Sclerochronology is the term applied to the use of hard, usually carbonate, deposits produced by living organisms as a dating tool for the study of past environments.  If deposition is periodic it can be detected in the form of growth increments which can be counted back from a known date of death so the precise date of each increment can be determined. Most commonly, periodicity is annual (as carbonate precipitation often varies seasonally), and this is most useful for the timescales used in SEACHANGE.

Sclerochronology in SEACHANGE makes use of the annual banding in the shells of bivalve molluscs. Because some species of bivalve can live for hundreds of years (over 500 years in the case of the North Atlantic species Arctica islandica) and because they grow synchronously within populations, we can use the technique of crossdating derived from tree ring research to assign dates to dead shell material and create absolutely dated chronologies that can go back more than 1,000 years. Once we have the dated shells we can create timelines of physical, geochemical and genetic variability to study past environmental change in great detail.

In SEACHANGE, sclerochronology will play an essential part in all the work packages.  We have Arctica islandica chronologies for all the North Atlantic sites, although for the early Holocene (WP1) these are floating chronologies (meaning that shells are dated with respect to each other but haven’t been crossdated to the present day).  For Australia (WP3) and Antarctica (WP5), the creation of long chronologies will be novel and challenging because suitable species have not yet been identified, but even if we don’t find these, it will still be possible to use radiocarbon dating with morphological, geochemical and eDNA analysis to extract useful palaeoenvironmental information.

One especially exciting prospect in SEACHANGE is the possibility of directly linking shells found in middens with shells from offshore chronologies of known age by comparing the growth patterns.  This has the potential to allow us to date archaeological sites with much greater precision than has been possible up to now.

The Penryn campus of University of Exeter is a major centre for bivalve sclerochronology, and we’ll have some of the world’s leading experts in the field working on SEACHANGE, including Dr David Reynolds (WP1, WP2, WP3 and WP4), Dr Alejandro Román González (WP5) and Dr Paul Butler (WP1, WP2 and WP4).