Abstract
A suite of four new benthic foraminiferal (Cibicidoides wuellerstorfi) stable carbon isotope records produced from South China Sea (SCS) sediment cores ranging in water depth from 1515 and 3766 m are used here to evaluate deep-water circulation in the SCS over the last complete glacial-interglacial cycle (i.e., the last 200 kyrs). A common pattern of benthic δ13C variations is observed between cores, with pronounced δ13C depletions recorded during glacial periods and δ13C enrichments during interglacials. The overall similarity of δ13C values between sites indicates a homogeneous water mass below 1500 m in the SCS basin through time, except for the interval between 120 and 65 ka. Temporal changes in ventilation and exchange between the SCS and western Pacific are indicated by comparison with records from the Ontong Java Plateau (OJP). The presence of Pacific Intermediate Water can be inferred based on the bathymetric gradient of δ13C between SCS and OJP (Δδ13C). The Δδ13C patterns do not appear to be correlated with glacial-interglacial cycles. However, the Δδ18O is greater in warm intervals (late MIS 4 and early MIS 3; MIS 1) than during cold intervals.
Highlights
The distribution of o13C of LC02 in the surface ocean is largely controlled by biological activity and air-sea exchange, whereas seawater o13C below the permanent thermocline is largely a function of deep circulation and the effects of remineralization of sinking organic material (Kroopnick 1980, 1985)
This is because the processes that control deepwater o13C are less
A large number of investigations have utilized o13C records of benthic foraminifera as deepwater paleoceanographic tracers (e.g., Broecker 1982; Shackleton et al 1983; Duplessy et al 1988; Oppo and Fairbanks 1987; Oppo et al 1990; Mix et al 1991; Mackensen et al 1993; Bicker! and Wefer 1999). In most of these studies, the benthic foraminifer species Cibicidoides wuellerstorfi and related taxa have been measured since they appear to calcify their tests with respect to o13C composition close to that of the ambient bottom-water LC02 (e.g., Zahn et al 1986)
Summary
The distribution of o13C of LC02 in the surface ocean is largely controlled by biological activity and air-sea exchange, whereas seawater o13C below the permanent thermocline is largely a function of deep circulation and the effects of remineralization of sinking organic material (Kroopnick 1980, 1985). Forarniniferal o13C measurements made on benthic taxa were the first applied to paleo-reconstructions, to infer past variability in deep water circulation patterns. This is because the processes that control deepwater o13C are less. In most of these studies, the benthic foraminifer species Cibicidoides wuellerstorfi and related taxa have been measured since they appear to calcify their tests with respect to o13C composition close to that of the ambient bottom-water LC02 (e.g., Zahn et al 1986). The present study focuses on benthic o13C records from different water depths in the SCS basin and on their comparison with the western equatorial Pacific record to infer past variations in the ventilation of deep water
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