Water crystallization is a different effect and not relevant here. It has the same mass so it doesn't effect sea levels when it's frozen and it's not a linear e

Water crystallization is a different effect and not relevant here. It has the same mass so it doesn't effect sea levels when it's frozen and it's not a linear effect, it won't continue to shrink as it warms. But like everything else (to various extents) it will expand when it's warmer.