Admittedly SST over land sounds pretty weird, so why bother? The initial conditions for OpenIFS contain SSTK in the ICMGG*INIT file with reasonable values over the ocean. Over land the values are close to 273 (K) bot not exactly the same everywhere.  For  some EC-Earth development I changed the value of SST over land, and found it had an impact on the result. I was able to crate similar differences when changing the SST in the initial conditions. Here are timesries from a gridpoint at the Black Sea coast in Georgia:

The blue line is the control, and for the orange line the SST in all land points (i.e. where CL LSM>0.5) has been replaced by 321.35. The plots show SST, surface temperature, sensible and latent heat fluxes in this point. There is a dramatic heat flux during the 2nd timestep. Interestingly enough, the gridpoint next to this point doesn't show any response to an SST change:

Here is a map indicating where heat fluxes during the 2nd timestep get unusually high:

It's not everywhere, but there are a few gridpoints where heat fluxflux seem off. It's not just along coastlines, it can also happen in the interior of land. It seems to be unrelated to lakes.

The thing that puzzles me is that the value of SST over land shouldn't play any role. There is no value for missing/undefined in GRIB, therefore there must be some value for the SST even over land in the initial conditions which is usually never updated during a simulation and constant over time. The IFS documentation Part IV Section 8.2.1 clearly states: "A mixture of land and water (ocean/inland water) tiles is not allowed, i.e. a grid box is either 100% land or 100% sea." Thus, any value of SST shouldn't be used anywhere in the surface scheme where CL LSM>0.5. However, my tests that change SST over land points tell something else.

Could there be a bug somewhere in the surface scheme that uses SST for some computations even in gridpoints over land?