Abstract
AbstractHigh overall rates of permafrost cliff retreat, coupled with spatial variability, have been accompanied by increased uncertainty over future landscape dynamics. We map long‐term (>80 years) retreat of the shoreline and photogrammetrically analyze historic aerial imagery to quantify the processes at a permafrost coast site with massive ground ice. Retreat rates have been relatively constant, but topographic changes show that subsidence is a potentially critical but often ignored component of coastal sensitivity, exceeding landward recession by over three times during the last 24 years. We calibrate novel passive seismic surveys along clear and variable exposures of massive ground ice and then spatially map key subsurface layers. Combining decadal patterns of volumetric change with new ground ice variation maps enables past trends to be interpreted, future volumetric geomorphic behavior to be better constrained, and improves the assessment of permafrost coast sensitivity and the release of carbon‐bearing material.
Highlights
Arctic permafrost is found on 34% of Earth's coasts (Lantuit et al, 2012) and is estimated to release 14 teragrams of particulate organic carbon to the nearshore zone each year, equivalent to the annual Arctic riverine inputs or vertical net methane emissions from terrestrial permafrost (Fritz et al, 2017)
The mapped positions of the shoreline at Peninsula Point reveal a relatively continuous retreat rate of 3.47 m a−1 since 1935 (Figure 1c). This rate is within the long‐term range (1 m–5 m a−1) for the area (Solomon, 2005) but lower than the 5 m a−1 rate for ice face retreat the site determined by French et al (1983) and significantly higher than rates from 1952 (0.5–1.3 m a−1) established to the west along the Yukon coastline (Lantuit & Pollard, 2008; Radosavljevic et al, 2016)
Massive ice collapse remains a critical but poorly quantified driver of ice rich permafrost coast erosion processes and as such is a threat to Arctic ecosystems, infrastructure, and biogeochemical cycles (O'Neill et al, 2019)
Summary
Arctic permafrost is found on 34% of Earth's coasts (Lantuit et al, 2012) and is estimated to release 14 teragrams of particulate organic carbon to the nearshore zone each year, equivalent to the annual Arctic riverine inputs or vertical net methane emissions from terrestrial permafrost (Fritz et al, 2017). Massive ice can have multiple forms and origins (Gilbert et al, 2016; Mackay, 1980) but can generally be defined as large bodies of ground ice where gravimetric moisture contents exceed 250% by weight (Pollard, 1990) This epigenetic volume expansion (formed within existing sediments as permafrost aggrades) typically results in uplift, altering local morphology and producing a landscape of domed. A sequence of volumetric changes shows that despite high rates of coastal erosion the area was dominated by the rapid collapse of a massive ice dome Within this context we use a passive seismic survey approach to map massive ice layers for the first time, to better understand and constrain the future evolution of the site and to assess the implications for improving estimates of organic, potentially carbon‐rich material release into the sea
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