70万年来西太平洋暖池北缘有孔虫氧碳同位素特征及其古海洋学意义

选取西太平洋暖池北缘西菲律宾海本哈姆高原的MD06-3047B孔沉积物柱状样为研究材料,通过分析70万年来有孔虫氧碳同位素变化特征发现: 在MIS 14~13期,西菲律宾海由于受夏季风影响增强,可能存在上升流活动; 在冰期终止期Ⅰ、Ⅱ、Ⅳ 和Ⅴ期出现Pulleniatina obliquiloculata δ13C 极小值事件,表明在这几个冰期终止期来自南极的低δ13C 海水到达了西太平洋暖池北部边缘地区.次表层种P. obliquiloculata与表层种Globigerinoides ruber氧同位素差值恢复的温跃层变化具有冰期逐渐变浅,间冰期逐渐变深的特点.进一步将其与西太平洋暖池核心区ODP805站和赤道东太平洋ODP847站的次表层、表层有孔虫氧同位素差值进行对比,结果显示在过去70万年来西太平洋暖池效应逐渐加强,并且存在长时间尺度的类厄尔尼诺-南方涛动(ENSO)式变化,冰消期时表现为类厄尔尼诺状态.

FORAMINIFERAL CARBON AND OXYGEN ISOTOPE COMPOSITION CHARACTERISTICS AND THEIR PALEOCEANOGRAPHIC IMPLICATIONS IN THE NORTH MARGIN OF THE WESTERN PACIFIC WARM POOL OVER THE PAST ABOUT 700,000 YEARS

Core MD06-3047B(17°00.44'N, 124° 47.93'E, length 8.90m, water depth 2510m)was retrieved during Marco Polo 2 IMAGES XIV Cruise from the Benham Rise, east off Luzon Island in the Western Philippine Sea, was used to investigate paleoceanographic variations at the north margin of the Western Pacific Warm Pool (WPWP) over the past 700,000 years. The core mainly consists of yellow silty mud without obvious hiatus and turbidite layers, and the foraminifer fossils were well preserved.In this study, stable carbon and oxygen isotope measurements were carried on 445 samples of benthic foraminifera Cibicidoides wuellerstorfi(300~350μm)sampled at 2-cm intervals and 222 samples of two planktonic foraminifera Globigerinoides ruber(250~300μm)and Pulleniatina obliquiloculata(300~400μm)sampled at 4-cm intervals respectively. Stable isotope ratios of foraminiferal tests were measured on the GV IsoPrime mass spectrometer at the Key Laboratory of Marine Geology and Environment, Institute of Oceanography, Chinese Academy of Sciences. The analytical precision is better than ±0.06‰ for δ18O and ±0.03 ‰ for δ13C. The age model of Core MD06-3047B was established by comparing benthic foraminifera C. wuellerstorfi δ18 O curve with the LR04 stack combining the last appearance datum of G. ruber(pink)which indicates a numerical age of 120ka, and the results showed that the age of bottom of the core was about 700ka B.P. (MIS 17). The results of the stable oxygen isotope records of C. wuellerstorfi, G. ruber and P. obliquiloculata show obvious changes over glacial-interglacial cycle except of the stable oxygen isotope records of G. ruber during MIS 14~13. Unlike G. ruber and P. obliquiloculata,the stable carbon isotope records of C. wuellerstorfi also show glacial-interglacial changes. And the stable carbon isotope records of P. obliquiloculata occur intense negative excursions during termination Ⅰ, Ⅱ, Ⅳ and Ⅴ and obvious positive excursion during MIS 13. Based on these records, obvious upwelling activities occurred in this study area during MIS 14~13. The intense negative δ13C excursions at thermocline during termination Ⅰ, Ⅱ, Ⅳ and Ⅴ indicates that the low δ13C waters from Southern Ocean had arrived at the north margin of the WPWP. The δ18O difference between the subsurface dwelling P. obliquiloculata and the surface dwelling G. ruber in the Core MD06-3047B suggests shallower thermocline during most glacial episodes and deeper thermocline during interglacial intervals. By comparing the δ18O differences of Core MD06-3047B in the north margin of WPWP, Site ODP805 in the center of WPWP and Site ODP847 in the eastern tropical Pacific, the WPWP is suggested to have been intensified over the past 700,000 years; and there were "El Niño-like" state of climate during the deglacial periods.