An increased amount of thick sea ice flowing south from the Arctic Ocean shortened the ice-free shipping season in several parts of the Northwest Passage between 2007 and 2021, according to an analysis in Communications Earth & Environment. An increased amount of thick sea ice flowing south from the Arctic Ocean shortened the ice-free shipping season in several parts of the Northwest Passage between 2007 and 2021, according to an analysis in Communications Earth & Environment. Earth Sciences Environment Phys.org – latest science and technology news stories