Name: Arctic Open-Water Window
Creator: Heimdall Research
License: https://creativecommons.org/licenses/by/4.0/

Status: Released
Version / DOI: Published 2026-10-10. Version 1.1, DOI 10.5281/zenodo.23147722.
Coverage: 15 named gates in Bering Strait, the Northwest Passage, the Northern Sea Route and Fram Strait chokepoints
Period: 1978-10-26 to 2026-10-01 (1978 and 2026 are partial seasons)
Resolution: 25 km sea-ice grid cells within each gate; daily values and seasonal summaries
Free updates: Latest day in the live feed: 22 October 2026. The published version 1.1 ends on 1 October 2026. The live feed is newer data from the API. It can change and is not part of the cited version.
After the release: Provisional values after 2026-10-01 are available through the API with include=latest. They can change and are not part of the cited version.
Paid updates: No paid version
Formats: CSV and Parquet tables; gate geometry as GeoJSON
Access: Free
License: CC BY 4.0, with upstream attribution below
API and MCP: Access with a free key.

Download and API key

In the download

Version 1.1, published on Zenodo, Hugging Face and Kaggle: the daily, yearly, climatology and trend tables for 15 gates (CSV and Parquet), the gate geometry (GeoJSON), the citation and the data dictionary. The Kaggle copy also has the notebook.
With a free API key

Full-size COG files for a gate, from GET /v1/arctic/gates/{gate}/imagery. The MCP tool is get_arctic_imagery.

Not in this download, free through the API: full-size radar images of the 15 gates, 2015 to 2026, for the weeks that have a usable one. Get a free key.

Sample rows

Bering Strait, 15 comparable years ending with the latest in the table (gate_seasons.csv)

Bering Strait, 15 comparable years ending with the latest in the table (`gate_seasons.csv`)
`year`	`first_open_15`	`last_open_15`	`open_days_15`
`2011`	`2011-05-30`	`2011-11-19`	`174`
`2012`	`2012-06-02`	`2012-11-16`	`166`
`2013`	`2013-06-05`	`2013-12-14`	`193`
`2014`	`2014-05-27`	`2014-12-10`	`198`
`2015`	`2015-05-12`	`2015-12-01`	`191`
`2016`	`2016-05-11`	`2016-12-18`	`212`
`2017`	`2017-01-07`	`2017-12-28`	`234`
`2018`	`2018-04-28`	`2018-12-04`	`214`
`2019`	`2019-05-10`	`2019-12-21`	`210`
`2020`	`2020-05-28`	`2020-12-16`	`194`
`2021`	`2021-05-29`	`2021-11-03`	`158`
`2022`	`2022-05-19`	`2022-12-19`	`204`
`2023`	`2023-05-26`	`2023-12-07`	`192`
`2024`	`2024-06-14`	`2024-12-02`	`171`
`2025`	`2025-05-31`	`2025-11-29`	`176`

Rows from the published Arctic Open-Water Window 1.1 table (gate_seasons.csv). Not for navigation. Use at your own risk. Provided as is, without warranty of any kind. For ice conditions, use your national ice service.

Open and close

Satellite radar image of the Diomede Islands in the Bering Strait on 16 November 2024, surrounded by open water.

2024-11-16

$The same area on 4 March 2025, with the islands surrounded by fractured pack ice.$

2025-03-04

Bering Strait, open water on 16 November 2024 and pack ice on 4 March 2025.

Not for navigation. Use at your own risk. Provided as is, without warranty of any kind. For ice conditions, use your national ice service.

Try it

Bering Strait: usual opening 29 May, usual closing 24 Nov (the median date), at the 15% ice threshold, from 1979 to 2025 (45 years). A year can open in January when the threshold is already open, and it can close in December.

Bering Strait, last 5 comparable years in gate_seasons.csv
Year	First open	Last open	Open days
`2021`	`2021-05-29`	`2021-11-03`	`158`
`2022`	`2022-05-19`	`2022-12-19`	`204`
`2023`	`2023-05-26`	`2023-12-07`	`192`
`2024`	`2024-06-14`	`2024-12-02`	`171`
`2025`	`2025-05-31`	`2025-11-29`	`176`

Create a free account for the full result, videos and your AI assistant.

