Diatom records in the Quaternary marine sequences around the Japanese Islands

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• 作者：Itaru Koizumi^a ; ^{itaru@sci.hokudai.ac.jp" class="auth_mail" title="E-mail the corresponding author} ; Hirofumi Yamamoto^b
• 关键词：Td'-derived paleo-SSTs ; Twt ; Wavelet analysis ; DSDP-ODP ; Tohoku Area ; Japan Sea
• 刊名：Quaternary International
• 出版年：2016
• 出版时间：18 March 2016
• 年：2016
• 卷：397
• 期：Complete
• 页码：436-447
• 全文大小：2367 K

文摘

Understanding the Quaternary is a key to estimating what the Earth's climate will be like in the future. Such studies demand high-resolution analyses based on paleoclimatic proxy records of changing Earth's orbital forcing and solar insolation that affect the climate system. Quaternary diatom biostratigraphy and paleoceanography have been well established based on the Quaternary marine sequences obtained by piston coring and deep-sea drilling around the Japanese Islands. This paper firstly reviews the Quaternary diatom datum levels that are directly tied to magnetic polarity, and then the late Pleistocene and Holocene rhythmic fluctuations in Td'-derived SSTs (°C) which correlate with the Earth's orbital parameters, and finally reveals the large and abrupt climatic changes that have occurred around the Japanese Islands on centennial to millennial time scales.

The main aim is to provide the results of Td'-SSTs (°C) based on the late Pliocene to Pleistocene sequences from three holes obtained by deep-sea drilling (DSDP-ODP). The main difference between Td' and Twt is that Twt gives 0.5 values to Xt (warm transitional taxa). Thalassiosira oestrupii is grouped with Xt in Twt but with warm-water species in Td'. Differences between the Twt and Td'-SSTs (°C) curves at Hole 436 are unremarkable. The remarkable variations of paleo-temperatures based on Td'-SSTs (°C) show four conspicuous episodes which correspond to the double precession cycle of MIS 11. In the Japan Sea, the Twt ratio remarkably decreases at 2.6 Ma due to a large increase in cold-water taxa, and indicates the beginning of the glacial age defined as the Pliocene/Pleistocene boundary. Both Twt and Td'-SSTs (°C) increase at 2.60–2.0 Ma, and coincide with the lithologic change from diatom-bearing clay with few dark-colored layers to fine-grained sediments with distinct dark–light colored cycles. Wavelet analysis of Td'-SSTs (C) at Site 798 indicates a reversed saw-tooth pattern of 48 to 24-ky periods during 1.2–0.7 Ma, and 24 to 12-ky periods during 0.7–0 Ma, resulting in a change from longer to shorter cycles. These fluctuations correlate with the Earth's orbital parameters and climatic changes on a millennial time scale.