DECADAL AND ANNUAL CHANGES IN BIOGENIC OPAL AND CARBONATE FLUXES TO THE DEEP SARGASSO-SEA

Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of t he sinking fluxes of biogenic calcium carbonate and silica. Although t here are pronounced seasonal cycles for both flux components, the over all opal/CaCO3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total flux had no significant trend. T hese results suggest that plankton communities respond rapidly to subt le climate change, such as is evident in regional variations of wind s peed, precipitation, wintertime Ventilation and midwater temperatures. If the trends we observe in the makeup of sinking particulate matter occur on a large scale, they may in turn modify climate by modulating ocean-atmosphere CO2 exchange and albedo over the ocean.