Upper ocean flux of calcite produced by the Arctic planktonic foraminifera Neogloboquadrina pachyderma

Abstract

<p>Planktonic foraminifera, marine protists and calcifiers, are globally responsible for about one quarter of the global pelagic calcite flux, but their contribution to it in the subarctic and Arctic realm has not been fully resolved. With ongoing warming and sea ice loss, the Arctic Ocean and its marginal seas are becoming more hospitable to pelagic calcifiers like planktonic foraminifera, resulting in modifications of the regional carbonate cycle and the composition of the seafloor sediment. To quantify planktonic foraminifera Arctic calcite production and loss in the upper water layer, we compile and analyze data on the dominant planktonic foraminifera species of the Arctic realm, <em>Neogloboquadrina pachyderma</em>, from vertical profiles in the upper water column. Using summertime observations of shell concentrations, sizes and weights of this species across the Arctic, we calculate the base of the productive zone of <em>N. pachyderma</em> to be regionally highly variable, on average located at 125 m, at maximum at 300 m. The calcite flux immediately below the productive zone (production flux) is on average 8 mg CaCO<sub>3</sub> m<sup>-2</sup> d<sup>-1</sup>, and we observe that this flux is attenuated until at least 300 m below the base of the productive zone. Across the Arctic realm, the summer production flux of <em>N. pachyderma</em> calcite varies by more than two orders of magnitude and the estimated mean export flux below the twilight zone is sufficient to account for about a quarter of the total pelagic carbonate flux in the region. These results indicate that estimates of the Arctic pelagic carbonate budget will have to account for large regional differences in production flux of the major pelagic calcifiers and confirm that substantial attenuation of the production flux occurs in the twilight zone.</p>