Carbon dioxide partial pressure and super(13)C content of north temperate and boreal lakes at spring ice melt

Carbon dioxide (CO sub(2)) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO sub(2) pulse is not typically considered in surface-atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO sub(2) partial pressure (pCO sub(2)) of lake surface water ranged from 8.6 to 4,290 Pa (85-4,230 mu atm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO sub(2) less than or equal to atmospheric pCO sub(2), whereas 75% had pCO sub(2) >5 times atmospheric. The delta super(13)C sub(DIC) (DIC = capital sigma CO sub(2)) of 142 of the lakes ranged from -26.28ppt to +0.95ppt. Lakes with the greatest pCO sub(2) also had the lightest delta super(13)C sub(DIC), which indicates respiration as their primary CO sub(2) source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO sub(2). Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO sub(2) and the heaviest delta super(13)C sub(DIC), which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 plus or minus 1.44 mol CO sub(2) m super(-2) for lakes with average pCO sub(2) values and were as large as 13.7 plus or minus 8.4 mol CO sub(2) m super(-2) for lakes with high pCO sub(2) values.