Assessment of Cadmium Isotopes as a Paleoclimate Proxy

作为古气候代理的镉同位素评估

• 批准号: NE/G008973/1
• 负责人: Mark Rehkamper
• 金额: $ 2.96万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG008973%2F1
• 关键词: Assessment; Cadmium; Isotopes; Paleoclimate; Proxy

It has long been known that the biological activity of the oceans is regulated by the availability of the major nutrient ions phosphate, nitrate, and silicate. More recently, however, it has been recognized that micronutrient trace elements also play an important role in limiting marine productivity. As biological activity draws down CO2 from the atmosphere, micronutrients play a significant role in regulating the Earth's carbon cycle and climate. This study focuses on the micronutrient element cadmium (Cd). The geochemistry of Cd in seawater has attracted significant interest for more than 30 years because its marine distribution mimics the distribution of the macronutrient phosphate. This correlation forms the basis for the application of foraminiferal Cd/Ca ratios as a paleoclimate proxy. The application of this proxy is hindered, however, by our limited understanding of the role and cycling of bioactive Cd in the oceans. A recent pilot investigation of the PI indicates that analyses of Cd stable isotope compositions are able to address such limitations. In particular, the pilot study was the first investigation to identify large Cd isotope variations in seawater, which primarily reflect isotope fractionation from biological uptake of dissolved seawater Cd. The strikingly systematic nature of the fractionations, provide new insights into the marine cycling of Cd and demonstrate that Cd isotopes may be a useful paleoclimate proxy. The present study will build on and verify the results of the pilot investigation. To this end, we will first acquire a significantly larger Cd isotope dataset for seawater. We will then carefully evaluate this new dataset to re-examine the conclusion, that combined analyses of seawater Cd contents and isotope compositions uniquely inform on climate-relevant processes, such as variations in marine productivity. Whilst the interpretation of the new analytical data is expected to be straightforward, we will also address this goal by expanding a currently available global ocean model of Cd cycling to Cd isotopes. This approach will allow us to assess whether the model can reproduce reasonable Cd concentrations and isotope distributions for the oceans, based on known processes and fractionation factors. Any discrepancies between the model results and data will thus help to identify deficiencies in our understanding of the processes that regulate marine Cd contents and isotope compositions. A confirmation of the hypothesis that combined Cd concentration and isotope measurements provide unique constraints on the cycling of Cd and other nutrients in the oceans would be exciting. Such a result provides a basis for the application of Cd isotopes as a paleonutrient proxy in climate research. For example, combined Cd/Ca and Cd isotope data for foraminifera from sediment cores could be used to investigate temporal changes in marine nutrient utilization and the upwelling of nutrient-rich water masses. Such studies are important because they allow an assessment of past changes in the marine carbon cycle and their effect on climate.

人们早就知道，海洋的生物活动是由主要营养离子磷酸盐、硝酸盐和硅酸盐的可用性来调节的。然而，最近人们认识到，微量营养素也在限制海洋生产力方面发挥重要作用。随着生物活动从大气中吸收二氧化碳，微量营养素在调节地球碳循环和气候方面发挥着重要作用。本研究主要针对微量营养元素镉(Cd)。30多年来，海水中Cd的地球化学研究引起了人们的极大兴趣，因为它在海洋中的分布与常量营养元素磷酸盐的分布相似。这种相关性为有孔虫Cd/Ca比值作为古气候指标的应用奠定了基础。然而，由于我们对生物活性镉在海洋中的作用和循环的了解有限，这一代理的应用受到了阻碍。最近对PI的初步调查表明，对Cd稳定同位素成分的分析能够解决这种限制。特别是，这项初步研究是确定海水中Cd同位素变化较大的第一次调查，这些变化主要反映了溶解海水Cd的生物吸收所产生的同位素分馏。Cd分馏具有惊人的系统性，为Cd的海洋循环提供了新的见解，并表明Cd同位素可能是一个有用的古气候指标。本研究将以试点调查的结果为基础并加以核实。为此，我们将首先获得一个大得多的海水Cd同位素数据集。然后，我们将仔细评估这一新的数据集，以重新检查这一结论，即结合海水Cd含量和同位素组成的分析可以独特地提供与气候有关的过程的信息，例如海洋生产力的变化。虽然对新的分析数据的解释预计将是直截了当的，但我们也将通过扩展目前可用的Cd循环到Cd同位素的全球海洋模型来实现这一目标。这一办法将使我们能够根据已知的过程和分馏系数来评估该模型是否能够重现海洋中合理的Cd浓度和同位素分布。因此，模型结果和数据之间的任何差异将有助于查明我们对管理海洋Cd含量和同位素组成的过程的理解的不足之处。如果确认这样一种假设，即结合镉浓度和同位素测量对海洋中镉和其他营养物质的循环提供独特的限制，将是令人兴奋的。这一结果为Cd同位素在气候研究中作为古营养素替代物的应用提供了依据。例如，来自沉积物岩心的有孔虫的Cd/Ca和Cd同位素组合数据可以用来调查海洋营养物质利用的时间变化和营养丰富的水团的上升流。这类研究很重要，因为它们可以评估过去海洋碳循环的变化及其对气候的影响。

项目成果

In search of a common reference material for cadmium isotope studies

寻找镉同位素研究的通用参考材料

• 发表时间: 2010
• 期刊: GEOCHIMICA ET COSMOCHIMICA ACTA
• 影响因子: 5
• 作者: Abouchami W.

Cadmium-isotopic evidence for increasing primary productivity during the Late Permian anoxic event

• DOI: 10.1016/j.epsl.2014.11.010
• 发表时间: 2015-01
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: S. Georgiev;T. Horner;H. Stein;J. Hannah;B. Bingen;M. Rehkämper

Interactions of dissolved CO2 with cadmium isotopes in the Southern Ocean

• DOI: 10.1016/j.marchem.2017.06.010
• 发表时间: 2017-10
• 期刊: Marine Chemistry
• 影响因子: 3
• 作者: Henricus van Heuven;Steven Abouchami;Wafa Xue;Zichen Galer;Stephen J. G. Rehkamper;M. Middag;Rob van Ooijen;H. J. D. Baara;S. Heuven;W. Abouchami;Z. Xue;S. Galer;M. Rehkämper;R. Middag;J. Ooijen

A Common Reference Material for Cadmium Isotope Studies - NIST SRM 3108

• DOI: 10.1111/j.1751-908x.2012.00175.x
• 发表时间: 2013-03-01
• 期刊: GEOSTANDARDS AND GEOANALYTICAL RESEARCH
• 影响因子: 3.8
• 作者: Abouchami, Wafa;Galer, Stephen J. G.;Holdship, Philip F.
• 通讯作者: Holdship, Philip F.

Ferromanganese crusts as archives of deep water Cd isotope compositions

• DOI: 10.1029/2009gc002987
• 发表时间: 2010-04-01
• 期刊: GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
• 影响因子: 3.5
• 作者: Horner, T. J.;Schonbachler, M.;Hein, J. R.
• 通讯作者: Hein, J. R.