Persistent intensification of the Kuroshio Current during late Holocene cool intervals

Abstract

The Kuroshio Current (KC), which redistributes heat and moisture from the tropics toward mid-latitudes, considerably affects ocean–atmosphere–land interactions along its pathways. However, our knowledge about the KC strength and associated forcing, based on investigations of instrumental data and model simulations, is controversial, impeding assessment of its possible change in the near future. In this study, we investigated KC strength over the past 4400 yr by analyzing alkenone (U37K′) sea surface temperature (SST) signal in a sediment core under the influence of the Yellow Sea Warm Current (YSWC), a branch of the KC in the western North Pacific, along with a coastal SST record over the last 1000 yr outside of the YSWC effect. Our SST record in the warm current pathway, opposite to the patterns of coastal SST and solar irradiance changes at multi-centennial timescales, effectively manifests variations of YSWC strength. In conjunction with published records, we show a remarkably intensified YSWC, and probably the KC as well, during the cool interval between 1400–1850 AD (the Little Ice Age, LIA). We suggest that cold climate conditions, perhaps in relation to strengthened East Asian winter monsoon and Pacific Walker circulation, were more favorable for KC enhancement.