Madelyn J. Mette, PhD
Paleoclimatology  -  Oceanography  -  Sclerochronology

Arctica islandica is a marine bivalve common across the northern North Atlantic Ocean.  It can live in shallow water (5 meters / 16 feet) or in deeper water (300 m / 980 feet), depending on the temperature and food conditions in the environment. When juveniles settle to the ocean floor, they stay in the same spot for the rest of their lives unless moved by storms or other disturbances. And they can live for several hundred years!  The clams live within the sediment and extend a siphon up into the water column to filter food particles and expel waste.  

​

A. islandica is a valuable tool for climate research because of its shell.  Just like trees, these clams form yearly growth bands within the shell that can be best viewed by looking at a polished cross-section under a microscope.  The yearly bands vary in width depending on the environmental conditions each year.  Thus the shells can be said to "record" environmental variability throughout their lifetimes.  The chemistry within each band can also be measured, providing even more information about the environment. The pattern of wide and narrow increments in shells can be matched between individuals living in the same environment.  Specific years can be identified and "cross-matched" to determine a precise chronology for shell growth.  This bar-code approach to dating the shells means very long shell growth chronologies are created by using older (sub-fossil) shells found in the same environment.