Onset and evolution of millennial-scale variability of Asian monsoon and its possible relation with Himalaya and Tibetan uplift
20 August – 28 September, 2013
It is well demonstrated that Asian monsoon varied with the Dansgaard-Oeschger Cycles [DOC]. Recent studies further suggest that such variability may have been caused by oscillations in westerly jet circulation between two different modes of meandering. Because topographic effect of Himalaya and Tibetan Plateau [HTP] is considered as the probable cause of different modes of the westerly jet meandering, and increasing evidences suggest final uplift of HTP commenced during Plio-Pleistocene, it is hypothesized that Plio-Pleistocene uplift of HTP, and consequent emergence of the two discrete modes of westerly jet meandering is the cause of the millennial-scale variability of the Asian monsoon and amplification of the DOC.
In this project, we aim to collect the geological evidence necessary to test this hypothesis through drilling in the Japan Sea and northern part of the East China Sea. We propose to drill two latitudinal transects in the Japan Sea to monitor the behaviors of the westerly jet and winter monsoon. We also propose to drill at the northern part of the East China Sea to monitor the Yangtze River discharge history that should have been reflecting variations in summer monsoon intensity. The southern transect will be used to reconstruct the behavior of the subpolar front and examine its relationship with the westerly jet and the sea level changes. Whereas the northern transect will be used to identify ice-rafted debris [IRD] events and reconstruct temporal variation in its southern limit, which we consider as winter monsoon proxies. Finally, we arrange two depth transects to reconstruct the ventilation history of the sea. We will examine the relation between the ventilation in the sea, and the nature of the influx through the Tsushima Strait and/or winter cooling.
Through the proposed drilling, we hope to 1) specify the onset timing of orbital and millennial-scale variabilities of East Asian monsoon and westerly jet, and reconstruct their evolution process and spatial variation patterns, and 2) reconstruct orbital and millennial-scale paleoceanographic changes in the Japan Sea during the last 5 m.y. to clarify the linkage between the paleoceanographic changes in the Japan Sea and variabilities of East Asian monsoon and/or sea level changes. Comparison of the obtained results with the uplift history of HTP will enable us to test the idea that topographic evolution of HTP was responsible for creation of bimodality in westerly jet circulation that caused amplification of millennial-scale variability of Asian monsoon.
We hypothesize that there have been two quasi-stable modes of the westerly jet meandering, and oscillation between the two modes could be the essential part of the Dansgaard-Oeschger Cycles. We further speculate that Himalaya-Tibetan Plateau [HTP] play a role of topographic barrier that creates the two quasi-stable modes of the westerly jet meandering and Plio-Pleistocene uplift of HTP could have triggered the onset of millennial-scale abrupt climatic changes in northern hemisphere. In this proposal, we plan to collect paleoclimatological and paleoceanographical constraints critical to test this hypothesis through IODP drilling of the Japan Sea and northern part of the East China Sea. The drilling will enable us to reconstruct the history of onset and evolution of the orbital and millennial-scale variabilities of summer monsoon, winter monsoon, westerly jet position and intensity, and desertification in East and Central Asia during the last 5 m.y. We also propose to explore the linkage between orbital and millennial-scale variabilities of the East Asian monsoon, discharge of the Yangtze and Yellow Rivers, and paleoceanography in the Japan Sea.
Aims of the proposed drilling are two folds.
- Specify the onset timing and reconstruct evolution process of orbital and millennial-scale variabilities of East Asian monsoon (summer monsoon, winter monsoon, and westerly jet axis), reconstruct their spatial patterns, and examine their interrelationship.
- Reconstruct orbital- and millennial-scale changes in surface- and deep-water circulations in the Japan Sea, and examine their relation with variabilities of East Asian monsoon and glacio-eustatic sea level changes.
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Ryuji Tada (The University of Tokyo) & Rick Murray
Shipboard scientists from J-DESC
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1 August, 2012
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