Not for navigation. Use at your own risk. Provided as is, without warranty of any kind. For ice conditions, use your national ice service.

Download the data

Arctic Open-Water Window

Open-water days each season at fixed gates on Arctic passages. Version 1.1, 15 gates.

Citable copy (Zenodo) · Dataset (Kaggle) · Run the notebook (Kaggle) · Discussion (Kaggle) · Load in Python (Hugging Face)

What the data shows

5 findings from the published version.

76.8 days Finding

Vilkitsky Strait: 6 open days a year then, 83 now

At Vilkitsky Strait, mean open days at the 15 percent ice cutoff rose from 5.8 days a year in 1979-1988 to 82.6 days in 2016-2025 (difference +76.8 days).

Read the finding

Breakdown

For Vilkitsky Strait (nsr-vilkitsky), the mean of open_days_15 on full seasons with a numeric value is 5.8 in 1979-1988 (n=9) and 82.6 in 2016-2025 (n=10). That is a rise of 76.8 days. Seasons with a blank open_days_15 are skipped. An open day is a day when average sea-ice concentration inside the gate polygon sits below the 15 percent cutoff.
8 seasons Finding

Vilkitsky Strait stayed shut in 8 early years. It opened every year from 2016 through 2025.

Vilkitsky Strait had 8 seasons with zero open days in 1979-1988 and 0 such seasons in 2016-2025.

Read the finding

Breakdown

In 1979-1988, 8 full seasons at nsr-vilkitsky have open_days_15 equal to zero. In 2016-2025, that count is 0. Blank open_days values are not counted as zero.
53.3 days Finding

Bering Strait is open 53 more days a year than it was

At Bering Strait, mean open days at the 15 percent cutoff rose from 143.2 days a year in 1979-1988 to 196.5 days in 2016-2025 (difference +53.3 days).

Read the finding

Breakdown

For bering-strait, mean open_days_15 on full seasons with a numeric value is 143.2 in 1979-1988 (n=8) and 196.5 in 2016-2025 (n=10). The difference is +53.3 days. Seasons with a blank open_days_15 are skipped.
173 days Finding

A typical year at Bering Strait has 173 open days

Over 45 full seasons (1979 to 2025), Bering Strait had a median of 173 open days at the 15 percent cutoff (range 118 to 234).

Read the finding

Breakdown

The gate_trends row for bering-strait at threshold 15 reports median_open_days 173.0 over 45 seasons (2 excluded). Across non-blank open_days_15 values in gate_seasons, the range is 118 to 234.
40.2 days Finding

Barrow Strait, Canada: 11 open days a year in 1979-1988, 51 in 2016-2025.

At Barrow Strait, mean open days at the 15 percent cutoff rose from 11.1 days a year in 1979-1988 to 51.3 days in 2016-2025 (difference +40.2 days).

Read the finding

Breakdown

For nwp-barrow, mean open_days_15 on full seasons with a numeric value is 11.1 in 1979-1988 (n=9) and 51.3 in 2016-2025 (n=10). The difference is +40.2 days.

All findings

What it is for

Intended use: Research on long-term change in open-water days and season timing at Arctic passages.
Not intended for: Route planning or navigation safety, ice thickness or type, or conditions in channels narrower than the 25 km grid. For ice conditions, use your national ice service.

Where the measurements are

Each gate is a fixed polygon on the 25 km sea-ice grid. Most gates lie across a passage or a sea area. Two are approaches to Dmitry Laptev Strait, and two cover part of a strait. Values describe the sea ice inside the polygon, day by day, since late 1978.

