Shaping DOM Signatures in East Antarctic Lakes: Penguins, Mosses, Meltwater, and Processing Mechanisms

Rapid environmental changes in Antarctica highlight the need to understand the role of its lakes as potential carbon cycling hotspots. Dissolved organic matter (DOM) in these lakes drives biogeochemical processes, yet its sources and transformations remain poorly characterized. We investigated DOM molecular composition in five lakes from the Windmill Islands, East Antarctica, combining molecular‐level data with biogeochemical data to infer DOM sources. Our findings revealed that DOM formulas in the lakes match many formulas identified in penguin guano (PG). Lakes with high amounts of formulas matching guano‐derived DOM were enriched in nitrogen‐containing formulas (e.g., CHON, p < 0.05) and bioactive metals (Cu, Ni, and Mn; p < 0.05) linked to penguin diet. Fresh snowmelt also contributed DOM, with inputs increasing with decreasing lake elevation ( p < 0.01). Additionally, many lake DOM formulas matched secondary organic aerosols or photodegradation by‐products identified in Antarctic snow, characterized by elevated aliphatics ( p < 0.01). Moss‐derived DOM further contributed to the pool, resulting in relatively higher O/C ratios and aromaticity ( p < 0.05). A comparison of mass differences between molecular formulas suggested that abiotic transformations largely governed lake DOM processing. As environmental conditions continue to shift, altering moss cover and penguin populations, the composition and transformation pathways of lake DOM may change, with ramifications for carbon cycling. These results highlight a surprising diversity and complexity in DOM sources and cycling dynamics across a small number of Antarctic lakes and underscore the need for further research to fully understand regional carbon dynamics in this rapidly changing environment.