HR: 11:30h
AN: B11F-05 INVITED     [PDF]
TI: The Biogeochemical Impact of Global and Local Dust on Hawaiian Ecosystems
AU: * Chadwick, O A
EM: oac@geog.ucsb.edu
AF: Oliver Chadwick, Department of Geography, University of California, Santa Barbara, CA 93106
AU: Kurtz, A C
EM: kurtz@bu.edu
AF: Andrew Kurtz, Department of Earth Science, Boston University, Cambridge, MA 02215
AU: Derry, L A
EM: lad9@cornell.edu
AF: Louis Derry, Department of Geological Department of Geological Sciences, Cornell University, Ithaca, NY 14853
AU: Vitousek, P M
EM: vitousek@stanford.edu
AF: Peter Vitousek, Department of Biological Sciences, Stanford University, Stanford, CA 94305
AU: Wiegand, B
EM: bwiegand@pangea.Stanford.EDU
AF: Peter Vitousek, Department of Biological Sciences, Stanford University, Stanford, CA 94305
AB: Hawaii is distant from continental sources of dust, yet there is abundant evidence that continental dust accumulates in soils on stable land surfaces. The physical evidence for dust accumulation is a dark grayish purple horizon that resides just below the O horizon; it is evident to a trained eye in 20 ky soils but becomes quite obvious in 150 ky soils. The continental dust contains about 20% quartz and a greater amount of mica, minerals that are not found in the local basalt and tephra. Thus presence of quartz and mica in Hawaiian soils identifies present, and in the case of buried horizons, past stable surfaces. In older soils near surface soil horizons can contain up to 30% quartz after 150 ky of accumulation. Soils on older lava flows do not necessarily contain greater amounts of dust because chemical and physical erosion removes variable amounts from different landscape positions. In soils older than 20 ky there is a progressive increase in the quartz to mica ratio suggesting that mica is preferentially weathered in locations where physical erosion is limited. In addition to mineralogy, the isotopes of Sr and Nd provide distinctive indications of dust contribution to soil profiles because the mantle-derived lavas have different isotopic signatures that the more highly evolved continental components. In horizons greatly impacted by dust the basaltic derived Sr and Nd signatures are nearly completely overprinted by continental signatures. Strontium concentrations are highly depleted due to leaching whereas Nd is less labile. Using quartz and Nd as tracers of continental dust we calculate a minimum long-term dust accumulation rate of 125 mg/cm2/ky. Dust has a profound effect on the budgets of elements that are susceptible to leaching losses and becomes the dominant source of labile nutrients, Si and P in the oldest, most intensely weathered soils. We calculate a dust-derived P input flux of 0.8 mg/cm2/ky and a dust-derived Si input flux of 35 mg/cm2/ky. Leaching losses of Si and P are high in young soils but decline to values that balance the dust input in the oldest soils. Extremely refractory elements, such as Nb, that are concentrated by residual enrichment are much less readily impacted by dust additions. For example, 150 ky soils show strong continetal dust signatures when considering mineralogy, or Sr and Nd isotopes, but dust can have contributed less than 4% of the Nb in the profile. Calcium and Sr, labile elements in humid soils are little impacted by dust additions because far greater quantities of these ions are dissolved in rainwater.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting