Craig Stevens/NIWA/Supplied The formation of Antarctic sea ice causes cold, salty water to sink to the sea floor, where it flows away and links to the global oceanic conveyor belt, the thermohaline circulation. Recent studies reveal surprising changes in the Ross Sea region, a choke-point in ocean circulation. David Williams reports. As the three-masted British ship Erebus sailed south in Antarctic waters with the slightly smaller Terror in January 1841, commander James Clark Ross, the world’s most experienced polar explorer, saw a low white line extending as far as the eye could see. “It presented an extraordinary appearance,” he wrote, “gradually increasing in height, as we got nearer to it, and proving at length to be a perpendicular cliff of ice, between one hundred and fifty feet and two hundred feet above the level of the sea, perfectly flat and level at the top, and without any fissures or promontories on its even seaward face.”