Environmental reconstructions of the upper 500 m of the southern Indian Ocean over the last 40 ka using Radiolarian (Protista) proxies |
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| Authors: | John Rogers Patrick De Deckker |
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| Institution: | 1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction, College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China;3. Key Laboratory of Ocean and Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China;1. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;2. Radiogenic Isotope Facility, School of Earth Sciences, The University of Queensland, Brisbane, Qld 4072, Australia;3. ARC Center of Excellence for Core to Crust Fluid Systems (CCFS), Curtin University, Perth, WA 6845, Australia;4. The Institute for Geoscience Research, Department of Applied Geology, Curtin University, Perth, WA 6845, Australia;5. Department of Geography and Environmental Science, Monash University, Clayton, Vic. 3168, Australia |
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| Abstract: | In 2007, we demonstrated that radiolarians are proxies for a wide range of oceanic physico-chemical properties from the surface to depths of up to 500 m below sea level. In this study, our results are refined and Correspondence Analysis (CA) scores derived from census counts of radiolarian subfossils from southern Indian Ocean core-tops are correlated with the physico-chemical properties of the region obtained from the 2005 World Ocean Database.Calibration and regression techniques are employed to reconstruct palaeoenvironmental conditions spanning the last 40 ka for four Indian Ocean cores MD88-769 46°04′S 90°06′E], MD88-770 46°01′S 96°27′E], MD94-102 43°30′S 79°50′E], and MD94-103 45°35′S 86°31′E], all from close to the Southeast Indian Ridge. For the first time, reconstructions of temperature, salinity, dissolved oxygen, and the silicate, nitrate, and phosphate concentrations for a range of water depths are proved possible.Changes of the oceanic environment and the movement of water masses over the last 40 ka, as suggested by these reconstructions, are discussed. During Marine Isotope Stages 2 and 3 (MIS-2 and MIS-3), the water column at some of the core sites has similar characteristics to the waters south of the Polar Front today. At the MIS-1/MIS-2 transition, the development of the Subantarctic Mode Water is apparent. Temperature reconstructions include evidence of the Antarctic Cold Reversal and the Holocene Optimum. |
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