Scheme: Leverhulme Trust Senior Research Fellowship
Organisation: Bangor University
Dates: Oct 2008-Sep 2009
Summary: I am studying exceptionally long-lived bivalve molluscs in order to generate annually-resolved records of marine climate change. We require good reliable and long records of past climate in order to understand the main mechanisms causing climate change and to constrain dynamical models of the global climate system. Whilst we have good instrumental records and proxy climate records of atmospheric climate change, such as tree-rings and ice cores, marine instrumental records are often short and widely dispersed, and other than annually-banded corals from the low latitudes, proxy records from marine sediments are often of relatively low resolution. Bivalve mollusc shells such as the ocean quahog, Arctica islandica (L.), the “tree of the sea”, often contain internal annual growth increments. We know that the increments in A. islandica are annual on the basis of seasonal stable oxygen isotope profiles and mark-recapture experiments. Individual records therefore represent windows of time. Increment-counting in my laboratory has identified A. islandica as the longest-lived bivalve mollusc species known. Recently we measured an Icelandic specimen at over 500 years; this is the longest-lived non-colonial animal known to science. I have adapted statistical methods used in the parallel field of tree-ring science to successfully cross-match the growth increment series between live- and dead-collected specimens (fossils) to construct shell chronologies, or series, that extend the record beyond the lifetime of an individual animal. This connects the individual windows, or segments, together and, crucially, transforms the series into a fully dated record if the collection date of the anchoring live specimens are known. By splicing multiple individual shell series together the statistical strength of the resulting growth increment chronology can be developed to the point where it can be described as a master chronology. The successful correlation of the growth records between coeval individuals demonstrates, de facto, that the different individuals within a population respond to the same environmental stimuli and thus display synchronous growth. In some settings this growth is modulated climatically, by seawater temperature for instance, meaning that the growth increment series are not only an in-built chronometer but also a record of climate.