Consistency of Isotopes in Surface Mass Balance from CLM

[Katetc]

If there is a tendency in isotope concentrations due to melting and freezing, then this will likely be handled by CTSM in the construction of the surface mass balance for CISM.

When CTSM freezes snow, it should have the isotopic concentrations of that snow available in the snowpack in the model and can use that to update any isotopic tendencies associated with a positive mass balance.

When CTSM melts ice, it will only have the isotopic concentrations of the ice that were last passed to CTSM through the coupling time step for the surface amounts. These could be as much as 1 year (or 10 ice sheet transport time steps) different from the isotopes at the top of the ice sheet at the next coupling step.

@whlipscomb Feels that this lag between freezing and melting will not have much impact on concentrations, but we are curious about if it might impact conservation, and if we should add some method to "adjust" values in previous coupling time steps once there is appropriate info from the icesheet for the melt values? @billsacks is this associated with any CTSM issues or discussions yet?

[billsacks]

No, I don't think there are any CTSM issues or discussions of this yet.

I'm having trouble understanding the possible issues here, so for me to contribute any more thoughts I think I'd need to talk to you about this... but if your only question for me at this point is whether there has been any thinking about this on the CTSM side, then I'm pretty sure that the answer is "no".