The Arctic hydrological cycle throughout the Holocene is analyzed based on the results of transient simulations with the coupled atmosphere-ocean circulation model ECHO-G. The results suggest a ~ 2 % increase of mid-Holocene to preindustrial Arctic river discharges for the Eurasian continent. However, rivers of the North America Arctic realm show a moderate runoff decline of approximately 4 to 5 % for the same period. The total river discharge into the Arctic Ocean has remained at an approximately constant preindustrial level since the mid Holocene. The positive discharge trend within Eurasia is caused by a more rapid decrease in local net evaporation compared to a smaller decline in advected moisture and hence precipitation. This effect is neither recognized within the North American Arctic domain nor in the far eastern part of the Eurasian Arctic realm. A detailed comparison of these model findings with a variety of proxy studies is conducted. The collected proxy records show trends of continental surface temperatures and precipitation rates that are consistent with the simulations. A continuation of the transient Holocene runs for the 19th and 20th century with increased greenhouse gases indicates an increase of the total river influx into the Arctic Ocean of up to 7.6 %. The Eurasian river discharges increase by 7.5 %, the North American discharges by up to 8.4 %. The most rapid increases have been detected since the beginning of the 20th century. These results are corroborated by the observed rising of Arctic river discharges during the last century which is attributed to anthropogenic warming. The acceleration of the Arctic hydrological cycle in the 20th century is without precedence in the Holocene.
Model simulations have been conducted with the coupled atmosphere-ocean general circulation model ECHO-G. The horizontal resolution of the atmospheric Gaussian grid is 3.75°. Continental river discharges are computed by a river transport scheme designed by Sausen et al. (1994, doi:10.1016/0022-1694(94)90177-5). Computation of the orbital parameters has been performed following Berger (1978, doi:10.1175/1520-0469(1978)0352.0.CO;2). Other forcings like solar variations due to varying sunspot activities or volcanic eruptions are not included. Model runs have been accelerated by the factor 10. The applied acceleration technique has been used for the time period covering the mid-Holocene (7 ka BP) to the preindustrial (1800 AD; Lorenz and Lohmann, 2004, doi:10.1007/s00382-004-0469-y, simulations: a22 and a29). For the industrial period (last 200 years, a32 and a33), no acceleration of the orbital forcing has been performed to catch a closer look at the anthropogenic effect on climate parameters. Detailed information about the acceleration method and the greenhouse gas configurations of the analyzed model runs are circumstantiated in Lorenz and Lohmann (2004).A set of two model runs has been conducted for the simulation of mid-Holocene to preindustrial (7 ka BP until 1800 AD) climate conditions. Subsequently, the two Holocene model simulations (a22 and a29) have been restarted at 1800 AD as a32 and a33. All variables exist as monthly mean datasets.Sub-Project: Holocene variability in the Arctic gateway (HOVAG). This project is part of INTERDYNAMIK.
Supplement to: Wagner, Axel; Lohmann, Gerrit; Prange, Matthias (2011): Arctic river discharge trends since 7 ka BP. Global and Planetary Change, 79(1-2), 48-60
