Antarctica Exam Flashcards
Introduction:
Equilibrium line is accumulation = ablation
Mass balance (b) = accumulation (c) + ablation (a)
Positive mass balance
- More accumulation than melting so glacier advance
Negative mass balance
- More ablation than accumulation than accumulation so glacier retreats
Glaciers respond to variations in climate, primarily snowfall and temperature, by changing in length and thickness.
Mass balance of a glacier (also referred to as “surface mass balance”) is the difference between the snow accumulated in the winter and the snow and ice melted over the summer.
Temperatures are rising:
This is a region of very rapid warming, and this has resulted in a whole suite of glaciological changes.
Around the Antarctic Peninsula, temperatures are warming at a rate that is approximately six times the global average.
Air temperatures increased by ~2.5°C from 1950-2000 (Tuner et al., 2005)
The annual mean air temperature -9°C isotherm has moved southwards, resulting in ice-shelf collapse and glacier recession (Morris and Vaughan, 2003).
Warming over the Antarctic Peninsula is exacerbated by a strengthening of the Antarctic Oscillation, which is a periodic strengthening and weakening of the tropospheric westerlies that surround Antarctica (van den Broeke and van Lipzig, 2004).
Changing pressure patterns result in flow anomalies, with cooling over East Antarctica and warming over the Antarctic Peninsula.
Measuring changes in climate
Ice core records provide a longer-term perspective on climate over the past four glacial cycles or longer (Augustin et al, 2004).
Ice core records show that methane and carbon dioxide atmospheric concentrations are higher than at any point in the last 650,000 years (Solomon et al., 2007).
Ice shelves are collapsing
On-shore glaciers have rapidly thinned and receded following removal of ice shelf (Glasser and Scambos, 2008).
Higher air temperatures around the Antarctic Peninsula contribute to ice shelf collapse by increasing the amount of meltwater on the surface (Glasser and Scambos, 2008).
Melting from below following the incursion of warm ocean currents (Viela et al., 2010).
With one particularly warm summer, a thinned ice shelf that is close to its threshold is liable to break up very quickly as meltwater ponding on its surface propagates downwards and initiates iceberg calving by hydrofracture. Some of these ice shelves have collapsed for the first time (Sheperd et al., 2003).
Larsen Ice Shelf
The Larsen Ice Shelf collapsed dramatically and very rapidly in the summer of 2002
Glaciers that previously fed into the Larsen Ice Shelf have since accelerated, thinned and receded.
The Larsen B Ice Shelf has been stable throughout the Holocene and this is the first time it has collapsed in the last 10,000 years.
Pine Island Glacier
Ice shelves are warmed from below, and the ice shelves around Pine Island Glacier are thinning and receding.
The thinning of these ice shelves may limit their ability to support the flow of ice from the interior of the ice sheet.
Pritchard et al. (2012) say in their paper in Nature that melting from the base of ice shelves is the primary driver of Antarctic Ice Sheet ice loss, by reducing the buttressing capability of the ice shelves.
The rapid thinning of the Pine Island Glacier ice shelf is caused by warm oceanic water at depth that reaches the underside of ice shelves by travelling along troughs on the continental shelf.
Glaciers are thinning
12 glaciers around the Antarctic Peninsula glaciers are thinning due to oceanic and atmospheric warming (Kunz et al., 2012).
Higher rates of thinning for glaciers on the north-western Antarctic Peninsula.
Thinning is bringing them nearer to floatation.
Glaciers are accelerating
Thinning glaciers are easier to float. Once warm ocean water can access the underside of a glacier, melting from below exacerbates thinning from above, resulting in increased and rapid glacier thinning.
Pritchard and Vaughan (2007) argue that thinning as a result of a negative mass balance will reduce the effective stress of a glacier’s bed near the margin, reducing basal resistance and increasing sliding.
This leads to further thinning, floatation, rapid calving and increased glacier recession (Pritchard and Vaughan, 2007).
Sea level is rising
Global sea levels are currently rising at a rate of about 3 mm per year (Solomon et al., 2007).
Most modern sea level rise, and sea level rise predicted over the next 100 years, comes from ocean expansion and the melting of small glaciers and ice caps.
However, the amount that the sea level will rise in the future depends not only on temperature, glacier recession and ocean warming and expansion, but also the dynamic behaviour of the West Antarctic Ice Sheet.
Marine Ice Sheet Instability may result in rapid future sea level rise, contributed to by ice-shelf collapse and the dynamic behaviour of ice streams.
Impact of climate on glaciers
The Antarctic Peninsula is particularly vulnerable to climate change due to its small size and northerly latitude (Vaughn et al., 2003).
It receives high snowfall but high melt, with a large number of days above 0°C in the summer months (Pritchard and Vaughan, 2007).
It interrupts the Circumpolar Westerlies and is liable to be affected by small changes in these winds.
Increased numbers of positive degree days coincide with increased rates of thinning on Antarctic Peninsula marine-terminating glaciers, and increased meltwater ponding and hydrofracture on ice shelves.
Glaciers are thinning and receding in response to warmer temperatures, and thinning glaciers are easier to float.
Basal melting of ice shelves drives ice sheet loss.
Measuring mass balance
Accumulation zone
Ablation zone
Pits (to check how much snow has fallen)
You can dig down into the glacier and see how much snow is deposited each year (quite easy to see)
Stakes
You can dig down into the glacier and see how much baroon is deposited each year (quite easy to see)
Everything
Introduction
Temperatures are rising:
Measuring changes in climate
Ice shelves are collapsing
Larsen Ice Shelf
Pine Island Glacier
Glaciers are thinning
Glaciers are accelerating
Sea level is rising
Impact of climate on glaciers
Measuring mass balance
