Multi-Year Sea Ice Conditions in the Northwest Passage: 1968-2020

The Northwest Passage is often referred to as the "Holy Grail" of ship navigation as it provides a shorter route connecting the Atlantic and Pacific Oceans compared to the Northern Sea Route, Panama Canal, Suez Canal, and transiting around Cape Horn. Here, we summarize 52 years of observed multi-year ice (MYI) conditions from 1968 to 2020 in the western Canadian Arctic regions of the Northwest Passage updating a previous study that considered 1968-2006. Results indicate that on average, MYI area anomalies during the shipping season were +28% from 1968 to 2006 but -33% from 2007 to 2020 relative to the 1991-2020 climatology. The frequency of negative MYI area anomalies from 2007 to 2020 was unprecedented over the 52-year record. 13 of the past 14 years were negative in the Beaufort Sea, Franklin, and the Western Arctic Waterway; 10 of the past 14 years were negative in Western Parry Channel and Queen Elizabeth Islands; and 9 of the past 14 years were negative in the M'Clintock Channel. Despite strong and frequent negative MYI anomalies from 2007 to 2020, MYI recovery from first-year ice (FYI) aging and MYI dynamic import continued, but was reduced by 47% and 22%, respectively compared to 1968-2006. We demonstrate that from 2007 to 2020 (i) MYI dynamic recovery decreased because Arctic Ocean MYI has been primarily flowing into the Canadian Arctic via the smaller apertures in the Queen Elizabeth Islands and not from the Beaufort Sea via the M'Clure Strait and (ii) FYI aging decreased because recent changes in thermodynamic forcing have contributed to more melt. Overall, our results re-affirm that light MYI years in the Northwest Passage may occur more frequently as the Arctic continues to warm, but MYI recovery will continue to present a significant hazard to navigation for the foreseeable future.