Abstract
Sea ice albedo is an important component of the Earth’s climate and is affected by low background concentrations of oil droplets within the ice matrix that absorb solar radiation. In this study the albedo response of three different types of sea ice (multi-year, first-year, and melting sea ice) are calculated at increasing mass ratios (0–1000 ng g−1) of crude oil by using a coupled atmosphere-sea ice radiative-transfer model (TUV-snow) over the optical wavelengths 400–700 nm. The different types of quasi-infinite thickness sea ice exhibit different albedo responses to oil pollution, with a 1000 ng g−1 mass ratio of oil causing a decrease to 70.9 % in multi-year sea ice, 47.9 % in first-year sea ice, and 22 % in melting sea ice relative to the unpolluted albedo at a wavelength of 400 nm. The thickness of the sea ice is also an important factor, with realistic thickness sea ices exhibiting similar results, albeit with a weaker albedo response for multi-year sea ice to 75.3 %, first-year sea ice to 66.7 %, and melting sea ice to 35.7 %. The type of oil also plays a significant role on the response of sea ice albedo, with a relatively opaque and heavy crude oil (Romashkino oil) causing a significantly larger decrease in sea ice albedo than a relatively transparent light crude oil (Petrobaltic oil). The size of the oil droplets polluting the oil also plays a minor role in the albedo response, with weathered submicron droplets (0.05–0.5 µm radius) of Romashkino oil being the most absorbing across the optical wavelengths considered. Therefore, the work presented here demonstrates that low background concentrations of small submicron to micron-sized oil droplets have a significant effect on sea ice albedo. All three types of sea ice are affected, however first-year sea ice and particularly melting sea ice are very sensitive to oil pollution; thus, the Arctic may become more vulnerable to oil pollution as the ice becomes progressively thinner and younger in response to a changing climate.
Highlights
10 of quasi-infinite thickness sea ice exhibit different albedo responses to oil pollution, with a 1000 ng g-1 mass ratio of oil causing a decrease to 70.9% in multi-year sea ice, 47.9% in first-year sea ice, and 22% in melting sea ice relative to the unpolluted albedo at a wavelength of 400 nm
The results are separated into five sections: how the type of oil and increasing mass ratios of oil effect quasi-infinite sea ice albedo, the sensitivity of each type of quasi-infinite sea ice to increasing oil, the effect of droplet size distribution on quasi-infinite sea ice albedo, the impact that increasing background mass ratios of black carbon have on the further reduction of quasi-infinite sea ice albedo by oil, and the effect oil has on each type of realistic thickness sea ice
The albedo response is dependent on the type of oil, with the relatively light absorbing Romashkino oil having the largest effect owing to its large mass absorption coefficient
Summary
Arctic sea ice has significantly declined from its 1981–2010 spring and summer averages, both in extent and thickness of sea ice cover (Fetterer et al, 2017). The summer sea ice minimum has decreased 13.1% per decade from the 1981–2010 average, with an average extent of 6.85 million km in 1979–1992 compared to an average extent of 4.44 million km from 2007–2020 (Thoman et al, 2020). Perennial sea 30 ice cover decline is between 12.2% and 13.5% for first-year sea ice, and 15.6% and 17.5% for multiyear sea ice per decade, respectively (Comiso, 2012; Tschudi et al, 2019). It is very likely that an ice-free Arctic Ocean, a so called ‘Blue Ocean Event’, will be realised by the mid-century unless there is a rapid reduction in greenhouse gas emissions (Notz and Stroeve, 2018).
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