THE PRESERVATION OF PTEROPODS FROM THE CARIBBEAN SEA AS AN INDICATOR OF PAST OCEAN ACIDIFICATION

It is now widely accepted that ocean acidification is an imminent threat to our oceans and although we have a good understanding of the related changes in ocean chemistry, the biological response is still largely understood. It is generally considered that calcifying organisms will be greatly affected by ocean acidification due to under saturation with respect to calcium carbonate. Experimental evidence has already been gathered which demonstrates that a reduction in pH will generally lead to a decrease in calcification rates of a number of, but not all, organisms. Such studies have shown that the response will be complicated and species specific. However, to date, little information is available for important planktonic producers of calcium carbonate; some studies have looked at the effects on coccolithophores and planktic foraminifera, but only three have directly considered the effects on the aragonite producing thecosome pteropods. Due to their highly soluble aragonite shells, thecosome pteropods are likely to be the most vulnerable of the major planktonic producers of CaCO₃. They are also likely to be the first to experience persistent decreased CaCO₃ saturation states. As an important part of the food web, especially in the Arctic and Southern Oceans, their demise is of significant importance.

In a study of marine cores collected from the Caribbean Sea near the island of Montserrat, it is found there is an exceptional record of thecosome pteropods from the modern sea floor back to Marine Isotope Stage 8. Our research applies a technique, the Limacina Dissolution Index (LDX), to an assessment of the dissolution of pteropod shells through the most recent glacial and interglacial stages of the Earth’s history (~250 kyrs). It was found that the dissolution of pteropod shells correlates well with climate data (Vostok CO₂, oxygen isotopes and G. menardii counts), showing increased dissolution during interglacial periods and enhanced preservation during glacial periods. This method of observing the effects of past ocean acidification on important calcifying plankton can be directly related to the changes occurring in the modern ocean and could be extremely useful in predicting future effects of ocean acidification.