Project Investigators

Sclerochronology and Scleroclimatology

Sclerochronology: the use of long-lived annually-banded bivalve molluscs for detailed study of past environments

Marine biogenic carbonates are natural archives of palaeoenvironmental information, and can provide high-resolution proxy records of past and present ocean climate variability. We use growth increment data (sclerochronology) and geochemical information (sclerochemistry) from molluscs and other biogenic carbonates to study modern and ancient ocean environments. In particular, we use the long-lived marine bivalve Arctica islandica (Linnaeus, 1767) (ocean quahog or mahogany clam) to study ocean circulation and seawater temperature in the North Atlantic region during the Holocene. A. islandica is a large (up to 120mm length) clam commonly found at 10 - 150m water depths along the continental shelves of the temperate and boreal North Atlantic. Its most important distinguishing characteristic is its remarkable longevity. For example, one specimen of A. islandica, collected from the North Icelandic Shelf, was found to have lived for 507 years, making it the longest-lived non-colonial animal whose age has been precisely verified (Butler et al 2013). It is possible to determine the ages of these specimens by counting the prominent annual increments deposited in the shell, and it is these increments that are the key to the palaeoenvironmental potential of A. islandica.

Crucially, shell growth (determined by measuring increments) is synchronous within and between populations, indicating the expression of a common environmental signal in the shell growth response and enabling A. islandica to be used as a high-resolution proxy archive in the climatically important North Atlantic region. It is possible to use the technique of crossdating (derived from tree-ring research) to ascribe absolute dates to fossil shell material (Marchitto et al., 2000) and then to construct master shell chronologies using a mean value function of crossdated growth series (Witbaard et al., 1997). The longest published master shell chronologies have been developed by scientists in the sclerochronology and scleroclimatology group at SOS Bangor, using live caught and fossil A. islandica shells. For sites in the Irish Sea off the west coast of the Isle of Man, Butler et al (2009, 2010) built a 487-year chronology, and more recently a 1,357-year archive has been developed for a site off the island of Grimsey on the North Icelandic Shelf (Butler et al, 2013). This chronology is illustrated in the plot below.

We are currently using shell growth patterns and geochemical data from the shells to study ocean circulation and seawater temperature variability in North Atlantic waters. The master chronologies can be compared with records from nearby instrumental stations to determine the extent to which shell growth is responding to environmental variables such as temperature and food supply. Depending on the strength of the response, it may then be possible, using statistical calibration and verification techniques, to reconstruct environmental conditions before the start of instrumental records.

An ultra-high-resolution 1,000-year temperature record for the North Icelandic Shelf

In a major project funded by NERC (ULTRA NE/H023356/1) we are analysing the stable isotope geochemistry of A. islandica shells from the Iceland chronology. Because of the high resolution and precise dating of the shell material, the results from this project - reconstructions of seawater temperatures and water mass changes - are expected to mark a significant advance in the detail with which past marine variability can be reconstructed, improving our ability to discriminate between natural and anthropogenic signals in ocean climate variability. This work is currently being prepared for publication by Dr David Reynolds, who carried out the stable isotope work during a postdoc at Bangor and who is now a lecturer at Cardiff.

Dr Reynolds is now collaborating with researchers from Bangor and Exeter on a recently funded NERC project CLAM (NE/N002733/1): Climate of the Last Millennium: An integrated data-model approach to reconstruct and interpret annual variability. The goal of CLAM is to use a pan-Atlantic network of sclerochronological archives from NW Scotland, the North Icelandic shelf and the Gulf of Maine, together with high-resolution climate models, to investigate the mechanisms that are driving variability of the circulation patterns in the North Atlantic over the past millennium.


Our research into scleroclimatology has led to the first multi-centennial absolutely-dated records of seawater temperature change from the mid-latitude North Atlantic. These invaluable records allow direct correlation with tree-ring and ice core records of Northern Hemisphere climate change over the last millennium. As a result we have become involved in some large collaborative efforts that attempt to understand the relative significance of external forcing (solar, volcanic) and internal variability, and modes of climate variability (North Atlantic Oscillation/Atlantic Multidecadal Oscillation), in the coupled ocean-atmosphere system over the last 1000 years. This is resulting in increasingly close collaboration with climate modelling groups.

Annually Resolved Archives of Marine Climate Change

The latest sclerochronology project to be based here at SOS is a European-funded collaborative project: ARAMACC ("Annually Resolved Archives of Marine Climate Change"). Here, we are studying nothing less than the history of the North Atlantic Ocean over the past few hundred years, using shells from multiple sites, and incorporating – in addition to the chronology building and geochemistry – climate modelling, biological and ecological drivers of shell growth, and the application of sclerochronology in the commercial and regulatory sectors. ARAMACC science is implemented in the context of a Marie Curie Initial Training Network, so that ten PhD students based in centres across Europe are being formally trained in techniques relevant to the field of sclerochronology at the same time as they carry out their research.

The use of long-lived molluscs in research into human ageing processes

Another important strand to our work with A. islandica focuses on the relevance of this extraordinarily long-lived animal to research into ageing processes. A. islandica can be used as a model of longevity in the evaluation of the mechanisms that determine lifespan in shorter-lived species. It stands at the high end of a wide range of typical longevities characteristic of the bivalve molluscs. By comparing different species in the bivalve class in their expression of three distinct ageing mechanisms we hope to discover which mechanism (or combination of mechanisms) can best explain the spread of longevities.

Associated publications

Butler, P.G., Richardson, C.A., Scourse, J.D., Wanamaker, A.D., Jr., Shammon, T.M., Bennell, J.D. (2010).
Marine climate in the Irish Sea: analysis of a 489-year marine master chronology derived from growth increments in the shell of the clam Arctica islandica. Quaternary Science Reviews, 29, 1614-1632.

Butler, P.G., Scourse, J.D., Richardson, C.A., Wanamaker, A.D., Jr., Bryant, C.L., and Bennell, J.D. (2009)
Continuous marine radiocarbon reservoir calibration and the 13C Suess effect in the Irish Sea: results from the first absolutely dated multi-centennial shell-based marine master chronology, Earth and Planetary Science Letters, 279, 230-241

Butler, P.G., Wanamaker, A.D. Jr., Scourse, J.D., Richardson, C.A. and Reynolds, D.J. (2013)
Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica.
Palaeogeography, Palaeoclimatology, Palaeoecology. 373, 141-151.
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Marchitto, T.M., Jones, G.A., Goodfriend, G.A., Weidman, C.R., 2000.
Precise temporal correlation of Holocene mollusk shells using sclerochronology. Quaternary Research 53 (2), 236-246.

Witbaard, R., Duineveld, G.C.A., DeWilde, P.A.W.J., 1997.
A long-term growth record derived from Arctica islandica (Mollusca, Bivalvia) from the Fladen Ground (northern North Sea). Journal of the Marine Biological Association of the United Kingdom 77 (3), 801-816.