PNut · A Multi-Isotope Assessment of the past Arctic Nutrient Cycle

The ongoing radical decline in sea-ice cover and the Greenland Ice Sheet (GIS) melt is causing the oceans in the Arctic to freshen. In the western North Atlantic decreasing salinity again results in changes in ocean stratification and a shift in the nutrient distribution between Atlantic- and Pacific-sourced waters. Stratification and nutrient flux strongly impact surface productivity and phytoplankton community structures, but the collective influence of these mechanisms is not yet known and might regionally vary. The aim of pNut is to study the effects of sea-ice loss, GIS melting and water-mass re-distribution of nutrients during previous warming phases of the deglacial and Holocene. To achieve this, I will investigate the effects of past climate change on nutrient distribution and utilization by phytoplankton off Greenland. For a high spatial and regional evaluation, the study is based on five available sediment cores, one from the East Greenland shelf, and five cores along a North-South transect from Baffin Bay to the West Greenland shelf. In a novel approach, I will differentiate between silicic acid utilization based on silicon isotope compositions of sea ice and spring/summer bloom diatoms. Silicic acid concentrations will be evaluated based on silicon isotope compositions of sponge spicules. The net productivity, nitrate utilisation and stratification will be investigated based on bulk sedimentary nitrogen isotope analyses. The new results will be combined with records of sea surface temperature, diatom abundance, primary productivity, water-mass mixture, stratification, and sea-ice extent to synthesise a synoptic understanding of the influence of further future warming on the Arctic marine nutrient cycle and the biological pump.