Sea Ice Melting Drives Substantial Change in Dissolved Organic Matter in Surface Water off Prydz Bay, East Antarctic

Abstract

AbstractPolar ecosystems are vulnerable to climate warming and are characterized by a rapid decline in sea ice. In this study, we collected surface water samples from the Southern Ocean off Prydz Bay during and after sea ice melting season (SIM). After removing the particles using 0.7‐μm pore size filters, we measured the concentration of dissolved organic carbon (DOC) and the composition of dissolved organic matter (DOM) by using the total organic carbon analyzer, optical spectrometry, and high‐resolution mass spectrometry. The mean DOC concentration during the SIM is 1.3‐fold higher than that during the post‐SIM, whereas the a350 value, an indicator of chromophoric DOM, showed the opposite trend by a factor of 2.8. Five components, including three humic‐like and two protein‐like substances were identified by fluorescence excitation emission matrices‐parallel factor analysis, in which protein‐like biolabile components were enriched during the SIM and humic‐like refractory components were enriched during the post‐SIM. The DOM in the water samples from the SIM had higher proportions of polycyclic aromatics, polyphenols, and compounds within molecular lability boundary, whereas the DOM from the post‐SIM had a higher proportion of highly unsaturated compounds. Statistical analysis revealed significant correlations between DOM and sea‐ice melting/associated environmental factors (e.g., water temperature, salinity, and microbial activity). These collective results suggest that sea ice melting is an important factor driving a transition from more labile to more refractory DOM in the surface water off Prydz Bay, which may have a profound impact on the marine ecosystem and carbon cycle in the polar ocean.