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。然而，海洋温度和冰量的传统指标（例如稳定氧同位素和有孔虫的镁/钙值）受到生物过程或变化的破坏。在海洋化学中，丛同位素测温法是一种有前途的新型替代物，它可以解决这些问题，碳酸盐丛同位素测温法完全基于热力学，因此可以提供独立于原始温度的估计。与其他碳酸盐温度代理（氧同位素和 Mg/Ca 比率）相比，源水的同位素或化学成分可以通过对碳酸盐样品进行配对氧簇同位素测量来计算水的氧同位素组成，从而计算出水的氧同位素组成。这意味着，凝结同位素测温法还可以洞察全球冰体积的变化。这里使用的凝结同位素方法可以测量小样本。尺寸和分析误差小至+/-1-2°C，与其他温度指标相当。渐新世是一个重要的气候时期，因为它标志着古新世温暖的温室气候之后冰室世界的开始。渐新世的开始是全球气候最基本的重组之一，因为第一个永久性的大型大陆冰盖在南极洲形成。南大洋地点的始新世-渐新世转变（EOT）表明在这次冰生长事件中没有明显的温度变化，这种意外的温度变化可能是由于低温下聚集同位素 T 校准的不确定性造成的。建立南大洋高纬度地区现代地表、温跃层和底栖有孔虫的丛同位素 T 校准，以改进已发表的丛同位素校准方程最后，本研究将通过对跨越不同纬度和海洋盆地的有孔虫簇同位素值和 Mg/Ca 比率的配对测量来重建可靠的底部和表面海水温度。这些分析将针对特定的时间间隔。渐新世，例如 EOT（重新评估南大洋研究的结果）和关键冰川期（Oi-2b、Mi-1） Oi-2b 冰川期发生。在整个渐新世冰量最大期间，底栖有孔虫氧同位素记录显示了与 EOT 间隔类似的增加，这提出了冰生长可比估计的问题。 总之，研究这些间隔将评估海水。在全球气候主要由南半球气候机制驱动的时期，温度、海水氧同位素组成和全球冰量的变化。