albedo antarctic bottom water antarctic ice sheet antarctica arctic ocean arctic shrinkage beluga bottom water bremen climate model earth east greenland current geophysical fluid dynamics laboratory germany global warming greenland sea jurassic lancaster sound marine modeling and analysis branch nasa nathaniel bowditch national snow and ice data center north pole northern sea route northwest passage norwegian language polar ice cap polar region scanning multichannel microwave radiometer seawifs sea ice seawater severnaya zemlya southern ocean thermohaline circulation triassic water mass