Fremont Glacier 1991 Core Tritium Data ----------------------------------------------------------------------- NOAA Paleoclimatology Program and World Data Center for Paleoclimatology, Boulder ----------------------------------------------------------------------- NOTE: PLEASE CITE CONTRIBUTORS WHEN USING THIS DATA!!!!! NAME OF DATA SET: Fremont Glacier 1991 Core Tritium Data LAST UPDATE: 11/2004 (Original Receipt by WDC Paleo) CONTRIBUTOR: Paul Schuster, USGS IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2004-079 SUGGESTED DATA CITATION: Schuster, P.F., et al., 2004, Fremont Glacier 1991 Core Tritium Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2004-079. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Schuster, P.F., D.E. White, D.L., Naftz, and L.D. Cecil. 2000. Chronological refinement of an ice core record at upper Fremont Glacier in south central North America. Journal of Geophysical Research, Vol. 105, p. 4657-4666. ABSTRACT: The potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized. Although excellent paleoclimatic records exist for the polar regions, paleoclimatic ice core records are not common from midlatitude locations. An ice core removed from the Upper Fremont Glacier in Wyoming provides evidence for abrupt climate change during the mid-1800s. Volcanic events (Krakatau and Tambora) identified from electrical conductivity measurements (ECM) and isotopic and chemical data from the Upper Fremont Glacier were reexamined to confirm and refine previous chronological estimates of the ice core. At a depth of 152 m the refined age-depth profile shows good agreement (1736 +/- 10 A.D.) with the 14C age date (1729 +/- 95 A.D.). The d18O profile of the Upper Fremont Glacier (UFG) ice core indicates a change in climate known as the Little Ice Age (LIA). However, the sampling interval for d18O is sufficiently large (20 cm) such that it is difficult to pinpoint the LIA termination on the basis of d18O data alone. Other research has shown that changes in the d18O variance are generally coincident with changes in ECM variance. The ECM data set contains over 125,000 data points at a resolution of 1 data point per millimeter of ice core. A 999-point running average of the ECM data set and results from f tests indicates that the variance of the ECM data decreases significantly at about 108 m. At this depth, the age-depth profile predicts an age of 1845 A.D. Results indicate the termination of the LIA was abrupt with a major climatic shift to warmer temperatures around 1845 A.D. and continuing to present day. Prediction limits (error bars) calculated for the profile ages are +/- 10 years (90% confidence level). Thus a conservative estimate for the time taken to complete the LIA climatic shift to present-day climate is about 10 years, suggesting the LIA termination in alpine regions of central North America may have occurred on a relatively short (decadal) timescale. GEOGRAPHIC REGION: Wyoming, USA PERIOD OF RECORD: 1717-1991 AD. DESCRIPTION: Fremont Glacier 1991 Core Tritium Data DATA: Depth m. Tritium (TU) 0.25 6 1.88 7 2.275 7 2.925 17 4.085 12 6.48 14 7.96 16 9.465 22 11.56 22 13.765 28 14.425 38 14.99 19 15.86 19 17.12 32 18.04 49 19.025 33 19.485 55 20.17 58 20.605 49 21.585 35 21.965 37 22.205 47 22.41 40 22.59 43 22.76 38 23.015 103 23.425 78 23.7 101 23.935 78 24.145 83 24.34 89 24.54 95 24.7525 91 25.0525 231 25.335 146 25.55 128 25.785 165 26.08 263 26.34 264 26.53 317 26.77 294 27.025 241 27.24 137 27.42 115 27.615 148 27.81 175 28 166 28.18 187 28.35 194 28.565 241 28.7875 121 28.9725 106 29.145 159 29.32 365 29.5025 232 29.685 181 29.8825 230 30.095 205 30.29 179 30.505 140 30.71 129 30.95 139 31.2025 196 31.3775 96 31.5725 93 31.82 143 32.1175 147 32.3675 136 32.5375 136 32.74 156 32.9775 191 33.1975 75 33.435 86 33.6925 116 33.9325 122 34.1475 155 34.39 138 34.6125 143 34.955 198 35.1725 303 35.385 41 35.6075 44 35.84 55 36.045 33 36.2275 21 36.4225 101 36.6175 104 36.8325 78 37.055 77 37.275 65 37.55 72 37.835 64 38.0575 69 38.2625 71 38.47 54 38.675 -5 38.9025 49 39.1175 64 39.305 67 39.49 83 39.6775 105 39.8725 108 40.0675 125 40.2775 138 40.48 133 40.675 143 40.8775 164 41.12 179 41.39 176 41.64 169 41.845 191 42.03 144 42.2225 83 42.4225 33 42.635 37 42.855 11 43.055 25 43.2325 9 43.4325 1 43.645 2 43.87 15 44.065 24 44.2475 29 44.465 42 44.685 46 44.8925 34 45.085 45 45.3525 27 47.7975 12 51.105 12 51.31 17 51.495 41 54.715 12 65.6425 3 76.43 0 87.79 0 96.955 3 107.2475 -1 116.875 -2 126.5375 -1 136.9275 1 146.32 1 156.3625 1 158.355 0