| Summary: | ASLO Aquatic Sciences Meeting, Resilience and Recovery in Aquatic Systems, 4-9 June 2023, Palma de Mallorca, Spain.-- 1 page, figures Understanding mesopelagic carbon budgets is central to answering pressing ecological, climatic, and economic questions: from the oceans’ role in carbon sequestration to the transfer of primary production to higher trophic levels. However, biogeochemical models used to simulate and predict mesopelagic carbon budgets still suffer from large uncertainties, which arise in part from poorly constrained parameters. Global ocean biogeochemistry models are typically optimized using climatological fields (e.g., nutrients, oxygen, export fluxes) as observational targets, therefore tuning them to reproduce the long-term mean state of the ocean. Our working hypothesis is that model parameters can be further constrained using high-resolution profiles from biogeochemical (BGC-) Argo floats, using particulate backscattering as a proxy for particulate organic carbon (POC). To test this hypothesis, we selected single-float coherent annual time series in the Labrador Sea (subpolar North Atlantic) and matched them to 1D biogeochemical model simulations (NEMO4-PISCESv2_RC). We then identified the model parameters that control mesopelagic POC budgets to (i) run comprehensive sensitivity analyses via parameter perturbations, (ii) optimize the most sensitive parameters against BGC-Argo observations using a genetic algorithm, and (iii) quantify the impact of parameter optimization on tridimensional POC fluxes. Our approach sheds new light on elusive mesopelagic POC budgets and their modulation by intense events in productive high-latitude oceans
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