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Recent low sea ice extents across Distributed Biological Observatory (DBO) sites in the northern Bering, Chukchi, and Beaufort seas of the Pacific Arctic region have been due to both later fall/winter freeze-up and earlier spring breakup, which in turn have important cascading impacts on the physical, biological, and biogeochemical state of the overall marine environment throughout this region. Satellite observations of the DBO sites that span across a large latitudinal gradient (~62–72°N) include sea surface temperature (SST), sea ice concentration, annual sea ice persistence and the timing of sea ice breakup/formation, chlorophyll-a concentrations, and primary productivity. While we observe significant trends in SST, sea ice, and chlorophyll-a/primary productivity throughout the year, the most significant and synoptic trends for the DBO sites have been those during late summer and autumn (warming SST during October/November, later shifts in the timing of sea ice formation, and increases in chlorophyll-a/primary productivity during August/September). Measurements of the transmittance of solar radiation through the ocean water column is also one of the critical elements for understanding the potential implications of these recent shifts in sea ice, including impacts on primary production, damaging effects of UV radiation on phytoplankton, photodegradation of dissolved organic matter, and upper ocean heating. Field-based observations of downwelling irradiance and upwelling radiance profiles in the top ~30-50 meters of ocean waters are also presented, collected at discrete stations across DBO sites 1–5 in the northern Bering and Chukchi Seas. Profiles were collected during July 2018, 2019, 2021, 2022, and 2023 as part of the DBO program onboard the Canadian Coast Guard Ship (CCGS) Sir Wilfrid Laurier, and represent a first time series of optical measurements across these DBO sites. Continued monitoring of the transmittance of solar radiation through the water column at these DBO sites will be crucial for understanding changes in the underwater light field as the duration of the open water season continues to lengthen with declining seasonal sea ice cover.
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Sea ice breakup and freeze-up indicators for users of the Arctic coastal environment
The timing of sea ice retreat and advance in Arctic coastal waters 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 af- fected by variations in the timing of breakup and freeze-up, resulting in a need for indicators to document the regional and temporal variations in coastal areas. The primary objec- tive of this study is to use locally based metrics to construct indicators of breakup and freeze-up in the Arctic and subarc- tic coastal environment. The indicators developed here are based on daily sea ice concentrations derived from satellite passive-microwave measurements. The “day of year” indica- tors are designed to optimize value for users while building on past studies characterizing breakup and freeze-up dates in the open pack ice. Relative to indicators for broader adja- cent seas, the coastal indicators generally show later breakup at sites known to have landfast ice. The coastal indicators also show earlier freeze-up at some sites in comparison with freeze-up for broader offshore regions, likely tied to ear- lier 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 varia- tions shows that the local breakup and freeze-up indicators have greater spatial variability than corresponding metrics based on regional ice coverage. However, the trends towards earlier breakup and later freeze-up are unmistakable over the post-1979 period in the synthesized metrics of coastal breakup and freeze-up and the corresponding regional ice coverage. The findings imply that locally defined indicators can serve as key links between pan-Arctic or global indica- tors such as sea ice extent or volume and local uses of sea ice, with the potential to inform community-scale adaptation and response.
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- Award ID(s):
- 1749081
- PAR ID:
- 10389260
- Date Published:
- Journal Name:
- The cryosphere
- Volume:
- 16
- Issue:
- 11
- ISSN:
- 1994-0416
- Page Range / eLocation ID:
- 4617-4635
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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