Expedition 346 synthesis

Operations during Integrated Ocean Drilling Program (IODP) Expedition 346 drilled seven sites in the marginal sea bordered by the Eurasian continent, the Korean Peninsula, and the Japanese Islands (hereafter referred as the “marginal sea”),1 as well as two closely spaced sites in the East China Sea in August and September 2013. Six of the marginal sea sites were drilled in oceanic basins (Japan, Yamato, and Ulleung Basins), and one site was drilled on a bank named the Yamato Rise (Fig. F1). In total, we recovered 6135.3 m of core, with an average recovery of 101%. To our knowledge, this 6135 m is a record amount of core to be recovered by any single expedition during IODP. We gathered an unparalleled archive of atmospheric-ocean linkages relating to the East Asian monsoonal system and, partly because of the implementation of new coring, sampling, and analytical strategies, we are confident that researchers studying this sediment will be able to propel the field of climate dynamics significantly forward.

This marginal sea was last investigated by scientific ocean drilling during Ocean Drilling Program (ODP) Legs 127 and 128, nearly 25 y ago. Prior to those tectonically oriented research legs of ODP, the Deep Sea Drilling Project (DSDP) had conducted drilling operations during DSDP Leg 31 in 1973 in a challenging and ambitious attempt to reach basement objectives as the plate tectonic revolution was achieving widespread acceptance. Thus, Expedition 346 was the first scientific drilling expedition ever to focus exclusively on the climate system in this area that is at once so critical, yet potentially vulnerable, to the challenges society faces in the coming years of global climate change. With the East Asian Monsoon directly affecting the water supply of one-third of the global population, this research has direct bearing on society’s understanding of this complex atmosphere-ocean climate system.

The original research goals of Expedition 346 were oriented toward exploring the relationships between atmospheric processes (e.g., the positioning of the atmospheric Westerly Jet circulation), rainfall (e.g., Yangtze River discharge), and oceanic processes (e.g., surface water circulation, sea ice formation, deepwater convection and oxygenation, and surface biological productivity in the marginal sea). Multiple timescales were targeted, and assessing climate sensitivity variations through time and space was an important component of the research plan. We aimed to reconstruct the onset and evolution of orbital- and millennial-scale variations of summer and winter monsoons, Westerly Jet position and intensity, desertification in East and Central Asia, and their interrelationships during at least the last 5 m.y. In detail, we targeted 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, position of Westerly Jet, and paleoceanography of the marginal sea.

1Due to a sensitive intergovernmental naming dispute between Japan and the Republic of South Korea about the naming of the body of water between these countries, the U.S. National Science Foundation, with the goal of minimizing intrusion of politics into the scientific program and continuing with contractually mandated publication of these international science documents, instructed IODP to publish the Expedition 346 Preliminary Report and Proceedings using the words “marginal sea,” “marginal basin,” and basinal names for geographic reference.