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TitleSubsidence drives habitat loss in a large permafrost delta, Mackenzie River outlet to the Beaufort Sea, western Arctic Canada
AuthorForbes, D LORCID logo; Craymer, M RORCID logo; James, T SORCID logo; Whalen, DORCID logo
SourceCanadian Journal of Earth Sciences vol. 59, no. 11, 2022 p. 914-934, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20210607
PublisherCanadian Science Publishing
Mediaon-line; digital
File formatjpg
NTS107B/03; 107B/04; 107B/05; 107B/06; 107B/11; 107B/12; 107B/13; 107B/14; 107C/03; 107C/04; 107C/05; 107C/06; 107C/11; 107C/12; 107C/13; 107C/14; 117A/01; 117A/02; 117A/07; 117A/08; 117A/09; 117A/10; 117A/15; 117A/16; 117D/01; 117D/02; 117D/07; 117D/08; 117D/09; 117D/10; 117D/15; 117D/16
AreaBeaufort Sea; Mackenzie Bay
Lat/Long WENS-138.0000 -134.0000 70.0000 68.0000
Subjectsenvironmental geology; Nature and Environment; arctic geology; climate, arctic; submergence; coastal studies; coastal environment; subsidence; sea level changes; climate; climate effects; Climate change impacts
Illustrationslocation maps; photographs; tables; plots
ProgramClimate Change Geoscience Coastal Infrastructure
Released2022 11 01
AbstractThe Mackenzie Delta is a large river-mouth depocentre receiving an annual discharge of 284 km3 water and 124 Mt sediment from an expansive drainage basin in northwestern Canada. It is the second largest delta on the Arctic Ocean and lies in the zone of continuous permafrost, with 96% of near-surface sediment in the outer delta perennially below 0 °C, much of it ice-bonded. Rates of natural subsidence in a permafrost delta were unknown prior to this study. We demonstrate that consolidation subsidence is not precluded by permafrost and ice-bonding. In addition, near-surface excess ice may drive shallow thaw subsidence in a warming climate. Several years of episodic GPS records on a network of 15 stable monuments throughout the central and outer delta reveal downward motion between 1.5 ± 0.7 and 5.3 ± 1.1 mm/yr relative to a nearby monument on stable bedrock. Sedimentation rates on the outer delta, away from channel levees, appear to be less than the rate of subsidence combined with rising sea level. Scenarios for future inundation are evaluated for a representative area using interpolated IPCC AR5 projections and the NAD83v70VG crustal velocity model, for realistic consolidation, thaw subsidence, and sedimentation rates, on time scales of 40 and 90 years from 2010. These reveal increases in mean water level extent from 33% in 2010 to 37% and 43% in 2050 and 65% in 2100 (intermediate-emissions scenario RCP4.5 median) and to 85% in 2100 (high-emissions scenario RCP8.5 upper limit), permanently removing a large proportion of internationally significant avian nesting habitat. Subsidence may drive delta front retreat at a rate exceeding shoreline erosion. Furthermore, with southward delta retreat and a northward advancing tree line, landward migration may not serve to maintain the area of distinctive outer delta sedge and shrub-willow habitat.
Summary(Plain Language Summary, not published)
The Mackenzie Delta is the second largest delta on the Arctic Ocean and lies in the zone of continuous permafrost. Subsidence in deltas results from progressive compaction of sediment as more sediment is added on top, and is a key factor in the vulnerability of deltas to sea-level rise. Until now, it was thought that permafrost and ice-bonded sediments in the Mackenzie Delta would limit compaction. Through GPS monitoring, we show that the delta is subsiding relative to nearby stable bedrock, and at rates comparable to non-permafrost deltas. Combined with limited rates of sedimentation and shallow thaw subsidence, we show that a representative part of the delta may see the area currently under water (33%) increase to as much as 85% by 2100, dramatically increasing the loss of internationally important bird nesting habitat already threatened by coastal erosion and an advancing tree line.

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