Minerals Management Service 

Alaska OCS Region 

Technical Summary: MMS Publication 2005-068

Mapping and Characterization of Recurring Spring 

Leads and Landfast ice in the Beaufort and Chukchi 

Seas 

BACKGROUND: 

Spring leads in the Beaufort Sea occur every year to the east of Barrow. The size, frequency, and 

latitudinal extent of these leads, particularly further east from Barrow, are poorly known. In recent years, 

we have become aware that the Arctic Ocean, and especially the Beaufort Sea, responds to alternating 

climate states lasting a few to several years. A primary difference between the two alternating states is a 

weakening or reversal in the Beaufort gyre. Superimposed on, and interacting with the alternating climate 

states, is the estimated 40 percent thinning of Arctic ice pack over the last 30 years. The effects of 

climate state and ice thinning on spring lead characteristics in the Beaufort Sea are unknown. 

Better information on how spring leads and moving ice pack interact is another issue, because this 

interaction is the key to how much risk spilled oil encapsulated in pack ice has to localized biota. 

Bowhead whales migrate past Barrow along these leads and eastward, toward the Canadian Beaufort in 

the spring. The leads are also heavily used by spring migrating waterfowl. Risk from encapsulated oil 

would be less if the ice pack diverges along the lead lines as opposed to breaking up and crossing the 

leads. 

The spatial location of landfast ice on a monthly basis is known in only a very generalized sense as 

shown in climatic or ice atlases. The new MMS sponsored sea ice atlas is being developed from the Joint 

Ice Center products, which are at a 25 km grid resolution and are too coarse for the detail needed. The 

spatial distribution of landfast ice was documented in the Beaufort Sea by Stringer in the mid 1970’s on a 

seasonal basis. The seaward limit of stable fast ice defines where under-ice pooling of spilled oil might 

take place and where fast ice conditions apply to design and operation of offshore facilities. It defines the 

location where no ice movement occurs. It is also the extreme landward boundary of possible whale 

migration routes during the springtime migration period. 

OBJECTIVES: 

1. Document and map the spatial and temporal distribution of recurring spring leads system and 

polynyas from the eastern Chukchi Sea, southwest of Barrow to Wainwright, Alaska across the 

Beaufort Sea to the Canadian Mackenzie River Delta System for the time period 1993 to 2004 based 

on Advanced Very High Resolution Radiometer (AVHRR) data. Draw on older archived AVHRR data 

from the 1970s and 1980s as well as publications from that time period to document potential 

changes in the lead regime. 

2. Document and map the yearly spatial and temporal changes by month of the stable landfast ice 

distribution across the Eastern Chukchi Sea and the Alaska Beaufort Sea to the Canadian 

Mackenzie Delta based on analysis of high-resolution Radarsat Synthetic Aperture Radar (SAR) 

imagery. 

3. Document trends in lead and stable landfast characteristics over the time period covered and in 

relation to earlier studies from the 1970s and 1980s, especially as related to large-scale ice thinning 

and shrinking of summer minimum ice extent in the region. Offer up preliminary explanations of these 

changes in the context of atmosphere-ice-ocean interaction. 

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4. Document and discuss the dominant mode(s) of spring lead/ice pack interaction as well as any 

potential significance these might have on the landfast ice regime. 

DESCRIPTION: 

The aim of this project was to map and document the spatial and temporal distribution of recurring lead 

systems and coastal polynyas and landfast ice off the coast of northern Alaska in the Chukchi and 

Beaufort Seas between Wainwright bordering the Chukchi Sea and the Mackenzie River Delta in the 

Canadian Beaufort Sea. The extent and duration of the landfast ice along this stretch of coast was 

analyzed with Radarsat Synthetic Aperture Radar (SAR) between 1996 and 2004 and supplemented with 

Advanced Very High Resolution Radiometer (AVHRR) data, for the time period between 1993 and 1996. 

Lead distributions were quantified from AVHRR data for the period between 1993 and 2004. These data 

were compared to older AVHRR imagery and older published data from the 1970's and 1980's. Monthly 

mean landfast ice edge positions and spatial statistics of lead distributions were derived from these data 

for the time period of stable, closed sea-ice cover. Longer-term spatio-temporal variations in landfast ice 

extent and lead patterns were assessed in the context of large-scale atmospheric and oceanic change. 

Project products and deliverables include ArcGIS grids and shapefiles of monthly landfast ice extents and 

lead distributions with accompanying metadata. Published articles and reports of relevance to the project 

were also compiled in a Procite bibliography database. 

SIGNIFICANT CONCLUSIONS: 

Major conclusions from this work include the following: (1) Lead distribution and landfast ice extent 

patterns are consistent throughout the study period between 1993 and 2004 and compare well with 

observations from earlier studies completed in the 1970s. (2) Landfast ice extent is controlled by the 

combination of coastal bathymetry, heat exchange with the atmosphere (and to a lesser extent 

atmospheric circulation) and ice-pack interaction. (3) With a general warming trend in the region during 

the study period, the landfast ice season is significantly shorter, with a less stable ice cover. Lead 

patterns and fractions or sizes, on the other hand do not show any significant trend over the study period. 

