A crab and several squat lobsters in Saanich are curious about the shells that were deployed near the VENUS camera between August and November, 2006.
The most abundant shells and skeletons of marine animals are made of calcium carbonate. When and if these skeletons are buried, they form a large part of the fossil record and are the main way carbon is removed from the surface global carbon cycle into the earth’s crust. Understanding the “when and if” is therefore key to knowing how to read the biological history of climate change on earth and how to estimate changes such as marine acidification in the carbon cycle. My lab has pursued research into marine skeletal carbonate preservation (part of a field called “taphonomy” or the “study of the grave”) across latitudes and environments to understand what controls net preservation and potential bias. VENUS now provides the opportunity to document occasional events that affect the net preservation of skeletons. For example, using the VENUS camera we observed that squat lobsters and crabs handle dead shells frequently (a phenomenon dubbed “mistaken predation”) resulting in scrapes and breakage. During Saanich Inlet’s seasonal hypoxia events we can observe what impact these chemical changes have on the crab population and therefore on shell preservation. From these and other processes, between August to November 2006, experimentally deployed mussel shells lost ~4.5% of their weight; mostly the mother of pearl that normally lines their inside. Previous experiments indicate this shell loss won’t proceed linearly, however it is a significant amount in a short period of time, raising the possibility that shells in this setting may have a poor chance at final preservation.
This research assesses processes, agents and rates of modification during shell preservation. This greatly increasing our confidence in turning to these records for both short and long-term environmental baselines and in comparing shell accumulations through time as a proxy for tracking climate change or evolutionary patterns. As the burial patterns of skeletal carbonate become better understood at a global scale, it will then be possible to assemble a burial model of carbonate and assess where the major carbonate sinks are, thereby clarifying a poorly understood part of the carbon cycle.
by Mairi Best, Assistant Professor, Earth and Planetary Sciences, McGill University
For more images and a complete article about Mairi’s research, see the Fall 2006 newsletter.
