Coastal Erosion of Permafrost Soils Along the Yukon Coastal Plain and Fluxes of Organic Carbon to the Canadian Beaufort Sea

Abstract

Reducing uncertainties about carbon cycling is important in the Arctic where rapid environmental changes contribute to enhanced mobilization of carbon. Here we quantify soil organic carbon (SOC) contents of permafrost soils along the Yukon Coastal Plain and determine the annual fluxes from coastal erosion. Different terrain units were assessed based on surficial geology, morphology, and ground ice conditions. To account for the volume of wedge ice and massive ice in a unit, SOC contents were reduced by 19% and sediment contents by 16%. The SOC content in a 1 m2 column of soil varied according to the height of the bluff, ranging from 30 to 662 kg, with a mean value of 183 kg. Forty‐four per cent of the SOC was within the top 1 m of soil and values varied based on surficial materials, ranging from 30 to 53 kg C/m3, with a mean of 41 kg. Eighty per cent of the shoreline was erosive with a mean annual rate of change of −0.7 m/yr. This resulted in a SOC flux per meter of shoreline of 132 kg C/m/yr, and a total flux for the entire 282 km of the Yukon coast of 35.5 × 106 kg C/yr (0.036 Tg C/yr). The mean flux of sediment per meter of shoreline was 5.3 × 103 kg/m/yr, with a total flux of 1,832 × 106 kg/yr (1.832 Tg/yr). Sedimentation rates indicate that approximately 13% of the eroded carbon was sequestered in nearshore sediments, where the overwhelming majority of organic carbon was of terrestrial origin.

Rapid CO2 Release From Eroding Permafrost in Seawater

“…We show that a fraction of eroded permafrost OC is quickly mineralized into CO 2 , with or without seawater added, indicating potential CO 2 release to the atmosphere during coastal erosion. This corresponds with findings from Siberia that showed extensive outgassing of CO 2 from the coastal zone and oversaturated CO 2 conditions in coastal waters, potentially as a result of OC mineralization from terrestrial sources (Semiletov et al, ) or studies from the Yukon Coast, which show that only ~13% of eroded OC is sequestered in nearshore sediments with the remainder being potentially available for turnover processes (Couture et al, ).…”

“…that only~13% of eroded OC is sequestered in nearshore sediments with the remainder being potentially available for turnover processes (Couture et al, 2018).…”

“…Permafrost coasts make up approximately 34% of the Earth's total coastline (Lantuit et al, 2012). Erosion of these coasts releases large amounts of permafrost OC directly into the Arctic Ocean (Couture et al, 2018; ©2019. The Authors.…”

Long-Term High-Resolution Sediment and Sea Surface Temperature Spatial Patterns in Arctic Nearshore Waters Retrieved Using 30-Year Landsat Archive Imagery

“…The focus of this study is on the Beaufort Sea inner shelf waters around HIQ (69°36′ N; 139°04′ W, Figure 1). The study area was chosen because of its close proximity to the Mackenzie Delta, the presence of a strongly eroding coast [22,24,25], and changing hydrodynamics of the Mackenzie River outflow [9]. HIQ is located on the Canadian Beaufort Shelf, which covers less than 2% of the Artic coast shelf area (~64 000 km 2 ) and which is narrow (~100 km) compared to the Eurasian shelves [26,27].…”

A decade of remotely sensed observations highlight complex processes linked to coastal permafrost bluff erosion in the Arctic

“…Ongoing and anticipated changes in the Arctic System such as reductions in sea ice extent (Perovich et al 2017), rising air (Overland et al 2017) and sea surface temperatures (SSTs) (Steele and Dickinson 2016), relative sea-level rise (Richter-Menge et al 2011), warming permafrost (Romanovsky et al 2010, and increased storminess (Simmonds and Rudeva 2012) involving more frequent storm surges (Vermaire et al 2013) may all interact to amplify arctic coastal dynamics (AMAP 2017). Changes in the Arctic System will likely increase the vulnerability of these coasts to erosion and alter coastal morphologies, ecosystems, carbon export to oceans, infrastructure, and human subsistence lifestyles (Arp et al 2010, Radosavljevic et al 2016, Obu et al 2017, Couture et al 2018, Farquharson et al 2018b.…”