Distinct optical properties of dissolved organic matter near Getz and Dotson ice shelves in the Amundsen Sea

The Amundsen Sea, located in West Antarctica, is undergoing rapid melting due to the intrusion of Circumpolar Deep Water. This intrusion results in ice sheet thinning and basal melting, which can have cascading effects on the biogeochemical cycle of dissolved organic matter (DOM) by introducing iron from sea ice and glaciers and by affecting ocean circulation. Therefore, it is crucial to understand the dynamics of the DOM in this region. Our study focused on assessing the optical properties of DOM in the oceanic areas adjacent to the West Getz Ice Shelf (WGIS) and the Dotson Ice Shelf (DIS). Notably, the WGIS regions exhibited relatively high dissolved organic carbon (DOC) and chromophoric DOM (CDOM) absorption coefficient at 350 nm (a₃₅₀). Molecular weight indices, including spectral slope coefficient (S_275-295) and specific UV absorbance at 254 nm (SUVA₂₅₄), suggested that high molecular weight DOM with a substantial aromatic component predominated in the WGIS regions. Conversely, the DIS regions showed low CDOM values, low SUVA₂₅₄ values, and elevated S_275-295 values, indicative of low molecular weight CDOM with lower aromaticity. Furthermore, we observed significant negative correlations between the biomass of Phaeocystis antarctica (P. antarctica) and phosphate (PO₄) in the WGIS regions. However, no such relationship was found in the DIS region. These findings imply that the high concentration and molecular weight of a₃₅₀ in the WGIS regions, spanning from the surface layer to deeper depths, are predominantly driven by autochthonous sources, notably the colony-forming blooms of P. antarctica. The results of this study highlight the crucial role of bloom conditions in shaping both the quantity and quality of DOM in the Amundsen Sea.