Airborne Observations of Summer Thinning of Multiyear Sea Ice Originating From the Lincoln Sea

Abstract

To better understand recent changes of Arctic sea ice thickness and extent, it is important to distinguish between the contributions of winter growth and summer melt to the sea ice mass balance. In this study we present a Lagrangian approach to quantify summer sea ice melt in which multiyear ice (MYI) floes that were surveyed by airborne electromagnetic thickness sounding within Nares Strait during summer were backtracked, using satellite imagery, to a region in close proximity (3–20 km) to spring ice thickness surveys carried out in the Lincoln Sea. Typical modal total MYI thicknesses, including ~0.4‐m snow, ranged between 3.9 and 4.7 m in the Lincoln Sea during April. Ice‐only modal thicknesses were between 2.2 and 3.0 m in Nares Strait during August. Total thinning including snow and ice was 1.3 ± 0.1 m including 0.4 ± 0.09 m of snow melt and 0.9 ± 0.2 m of ice melt. This translates to a seasonal net heat input of 305 ± 69 MJ/m2 (262 ± 60 MJ/m2 for ice only) and seasonal net heat flux of 57 ± 13 W/m2 (45 ± 10 W/m2 for ice only), which is unlikely to be explained by solar radiation fluxes alone. Furthermore, our approach provides an improvement on traditional ice mass balance buoy estimates because it integrates melt over larger spatial scales, where melt can be highly variable due to differential melt experienced between melt ponds, bare ice, hummocks, and ridges.

Thermodynamic and dynamic contributions to seasonal Arctic sea ice thickness distributions from airborne observations

“…Because the surveys covered only a finite number of ridges, leads, and different ice types, we needed to ensure that the surveys were sufficiently long to represent the surrounding ice as well as possible. To test for adequate representation, we used the established criterion of the standard error that serves as a measure for the expected variability in a statistically homogeneous field (Wadhams, 1997;Rabenstein et al, 2010;Lange et al, 2019). We calculated the subsection length at which the standard error dropped below the 0.1-m measurement uncertainty of the EM instrument (Section 2.1.1) and compared it to the total survey length (Rabenstein et al, 2010).…”

“…Recently, satellite thicknesses retrievals added large-scale insights but generally lack observations in the melt season (e.g., Ricker et al, 2017;Kwok, 2018;Petty et al, 2020). Few airborne Lagrangian campaigns were carried out over the same ice, and only over periods of a few months at best (Itkin et al, 2018;Lange et al, 2019). Lagrangian studies conducted during longer drift stations were normally collected on foot and therefore the data lack information about very thin and thick ice (Untersteiner, 1961;Haas et al, 2011).…”

Large-Scale Variability of Physical and Biological Sea-Ice Properties in Polar Oceans

“…Ice thickness was computed by using a fixed density value (ρ = 0.917 g cm −3 ) for the sea ice. By doing this, final ice thickness values include both sea ice and snow, and we will refer to it as total thickness in the following (Lange et al, 2019). Mean and median thicknesses were computed for H i > 0 and they include ridges.…”

Multi-year spatial distribution of Antarctic sea ice (1988 - 2017)

“…Generally, multi-year ice refers to the sea ice that still exists after melting for at least one summer. In the present study also, we considered the sea ice existing after the melting season as the multi-year ice of that year (Lange et al 2019;Bi et al 2020). Hence, by determining the minimum sea-ice range for each year from 1987 to 2017, the annual average ice distribution during 1988 -2017 was obtained.…”