The role of the Mackenzie River in the carbon biogeochemistry of the Beaufort Sea coastal waters (Arctic Ocean)

• Main Author: Bertin, Clément
• Other Authors: LIttoral ENvironnement et Sociétés (LIENSs), Institut national des sciences de l'Univers (INSU - CNRS)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Université de La Rochelle, Vincent Le Fouest
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: CCSD 2023
• Subjects: Arctic; Land-to-sea interface; Riverine plumes; Terrigenous dissolved carbon; Ocean-sea icebiogeochemical modeling; Arctique; Interface terre/mer; Panaches fluviaux; Carbone dissout terrigène; Modélisation océan/glace/biogéochimie; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Arctic Ocean; Fleuve Mackenzie; Mackenzie River; Mer de Beaufort; Arctique*; Beaufort Sea; Global warming; Mackenzie river; Océan Arctique; Sea ice
• Online Access: https://theses.hal.science/tel-04288860; https://theses.hal.science/tel-04288860v1/document; https://theses.hal.science/tel-04288860v1/file/2023Bertin206378.pdf

About 10 % of atmospheric carbon dioxide is sequestered in the ocean above 60°N, half of which is in coastal seas where 10 % of the global riverine freshwater volume flows in. Five of the world’s largest rivers convey in the Arctic Ocean (AO) huge quantities of dissolved carbon in the organic (DOC) and inorganic (DIC) form. The response of the coastal ocean to this supply is still highly uncertain, which makes the assessment of air-sea CO2fluxes challenging in this remote region. It is thus timely to gain a better understanding of the impact of terrestrial carbon released by watersheds on air-sea CO2 fluxes in Arctic rivers plumes, especially in a context of global warming. In the present PhD thesis, the ECCO-Darwin ocean-sea ice-biogeochemical model is used to investigate the synoptic to interannual response of the South eastern Beaufort Sea (Western AO) to the Mackenzie River’s carbon exports. The model includes the very first daily terrestrial DOC (tDOC) runoff forcing estimated through merging riverine in situ measurements and coastal remotely sensed data at three major delta outlets, over the last two decades (2000-2019). We find that interannual variability in river discharge modulates localized air-sea CO2flux in the coastal plume with riverine DIC contributing twice as much as riverine DOC to CO2 outgassing. As current knowledge on tDOC remineralization in Arctic plume regions is still uncertain, the range of air-sea CO2 flux variability due to microbial remineralization is estimated to ±0.39 TgC yr−1 in 2009. Other biophysical processes also contribute to the high CO2 flux variability, such as tDOC flocculation (+0.14 TgC yr−1 in gassing) and enhanced plume stratification (+0.35 TgC yr−1 outgassing). To conclude, the work presented here intends to pave the way toward a better representation of the land-to-ocean continuum (LOAC) in regional Arctic models with the aim to improve the simulated carbon cycle in rapidly changing Arctic watersheds and coastal seas. Cinq des plus grands fleuves mondiaux sont ...