DEGRADATION OF INTERNAL ORGANIC MATTER IS A MAJOR CONTROL ON PTEROPOD SHELL DISSOLUTION AFTER DEATH

Thecosome pteropods are a group of aragonitic molluscs found throughout the worlds oceans. Their preservation in the fossil records is largely thought to be controlled by aragonite saturation of seawater. Some studies, however, have found that dissolution occurs above the saturation horizon, implying an additional control. Here we investigate how the oxidation of the organic pteropod body contributes to the dissolution of the pteropod shell.

Decay experiments were conducted on two cruises to the Scotia Sea. Terminated pteropods were incubated in ambient seawater, and seawater which was adjusted to be supersaturated, undersaturated, and highly undersaturated with respect to aragonite. We find that the oxidation of the internal organic pteropod body had a greater control on shell dissolution than the saturation state of seawater. Using micro-CT scanning and nano-SEM imaging, the amount of shell loss over the timescales of days to weeks was quantified to be over 10% of the initial shell volume.

These findings have implications for the interpretation of pteropod shell condition from sediment trap samples, and for the preservation of pteropod shells in the fossil record. The dissolution of 10% of the carbonate shell will make it less stable, decreasing the chance that it will reach sediment traps, or make it into the fossil record. These findings have broader implications for the export of carbonates from the surface ocean, and the preservation of calcareous plankton once they reach the sediment-water interface.