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

Abstract

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 high-latitude 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/yr 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.

Remote Sensing of Multitemporal Functional Lake‐To‐Channel Connectivity and Implications for Water Movement Through the Mackenzie River Delta, Canada

“…The sensitivity of connectivity to water level indicates that predicted future changes to the northern Mackenzie River hydrologic cycle, such as increasing winter and spring streamflow at the expense of summer streamflow (Scheepers et al., 2018) and increasingly frequent and intense future precipitation events (Kuo et al., 2020), are cause for future monitoring. Additionally, permafrost thaw (Lantz & Kokelj, 2008) and resulting increased erosion rates (Rowland et al., 2023), and subsidence (Forbes et al., 2022) are predicted to influence the Mackenzie River Delta region going forward. Each of these projected changes may influence functional and structural lake‐to‐channel connectivity in different ways; with changes to streamflow resulting in higher and earlier springtime connectivity but decreased summertime connectivity, increased erosion leading to higher TSS and therefore higher functional connectivity, and increased subsidence leading to shifting lake sill elevations and functional connectivity elevation thresholds.…”

Landscape and Seascape Responses to Canada’s Changing Climate

“…The Mackenzie Delta is the second largest Arctic delta (after the Lena Delta in Russia). Forbes et al (2022) are the first to show that consolidation subsidence can occur in a permafrost delta underlain by ice-bonded sediments. Combined with climate-driven shallow thaw subsidence, the consolidation subsidence contributes to measured surface downward motion relative to nearby bedrock.…”

Geologic controls on the genesis of the Arctic permafrost and sub-permafrost methane hydrate-bearing system in the Beaufort–Mackenzie Delta

“…The Mackenzie Delta (MD) is a river-mouth depocentre, and the second largest Arctic delta (Forbes et al, 2022). It is the most economically accessible area along the Arctic coast of the Beaufort-Mackenzie Delta Basin (Dixon et al, 2019).…”