HR: 1340h
AN: PP53B-1390    [Abstracts]
TI: Does the Rain Ratio Reign in the Eastern Equatorial Pacific? In Search of the Ideal Carbonate Dissolution Index and Changes in Bottom Water Carbonate Ion Saturation over the Last 25,000 Years
AU: * Mekik, F A
EM: mekikf@gvsu.edu
AF: Grand Valley State University, Department of Geology, Allendale, MI 49401 United States
AU: Loubere, P W
EM: paul@geol.niu.edu
AF: Northern Illinois University, Department of Geology and Environmental Geosciences, De Kalb, IL 60115 United States
AU: Archer, D E
EM: d-archer@uchicago.edu
AF: University of Chicago, Department of Geophysical Sciences, 5734 S. Ellis Ave., Chicago, IL 60637 United States
AB: Testing mechanisms for changing atmospheric pCO2 on millennial timescales depends on accurate reconstructions of deep sea carbonate ion concentration and the organic carbon to calcite flux ratio [rain ratio] for both core-top and down-core samples. Both of these reconstructions require a reliable carbonate dissolution proxy. Accurate percent calcite dissolved values combined with pH data can be used to calculate dissolved inorganic carbon. To this end, we tested the sensitivity of two methods in estimating percent calcite dissolved at the sea floor: the menardii fragmentation index [MFI] and the foram weight loss method. Although MFI's response to dissolution is consistent with regional oceanographic parameters combining bottom water [CO3=] and respiration related dissolution associated with variable org C flux, our foram weight loss data show that only P. obliquiloculata lose weight in response to dissolution. Obliquiloculata weight loss, however, also shows a linear response to [CO3=] at 100 m water depth, the rain ratio and apparent oxygen utilization at thermocline depths. G. menardii and N. dutertrei shell weights appear to have multiple populations in the Eastern Equatorial Pacific [EEP] with different original shell weights. Furthermore, we present 230-Thorium-normalized calcite flux data for closely spaced core-top samples from the EEP. This new data is crucial for ground-truthing the rain ratio map for the EEP we had previously generated using biogeochemical modeling and MFI alone. Application of the MFI-reverse modeling approach to estimating paleo-delta calcite downcore in the EEP reveals a consistent LGM to Present pattern in four cores. Using MFI and reverse modeling, we estimate a 20 umol/kg increase in carbonate ion saturation during the LGM. Foram weight loss data for these cores, however, are unreliable in reconstructing paleo- delta carbonate. This is possibly related to the influence of strong gradients in productivity and pCO2 in surface waters as well as differing biological niches.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4842 Modeling
DE: 4231 Equatorial oceanography
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting