New paper shows ocean 'acidification' was about the same during the last interglacial period as today

A paper published today in Quaternary Science Reviews shows that reconstructed ocean pH during the last [Eemian] interglacial 130,000-114,000 years ago was naturally about the same as today [estimated alkaline pH of 8.14]. The paper also shows that the snail shell degradation index [LDX] was faster/greater during the last interglacial period than modern times, and increased at a faster rate during the last interglacial period than modern times. Thus, natural ocean 'acidification' was about the same as today, but increased at a faster rate and had a greater effect on dissolving shells during the last interglacial period in comparison to modern times. 

The paper once again demonstrates alarmist claims about ocean 'acidification' are overblown. 

Second graph from top shows reconstructed ocean pH was about the same during the last interglacial 130,000 - 114,000 years ago as today [estimated at 8.14 pH]. The snail shell degradation index [LDX] shown in bottom graph was faster/greater during the last interglacial period than modern times, and increased at a faster rate during the last interglacial period than modern times. 

In-life pteropod shell dissolution as an indicator of past ocean carbonate saturation

• Deborah Wall-Palmer^, , 
• Christopher W. Smart, 
• Malcolm B. Hart

• School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth PL4 8AA, UK

Highlights

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In-life dissolution of fossil pteropod shells was examined using the LDX scale.

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Average shell diameter was used as an indicator of calcification rate.

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LDX shows significant correlation to CO₂ and surface water carbonate concentration.

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Smaller, more corroded shells were found during interglacial periods.

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Larger, pristine shells were found during glacial periods.

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Abstract

Recent concern over the effects of ocean acidification upon calcifying organisms has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Both in-situ and laboratory studies have shown that an increased dissolved CO₂ concentration, leading to decreased water pH and low carbonate concentration, causes reduced calcification rates and enhanced dissolution in the shells of living pteropods. In fossil records unaffected by post-depositional dissolution, this in-life shell dissolution can be detected. Here we present the first evidence of variations of in-life pteropod shell dissolution due to variations in surface water carbonate concentration during the Late Pleistocene by analysing the surface layer of pteropod shells in marine sediment cores from the Caribbean Sea and Indian Ocean. In-life shell dissolution was determined by applying the Limacina Dissolution Index (LDX) to the sub-tropical pteropod Limacina inflata. Average shell size information shows that high in-life dissolution is accompanied by smaller shell sizes inL. inflata, which may indicate a reduction in calcification rate. Comparison of the LDX profile to Late Pleistocene Vostok atmospheric CO₂ concentrations, shows that in-life pteropod dissolution is closely associated to variations in past ocean carbonate saturation. This study confirms the findings of laboratory studies, showing enhanced shell dissolution and reduced calcification in living pteropods when surface ocean carbonate concentrations were lower. Results also demonstrate that oceanic pH levels that were less acidic and changing less rapidly than those predicted for the 21st Century, negatively affected pteropods during the Late Pleistocene.