Impact of anthropogenic perturbation on the biogeochemistry of the global coastal ocean

• Main Author: Bourgeois, Timothée
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Université Paris Saclay (COmUE), Laurent Bopp
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2017
• Subjects: Ocean; Coastal; Biogeochemistry; Carbon; Modelling; Océan; Côtier; Biogéochimie; Carbone; Modélisation; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Ocean acidification
• Online Access: https://theses.hal.science/tel-01565302; https://theses.hal.science/tel-01565302/document; https://theses.hal.science/tel-01565302/file/70561_BOURGEOIS_2017_archivage.pdf

The coastal ocean suffers from the convergence of multiple anthropogenic stressors with climate change at the forefront. Combined stresses from global warming, ocean acidification, eutrophication and deoxygenation threaten coastal ecosystems and thus their services that humans rely on. Unfortunately, the coastal ocean's large spatiotemporal heterogeneity limits our understanding of the biogeochemical processes involved and their responses to anthropogenic perturbations. The current database of coastal observations remains insufficient, and global biogeochemical ocean models have long been inadequate to the study of the global coastal ocean. Indeed, the spatial resolution of these models has been too coarse to resolve key small-scale coastal processes. However, continual improvements in computational resources now allow global simulations to be made with sufficiently high model resolution that begins to be suitable for coastal ocean studies. In this thesis, we propose to study the evolution of the coastal ocean biogeochemistry at the global scale over recent decades using higher resolution versions of the global physical-biogeochemical model NEMO-PISCES. After evaluating of the global representation of the coastal biogeochemistry in this ocean model, we estimate the current role of the coastal ocean in the ocean uptake of anthropogenic carbon and we study the impact of the anthropogenically driven changes in riverine inputs on the coastal biogeochemistry. From simulations made at 3 different spatial resolutions (200 km, 50 km, 25 km), we esteem that the 50-km model grid offers the best compromise between quality of results and computational cost. The upgrade to 25 km does not appear to provide significant improvement in model skill of simulating coastal biogeochemical fields. After evaluating the model, we provide an estimate of the coastal-ocean sink of anthropogenic carbon, the first study to do so with a global 3-D model. In our simulation, the coastal zone absorbs only 4.5% of the anthropogenic carbon taken ...