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The Kuroshio Current is a major western boundary current controlled by the North Pacific Gyre. It brings warm subtropical waters from the Indo-Pacific Warm Pool to Japan exerting a major control on Asian climate. The Tsushima Current is a Kuroshio offshoot transporting warm water into the Japan Sea. Various proxies are used to determine the paleohistory of these currents. Sedimentological proxies such as reefs, bedforms, sediment source and sorting reveal paleocurrent strength and latitude. Proxies such as coral and mollusc assemblages reveal past shelfal current activity. Microfossil assemblages and organic/inorganic geochemical analyses determine paleo-sea surface temperature and salinity histories. Transportation of tropical palynomorphs and migrations of Indo-Pacific species to Japanese waters also reveal paleocurrent activity. The stratigraphic distribution of these proxies suggests the Kuroshio Current reached its present latitude (35°N) by~3 Ma when temperatures were 1 to 2°C lower than present. At this time a weak Tsushima Current broke through Tsushima Strait entering the Japan Sea. Similar oceanic conditions persisted until~2 Ma when crustal stretching deepened the Tsushima Strait allowing inflow during every interglacial. The onset of stronger interglacial/glacial cycles~1 Ma was associated with increased North Pacific Gyre and Kuroshio Current intensity. This triggered Ryukyu Reef expansion when reefs reached their present latitude (~31°N), thereafter the reef front advanced (~31°N) and retreated (~25°N) with each cycle. Foraminiferal proxy data suggests eastward deflection of the Kuroshio Current from its present path at 24°N into the Pacific Ocean due to East Taiwan Channel restriction during the Last Glacial Maximum. Subsequently Kuroshio flow resumed its present trajectory during the Holocene. Ocean modeling and geochemical proxies show that the Kuroshio Current path may have been similar during glacials and interglacials, however the glacial mode of this current remains controversial. Paleohistorical studies form important analogues for current behavior with future climate change, however, there are insufficient studies at present in the region that may be used for this purpose. Modeling of the response of the Kuroshio Current to future global warming reveals that current velocity may increase by up to 0.3 m/sec associated with a northward migration of the Kuroshio Extension.

Millennial‐scale variability in the behavior of North Pacific Intermediate Water during the last glacial and deglacial period, and its association with Dansgaard‐Oeschger (D‐O) cycles and Heinrich events, are examined based on benthic foraminiferal oxygen and carbon isotopes (δ18Obf and δ13Cbf) and %CaCO3 using a sediment core recovered from the northeastern slope of the Bering Sea. A suite of positive δ18Obf excursions at intermediate depths of the Bering Sea, which seem at least in part associated with increases in the δ18Obf gradients between the Bering and Okhotsk Seas, suggest the Bering Sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period. Absence of such δ18Obf gradients during periods of high surface productivity in the Bering and Okhotsk Seas, which we correlate to D‐O interstadials, suggests a reduction in intermediate water production in the Bering Sea and subsequent introduction of nutrient‐rich deep waters from the North Pacific into intermediate depths of the Bering Sea. We argue that a reorganization of atmospheric circulation in the high‐latitude North Pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern Bering Sea. The resulting salinity increase in the cold surface waters could have initiated intermediate (and deep) water formation that spread out to the North Pacific.

A new radiolarian data set for transfer function estimates of past sea surface temperature (SST) and intermediate water temperature was developed in this study for the northwestern Pacific Ocean covering a region from 1° to 50°N and 120° to 167°E. We analyzed 87 sediments surface samples, selected 30 species and/or species group found in shallow water for estimating past summer SST and 17 species and/or species group found in the intermediate water for estimating past intermediate water temperature. Since the intermediate water temperature changes greatly between 200 and 500 m, our estimates provide values at 500 m because temperatures are relatively stable between 500 and 1000 m. In this context, we estimated past summer SST and intermediate water (at ~500 m) temperature within an error margin of 0.9 and 1.2°C, respectively. A test of the accuracy of our transfer functions, conducted on core samples provided by IODP Expedition 346 Site U1429 in the northern East China Sea, showed that the reconstructed summer SSTs fluctuated between 17.2 and 26.5°C in selected late Pleistocene sequences. These temperatures corresponded to modern winter and summer SST, respectively, which highlights the ability of our new database to accurately reconstruct summer SST. The reconstructed intermediate water temperature fluctuates between 3 and 8°C, which corresponds to the observed temperature range at depths of ~500 m at high and midlatitudes, respectively.

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