scholarly journals Physical Processes determining the Antarctic Sea Ice Environment

1997 ◽  
Vol 50 (4) ◽  
pp. 759 ◽  
Author(s):  
Ian Allison
Keyword(s):  
Sea Ice ◽  
Thickness Distribution ◽  
Arctic Basin ◽  
Open Water ◽  
Ice Cover ◽  
Dynamic Processes ◽  
Surface Absorption ◽  
Antarctic Sea Ice ◽  
Ocean Atmosphere ◽  
The Antarctic

The Antarctic sea ice zone undergoes one of the greatest seasonal surface changes on Earth, with an annual change in extent of around 15 × 10 6 km 2 . This ice, and its associated snow cover, plays a number of important roles in the ocean-atmosphere climate system: the high albedo ice cover restricts surface absorption of solar radiation and acts as a barrier to the exchange of mass and energy between the ocean and atmosphere, and salt rejected by the growing ice cover affects the ocean structure and circulation. Additionally, a number of sea ice feedback processes have the potential to play an important role in climate change. The extent to which a sea ice cover modifies ocean-atmosphere interaction is primarily determined by the thickness and concentration of the ice, but these themselves are determined by ocean and atmospheric interaction. The thickness distribution of the pack is determined by both thermodynamic and dynamic processes: most important at the geophysical scale are the dynamic processes of ice drift and deformation, and of lead formation. Compared to the ice cover in the central Arctic Basin, the Antarctic sea ice is highly mobile. Drifting buoy studies show that the Antarctic pack can move at speeds of up to 60 km per day or greater, and that around most of the Antarctic coast, the drift of the pack ice is generally divergent, with divergence rates of 10% or more per day being observed under some circumstances. Consequently there is generally some open water within the Antarctic pack and much of the total ice mass forms by rapid growth within these areas. This influences the crystal structure of the ice and results in a considerable portion of the Antarctic pack (up to 25% in spring-time) having a thickness of less than 0 · 3 m. In general much of the Antarctic sea ice only grows thermodynamically to about 0·5 m thick, with thickness increases beyond that resulting from the deformational processes of rafting and ridge-building.

scholarly journals Seasonal Variations In The Surface Energy Exchanges Over Antarctic Sea Ice and Coastal Waters

1982 ◽  
Vol 3 ◽  
pp. 12-16 ◽  
Author(s):  
I. Allison ◽  
C.M. Tivendale ◽  
G.J. Akerman ◽  
J.M. Tann ◽  
R.H. Wills
Keyword(s):  
Heat Transfer ◽  
Sea Ice ◽  
Seasonal Variations ◽  
Lower Boundary ◽  
Open Water ◽  
Ice Cover ◽  
Turbulent Fluxes ◽  
Turbulent Heat ◽  
Radiative Heat Loss ◽  
Antarctic Sea Ice

Seasonal variations in radiative and turbulent fluxes at the surface of, and in the heat transfer within, sea ice are discussed from results of energy balance studies at a site of annual ice cover near Mawson, Antarctica. In mid-summer, the open water gains heat mostly by radiation but by early February the ocean is cooling predominantly by strong turbulent losses, with some radiative heat loss occurring also by March. When an ice cover forms, turbulent fluxes decrease from several 100 W m−2over open water to only 40 w m−2over ice less than 0.2 m thick and even less over thicker ice.Net radiative losses over mature ice in mid-winter are balanced mostly by conduction through the ice cover but with some turbulent heat gain at the surface. By mid-spring, there is a net radiative gain, the turbulent fluxes are again outgoing, and there is little total heat transfer through the ice. At break-out, the albedo increase from ice to open water causes a large increase in the net radiative gain.At the lower boundary of the ice, the oceanic heat flux provides an important contribution. A net advection of heat into the region is shown from temperature profiles in the water under the ice. Salinity changes in the water during the period of ice melt are also discussed.

scholarly journals Surface Albedo of the Antarctic Sea Ice Zone

2005 ◽  
Vol 18 (17) ◽  
pp. 3606-3622 ◽  
Author(s):  
Richard E. Brandt ◽  
Stephen G. Warren ◽  
Anthony P. Worby ◽  
Thomas C. Grenfell
Keyword(s):  
Sea Ice ◽  
Surface Albedo ◽  
Near Infrared ◽  
Field Experiments ◽  
Climate Models ◽  
Solar Spectrum ◽  
Open Water ◽  
Visual Observation ◽  
Antarctic Sea Ice ◽  
The Antarctic

