Fast Ice Thickness Distribution in the Western Ross Sea in Late Spring

Abstract

We present a 700 km airborne electromagnetic survey of late‐spring fast ice and sub‐ice platelet layer (SIPL) thickness distributions from McMurdo Sound to Cape Adare, providing a first‐time inventory of fast ice thickness close to its annual maximum. The overall mode of the consolidated ice (including snow) thickness was 1.9 m, less than its mean of 2.6 ± 1.0 m. Our survey was partitioned into level and rough ice, and SIPL thickness was estimated under level ice. Although level ice, with a mode of 2.0 m and mean of 2.0 ± 0.6 m, was prevalent, rough ice occupied 41% of the transect by length, 50% by volume, and had a mode of 3.3 m and mean of 3.2 ± 1.2 m. The thickest 10% of rough ice was almost 6 m on average, inclusive of a 2 km segment thicker than 8 m in Moubray Bay. The thickest ice occurred predominantly along the northwestern Ross Sea, due to compaction against the coast. The adjacent pack ice was thinner (by ∼1 m) than the first‐year fast ice. In Silverfish Bay, offshore Hells Gate Ice Shelf, New Harbor, and Granite Harbor, the SIPL transect volume was a significant fraction (0.30) of the consolidated ice volume. The thickest 10% of SIPLs averaged nearly 3 m thick, and near Hells Gate Ice Shelf the SIPL was almost 10 m thick, implying vigorous heat loss to the ocean (∼90 W m−2). We conclude that polynya‐induced ice deformation and interaction with continental ice influence fast ice thickness in the western Ross Sea.

Antarctic Landfast Sea Ice: A Review of Its Physics, Biogeochemistry and Ecology

“…Giles et al (2008) estimate using remote sensing that 33% of the area of East Antarctic fast ice in 1997-1999 was rough, indicating that deformation is a major determinant of overall fast-ice volume (assuming their estimated values of 1.7 and 5.0 m for smooth and rough fast ice, respectively), and providing strong rationale for studies of rough fast ice to be prioritized. Recently Langhorne et al (2023) confirmed the pervasiveness of deformed fast ice in the western Ross Sea where rough ice occupied 50% of the volume of a 700 km airborne electromagnetic (AEM) thickness transect. The rough ice had a modal thickness of 3.3 m, while the level ice was 2.0 m. Near Inexpressible Island in the Ross Sea (163.7°E, 74.9°S), the dynamic formation of rough fast ice up to 3-4 m thick was observed after pack ice was blown into a small bay after almost 3 days of persistent onshore winds (Zhai et al, 2019).…”

“…Recently Langhorne et al. (2023) confirmed the pervasiveness of deformed fast ice in the western Ross Sea where rough ice occupied 50% of the volume of a 700 km airborne electromagnetic (AEM) thickness transect. The rough ice had a modal thickness of 3.3 m, while the level ice was 2.0 m. Near Inexpressible Island in the Ross Sea (163.7°E, 74.9°S), the dynamic formation of rough fast ice up to 3–4 m thick was observed after pack ice was blown into a small bay after almost 3 days of persistent onshore winds (Zhai et al., 2019).…”

“…Moreover, Haas et al (2021) recently demonstrated the ability of AEM to measure both the thicknesses of fast ice and the unconsolidated SIPL beneath. The technique has been used in McMurdo Sound (Haas et al, 2021), and on a transect covering ∼700 km of springtime fast ice along the Victoria Land coast (∼165°E, 75°S) in the western Ross Sea (Langhorne et al, 2023).…”

Ice Shelf Water-influenced Fast Ice and Sub-Ice Platelet Layer Thickness Distributions beside the Campbell Ice Tongue in Terra Nova Bay, Antarctica

“…In north Terra Nova Bay, marine ice (Souchez et al, 1995) and basal freezing (Han and Lee, 2015) occur beneath the Campbell Ice Tongue (Figure 1). Beneath adjoining fast ice, a SIPL was detected in biological studies in late spring of 2002, 2005, and 2006(Vacchi et al, 2004 and in AEM surveys in late spring of 2017 (Langhorne et al, 2023). The presence of marine ice and SIPL signal that in situ supercooled ISW is circulating in the region, which the AEM surveys indicated could be locally sourced from the ice tongue (Langhorne et al, 2023).…”

“…South of the Drygalski Ice Tongue, platelet ice was observed in a sea ice core (Jeffries and Weeks, 1993) and beneath fast ice (Stevens et al, 2017). The edge of Hells Gate Ice Shelf is comprised entirely of marine ice (Souchez et al, 1991), with thick frazil and platelet ice layers observed beneath the ice shelf (Tison et al, 1993, Souchez et al, 1991, and adjoining fast ice (Langhorne et al, 2023;Tison et al, 1998). An extensive airborne electromagnetic induction (AEM) survey of fast ice along the Victoria Land Coastline identified that smaller ice bodies including ice tongues and marine-manuscript submitted to Journal of Geophysical Research: Oceans terminating outlet glaciers also contribute to the formation of in situ supercooled ISW and platelet ice in the western Ross Sea (Langhorne et al, 2023).…”