Impact of Regional Warming on Primary Production of the Kara Sea in the Last Two Decades (2002–2021)

Abstract The interannual (2002–2021) variability of primary production (PP) of the Kara Sea and associated environmental factors was assessed by MODIS-Aqua data and model calculations. Warming in the Kara Sea region during the last two decades was characterized by a pronounced positive trend of the sea surface temperature (T0) and weak positive trend of the ice-free area (S) averaged for the growing season (April–October). During the investigated period, T0 increased by 3.55°C with a trend of 10% y–1 and S increased by 110 × 103 km2 with a trend of 1.4% y–1, on average. The values for the water column PP (IPP) averaged over the growing season statistically significantly (p < 0.05) decreased in the all Kara Sea regions (R 2 = 0.22–0.59). For the entire Kara Sea, IPP declined by 38 mgC m–2 d–1 with a moderate trend of 1.1% y–1 (R 2 = 0.37). The value of photosynthetically active radiation (PAR) averaged over the growing season weakly, but statistically significantly (p < 0.05), decreased in the entire Kara Sea areas (R2 = 0.20–0.31). Also, in all regions, significant (R 2 = 0.24 – 0.38) weak or moderate negative trends of surface chlorophyll (chl) a were specified. The total annual PP (PPtot) increased insignificantly in accordance with an increase in S (0.7% y–1, R 2 = 0.08). The most significant decrease in IPP was specified for spring (R 2 = 0.28). In autumn, a statistically significant positive trend of S (R 2 = 0.24) was observed. Owing to such an increase in S, the notable growth of PPtot was noted in autumn. This study demonstrates that the decrease of IPP, resulting from the decrease in PAR and chl, in some degree was the reason for moderation of PPtot. It should be concluded that in a period of intense warming, the decrease in IPP of the Kara Sea should affect the productivity of higher trophic levels of the food web.