Sources and composition of suspended particulate organic matter in Admiralty Bay and the Bransfield Strait, Antarctic Peninsula

Suspended particulate organic matter (POM) plays a central role in carbon cycling and trophic transfer in Antarctic waters, yet its sources, composition, and degree of transformation remain poorly constrained in nearshore Antarctic Peninsula. Here, we characterize the elemental (C and N), isotopic (δ 13 C and δ 15 N), and lipid biomarker (alcohols, sterols, and fatty acids) composition of suspended POM collected in Admiralty Bay and the Bransfield Strait, south of King George Island, during late austral spring 2019. Surface samples were collected at 12 stations, whereas DCM samples were collected at 6 of these stations. Suspended particulate matter concentrations ranged from 5.4 to 21.9 mg L −1 and showed marked variability between the two sampling campaigns. Molar C/N ratios and lipid biomarker distributions indicate a predominance of marine-derived, phytoplankton-associated OM, largely linked to diatom-rich assemblages with minor contributions from other marine sources. Diagnostic lipid biomarker ratios further suggest that suspended POM was relatively fresh and had undergone limited early diagenetic alteration. Paired comparisons between surface and DCM samples revealed no statistically significant depth-related differences, indicating limited vertical variability in OM composition within the upper water column. The results show that physical forcing primarily regulates particle loads, whereas biological production exerts stronger control on OM composition and quality, highlighting the sensitivity of Antarctic coastal carbon cycling to ongoing environmental changes along the Antarctic Peninsula.