Abstract
Abstract. The meltwater scavenging coefficient (MSC) of black carbon (BC) is a crucial parameter in snow and sea ice models, as it determines the BC enrichment in the surface layer of melting snow over sea ice and therefore modulates the BC–snow–albedo feedbacks. We present a new method for MSC estimation by sampling the melt–refreeze ice layer that is produced from refreezing of the meltwater within snowpack and its overlying snow and measuring their physical characteristics in Elson Lagoon northeast of Utqiaġvik (formerly Barrow), Alaska, during the melting season. The bias of estimated MSC ranges from −5.4 % to 7.3 %, which is not exactly dependent on the degree of ablation. The average MSC value calculated with this proposed method is slightly lower than that derived from the repeating sampling (RS) method in Elson Lagoon while still being within its best estimate range. Further estimation demonstrates that the MSC in the Canada Basin (23.6 %±2.1 %) is close to that in Greenland (23.0 %±12.5 %) and larger than that in the Chukchi Sea (17.9 %±5.0 %) in the northwest of Utqiaġvik. Elson Lagoon has the lowest MSC (14.5 %±2.6 %) in the study areas. The method suggested in this study provides a possible approach for large-scale measurements of MSC over the sea ice area in the Arctic. Of course, this method depends on the presence of a melt–refreeze ice layer in the observation area.
Highlights
Black carbon (BC) is among the most efficient particulate species at absorbing visible light, which can reduce the surface albedo and potentially accelerate snowmelt (Flanner et al, 2007; Goldenson et al, 2012; Dou et al, 2012; 2017)
In present snow and sea ice models (e.g. Flanner et al, 2007; Goldenson et al, 2012; Holland et al, 2012), meltwater scavenging coefficient (MSC) is valued as a constant of 20 % and 3 % for hydrophilic BC and hydrophobic BC, respectively, which were derived from the observations conducted at Snow Dome (2050 m) of the mid-latitude Blue Glacier (Conway et al, 1996)
During the field measurements in Elson Lagoon in 2015, we recorded that the ice layer came into existence on 18 and 22 May, the early stage of the sea-ice melting season
Summary
Black carbon (BC) is among the most efficient particulate species at absorbing visible light, which can reduce the surface albedo and potentially accelerate snowmelt (Flanner et al, 2007; Goldenson et al, 2012; Dou et al, 2012; 2017). Significant uncertainties still exist in the sea ice region due to lack of field measurements and poor understanding of BC enrichment by overlying snowmelt. The MSC of BC was re-evaluated based on the field measurements in Elson Lagoon (Utqiagvik, formerly Barrow, Alaska) and at DYE-2 station (Greenland) during the melting season (Doherty et al, 2013). They suggested a rough range of 10 % to 30 % in the study area. After constraining the uncertainties of this new method, the estimated MSC is compared to those derived from the repeating sampling (RS) method in the same area; further, the spatial variability of MSC in the western Arctic will be discussed
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