Primary production in relation to algal species composition in a warming Western Antarctic peninsula

The Western Antarctic Peninsula is a key area in the Southern Ocean ecosystem. Dense microalgal communities not only support diverse wildlife, but can also exert a climatic influence through CO2-uptake and the emission of climate-active gases like dimethylsulfide. The build-up of biomass is driven by high rates of primary production. In this paper, data are presented on primary production in Ryder Bay, a biologically-rich coastal area. Primary production was measured by means of 13C-uptake, in spring and summertime between 2012 and 2022. Production rates were linked to algal community composition and oceanographic data collected at the site of the Rothera Time Series. To get more detailed information on species-specific production rates, specific algal growth rates were obtained from laboratory studies and historical data. In Ryder Bay, primary production rates were 0.025 (± 0.024) mg C l−1 h−1 on average across all studies, and highest in February 2017. In spring, production was dominated by haptophyte algae with a low temperature optimum. Diatoms with higher growth rates and a higher temperature optimum thrive later in summer. For the near future, our data support the predictions that the warming of surface waters will stimulate algal growth rates, which will result in increased primary production. On longer timescales, ongoing ocean warming is expected to have strong negative effects on the occurrence of haptophytes like Phaeocystis antarctica. For polar diatoms, a temperature growth optimum may be passed. A potential shift in species composition is predicted, with ensuing consequences for primary production and biogeochemical cycles.