CO2 sink and source zones delimited by marine fronts in the Drake Passage

Abstract

Net sea-air CO₂ fluxes (FCO₂) in the Drake Passage (DP) were studied at a climatological scale (1999–2019) using observations from the Surface Ocean CO₂ Atlas (SOCAT) database. Based on the monthly climatological position of the main circumpolar fronts of the DP (the Subantarctic Front (SAF), the Polar Front (PF) and the Southern Antarctic Circumpolar Current Front (SACCF)) and the thermal and nonthermal contributions to FCO₂, we present a regional subdivision into different regimes that provide new insights into the processes controlling these fluxes. Our results indicate that the region in the north of SAF (R1) behaves as an annual CO₂ sink (-1.3 ± 1.0 mmol m⁻² d⁻¹); this sink weakens between SAF-PF (R2) and PF-SACCF (R3) and the region south of SACCF (R4) acts as an annual CO₂ source (2.2 ± 3.3 mmol m⁻² d⁻¹). The annual mean CO₂ uptake in DP is 1.3 ± 15.5 Tg C yr^-1. Analysis of thermal (TE) and nonthermal (nonTE) effects on seasonal sea surface CO₂ partial pressure (pCO₂^sw) variability indicates that DP is mainly dominated by nonTE. Results emphasize that carbon fluxes are driven by mesoscale and submesoscale processes north of the PF and by the upwelling of Upper Circumpolar Deep Waters in the Antarctic boundary of the DP, while seasonal patterns are mostly modulated by local factors such as nutrient availability, biological activity and ice cover.