Attenuation of Ocean Surface Waves in Pancake and Frazil Sea Ice Along the Coast of the Chukchi Sea

• Published in: Journal of geophysical research. Oceans Vol. 125; no. 12
• Main Authors: Hošeková, Lucia, Malila, Mika P., Rogers, W. Erick, Roach, Lettie A., Eidam, Emily, Rainville, Luc, Kumar, Nirnimesh, Thomson, Jim
• Format: Journal Article
• Language: English
• Published: 01.12.2020
• Subjects: Arctic; coastal; ocean waves; sea ice
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2020JC016746

Alaskan Arctic coastlines are protected seasonally from ocean waves by the presence of coastal and shorefast sea ice. This study presents field observations collected during the autumn 2019 freeze up near Icy Cape, a coastal headland in the Chukchi Sea of the Western Arctic. The evolution of the coupled air‐ice‐ocean‐wave system during a 4‐day wave event was monitored using drifting wave buoys, a cross‐shore mooring array, and ship‐based measurements. The incident wavefield with peak period of 2.5 s was attenuated by coastal pancake and frazil sea ice, reducing significant wave height by 40% over less than 5 km of cross‐shelf distance spanning water depths from 13 to 30 m. Spectral attenuation coefficients are evaluated with respect to wave and ice conditions and the proximity to the ice edge. Attenuation rates are found to be three times higher within 500 m of the ice edge, relative to values farther in the ice cover. Attenuation coefficients are in the range of 〈2.3, 2.7〉x10‐3 m−1, and follow a power‐law dependence on frequency. Plain Language Summary Changes in Arctic sea ice cover have consequences for coastal Alaskan regions. Relative to recent decades, nearshore sea ice now melts earlier and forms later in the year, exposing the coastlines to increased ocean wave energy and storm surges. Recent reports show that erosion along Arctic coasts is increasing and poses a threat to local habitats and human communities. This study aims to improve our understanding of the protective role of sea ice by measuring wave energy across the nearshore ice cover. Using drifting buoys deployed inside and outside fragmented sea ice, we monitored ocean waves during an autumn storm event typical for coastal regions in the Chukchi Sea. We found that the wave heights were reduced by 40% over 5 km distance, and the effects of this type of ice on waves were consistent with previous studies. Thanks to the high resolution of our measurements, we were able to determine that the dampening effect was stronger immediately next to the ice edge. Our measurements may be applied to improve present and future operational and climate models used to forecast and understand wave activity near the Arctic coasts. Key Points Buoy observations are used to calculate spectral attenuation rates of surface waves in pancake and frazil sea ice near the coast of Alaska Consistently higher attenuation is observed near the ice edge than further in the ice cover Attenuation rates follow a power‐law dependence on frequency and are applicable to parametrization schemes in wave forecast models