Gates in version 1.1
Gate	Route	Location	Footprint
Bering Strait `bering-strait`	Bering Strait	65.5 to 66.2 N, 170.3 to 168.1 W	Across the passage or sea area
Barrow Strait (Northwest Passage) `nwp-barrow`	Northwest Passage	74.0 to 74.7 N, 94.8 to 91.3 W	Across the passage or sea area
Vilkitsky Strait (Northern Sea Route) `nsr-vilkitsky`	Northern Sea Route	77.8 to 78.0 N, 100.2 to 103.8 E	Across the passage or sea area
Amundsen Gulf (Northwest Passage) `nwp-amundsen-gulf`	Northwest Passage	70.2 to 71.6 N, 122.5 to 118.0 W	Across the passage or sea area
McClure Strait (Northwest Passage) `nwp-mcclure`	Northwest Passage	74.8 to 75.8 N, 122.0 to 115.0 W	Across the passage or sea area
Viscount Melville Sound (Northwest Passage) `nwp-viscount-melville`	Northwest Passage	74.2 to 75.4 N, 110.0 to 104.0 W	Across the passage or sea area
Lancaster Sound (Northwest Passage) `nwp-lancaster`	Northwest Passage	73.9 to 74.7 N, 85.0 to 80.0 W	Across the passage or sea area
Victoria Strait (Northwest Passage) `nwp-victoria`	Northwest Passage	69.0 to 70.2 N, 100.5 to 98.5 W	Across the passage or sea area
Kara Gate (Northern Sea Route) `nsr-kara-gate`	Northern Sea Route	70.2 to 71.0 N, 57.0 to 59.5 E	Across the passage or sea area
Sannikov Strait (Northern Sea Route) `nsr-sannikov`	Northern Sea Route	74.4 to 74.9 N, 140.0 to 142.5 E	Across the passage or sea area
Long Strait (Northern Sea Route) `nsr-long`	Northern Sea Route	69.8 to 70.8 N, 178.0 E to 176.0 W	Across the passage or sea area
Dmitry Laptev Strait, eastern approach (Northern Sea Route) `nsr-dmitry-laptev-east`	Northern Sea Route	72.9 to 73.8 N, 144.5 to 147.5 E	Approach to the strait. Open sea east of Bolshoy Lyakhovsky Island, at the eastern end of the strait.
Dmitry Laptev Strait, western approach (Northern Sea Route) `nsr-dmitry-laptev-west`	Northern Sea Route	72.8 to 73.6 N, 138.0 to 140.5 E	Approach to the strait. Open sea at the western end of the strait.
Peel Sound, southern end (Northwest Passage) `nwp-peel-south`	Northwest Passage	71.6 to 72.1 N, 96.3 to 94.9 W	Part of the strait. Southern end of Peel Sound, where it widens toward Franklin Strait. It covers part of the sound. 3 cells, all next to land; the land share is close to the limit.
Fram Strait, west side (East Greenland Current) `fram-strait-west`	Fram Strait	77.5 to 78.5 N, 8.0 to 3.0 W	Part of the strait. West side of Fram Strait only, west of the usual summer ice edge, in the southward ice drift. Open days here mean thin or open pack ice.

Columns in each table

These are the columns carried over from version 1.0. Version 1.1 adds columns to both tables and adds the gate_climatology and gate_trends tables. data/variables.csv in the download lists every column.

gate_daily: one row per gate per day
Field	Type	Unit	Description
`gate_id`	string	none	Gate identifier
`date`	date	none	Day (UTC), 1978-10-26 to 2026-10-01
`sic_mean`	number	fraction, 0 to 1 (0.15 means 15% ice cover)	Mean sea-ice concentration over ocean cells in the gate
`open_15`	boolean	none	Open water at the 15% threshold
`open_30`	boolean	none	Open water at the 30% threshold
`open_50`	boolean	none	Open water at the 50% threshold
`valid_fraction`	number	none	Share of gate cells with data
`provisional`	boolean	none	True when the row comes from the near-real-time product
`source`	string	none	NSIDC product that supplied the row: G02202v6 or G10016v4

gate_seasons: one row per gate per calendar year
Field	Type	Unit	Description
`gate_id`	string	none	Gate identifier
`year`	integer	none	Calendar year
`open_days_15`	integer	days	Open-water days at 15%. Empty for a blank season
`open_days_30`	integer	days	Open-water days at 30%. Empty for a blank season
`open_days_50`	integer	days	Open-water days at 50%. Empty for a blank season
`first_open_15`	date	none	First open day at 15%
`last_open_15`	date	none	Last open day at 15%
`missing_days`	integer	days	Days with too little valid data
`partial`	boolean	none	True for an incomplete season: 1978 and 2026

