T131 Ocean Acidification and Other Societally Relevant Environmental Changes: Using the Past to Infer Our Future (Cushman Session)

Monday, 1 November 2010
1:30 PM - 5:30 PM
Room 603

MODERN SEAWATER ACIDIFICATION: THE RESPONSE OF FORAMINIFERA TO HIGH CO2 CONDITIONS IN THE MEDITERRANEAN SEA AND PTEROPODS IN THE CARIBBEAN SEA

Paper number: T131-10
Program: Technical Sessions
Time: 3:55 PM – 4:15 PM

Authors

Abstract

The seas around the island of Ischia (Italy) have a variable and, on average, lowered pH as a result of volcanic gas vents that emit carbon dioxide from the sea floor at ambient seawater temperatures. These areas of acidified seawater provide natural laboratories in which to study the long-term biological response to rising CO2 levels. Benthic foraminifera are routinely used to interpret the effects of climate change as they have short life histories, are environmentally sensitive and have an excellent fossil record. Here, we examined changes in foraminiferal assemblages along gradients in pH at CO2 vents on the coast of Ischia as they may provide a useful model on which to base future predictions of the consequences of ocean acidification. We show that foraminiferal abundance, diversity and ability to calcify decreased markedly in living and dead assemblages as pH decreases, the result of CO2 percolating through the seawater. These results are in accord with the responses recorded by coralline algae, corals, molluscs, barnacles and echinoderms at the same sites.

Samples from the normal (pH8.17) environments around Ischia contain a diverse fauna dominated by miliolid foraminifera (e.g., Peneroplis planatus, P. pertusus, Quinqueloculina spp.) while those from areas with reduced pH (7.8 to 7.6) have faunas that are progressively less diverse and composed of <100% agglutinated taxa (e.g., Ammoglobigerina globigeriniformis, Miliammina fusca, Trochammina inflata, Textularia sp. cf. T. bocki). The changes in the benthic foraminifera are quite dramatic for only a slight reduction in pH and confirm the possibility that events, such as the PETM, could quite easily record a widespread loss of diversity or extinction as a result of ocean acidification.

In Cornwall a leak of mine leachate entered Restronguet Creek in 1991 with a pH of 3.0 – 4.0. This decimated the foraminifera, which gradually recovered over 5 years. The high marsh species have not recovered to the same degree, presumably because migration into the head of the estuarine system is almost impossible.

Analysis of ice cores shows that pCO2 has varied through time, coinciding with glacial/inter-glacial cycles. Using the Limacina Dissolution Index (LDX) the preservation of pteropods over time can be used to plot possible pH variations in marine cores in the Caribbean Sea.