An ice-choked sea now covered much of the north. Vastitas Borealis had lain a kilometer or two below the datum, in some places three; now with sea level stabilizing at the minus-one contour, most of it was underwater. If an ocean of similar shape had existed on Earth, it would have been a bigger Arctic Ocean, covering most of Russia, Canada, Alaska, Greenland, and Scandinavia, and then making two deeper incursions farther south, narrow seas that extended all the way to the equator; on Earth these would have made for a narrow North Atlantic, and a North Pacific occupied in its center by a big squarish island.

This Oceanus Borealis was dotted by several large icy islands, and a long low peninsula that broke its circumnavigation of the globe, connecting the mainland north of Syrtis with the tail of a polar island. The north pole was actually on the ice of Olympia Gulf, some kilometers offshore from this polar island.

And that was it. On Mars there would be no equivalent of the South Pacific or the South Atlantic, or the Indian Ocean, or the Antarctic Ocean. In its south there was only desert, except for the Hellas Sea, a circular body of water about the size of the Caribbean. So while ocean covered seventy percent of the Earth, it covered about twenty-five percent of Mars.

In the year 2130, most of Oceanus Borealis was covered by ice. There were large pods of liquid water under the surface, however, and in the summer, melt lakes scattered on top of the surface; there were also many polynyaps, leads and cracks. Because most of the water had been pumped or otherwise driven out of the permafrost, it had deep groundwater’s purity, meaning it was nearly distilled: the Borealis was a freshwater ocean. It was expected to become salty fairly soon, however, as rivers ran through the very salty regolith and carried their loads into the sea, then evaporated, precipitated, and repeated the process— moving salts from the regolith into the water until a balance was reached— a process which had the oceanographers transfixed with interest, for the saltiness of Earth’s oceans, stable for many millions of years, was not well understood.