Reassessing primary production in polar ocean: A novel approach using mooring systems

Rapid changes in the polar marine environment, driven by climate change, are altering the variability of nutrient and light distribution, with significant impacts on primary producer growth. However, access to polar regions is limited, and satellite data from high-latitude areas are typically available only during the summer, complicating the acquisition of continuous in-situ data. To address this, we collected year-round chlorophyll-a (Chl-a) concentration data in polar regions using a mooring system and compared the results with reanalysis data. Unlike previous satellite-based studies that rely on surface measurements, we applied the annual vertical distribution of Chl-a to the Vertically Generalized Production Model (VGPM) to estimate annual primary production more accurately. Our findings reveal that phytoplankton exhibited a subsurface chlorophyll maximum (SCM) as sea ice retreated, with the SCM layer persisting for approximately four months—contrary to the gradually deepening SCM distribution predicted by model-based reanalysis data. This suggests that light and nutrient conditions within the SCM remained stable, supporting continuous phytoplankton growth. The estimated annual primary production, based on this vertical distribution of Chl-a, was 6.85 gC m⁻² yr⁻¹, which is more than ten times higher than estimates based on satellite data alone, highlighting significant underestimation by satellite-based approaches. Furthermore, this value was comparable to the average satellite-derived primary production of surrounding coastal and shelf areas (15.80 ± 10.65 6.85 gC m⁻² yr⁻¹). These results emphasize the importance of incorporating vertical distribution of phytoplankton and light in polar marine ecological models to enhance our understanding of carbon cycling and food web dynamics in these regions.