HR: 1340h
AN: PP43A-0599    [Abstracts]
TI: Holocene Climate History of North Central Minnesota, Interpreted From $\delta$D and $\delta$$\^{18}$O of Lake Sediments
AU: Zabielski, V
EM: vzabielski@nvcc.edu
AF: Dept of Geology, Northern Virginia Community College, 3001 North Beauregard Street, Alexandria, VA 22311 United States
AU: * Ito, E
EM: eito@umn.edu
AF: Limnological Research Center, University of Minnesota, 310 Pillsbury Drive, SE, Minneapolis, MN 55455 United States
AU: Wright, H
EM: hew@umn.edu
AF: Limnological Research Center, University of Minnesota, 310 Pillsbury Drive, SE, Minneapolis, MN 55455 United States
AU: Huang, Y
EM: Yongsong_Huang@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook Street, Providence, RI 02912 United States
AU: Van Leeuwen, J
AF: Geobotanical Institute, University of Bern, Altenbergrain 21, Bern, CH-3013 Switzerland
AU: Stefanova, I
EM: stefa014@tc.umn.edu
AF: Limnological Research Center, University of Minnesota, 310 Pillsbury Drive, SE, Minneapolis, MN 55455 United States
AU: Wenger, D
AF: Geobotanical Institute, University of Bern, Altenbergrain 21, Bern, CH-3013 Switzerland
AU: Williams, J W
EM: jww@geography.wisc.edu
AF: Dept of Geography, University of Wisconsin, 550 N Park Street, Madison, WI 53706 United States
AU: Person, M
EM: maperson@indiana.edu
AF: Dept. of Geological Sciences, Indiana University, 1001 East 10th St, Bloomington, IN 47405 United States
AB: Stable isotopes of authigenic carbonates in lake sediments are routinely used to reconstruct past climate. When carbonates are absent, other stable isotope records such as cellulose oxygen and $\delta$D of specific organic compounds such as palmitic acid (PA) are being used to infer water temperature. Here we show that $\delta$D of PA can be used to reconstruct aridity in appropriate climatic settings. Cored sediment from Moody Lake, located near the base of the Crow Wing River watershed, was analyzed for lithological variations indicative of lake-level, total organic and inorganic carbon, pollen, O and C isotopes of authigenic calcite and H isotopes of PA. Modern sediments in Moody Lake contain no authigenic carbonates, but lower sections contain 5$\sim$10% total inorganic carbon. Total organic carbon varies between 10$\sim$35% in the deep-water core. The $\delta$$\^{18}$O values varies from -8$\permil$ at about 11ka $\^{14}$C increasing to -2$\permil$ at ca. 4ka $\^{14}$C. The $\delta$D values are approximately -210$\permil$ at 11ka $\^{14}$C and -180$\permil$ at the top, with a peak of -170$\permil$ in the mid-section. The $\delta$D values of PA can be converted to that of water using a published equation. If we assume that authigenic carbonate is formed only during warm summer months, say at $25\deg$C, the small temperature dependence of carbonate oxygen isotope fractionation allows us to estimate the $\delta$$\^{18}$O of water without introducing a large error, given the range of 6$\permil$ in $\delta$$\^{18}$O values. When the two calculated isotope values are compared to the Global Meteoric Water Line and to local (Minneapolis) precipitation, they fall on an evaporation line of slope $\sim$5, a typical slope observed for the region. Mid-Holocene values are farthest from the local meteoric precipitation indicating greater aridity, and early Holocene values closer to the meteoric precipitation. The overall pattern is interpreted as reflecting cooler and wetter conditions in the early Holocene, gradually increasing temperatures toward the mid-Holocene, much higher aridity during the mid-Holocene, and a return to cooler and wetter conditions during the late-Holocene. Lake-level history derived from stratigraphic correlation of sand layers in shoreline transects is broadly coincident with mid-Holocene aridity. The start of the increase of oak pollen and the highest concentration of herb pollen indicating increased aridity and warmth at $\sim$8ka $\^{14}$C coincide with the beginning of the highest values in $\delta$D and $\delta$$\^{18}$O.
DE: 3344 Paleoclimatology
DE: 1833 Hydroclimatology
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting