Saturday, 18 April 2009


by Paul Butler, College of Natural Sciences, Bangor University

Some of the more long-established members of Haringey Green Party may remember me as an active member and occasional agent and candidate back in the 1990s who left in 2001 to continue his education in North Wales (although I’m still a paper member of HGP). Having submitted my thesis and undergone a viva voce (defence of the thesis) I have now achieved a doctorate, and Mary Hogan has asked me to write about it for the Haringey GP blog.

The subject is strongly relevant to current issues in climate science, since it’s concerned with the investigation of the marine climate of the past, and in fact the academic who assessed my thesis, Keith Briffa, is one of the lead authors of the Intergovernmental Panel on Climate Change reports. We can find evidence of past environments in natural archives, such as ice cores, stalagmites/stalactites and tree rings. What’s important is that they preserve some kind of timeline, so that we can work out the sequence in which the material was produced. It’s then possible to use our knowledge of how the material in the archive was produced to say something about its environment (temperature or rainfall, for example). For my work on the marine environment, I’ve been using the shells of clams. So my PhD has been dotted with cruises to various parts of the seas around the UK (and, in one case, to the north coast of Iceland) to collect shells of a particular clam – common right across the North Atlantic region - called the ocean quahog. Why are these shells useful? Well, they’re annually banded (you can see the banding in the picture), so that the material created each year is demarcated with an identifiable line which indicates a period of no growth, and they’re very long-lived (we found one off Iceland which had lived for just over 400 years). Importantly, all the shells in a population grow synchronously – in a strong growth year all the clams secrete large amounts of shell material and they all have wider bands, while in a weaker year they don’t secrete so much and have narrower bands. So the patterns in the shells can be matched, which means that by comparing patterns in shells of known date (from live caught clams) with patterns in dead shells, it is possible to work out when the animals which created the dead shells were alive. Using this process, I’ve been able to create an archive of material using shells from just off the Isle of Man which goes back to 1516. This is exactly what is done with tree rings, but they are only relevant for the terrestrial environment. Up until now, it has been very difficult to find an equivalent archive for the marine environment.

I expect anybody who’s got this far will be wanting to know if I’ve actually found anything in this groundbreaking archive. Well, yes I have, but to describe it would take up a lot more space than I have here, since I’d have to explain a whole lot of other rather complex stuff in the process. However, in the field of climate science just the creation of this archive is regarded as pretty important, so I am quite pleased with what I have achieved already, and I hope eventually that my work will feed into the models used to assess the impacts of climate change.

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