Long-term biogenic particle fluxes in the Bering Sea and the central subarctic Pacific Ocean, 1990-1995

Time-series sediment traps were deployed for five consecutive years in two distinctively different subarctic marine environments. The centrally locate d subarctic pelagic Station SA (49 degrees N, 174 degrees W; water depth 54 06 m) was simultaneously studied along with the marginal sea Station AB (53 .5 degrees N, 177 degrees W; water depth 3788 m) in the Aleutian Basin of t he Bering Sea. A mooring system was tethered to the sea-floor with a PARFLU X type trap with 13 sample bottles, which was placed at 600 m above the sea -floor at each of the two stations. Sampling intervals were synchronized at the stations, and they were generally set for 20 days during highly produc tive seasons, spring through fall, and 56 days during winter months of low productivity. Total mass fluxes, which consisted of mainly biogenic phases, were significantly greater at the marginal sea Station AB than at the pela gic Station SA for the first four years and moderately greater for the last year of the observations. This reflects the generally recognized higher pr oductivity in the Bering Sea. Temporal excursion patterns of the mass fluxe s at the two stations generally were in parallel, implying that temporal ch anges in their biological productivity are strongly governed by a large-sca le seasonal climatic variability over the region rather than local phenomen a. The primary reason for the difference in total mass flux at the two stat ions stems mainly from varying contributions of siliceous and calcareous pl anktonic assemblages. A significantly higher opal contribution at Station A B than at Station SA was mainly due to diatoms. Diatom fluxes at the margin al sea station were about twice those observed at the pelagic station, resu lting in a very high opal contribution at Station AB. In contrast to the op al fluxes, CaCO3 fluxes at Station AB were slightly lower than at Station S A. The ratios of C-org/C-inorg were usually significantly greater than one in both regions, suggesting that preferentially greater organic carbon from cytoplasm than skeletal inorganic carbon was exported from the surface lay ers. Such a process, known as the biological pump, leads to a carbon sink w hich effectively lowers p CO2 in the surface layers and then allows a net f lux of atmospheric CO2 into the surface layer. The efficiency of the biolog ical pump is greater in the Bering Sea than at the open-ocean station. (C) 2000 Elsevier Science Ltd. All rights reserved.