WATER COLUMN AND SEDIMENT CARBON ISOTOPE GEOCHEMISTRY OF PERMANENTLY REDOX-STRATIFIED FAYETTEVILLE GREEN LAKE, NEW YORK, USA

Carbon cycling in natural ecosystems is a biologically mediated process with global consequences on time scales that range from months to billions of years. While much is known regarding biogeochemical cycling of carbon in the water column and underlying sediments of freshwater and marine systems, less is known about permanently redox-stratified water bodies. The modern ocean is fully oxygenated, and most fresh water systems are typically oxic as well. However, the ocean is thought to have been redox-stratified throughout much of Earth's history, and seasonal redox-stratification is an increasing problem in many freshwater systems due to anthropogenic activities, including eutrophication driven by human land usage and warming resulting from global climate change. To better understand the carbon signals preserved in the rock record from times of ocean redox stratification as well as the effects of increasing redox-stratification on carbon cycling in modern fresh water systems, we have characterized the concentration and isotopic signal of inorganic and organic carbon in permanently redox-stratified Fayetteville Green Lake (FGL), New York. The results of these analyses indicate that: i) groundwater is the primary source of DIC at FGL; ii) organic carbon is extensively cycled and mineralized within the water column and upper sediments resulting in an increasingly isotopically depleted dissolved inorganic carbon pool (δ¹³C values approaching -25 ‰); iii) cyanobacterial-driven carbonate precipitation in the oxic zone is the primary source of carbonate in the sediments; iv) methane concentrations increase below the chemocline with extremely negative δ¹³C values (-99.1 to -102.3 ‰).