A diatom record of mid- to late Holocene palaeoenvironmental changes in the southern Okinawa Trough

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  • Dongling Li, Ukendt
  • Hui Jiang, Key Laboratory of Geographic Information ScienceEast China Normal UniversityShanghaiChina, Danmark
  • Karen Luise Knudsen
  • Svante Björck
  • ,
  • Jesper Olsen
  • Meixun Zhao, Key Laboratory of Marine Chemistry Theory and Technology of the Ministry of EducationOcean University of ChinaQingdaoChina, Ukendt
  • Tiegang Li, Chinese Academy of Sciences, Ukendt
  • Jialin Li, Ukendt

Palaeoceanographic changes over the last 6800 years are documented in a diatom record from core MD05-2908 from the southern Okinawa Trough. Changes in diatom components are used to reflect variations in the strength of the Kuroshio Current and the influence of coastal waters, and these changes are compared with records of the East Asian summer monsoon, which exerts an important influence on regional climate and oceanography. A decreasing trend in the contribution of coastal diatoms during the last 6800 years is related to the weakening of the East Asian summer monsoon during the Holocene in response to diminishing insolation and a southward shift in the intertropical convergence zone. Relatively high abundances of the Kuroshio Current indicator species during the intervals 2600-2200 and 4800-3600 cal a BP, and lower abundances during the intervals 3200-2800 and 2200-1300 cal a BP, imply that there is no consistent weakening of the Kuroshio Current during the interval 4500-3000 cal a BP-the Pulleniatina Minimum Event, which is a widespread feature in the East China Sea and the South China Sea. A major reduction in coastal diatoms at 3200cal a BP and a slight decrease in the Kuroshio Current indicator species during the interval 3200-2800 cal a BP indicate that a palaeoceanographic shift occurred in the southern Okinawa Trough, which coincided with a Northern Hemisphere climatic cooling, denoted the Neoglaciation in Europe. In addition, changes in the freshwater species component of the record are suggested mainly to result from variations in flood frequency in north-eastern Taiwan caused by typhoons. A dramatic increase in the frequency of flood events during the last millennium may have been caused by relatively strong El Niño-Southern Oscillation activity, compared with the more stable period between 6800 and 1000 cal a BP, which experienced a low frequency of flood events.

TidsskriftJournal of Quaternary Science
Sider (fra-til)32-43
Antal sider12
StatusUdgivet - 2015

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