Auxiliary material and basic geochemical and benthic foraminiferal stable isotope data for the interval bracketing Eocene Thermal Maximum 2 (ETM2) at DSDP Sites 401 and 550 in the northeastern Atlantic Ocean@en

Ever since its discovery, Eocene Thermal Maximum 2 (ETM2; ~53.7 Ma) has been considered as one of the \"little brothers\" of the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) as it displays similar characteristics including abrupt warming, ocean acidification, and biotic shifts. One of the remaining key questions is what effect these lesser climate perturbations had on ocean circulation and ventilation and, ultimately, biotic disruptions. Here we characterize ETM2 sections of the NE Atlantic (Deep Sea Drilling Project Sites 401 and 550) using multispecies benthic foraminiferal stable isotopes, grain size analysis, XRF core scanning, and carbonate content. The magnitude of the carbon isotope excursion (0.85-1.10 per mil) and bottom water warming (2-2.5°C) during ETM2 seems slightly smaller than in South Atlantic records. The comparison of the lateral d13C gradient between the North and South Atlantic reveals that a transient circulation switch took place during ETM2, a similar pattern as observed for the PETM. New grain size and published faunal data support this hypothesis by indicating a reduction in deepwater current velocity. Following ETM2, we record a distinct intensification of bottom water currents influencing Atlantic carbonate accumulation and biotic communities, while a dramatic and persistent clay reduction hints at a weakening of the regional hydrological cycle. Our findings highlight the similarities and differences between the PETM and ETM2. Moreover, the heterogeneity of hyperthermal expression emphasizes the need to specifically characterize each hyperthermal event and its background conditions to minimalize artifacts in global climate and carbonate burial models for the early Paleogene.自始新世热极值2（Eocene Thermal Maximum 2, ETM2；约53.7 Ma）被发现以来，其一直被视作古新世-始新世热极值（Paleocene-Eocene Thermal Maximum, PETM；约56 Ma）的“小兄弟”之一，因二者具备诸多相似特征，包括突发性增温、海洋酸化以及生物群更替。当前尚存的核心科学问题之一是，这类强度稍弱的气候扰动对海洋环流与通风作用，乃至最终的生物群扰动产生了何种影响。本文依托多物种底栖有孔虫稳定同位素、粒度分析、X射线荧光（XRF）岩芯扫描以及碳酸盐含量测定，对北大西洋东北部（深海钻探计划（Deep Sea Drilling Project, DSDP）401与550站位）的ETM2地层开展了系统表征。ETM2期间的碳同位素漂移幅度（0.85~1.10‰）与底层水增温幅度（2~2.5℃）似乎略低于南大西洋的相关记录。对比南北大西洋的横向d¹³C梯度可见，ETM2期间发生了一次短暂的环流转型，这一模式与PETM观测到的现象高度相似。新获取的粒度数据与已发表的生物群数据均支持这一假说，二者均指示深水水流速度出现显著降低。ETM2结束后，我们观测到影响大西洋碳酸盐沉积与生物群落的底层水流出现明显增强；与此同时，黏土含量的急剧且持续性下降则暗示区域水文循环出现减弱。本研究成果凸显了PETM与ETM2之间的异同之处。此外，热极值事件表现的非均一性也提示，需针对每一次热极值事件及其背景环境开展专门表征，以尽可能降低早古近纪全球气候与碳酸盐埋藏模型中的人为偏差。