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Controls on the Spatial Dimensions of Wetted Hydrologic Margins of Two Antarctic Lakes

^a Dep. of Civil & Environmental Engineering, Pennsylvania State Univ., University Park, PA 16802
^b Dep. of Biological Sciences, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^c Dep. of Geology & Geological Engineering, Colorado School of Mines, Golden, CO 80401
^d Environmental Studies Program, Dartmouth College, Hanover, NH 03755
^e Dep. of Geography, Univ. of Colorado, Boulder, CO 80322
^f Dep. of Biology, Univ. of New Mexico, Albuquerque, NM 87131

View larger version (93K): [in this window] [in a new window]   FIG. 1. Location map of the McMurdo Dry Valleys, LANDSAT image of Taylor Valley, and maps of surveyed lakes: (A) east lobe of Lake Bonney, and (B) Lake Fryxell. Circles denote transects at which all measurements were made and samples were collected, and gaps in Panel A represent surface bedrock at the lakeshore. Transect numbering is sequential around each lake.

View larger version (58K): [in this window] [in a new window]   FIG. 2. (A) Conceptual model of observed horizontal (HW), vertical (ZW), and lengthwise (LW) hydrologic margins adjacent to a lake and the horizontal dimension of the water table in the active layer (HWT), computed from measurements to point of refusal, (B) plan view of sampling transects, and (C) image of the hydrologic margin along the north shore of Lake Joyce, as viewed from the shoreline. Hydrologic margin is approximately 5 m in length from the shoreline.

View larger version (18K): [in this window] [in a new window]   FIG. 3. Measurements of depth to ice cement in six pits dug near Lake Fryxell correlated to adjacent depths of refusal, measured with an active layer t-bar probe.

View larger version (29K): [in this window] [in a new window]   FIG. 4. Calculated (A) hydrologic margin horizontal lengths (HW) and (B) transect slopes (S) from circumnavigation survey of Lake Fryxell. Small plots within each panel are the normalized frequency distributions for each data set. Order of survey transect numbering noted between panels (see Fig. 1B).

View larger version (22K): [in this window] [in a new window]   FIG. 5. Calculated (A) hydrologic margin horizontal lengths (HW) and (B) transect slopes (S) from circumnavigation survey of the east lobe of Lake Bonney. Small plots within each panel are the normalized frequency distributions for each data set. Order of survey transect numbering noted between panels (see Fig. 1A).

View larger version (12K): [in this window] [in a new window]   FIG. 6. Mean sediment size distribution for all samples, grouped by site within each transect for (A) Lake Fryxell, and (B) the east lobe of Lake Bonney.

View larger version (29K): [in this window] [in a new window]   FIG. 7. Horizontal position as a function of sediment size proportions for (A and B) >4.5 mm, (C and D) <4.5 but >2 mm, (E and F) <2 mm but >425 µm, (G and H) <425 but >75 µm, and (I and J) <75 µm.

View larger version (22K): [in this window] [in a new window]   FIG. 8. Regression analysis of lateral hydrologic margin dimension (HW) as a function of shoreline slope (S) for transects measured around Lake Fryxell (LF) and the east lobe of Lake Bonney (ELB). Best-fit regressions based on highest R2 for LF data alone is HW = 0.55S–1.02, R2 = 0.73; and for ELB data alone is HW = 6.48exp(–2.70S), R2 = 0.31.

View larger version (20K): [in this window] [in a new window]   FIG. 9. Relationships between the lateral dimension (HW) and vertical extent (ZW) of hydrologic margins around A) Lake Fryxell, and B) the east lobe of Lake Bonney. See Fig. 2 for a diagram of dimensions.

View larger version (23K): [in this window] [in a new window]   FIG. 10. Average horizontal and vertical locations of sampling sites (points), and corresponding active layer depth ranges for hydrologic margins of (A) Lake Fryxell and (B) the east lobe of Lake Bonney.

View larger version (19K): [in this window] [in a new window]   FIG. 11. Relationship between the lateral extent of the water table (HWT) estimated from the geometry of measurements, and the lateral extent of the hydrologic margin (HW) at each transect for (A) Lake Fryxell and (B) the east lobe of Lake Bonney. Note that at most transects, HW is greater than HWT, indicating a lateral component to the wicking of lake water into the shore sediments.