Snow-ice contribution to the structure of sea ice in the Amundsen Sea, Antarctica

Abstract

The widespread occurrence of snow-ice formation on the pack ice plays a critical role in the mass balance of Antarctic sea ice. The stable isotope composition, ice texture and salinity of eight ice cores, obtained from the Amundsen Sea during the Oden Southern Ocean 2010/11 expedition from late December 2010 to January 2011, were investigated to illustrate the snow-ice growth process and its contribution to sea-ice development. Most previous research has utilized δ18O as an index tracer to determine the percentages of core length that contain meteoric water, i.e. snow ice. However, this standard practice of snow-ice identification might be biased due to normally low-resolution isotopic measurements and mixing/diffusion processes between the snow ice and underlying ice layers. Snow-ice contributions in these ice cores based instead on an updated isotope mixing model are also presented. Depth profiles of ice texture and salinity are described to serve as representations of the structures of these ice cores. Our isotope mixing model produced an average of 15.9% snow-ice contribution for pack ice in the Amundsen Sea, and meteoric water occupying 40% of snow-ice mass for all ice stations. These results are compared to previous investigations of snow-ice occurrence around Antarctica.

Recent observations of superimposed ice and snow ice on sea ice in the northwestern Weddell Sea

“…However, the mean superimposed ice thickness of 0.11 ± 0.11 m observed in February and March 2019 is similar to the 0.08 ± 0.06 m found by Haas et al (2001) in February 1997 in the same region. It is slightly larger than the 0.05 to 0.10 m found by Nicolaus et al (2009) and Tison et al (2008) in December 2004 in the ISPOL region slightly earlier and further south and in a year with no exceptional February ice extent (Fig. 5a).…”

“…In contrast, snow ice mostly forms during winter when seawater flooding of the snow-ice interface occurs where the ice has negative freeboard, i.e., when its surface is below the water level. This occurs when the snow depth approaches or exceeds approximately one-third of the ice thickness, which is frequently observed on Antarctic sea ice due to its relatively thin ice and typically thick snow cover (Eicken et al, 1994;Jeffries et al, 1997Jeffries et al, , 2001Tian et al, 2020). Snow ice thus forms from the refreezing of seawater-soaked snow, is therefore fine-grained and saline, and has δ 18 O oxygen isotope concentrations between those of superimposed ice and sea ice (e.g., Eicken, 1998;Granskog et al, 2017).…”

Recent observations of superimposed ice and snow ice on sea ice in the northwestern Weddell Sea

“…when its surface is below the water level. This occurs when the snow depth approaches or exceeds approximately one-third of the ice thickness, which is frequently observed on Antarctic sea ice due to its relatively thin ice and typically thick snow cover (Eicken et al, 1994;Jeffries et al, 2001;Jeffries et al, 1997;Tian et al, 2020). Snow ice thus forms from the refreezing of seawater-soaked snow, and is therefore fine-grained and saline, and has 18 O oxygen isotope concentrations between those of superimposed ice and sea ice (e.g., Eicken, 1998;Granskog et al, 2017).…”

Snow Loss into Leads in Arctic Sea Ice: Minimal in Typical Wintertime Conditions, but High During a Warm and Windy Snowfall Event

“…Here, we present the first measurements of snow loss into Arctic leads from four cases we observed in detail in winter 2020 in the Atlantic sector of the Central Arctic Ocean. Snow loss into leads was determined from the δ 18 O of the lead ice, a signature routinely used to identify snow contributions to sea ice (Jeffries et al, 1994(Jeffries et al, , 2001Kawamura et al, 2001;Granskog et al, 2003Granskog et al, , 2004Tian et al, 2020;Arndt et al, 2021). When snow enters seawater in a lead, the snow is less dense than seawater and consequently floats at the surface.…”