Dot Earth Blog: A Closer Look at Melting Ice in the Andes and Antarctica

Fascinating new studies of two of the world?s regions with accelerated melting, the Antarctic Peninsula and the Andes, are worth a closer look:

One paper, published in The Cyrosphere, finds that glaciers throughout the tropical Andes have been melting in the last 30 years at a faster rate than at any time since the peak of the ?little ice age? 300 years ago. Here?s a direct link: ?Current state of glaciers in the tropical Andes: a multi-century perspective on glacier evolution and climate change.?

The other, published in Nature Geoscience, is ?Glacial discharge along the west Antarctic Peninsula during the Holocene.? Researchers measured variations in the composition of fossilized plankton to gauge the amount of ice flowing into the sea over the last 12,000 years. The abstract below is quite clear in finding no evident relationship between ice loss and atmospheric or marine factors related to greenhouse-driven global warming:

The causes for rising temperatures along the Antarctic Peninsula during the late Holocene have been debated, particularly in light of instrumental records of warming over the past decades. Suggested mechanisms range from upwelling of warm deep waters onto the continental shelf in response to variations in the westerly winds, to an influence of El Ni?o?Southern Oscillation on sea surface temperatures. Here, we present a record of Holocene glacial ice discharge, derived from the oxygen isotope composition of marine diatoms from Palmer Deep along the west Antarctic Peninsula continental margin. We assess atmospheric versus oceanic influences on glacial discharge at this location, using analyses of diatom geochemistry to reconstruct atmospherically forced glacial ice discharge and diatom assemblage ecology to investigate the oceanic environment. We show that two processes of atmospheric forcing?an increasing occurrence of La Ni?a events and rising levels of summer insolation?had a stronger influence during the late Holocene than oceanic processes driven by southern westerly winds and upwelling of upper Circumpolar Deepwater. Given that the evolution of El Ni?o?Southern Oscillation under global warming is uncertain, its future impacts on the climatically sensitive system of the Antarctic Peninsula Ice Sheet remain to be established.

There?s more in a news release from Cardiff University, in which Dr. Jennifer Pike, of the School of Earth and Ocean Sciences, said:

The implications of our findings are that the modern observations of ocean-driven warming along the western Antarctic Peninsula need to be considered as part of a natural centennial timescale cycle of climate variability, and that in order to understand climate change along the Antarctic Peninsula, we need to understand the broader climate connections with the rest of the planet.

I?m particularly interested in the link between higher ice loss and periods with more La Ni?a events. A study of 7,000 years of coral data published in Science earlier this month found a recent uptick in El Ni?o activity but no evident relationship between occurrences of El Ni?o and La Ni?a episodes and overall climate conditions.

I?ve sent the paper to a batch of Antarctic specialists and will add updates as they come in.

Source: http://dotearth.blogs.nytimes.com/2013/01/23/a-closer-look-at-melting-ice-in-the-andes-and-antarctica/?partner=rss&emc=rss

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