Does Wind-Driven Mixing Sustain Post-Bloom New Production in the Barents Sea?

Abstract

Wind-driven mixing is one of the primary factors likely to regulate changes in primary production in the future Arctic Ocean with reduced sea ice coverage. Quantifying this effect requires an understanding of whether this mechanism will resupply nutrients to surface waters during the post-bloom season. We therefore investigated the role of wind-driven mixing events in initiating new production in the Barents Sea by combining measurements of turbulence, nitrate fluxes, and proportional uptake of nitrate during primary production. We calculated the resupply of nitrate, and the relationship between nitracline and wind-driven mixing depths was evaluated to investigate mechanisms for resupply of nitrate over the post-bloom summer. In the weakly stratified waters of the central Barents Sea, wind-driven resupply of nitrate to the surface was not found at the time of sampling. Nor was such resupply predicted based on empirical modeling of wind-driven mixing depth and the depth of the upper boundary of the nitracline for the post-bloom summer season. In the strongly stratified waters of the northern Barents Sea, new production was low at the time of sampling, but modeling suggests that wind-driven nitrate resupply is likely to occur during the post-bloom summer, differing from previous findings. The highest nitrate fluxes were found over the shelf slope north of Svalbard, which were 10 times higher than in the central Barents Sea, supporting 47% of the net primary productivity, accounted for as new production. Our model suggested that wind-driven nitrate resupply is to be expected for the shelf slope during the post-bloom season.