Tracing Biogeochemical Cycles in the Weathering Environment using Mg and Li isotopes.

Project Description: 

Ca and Mg are released from silicate minerals during chemical weathering, react with atmospheric CO2, and are deposited as carbonate in the oceans, regulating global climate on geological time scales. Thus to estimate and predict CO2 consumption rates, it is important to identify and quantify the sources and fluxes of Ca and Mg that are discharged to the world’s oceans via rivers, and the weathering processes that produce those fluxes. Isotopes of mineral-derived elements (such as Mg) in marine-deposited rocks and sediments are increasingly used to deduce paleoclimates, ancient ocean temperatures and circulation, and past river fluxes. However, it is becoming apparent that the utility of such isotopic proxies is dependent on establishing the dynamics of the isotope systems in the weathering environment, before they enter the rivers. Therefore a solid knowledge of the isotopic signatures in critical zone materials and the mechanisms that fractionate isotopes during weathering and (bio)geochemical cycling, is crucial for both interpreting the historical rock record and predicting future CO2 sequestration.

To investigate the behavior of Mg and Li isotopes in the soil environment, we are analyzing Mg and Li isotopes at the University of Bristol in the UK. We are measuring the isotopic compositions of a large suite of LCZO samples from the Bisley watersheds, including rocks, soils, saprolites, plants, streams, and precipitation. The Puerto Rican environment will be used as a case study, complemented by analysis of a suite of soil samples from a variety of climates, latitudes, and rock types to obtain a global perspective.
These data will provide crucial new insights into chemical weathering in the tropical critical zone, and advance our understanding of the terrestrial Mg and Li cycles and their influence on the isotopic signatures of rivers. We plan to extend this work to the Rio Icacos watershed in the next phase of research.

Research Location: 
Source of Funding: 
USGS WEBB Project, LCZO
Dissemination: 
restricted
Contact Information
Person(s) Completing This Form: 
Heather L. Buss
Investigators: 
Heather L. Buss (hlbuss@usgs.gov), U.S. Geological Survey, Menlo Park, CA
Investigator E-mail Addresses: 
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