Arctic Open-Water Window

All datasets · API reference · Dataset page on heimdallresearch.com

Open-water days each season at fixed gates on the Bering Strait, Northwest Passage and Northern Sea Route, from the NOAA/NSIDC passive-microwave sea-ice concentration record since 1978. A historical indicator, not a navigation product.

Status: In preparation. Version 1.0 is estimated for December 2026. It is built on the NOAA/NSIDC sea-ice record; the radar table is experimental.

Themes	ice-and-snow, coasts
Coverage	Bering Strait, Northwest Passage and Northern Sea Route gates
Period	1979 to present
Resolution	Gate by day, 25 km sea-ice record
Free updates	Yearly release after each season, with provisional values during the season
Paid updates	No paid version
License	CC-BY-4.0
Free	The full dataset, as files and through the API and MCP server with a free key.
Paid	There is no paid version. The dataset describes past seasons and is not navigation or operational advice.
Intended use	Long-term change in how many days Arctic passages are open, season timing, and background for shipping, emergency response and security research.
Not intended for	Route planning or navigation safety, ice thickness or type, or conditions in channels narrower than the 25 km grid. Use national ice service charts for operations.

Tables

Table	One row per	Fields
gate_daily	gate_id, date	8
gate_seasons	gate_id, year	8
radar_experimental	gate_id, date, variant	9

Access

API: GET /v1/arctic/gates, GET /v1/arctic/gates/{gate_id}/daily. See the API reference.

MCP tools: get_arctic_gate, get_download_link. See Use it in your AI assistant.

Files: CSV and Parquet on Zenodo and Hugging Face, with datapackage.json, a Croissant file and SHA256SUMS, from the first release.

How values are produced

Each gate is a fixed polygon across a passage. For each day, sea-ice concentration is averaged over the grid cells inside the gate, excluding cells contaminated by 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. Seasonal counts and first and last open dates follow from the daily series. Near-real-time values are marked provisional and replaced when the final record is released.

Table gate-daily

File gate_daily.csv. One row per gate per day.

One row per gate_id, date.

Field	Type	Unit	Description
gate_id	string		Gate identifier.
date	date		Day.
sic_mean	number	percent	Mean sea-ice concentration over ocean cells in the gate. May be empty.
open_15	boolean		Open water at the 15% threshold. May be empty.
open_30	boolean		Open water at the 30% threshold. May be empty.
open_50	boolean		Open water at the 50% threshold. May be empty.
valid_fraction	number		Share of gate cells with data.
provisional	boolean		True for near-real-time values.

Table gate-seasons

File gate_seasons.csv. One row per gate per season year.

One row per gate_id, year.

Field	Type	Unit	Description
gate_id	string		Gate identifier.
year	integer		Season year.
open_days_15	integer	days	Open-water days at 15%.
open_days_30	integer	days	Open-water days at 30%.
open_days_50	integer	days	Open-water days at 50%.
first_open_15	date		First open day at 15%. May be empty.
last_open_15	date		Last open day at 15%. May be empty.
missing_days	integer	days	Days with too little valid data.

Table radar-experimental

File radar_experimental.csv. Experimental Sentinel-1 radar open-water layer for freeze-up windows only. Not for navigation. Agreement with MASIE is reported per window in the dataset card..

One row per gate_id, date, variant.

Field	Type	Unit	Description
gate_id	string		Gate identifier.
date	date		Day.
radar_ice_fraction	number		Coverage-weighted ice fraction from radar.
open_15	boolean		Open water at 15% ice-fraction threshold.
variant	string		Classifier variant.
masie_test_agreement	number		Held-out MASIE agreement for the window. May be empty.
window_label	string		Prototype window label.
layer	string		Always experimental.
note	string		Usage note.

Limits

• Narrow straits span only one to three 25 km cells, so gate values describe the surrounding sea, not the channel itself.
• The two concentration algorithms in the record disagree most at low concentrations; the spread is published as an uncertainty measure.

Sources

Source	Role	Terms
NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 6 (G02202), DOI 10.7265/b18j-z797	Measured, final record	Free; citation required
NOAA/NSIDC near-real-time sea-ice concentration CDR, Version 4 (G10016), DOI 10.7265/tm2n-1m33	Provisional current-season values	Free; citation required
Gate geometry	Defined by Heimdall Research	CC0

All datasets · API reference