Melting Ice in Seawater

Using a 30kg cubic block Ice at -20degC, I want to cool down a piece of steel which is resting on the seabed. The mass of steel is 1kg and the ice block is place on top of the steel.
The current sea temperature as well as the steel temp is estimated at 12degC

Assuming that the piece of steel is not "heated" by the seabed, nor the sea water, the ice melts while cooling the steel.

Question is till what temperature can the steel be cooled before the ice is completely melted and dissolved.

I'm kinda lost here on the thermodynamics, since the "energy out" does not equal the "energy in" as the unlimited amount of seawater volume will melt the ice without increasing in temperature.

can someone push me in the right direction please.

thanks
Patrick