If the air is still and cold enough, usually under 10 degrees, great wisps of sea smoke hover and drift above the ocean surface. That "smoke" actually is water vapor that forms when really cold air moves over relatively warmer water and the thin boundary layer of warm air just above the surface. When the evaporating water rises, the cold air can only hold so much moisture, forcing the liquid to condense into fog. Clouds rise like smoke from the sea's surface, dispersing and reforming, turning bays and coves into ephemeral cauldrons of submarine fire. North Atlantic fishermen called it white frost or black frost.