THE GEOMICROBIOLOGY OF SUPEROXIDE IN THE MARINE WATER COLUMN: A CASE STUDY FROM THE BALTIC SEA

The production and decay of the reactive oxygen species (ROS), superoxide, remains a poorly constrained component of marine oxygen dynamics. Apart from abiotic reactions, superoxide, the single electron reduced form of oxygen, can be generated via intracellular and extracellular processes associated with organisms ranging from heterotrophic bacteria to eukaryotes. Recent lab-based studies have illuminated the potential relevance of microbial particle-associated ROS production to superoxide levels in both photic and aphotic marine waters. Enzymatic degradation plays a substantial role in the removal of superoxide, but the reaction with redox active metals and dissolved organic compounds similarly eliminates superoxide, leaving an ecologically relevant fingerprint in the environment. Although theory and lab-based work have demonstrated the multitude of ways in which superoxide is relevant in controlling the interface between biological life and the environment, we don’t have a comprehensive understanding to what extent superoxide shapes the observed marine environment due in part to a lack of in situ sensors capable of constraining superoxide throughout the water column. To study the dynamics of superoxide in the marine water column as it relates to microbial activity and local seawater chemistry we collected water-column profiles of superoxide with a recently developed submersible in situ chemiluminescent analyzer (SOLARIS) on a transect crossing a site of ocean hypoxia in the Baltic Sea. Superoxide concentrations were then analyzed with corresponding profiles of various biogeochemical parameters, including oxygen, light, and dissolved metal concentrations. This work will be continued in the future with incubations serving to evaluate the microbial community throughout the water column and quantify how production and decay rates are influenced by particles, and the lability of organic matter. As a consequence of restricted oxygen flow and increasing eutrophication, the Baltic Sea is an archetype of growing ocean hypoxia. It is a particularly relevant site for this study, which aims to contribute to a growing body of work deciphering the factors affecting the evolution of marine biogeochemical cycles in the light of climate change.