Monday, 21 January 2013

Tiny fossils reveal evidence for climate change and melting of Antarctica by Melanie Leng

About a decade ago I had an idea, it wasn’t the only idea I had at that time, but it was a particularly good one! We needed to start analysing the chemistry of the hard skeletons of a type of microscopic algae called diatoms to obtain environmental information.

Diatoms occur in all ponds, lakes and oceans but are less than the width of a human hair so difficult to see and analyse, and they are particularly sensitive to environmental change. Their skeletons accumulate in the bottom of oceans and lakes in layers – year by year, decade by decade, piling on top of each other. By taking a “core” of sediment through these accumulations we can obtain a time sequence of environmental history much like an old fashioned tape recorder captures information. The environmental history information comes from tiny differences in the chemical composition of the oxygen atoms in the diatoms skeleton.

A collection of diatom  skeletons from Antarctica, these shells are less than the width of a human hair.

In the Southern Ocean surrounding Antarctica these differences are due to changes, through time, of the amount of freshwater entering the ocean from the melting of glaciers that fringe the continent. Recently we measured these differences over the last 12,000 years from sediments that had accumulated off the Antarctic Peninsula and showed changes through time related to the rate of melting of glaciers.

Another example of a diatom skeleton from Antarctica

The equipment to do the measurements was already at the British Geological Survey but we had to develop the method, and prove we could do it exceptionally well. At that time there was really one other laboratory in the world that was doing this type of analysis.

Me stood by the equipment used to gain information on environmental change from microscopic algae.
Technologically the analysis of the oxygen isotope composition of diatom silica is extremely difficult, the British Geological Survey are world leading pioneers in this technique.

We showed that there was a significant melting due to global warming around 9,000 years ago when ice shelves around Antarctica collapsed, and that a second significant warming occurred between 3500-250 years ago. During this latter period, cycles of atmospheric warming occurred every 400-500 years and these have been linked to changes in the temperature of the low latitude Pacific Ocean (the El Niño – Southern Oscillation phenomenon).

Overall this research shows that changes in temperatures of the equatorial ocean can influence high latitude climate.  It is very important to understand changes in the polar regions, the western Antarctic Peninsula for example is one of the fastest warming regions on the planet. Scientists continue to debate the causes of this warming, particularly in light of recent instrumental records of both atmospheric and oceanic warming from the region.  As our  atmosphere and oceans warm, so the ice caps are in danger of disappearing.

Ross Island off the western Antarctic Peninsular
This research was published by Nature Geoscience this week and involves scientists at the British Geological Survey, and universities of Cardiff, Nottingham and Leicester.
By Mel Leng

Further reading: BGS Press Release (opens PDF in new window) Cardiff University Press Release (opens link in new window)


city said...

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