Deep-sea Core From Okinawa Trough Gives 200,000-year Environmental History Of Continental Shelf
September 26, 2013

Deep-sea Core From Okinawa Trough Gives 200,000-year Environmental History Of Continental Shelf

Science China Press

A new research paper shows that a great number of nearby terrigenous pollen and charcoal have been found from the deep-sea sediments of the last 200 kyrs in Okinawa Trough. It is tesitfied that the continental shelf of the East China Sea was exposed and covered with the huge wetland and grassland ecosystems during the the last two glacial periods. They discovered that the variation of terrestrial sources is concordent with global glacial volume and sea-level changes at orbital-scale since 200 kyrs before present. Their work, entitled "A ~200 ka pollen record from Okinawa Trough: Paleoenvironment reconstruction of glacial-interglacial cycles", was published in SCIENCE CHINA Earth Sciences.

This research work concerns mainly the Quaternary environment and global changes based on pollen analysis from a deep-sea core in Okinawa Trough. The project was directed by Department of Earth Sciences, Sun Yat-sen University, with colaboration of University Claude Bernard-Lyon 1 and Laboratory of Climate and Environment Sciences in Gif-sur-Yvette. The first author is professor ZHENG Zhuo from Sun Yat-sen University. Their research work was supported by the National Natural Science Foundation of China (grant no. 40772113, 41072128).

The discoveries show that terrestrial-source materials vary greatly during the transition of glacial and interglacial periods, proving the sensitive response on the global ice volume and sea-level changes. This deep-sea record has firstly documented high percentage of sedge, grass and many freshwater algae in the glacial interval, which indicates that the offshore distance of Okinawa Trough has obviously shortened due to the exposed continental shelf during the glacial stages. The vegetation on the exposed continental shelf was dominated by intrazonal communities such as halophyte grasslands and freshwater wetlands. New evidence demonstrated that the fundamental changes of sediment sources in Okinawa Trough since ~200 ka BP were affected by combine factors including the offshore coastline distance, monsoon variability and sea-level changes.

This new research provides an oldest record of Quaternry environment reconstruction so far in the Okinawa Trough. It has a great scientific significance on highlighting the evolution history of continental shelf extension, the tracing of the sediment source areas of the Okinawa Trough and global climate changes since the last 200 kyrs.


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