As part of the U.S. Joint Global Ocean Flux Studies (JGOFS) in the central equatorial Pacific, the proposed research is a study of the upper water-column distribution of naturally occurring uranium and thorium decay series nuclides and cosmogenic isotopes of beryllium along a N-S transect across the Equator. The radioisotopes are used as tracers to gather information about the rates of biogeochemical processes that influence the scavenging of chemical species and the behavior/fate of biogenic particles in the sea. Specifically, the data obtained from the distribution of 228Ra and 10Be- normalized 7Be activities, coupled with those of nitrate and dissolved carbon, will enable us to estimate the vertical flux of nitrate and new production at various levels in the surface ocean. By measuring the specific activities of 234Th, 230Th, 228Th, 210Pb, 210PO and 7Be/10Be in the dissolved the P.I:s' will evaluate the forward and backward exchange rate constants for reactions involving dissolved small suspended particulate large settling particulate in three depth zones of the surface ocean, and the scavenging residence time of large particulates in the euphotic zone. It is anticipated that the study will enhance our understanding of the upper ocean biogeochemical dynamics and cycling in the equatorial Pacific, an area thought to play an important role in global carbon fluxes.
