The thickness distribution of sea ice and snow cover during late winter in the Bellingshausen and Amundsen Seas, Antarctica

Abstract

Data collected from a voyage of RV Nathaniel B. Palmer to the Bellingshausen and Amundsen Seas during August–September 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first‐year pack ice. The data are a combination of in situ and ship‐based measurements and show that the process of floe thickening is highly dependent on ice deformation; in particular, rafting and ridging play important roles at different stages of floe development. Rafting is the major mechanism in the early stages of development, and core structure data show the mean thickness of individual layers of crystals to be only 0.12 m. Most ice <0.3 m is not ridged but is usually rafted before attaining this thickness, well before thermodynamic growth has ceased. In thicker floes, ridging is more common, with most floes >0.6 m having some surface deformation. Blocks within ridge sails are typically in the range 0.3–0.6 m thick, and ship‐based observations estimate approximately 25% of the pack exhibits surface ridging. When corrected for biases in the observational methods, the data show that the dominant ice and snow thickness categories are >0.7 m and 0.2–0.5 m, respectively, and account for 40% and 36% of the surface area of the pack ice. Approximately 8% of the pack is open water. An estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75% of the total mass is contained within the 25% of the pack that exhibits surface ridging.

Glacial meltwater dynamics in coastal waters west of the Antarctic peninsula

“…We can conduct a simple mass balance calculation of the surface salinity that would result from melting of a typical layer of sea ice. For the Western Antarctic Peninsula region, the sea ice thickness varies from 0.5 to 1 m, the salinity from 3 to 15 psu, and the resulting bulk sea ice density ranges from 0.6 to 0.9 g/cm 3 depending on the amount of voids within the ice and the amount of unconsolidated snow (29,30). If we assume an initial water column salinity of 34, water temperature of 0°C, and a mixing within the top 50 m of water (Fig.…”

Winter snow cover variability on East Antarctic sea ice

“…In the outer pack, floe-floe jostling and wave overwashing cause wide-scale flooding of the snow and ice surface and even complete removal of the snow. Wave overwashing may also be significant adjacent to leads and polynyas and as such may affect a large proportion of the East Antarctic pack due to its largely divergent behavior [Worby et al, 1996a]. In the process of brash ice formation, ice and snow become pulverized to form a conglomeration of floe fragments and interstitial brash (Figure 12b).…”

Role of sea ice in global biogeochemical cycles: emerging views and challenges

“…Because the long-term ice retreat is more pronounced in summer than in winter [see, e.g., Deser and Teng, 2008], the amplitude of the seasonal cycle of Arctic sea ice extent has been increasing, which means that the total annual sea ice growth and melt has been increasing and should continue to increase in the future [e.g., Holland et al, 2006]. In the Southern Ocean, observations and models indicate that ice formation mechanisms are more diverse than in the Arctic: congelation, frazil ice and snow-ice formation all contribute significantly [Worby et al, 1996;Jeffries et al, 1997;Vancoppenolle et al, 2009b]. The direct exposure of the Southern Ocean sea ice pack to ocean swell results in a higher contribution of frazil ice than in the Arctic, associated with so-called pancake ice formation [Lange et al, 1989].…”