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Ca cycling and isotopic fluxes in forested ecosystems in Hawaii
Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA
Department of Geography, University of California, Santa Barbara, California, USA
Department of Biological Sciences, Stanford University, Stanford, California, USA
Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA
Biogeochemical processes fractionate Ca isotopes in plants and soils along a 4 million year developmental sequence in the Hawaiian Islands. We observed that plants preferentially take up 40Ca relative to 44Ca, and that biological fractionation and changes in the relative contributions from volcanic and marine sources produce a significant increase in 44Ca in soil exchangeable pools. Our results imply moderate fluxes enriched in 44Ca from strongly nutrient-depleted old soils, in contrast with high 40Ca fluxes in young and little weathered environments. In addition, biological fractionation controls divergent geochemical pathways of Ca and Sr in the plant-soil system. While Ca depletes progressively with increasing soil age, Sr/Ca ratios increase systematically. Sr isotope ratios provide a valuable tracer for provenance studies of alkaline earth elements in forested ecosystems, but its usefulness is limited when deciphering biogeochemical processes involved in the terrestrial Ca cycle. Ca isotopes in combination with Sr/Ca ratios reveal more complex processes involved in the biogeochemistry of Ca and Sr.
Received 17 February 2005; accepted 13 May 2005; published 14 June 2005.
Citation: (2005), Ca cycling and isotopic fluxes in forested ecosystems in Hawaii, Geophys. Res. Lett., 32, L11404, doi:10.1029/2005GL022746.
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