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Pacific CaCO 3 Preservation and δ 18 O Since 4 Ma: Paleoceanic and Paleoclimatic Implications

1991; American Geophysical Union; Volume: 6; Issue: 4 Linguagem: Inglês

10.1029/91pa00877

1944-9186

John W Farrell, Warren L Prell,

Marine Biology and Ecology Research

The Pliocene‐Pleistocene history of CaCO 3 preservation in the central equatorial Pacific is reconstructed from a suite of deep‐sea cores and is compared to fluctuations in global ice volume inferred from δ 18 O records. The results are highlighted by: (1) a strong covariation between CaCO 3 preservation and ice volume over 10 4 to 10 6 year time scales; (2) a long‐term increase in ice volume and CaCO 3 preservation since 3.9 Ma demonstrated by a deepening of the lysocline and the carbonate critical depth; (3) a dramatic shift to greater CaCO 3 preservation at 2.9 Ma; (4) distinctive ice‐volume growth and CaCO 3 preservation events at 2.4 Ma, which are associated with the significant intensification of northern hemisphere glaciation; (5) a mid‐Pleistocene transition to 100‐kyr cyclicity in both CaCO 3 preservation and ice volume; and (6) a 600‐kyr Brunhes dissolution cycle superimposed on the late Pleistocene glacial/interglacial 100‐kyr cycles. CaCO 3 preservation primarily reflects the carbonate chemistry of abyssal waters and is controlled by long‐term (10 6 year) and short‐term (10 4 to 10 5 year) biogeochemical cycling and by distinct paleoclimatic events. We attribute the long‐term increase in CaCO 3 preservation primarily to a fractionation of CaCO 3 deposition from continental shelf to ocean basin, and secondarily to a gradual rise in the riverine and glaciofluvial flux of Ca ++ . On shorter time scales, the fluctuations in CaCO 3 preservation slightly lag ice volume fluctuations and are attributed to climatically induced changes in the circulation and chemistry of Pacific deep water.