This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Researchers at the University of Maryland will conduct a laboratory study of carbonate co-precipitation and phosphate complexation of yttrium and the rare earth elements (YREEs). These processes are anticipated to be sensitive to minor pH variations, thus changes in ocean acidification could play a role in their chemistry. YREEs have carbonate-dominated solution speciation in seawater, and carbonate and phosphate both form biogenic minerals that are known to contain these elements. The relative concentrations of YREE in many biogenic and geological carbonate and phosphate accretions have been interpreted in terms of 'vital' and diagenetic effects. However, these explanations require an understanding of the basic principles underlying the YREE adsorption process, which is presently lacking. The experiments that will be conducted during this project provide a theoretical framework against which interpretations of YREE/Ca ratios in biogenic aragonite can be made. In particular, this research will allow an assessment of their pH dependence and potential usefulness as indicators of ocean acidification.
Progressive acidification of the oceans essentially lowers the saturation states of aragonite and calcite in seawater. While most ocean acidification studies are concerned with the immediate consequences for the health of calcifying organisms, there is a growing awareness that other marine geochemical cycles may be affected in various ways, for example through shifts in the chemical speciation and surface reactivity of trace metals. The focal elements for this study, by virtue of their incorporation into biogenic minerals, might act as recorders of seawater pH on historic to geological time scales.
Broader Impacts: Yttrium and the rare earth element fractionation patterns, abundance anomalies, and radiogenic isotopes have long been utilized as geochemical tools. Numerous applications are found across many branches of the geological and environmental sciences and new ones continue to emerge. In view of the widespread importance of carbonate and phosphate minerals in marine and terrestrial systems, the insights generated from this study are expected to be of broad relevance to many current problems in low-temperature geochemistry. The collection of pteropod shell material by the PI will involve participation in two research missions to the Northeast Pacific Ocean, which would allow for collaboration with Canadian scientists. The work will involve graduate student training and offers opportunities for educational outreach to the general public.
