Riverine Inorganic Carbon Subsidy Drives CO2 Evasion and Metabolic Processes in Arctic Alaskan Lagoon

Soils in the northern circumpolar permafrost region contain approximately 50% of the estimated global belowground organic carbon (C) pool and Alaskan Arctic Coastal Plain tundra is among the highest carbon content soils in this region. As warming in the Arctic drives thickening active layers, increased subsurface flow, and higher river discharge, the large carbon stores in frozen soils are increasingly at risk of mineralization and export to aquatic systems, the coast, and atmosphere. Few studies have tracked the transport of inorganic C through the Arctic aquatic conduit to estuarine systems, nor has any study directly measured CO₂ flux from Arctic Alaskan lagoons. Our preliminary evidence, however, recognizes Beaufort Sea coastal lagoons as net sources of CO₂ during parts of the year. The purpose of this study is to describe CO₂ evasion in a Beaufort coast lagoon during the open water season and investigate the influence of a riverine C subsidy on C cycling and ecosystem metabolism. We present preliminary results from simultaneous 2-week deployment of pCO₂ and dissolved oxygen sensors in an intermediate sized river and corresponding site in Elson Lagoon, near Utqiagvik, AK, where this river empties. We found that during this period riverine influence may be an important driver for evasion and ecosystem production in the lagoon. In addition to a significant relationship between pCO₂ at the river and lagoon site, river pCO₂ explains 70% of the variability in daily average metabolic rates in the lagoon. The synchronicity of lagoon-river coupling, however, is not consistent over the entire deployment period, indicating that riverine influence may vary with changing lagoon conditions during the open water season. As small coastal watersheds on the Arctic Coastal Plain continue to change dramatically in response to a warming climate, it is important to identify implications of coupled river-lagoon C cycling for regional coastal Arctic CO₂ flux.