TERRIGENOUS FE INPUT AND BIOGENIC SEDIMENTATION IN THE GLACIAL AND INTERGLACIAL EQUATORIAL PACIFIC-OCEAN

Many ocean regions important to the global carbon budget, including th e equatorial Pacific Ocean, have low chlorophyll concentrations despit e high levels of conventional nutrients. iron may instead be the limit ing nutrient, and elevated input of terrigenous Fe during windy glacia l episodes has been hypothesized to stimulate oceanic productivity thr ough time and thus regulate the oceanic and atmospheric CO2 balance. T o test whether particulate Fe input is related to the accumulation of biogenic matter in one important low chlorophyll-high nutrient area, t hat is, the equatorial Pacific Ocean, we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial-interglacial cycles (similar to 600,000 years). Our data set includes new chemical data on total Fe, terrigenous, and biogenic components in three cores as well as previously published min eralogic records of eolian input to the region. Chemical, spectral, an d stratigraphic analysis indicates that (1) terrigenous input to the r egion shows no consistent pattern of either glacial or interglacial ma xima, (2) the accumulation of particulate Fe is closely related to the accumulation of terrigenous matter (Linear r(2) = 0.81 - 0.98), (3) t here are no coherent spectral relationships between Fe input and glaci al periodicity (i.e., delta(18)O) in any of the orbital frequency band s, (4) the linear and cross-spectral correlations between Fe or eolian input and CaCO3 concentration are most Commonly the strongest observe d relationships between Fe and any biogenic component, yet indicate a largely inverse pattern, with higher Fe being associated with low CaCO 3, (5) there is no consistent linear r(2) correlation or spectral cohe rence between the accumulation of Fe and that of CaCO3, C-org, Or opal . Thus in total there is no relationship between terrigenous Fe input and sedimentary sequestering of carbon. Additionally, although we cann ot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositiona l change, the Fe/Ti ratio (which monitors first-order mineralogic chan ges) records only slight variations that also are linearly and spectra lly unrelated to glacial periodicity, the bulk Fe flux, and the accumu lation of any biogenic component. Finally, we find that the paleoceano graphic flux of Fe is several order-of-magnitudes larger than modem ob servations of eolian Fe input, suggesting that the long-term importanc e of Fe input by dust storms (which deliver Fe on the order of the sed imentary burial) may be underestimated. The removal of particulate ter rigenous Fe from the recently discovered source within the Equatorial Undercurrent, however, remains unquantified and may also prove signifi cant.