Pliocene-Pleistocene Carbon Isotope Record, Site 586, Ontong Java Plateau

Abstract

Oceanographic changes in the western equatorial Pacific during the past 6 m.y. are inferred from carbon isotopic analyses of planktonic and benthic foraminifers from Ontong Java Plateau (DSDP Site 586). Sample spacing is 1.5 m (ca. 35,000-75,000 yr). An overall trend of δ 13 C toward lighter values is evident for the last 5 m.y. in all four foraminiferal taxa analyzed (G. sacculifer, Pulleniatina, P. wuellerstorfi, and O. umbonatus). This trend is interpreted as an enrichment of the global ocean with 12 C, because of the addition of carbon from organic carbon reservoirs (or lack of removal of carbon to such reservoirs), as a consequence of an overall drop in sea level. Differences between shallow-and deep-water δ 13 C decrease slightly during this time interval, suggesting a moderate drop in productivity. This drop is not sufficient to explain the drop in sedimentation rate, however, much of which apparently must be ascribed to winnowing effects.A marked convergence in the δ 13 C values of planktonic taxa exists within the last 2 m.y. We propose that this convergence indicates nutrient depletion in thermocline waters, caused by the vigorous removal of phosphate in marginal upwelling regions, or by the stripping of intermediate waters in their source regions. No large shifts are seen in the carbon isotope record of the last 6 m.y., in contrast to the oxygen isotope record. Some indication of cyclicity is present, with a period between 0.5 and 1.0 m.y. (especially in the earlier portion of the record).

Pliocene Changes in Tropical East Pacific Upper Ocean Stratification: Response to Tropical Gateways?

“…As similar changes were also observed in a deep-dweller record from the western tropical Pacific (Whitman and Berger, 1993), it is likely that the δ 13 C increase is a regional phenomenon affecting the entire tropical Pacific thermocline, rather than resulting from local changes in upper ocean nutrient cycling.…”

The evolution of the equatorial thermocline and the early Pliocene El Padre mean state

“…The δ 13 C values of thermocline dwelling planktonic foraminifera support the interpretation that the long‐term subsurface cooling trend in G. tumida is related to changing thermocline conditions rather than a change in its depth habitat [ Whitman and Berger , ; Cannariato and Ravelo , ; Steph et al, , ; Ford et al, ]. While subsurface temperatures cooled over the last 5 Ma [ Steph et al, , ; Ford et al, ; this study], the δ 13 C values of thermocline dwelling planktonic foraminifera increased [ Whitman and Berger , ; Cannariato and Ravelo , ; Ford et al, ]. If the cooling trend in G. tumida ‐derived temperatures were related to a deepening its depth habitat, then the opposite δ 13 C trend would be expected because δ 13 C values are lower at depth [ Cannariato and Ravelo , ; Ford et al, ].…”

Environmental Change in the Great Plains: An Isotopic Record from Fossil Horses

“…The value is variable in mod- * PFϪCO 2 ern environments and is influenced by biological disequilibria (often termed "vital effects"; see Spero et al 1991), the depth at which foraminifera tests are precipitated (because the d 13 C of dissolved inorganic carbon decreases with depth), concentration of seawater carbonate (Spero et al 1997) ). We use the value for the offset be-Ϫ12.7 ‫ע‬ 1.1 Whitman and Berger (1993), Pagani et al (1999aPagani et al ( , 1999b, and Veizer et al (1999). These records were used because they are from low-latitude, low-productivity regions, because measurements were made on 1200-mm-size fractions, and because they are from relatively continuous and well-dated cores.…”