Seasonality in the supply of sediment to the deep Sargasso Sea and implications for the rapid transfer of matter to the deep ocean

Abstract

The flux of particles approaching the sea floor near Bermuda has been sampled by sediment trap nearly continuously for more than two years. The trap was placed at a depth of 3200 m, 1000 m above the bottom, and samples were recovered at two-month intervals. All major components of the sediment (biogenic carbonate and silicate, and organic matter) and a minor, presumably aeolian, clay component, as well as all size fractions (after sieving) were delivered in seasonally fluctuating amounts. The flux variations appear closely tied to the annual cycle of primary production in the surface water, which in the Sargasso Sea peaks in early spring and reaches a low in late fall. The total particulate flux varied by a factor of three (20 to 60 mg m −2 d −1), but some components varied by more than an order of magnitude. The close synchroneity between surface production and deep-water arrival of even fine particles, which presumably sink as components of larger aggregates, indicates extremely rapid settling of the bulk of the sediment. The evidence that even the flux of inorganic particles varies in phase with the primary production cycle suggests that an efficient mechanism exists for rapid removal from the mixed layer and transfer to deep water of many chemicals, including pollutants, which are associated with, or scavenged by, biogenic and aeolian particles.