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Paleoceanography of the South China Sea and the western equatorial Pacific: Testing linkages between Indonesian Seaway closure and sea level change during the Middle to Late Miocene ([approximates]13--5 Ma)

by Nathan, Stephen A

Abstract (Summary)
The tectonic opening and closing of ocean gateways played a key role in global climate change during the Cenozoic. Although changes in these gateways affected ocean circulation and heat transport, many of their paleoceanographic effects are still unknown. This dissertation examines the tectonic constriction of the Indonesian Seaway through the middle to late Miocene (i.e., 13.6 to 5.6 Ma) by studying changes in foraminiferal populations and stable isotopes (�´ 13 C and �´ 18 O). The purpose is to better understand the development of the Western Pacific Warm Pool (WPWP) and its interaction with the East Asian monsoon. To study this gateway, three locations are considered: Ocean Drilling Program Site 806 (Ontong Java Plateau, located in the heart of the modern WPWP) and Ocean Drilling Program Sites 1143 and 1146 (southern and northern South China Sea, respectively). At â¼12.1 Ma, tectonic constriction of the Indonesian Seaway and a succession of sea level falls resulted in the cessation of trans-equatorial Pacific circulation and the initiation of a circulation pattern resembling the modern day. The constriction and sea level falls also resulted in the piling of waters in the western equatorial Pacific (WEP), forming a proto-warm pool. At Ontong Java Plateau the proto-warm pool established La Ni�±a-like conditions, initiated the Equatorial Undercurrent and strengthened the Trade Winds, and sustained productivity in the eastern equatorial Pacific (EEP). The sea level falls also greatly restricted flows through the South China Sea and consequently initiated a proto-warm pool in this basin. After â¼9.8 Ma, rising sea level weakened the proto-warm pools as an El Ni�±o-like state became established across the Pacific. The shoaling thermocline in the WEP initiated an interval of increased biological productivity while the EEP underwent a "carbonate crash". The "biogenic bloom" in the WEP after â¼9 Ma was due to renewed Northern Component Water production and/or Himalaya-Tibetan Plateau uplift. The bloom was most pronounced after â¼8.5, coincident with plateau uplift and intensification of the Indian/East Asian monsoons. After 6.5 Ma, reestablishment of La Ni�±a-like conditions produced a resurgent proto-warm pool in the WEP and a "biogenic bloom" in the EEP.
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School:University of Massachusetts Amherst

School Location:USA - Massachusetts

Source Type:Master's Thesis

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Date of Publication:01/01/2005

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