ICECOLOR: biogeochemical contrasts and chlorophyll dynamics across a melting Antarctic ice-water mosaic

Authors: names of authors including presenter Caio Cesar Ribeiro, Caroline Duarte, Jaqueline Joosten, Alexandra Warkentin, Inês Oliveira and Maria Fernanda Palanch

Affiliations: for each author ECHO - Ecotoxicology and Chemical Oceanography Group, Centre of Marine Sciences (CCMAR), University of Algarve, Faro, Portugal.

Abstract: Seasonal melting rapidly reorganizes Antarctic microbial habitats, yet short-term links among ice loss, nutrient availability, photosynthetic biomass and microbial dispersal remain poorly resolved. ICECOLOR investigated an ice–water mosaic on Fildes Peninsula, King George Island, during three campaigns (17 January, 25 January and 2 February 2026), integrating in situ physicochemical measurements, nutrient analyses, fluorimetric chlorophyll-a and three-dimensional holotomography. Over 16 days, seasonal ice progressively disappeared, while freshwater habitats warmed from initial medians of 4.05–5.00 °C to 9.78–10.07 °C; coastal water remained cooler. Silicate clearly differentiated liquid water (58.54–93.55 µmol L−1) from ice-derived material (1.76–7.76 µmol L−1), whereas phosphate was generally enriched in the ice-associated matrix. Chlorophyll-a increased between the first and final campaigns by 2.62-fold in the lake, 1.42-fold in the stream and 2.08-fold in the pond. In the GREEN ice-derived series, chlorophyll-a reached 4.34, 0.81 and 5.17 µg L−1, indicating persistence of photosynthetic biomass even after visible ice disappearance. Holotomography revealed filamentous cyanobacterial morphotypes attributable to Anabaena and rounded snow-algal cells consistent with Chlamydomonas nivalis, suggesting that melting can release cryospheric phototrophs into surrounding freshwater habitats and promote their reinoculation. This transition may also generate a positive bio-albedo feedback: pigmented snow algae darken ice and snow, reduce surface reflectance and can accelerate melting, thereby further expanding liquid-water habitat. ICECOLOR highlights the value of repeated chemical, pigment and cellular-scale observations for resolving rapid climate-sensitive ecological transitions in Antarctic coastal systems.

Keywords: ICECOLOR, Antarctica, snow algae, chlorophyll-a, nutrient dynamics, seasonal melting, holotomography