Spatial variability of marine carbonate system along the Drake Passage and northern Antarctic Peninsula during the austral summer

The influence of physical and biogeochemical processes on the variability of the carbonate system in the Southern Ocean remains poorly constrained. Understanding this influence is crucial to distinguish natural variations from anthropogenic impacts and accurately interpret observed trends. Here, we investigate how physical and biogeochemical processes influence the spatial distribution of summer carbonate system variables along the Drake Passage and northern Antarctic Peninsula. Continuous, high-frequency surface partial pressure of CO₂ (pCO₂), dissolved oxygen (O₂) and essential hydrographic variables were collected during the austral summer of 2019, whereas other carbonate system variables were estimated after the reconstruction and evaluation of total alkalinity. Our findings show that in the Drake Passage, Circumpolar Deep Water upwelling increases the pCO₂ (> 400 μatm) and dissolved inorganic carbon (> 2175 μmol kg⁻¹), leading to reduced pH (< 7.99) south of the Polar Front. North of the Polar Front, photosynthesis lowers pCO₂ (< 390 μatm), while increasing pH (> 8.00) and carbonate ions (> 110 μmol kg⁻¹), with enrichment occurring in the Subantarctic coccolithophore growth region. Along the northern Antarctic Peninsula, including Gerlache Strait, Antarctic Sound, and Admiralty Bay, photosynthesis and sea ice/glacial melt are the main drivers of pCO₂ reductions to levels below 350 μatm. The mixing of Circumpolar Deep Water with Weddell Sea Dense Shelf Water can naturally and anthropogenically raise pCO₂ and decrease pH in northern Antarctic Peninsula waters, where pH is generally lower (as low as 7.90) compared to adjacent areas. Nevertheless, most environments remain supersaturated with respect to carbonate minerals calcite and aragonite, although signs of aragonite undersaturation have occur in surface waters influenced by Dense Shelf Water. These findings offer new insights into carbonate system processes across a large Southern Ocean region, improving understanding of spatial variability in marine carbon dynamics.