The carbon cycle in the coastal zone under the effects of climate change

• Main Author: Lansard, Bruno
• Other Authors: Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), 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, Edwige PONS-BRANCHU
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: coastal ocean; sediment; carbon; oxygen; carbonate; early diagenesis; eutrophication; hypoxia; acidification; diagenèse précoce; eutrophisation; hypoxie; océan côtier; sédiment; carbone; oxygène; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Arctic; Arctic Ocean; Beaufort Sea; Climate change; Mackenzie river; Ocean acidification
• Online Access: https://theses.hal.science/tel-04469382; https://theses.hal.science/tel-04469382/document; https://theses.hal.science/tel-04469382/file/HDR%20Bruno%20Lansard.pdf

Coastal zones are particularly vulnerable to the multiple effects of climate change and anthropogenic pressures. Thermohaline stratification of surface waters, eutrophication, deoxygenation and acidification of bottom waters are at the origin of multiple stress factors. In this context, the carbon cycle is undergoing numerous disturbances, and the role of the coastal ocean as a carbon sink or source is still very uncertain. The sedimentary component of these shallow, heterogeneous environments is complex, relatively undocumented and particularly variable in space and time. This manuscript presents the state of knowledge on the carbon cycle at coastal interfaces. It pays a particular attention to sediment biogeochemistry and ocean acidification, with a special focus on early diagenesis and the carbonate system at the sediment-water interface. These issues are addressed on 3 main RiOMars (River-dominated Ocean Margins) systems with very contrasting characteristics: (i) in the Arctic Ocean with the Mackenzie River and the Beaufort Sea, (ii) in the Mediterranean with the Rhône River and its prodeltaic sediments, and (iii) in the northern Gulf of Mexico under the influence of the Mississippi River. Below the water-sediment interface, the characterization of mineralization processes (oxic and anoxic) and their interactions with the carbonate system provide a better understanding of benthic fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA). Under the influence of ocean acidification, dissolution of sedimentary carbonates may well increase in RiOMars systems. At the sediment-water interface, DIC fluxes enhance the acidity of bottom waters, while TA fluxes buffer bottom waters. This work is the fruit of teamwork resulting from the co-supervision of 3 PhD theses and several M2 internships. Our results contribute to a better understanding of the role of coastal zones, in general, and sediments, in particular, in the carbon cycle at the continent-ocean interface. Les zones côtières sont particulièrement ...