Seasonal and interannual variations in deep-water particle fluxes in the Sargasso Sea and their relation to surface hydrography

Abstract

Six years of almost continuous sediment trapping, with bimonthly sample recovery, in the deep Sargasso Sea reveal a pattern of annual flux variations as well as significant interannual differences. Spectral analysis of the data shows, however, that the temporal variability also has a large random component. Coherence among all constituent fluxes is very high, indicating that the composition of the sinking material is remarkably uniform throughout periods of greatly changing flux levels. The oxygen isotopic composition of tests of the epipelagic foraminifer Globigerinoides ruber intercepted by the trap at a depth of 3200 m represents a reliable recorder of near-surface hydrography one month prior to the tests' arrival in the trap. This tie between hydrographic changes at the surface and changes in quality and quantity of the sediment-trap samples reveals an inverse relationship between surface temperature and the amount of material sinking out of the euphotic zone and injected into deep water. That inverse relationship relates primary sedimentation in the deep sea to the annual cycle of seasons at the sea surface. As the period of lowest surface temperature coincides with the period of greatest mixed-layer depth, and thereby highest nutrient availability, it also confirms the close coupling of sedimentation, including that of abiogenic particles, in the open ocean to primary productivity. © 1986.