Eccentricity cycles shown by early Pleistocene planktonic foraminifers of the Omma Formation, Sea of Japan

Abstract

There is a continuous record of planktonic foraminifers for oxygen isotope stages 50 to 26 (ca. 1.5-1.0 Ma) in the early Pleistocene Omma Formation near Kanazawa City, Central Japan, on the Sea of Japan coast. The warm-water species Globigerinoides ruber entered the Sea of Japan with the Tsushima Current during all interglacial periods and went locally extinct in the succeeding glacial periods. This implies that the marine climate of the Sea of Japan varied predominantly with the 41,000-year period of Earth's orbital obliquity. However, the relative abundances of G. ruber in marine isotope stages 47, 43 and 31 are significantly higher than those in other interglacial stages. These stages correspond to periods when eccentricity-modulated precession extremes were aligned with obliquity maxima. The Tsushima Current is a branch of the warm Kuroshio Current which is the strong northwestern component of the subtropical North Pacific Ocean gyre. Our data imply that the early Pleistocene climate in the northwestern Pacific was influenced not only by obliquity cycles but also by eccentricity cycles. This study also supports the climate model regarding eccentricity's role in the origin of low-frequency climate changes before the late Pleistocene ice ages.

The Pliocene to recent history of the Kuroshio and Tsushima Currents: a multi-proxy approach

“…Kitamura and Kimoto (2007) summarized the stratigraphic distribution of molluscan fossils in the Pliocene to lower Pleistocene marine strata along the Japan Sea coastal area (Amano et al 1987(Amano et al , 1988(Amano et al , 1990(Amano et al , 2000Amano and Kanno 1991;Arai et al 1991Arai et al , 1997Cronin et al 1994;Miwa et al 2004) and the lower Pleistocene Omma Formation in the Hokuriku area (HO: Fig. 3: Kitamura and Kondo 1990;Kitamura 1991Kitamura , 1994Kitamura et al 1994;Kitamura and Kawagoe 2006).…”

Early Pleistocene evolution of the Japan Sea Intermediate Water

“…Thus it is possible that an increase in precipitation resulted from an intensification of the East Asian summer monsoon. As noted above, an increase in the sea surface temperature of the Kuroshio Current was associated with high summertime boreal insolation during interglacial stages 47 and 43 (Kitamura and Kimoto, 2007). Therefore I believe that lowsalinity and warm wintertime surface water caused the reduction of thermally driven convection and brine rejection.…”

“…According to Kitamura and Kimoto (2007), sea surface waters during interglacial stages 47 and 43 were significantly warmer than during other interglacial stages of the Early Pleistocene. Because these periods correspond to high boreal summer insolation, when eccentricity-modulated precession extremes were aligned with obliquity maxima, Kitamura and Kimoto (2007) suggested that orbital-induced changes in the strength of the subtropical North Pacific Ocean gyre acted to intensify the Tsushima Current. There exists the possibility that a relatively warm current restricted the formation of deep-sea water and led to the formation of warm intermediate water; however, this explanation may be insufficient.…”

The evolution of the Tsushima Current during the early Pleistocene in the Sea of Japan: An example from marine isotope stage (MIS) 47

“…Samples were initially studied from the horizon containing the maximum relative abundance (MRA) of planktic foraminifera Globigerinoides ruber corresponding with warm water molluscan fossils (Kitamura et al, 2001; Kitamura and Kimoto, 2007) from each depositional sequence in the lower and middle parts of the Omma Formation. Samples were subsequently collected and analysed from surrounding horizons and other sections not previously studied (e.g.…”