Year-round dynamics and drivers of the Biological Carbon Pump in the Weddell Sea revealed by autonomous sampling

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The biological carbon pump (BCP) mediates carbon supply, consumption and storage in the world’s oceans. A mechanistic understanding of the BCP requires continuous observations that contextualize biology, oceanography and geochemistry across time, water layers and environmental conditions. Year-round observations of the BCP in the Southern Ocean are missing, and require autonomous approaches. Based on autonomous samplers and sensors on a seafloor mooring, YIPPEE will establish mechanistic insights into taxonomic, functional and physicochemical signatures of the BCP over a full annual cycle in the Weddell Sea. This “Last Ice Area” with central importance for the global climate represents a natural laboratory to understand polar processes and their potential response to climate change. The mooring has been successfully deployed between March 2021 and March 2022. Preliminary analyses of eDNA and environmental parameters confirm the consistency of the data set. Three work packages will portray biodiversity and functional genomics over a complete annual cycle in context of water masses, sea-ice cover and nutrient concentrations. The key asset is the high-resolution biological and environmental sampling; connecting biological dynamics in the photic zone with geochemical fluxes to deep waters. Specifically, eDNA metabarcoding will elucidate signature populations of distinct ecosystem states, from bacteria to metazoans, and their temporal and ecological connectivity. This will reveal unexplored transition periods and central turning points in the annual cycle: the threshold of daylight initiating phytoplankton growth, bacterial activities following the photosynthetic pulse, the succession of protist and zooplankton grazers, and the temporal scale of deep-sea responses to sinking detritus. Long-read metagenome sequencing will reveal functional signatures of seasonal ecosystem states, and quantify the contribution of individual biogeochemical pathways over environmental gradients. This evidence allows distinguishing the annual cycle into periods of autotrophy and (chemo)heterotrophy, and the key underlying pathways. Emphasis on functions prevalent during high-ice cover will set a benchmark of the “true” Weddell Sea before the impact of climate change. Third, gene catalogues for Antarctic vs Arctic seasonal states will establish bi-polar perspectives on functional seasonality and community assembly. This unprecedented, high-resolution picture of keystone taxa, genetic diversity, ecological networks and nutrient fluxes has important implications for the Antarctic BCP, and polar ecosystem functioning in general. YIPPEE aligns with ~10 other SPP projects and central SPP goals, including suggested long-term observations. All data and bioinformatic code will be immediately shared. In addition to joint papers with collaborating scientists, results will be disseminated with science and society via an interactive web-app and public communication channels.