Sources and required attribution

Every input, its role, and its terms
Input	Role	License or terms	Attribution
NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 6 (G02202, DOI 10.7265/b18j-z797)	Measured	Free to use and redistribute; citation required	NSIDC-provided citation with DOI and version
NOAA/NSIDC near-real-time sea-ice concentration CDR, Version 4 (G10016, DOI 10.7265/tm2n-1m33)	Provisional current-season values	Free to use and redistribute under NSIDC terms; citation required	NSIDC-provided citation
Gate geometry	Defined by Heimdall Research	CC0	Heimdall Research
NSIDC Multisensor Analyzed Sea Ice Extent (MASIE-NH), Version 1 (G02186), 4 km	Used to check gate footprints (land share and open or ice agreement); also the source of the MASIE 4 km enhancement tables	Free; citation required	NSIDC-provided citation
Copernicus Sentinel-1 data (ESA), accessed through Microsoft Planetary Computer	Gate imagery (80 m), 2015 to 2026, for the weeks that have a usable one	Free, full and open; attribution required	Contains modified Copernicus Sentinel data 2015-2026

How values are produced

Each gate is a fixed polygon on the 25 km sea-ice grid. For each day, sea-ice concentration is averaged over the grid cells inside the gate that hold a value, leaving out cells the source record marks as land. A day is open water when that average is below the threshold; three thresholds (15, 30 and 50 percent) are published so users can see how sensitive the answer is. Yearly counts of open days, first and last open dates, the longest unbroken open spell, a 1991 to 2020 daily climatology and trends follow from the daily series. Near-real-time values are marked provisional and replaced when the final record is released. An experimental Sentinel-1 radar table for two gates (freeze-up and breakup windows only) ships in data/experimental/radar_experimental.csv and is labeled experimental.

How it is checked

Gate footprints: Each of the 15 gates was checked against the MASIE 4 km ice analysis on 120 sample days, 2015 to 2024. All 15 pass: land share 0.00 to 0.28, and open or ice agreement at the 15% threshold 0.87 to 0.97.
Days near the threshold: For the three version 1.0 gates, agreement with MASIE is 94.4% (68 of 72) on clear-ice or clear-open days, 47.2% (17 of 36) on breakup days and 77.8% (28 of 36) on freeze-up days.
Known limits: The gates hold between 3 and 40 cells of the 25 km grid. Values describe the sea inside the footprint and do not resolve a channel narrower than one cell.

How it compares with existing products

NSIDC publishes open-water periods on a 25 km grid, and national ice services publish operational charts. This dataset gives one daily series for each gate, at three thresholds, with data-quality fields on every row.

Free and paid access

Free: The full dataset: files on Zenodo, Hugging Face and Kaggle with no sign-up, and the API and MCP server with a free key.
Paid: There is no paid version. The dataset describes past seasons. Not for navigation. Use at your own risk. Provided as is, without warranty of any kind.

How to cite

Heimdall Research (2026). Arctic Open-Water Window (Version 1.1) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.23147722 Concept DOI https://doi.org/10.5281/zenodo.23021977. New version of https://doi.org/10.5281/zenodo.23021978.

Please also cite the NOAA/NSIDC sea-ice record.

Versions and corrections: Version 1.0 (3 gates) has DOI https://doi.org/10.5281/zenodo.23021978. Version 1.1 (15 gates) has DOI https://doi.org/10.5281/zenodo.23147722. DOI https://doi.org/10.5281/zenodo.23021977 covers all versions. Version 1.1 carries the corrections to version 1.0. The changelog in the download records changes. Report problems through the collaboration form.
Download: Zenodo (CSV and Parquet, DOI) · Hugging Face (same files; loads with the datasets library) · Kaggle (notebook, discussion) · API and MCP with a free account. Downloads need no account.
Use notice: Not for navigation. Use at your own risk. Provided as is, without warranty of any kind. For ice conditions, use your national ice service.

Arctic Open-Water Window

In the download

With a free API key

Arctic Open-Water Window

Vilkitsky Strait: 6 open days a year then, 83 now

Vilkitsky Strait stayed shut in 8 early years. It opened every year from 2016 through 2025.

Bering Strait is open 53 more days a year than it was

A typical year at Bering Strait has 173 open days

Barrow Strait, Canada: 11 open days a year in 1979-1988, 51 in 2016-2025.

Release emails