Pliocene climate change of the Southwest Pacific and the impact of ocean gateways |
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| Authors: | Cyrus Karas Dirk Nürnberg Ralf Tiedemann Dieter Garbe-Schönberg |
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| Institution: | 1. GNS Science, P.O. Box 30368 Lower Hutt 5040, New Zealand;2. School of Earth Sciences, Stanford University, Stanford, CA 94305-2210, USA;3. Department of Computer Science, University of Otago, P.O. Box 56 Dunedin 9054, New Zealand;4. U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA;5. Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC 29208, USA;1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2. First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;3. Department of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands |
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| Abstract: | The transition from the early Pliocene “Warmhouse” towards the present “Icehouse” climate and the role of Gateway dynamics are intensively debated. Both, the constrictions of the Central American Seaway and the Indonesian Gateway affected ocean circulation and climate during the Pliocene epoch. Here, we use combined δ18O and Mg/Ca ratios of planktonic foraminifera (marine protozoa) from surface and subsurface levels to reconstruct the thermal structure and changes in salinities from the Southwest Pacific Deep Sea Drilling Project (DSDP) Site 590B from 6.5 to 2.5 Ma. Our data suggest a gradual cooling of ~ 2 °C and freshening of the sea surface during ~ 4.6–4 Ma with an increased meridional temperature gradient between the West Pacific Warm Pool and the Southwest Pacific when the closing of the Central American Seaway reached a critical threshold. After ~ 3.5 Ma, the restricted Indonesian Gateway might have amplified the East Australian Current, allowing enhanced heat transport towards the Southwest Pacific with reduced meridional temperature gradients when the global climate gradually cooled. At the same time our data suggest a cooling and freshening of Subantarctic Mode Water (SAMW) or/and an increased northward flow of SAMW towards Site 590B, possibly a first step towards the present Antarctic Frontal System. |
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