Preliminary results obtained from a north-south transect in the equatorial Pacific suggest that the &15N in the surficial sediments of this region is strongly affected by the nitrate concentration in the overlying euphotic zone. Similarly, carbon isotopic composition of phytoplankton reflects ambient ?CO2(aq)! and evidence exists that &13C in sedimentary organic matter is a measure for this parameter in the equatorial Pacific. This raises the possibility that &15N and &13C of sedimentary organic matter might respectively record past nitrate and ?CO2(aq)! distributions in surface waters. There is evidence for glacial to interglacial changes in both the magnitude and latitudinal distribution of production in the equatorial Pacific that might have influenced the global carbon cycle. Sedimentary isotopic composition (&15N and &13C - both bulk and fractions thereof) will be used for the reconstruction of past changes in the distribution of nitrate and CO2(aq) in equatorial Pacific surface waters over the last 160 kyrs, as a means both to confirm and to delineate the mechanisms for these past changes in productivity. Studies will be made of water column and early diagenetic processes which control the isotopic composition of buried organic matter. Also sediment analyses will be used to reconstruct paleoceanographic nutrient and CO2(aq) distributions in surface waters.
