HR: 1330h
AN: GC12A-0146    [PDF]
TI: An oxygen and hydrogen isotope record of Holocene climate change in the northern Rocky Mountains from hydrous iron-oxide chronosequences.
AU: * Hren, M
EM: hren@stanford.edu
AF: Stanford University, Dept. of Geological & Environmental Sciences Building 320 Lomita Mall, Stanford, CA 94305 United States
AU: Sjostrom, D
EM: sjostrom@rocky.edu
AF: Rocky Mountain College, Earth and Environmental Sciences 1511 Poly Dr., Billings, MT 59102 United States
AU: Waldbauer, J
EM: jwal@stanford.edu
AF: Stanford University, Dept. of Geological & Environmental Sciences Building 320 Lomita Mall, Stanford, CA 94305 United States
AU: Chamberlain, C P
EM: chamb@pangea.stanford.edu
AF: Stanford University, Dept. of Geological & Environmental Sciences Building 320 Lomita Mall, Stanford, CA 94305 United States
AB: In naturally-acidic, iron-rich stream systems, hydrous iron-oxide chronosequences can provide long-term records of climatic changes. We analyzed hydrogen isotopes preserved in low-temperature, hydrous, iron-oxides from two northern Rocky Mountain stream systems to assess the use of a combined oxygen and hydrogen isotope approach as a means of determining sourcewater and stream temperature changes through time. The results of this work show a 30 per mil increase in the $\delta$D of goethite cement over the past 9,000 years. This dramatic increase in the $\delta$D value suggests an increase in isotopically heavy summer precipitation since the early Holocene, which agrees with palynological studies of the region. This isotopic shift is similar in degree to the 3 per mil increase in the oxygen isotopes of these samples. However, the hydrogen isotope values exhibited in goethites from both Montana stream sites are significantly heavier than would be expected based on modern stream oxygen isotope values and previously quantified goethite-water hydrogen fractionation factors. This result suggests that non-stoichiometric water or an exchangeable hydrogen component may present challenges in the use of a combined isotope-paleothermomter in these systems. Despite the potential limitations, the combination of the oxygen and hydrogen isotope systems appears to provide a valuable record of long-term Holocene climate change and may be useful in assessing paleoclimatic changes in other naturally-acidic stream systems.
DE: 1045 Low-temperature geochemistry
DE: 3344 Paleoclimatology
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting