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Contributions from Earth's Atmosphere to Soil

¹ Cornell University, Department of Earth & Atmospheric Sciences
Ithaca, NY 14853-1506, USA
E-mail: lad9{at}cornell.edu
² University of California, Department of Geography
Santa Barbara, CA 93106-4060, USA
E-mail: oac{at}geog.ucsb.edu

View larger version (11K): [in this window] [in a new window]   FIGURE 1 Cation concentration ratios relative to chloride in precipitation normalized to seawater. The data are from 12 U.S. coastal or island sites and in most cases are five-year means of annual precipitation-weighted chemistry. At all sites Ca is considerably enriched over what is predicted from a sea salt model, while Mg is often slightly depleted. K is typically enriched, while Na is indistinguishable from sea salt composition. The deviations from sea salt composition are mostly the result of dissolution of mineral aerosols, of which calcium carbonate is the most important source.

View larger version (24K): [in this window] [in a new window]   FIGURE 2 Integrated wet deposition flux (ions delivered in the fog plus rain) (solid lines) for Ca and K calculated for the Kilauea volcano area compared to substrate inventory calculated over the top meter. Dashed lines show substrate inventory assuming no weathering losses. Dotted lines show substrate inventory assuming quasi-first-order losses with a time constant of 7000 years for the first 104 years and declining losses after that time. Wet deposition of K exceeds the basalt inventory in ca. 2300-3300 years, depending on the rate of weathering loss; for Ca the timescale is 12,000-70,000 years. DEPOSITION DATA FROM CARILLO ET AL. (2002)

View larger version (16K): [in this window] [in a new window]   FIGURE 3 Effect of surface erosion on foliar 87Sr/86Sr and phosphorous levels, Hawai'i. Samples of native O'hia (Metrosideros polymorpha) leaves from locations where erosion has cut deeply into the original constructional volcanic shield surface have more "basaltic" Sr and higher P levels than leaves in trees growing on undisturbed, highly weathered shield surfaces. Erosion makes more basalt-derived Sr and P available. Note reversal of Sr axis. The value of 87Sr/86Sr in basalt is near 0.703, while atmospheric sources are mostly sea salt (0.709) with some dust (near 0.720). FIGURE MODIFIED FROM THE ORIGINAL IN PORDER ET AL. (2005)

View larger version (145K): [in this window] [in a new window]   FIGURE 4 A NASA SeaWiFS image collected on August 19, 2004. Dust from North Africa often blows across the Mediterranean Sea into southern Europe. An uncropped version of this image and others showing dust storms originating in desert regions can be found at http://oceancolor.gsfc.nasa.gov/cgi/image_archive.cgi?c=DUST.

View larger version (17K): [in this window] [in a new window]   FIGURE 5 Mixing diagram for Sr and Nd isotope ratios in bulk Hawaiian soil samples. Data from dust-impacted horizons at Laupahoehoe and Kohala plot on a mixing hyperbola between depleted soil and Asian dust. Mineral aerosol addition initially shifts 87Sr/86Sr but has less impact on Nd values (143Nd/144Nd normalized relative to a chondritic meteorite reference, CHUR), because of the low Sr/Nd ratio in weathered basalt. Increasing addition of mineral aerosol impacts Nd values as the input of dust Nd gradually over-whelms the depleted reservoir of basaltic Nd. Over time, the largest input of Sr to the soils is from marine arosol, so 87Sr/86Sr ratios in near-surface weathered basalt tend to approach the seawater value, irrespective of dust or basaltic inputs. However, the impact of mineral or marine aerosol deposition on deep soil horizons is negligible. FIGURE MODIFIED FROM THE ORIGINAL IN KURTZ ET AL. (2001)