Clumped isotope thermometry and oxygen isotope composition of seawater of key climate events during the Oligocene

渐新世关键气候事件海水的丛同位素测温和氧同位素组成

• 批准号: 428605926
• 负责人: Professor Dr. Heiko Pälike, Ph.D.
• 金额: --
• 依托单位: Institutt for geovitenskap
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/428605926?language=en
• 关键词: Clumped; isotope; thermometry; oxygen; composition

Understanding past climate changes and their underlying causes requires reconstructions of past ocean composition and temperatures. However, traditional proxies of ocean temperatures and ice volume (e.g., stabile oxygen isotopes and Mg/Ca values of foraminifera) are undermined by biological processes or changes in ocean chemistry. Clumped isotope thermometry, a promising, novel proxy, circumvents these problems. Carbonate clumped isotope thermometry is entirely thermodynamically based and therefore provides temperature estimates independent of the original isotopic or chemical composition of the source water, in contrast to other carbonate temperature proxies (oxygen isotopes and Mg/Ca ratios). Paired oxygen-clumped isotope measurements on carbonate samples thus enable the calculation of the oxygen isotope composition of the water, from which the carbonates precipitated. That means, clumped isotope thermometry also provides insights into global ice volume changes. The clumped isotope method used here allows measurement of small sample sizes and has an analytical error as small as +/-1-2°C, which is comparable to other temperature proxies. The Oligocene is an important climate epoch as it marks the inception of the icehouse world following the warm greenhouse climate of the Palaeocene and Eocene. The onset of the Oligocene is one of the most fundamental reorganisations of global climate, as the first permanent, large continental ice sheets formed on Antarctica. However, a recent study using clumped isotopes across the Eocene-Oligocene transition (EOT) at a Southern Ocean site indicates no evident temperature change across this ice growth event. This unexpected lack of temperature change could arise from uncertainties in the clumped isotope-T calibration at low temperatures. Therefore, this proposed study aims to establish a clumped isotope-T calibration of modern surface-, thermocline-dwelling and benthic foraminifera of high latitude Southern Ocean sites to improve published clumped isotope calibration equations on the low-temperature end. Finally, this study will reconstruct reliable bottom and surface seawater temperatures, using paired measurements of foraminiferal clumped isotope values and Mg/Ca ratios, at sites spanning different latitudes and ocean basins. These analyses will target specific time intervals of the Oligocene, such as the EOT (to reassess the findings of the Southern Ocean study) and key glaciation phases (Oi-2b, Mi-1). The Oi-2b glaciation occurred during maximum ice volume of the entire Oligocene. During the Mi-1 glaciation, benthic foraminiferal oxygen isotope records illustrate an increase similar to the EOT interval, raising the question of comparable estimates of ice growth. In summary, investigating these intervals will evaluate the seawater temperatures, seawater oxygen isotope composition and global ice volume changes during a time when global climate was mainly driven by Southern Hemisphere climate mechanisms.

了解过去的气候变化及其根本原因需要重建过去的海洋成分和温度。但是，海洋温度和冰容量的传统代理（例如，稳定氧同位素和有孔虫的mg/ca值）被生物学过程或海洋化学变化所破坏。团结的同位素温度计，一种有希望的新型代理，绕过了这些问题。与其他碳酸盐温度代理相反（氧同位素和mg/ca比）相比，碳酸盐簇的同位素温度计完全是基于热力学的，因此提供了与原始水的原始同位素或化学组成无关的温度估计值。因此，对碳酸盐样品的配对氧气混合同位素测量值可以计算水的氧同位素组成，碳酸盐是精确的。这意味着，聚类的同位素温度计还提供了对全球冰量变化的见解。此处使用的群集同位素方法允许测量小样本量，并且具有小于+/- 1-2°C的分析误差，与其他温度代理相当。渐新世是一个重要的气候时代，因为它标志着古镇和始新世温暖的温室气候之后的冰屋世界的成立。渐新世的发作是全球气候中最基本的重组之一，作为在南极洲上形成的第一个永久性连续冰盖。然而，最近在南大洋地点使用始新世 - 寡新世过渡（EOT）的聚类同位素的一项研究表明，这一冰生长事件的温度没有变化。低温下聚类的同位素-T校准的不确定性可能导致这种意外的温度变化。因此，这项拟议的研究旨在建立簇状的同位素-T校准，对高纬度高纬度位点的现代表面，热层栖息和底栖有孔虫，以改善低温端上已发表的聚类的同位素校准方程。最后，这项研究将使用有孔虫簇的同位素值和mg/ca比率的配对测量值，在跨越不同纬度和海洋鲈鱼的位置，重建可靠的底部和表面海水温度。这些分析将针对渐新世的特定时间间隔，例如EOT（重新评估南方海洋研究的发现）和关键的冰川阶段（OI-2B，MI-1）。 OI-2B冰川发生在整个渐新世的最大冰量期间发生。在MI-1冰川期间，底栖有孔虫的氧同位素记录说明了与EOT间隔相似的增加，从而提出了相当的冰生长估计值的问题。总而言之，研究这些间隔将评估海水温度，海水氧同位素组成和全球冰的体积变化，而全球气候主要由南半球气候机制驱动。