SINGLE CELL NITROGEN AND CARBON UPTAKE RATES OF CENTRAL ARCTIC OCEAN PHYTOPLANKTON

The central Arctic Ocean is rapidly warming which has led to a sharp reduction in sea ice with increased light penetration, phytoplankton abundance and primary production. While pelagic diatoms (20-200 µm) are known to be important primary producers, increased stratification due to warming is likely to increase the contribution of nanoplankton (2-20 µm) and picophytoplankton (<2 µm) which have an advantage in nutrient acquisition. Such shifts have the potential to reduce overall primary production and carbon (C) export. In this study, we investigated nitrogen (N) uptake preferences in the central Arctic Ocean during summer. Short-term incubation experiments using dual stable isotope labeling (¹⁵N and ¹³C) were performed to measure N assimilation (nitrate, ammonium, urea and amino acids) and C fixation at six locations representing different environmental conditions and phytoplankton community composition. Total community uptake rates were measured with isotope ratio mass spectrometer (IRMS) and single cell rates using secondary-ion mass spectrometry (SIMS) and NanoSIMS to assess the contribution of different size classes of phytoplankton to total uptake. The results show that picophytoplankton have different nutrient acquisition strategies compared to diatoms and dinoflagellates. For inorganic N sources, N-specific uptake rates were generally well correlated with C fixation. While N-specific uptake of amino acids was low, the rates were highest for ammonium illustrating the importance of regenerated nutrients to the success of picophytoplankton in the future Arctic Ocean.

Presentation Preference: Oral

Primary Presenter: Hanna Farnelid, Linnaeus University (hanna.farnelid@lnu.se)

Authors:

Hanna Farnelid, Linnaeus University  (hanna.farnelid@lnu.se)

Christien Laber, The Arctic University of Norway  (christien.p.laber@uit.no)

Lisa Winberg von Friesen, Linnaeus University  (lisa.winbergvonfriesen@lnu.se)

Lucie Goraguer, The Norwegian Polar Institut  (lucie.h.goraguer@uit.no)

Pauline Snoeijs Leijonmalm, Stockholm University  (pauline.snoeijs-leijonmalm@su.se)

Elin Lindehoff, Linnaeus University  (elin.lindehoff@lnu.se)