Award: OPP-2512432

Intellectual Merit: This award supported the investigation of the effects of meltwater input from tidewater glaciers on dissolved organic matter (DOM) composition and variability off Antarctica, focusing on the West Antarctic Peninsula (WAP). Coastal waters around Antarctica are influenced by increasing rates of mass losses from ice sheets and glaciers. In tidewater glaciers, where meltwater is introduced into the ocean at subsurface, buoyancy-driven upwelling is observed, bringing deep water to the surface and potentially influencing DOM dynamics. Melting can also introduce dissolved organic carbon (DOC) contained in the ice itself into the ocean. In this project, samples were collected in early 2025 along 4 transects extending offshore from glaciers along the WAP, and analyzed for DOM composition using Fourier-transform ion cyclotron resonance mass spectrometry. Our analyses revealed gradients in DOM composition along the transects, with coastal waters being relatively enriched with small molecules containing a small number of carbon, hydrogen and oxygen atoms compared to offshore DOM. Coastal DOM is also characterized by a relative depletion in nitrogen-containing molecules. The influence of meltwater was generally observed in coastal waters near glaciers, progressively decreasing with increasing distance from the glacier face. Analyses of samples collected near the Thwaites Glacier in the Amundsen Sea in 2022 revealed a similar pattern, with substantial overlap in the molecular formulae enriched in coastal DOM in the Amundsen Sea and in the WAP. This indicates that similar biogeochemical processes may be at play controlling the composition of coastal DOM in different regions and times around Antarctica. DOM composition in the WAP is now being compared to that from coastal waters around the Kerguelen Islands, in the Indian Ocean sector of the Southern Ocean. The Kerguelen Islands are characterized by multiple land-terminating glaciers, providing a contrast to the WAP for identifying how subsurface meltwater inputs influence DOM dynamics in coastal polar environments.

Broader Impacts: This project supported the training of three graduate students. Findings supported by this study are described in two scientific articles in preparation, and were presented in scientific conferences. Observations have been made publicly available at BCO-DMO (https://www.bco-dmo.org/project/999485) and USAP-DC. During the expedition, multiple presentations were delivered to guests aboard the National Geographic Endurance vessel.

Last Modified: 06/03/2026
Modified by: Patricia M Medeiros