摘要
大洋内部蒸发、水汽输送和降水过程构成了全球水文循环的主体,但长久以来对全新世大洋内部水文循环的演变历史和驱动机制缺乏认识。利用全球热带海区98个站位混合层浮游有孔虫壳体的δ18O和Mg/Ca温度记录,计算了全新世以来表层海水δ18O以及海水剩余δ18O的波动历史。发现最显著的特征是全新世以来热带西太平洋和东印度洋表层海水剩余δ18O具有不同的变化趋势。早—中全新世时期(11.5~6.0 ka BP),热带西太平洋表层海水剩余δ18O比东印度洋偏重约0.2‰,而晚全新世(2.0~0 ka BP),两个海区的重建值几乎相同。结合同位素数值模拟结果,发现岁差通过一系列机制控制了两个大洋不同的剩余δ18O变化信号。早全新世较低的岁差值可以驱动西太平洋往印度洋的大气水汽净输送并降低印度洋降水同位素,同时强盛的南亚季风通过河流体系向孟加拉湾倾注了大量陆地冲淡水。这些机制都有利于东印度洋海水剩余δ18O出现相对负偏移信号。但较低的岁差值导致开放的西太平洋净降水量下降,并通过大气传输损失淡水,因此海水剩余δ18O值较为偏重。本次研究结合大空间尺度上的δ18O重建记录和模拟结果,较为可靠地刻画了岁差调控下洋盆之间的水汽转移过程和机理。
Precipitation,evaporation and moisture transport within the oceans are the main components of the global hydrological cycle.However,the evolution of the oceanic hydrological cycle over the Holocene remains a knowledge gap.In this study,through compiling paired planktonic foraminiferalδ18O and Mg/Ca sea surface temperature reconstructions from 98 locations in the tropical ocean,we calculate the fluctuation of sea surfaceδ18O and residualδ18O for the Holocene period.We notice a striking feature that the residualδ18O records of the tropical western Pacific and eastern Indian Ocean show a different change over the Holocene.The mean residualδ18O of the tropical western Pacific was about 0.2‰heavier than that of the eastern Indian Ocean during the early-mid Holocene(11.5~6.0 kaBP),but they were almost identical over the late Holocene(2.0~0 kaBP).Combined with the transient climate simulations,we suggest that precession forcing is responsible for this different pattern through modulating a set of climate processes.The lower precession over the early Holocene drove a net atmospheric moisture transport from the western Pacific to the eastern Indian Ocean and lowered precipitationδ18O over the eastern Indian Ocean.Moreover,the strengthened South Asian monsoon delivered large amounts of diluted freshwater into the Bay of Bengal via river systems.All these three mechanisms contribute to a relatively negative excursion of residualδ18O in the eastern Indian Ocean.In contrast,the lower precession resulted in a decrease of net precipitation in the open western Pacific and a loss of freshwater via the atmospheric transport,thus generating heavier residualδ18O values.Through combining seawaterδ18O reconstructions from a large spatial extent with the isotope-enabled simulations,this study has provided a reliable picture of the moisture transfer between different ocean basins and unveiled the underlying mechanisms regulated by precession.
作者
刘冰瑾
黄恩清
田军
LIU Bingjin;HUANG Enqing;TIAN Jun(State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China)
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2023年第4期56-70,共15页
Marine Geology & Quaternary Geology
基金
国家自然科学基金优秀青年科学基金项目“低纬水循环地质演变”(42122042)
中央高校基本科研业务费专项资金项目“温室期低纬水文循环的地质演变”(22120220531)。
关键词
低纬水循环
轨道周期
海水氧同位素
浮游有孔虫
low-latitude hydrological cycle
orbital cycle
seawater oxygen isotope
planktonic foraminifera