Physical-biological processes regulating summer sea-air CO2 exchanges along the Drake Passage and northern Antarctic Peninsula

Abstract

We determined the sea-air carbon dioxide (CO₂) exchanges and investigated the main physical-biological processes responsible for regulating the sea surface partial pressure of CO₂. This was done through the analysis of continuous and discrete measurements of oceanographic and atmospheric variables measured during the NAUTILUS V cruise (January 2019) crossing the main fronts along the Drake Passage and several distinct biogeochemical provinces along the northern Antarctic Peninsula. The main findings indicated that the Drake Passage acted as a weak net CO₂ outgassing area (∼0.1 mmol m⁻² d⁻¹), although contrasting regions with close sea-air CO₂ fluxes magnitudes of ∼3 mmol m⁻² d⁻¹ were identified north (a net CO₂ sink zone regulated by net photosynthesis) and south (a net CO₂ source zone regulated by net respiration) of the Polar Front. On the other hand, the northern Antarctic Peninsula areas demonstrated a more heterogeneous sea-air CO₂ exchanges behaviour varying from moderate net CO₂ outgassing of ∼1.3 mmol m⁻² d⁻¹ (Bransfield Strait, western Antarctic Peninsula and Weddell Sea continental shelves) to a moderate (∼ −2.4 mmol m⁻² d⁻¹) or weak (∼ −0.1 mmol m⁻² d⁻¹) net CO₂ ingassing in Antarctic Sound surroundings and Gerlache Strait, respectively. It is interesting to note that a huge intensification of the net CO₂ outgassing of ∼5 mmol m⁻² d⁻¹ was identified in the area under the influence of the Antarctic Slope Front bifurcation eddy south of Clarence Island. The CO₂ outgassing is expected in this stationary and anticyclonic feature, but its magnitude was ∼75 % higher than the known estimate, which was associated with strengthen winds and eddy dynamics. Net respiration was the leading biological process occurring in the study area, except north of Polar Front where net photosynthesis prevailed. The patchy distribution of sea-air CO₂ exchanges behaviour along the Drake Passage and northern Antarctic Peninsula reinforced the needs for better understanding and focus on finer resolution of the CO₂ chemistry and processes at regional and local investigations, especially in a region suffering with multiple climate stressors, located in a transition zone of warm and cold environments, and key to connect the Southern Ocean ecosystems in a circumpolar way.