van Peer Tim E, Liebrand Diederik, Taylor Victoria E, Brzelinski Swaantje, Wolf Iris, Bornemann André, Friedrich Oliver, Bohaty Steven M, Xuan Chuang, Lippert Peter C, Wilson Paul A
University of Southampton, Waterfront Campus, National Oceanography Centre Southampton, Southampton, UK.
Department of Earth Sciences, University College London, London, UK.
Nat Commun. 2024 Dec 5;15(1):10600. doi: 10.1038/s41467-024-54186-1.
Earth's obliquity and eccentricity cycles are strongly imprinted on Earth's climate and widely used to measure geological time. However, the record of these imprints on the oxygen isotope record in deep-sea benthic foraminifera (δO) shows contradictory signals that violate isotopic principles and cause controversy over climate-ice sheet interactions. Here, we present a δO record of high fidelity from International Ocean Drilling Program (IODP) Site U1406 in the northwest Atlantic Ocean. We compare our record to other records for the time interval between 28 and 20 million years ago, when Earth was warmer than today, and only Antarctic ice sheets existed. The imprint of eccentricity on δO is remarkably consistent globally whereas the obliquity signal is inconsistent between sites, indicating that eccentricity was the primary pacemaker of land ice volume. The larger eccentricity-paced early Antarctic ice ages were vulnerable to rapid termination. These findings imply that the self-stabilizing hysteresis effects of large land-based early Antarctic ice sheets were strong enough to maintain ice growth despite consecutive insolation-induced polar warming episodes. However, rapid ice age terminations indicate that resistance to melting was weaker than simulated by numerical models and regularly overpowered, sometimes abruptly.
地球的倾斜度和偏心率周期在地球气候中留下了深刻印记，并被广泛用于测定地质时间。然而，这些印记在深海底栖有孔虫的氧同位素记录（δO）中的表现却显示出相互矛盾的信号，这些信号违反了同位素原理，引发了关于气候与冰盖相互作用的争议。在此，我们展示了来自西北大西洋国际大洋发现计划（IODP）U1406站点的高保真δO记录。我们将我们的记录与2800万至2000万年前这一时间间隔内的其他记录进行了比较，当时地球比现在更温暖，且仅存在南极冰盖。偏心率对δO的印记在全球范围内显著一致，而倾斜度信号在不同站点之间并不一致，这表明偏心率是陆地冰量的主要起搏器。由偏心率驱动的规模更大的早期南极冰期容易迅速结束。这些发现意味着，尽管连续出现由日照引起的极地变暖事件，但大型陆基早期南极冰盖的自我稳定滞后效应强大到足以维持冰的增长。然而，冰期的迅速结束表明，其对融化的抵抗力比数值模型模拟的要弱，且经常被克服，有时甚至是突然被克服。
