Multiproxy reconstruction for Kuroshio responses to northern hemispheric oceanic climate and the Asian Monsoon since Marine Isotope Stage 5.1 (∼88 ka)

Clim. Past, 10, 1735–1750, 2014 www.clim-past.net/10/1735/2014/ doi:10.5194/cp-10-1735-2014 © Author(s) 2014. CC Attribution 3.0 License. Multiproxy reconstruction for Kuroshio responses to northern hemispheric oceanic climate and the Asian Monsoon since Marine Isotope Stage 5.1 (∼ 88 ka) X. Shi1 , Y. Wu1 , J. Zou1 , Y. Liu1 , S. Ge1 , M. Zhao2 , J. Liu1 , A. Zhu1 , X. Meng1 , Z. Yao1 , and Y. Han1 1 Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China 2 Key Laboratory of Marine Chemistry Theory and Technology (Ocean University of China), Ministry of Education/Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China Correspondence to: X. Shi () Received: 26 February 2014 – Published in Clim. Past Discuss.: 4 April 2014 Revised: 7 August 2014 – Accepted: 19 August 2014 – Published: 18 September 2014 Abstract. The Kuroshio, a western boundary current in the northwestern Pacific, plays a key role in regulating ocean and climate in East Asia. The evolution of the Kuroshio and its branches has been the focus of paleoceanographic studies. In this study, we applied a multiproxy (grain size, planktonic foraminiferal species, δ 18 O, alkenone sea surface temperature (SST) and salinity) reconstruction from sediment core CSH1, which is located at the main axis of the Tsushima Warm Current, a branch of the Kuroshio, in the northern Okinawa Trough (OT). This study, extended the paleoceanographic record of the Kuroshio to Marine Isotope Stage (MIS) 5.1 (∼ 88 ka) from the far northern site in the OT. Planktonic foraminiferal species identified from this core contain warm-water species related to the Kuroshio and coldwater species related to subarctic water mass. The relative abundances of the warm-water species are high during MIS 1 and MIS 5.1, while cold-water species are high during MIS 2. An organic biomarker proxy, alkenone SST measured from core CSH1 ranges between 21 and 25 ◦ C, with higher values during interglacials (MIS 1, 3.3, 5.1) and interstadials and lower values during glacials and Heinrich (H)/stadial events. Sea surface salinity (SSS) and the depth of the thermocline (DOT), reconstructed based on foraminifera isotopes and faunas, indicate dominant Kuroshio responses to an abrupt climate change event recorded in Greenland ice cores and in stalagmites in East China since ∼ 88 ka. The CSH1 SSS appears to be mainly controlled by the local river runoff and the Kuroshio, while the DOT change seems to be closely re- lated to the strength of the Kuroshio and the latitudinal shift of the subarctic frontal zone. Our records suggest that, during MIS 1 and MIS 5.1, while global sea level was high, the Kuroshio was dominant; while during MIS 2, MIS 3 and MIS 4, with a low sea level, stronger winter Asian Monsoon (AM) and a more southerly subarctic front played important roles in governing the hydrographic characteristics in the OT. Spectral analysis of our multiproxy hydrographic records shows a dominant precessional period at ∼ 24 ka. Our hydrographic records, such as SST, SSS and DOT, from a site near the modern Tsushima Warm Current show regional responses corresponding mainly to the global sea level, the Kuroshio, AM and subarctic front, factors which are consistently invoked in the interpretations of other regional records from the OT. 1 Introduction The meridional heat transport by ocean currents, such as the Gulf Stream in the North Atlantic and the Kuroshio in the North Pacific, plays a critical role in setting the global energy balance and regulating climate change. The Kuroshio carries large amounts of heat, salt and moisture from low latitudes; it enters the Okinawa Trough (OT) with a high current velocity, great volume transport and a narrow width and extends to the far northwestern Pacific. It exerts great influence on the climate and environmental conditions of East Published by Copernicus Publications on behalf of the European Geosciences Union. 1736 Asia (Hsueh, 2000; Hsueh et al., 1992). In the northern OT, two branches of the Kuroshio, the Tsushima Warm Current (TWC) and the Yellow Sea Warm Current, enter into the Sea of Japan through the shallow Tsushima Strait, with a sill depth of 130 m, and into the Yellow Sea, respectively, while the main stream of the Kuroshio continues to flow northwardly along the east coast of Japan and turns across the northwestern Pacific at ∼ 38◦ N. Besides the Kuroshio, the climate of the western Pacific is also regulated by the Asian Monsoon (AM). The freshwater discharged by the Yangtze and Yellow Rivers directly influences the surface water salinity and the primary productivity and, therefore, the organic carbon export and burial in the adjoining continental margins. Since OT is located adjacent to the wide shelf of the East China Sea (ECS), abundant high-resolution information on past climate and oceanographic changes could be extracted from marine sediment cores from the OT because of the very high sedimentation rate in the OT. Previous studies on past climate changes using sediment cores from the OT show orbital-scale (Ijiri et al., 2005; Kao et al., 2006a; Kawahata et al., 2006; Zhou et al., 2007), millennial and abrupt climatic responses, such as the 8.2 ka event, the Younger Dryas, Heinrich (H) events and the Dansgaard– Oeschger cycles of the Kuroshio (Chang et al., 2008, 2009; Ijiri et al., 2005; Li et al., 2001; Liu et al., 2001; Yu et al., 2009). However, most of these studies were limited by either shorter cores or single-proxy reconstruction (Jian et al., 1998; Kao et al., 2006b; Lee et al., 2013; Ujiié and Ujiié, 1999) that covered only a small spatial scale of the OT which the Kuroshio has entered. In this study, we present a multiproxy reconstruction of the Kuroshio responses from core CSH1, located at the northernmost site of the OT (Fig. 1). Our records of Kuroshio responses reconstructed here date back to Marine Isotope Stage (MIS) 5.1 (∼ 88 ka); this is the longest record to date, with a resolution high enough to infer orbital- to millennial-scale climate and oceanographic changes in the northern OT. 2 Oceanographic background The OT is a back-arc basin of the Ryukyu trench–arc–basin system (Lee et al., 1980). It is bounded by the Ryukyu Ridge and Trench to the east and the wide shelf of the East China Sea (ECS) to the west. The entire complex is arcuate, convex toward the Pacific with a NNE–SSW alignment from Japan to Taiwan (Lee et al., 1980). The OT is a big graben, consisting of the topographic depression behind the Ryukyu Arc with a length of 1200 km and a width of 100– 150 km. Since the middle Miocene with the opening of the OT (Sibuet et al., 1987), it has been a depositional center in the ECS and has received a very large supply of sediment from nearby continents. The modern hydrographic characteristics of surface water masses in the OT are controlled by t (...truncated)