The Calcium and Strontium (radiogenic and stable) isotope geochemistry of weathering in Iceland

GSTDTAP

项目编号	1613359
	The Calcium and Strontium (radiogenic and stable) isotope geochemistry of weathering in Iceland
	Andrew Jacobson
主持机构	Northwestern University
项目开始年	2016
	2016-10-01
项目结束日期	2019-09-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	375000(USD)
国家	美国
语种	英语
英文摘要	This project aims to elucidate the role of basalt weathering in Earth's long-term carbon cycle. While basalt represents only ~5% of the crustal rocks exposed at the Earth's surface, basalt weathering may have a disproportionately large effect on long-term climate change because Calcium-bearing silicate minerals composing basalt appear to dissolve easily, thereby consuming atmospheric carbon dioxide (CO2) at a relatively rapid rate. Several studies have examined basalt weathering in Iceland. A major assumption is that all of the riverine Calcium (Ca)and carbonate alkalinity originates from silicate weathering. However, hydrothermal calcite occurs throughout Iceland, and even trace levels are expected to impact river geochemistry owing to the mineral's high solubility and fast dissolution rate. Understanding the role of hydrothermal calcite weathering has several implications for quantifying the strength of the basalt weathering feedback and the factors that appear to control it, such as runoff, temperature, and mechanical erosion. The project will foster a new international partnership with Icelandic researchers and students. The investigator will supervise research by graduate and undergraduate students, and he will incorporate project findings into his radiogenic isotope geochemistry course. The investigator and his students will engage K12 underrepresented minorities in education and outreach activities related to the project award. The project will benefit society by providing new insight into the long-term carbon cycle and related geochemical phenomena that explain why the Earth is a habitable planet. This project will test several hypotheses surrounding controls on the Ca isotope composition of Icelandic rivers, which in turn can provide insight into sources of riverine alkalinity and from there, the impact of basalt weathering on long-term atmospheric CO2 levels. The research will also include analyses of radiogenic and stable Strontium (Sr) isotope ratios (87Sr/86Sr and δ88/86Sr), which should provide additional constraints on the sources and cycling of riverine Ca. Fieldwork conducted during the spring, summer, and fall will mostly concentrate on the Skagafjördur Valley in northern Iceland. Investigators will collect river water, spring water (thermal and non-thermal), rocks, minerals, soils, and plants. They also plan to collect rock and mineral specimens from the Berufjördur region in eastern Iceland. Calcite and the zeolite mineral heulandite form during burial metamorphism of basalt in the deep lava pile and often occur together in metabasalts now exposed at the surface. Heulandite Ca isotope values are lower than those for bulk basalt, while calcite Ca isotope values are higher. The Ca isotope composition of heulandite likely reflects the preferential incorporation of 40Ca during equilibrium isotope exchange at hydrothermal temperatures, implying that the residual 44Ca-enriched waters determine the high Ca isotope values of calcite. To test this hypothesis, the proposed study also includes bench-scale experiments designed to quantify the heulandite Ca isotope fractionation factor under a range of physicochemical conditions. The project is potentially transformative because it will test a long-standing paradigm surrounding the role of basalt weathering in long-term climate regulation. Because zeolite facies metamorphism and hydrothermal fluid circulation are ubiquitous characteristics of basaltic eruptions, findings for Iceland may apply generally to other flood basalt provinces. The research will also advance novel double-spike TIMS methods for measuring Ca isotopes and Sr isotope values recently developed by this group.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70498
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Andrew Jacobson.The Calcium and Strontium (radiogenic and stable) isotope geochemistry of weathering in Iceland.2016.