Seasonal pteropod sedimentation in the Norwegian Sea

Abstract

Pteropods of the species Limacina helicina (Dalli) (polar species) and Limacina retroversa (Fleming) subpolar species), were collected in three sediment traps deployed in the Norwegian-Greenland Sea. The three traps were stationed in the Lofoten Basin (69°N), near Bear Island (76°N), and in the Fram Strait (79°N). In the Lofoten Basin, the relatively warm and saline Atlantic water provides optimal living conditions for the subpolar pteropod species Limacina retroversa. Pteropod sedimentation in the Lofoten Basin was limited to the time period between August and November. Changes in the abundance distributions of shell sizes indicate that reproduction was taking place at a high rate during this time. At this station, pteropod shells contributed 11% to the total carbonate collected during the study period. The pattern of pteropod sedimentation in the Fram Strait and in the vicinity of Bear Island differed from that observed in the Lofoten Basin. Colder and less saline water produced by mixing of the East Greenland Current with the Norwegian Current is found in the area of these stations. In contrast to observations in the Lofoten Basin, the pteropod population in these two regions was comprised of the two species Limacina helicina and Limacina retroversa. The sedimentation of pteropods at the two northern traps did not begin until September (Bear Island)/October (Fram Strait), and continued until February (Bear Island)/March (Fram Strait). Reproduction at significant rates was not observed at these locations. It is likely that currents transported pteropods northwards to these areas from regions such as the Lofoten Basin, an area of vigorous reproduction of subpolar species, and the East Greenland Shelf, which provides favourable living conditions for polar species. The flux of pteropod carbonate in the Lofoten Basin is 52- and 57-times higher than that of Bear Island and the Fram Strait, respectively. The contribution of pteropod carbonate to the total carbonate over the course of the study was less than 1% in the vicinity of Bear Island, and 1.7% in the Fram Strait. Scanning electron microscope photographs of Limacina retroversa from the Lofoten Basin displayed dissolution structures. However, it was not possible to quantify the carbonate loss due to dissolution.