南海北部4MaB.P.以来古海洋变迁的长链烯酮记录

通过对ODP184航次1147/1148站位约4MaB.P.以来沉积物中来源于定鞭金藻的生物标志化合物的研究,对南海北部晚上新世以来的古海洋生产力、表层海水温度及CO₂分压的变化情况进行了探讨.定鞭金藻生产力与硅藻生产力一样在0.9MaB.P.以前比较稳定地保持在较低水平,而0.9MaB.P.后定鞭金藻生产力较高,且呈现冰期低间冰期高的波动,硅藻生产力则呈现持续升高的趋势.由C37烯酮不饱和度指标获得的南海北部4MaB.P.以来表层海水的UK′37温度与浮游有孔虫壳体δ18O具有较好的相关性,且能显示出0.9MaB.P.来的19个氧同位素期,表明将U37K′37温标应用到晚第四纪以前基本上是可行的.由δ13C37:2计算的表层海水pCO₂显示,晚上新世的pCO₂要高于300μL/L,而第四纪的pCO₂尽管存在波动,却基本上在300μL/L以下.计算出的晚第四纪的pCO2十分稳定,与同期的大气pCO₂历史变化不一致.这可能与计算中简单地假定某些参数(如生长速率)为常数有关,这些参数在第四纪冰期间冰期旋回中可能有较大变化.

LONG-CHAIN ALKENONE RECORDS OF PALEOCEANOGRAPHY IN THE NORTHERN SOUTH CHINA SEA SINCE 4 Ma B.P.

This paper studies the paleoproductivity, sea surface temperature (SST) and marine p CO₂since the late Pliocene in the northern South China Sea by sedimented alkenone biomarkers from haptophyceae in the site 1147/1148, ODP leg 184. Paleoproductivity of both haptophyceae and diatom (biogenic SiO₂ as proxy) remained stable and low before 0.9MaB.P. But after 0.9MaB.P., haptophyceae productivity became fluctuant with high in the interglacial time and low in the glacial time, and diatom productivity exhibited increasing trend. These changes in paleoproductivity were perhaps resulted from increasing nutrient induced by increasing terrestrial inputs in Quaternary, especially the late Quaternary. Diatom bloomed in the higher nutrient conditions during the glacial time, depressing haptophyceae productivity in the same time. The good correlation between U K′ 37 -SST and δ¹⁸O of planktonic foraminifera since 4MaB.P. and successful distinguish of 19 oxygen isotopic stages during the last 0.9MaB.P. on U K′ 37 -SST curve suggest that the extended application of U K′ 37 paleothermometer to pre late Quaternary is tentatively feasible. Marine p CO₂calculated from δ¹³C₃7∶2 was higher than 300 μL/L in the late Pliocene and lower than 300 μL/L in Quaternary. The calculated marine p CO₂ were very stable in the late Quaternary, inconsistent with atmospheric p CO₂records in the corresponding period. The abnormity of the results was perhaps caused by simple assumption of parameters, such as growth rate, as a constant, which they might in nature be varied greatly during glacial-interglacial cycles.