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Narrowing 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 erosion. Different terrain units are assessed based on surficial geology, morphology, and ground ice conditions. To account for the volume of wedge ice and massive ice in a unit, sample SOC contents are reduced by 19% and sediment contents by 16%. The SOC content in a 1 m**2 column of soil varies 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 is within the top 1 m of soil and values vary based on surficial materials, ranging from 30 to 53 kg C/m**3, with a mean of 41 kg. Eighty per cent of the shoreline is erosive with a mean annual rate of change is 0.7 m/a. This results in a SOC flux per meter of shoreline of 131 kg C/m/a, and a total flux for the entire Yukon coast of 35.5 10**6 kg C/a (0.036 Tg C/a). The mean flux of sediment per meter of shoreline is 5.3 10**3 kg/m/a, with a total flux of 1,832.0 10**6 kg/a (1.832 Tg/a). Sedimentation rates indicate that approximately 13% of the eroded carbon is sequestered in nearshore sediments, where the overwhelming majority of organic carbon is of terrestrial origin.

Helicopter-borne laser profiling of sea ice surface roughnessLaser profiler measurements were performed during the CCGS Henry Larsen cruise: Canadian Arctic Through flow (CATs) 2009 cruise to Nares Strait. Airborne surveys were conducted on August 16, 18 and 19, 2009.A laser was mounted on a helicopter pointing vertically downwards to measure the altitude above the ice surface which nominally was 30 m. Depending on flight speed, the spatial sampling interval ranged between 0.02 and 0.15 m. Positioning of the profiles was performed by means of a Global Positioning System (GPS).After eye inspection of the data and removal of outliers, the low frequency helicopter motion is eleminated from the data using a multiple filter procedure described by Hibler (1972, doi:10.1029/JC077i036p07190), Dierking (1995, doi:10.1029/94JC01938), and Haas et al. (1998, doi:10.1016/S0165-232X(97)00019-0). It takes advantage of the fact that the helicopter height variations are only at low frequencies, whereas the surface roughness is a superimposed, high frequency signal. The resulting ice morphology is obtained relative to the surface of the surrounding level ice. Absolute freeboard, i.e. the height of the surface above the water level, cannot be obtained unless the helicopter height variations are independently determined by means of differential GPS and Inertial navigation systems. The resulting surface profiles can be used to identify pressure ridges, e.g. by a Rayleigh criterion. By this criterion only local maxima which are twice as high as the surrounding local minima are defined as pressure ridges.