Melt regimes, stratigraphy, flow dynamics and glaciochemistry of three glaciers in the Alaska Range

Abstract

We used ground-penetrating radar (GPR), GPS and glaciochemistry to evaluate melt regimes and ice depths, important variables for mass-balance and ice-volume studies, of Upper Yentna Glacier, Upper Kahiltna Glacier and the Mount Hunter ice divide, Alaska. We show the wet, percolation and dry snow zones located below ~2700ma.s.l., at ~2700 to 3900ma.s.l. and above 3900ma.s.l., respectively. We successfully imaged glacier ice depths upwards of 480 m using 40-100 MHz GPR frequencies. This depth is nearly double previous depth measurements reached using mid-frequency GPR systems on temperate glaciers. Few Holocene-length climate records are available in Alaska, hence we also assess stratigraphy and flow dynamics at each study site as a potential ice-core location. Ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in GPR profiles collected on Upper Yentna Glacier suggest that regions below 2800ma.s.l. are inappropriate for paleoclimate studies because of chemical diffusion, through melt. Flow complexities on Kahiltna Glacier preclude ice-core climate studies. Minimal signs of melt or deformation, and depth-age model estimates suggesting ~4815 years of ice on the Mount Hunter ice divide (3912ma.s.l.) make it a suitable Holocene-age ice-core location.

Brine, englacial structure and basal properties near the terminus of McMurdo Ice Shelf, Antarctica

“…Diffusion of chemistry within snow and firn caused by melt, and an associated lack of stratigraphy or more diffuse horizons imaged in radar profiles are well-documented phenomena (e.g. Campbell and others, 2012).

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High‐frequency observations of melt effects on snowpack stratigraphy, Kahiltna Glacier, Central Alaska Range

“…Perhaps the best illustration of the effects of melt on stratigraphy is the snowpack stable isotope profile. Although isotope stratigraphy is altered within the upper snow layers, at least compared with profiles from higher sites (Campbell et al ., ), below the ash layer, the record of variability nearly disappears. Oerlemans () and Takeuchi and Li () have demonstrated that a decrease in the albedo (in this case from volcanic ash) will lead to intensified melting.…”

Denali Ice Core Methanesulfonic Acid Records North Pacific Marine Primary Production

“…and cold mean annual temperature (−17 °C), the Mt. Hunter drill site has flat‐lying and conformable subsurface stratigraphy in ice‐penetrating radar profiles indicating that the record is not disturbed by complex glacier flow (S. Campbell et al, ). After processing at the National Ice Core Laboratory in Denver, CO, the ice cores were transported frozen to Dartmouth College and sampled using a continuous ice core melter system (see Breton et al, ; Osterberg et al, , for melter system details and detection limits).…”