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

Inter-annual (2002–2021) variability of the Kara Sea PP 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 the pronounced positive trend of surface water temperature (T0) and weak positive trend of free-ice 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 of water column PP (IPP) statistically significant (p 0.05) decreased in the all of the Kara Sea regions (R2 = 0.22 – 0.59). For the entire Kara Sea the IPP declined by 38 mgC m–2 d–1 with a moderate trend of 1.1% y–1 (R2 = 0.37). The growing season averaged value of photosynthetically available radiation (PAR) weak, but statistically significant (p 0.05), decreased in the all of the Kara Sea areas (R2 = 0.20 – 0.31). Also, in the all regions the significant (R2 = 0.24 – 0.38) weak or moderate negative trends of surface chlorophyll a (Chl) were specified. The total annual PP (PPtot) increased insignificantly in accordance with increase of S (0.7% y–1, R2 = 0.08). The most significant decline of IPP was specified for spring (R2 = 0.28). In autumn the statistically significant positive trend of S (R2 = 0.24) was observed. Due to such increase of S, the strongest growth of PPtot was noted in autumn. In the present work was shown that decrease of IPP, resulting from decline of PAR and Chl, was the reason of moderation of PPtot. Weak increase in PPtot was observed in autumn and in the north area of the sea. It should be concluded that during the period of intense warming, the decrease in the IPP of the Kara Sea should affect the productivity of the higher trophic levels of the food web.