DECOUPLING OF CARBONATE PRESERVATION, CARBONATE CONCENTRATION, AND BIOGENIC ACCUMULATION - A 400-KYR RECORD FROM THE CENTRAL EQUATORIAL PACIFIC-OCEAN

In order to investigate the paleoceanographic record of dissolution of calcium carbonate (CaCO3) in the central equatorial Pacific Ocean, we have studied the relationship between three indices of foraminiferal dissolution and the concentration and accumulation of CaCO3, opal, and C-org in Core WEC8803B-GC51 (1.3 degrees N, 133.6 degrees W; 4410 m). This core spans the past 413 kyr of deposition and moved in and out o f the lysoclinal transition zone during glacial-interglacial cycles of CaCO3 production and dissolution. The record of dissolution intensity provided by foraminiferal fragmentation, the proportion of benthic fo raminifera, and the foraminiferal dissolution index consistently indic ates that the past corrosion of pelagic CaCO3 in the central equatoria l Pacific does not vary with the observed sedimentary concentration of CaCO3. Although there is a weak low-frequency variation (similar to 1 00 kyr) in dissolution intensity, it is unrelated to sedimentary CaCO3 concentration. There are many shorter-lived episodes where high CaCO3 concentration is coincident with poor foraminiferal preservation, and where, conversely, low CaCO3 concentration is coincident with superb foraminiferal preservation. Spectral analyses indicate that dissolutio n maxima consistently lagged glacial maxima (manifest by the SPECMAP d elta(18)O stack) in the 100-kyr orbital band. Additionally, there is n o relationship between dissolution and the accumulation of biogenic op al or C-org or between dissolution and the burial ratio of C-org/C-INo rg (calculated from C-org and CaCO3). Because previous studies of this core strongly suggest that surface water productivity varied closely with CaCO3 accumulation, both the mechanistic decoupling of carbonate dissolution from CaCO3 concentration (and from biogenic accumulation) and the substantial phase shift between dissolution and global glacial periodicity effectively obscure any simple link between export produc tion, CaCO3 concentration, and dissolution of sedimentary CaCO3.