Sea ice forms and melts in sea water, as opposed to land-based ice such as glaciers, ice sheets or shelves, and grounded icebergs. In today's climate regime, sea ice has been observed as far south as Bohai Bay in China—a latitude comparable to the Mediterranean Sea. Sea ice begins to form when water temperature dips just below freezing, at around -1.8°C (or 28.8°F). It grows into small sheets that look like pancakes, and eventually merge together to form large ice floes which can span miles. As the ice forms, it expels the salt, which increases the density of the surrounding water and thus plays a critical role in global ocean circulation.