Huge Arctic sea-ice thickness

[flocolleoni@gmail_com]

Hi, I am simulating a glaciation using CESM 1.0.5, B compset, f09_gx1v6 resolution.So far it ran for 100 years. The climate is particularly cold over the Arctic sinceI introduced 4km high ice sheets over North America and Eurasia. After controlling the sea-ice thickness of the simulation I saw that sea-ice thickness was huge, up to 50 m after 100 years of simulation.I guess that the climate is so cold, that all precip is turned into snowfall and accumulates on top of the sea-ice.The problem is that as far as I understand, snow cover is turned into ice according to Achimede's law and it seemsand infinite process. Is there any parameter to control that? Flo

 

[dbailey]

Hi Flo,There is an issue in the CESM with the "ice runoff" from the ice sheets. This is part of the river transport that is routed as solid water in addition to liquid. The ocean receives both of the runoff fluxes and needs to melt the sold runoff flux. In the process, this cools off the ocean and in some cases leads to sea ice growth. This process can continue without a mechanism to turn it off as the sea ice only "feels" the top ocean layer. While not realistic, it is necessary to conserve heat in the coupled system. However, this process should be limited to small semi-enclosed bays like in the Canadian Arctic Archipelago gx1 (one-degree) and the northern end of Baffin Bay gx3 (3-degree) land/ocean mask. We've sometimes seen it around the Antarctic as well. If you are not concerned about the conservation of heat in the system and want to reduce the effects of this, you would set ice_runoff to .false. in the CLM namelist (in CESM 1.0.5).Dave

 

[flocolleoni@gmail_com]

Hi Dave, Thank you very much for this particulary helpfull answer. No, I am not too concerned aobut heat conservation for this experiment.I turned off the option ice_runoff in CLM namelist and after one year of simulation, I already see the difference. So do you thinkthat it could go back to more realstic thickness (for now I mistook, the mean thickness is 22 m) if I keep the simulation runninguntil spin-up? Or should I restart the simulation from the beginning? Flo  

 

[dbailey]

It's likely not a huge climate impact as long as the thick sea ice is limited to the semi-enclosed bays. I personally wouldn't restart the simulation from scratch, but that ultimately depends on your requirements.Dave