(4) The large-scale pattern of high lead activity and landfast ice variability in the eastern Chukchi Sea and 

the Mackenzie shelf area and much more quiescent conditions in the central Beaufort Sea are explained 

by a combination of coastal morphology in relation to prevailing wind direction, the rheology of the ice 

pack and its confinement in the “dead space” of the Beaufort Sea and Canadian Basin, and the impact of 

river influx on break-up in the Mackenzie Delta. 

STUDY RESULTS: 

The analysis of lead distributions shows a distinct seasonal cycle in the lead fraction as well as lead size 

and number density. While there is substantial interannual variability in lead characteristics, with no 

statistically significant trends or correlations to key atmospheric variables, spatial patterns of lead 

occurrence and size are consistent from year to year. A key event in the seasonal cycle is the transition 

between the regime of distinct linear leads in winter and the ubiquitous appearance of patches of open 

water surrounding floes in spring (“spring ice”), typically occurring in late April or early May. Monthly 

maps of lead occurrence probability reflect the key processes controlling lead patterns, including flaw 

leads and polynyas, advection of floes past grounded ice on Hanna Shoal, the appearance of arced leads 

that radiate from Point Barrow and propagate into areas of more stagnant ice in the central and eastern 

Beaufort Sea as well as arches that form along the margin of ice that is confined in the “dead space” of 

the eastern Beaufort Sea. These patterns have been examined and classified into about a dozen 

characteristic patterns and evolution sequences that occur throughout the years. 

Based on the landfast ice data set, the spatial and temporal variability in the extent of landfast ice, the 

water depth it occupies and the timing of key events in its annual cycle have been examined. We 

identified four zones of coherent seasonal variability and the key elements of coastal and bathymetric 

configuration that define these zones. In all four zones the seaward landfast ice edge (SLIE) was 
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observed to advance incrementally into deeper water with some sections advancing first, followed by 

neighboring sections. By the end of the season, prior to break-up, the distribution of water depths at the 

SLIE in all zones exhibited strong modes ranging between 16 m and 22 m. The similarity in water depth 

distributions at the start and end of the annual landfast ice cycle suggests that as the SLIE retreats, it 

occupies the same locations that it did while advancing. 

We also examined interannual variability and identified the components of atmospheric circulation and air 

temperature that are most important for the formation and break-up of the landfast ice. A comparison with 

earlier work from the 1970’s suggests that the annual cycle of landfast ice has been significantly shorter 

in recent years, caused by later formation and earlier break-up. We also note that any comparisons must 

take into account relevant definitions and methods. Examination of air temperatures over the region 

showed multi-decadal trends towards an earlier onset of thawing in spring, and later onset of freezing in 

fall. A strong interannual correlation suggests that the former is responsible for the early landfast ice 

break-up in recent years. However, the timing of landfast ice formation appears to correlate best with the 

timing of pack ice incursion into coastal waters, suggesting that the observed latening of landfast ice 

formation could be related to the more northward retreat of the perennial ice edge in recent years. 

STUDY PRODUCTS: 

Final Report, bibliographic database, Catalogues of AVHRR imagery, RADARSAT SAR imagery, 

Geodatabases of landfast ice, Geotiffs , grids and shapefiles of landfast ice and leads, summary statistics 

of lead data, monthly averages of landfast ice, metadata templates, monthly lead occurrence probability 

maps. 

CONTRACT NUMBER(S): 0103CT71707 

SPONSORING OCS REGION: Alaska OCS Region 

APPLICABLE PLANNING AREA(S): Beaufort Sea and Chukchi Sea 

FISCAL YEAR(S) OF PROJECT FUNDING: 2003-2005 

COMPLETION DATE OF REPORT: April 2006 

COST(S): $397,000 

CUMULATIVE PROJECT COST: $397,000. 

PROJECT MANAGER(S): Warren Horowitz 

AFFILIATION: MMS 

ADDRESS: 3801 Centerpoint Drive, Suite 500, Anchorage, AK 99503-5823 

PRINCIPAL INVESTIGATOR(S): Hajo Eicken, Lewis Shapiro, Allison Graves Gaylord, Andrew Mahoney, 

Patrick Cotter 

KEY WORDS: Beaufort Sea, Chukchi Sea, leads, landfast ice, GIS, 

REPORT AVAILABILITY: 

This report, OCS Study MMS 2005-068, is available on paper with enclosed CD from the 

Minerals Management Service, Public Information Office, 3801 Centerpoint Drive, Suite 500, 

Anchorage, AK 99503-5823, or can be downloaded from our website at 

www.mms.gov/alaska/ref/akpubs.htm. Report copies are available free of charge, as long as 

the supply lasts, from the above address. Telephone requests may be placed at 1-800-764-

2629 or (907) 334-5206. E-Mail requests may be sent to akwebmaster@mms.gov. Once the 

limited supply is gone, copies will be available from the National Technical Information Service, 

Springfield, Virginia 22161, or may be inspected at selected Federal Depository Libraries. 
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