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Global oceanic simulations of trace elements

AuthorsLe Gland, Guillaume; Mémery, L.; Aumont, O.; Gorgues, Thomas
Issue DateMay-2015
Citation47th International Liege Colloquium on Marine Environmental Monitoring, Modelling and Prediction (2015)
AbstractThe biogeochemical fluxes and ecosystem functioning are tightly controlled bythe ocean dynamics and by a wide range of sources and sinks associated with biological, chemical and physical phenomena. Our knowledge of tracer distributions, which relies mostly on aliased observations in space and time, is flawed. It is mostly noticeable in models where parameterizations of subgrid processes, limited understanding of biogeochemistry, and imprecise atmospheric forcing hamper our capacity to realistically simulate the fluxes. One way to better constrain poorly known parameters in models is to use the integrated information contained in “proxy” tracers depending on only a few key processes. In this study, we will model two trace elements at a global scale and a spatial resolution of 1° with ocean dynamics model NEMO (Nucleus for a European Modeling of the Ocean) and compare them with data from the GEOTRACES international program in order to better understand the cycle of carbon and associated elements. As a first step, complementary numerical tracers and water mass ages have been computed to understand the circulation model behavior and to better describe the time scales associated with ventilation processes and continental shelves – open ocean exchanges : these simulations will be used in the analyze the results.Radium, a conservative tracer unaffected by chemistry, is emitted mainly by submarine groundwater discharge and sediments and removed only by radioactive decay. Because of its half-life of 5.75y, 228Ra is a good proxy of exchanges between the sediments and the open ocean. A consistent pattern will be searched for between model horizontal dynamics, radium data and boundary conditions. We will perform an inversion of the data into sediment fluxes by using the transport matrix of the model, and transposing it to reconstruct the transit time distribution and origin of water masses, as described in Khatiwala [1]. Thorium is produced by the decay of uranium, which is proportional to salinity, and removed by its own decay and by scavenging by particles, since thorium is much less soluble than uranium. With a half-life of 24.1h, on the same order of magnitude as the sinking time of large particles, 234Th is a proxy of biogenic particle dynamics and the carbon pump. A nonlinear inversion of the data will be performed to improve the biogeochemical parameterization of vertical particle dynamics. [1] Khatiwala, S. (2007). A computational framework for simulation of biogeo-chemical tracers in the ocean. Global Biogeochemical Cycles, 21, GB3001, doi:10.1029/2007GB002923
Description47th International Liege Colloquium on Marine Environmental Monitoring, Modelling and Prediction, 4-8 May 2015, Liège, Belgium.-- 1 page
Publisher version (URL)http://gher-diva.phys.ulg.ac.be/PresentationManager/
Appears in Collections:(ICM) Comunicaciones congresos
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