Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA.
Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA.
Nature. 2021 Jan;589(7840):70-75. doi: 10.1038/s41586-020-03062-1. Epub 2021 Jan 6.
The prevailing mid-latitude westerly winds, known as the westerlies, are a fundamental component of the climate system because they have a crucial role in driving surface ocean circulation and modulating air-sea heat, momentum and carbon exchange. Recent work suggests that westerly wind belts are migrating polewards in response to anthropogenic forcing. Reconstructing the westerlies during past warm periods such as the Pliocene epoch, in which atmospheric carbon dioxide (CO) was about 350 to 450 parts per million and temperatures were about 2 to 4 degrees Celsius higher than today, can improve our understanding of changes in the position and strength of these wind systems as the climate continues to warm. Here we show that the westerlies were weaker and more poleward during the warm Pliocene than during glacial periods after the intensification of Northern Hemisphere glaciation (iNHG), which occurred around 2.73 million years ago. Our results, which are based on dust and export productivity reconstructions, indicate that major ice sheet development during the iNHG was accompanied by substantial increases in dust fluxes in the mid-latitude North Pacific Ocean, especially compared to those in the subarctic North Pacific. Following this shift, changes in dust and productivity largely track the glacial-interglacial cycles of the late Pliocene and early Pleistocene epochs. On the basis of this pattern, we infer that shifts in the westerlies were primarily driven by variations in Plio-Pleistocene thermal gradients and ice volume. By combining this relationship with other dust records and climate modelling results, we find that the proposed changes in the westerlies were globally synchronous. If the Pliocene is predictive of future warming, we posit that continued poleward movement and weakening of the present-day westerlies in both hemispheres can be expected.
盛行的中纬度西风带，也就是西风，是气候系统的基本组成部分，因为它们在驱动海洋表面环流和调节海气热、动量和碳交换方面起着至关重要的作用。最近的研究表明，西风带正在向北迁移，以响应人为强迫。重建上新世等温暖时期的西风带（当时大气二氧化碳（CO）约为 350 到 450 个ppm，温度比今天高 2 到 4 摄氏度）可以提高我们对这些风系位置和强度变化的理解，因为气候继续变暖。在这里，我们表明，与冰期后北半球冰原加强（大约 273 万年前）相比，上新世温暖时期的西风带较弱且更偏北。我们的结果基于尘埃和出口生产力重建，表明在北半球冰原加强期间，北大西洋中纬度地区的尘埃通量大幅增加，尤其是与亚北极北大西洋相比。在这种转变之后，尘埃和生产力的变化在很大程度上与上新世晚期和更新世早期的冰期-间冰期循环相一致。根据这一模式，我们推断西风带的变化主要是由上新世-更新世热梯度和冰量变化驱动的。通过将这种关系与其他尘埃记录和气候模型结果相结合，我们发现所提出的西风带变化在全球范围内是同步的。如果上新世可以预测未来的变暖，那么我们认为可以预计，目前在两个半球的西风带将继续向北移动并减弱。
