Rapid change of dissolved organic matter in surface water off Western Antarctic Peninsula during summers of 2018-2020

Recent warming has caused the rapid change of marine ecosystem in the Western Antarctic Peninsula (WAP). However, the response of dissolved organic matter (DOM) to this change is not well understood. In this study, we investigated the quantity and quality of DOM in surface water in the WAP during Austral summers of 2018, 2019 and 2020 using elemental analysis, optical spectrometry and high-resolution mass spectrometry. We found continuously augment for 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), and higher chromophoric DOM concentration in 2018 than that in 2019 and 2020. Additionally, samples in 2018 had the lowest BIX, SUVA254, HIX, AImod and photolabile humic-like component intensity, suggesting more extensive microbial transformation from biolabile protein-rich DOM to bio-refractory humic-like DOM. In contrast, samples in 2020 had the highest BIX and more bio-labile compounds, but the lowest a350, SUVA254, HIX and AImod, suggesting greater contributions of fresh biolabile compounds. A positive correlation between DOC concentration and salp abundance in 2020 suggests that salps may be an important contributor to DOM in surface water in the WAP. These data, plus significant correlations between environmental factors and DOM-derived parameters, suggest that the variability in zooplankton community (salps vs. krill), primary productivity and microbial activity are responsible for substantial changes of DOM in the WAP.