HR: 13:55h
AN: V13F-02    [Abstracts]
TI: Characterizing Dust Inputs to the Caribbean Region Using Radiogenic Isotopes
AU: * Pett-Ridge, J C
EM: juliep@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Derry, L A
EM: lad9@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University Snee Hall, Ithaca, NY 14853, United States
AB: The long-range transport of mineral aerosols (dust) in the atmosphere influences radiative transfer in the atmosphere and affects ocean productivity via Fe fertilization. Dust transport also affects terrestrial systems by contributing to geochemical fluxes of both sediments and solutes, adding nutrients and nutrient-holding capacity to ecosystems, and neutralizing acidic components of atmospheric deposition. The largest atmospheric dust source is the Sahara-Sahel region of Northern Africa. Of the dust derived from the Sahara-Sahel region, 50 million tons are transported west each year on the trade winds into the Caribbean atmosphere¹. Ratios of relatively immobile trace elements provide geochemical evidence that confirms the expected presence of African dust in soils of the Caribbean region. However, estimates of dust deposition fluxes to land in the Caribbean are lacking². A promising approach for calculating deposition fluxes is to quantify the streamwater Sr flux for a small monolithologic catchment, and then quantify contributions from local substrate, sea salt aerosols, volcanic ash, and long-range transported dust using their unique isotopic signatures. This approach has the advantage of giving a spatially and temporally integrated estimate of the dust deposition flux, which is necessary for assessing the importance of dust to geochemical fluxes and biogeochemical cycling. Many factors will control the importance of dust inputs for a given site. Local soil characteristics will determine the rate at which dust weathers once it enters the soil, and the extent to which dust may contribute to the nutrient budget of the ecosystem. The amount and style of rainfall will affect the rate at which dust particles are scrubbed from the atmosphere. Further, local erosion rates will determine the extent of dust accumulation over time. ⁸⁷Sr/⁸⁶Sr ratios are used to calculate the deposition flux of African dust into the small montane Rio Icacos watershed in Puerto Rico of 13 t km^-2 yr^-1. Nd isotope data show that African dust is incorporated into the regolith to at least 3 m depth. The degree of dust incorporation into the regolith is notable considering the relatively high erosion rates for this mountainous catchment (34 t km^-2 yr^-1) ³. We discuss the ecological importance of the nutrients (namely phosphorus) provided by the dust to the Rio Icacos ecosystem, as has been shown for dust inputs in Hawaii⁴, and has been hypothesized for dust inputs in the Amazon basin⁵. Additionally, considering the Caribbean region as a whole, we attempt to identify those areas where dust inputs may be expected to have the greatest impact on geochemical budgets and biogeochemical cycling. References [1] Colarco et al (2006) JGR-Atmospheres v. 108. [2] Muhs et al (2007) JGR-Atmospheres v. 112. [3] Riebe et al (2003) GCA v.67. [4] Chadwick et al (1999) Nature v. 397. [5] Swap et al (1992) Tellus Series B v. 44.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0486 Soils/pedology (1865)
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting