Subsidence drives habitat loss in a large permafrost delta, Mackenzie River outlet to the Beaufort Sea, western Arctic

The Mackenzie Delta is an extensive river-mouth depocentre, the second largest delta on the Arctic Ocean, and lies in the zone of continuous permafrost. We report the first measurements of natural consolidation subsidence in a highlatitude delta with ice-bonded sediments. 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/year relative to a nearby monument on bedrock. Additional shallow subsidence results from loss of near-surface excess ice with deeper seasonal thaw in a warming climate. Isostatic adjustment is a third component of subsidence, captured in the NAD83v70VG crustal velocity model. Sedimentation rates over much of the outer delta are less than the rate of subsidence combined with rising sea level. Scenarios for future inundation are evaluated using interpolated IPCC AR5 projections, NAD83v70VG, and a LiDAR DEM with realistic consolidation, thaw subsidence, and sedimentation rates, on time scales of 40 and 90 years. These reveal increases in area flooded at mean water level from 33% in 2010 to 65% or as much as 85% in 2100, depending on the emissions scenario, driving delta-front retreat and removing a large proportion of avian nesting habitat. The three components of subsidence together increase the relative sea-level rise by a factor of two to eight, depending on the scenario. Consolidation subsidence may also contribute to rising low-flow water levels in the central delta, increasing river-lake connectivity, with negative impacts on aquatic biodiversity and productivity.