State Key Laboratory of Marine Geology, Tongji University, 200092 Shanghai, China;
State Key Laboratory of Marine Geology, Tongji University, 200092 Shanghai, China.
Proc Natl Acad Sci U S A. 2020 Mar 31;117(13):7044-7051. doi: 10.1073/pnas.1915510117. Epub 2020 Mar 16.
The El Niño-Southern Oscillation (ENSO), which is tightly coupled to the equatorial thermocline in the Pacific, is the dominant source of interannual climate variability, but its long-term evolution in response to climate change remains highly uncertain. This study uses Mg/Ca in planktonic foraminiferal shells to reconstruct sea surface and thermocline water temperatures (SST and TWT) for the past 142 ky in a western equatorial Pacific (WEP) core MD01-2386. Unlike the dominant 100-ky glacial-interglacial cycle recorded by SST and δO, which echoes the pattern seen in other WEP sites, the upper ocean thermal gradient shows a clear half-precessional (9.4 ky or 12.7 ky) cycle as indicated by the reconstructed and simulated temperature (ΔT) and δO differences between the surface and thermocline waters. This phenomenon is attributed to the interplay of subtropical-to-tropical thermocline anomalies forced by the antiphased meridional insolation gradients in the two hemispheres at the precessional band. In particular, the TWT shows greater variability than SST, and dominates the ΔT changes which couple with the west-east SST difference in the equatorial Pacific at the half-precessional band, implying a decisive role of the tropical thermocline in orbital-scale climate change.
厄尔尼诺-南方涛动（ENSO）与太平洋赤道温跃层紧密耦合，是年际气候变率的主要来源，但它对气候变化的长期演变仍然高度不确定。本研究利用浮游有孔虫壳中的 Mg/Ca 重建了过去 142 千年来西赤道太平洋（WEP）MD01-2386 核心区的海面和温跃层水温（SST 和 TWT）。与 SST 和 δO 记录的主导 100 千年冰期-间冰期循环不同，后者反映了其他 WEP 站点的模式，上覆海洋热梯度显示出明显的半岁差（9.4 千或 12.7 千）周期，这是由重建和模拟的温度（ΔT）和温跃层水与海面之间的 δO 差异表明的。这种现象归因于在岁差带中，两个半球的反相经向太阳辐射梯度对亚热带到热带温跃层异常的相互作用。特别是，TWT 比 SST 具有更大的可变性，并且支配着与赤道太平洋东西 SST 差异耦合的 ΔT 变化，这在半岁差波段上暗示了热带温跃层在轨道尺度气候变化中的决定性作用。
