Hydrometeorological forcing of coastal dynamics in the Russian Arctic: link to erosion rates in the last decades

Abstract:

Coasts in the Russian Arctic are extremely vulnerable to the ongoing environmental changes. Temporal evolution of their retreat rates is driven by hydrometeorological processes. Permafrost of the coastal bluffs rapidly thaws under the influence of air and water temperature increase. Along with that, sea ice decline results in wave energy increase because of longer wave fetch and ice-free period when the waves are able to erode the unprotected coasts. The combined thermal and wave action is defined as hydrometeorological forcing of coastal erosion.

We estimated temporal variability of the air thawing index (sum of annual positive temperatures) reflecting the thermal factor, and the wind-wave energy flux since the 1970s for five sites in both the western and eastern Russian Arctic where observations of coastal erosion rates derived from both field measurements and remotely sensed data are available: Varandey (Pechora Sea), Yamal and Ural coasts of the Baydaratskaya Bay (Kara Sea), Cape Chukochiy (East Siberian Sea) and Lorino (Bering Sea). We further calculated the total hydrometeorological forcing of coastal erosion for the periods with known retreat rates and compared the temporal variability of the two parameters.

Comparison of the hydrometeorological forcing shows a link between erosion rates and the hydrometeorological forcing in all the areas. The best correlation is noted for sites where remotely sensed data for relatively long periods were analyzed. For areas with more frequent direct field observations, the variability of the two parameters shows more differences. Such findings imply that while long-term erosion rates are determined by general trends of climate and sea ice extent change in the Arctic seas, coastal retreat in one single year can be driven by local factors, such as lake drainage, random failure of large blocks or peat lenses, exposure and burial of ice bodies, and other reasons. Therefore estimation of mechanisms and trends of coastal erosion in the Russian Arctic should be made based on average retreat rates over relatively long timescales (several years or even decades).

Studies were funded by the RFBR grant 18-05-60300. B.Jones was supported by US National Science Foundation award OISE- 1927553.