Previous   |    Next

doi:10.2204/iodp.sp.346.2013

Introduction

The overall goal of Expedition 346 is to core and log sites on a latitudinal transect in the Japan Sea and one site in the northern East China Sea to test the hypothesis that Pliocene–Pleistocene uplift of the Himalaya and Tibetan Plateau (HTP) and the consequent emergence of the two discrete modes of Westerly Jet circulation caused the amplification of millennial-scale variability of the East Asian monsoon and provided teleconnection mechanism(s) for Dansgaard–Oeschger cycles (DOCs).

The research is oriented toward exploring the relationships between atmospheric processes (e.g., positioning of Westerly Jet circulation), rainfall (e.g., Yangtze River discharge), and oceanic processes (e.g., surface water circulation into and out of the Japan Sea and deepwater convection within the sea). Multiple timescales are targeted, and assessing climate sensitivity variations through time and space are an important component of the research plan. Results from this expedition will enable reconstruction of the onset and evolution of orbital- and millennial-scale variations of summer monsoon, winter monsoon, Westerly Jet position and intensity, desertification in East and Central Asia, and their interrelationships during the last 5 m.y. We will also be exploring the linkages between orbital- and millennial-scale variations of the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM), discharge of the Yangtze and Yellow Rivers, and the paleoceanography of the Japan Sea.

Specific scientific objectives are

• To address the timing of onset of orbital- and millennial-scale variability of the EASM and EAWM and their relation with variability of Westerly Jet circulation;
• To reconstruct orbital- and millennial-scale changes in surface and deepwater circulation and surface productivity in the Japan Sea during at least the last 5 m.y.;
• To reconstruct the history of the Yangtze River discharge using cores from the northern end of the East China Sea as it reflects variation and evolution in EASM and exert an impact on the paleoceanography of the Japan Sea; and
• To examine the interrelationship among EASM, EAWM, the nature and intensity of the influx through the Tsushima Strait, the intensity of winter cooling, surface productivity, ventilation, and the bottom water oxygenation in the Japan Sea and their changes during the last 5 m.y.

During Expedition 346, we aim to collect the geological evidence necessary to address these objectives by drilling and coring at seven sites in the Japan Sea and one site in the northern part of the East China Sea (Fig. F1). We plan to drill a latitudinal transect of the Japan Sea (proposed Sites JB-3, JB-2, JB-1, YR-1, UB-1, YB-2, and YB-1) to monitor the behaviors of the Westerly Jet, EAWM, and the Tsushima Warm Current (TWC). The southern part of the transect (proposed Sites YR-1, UB-1, and YB-2) also will be used to reconstruct the behavior of the Subpolar Front and examine its relationship with the Westerly Jet and sea level changes, whereas the northern part of the transect (proposed Sites JB-3, JB-2, JB-1, and YR-1) will be used to identify ice-rafted debris (IRD) events and reconstruct temporal variation in its southern limit. In addition, a depth transect (proposed Sites YB-1, YB-2, JB-1, JB-2, and JB-3) will reconstruct the ventilation history of the Japan Sea and examine the relation between ventilation and the nature of the influx through the Tsushima Strait and/or the intensity of winter cooling. We also will drill in the northern part of the East China Sea (proposed Site ECS-1B) to monitor the Yangtze River discharge history, which should reflect variations in EASM intensity (Kubota et al., 2010).

Top of page   |    Previous   |    Next