南京大学李伟强课题组及其成员，在研究不同气候状况下的现代近海碎屑沉积物的钾同位素特征及其意义中取得新进展。2024年1月22日出版的《中国科学：地球科学》发表了这项成果。

本研究报道了中国东海岸(ECC)大陆架和中国南海北部热带海南岛周围表层海底沉积物的K同位素数据。ECC沉积物的δ⁴¹K(参照NIST3141a)值分布相对较窄，范围从(-0.40±0.01)‰到(-0.57±0.04)‰，平均值为(-0.51±0.09)‰。相比之下，近海沉积物的δ⁴¹K值变幅度较大，变化范围为(-0.28±0.07)‰到(-0.67±0.02)‰。海南近海沉积物的δ⁴¹K值与化学蚀变指数(CIA)、Al/K、Ti/K和总铁(FeT)呈负相关，表明化学风化作用对海洋碎屑输入的钾同位素特征具有控制作用。研究人员还测量了相同样品的镁同位素组成；有趣的是，所有ECC和海南近海沉积物样品的δ²⁶Mg值的变化幅度都很小(约0.24‰)，δ²⁶Mg值与化学风化指标没有明显的相关性。

研究证明了碎屑沉积物的钾同位素变化与包括降雨强度在内的气候条件之间的联系，同时，海洋沉积物碎屑成分的K同位素可以用于研究地球的深层气候。研究结果强调，近岸碎屑沉积物的δ⁴¹K值变化明显小于远洋海相沉积物，表明利用碎屑沉积记录中的K同位素研究深时气候—风化联系时，区分粘土矿物的成岩作用和新生作用与大陆风化作用的重要性。

据了解，钾同位素是大陆风化的新型示踪剂。以往关于化学风化的钾同位素研究，通常针对特定气候区域下的风化剖面，但不同气候背景下化学风化对钾同位素的影响尚不清楚。此外，人们对现代松散碎屑沉积物的钾同位素特征知之甚少。

附：英文原文

Title: Potassium isotopic signatures of modern offshore detrital sediments from different climatic regimes and the implications

Author: Jun MU, Tianyu CHEN, Qian YU, Shichao AN, Jianfang CHEN, Xuefa SHI, Weiqiang LI

Issue&Volume: 2024-01-22

Abstract: Potassium isotopes are a novel tracer for continental weathering. Previous K isotope studies on chemical weathering generally targeted weathering profiles under a particular climate region, yet the effects of chemical weathering on K isotopes under different climatic backgrounds remain unclear. Moreover, little is known about the K isotope signatures of modern unconsolidated detrital sediments. Here, we report K isotopic data of surficial seafloor sediments from continental shelves along the east coast of China (ECC), as well as those around the tropical Hainan island in the northern South China Sea. The ECC sediments have a relatively narrow distribution of δ⁴¹K (with reference to NIST3141a) values, which range from (0.40±0.01)‰ to (0.57±0.04)‰, with an average of (0.51±0.09)‰. By contrast, δ⁴¹K values of Hainan offshore sediments display a larger variation, ranging from (0.28±0.07)‰ to (0.67±0.02)‰. The δ⁴¹K values of Hainan offshore sediments exhibit negative correlations with the chemical index of alteration (CIA), Al/K, Ti/K, and total iron (FeT), which underlines the control of chemical weathering on K isotopic signatures of detritus inputs into oceans. We also measured Mg isotope compositions for the same samples; interestingly, the variability in δ²⁶Mg of the samples is small (~0.24‰) for all ECC and Hainan offshore sediments, and δ²⁶Mg values do not show clear correlations with indexes of chemical weathering. Our study demonstrates the link between K isotopic variability of detrital sediments and climatic conditions including rainfall intensity, which indicates that K isotopes of the detrital component of marine sediments could be applied to study Earth’s climate in deep time. The δ⁴¹K values of the offshore detrital sediments are significantly less variable than those of pelagic marine sediments, highlighting the importance of distinguishing the effects of diagenesis and neoformation of clay minerals from continental weathering in attempts to study deep-time climate-weathering link by K isotopes in detrital sedimentary records.

DOI: 10.1007/s11430-023-1220-1

Source: https://www.sciengine.com/10.1007/s11430-023-1220-1