Pliocene–Pleistocene Surface and Intermediate Water Hydrography of the South Pacific Ocean

The reconstruction of past sea surface (SST) and intermediate water temperatures (IWT) is critical for understanding feedbacks within the ocean-climate system. Pliocene Southern Ocean dynamics are largely ambiguous, especially at intermediate water depths. However, the intermediate water reconstructions are particularly important since intermediate waters, including Antarctic Intermediate Water (AAIW), may be an important driver in high-low latitude teleconnections. Herein, we present the first Pliocene SST and IWT records from a sediment core in the Southwest Pacific (DSDP 593; 1068m water depth), in the core of modern AAIW.

Benthic paleotemperature proxies have caveats, including the ‘Carbonate Ion Effect’ on the magnesium to calcium ratio (Mg/Ca) of benthic foraminifera. However, recent studies demonstrated that the infaunal species, Uvigerina peregrina, is carbonate ion independent, affording the use of Mg/Ca_U.peregrina as a paleotemperature proxy (Elderfield et al., 2010). Our results suggest that Southern Ocean IWT was warmer during the Pliocene than during the Mid- to Late-Pleistocene. The range of IWT values during the Pliocene is nearly as large as the glacial-interglacial-scale IWT changes during the Pleistocene, despite smaller ice volume oscillations suggested by benthic δ¹⁸O time series (Lisiecki & Raymo, 2005). Alkenone-derived U^K₃₇' data show Pliocene SSTs are also, on average, warmer than those estimated for the Mid- to Late-Pleistocene. Orbital-scale SST changes are evident through the Pliocene, although the range is smaller than during the late Pleistocene. Our data are consistent with modeled SST and IWT reconstructions by Dowsett et al. (2009), but raise questions about the stability or dynamism of Pliocene climate relative to the modern.

References:

Dowsett et al. (2009) www.clim-past.net/5/769/2009.

Elderfield et al. (2010) doi:10.1594/PANGAEA.817473.

Lisiecki & Raymo (2005) doi:10.1029/2004PA001071.