Annual and seasonal variations of amino acid and hexosamine fluxes in the deep Bering Sea and the deep central Subarctic Pacific

Fluxes of amino acids and hexosamines were determined using time-series sediment trap samples collected at 3200 m in the Bering Sea (Station AB; 53°30′N, 177°00′W) and at the 4400 m in the central subarctic Pacific (Station SA; 49°00′N, 174°00′W) from August 1990 to July 1993. The annual and seasonal amino acid fluxes at Station AB were two to three times higher than those at Station SA. Seasonal changes of hexosamine fluxes correlated positively with those of the amino acid fluxes at both stations. However, the slope of the regression line between amino acid fluxes and hexosamine fluxes at Station SA is 3.2-fold higher than that at Station AB, meaning that the rate of increase of the particle fluxes originating from zooplankton at Station SA is larger than that at Station AB. Furthermore, the hexosamine contents showed a positive correlation with the amino acid fluxes at Station SA, whereas there was a negative correlation at Station AB. These results suggest that the grazing pressure at Station SA is apparently higher than that at Station AB. The intensity of zooplankton grazing may be a major factor controlling particulate organic flux, at least in the marine regions we investigated.