Slasher,
Gravity is a function of the mass and distance between of two objects, not the curvature of the earth, or the centrifugal force. Gravity is the acceleration on the aircraft mass that makes and aircraft weigh something.
The only other factor I can think of (_MAYBE_) is that the exhaust from the engines locally melted some of the ice to get humid air that would stick to the cold aircraft skin giving and increased TOW.
I do not believe 50 km TODR figure at all. In the cold conditions the engines and aircraft would perform well in the dense air, the drag force from the ice runway is not that significant.
Z