> You need mass to break ice.

this is one of the narrow cases where pounds comes off the bench to say, "actually, you need weight"

(icebreakers slide/ride up on top of the ice and the weight of the ship breaks breaks it ice downward)

That's because pounds use force as a base unit, mass is kind of incorporated into it the notion of a pound, whereas the metric system generally handles the units for force and mass separately.

The imperial system actually does have a rather obscure unit called a slug which is equivalent to the kilogram (in terms of being purely a mass quantity) in the metric system, but since the pound already incorporates that term ( bundled together with the gravitational acceleration factor) it seldom sees action.

On Earth's surface, it's not like gravity is optional.

To get real technical about it, gravity is inconstant at constant altitudes when varying latitude and longitude.

9.8m/s^2 at sea level, and it decreases with altitude all the way out to Lagrangian points where the gravitational attraction of the sun (and other local masses) is equal to that of earth; but solar pressure presumably displaces objects at zero-gravity rest.

Gravity is 'optional' with quantum locking. Gravity is a weak force.

Gravity is maybe the least lossy form of potential energy storage?

A key feature of ice-breakers is that they operate at sea level, and in fact rely on gravity.

They are also surrounded by fluid that as ballast affects the density/volume/buoyancy/displacement(?) of the hull (and the inertia of the craft), which could be steel-plated [3d printed and/or pressure molded] biocomposite that lasts for spec years in seawater.

Would water be enough ballast for a cutter built with organic biocomposites that weather sea air and water?

Well there's always reinforced ice: https://en.m.wikipedia.org/wiki/Project_Habakkuk

;-)