Research ArticleEARTH SCIENCES

Frost for the trees: Did climate increase erosion in unglaciated landscapes during the late Pleistocene?

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Science Advances  27 Nov 2015:
Vol. 1, no. 10, e1500715
DOI: 10.1126/sciadv.1500715
  • Fig. 1 Map of the Little Lake catchment and sample sites.

    Core data location for this study is marked with an asterisk. Previous paleoecology data collected in the fens near the Little Lake outlet are marked with a polygon. Modern stream sample locations are delineated with stars. Map shows only a portion of the larger landslide-dammed paleolake deposit that extends to the east of Triangle Lake. (Inset) Map showing the extent of ice sheets 21 ka, location of study area (dark-gray polygon), and Little Lake, OR. Modern analog ecosystem location is identified with a blue square. Continental extent 21 ka is outlined in black, and modern continental extent is outlined in gray.

  • Fig. 2 Compilation of Little Lake core observations and data.

    P. sitchensis (Sitka spruce) and A. lasiocarpa (subalpine fir) co-occurrence was observed at 29.5 to 22.6 ka based on depth-age model. Numbers to the left of the tree icons are macrofossil counts for each species at each interval. For simplicity, we only do not include macrofossil counts at 29.5 ka (three P. sitchensis and four A. lasiocarpa). Percentages of clay, sand, and silt in the core are based on visual observations. The entire core sequence consists of millimeter- to centimeter-scale laminated lacustrine deposits, with a significant reduction in fine-scale laminations and an increase in grain size ~26 ka, the start of the last glacial (MIS 2) interval. Median calibrated ages are based on the CLAM model best fit. Although the core extends over 50 ky, for the purpose of this study we only present data that are relevant to the time interval of interest.

  • Fig. 3 Annual temperature curves.

    Comparison of annual temperature curves based on mean monthly temperature data for modern Little Lake (a; dashed green line); the range of data from downscaled paleosimulations with temperatures above the frost-cracking window (b; gray band with CCSM4, GISS-E2-R, ISPL-CM5A-LR, MPI-ESM-P, and MRI-CGM3 delineated with light-gray lines); COSMOS-ASO (c; solid gray line); Hyder, AK, climate station data (d; dashed blue line); and MIROC-ESM data (e; blue line). All paleomodel data are from CMIP5/PMIP3 simulations (Materials and Methods).

  • Fig. 4 Contour map of frost-cracking intensity.

    Model output of frost-cracking intensity for peak amplitude ranging between 0 and 15 and for MAT ranging between −15°C and 15°C, representing Earth’s range of annual temperature variability. MAT and amplitude values for Little Lake at 21 ka and for the present are delineated by “a” and “b,” respectively.

  • Fig. 5 Elevation, MAT, amplitude, and frost-cracking intensity.

    Maps showing elevation, MAT, annual amplitude, and frost-cracking intensity 21 ka. All data are overlain on a present-day hillshade map delineating the continental extent of the OCR study area. Downscaled paleodata are adjusted for continental extent 21 ka. White circle delineates the Little Lake study area. (A) Present-day study area elevation. (B) Mean annual temperature 21 ka based on downscaled MIROC model output. (C) Amplitude values (half the temperature range) 21 ka based on mean monthly temperature data. (D) Frost-cracking intensity 21 ka in the OCR.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/10/e1500715/DC1

    Materials and Methods

    Fig. S1. Precipitation anomaly map.

    Fig. S2. Additional information on frost-cracking intensity phase map (Fig. 3).

    Fig. S3. Temperature anomaly map.

    Fig. S4. Frost-cracking intensity distributions for Little Lake and the OCR.

    Table S1. 14C data and depths used in depth-age model.

    Table S2. Cosmogenic nuclide data and calculated erosion rates.

    References (7580)

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. Precipitation anomaly map.
    • Fig. S2. Additional information on frost-cracking intensity phase map (Fig. 3).
    • Fig. S3. Temperature anomaly map.
    • Fig. S4. Frost-cracking intensity distributions for Little Lake and the OCR.
    • Table S1. 14C data and depths used in depth-age model.
    • Table S2. Cosmogenic nuclide data and calculated erosion rates.
    • References (75–80)

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