Surface topography

The surface topography (elevation of ice or snow surface above sea level or a reference water level, depth of melt ponds) has been determined along two profiles at regular time intervals (roughly once every 10 days) during the ablation season in 1998. Profile 1 was located in level second-year ice parallel to the ocean hut line towards Sediment City. Profile 2 was located in deformed multi-year ice extending at a right angle from The Pass (through the active ridge separating the Des Groseilliers from the location of the main camp) towards the logistics huts. At the endpoints of both profiles, marker poles had been installed and the profile itself was left undisturbed during the entire time period (no drilling of holes, no foot or vehicle traffic except for measurements). The maximum co-location error between measurement points along the profile at different time intervals is estimated at <0.5 m along-profile and <2 m across-profile. 

Pond depth measurements were carried out with a meterstick (error <10 mm). Surface elevation of the ice or pond surface was determined with a laser levelling device (maximum error <10 mm). Surface elevation has been measured relative to the water level in core holes or ponds in communication with the free water column (data have not been corrected for density structure of water column in hole or pond). For the data compilation, no effort has been made to distinguish between melting snow and melting ice surfaces. Stable-isotope data indicate, however, that only traces of snow were present along the profiles after day 175, and surface elevation data collected after this date reflect the elevation of the ablating ice surface relative to the reference water level.

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