七十四萬年來地軸傾角與西太平洋暖池擴張-收縮史
Other Title
Obliquity pacing of the expansion and contraction of the Western Pacific Warm Pool during the past 740,000 years
Date Issued
2007
Abstract
Magnesium/calcium ratios of planktonic foraminifer Globigerinoides. sacculifer in Ocean Drilling Project Leg 180 Core 1115B (ODP 180, 151o34’E, 9o14’S, water depth 1149 m) from the Solomon Sea were used to reconstruct paleo-sea surface temperature (paleo-SST) records in the western Pacific warm pool (WPWP) area over the past 740 kyrs. ODP 1115B locates at the marginal area of the annual 28℃ isotherms, thus severs as an excellent monitor to detect past warm pool extent variations. We can derive center-southern margin SST (ΔSSTC-S) gradient as an indicator of warm pool extent change, and to compare it with previous studies of western and eastern SST gradient (ΔSSTW-E) to yield a more comprehensive understanding the change in past warm pool extent variations.
The dynamic history of the WPWP can be subdivided into 4 Intervals: (1) 740-580 ka, (2) 580-320 ka, (3) 320-210 ka, and (4) 210-0 ka. (1) 740-580 ka: ΔSSTW-E and ΔSSTC-S fluctuated with relatively small amplitudes but did not covary at the same pacing. Northern Atlantic surface productivity increased, global benthic and planktonic carbon isotope values increased, and carbonate accumulation rate in eastern Pacific decreased but increased in Atlantic. These changes mark the beginning of a carbon reservoir redistribution event. (2) 580-320 ka: ΔSSTW-E and ΔSSTC-S covaried with each other and show positive correlation with obliquity. Both SST gradients reached the peak values with global benthic and planktonic carbon isotope values at Marine Isotope Stage 13 and gradually decreased then. Building of modern coral reef, strong carbonate dissolution, and establishment of modern interglacial CO2 level all took place at this Interval. (3) 320-210 ka: in the early period of this Interval, 250-320 ka, both SST gradients show similar pattern of the previous interval, following by long-term decreasing trends of both gradients. (4) 210-0 ka: ΔSSTW-E decreased through this interval, in consistent with previous study results of coccolith floral assemblages of the western and eastern equatorial Pacific. ΔSSTC-S shows good negative correlation with obliquity cycles. Annual insolation gradient between 30o and 60oS drives south Pacific gyre circulation. When insolation gradient is large, the enhancement of gyre circulation may be induced which resulting in large-scale warm pool with profound of warm water and a decreasing ΔSSTC-S. The implication is supported by Vostok ice core deuterium excess (d) data, reflecting moisture source changes and SST of source areas.
Subjects
西太平洋暖池
古氣候
學 古海洋學
晚第四紀
western Pacific warm pool
paleoclimatology
paleoceanography
late Quaternary
Type
thesis
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