Greenland holds enough ice that, if it melted, one-fifth of the world's rivers-worth of freshwater could flow into the north Atlantic.

格陵兰岛拥有足够的冰，如果它融化，世界上五分之一的河流——相当于淡水——可能流入北大西洋。

Or it could be that there was an underwater, an underground glacier that melted, flowed out into another place, creating another underwater water source or a river someplace, leaving behind a big cavity.

或者有可能是水下， 地下的冰川融化了，流出到另一个地方， 在某处形成了另一个水下水源或河流， 留下了一个大空洞。