1 Early spring submarine discharge plumes fuel under-ice primary 2 production at a Svalbard tidewater glacier 3 4 Tobias Reiner Vonnahme1, Emma Persson1, Ulrike Dietrich1, Eva Hejdukova2, Christine Dybwad1, Josef 5 Elster3, Melissa Chierici4,5, Rolf Gradinger1 6 1 Department of Arctic and Marine Biology, UiT – The Arctic University of Norway, Tromsø, Norway 7 2 Department of Ecology, Faculty of Science, Charles University, Prague, Czech Republic 8 3 University of South Bohemia, České Budějovice, and Institute of Botany ASCR, Třeboň, Czech Republic 9 4 Institute of Marine Research, Tromsø, Norway 10 5 University Centre in Svalbard (UNIS), Longyearbyen, Svalbard, Norway 11 Correspondence to: Tobias R. Vonnahme (
[email protected]) 12 Abstract. Subglacial upwelling of nutrient rich bottom water canis known to sustain elevated summer primary production in 13 tidewater glacier influenced fjord systems. However, during the early spring season, the importance of subglacial upwelling 14 has not been considered yet during the early spring season.. We hypothesized that submarine discharge under sea ice is present 15 in early spring and that its flux is sufficient to increase phytoplankton primary productivity. We evaluated the effects of the 16 submarine discharge on primary production in a seasonally fast ice covered Svalbard fjord (Billefjorden) influenced by a 17 tidewater outlet glacier in April/May 2019. We found clear evidence for subglacial discharge and upwelling. Although the 18 estimated bottom water entrainment factor (1.6) and total fluxes were lower than in summer studies, we still observed 19 substantial impact on the fjord ecosystem and primary production. at this time of the year.