenger. The parallel observed and forecast datasets, both evolving in real time, will be accessible through the same OOI EV tools, enabling student participation in a crowd-sourced ocean predictive skill experiment. The result will satisfy one of the important goals of the Challenger mission by enabling students to assess of the quality of the ensemble of available global scale ocean models. Student research team projects that use the new model data comparison capabilities will be conducted during the summer of 2014. Students will compare an ensemble of the global ocean models along the high velocity transport pathways by gliders on basin-scale missions, such as one that traverses the northern side of the South Atlantic gyre along the Brazilian shelfbreak. The lasting impact of the Challenger mission will be a global fleet available to respond to events, an assessment of the ocean models along the fastest ocean transport pathways, and the establishment of a network of gliderports for global response.