Improving the dynamics of a coupled physical-biogeochemical model of the North Atlantic basin through data assimilation : impact on biological tracers

• Published in: Journal of Marine Systems
• Main Authors: Berline, L., Brankart, Jean-Michel, Brasseur, Pierre, Ourmieres, Yann, Verron, Jacques
• Other Authors: Laboratoire des Écoulements Géophysiques et Industriels Grenoble (LEGI), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: Biogeochemical model; Physical-biological interactions; Data assimilation; SEEK filter; Mesoscale processes; Nutrient supply; North Atlantic; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
• Online Access: https://hal.science/hal-00220480; https://hal.science/hal-00220480/document; https://hal.science/hal-00220480/file/ber06.pdf; https://doi.org/10.1016/j.jmarsys.2006.03.007

Several studies on coupled physical–biogeochemical models have shown that major deficiencies in the biogeochemical fieldsarise from the deficiencies in the physical flow fields. This paper examines the improvement of the physics through dataassimilation, and the subsequent impact on the ecosystem response in a coupled model of the North Atlantic. Sea surfacetemperature and sea surface height data are assimilated with a sequential method based on the SEEK filter adapted to the couplingneeds. The model domain covers the Atlantic from 20°S to 70°N at eddy-permitting resolution. The biogeochemical model is aNPZD-DOM model based on the P3ZD formulation. The results of an annual assimilated simulation are compared with an annualfree simulation.With assimilation, the representation of the mixed layer depth is significantly improved in mid latitudes, even though the mixedlayer depth is generally overestimated compared to the observations. The representation of the mean and variance of the currents isalso significantly improved.The nutrient input in the euphotic zone is used to assess the data assimilation impact on the ecosystem. Data assimilation resultsin a 50% reduction of the input due to vertical mixing in mid-latitudes, and in a four- to six-fold increase of the advective fluxes inmid-latitudes and subtropics. Averaged zonally, the net impact is a threefold increase for the subtropical gyre, and a moderate (20–30%) decrease at mid and high latitudes.Surface chlorophyll concentration increases along the subtropical gyre borders, but little changes are detected at mid and highlatitudes. An increase of the primary production appears along the Gulf Stream path, but it represents only 12% on average for midand high latitudes. In the subtropical gyre centre, primary production is augmented but stays underestimated (20% of observations).These experiments show the benefits of physical data assimilation in coupled physical–biogeochemical applications.