Walters Andrew P, Tierney Jessica E, Zhu Jiang, Meyers Stephen R, Graves Katherine, Carroll Alan R
Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA.
Climate and Global Dynamic Laboratory, National Center for Atmospheric Research, Boulder, CO 80305, USA.
Sci Adv. 2023 Aug 4;9(31):eadg8022. doi: 10.1126/sciadv.adg8022.
The early Eocene Climatic Optimum (EECO) represents the peak of Earth's last sustained greenhouse climate interval. To investigate hydroclimate variability in western North America during the EECO, we developed an orbitally resolved leaf wax δH record from one of the most well-dated terrestrial paleoclimate archives, the Green River Formation. Our δH results show ∼60‰ variation and evidence for eccentricity and precession forcing. iCESM simulations indicate that changes in the Earth's orbit drive large seasonal variations in precipitation and δH of precipitation at our study site, primarily during the summer season. Our findings suggest that the astronomical response in δH is attributable to an asymmetrical climate response to the seasonal cycle, a "clipping" of precession forcing, and asymmetric carbon cycle dynamics, which further enhance the influence of eccentricity modulation on the hydrological cycle during the EECO. More broadly, our study provides an explanation for how and why eccentricity emerges as a dominant frequency in climate records from ice-free greenhouse worlds.
始新世早期气候适宜期（EECO）代表了地球最后一个持续的温室气候区间的峰值。为了研究EECO期间北美西部的水文气候变化，我们从年代测定最为精确的陆地古气候档案之一——格林河组，开发了一个轨道分辨率的叶蜡δH记录。我们的δH结果显示出约60‰的变化以及偏心率和岁差强迫的证据。iCESM模拟表明，地球轨道的变化驱动了我们研究地点降水和降水δH的大幅季节性变化，主要发生在夏季。我们的研究结果表明，δH中的天文响应归因于对季节周期的不对称气候响应、岁差强迫的“截断”以及不对称的碳循环动态，这进一步增强了偏心率调制在EECO期间对水文循环的影响。更广泛地说，我们的研究解释了在无冰温室世界的气候记录中，偏心率如何以及为何成为主导频率。
