Effects of Excess Atmospheric CO2 on Calcium Carbonate Producers along the Red Sea Coast of Yemen: Its Risk and Socio-economic Impacts.

Abstract

Abstract The formation of calcite and aragonite, integral components of marine organisms’ skeletons, is contingent on the degree of saturation (W) of seawater with respect to carbonate minerals. The decrease in W, driven by an excess of atmospheric carbon dioxide, poses challenges for calcifying organisms in their ability to create and maintain their skeletal structures and shells. As a result, we conducted a collection of surface seawater samples from various locations along the Red Sea coast of Yemen to address three key objectives: (1) ascertain the current W values for calcite and aragonite, (2) project alterations in these values attributable to seawater pH reduction (acidification) over the next 50 and 200 years, and (3) assess potential ecological consequences and risks associated with these impeding changes. During both winter and summer, we conducted measurements of various oceanographic parameters, including temperatures (ToC), salinities (S), pH values, and total alkalinities (TA). In winter season, these parameters were ToC = 26.4±0.5oC, S = 36.9±0.5, pH = 8.16±0.3 and TA = 2.409±0.104 meq/Kg, whereas in summer ToC = 34.6±0.6oC, S = 38.5±0.2, pH = 8.11±0.12 and TA = 2.428±0.036 meq/Kg. These measured parameters served as crucial inputs for the assessment of carbonate chemistry, including the determination of seawater’s W values with respect to both calcite and aragonite. The findings indicated that surface seawater was supersaturated with respect to both calcite and aragonite. The percent degree of saturation (%W) for calcite was 553±89% in winter and 607±77% in summer, while for aragonite was 367±58% in winter and 415±53% in summer. Over the course of the next five decades, the surface seawater %W with respect to calcite is projected to decrease approximately 464±111% during winter months and 499±78% during summer. At the same time, it is expected to decline to around 251±60% in winter and 341±53% in summer for aragonite. In the next two centuries, these percentages are anticipated to further decrease to 249±57% in winter and 281±48% in summer for calcite, and to 135±31% in winter and 192±33% in summer for aragonite. Acidification of seawater will have serious environmental consequences on the marine and coastal habitats of the Red Sea of Yemen and the entire region. Further studies are warranted to monitor and investigate the occurrence, distribution, mineralogy of corals, and the effects of physical and chemical parameter variations on their growth in the region.