Sea‐surface temperature and salinity changes in the northwest Pacific since the Last Glacial Maximum

Abstract

Oba, T. and Murayama, M. 2004. Sea-surface temperature and salinity changes in the northwest Pacific since the Last Glacial Maximum.ABSTRACT: The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea-surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12-13 C (maximum 15 C) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10 C at 10-11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10-11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom-water temperature decrease of 2.5 C at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea-surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 AE 0.1% at the LGM.

The LGM surface climate and atmospheric circulation over East Asia and the North Pacific in the PMIP2 coupled model simulations

“…This characteristic is more remarkable in the western North Pacific than in the eastern North Pacific (not shown). Since this pattern is also seen in annual-mean SST anomaly field, this is consistent with the paleoclimatic reconstructions in that the surface temperature decreases remarkably in the mid-latitude western North Pacific (Oba and Murayama, 2004).…”

Ventilation changes in the western North Pacific since the last glacial period

“…1 Sagawa et al (2006) confirmed the high quality of the core by comparing the sediment colour and planktic foraminiferal δ 18 O between this core and MD01-2421, another IMAGES piston core adjacent to the MD01-2420 site with well-established age control (Oba and Murayama, 2004;Oba et al, 2006). …”

Fluctuations in the East Asian monsoon over the last 144ka in the northwest Pacific based on a high-resolution pollen analysis of IMAGES core MD01-2421

“…Core MD01-2421 also showed that Cryptomeria maxima (indicating a strong East Asian summer monsoon) occurred later than the T p maxima (an indicator of solar insolation) by several to ten thousand years. Figure 5 shows the down-core T p values, summer insolation curves at 36 and 65°N, the SST curve calculated from the oxygen isotope difference between benthic and planktonic foraminifera (Oba and Murayama, 2004;Oba et al, in press), and the relative abundances of Cryptomeria and Sciadopitys in core MD01-2421. Except after 24 8 ka, the T p increased during the periods of high summer insolation, which had maxima around 127, 105, 83, and 11 ka and decreased during the low-insolation peaks around 138, 116, 94, 71, and 22 ka (Fig.…”