Dynamic changes of dissolved organic matter in surface water off the Northern Antarctic peninsula during summers of 2018–2020

The Southern Ocean, the region with the strongest carbon sink in global ocean, is sensitive to climate warming. Dissolved organic matter (DOM) is the largest reduced carbon reservoir in ocean and serves many crucial functions in marine ecosystems. Therefore, it is important for understanding the dynamics and response of DOM in the Southern Ocean in the context of climate warming. In this study, we investigated DOM in surface water off the Northern Antarctic peninsula (NAP) during the austral summers of 2018, 2019, and 2020 using elemental analysis, optical spectrometry, and high-resolution mass spectrometry. The results revealed a continuous increase in dissolved organic carbon (DOC) concentration from 2018 to 2020 (43.1 ± 12.7 vs. 60.2 ± 23.0 vs. 72.6 ± 24.5 μmol C L⁻¹), while chromophoric DOM concentration showed an opposite trend. Multiple optical parameters suggested that samples in 2018 had the lowest biological activity, highest humidification degree and more aromatic components, whereas samples in 2020 had the highest biological activity, the lowest humidification degree and more protein-like components. The significant correlations between DOM parameters and environmental factors (e.g., temperature, Chl-a) indicate that the variations in DOM within the NAP are a result of the complex biogeochemical processes in the Southern Ocean, influenced by factors such as sea ice melting, ocean acidification, shifts in zooplankton populations, and biological activity. Considering only the three years of data presented in this study, we recommend conducting long-term investigations into DOM in the Southern Ocean