| Summary: | The changing Arctic sea‐ice cover is likely to impact the trans‐border exchange of sea ice between the exclusive economic zones (EEZs) of the Arctic nations, affecting the risk of ice‐rafted contamination. We apply the Lagrangian Ice Tracking System (LITS) to identify sea‐ice formation events and track sea ice to its melt locations. Most ice (52%) melts within 100 km of where it is formed; ca. 21% escapes from its EEZ. Thus, most contaminants will be released within an ice parcel's originating EEZ, while material carried by over 1 00,000 km2 of ice—an area larger than France and Germany combined—will be released to other nations' waters. Between the periods 1988–1999 and 2000–2014, sea‐ice formation increased by ∼17% (roughly 6 million km2 vs. 5 million km2 annually). Melting peaks earlier; freeze‐up begins later; and the central Arctic Ocean is more prominent in both formation and melt in the later period. The total area of ice transported between EEZs increased, while transit times decreased: for example, Russian ice reached melt locations in other nations' EEZs an average of 46% faster while North American ice reached destinations in Eurasian waters an average of 37% faster. Increased trans‐border exchange is mainly a result of increased speed (∼14% per decade), allowing first‐year ice to escape the summer melt front, even as the front extends further north. Increased trans‐border exchange over shorter times is bringing the EEZs of the Arctic nations closer together, which should be taken into account in policy development—including establishment of marine‐protected areas.
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