Greenland Sea primary production in 1998–2022: monitoring and parameterization using satellite and field data

Abstract. Phytoplankton are responsible for releasing half of the World’s oxygen and for removing large amounts of carbon dioxide from the surface waters. Despite many studies on the topic conducted in the past decades, we are still far from a good understanding of ongoing rapid changes in the Arctic Ocean, and how they will affect phytoplankton and the whole ecosystem. An example is the difference in net primary production modeling estimates, which differ two times globally and fifty times when only the Arctic region is considered. Here we aim to improve the quality of Greenland Sea primary production estimates, by testing different versions of primary production model against in-situ data, and then calculating regional estimates and trends for 1998–2022 for those performing best. As a baseline we chose the commonly used global primary production model and tested it with different combinations of empirical relationships and input data. Local empirical relationships were taken from literature and derived from the unpublished Institute of Oceanology of Polish Academy of Sciences measurements across the Fram Strait. For validation we took historical net primary production ¹⁴C data from literature, and added to it our own gross primary production O₂ measurements to extend the limited validation dataset. The field data showed expected elevated values at the frontal zone together with differences between Arctic and Atlantic-dominated waters, and unexpected good agreement between primary production measured with ¹⁴C and O₂ evolution methods. From all the model setups, those including local chlorophyll-a profile and local absorption spectrum and using Level 2 photosynthetically active radiation data, reproduced in-situ data best. Our modeled regional annual primary production estimates equal 346 TgC/year for the Nordic Seas region and 342 TgC/year for the Greenland Sea sector of the Arctic defined as 45° W–15° E, 66°33′N–90° N. These values are higher those previously reported. Monthly values show a seasonal cycle with less monthly variability than previously reported, and with peak values observed in May. No significant increase or decrease in primary production was observed when studying regionally averaged trends. The accuracy of the selected here model setups to reproduce the field data in terms of Root Mean Square Difference is poorer than in the related global studies, but better than in the related Arctic studies.