euxinic

Euxinic refers to conditions within a body of water characterized by oxygen depletion and the presence of hydrogen sulfide. This environment is typically found in the deeper layers of stratified water bodies, such as some lakes and the Black Sea. In such conditions, the lack of dissolved oxygen prevents aerobic respiration, leading to the death of most aerobic organisms. The decomposition of organic matter in the absence of oxygen by anaerobic bacteria produces hydrogen sulfide, a gas with a characteristic rotten egg smell. This hydrogen sulfide is toxic to many forms of life.

The Black Sea is the most prominent example of a euxinic basin. Its unique geography, with a narrow connection to the Mediterranean Sea and a sill at the Bosporus Strait, limits water exchange. This leads to strong stratification, with a less saline, oxygenated surface layer and a deep, saline, anoxic layer. This deep layer has remained euxinic for thousands of years. While the term "euxinic" can be applied to any similar environment, it is most commonly associated with the Black Sea due to its scale and historical significance. The presence of euxinic conditions can significantly impact the biodiversity and ecological processes of a water body.