Drivers of surface distribution of dissolved organic carbon and nitrogen along the northern Antarctic Peninsula and the Atlantic Southern Ocean

Dissolved organic carbon and nitrogen (DOC and DON, respectively) are important components of the carbon and nutrient cycle in marine systems. However, there are still significant gaps in understanding the role of these compounds in the biogeochemical cycles of polar environments, due to the limitations of spatiotemporal sampling. Here, we present an overview of surface distributions of DOC and DON along the Northern Antarctic Peninsula (NAP) and Atlantic Southern Ocean (ASO), using the dataset available between 1992 and 2022, collected during different seasons. We used DOC data collected from RV Almirante Maximiano cruises by the Brazilian High Latitude Oceanography Group (GOAL), along the NAP, DOC and DON data collected from RV Polarstern cruises (Alfred Wegener Institute, Germany), along the ASO, as well as DOC and DON datasets from international repositories. DOC and total dissolved nitrogen were analyzed primarily with a Shimadzu TOC-L® Series. DON was calculated by subtracting dissolved inorganic nitrogen concentrations from total dissolved nitrogen. Excess DOC and DON were calculated by subtracting the respective deep concentrations. Surface DOC concentrations ranged from 42.0 to 127.0 μmol kg^–1, while surface DON concentrations ranged from 1.0 μmol kg^–1 to 11.3 μmol kg^–1. At the surface, the highest concentrations of DOC and DON were observed mainly in the western sector of the Southern Atlantic (longitudes > 20° W), due to the proximity of coastal areas such as in the Gerlache Strait in the NAP and South Georgia and the Falklands Islands in the ASO. Increase in the surface concentrations of both DOC and DON were also associated to frontal systems. The accumulation of DOC and DON along the NAP and western sector of the southern Atlantic seem to confirm the link between the production of organic matter and the proximity of iron-supplying land-masses leading to enhanced primary production and plankton biomass (chlorophyll-a concentrations and particulate organic carbon). The production of nitrogen-rich organic matter by zooplankton seemed to be the main factor determining DON distributions. The wide spatial coverage of DOC and DON made it possible to identify significant differences in DOC and DON distributions between different regions, as well as interannual and seasonal differences from data collected in the same regions. DOC and DON can be considered important indicators for evaluating the coupling between physical, biogeochemical, and climate processes over time.