Effects of Greenland's Runoff in a Regional Arctic System Model

Freshwater discharge into the pan-Arctic seas provides an important buoyancy forcing and must be accounted for in models as it can affect surface water properties (which affect sea ice formation), the evolution of narrow coastal boundary currents, the mixed layer depth and deep-water formation (which affect the magnitude of meridional overturning circulation). In this study, we use the high-resolution Regional Arctic System Model's (RASM) unique capability to more realistically simulate fresh water fluxes from land runoff and glacier ice discharge on processes and feedbacks of relevance to the climate system.

RASM is a coupled regional model, including ocean (Parallel Ocean Program - POP), sea ice (Community Ice - CICE), atmospheric (The Weather Research and Forecasting Model - WRF) and land hydrology (Vertical Infiltration Capacity - VIC) model components. The freshwater fluxes enter the pan-Arctic seas as a buoyancy forcing with interannual variability. The runoff data are provided by the Coordinated Ocean-ice Reference Experiments version 2 (CORE2). Experiments are conducted for 1948-2009 with active ocean and sea ice models, while the atmospheric model is replaced with a forcing provided by the CORE2 reanalysis. The default set-up, with no runoff from land to the ocean, is compared against results from simulations with freshwater fluxes equivalent to the volume of runoff in the Arctic region given by the CORE2 data interpolated to the RASM's 1/12 degree ocean model grid. Experiments are set up with incremental increases in Greenland's freshwater flux to the ocean to mimic past rates of discharge after the Last Glacial Maximum and to evaluate sensitivity of the physical system to such forcings. In addition, these runs allow investigation of possible future scenarios of runoff effects as the rate of Greenland Ice Sheet mass loss continues to increase.