Carbon export and cycling by the Yukon, Tanana, and Porcupine rivers, Alaska, 2001-2005

Loads and yields of dissolved and particulate organic and inorganic carbon (DOC, POC, DIC, PIC) were measured and modeled at three locations on the Yukon River (YR) and on the Tanana and Porcupine rivers (TR, PR) in Alaska during 2001 - 2005. Total YR carbon export averaged 7.8 Tg C yr(-1), 30% as OC and 70% as IC. Total C yields (0.39 - 1.03 mol C m(-2) yr(-1)) were proportional to water yields (139 - 356 mm yr(-1); r(2) = 0.84) at all locations. Summer DOC had an aged component (fraction modern (FM) = 0.94 - 0.97), except in the permafrost wetland-dominated PR, where DOC was modern. POC had FM = 0.63 - 0.70. DOC had high concentration, high aromaticity, and high hydrophobic content in spring and low concentration, low aromaticity, and high hydrophilic content in winter. About half of annual DOC export occurred during spring. DIC concentration and isotopic composition were strongly affected by dissolution of suspended carbonates in glacial meltwater during summer.