Divulgação

Palestra - "The response of foraminifera and pteropods to modern seawater acidification: a real-time proxy for geological acidification ”.

Data: 2013-07-08 02:00 PM
Orador/Formador: Malcolm B. Hart
Local: IPMA Algês Lisboa
Contacto email:
Contacto telefónico: 214770000

In collaboration with Bruna B. Dias, Alba N. M. Sanchez, Christopher W. Smart, Deborah Wall-Palmer, Laura Pettit, Joe Heyden, Rosa Maria Prol-Ledesma and  Jason M. Hall-Spencer

Modern ocean acidification is the ‘other CO2 problem’. Experimental work in microcosms and mesocosms is valuable, but observation of natural environments can provide much useful information that can be used to both predict the future and consider acidification events in the geological history of the Earth. 

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.

In the Wagner Basin (Gulf of California) there are CO2 and methane vents in the sea floor, creating low pH environments, but high carbonate saturation levels that allow the survival of the benthic foraminifera – until they die and then they begin to dissolve. 

 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. This shows that the natural record through the glacial/interglacial cycles can be traced up to CO2 levels of 320ppm. However, levels are now above 400 ppm and we are heading into unchartered waters. Planktic foraminifera have a history from the mid-Jurassic to the present day, but even in the present levels of pH, their carbonate tests are thinning and there is a general loss of weight. The changes may become more dramatic as pH levels fall further as pCO2 rises.