the variation of the thermocline structure in the southern marginal West Pacific Warm Pool during 2.2-3.2 million years ago

Abstract

Late Pliocene has been recognized as a good analog to the possible future global warming condition since it is warmer than toady, but already in a glacial-interglacial fluctuation mode. Pacific Ocean, and in particular, the West Pacific Warm Pool, is a key area of great interest for studying the climate evolution in the global warming context. We have reconstructed sea-surface salinities and temperatures of the West Pacific Warm Pool using oxygen isotopic (δ18O) and Mg/Ca ratio of planktonic foraminifera. The studied species are Neogloboquadrina dutertrei and its ancestor, Neogloboquadrina humerosa. The specimens were picked from the late Pliocene – early Pleistocene section of the deep-sea core ODP 1115B retrieved from the southern margin of the West Pacific Warm Pool off the east coast of Papua New Guinea. The δ18O curve shows a gradual increasing trend of about 0.6-0.7 permil. In addition, it appears that the periodicities the cycles changes from circa 11 thousand years to more than 14 thousand years. Comparison of it a δ18O curve of the subsurface from DSDP 214 in north-east Indian Ocean, shows an already ceased exchange of water between Indian Ocean and the WPWP. Comparison with surface δ18O shows possible variation of the thermocline. Similar trends exist in the sea surface condition in at least two occasions: between 3.05 and 3.15 million years ago and between 2.45 and 2.55 million years ago. Comparing the surface and thermocline δ18O of our site with surface and thermocline δ18O of the ODP 851 (east equatorial Pacific) reveal a consistent trend between the two sides of the ocean, and shows an ENSO-like condition in the Pacific Ocean around 2.1 – 2.2 Ma, with difference in sea surface value and tilting in the thermocline, shoal in east Pacific, more deep in west Pacific; corroborating with the hypothesis that the thermocline structure changed due to the formation of the Panama’s Isthmus and the closure of the Indonesian Seaway (Cane et al., 2001; Haug et al., 1998). Comparison of δ13C reveals a connection between Caribbean area deep ocean ventilation (ODP 999), east Pacific (ODP 851) upwelling and carbon isotope ratio (Haug & Tiedemann 1998, Steph et al. 2010) and the west Pacific water ventilation, although with some light variation, the trend is similar and the main changes are followed by all the three sites, although the curves of the Pacific started their trend from a lower value, after an abrupt increase around 3.0 Ma and then show a similar trend with that of the west Atlantic sites.