Hassan J. Basagic

Quantifying 20th Century Glacier Change in the Sierra Nevada, California

Abstract Numerous small alpine glaciers occupy the high elevation regions of the central and southern Sierra Nevada, California. An inventory based on 1∶24,000 topographic maps revealed 1719 glaciers and perennial snowfields for a total area of 39.15 ± 0.13 km2. The number of ‘true’ glaciers, versus non-moving ice, is estimated to be 122 covering 14.89 ± 0.08 km2 or 38% of the ice-covered area. Historic photographs, geologic evidence, and field mapping were used to determine the magnitude of area change over the past century at 14 glaciers. The area change between 1903 and 2004 ranged from −31% to −78%, averaging −55%. Based on these values rough estimates of volume change suggest an ice volume loss from 1903 (1.09 km3) to 2004 (0.43 km3) of 0.66 km3 (0.59 km3 water). Rapid retreat occurred over the first half of the 20th century beginning in the 1920s and continued through the 1960s after which recession ceased by the early 1980s and some glaciers advanced. Since the late 1980s glaciers resumed retreat with a rapid acceleration starting in the early 2000s. The relatively uniform timing of area changes in the study glaciers is a response to regional climate whereas the magnitude of change is influenced by local topographic effects. Area changes correlate significantly with changes in summer and winter air temperatures. Warmer winter temperatures warm the snowpack lengthening the summer melt season. Spring air temperatures and precipitation may also play an important role. The occurrence of spring snowfall can delay the onset of melt due to the increased surface albedo. Examining the influence of topographic variables we only found headwall height at the top of the glacier to show an influence on glacier change. Higher headwalls shadow the glacier from solar radiation reducing melt and enhancing snow accumulation via avalanching. If the glaciers continue to shrink at current (1972–2004) rates, most will disappear in 50–250 years.

Do Cryoconite Holes have the Potential to be Significant Sources of C, N, and P to Downstream Depauperate Ecosystems of Taylor Valley, Antarctica?

Abstract Nutrient recycling occurs in hydrologically isolated cryoconite holes on the glaciers of the McMurdo Dry Valleys, Antarctica. Biogeochemical processes enrich the cryoconite holes with solute and nutrients compared to the source sediment and glacier ice. The position of the glacier within the landscape affects the physical and biogeochemical character of the cryoconite holes, with those found in more biologically productive areas of the valley having higher concentrations of C., N, and P and higher pH. Comprehensive assessment of the quality and quantity of bioavailable C, N, and P shows that the cryoconite holes represent a significant store of nutrient in this depauperate landscape, since the total mass of C and N is similar to that found in the ephemeral streams. The dissolved nutrients within the holes, and a significant proportion of the particulate store, are released to the valley ecosystem via the network of ephemeral streams and perennially ice-covered lakes as a result of hydrological connection with the supraglacial drainage system. In most cases, cryoconite holes are flushed every several years, but during warm periods which occur with near decadal frequency, all holes connect and flush their contents off the glaciers. Simple mass balance modeling shows that an increase in primary productivity observed in Lake Fryxell that followed such a melt event in 2001/2002 can be explained by an influx of nutrients (specifically N) generated in the cryoconite holes. These features are hence an integral part of the Dry Valley ecosystem and should be considered in models of downstream biological processes.

A dynamic physical model for soil temperature and water in Taylor Valley, Antarctica

Abstract We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave and longwave radiation. Water fluxes included snowmelt, freezing/thawing of soil water, soil capillary flow, and vapour flows among atmosphere, soil, and snow. The model accounted for 96–99% of variation in soil temperature data. No long-term temporal trends in soil temperature were apparent. Soil water vapour concentration in thawed surface soil in summer often was higher than in frozen deeper soils, leading to downward vapour fluxes. Katabatic winds caused a reversal of the usual winter pattern of upward vapour fluxes. The model exhibited a steady state depth distribution of soil water due to vapour flows and in the absence of capillary flows below the top 0.5 cm soil layer. Beginning with a completely saturated soil profile, soil water was lost rapidly, and within a few hundred years approached a steady state characterized by dry soil (< 0.5% gravimetric) down to one metre depth and saturated soil below that. In contrast, it took 42 000 years to approach steady state beginning from a completely dry initial condition.

The Geography of Glaciers and Perennial Snowfields in the American West

ABSTRACT A comprehensive mid-20th century inventory of glaciers and perennial snowfields (G&PS) was compiled for the American West, west of the 100° meridian. The inventory was derived from U.S. Geological Survey 1:24,000 topographic maps based on aerial photographs acquired during 35 years, 1955–1990, of which the first 20 years or more was a cool period with little glacier change. The mapped features were filtered for those greater than 0.01 km2. Results show that 5036 G&PS (672 km2, 14 km3) populate eight states, of which about 1276 (554 km2, 12 km3) are glaciers. Uncertainty is estimated at ±9% for area and ±20% for volume. Two populations of G&PS were identified based on air temperature and precipitation. The larger is found in a maritime climate of the Pacific Northwest, characterized by warm winter air temperatures and high winter precipitation (~2100 mm). The other population is continental in climate, characterized by cold winter air temperatures, relatively low winter precipitation (~880 mm), and located at higher elevations elsewhere. The G&PS in the Pacific Northwest, especially in the Olympic Mountains, are particularly vulnerable to warming winter air temperatures that will change the phase of winter precipitation from snow to rain, further accelerating glacier shrinkage in the future. Comparison with a recent inventory suggests that the total G&PS area in the American West may have decreased by as much as 39% since the mid-20th century.

Glaciers and Perennial Snowfields of the U.S. Cordillera

Of more than 8,000 glaciers and perennial snow-fields on 21 mountain ranges in the western U.S. (excluding Alaska), only 120 are larger than 1 km2, and just one exceeds 10 km2. Where changes in size are known, the overwhelming majority of glaciers are shrinking. There are a few that are growing. These changes, with a few exceptions that relate mainly to rock debris abundances on the glaciers, are due overwhelmingly to climate change, though it is a complex relationship. Analysis of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) imagery has been used in special case studies, along with published field data, to track changes in debris loads of glaciers on Mt. Rainier, show the effects of a lahar from Mt. Rainier, and track the continued shrinkage of Grinnell Glacier in Glacier National Park. The response time of glaciers in the region varies from under a decade to over a century. Blue Glacier (Olympic Mountains) is a fast responder; its length, area, and volume fluctuation history indicates that it is responding to decadal climate fluctuations as well as local long-term warming in the 20th and 21st centuries, which is probably related to greenhouse gas-driven global warming.