Hidden Production: On the Importance of Pelagic Phytoplankton Blooms Beneath Arctic Sea Ice

Recent observations suggest that substantial phytoplankton blooms occur under sea ice on Arctic continental shelves during June and July. This is opposed to the traditional view that no significant biomass is produced in sea‐ice covered waters. However, no observational estimates are available on the Arctic‐wide primary production beneath sea ice. Here, using a fully coupled Arctic system model, we estimate that 63%/41% of the total primary production in the central Arctic occurs in waters covered by sea ice that is ≥50%/≥85% concentration. The total primary production there is increasing at a rate of 5.2% per decade during 1980–2018. Increased light transmission, due to the removal of sea ice, more extensive melt ponds, and thinner sea ice, is implicated as the main cause of increasing trends in primary production. Plain Language Summary At present, there are no Arctic‐wide observations and estimates of primary production beneath Arctic sea ice because it cannot be measured by satellite and is difficult to access via ship. Utilizing our state‐of‐the‐art Arctic system model, we have quantified the primary production beneath Arctic sea ice and our findings show that the majority of production occurs in waters covered by at least 50% ice. This analysis represents a major revision to the traditional view that no significant biomass is produced in sea‐ice covered waters. Our results are consistent with recent and very limited (in space and time) observational studies; however, we provide information for the entire Arctic Ocean, including increasing trends in production over the time period of 1980–2018. Key Points The majority of modeled primary production in the central Arctic is found beneath sea ice The annual cycle of primary production in the central Arctic peaks in June due to the under‐ice fraction of production Primary production and photosynthetically active radiation are increasing in the central Arctic over the period 1980–2018