Abstract
ABSTRACTThe McMurdo Dry Valleys are a cold, dry polar desert and the alpine glaciers therein exhibit small annual and seasonal mass balances, often <±0.06 m w.e. Typically, winter is the accumulation season, but significant snow storms can occur any time of year occasionally making summer the accumulation season. The yearly equilibrium line altitude is poorly correlated with mass balance because the elevation gradient of mass balance on each glacier can change dramatically from year to year. Most likely, winds redistribute the light snowfall disrupting the normal gradient of increasing mass balance with elevation. Reconstructed cumulative mass balance shows that the glaciers have lost <2 m w.e. over the past half century and area changes show minimal retreat. In most cases these changes are less than the uncertainty and the glaciers are considered in equilibrium. Since 2000, however, the glaciers have lost mass despite relatively stable summer air temperatures suggesting a different mechanism in play. Whether this trend is a harbinger of future changes or a temporary excursion is unclear.
Highlights
The glaciers of Taylor Valley, McMurdo Dry Valleys (MDV), have been shown to be in equilibrium with the current climate over the period, 1993–2001 (Fountain and others, 2006)
Mass-balance measurements have been made at Commonwealth and Howard glaciers for 20 years, 1993– 2013, the longest in the MDV and perhaps the longest record for an alpine glacier in Antarctica (Table A1)
Mass balance increases with elevation for both glaciers but Commonwealth Glacier exhibits a decrease above 500 m a.s.l. (Fig. 2)
Summary
The glaciers of Taylor Valley, McMurdo Dry Valleys (MDV), have been shown to be in equilibrium with the current climate over the period, 1993–2001 (Fountain and others, 2006) This finding is unusual in the global assessment of glacier stability because the majority of glaciers during that time period were receding, as they have over much of the past century, but their retreat was accelerating (Kaser and others, 2006; Lemke and others, 2007). In this report we update the measured mass-balance record to 2013 and reconstruct the time series back to 1965 to evaluate whether changes we observe in recent decades differ from previous decades This is important for distinguishing temporary variations from long-term trends and how the climate, as expressed by glacier variations, may be changing. Because so few programs have monitored the mass balance of polar glaciers, we examine whether some of the basic concepts for evaluating the balance of temperate glaciers apply to polar glaciers
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