Thermodynamic Forecasts of the Mediterranean Sea Acidification

Abstract

Anthropogenic CO2 is a major driver of the present ocean acidification. This latter is threatening the marine ecosystems and has been identified as a major environmental and economic menace. This study aims to forecast from the thermodynamic equations, the acidification variation (ΔpH) of the Mediterranean waters over the next few decades and beyond this century. In order to do so, we calculated and fitted the theoretical values based upon the initial conditions from data of the 2013 MedSeA cruise. These estimates have been performed both for the Western and for the Eastern basins based upon their respective physical (temperature and salinity) and chemical (total alkalinity and total inorganic carbon) properties. The results allow us to point out four tipping points, including one when the Mediterranean Sea waters would become acid (pH<7). In order to provide an associated time scale to the theoretical results, we used two of the IPCC (2007) atmospheric CO2 scenarios. Under the most optimistic scenario of the “Special Report: Emissions Scenarios” (SRES) of the IPCC (2007), the results indicate that in 2100, pH may decrease down to 0.245 in the Western basin and down to 0.242 in the Eastern basin (compared to the pre-industrial pH). Whereas for the most pessimistic SRES scenario of the IPCC (2007), the results for the year 2100, forecast a pH decrease down to 0.462 and 0.457, for the Western and for the Eastern basins, respectively. Acidification, which increased unprecedentedly in recent years, will rise almost similarly in both Mediterranean basins only well after the end of this century. These results further confirm that both basins may become undersaturated (< 1) with respect to calcite and aragonite (at the base of the mixed layer depth), only in the far future (in a few centuries).

Carbonate system properties and anthropogenic carbon inventory in the Algerian Basin during SOMBA cruise (2014): Acidification estimate

“…Near calcite and aragonite saturation states were observed in the western MS (Ω Ca = 2.5 and Ω Ar = 1.5) during a cruise in 1976 (Millero et al, 1979). According to our results, CaCO 3 oversaturation in the MS will probably persist for a few more centuries (Goyet et al, 2016). The increase in the CaCO 3 saturation state of waters caused by temperature increase will partly compensate for water acidification as the stoichiometric solubility product of calcium carbonate (K * ) decreases with increasing temperatures caused by global warming, and the faster temperature increase in the MS.…”

Coccolithophore community response to ocean acidification and warming in the Eastern Mediterranean Sea: results from a mesocosm experiment

“…Sea surface warming, marine heatwaves 8,14,[61][62][63][64][65] and OA 11,66 have been anticipated for this century in the Mediterranean Sea. The OA and OW conditions tested in our mesocosm experiment, which reflect those projected for 2,100 under the IPCC RCP8.5 scenario 12 , were found to cause drastic changes in the studied coccolithophore community ( Fig.…”

“…The Mediterranean region is considered particularly vulnerable to climate change 6 – 9 . Anthropogenic CO 2 has already invaded the whole Mediterranean basin 10 and a pH lowering of 0.245–0.457 units has been estimated for its surface waters by year 2,100 based on two IPCC atmospheric CO 2 scenarios 11 , 12 . Meanwhile, atmospheric warming is expected to proceed in the Mediterranean area 20% faster than the global average 13 .…”

Coralline Algae in a Changing Mediterranean Sea: How Can We Predict Their Future, if We Do Not Know Their Present?

“…Seasonal and depth-related warming trends were documented by Nykjaer (2009) and Coma et al (2009), respectively. Studies that measured and modeled pH changes since preindustrial times in the Mediterranean (Hassoun et al, 2015;Goyet et al, 2016) provided evidence of acidification related to excessive increase of atmospheric CO 2 . The mean surface pH has decreased by ∼0.002 units per year from 1994 to 2006 in the northwestern Mediterranean (Howes et al, 2015;Kapsenberg et al, 2017) and by 0.004 units at the Strait of Gibraltar (Flecha et al, 2015).…”