Skeptical Science: OA not OK

Skeptical Science has published a series of 18 blog articles on ocean acidification authored by Doug Mackie, Christina McGraw, and Keith Hunter.

Growth of threee species of Mediterranean cold-water corals exposed to ocean acidification

Increasing pCO2 in the atmosphere results in ocean acidification. The changes in ocean chemistry posed by such phenomenon pose an imminent threat to calcifying organisms such as cold-water waters corals. Very little information is available on the effect such threat poses on cold-water corals, particularly in the Mediterranean frontier. Three species of Mediterranean cold water corals (Lophelia pertusa, Madrepora oculata and Desmophyllum sp) were exposed to ocean acidification conditions. Four separate pCO2 treatments were represented: 412 ± 73 ppm, 497 ± 117 ppm, 665 ± 100 ppm, and 866± 191 ppm. Coral response was measured using several methods of assessing growth: buoyant weight, colour (area) projection, new polyp development, and skeletal density. Response to ocean acidification was shown to be species specific with Lophelia pertusa being generally more affected (a reduction of over 40% buoyant weight per day on higher pCO2 compared to lowest pCO2) than Madrepora oculata. Growth rate was not clearly influenced by ocean acidification in Desmophyllum sp. After 9 months of experiment, polyp development and skeletal density were not significantly altered by ocean acidification. A reduction in projected colour (area) was observed for both Madrepora oculata and Lophelia pertusa area under medium and high ocean acidification scenarios (Madrepora oculata over 50% colour (area) per day on higher pCO2 compared to lowest pCO2 ; Lophelia pertusa nearly 50% colour (area) per day on higher pCO2 compared to lowest pCO2). Response of the three species assessed was not linear, possibly due to several sources of variation interacting with acidification. That Lophelia pertusa consistently performs better at lower acidification scenarios has implications for the future of the deep-sea coral community and species associated. More studies are needed to assess whether the response observed here is consistent across other sites and cold-water species.

Anthropogenic CO2 fluxes in the Otranto Strait (e. Mediterranean) in February 1995

This study presents the distribution and fluxes of dissolved inorganic carbon (C_T), total alkalinity (A_T) and anthropogenic carbon (C_ant) along the Otranto strait, during February 1995. Based on a limited number of properties (temperature, dissolved oxygen, total alkalinity and dissolved inorganic carbon), the composite tracer TrOCA was used to estimate the concentration of anthropogenic CO₂ in the Otranto strait.

Total alkalinity exhibits high values and weak variability throughout the water column of the strait, probably associated with the dense water formation processes in the Adriatic basin, that induce a rapid transport of the coastal alkalinity to the deep waters. Elevated C_ant concentrations and high anthropogenic pH variations are observed in the bottom layer of the strait, associated with the presence of Adriatic Deep Water (ADW). The study shows that large amounts of C_ant have penetrated the highly alkaline Eastern Mediterranean waters, thereby causing a significant pH reduction since the pre-industrial era.

Estimates of the transports of C_T and C_ant through the strait indicate that during February 1995, the Adriatic Sea imports through the Otranto strait natural and anthropogenic carbon and acts as a net sink of carbon for the Ionian Sea. The anthropogenic carbon that is imported to the Adriatic Sea represents less than 1% of the net C_T inflow. The Levantine Intermediate Water (LIW) contributes to about one third of the total C_T and C_ant inflow. Although the amounts of C_ant annually transported by LIW and ADW are almost equal, the contribution of C_ant to the C_T transported by each water mass is slightly higher in ADW (3.1%) than in LIW (2.6%), as a result of its higher mean C_ant concentration. The ADW despite its weak contribution to the total outflow of C_ant, has a vital role for the sequestration and storage of the anthropogenic carbon, as this water mass is the main component of the Eastern Mediterranean Deep Waters and, thus, the anthropogenic CO₂ is transferred in the deep horizons of the Eastern Mediterranean, where it remains isolated for many years.