Holocene Paleoceanography in the Upper Reach of the Kuroshio
|Keywords:||黑潮;全新世;沖繩海槽;西北太平洋;古海洋學;Kuroshio;Holocene;Okinawa Trough;western North Pacific;Paleoceanography||Issue Date:||2005||Abstract:||
I have studied a suite of deep-sea cores (MD01-2403, OR715-21 and MD98-2188) located in the upper reach of the Kuroshio (from the Philippine Sea to off eastern coast of Taiwan) and the Southern Okinawa Trough (SOT) using both traditional methods (foraminiferal assemblages and stable isotopes) and a newly developed paleothermometer (Mg/Ca ratio). The goal of this research is to investigate paleoceanographic relationships among the East Asian monsoon (EAM), Equatorial Pacific (EP) and SOT during the Holocene, and to further unravel the Holocene history of the Kuroshio.
During the past decade, paleoceanographers have reported the so-called 'Pulleniatina Minimum Event (PME)' at 4.5-3.0 ka from the Okinawa Trough and South China Sea. The paleoenvironmental and ecological hypotheses for the PME were tested using our data in the upper reach area and the SOT. The three cores all witness the PME, implying this event is widespread in the western North Pacific. The results of Mg/Ca-based SSTs and thermocline hydrography reconstructed by multispecies isotopic analyses reveal nothing anomalous in the paleoceanographic proxies associated with the PME. Relative abundance of Neogloboquadrina dutertrei did not shows reciprocal pattern to that of P. obliquiloculata in the upper reach area. We proposed a biological hypothesis (epidemic mass mortality) originating in the EP that resulted in the PME. This new hypothesis may be testable by approaches in population dynamics. This PME study has two implications for paleoceanography. First, the discrepancy between the Mg/Ca-derived SSTs and fauna-based SSTs during the PME period is discussed. Second, P. obilquiloculata is not a faithful indicator for the Kuroshio in the Holocene epoch.
To discuss the Holocene SST front variability in the East China Sea, we present the surface water d18O (d18Osw) record in the SOT (MD01-2403), estimated from d18O of Globigerinoides ruber and Ma/Ca-based SST of Globigerinoides sacculifer. The Mg/Ca-based SSTs are quite stable throughout the Holocene, whereas a long-term decrease in d18Osw of ~0.5 o/oo was found over the past 8,000 yrs, equivalent to a decrease of 1 psu in salinity calculated from the local empirical equation: d18Osw=0.51S-17.28 (R2 = 0.81, n=37). We compare the d18Osw record from the SOT with climatic records of Greenland GISP2 ice core d18O, stalagmite d18O of the Dongge Cave in China, and d18Osw of MD98-2181 in the western terminus of the North Equatorial Current. The decreasing trend in SSS in the SOT is inconsistent with the record of Asian monsoon strength of the South China, but agrees better with the d18Osw record from the western tropical Pacific. Our study indicates that the decrease of d18Osw in the SOT might reflect either the decrease of SSS in the North Equatorial Current-Kuroshio system or to a larger extent, a basin-wide change in salinity of the Pacific Ocean.
By examining various paleoceanographic proxies of the upper reach of the Kuroshio, we evaluated previous interpretations and provided new perspectives on the Holocene paleoceanography of the Kuroshio. The extensive distribution of the PME and the freshening trend in the SOT imply an oceanographic teleconnection between the SOT and the EP.
|Appears in Collections:||地質科學系|
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