Pacific CaCO₃ Preservation and δ¹⁸O Since 4 Ma: Paleoceanic and Paleoclimatic Implications

Abstract

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/5180 records. The results are highlighted by: (1) a strong covariation between CaCO 3 preservation and ice volume over 104 to 106 year time scales; (2) a long-term increase in ice volume and CaCO3 preservation since 3.9 Ma demonstrated by a deepening of the lysocline and the carbonate critical depth; (3) a dramatic shift to greater CaCO3 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 nonhem hemisphere glaciation; (5) a mid-Pleistocene transition to 100kyr 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 (106 year) and short-term (104 to 105 year) biogeochemical cycling and by distinct paleoclimatic events. We attribute the long-term increase in CaCO3 preservation primarily to a fractionation of CaCO3 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. Paper number 91PA00877. 0883-8305/91/91 PA00877510.00 time scales [van Andel et al., 1975; Rea and Leinen, 1985; Farrell and Prell, 1989 and references therein]. Temporal variations in the depths of the CaCO 3 preservation levels can be reconstructed from cores retrieved from a small geographic area and a large bathymetric range [e.g., Balsam, 1983]. The cores should be selected from an area which is smaller than the spatial variability in sea surface productivity in order to minimize differences in the biogenic input at each core site. The cores should also be taken far from terrigenous sediment sources to reduce the effect of dilution on the %CaCO 3 record. In this paper we present both new and previously published •518 0 and %CaCO 3 data from the central equatorial Pacific. Percent CaCO 3 data from 16 cores, along an 800-m water depth transect, are used to reconstruct bathymctric patterns of CaCO 3 preservation spanning the past 3.9 m.y. We demonstrate that: (1) variations in CaCO 3 preservation are closely correlated with variations in ice volume; (2) the depth of the lysocline, which has changed significantly over time, determines the bathymctric position and thickness of the CaCO 3 transition zone; and (3) the CCrD remained relatively constant, deepening only slightly since 3.9 Ma. We infer that short-term (104 to 105 year) changes in CaCO 3 preservation are linked to global ice volume and are primarily caused by climatically-induce...

The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO2

“…The possibility that increased alkalinity affected wholeocean chemistry at the time of the MPT is suggested by the record of CaCO 3 preservation in the central equatorial Pacific (Farrell and Prell, 1991) (Fig. 18b).…”

“…The rate of increase accelerates markedly at $1500 ka with the onset of large $100-kyr variations, since (i) each major deglaciation produces a very large spike in chemical weathering, and (ii) in between the major deglaciations, the 20-and 40-kyr cycles (due to direct orbital forcing) produce minor chemical weathering spikes similar to or slightly larger than before 1500 ka. We note that the modeled increase in slope at 1500 ka coincides with the timing of the observed increase in slope in the 87 Farrell and Prell, 1991). Contour interval is 10%, with deeper red contour equal to 10% and shallower red contour equal to 80%.…”

Deep-water circulation, chemistry, and terrigenous sediment supply in the equatorial Atlantic during the Pliocene, 3.3–2.6 Ma and 5–4.5 Ma

“…The comparison of Atlantic and Pacific carbonate dissolution records indicates, however, that dissolution changes in the two basins are out of phase during the late Neogene (Farrell and Prell, 1991), excepting the northwest Pacific . In contrast to the Atlantic, glacial carbonate preservation was higher in the Pacific, which supports the hypothesis that oceanic alkalinity was higher in the glacial ocean than today (Boyle, 1988).…”

Biogenic CaCO3 and Opal Depositions and Their Latitudinal Comparison During the Past 600 ka in the Central Equatorial Pacific

“…The CaCO 3 MARs decreased in the equatorial Pacific since the last glacial period; however, CaCO 3 fluxes in the seawater have either remained nearly constant or increased (e.g., Farrell and Prell 1991). These findings indicate that enhanced CaCO 3 dissolution was a key factor in the decline of CaCO 3 MARs during interglacial periods.…”