Stable isotope record of benthic foraminifera from the Gulf of California

A high-resolution, accelerator radiocarbon dated climate record of the interval 8,000-18,000 years B.P. from Deep Sea Drilling Project site 480 (Guaymas Basin, Gulf of California) shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation. Nonlaminated sediments are associated with cooler climatic conditions during the late glacial (up to 13,000 years B.P.), and from 10,300 to 10,800 years B.P., equivalent to the Younger Dryas event of the North Atlantic region. We propose that the changes from laminated (varved) to nonlaminated sediments resulted from increased oxygen content in Pacific intermediate waters during the glacial and the Younger Dryas episodes, and that the forcing for the latter event was global in scope. Prominent events of low delta18O are recorded in benthic foraminifera from 8,000 to 10,000 and at 12,000 years B.P.; evidence for an earlier event between 13,500 and 15,000 years B.P. is weaker. Maximum delta18O is found to have occurred 10,500, 13,500, and 15,000 years ago (and beyond). Oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of Pacific waters of intermediate depth during deglaciation or environmental changes within the Gulf of California region. Several lines of evidence suggest that during deglaciation the climate of the American southwest was marked by increased precipitation that could have lowered salinity in the Gulf of California. Recent modelling studies show that cooling of the Gulf of Mexico due to glacial meltwater injection, which is believed to have occurred at least twice during deglaciation, would have resulted in increased precipitation with respect to evaporation in the American southwest during summertime. The timing of deglacial events in the Gulf of Mexico and the Gulf of California supports such an atmospheric teleconnection.

本数据集包含取自加利福尼亚湾瓜伊马斯盆地深海钻探计划（Deep Sea Drilling Project）480站位、经加速器放射性碳定年的高分辨率气候记录，覆盖距今8000至18000年的时段，该记录揭示了冰消期内具有海洋学与气候学意义的地球化学及岩性振荡特征。晚冰期（距今约13000年以前）及距今10300至10800年期间（对应北大西洋区域新仙女木事件（Younger Dryas）），非纹层沉积物与冷期气候条件存在关联。本研究提出，从纹层（纹泥，varved）沉积物向非纹层沉积物的转变，源于冰期及新仙女木事件期间太平洋中层水含氧水平的提升，且后者事件的驱动机制具有全球性。距今8000至10000年以及12000年前后的底栖有孔虫（benthic foraminifera）中，记录了显著的低δ¹⁸O（delta18O）事件；距今13500至15000年期间存在更早事件的证据则相对薄弱。研究发现δ¹⁸O峰值出现于距今10500、13500及15000年（及更早时段）。氧同位素的变化特征大概率反映了冰消期期间太平洋中层水温度与盐度特征的改变，或是加利福尼亚湾区域的环境变化。多项证据表明，冰消期期间美国西南部的气候以降水增加为典型特征，该过程可能降低了加利福尼亚湾的水体盐度。近期的模拟研究显示，冰川融水注入导致墨西哥湾降温（该过程被认为在冰消期至少发生过两次），会使得美国西南部夏季的降水多于蒸发量。墨西哥湾与加利福尼亚湾的冰消期事件时间序列，支持这类大气遥相关机制。