Productivity control of fine particle transport to equatorial Pacific sediment

Accumulation rates of He-3 (from cosmic dust), Th-230 (produced in the wate r column), barite (produced in the water column during decay of organic mat ter), and Fe and Ti (arriving with wind-borne dust) all are positively corr elated in an equatorial Pacific core (TT013-PC72; 01.1 degrees N, 139.4 deg rees W; water depth 4298 m). These accumulation rates are also positively c orrelated with the accumulation rates of noncarbonate material. They are no t significantly correlated to the mass accumulation rate of carbonate, whic h makes up the bulk of the sediment. The fluctuations in accumulation rates of these various components from different sources thus must result from v ariations in some process within the oceans and not from variations in thei r original sources. Sediment focusing by oceanic bottom currents has been p roposed as this process [Marcantonio et al., 1996]. We argue that the varia tions in the accumulation rates of all these components are dominantly link ed to changes in productivity and particle scavenging (He-3, Th-230, Fe, Ti ) by fresh phytoplankton detritus (which delivers Ba upon its decay) in the equatorial Pacific upwelling region. We speculate that as equatorial Pacif ic productivity is a major component of global oceanic productivity, its va riations over time might be reflected in variations in atmospheric levels o f methanesulfonic acid (an atmospheric reaction product of dimethyl sulfide , which is produced by oceanic phytoplankton) and recorded in Antarctic ice cores.