[1] The eastern equatorial Pacific (EEP) is an important center of biological productivity, generating significant organic carbon and calcite fluxes to the deep ocean. We reconstructed paleocalcite flux for the past 30,000 years in four cores collected beneath the equatorial upwelling and the South Equatorial Current (SEC) by measuring ex 230 Th-normalized calcite accumulation rates corrected for dissolution with a newly developed proxy for ''fraction of calcite preserved.'' This method produced very similar results at the four sites and revealed that the export flux of calcite was 30-50% lower during the LGM compared to the Holocene. The internal consistency of these results supports our interpretation, which is also in agreement with emerging data indicating lower glacial productivity in the EEP, possibly as a result of lower nutrient supply from the southern ocean via the Equatorial Undercurrent. However, these findings contradict previous interpretations based on mass accumulation rates (MAR) of biogenic material in the sediment of the EEP, which have been taken as reflecting higher glacial productivity due to stronger wind-driven upwelling.

[1] Theoretical considerations indicate that degree of bottom water calcite saturation, organic carbon flux, and the ratio of that flux to the calcite flux all are reflected in the carbonate preservation record of deep-sea sediments. Separating the influence of these various factors on the record depends first on estimating the percent of the calcite flux which is dissolved at the seabed. We have developed a new proxy for percent dissolved calcite by calibrating a foraminiferal fragmentation index to biogeochemical modelderived data. Application of our proxy, combined with geochemical modeling, to the surface sediments of the Eastern Equatorial Pacific [EEP], demonstrates the need for all three of the variables listed above to account for the observations. Further, we used reverse modeling to map the ratio of the biotic fluxes across the EEP. We observe a coherent regional pattern with highest ratio values, as expected, associated with areas of upwelling, particularly along South America. Our proxy appears to be unaffected by carbonate sediment properties such as percent calcite in samples or the amount of coarse fraction (>63 mm) in the calcareous portion of the sediments; therefore it reflects primarily the geochemical environment rather than characteristics of seabed deposits.

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The eastern equatorial Pacific Ocean is the site of approximately 20-50% of new biological production in the global oceans. This region is also responsible for the greatest efflux of CO2 from oceans to the atmosphere. New production, which fixes carbon in response to external inputs of nutrients as opposed to supply from local nutrient recycling, is thought to modulate the CO2 release. But what controls new production in this region is less clear. Here we present a quantitative reconstruction of biological production in the surface ocean for this region over the past 130,000 years, which shows that the equatorial Pacific Ocean exhibits higher-frequency variations than the South Equatorial Current. Comparison of these records with palaeotemperature reconstructions indicates that atmospherically driven mechanisms--such as aeolian flux of iron or wind-driven changes in upwelling rate of nutrient-rich waters--are unlikely to have influenced longer-term rates of production in this region. Instead, biological production appears to be governed by changes in ocean circulation and the chemical composition of upwelled water.

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