Sea ice break-up and freeze-up indicators for users of the Arctic coastal environment

• Main Authors: Walsh, John E., Eicken, Hajo, Redilla, Kyle, Johnson, Mark
• Format: Text
• Language: English
• Published: 2022
• Subjects: Arctic; Sea ice
• Online Access: https://doi.org/10.5194/tc-2022-21; https://tc.copernicus.org/preprints/tc-2022-21/

Arctic coastal waters are characterized by seasonal retreat and advance of sea ice. The timing of advance and retreat varies substantially from year to year. Various activities, ranging from marine transport to the use of sea ice as a platform for industrial activity or winter travel, are affected by variations in the timing of break-up and freeze-up, resulting in a need for indicators to document the regional and temporal variations in coastal areas. Here we develop indicators based on daily sea ice concentrations derived from satellite passive microwave measurements. The “day of year” indicators are designed to optimize value for users while building on past studies characterizing break-up and freeze-up dates in the open pack ice. Relative to indicators for broader adjacent seas, the coastal indicators show later break-up at sites known to have extensive landfast ice, for which break-up typically lags retreat of the adjacent, thinner drifting ice. The coastal indicators also show an earlier freeze-up at some sites in comparison with freeze-up for broader offshore regions, likely tied to earlier freezing of shallow water regions and areas affected by freshwater input from nearby streams and rivers. A factor analysis performed to synthesize the local indicator variations shows that the local break-up and freeze-up indicators have greater spatial variability than corresponding metrics based on regional ice coverage. However, the trends towards earlier break-up and later freeze-up are unmistakable over the post-1979 period in the synthesized metrics of the coastal break-up/freeze-up and their corresponding regional ice coverage. The findings imply that locally defined indicators can serve as key links between pan-Arctic or global indicators such as sea-ice extent or volume and local uses of sea ice, with the potential to inform community-scale adaptation and response.