Sea-ice thickness on the northern Canadian polar shelf: A second look after 40 years

Abstract. This paper presents a systematic record of multi-year sea-ice thickness on the northern Canadian polar shelf, acquired during the winter of 2009–10. The data were acquired by submerged sonar positioned within Penny Strait where they measured floes drifting south from the notional “last ice area”. Ice was moving over the site until 10 December and fast thereafter. Old ice comprised about half of the 1669-km long survey. The average old-ice thickness within 25-km segments of the survey track was 3–4 m; maximum keels were 12–16 m deep. Floes with high average draft were of two types, one with interspersed low draft intervals and one without. The presence or absence of thin patches apparently distinguished aggregate floes comprised of sub-units of various ages and deformation states from units of more homogeneous age and deformation state. The former were larger and of somewhat lower mean thickness (1–5 km; 3.5–4.5 m) than the latter (400–600 m; 6.5–14 m). Calculated ice accretion onto the multi-year ice measured in autumn 2009 was used to seasonally adjust the observations to a date in late winter, when prior data are available. The adjusted mean thickness for all 25-km segments with 4 tenths or more old ice was 3.6 m (sample deviation of 0.4 m), a value indistinguishable within sampling error from values measured in the same area during the 1970s. The recently measured ice-draft distributions were also very similar to those from the 1970s.