Abstract In three ship-based field experiments, spectral albedos were measured at ultraviolet, visible, and near-infrared wavelengths for open water, grease ice, nilas, young “grey” ice, young grey-white ice, and first-year ice, both with and without snow cover. From the spectral measurements, broadband albedos are computed for clear and cloudy sky, for the total solar spectrum as well as for visible and near-infrared bands used in climate models, and for Advanced Very High Resolution Radiometer (AVHRR) solar channels. The all-wave albedos vary from 0.07 for open water to 0.87 for thick snow-covered ice under cloud. The frequency distribution of ice types and snow coverage in all seasons is available from the project on Antarctic Sea Ice Processes and Climate (ASPeCt). The ASPeCt dataset contains routine hourly visual observations of sea ice from research and supply ships of several nations using a standard protocol. Ten thousand of these observations, separated by a minimum of 6 nautical miles along voyage tracks, are used together with the measured albedos for each ice type to assign an albedo to each visual observation, resulting in “ice-only” albedos as a function of latitude for each of five longitudinal sectors around Antarctica, for each of the four seasons. These ice albedos are combined with 13 yr of ice concentration estimates from satellite passive microwave measurements to obtain the geographical and seasonal variation of average surface albedo. Most of the Antarctic sea ice is snow covered, even in summer, so the main determinant of area-averaged albedo is the fraction of open water within the pack.

scholarly journals Positive Trend in the Antarctic Sea Ice Cover and Associated Changes in Surface Temperature

2017 ◽  
Vol 30 (6) ◽  
pp. 2251-2267 ◽  
Author(s):  
Josefino C. Comiso ◽  
Robert A. Gersten ◽  
Larry V. Stock ◽  
John Turner ◽  
Gay J. Perez ◽  
...  
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Climate Models ◽  
Ice Cover ◽  
Southern Annular Mode ◽  
Positive Trend ◽  
Growth Season ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
The Antarctic

Abstract The Antarctic sea ice extent has been slowly increasing contrary to expected trends due to global warming and results from coupled climate models. After a record high extent in 2012 the extent was even higher in 2014 when the magnitude exceeded 20 × 106 km2 for the first time during the satellite era. The positive trend is confirmed with newly reprocessed sea ice data that addressed inconsistency issues in the time series. The variability in sea ice extent and ice area was studied alongside surface ice temperature for the 34-yr period starting in 1981, and the results of the analysis show a strong correlation of −0.94 during the growth season and −0.86 during the melt season. The correlation coefficients are even stronger with a one-month lag in surface temperature at −0.96 during the growth season and −0.98 during the melt season, suggesting that the trend in sea ice cover is strongly influenced by the trend in surface temperature. The correlation with atmospheric circulation as represented by the southern annular mode (SAM) index appears to be relatively weak. A case study comparing the record high in 2014 with a relatively low ice extent in 2015 also shows strong sensitivity to changes in surface temperature. The results suggest that the positive trend is a consequence of the spatial variability of global trends in surface temperature and that the ability of current climate models to forecast sea ice trend can be improved through better performance in reproducing observed surface temperatures in the Antarctic region.

scholarly journals A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated?

2014 ◽  
Vol 8 (4) ◽  
pp. 1289-1296 ◽  
Author(s):  
I. Eisenman ◽  
W. N. Meier ◽  
J. R. Norris
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
Current Data ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Data Set ◽  
Antarctic Sea Ice ◽  
Ice Retreat ◽  
Bootstrap Algorithm ◽  
The Antarctic

Abstract. Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one-third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably smaller and statistically indistinguishable from zero. Here, we show that much of the increase in the reported trend occurred due to the previously undocumented effect of a change in the way the satellite sea ice observations are processed for the widely used Bootstrap algorithm data set, rather than a physical increase in the rate of ice advance. Specifically, we find that a change in the intercalibration across a 1991 sensor transition when the data set was reprocessed in 2007 caused a substantial change in the long-term trend. Although our analysis does not definitively identify whether this change introduced an error or removed one, the resulting difference in the trends suggests that a substantial error exists in either the current data set or the version that was used prior to the mid-2000s, and numerous studies that have relied on these observations should be reexamined to determine the sensitivity of their results to this change in the data set. Furthermore, a number of recent studies have investigated physical mechanisms for the observed expansion of the Antarctic sea ice cover. The results of this analysis raise the possibility that much of this expansion may be a spurious artifact of an error in the processing of the satellite observations.

scholarly journals A late spring surge in the open water of the Antarctic sea ice pack

1999 ◽  
Vol 26 (10) ◽  
pp. 1481-1484 ◽  
Author(s):  
Andrew B. Watkins ◽  
Ian Simmonds
Keyword(s):  
Sea Ice ◽  
Open Water ◽  
Late Spring ◽  
Antarctic Sea Ice ◽  
The Antarctic ◽  
Ice Pack

scholarly journals A 40-y record reveals gradual Antarctic sea ice increases followed by decreases at rates far exceeding the rates seen in the Arctic

2019 ◽  
Vol 116 (29) ◽  
pp. 14414-14423 ◽  
Author(s):  
Claire L. Parkinson
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Antarctic Sea Ice ◽  
Ice Coverage ◽  
Yearly Average ◽  
Precipitous Decline ◽  
The One ◽  
The Antarctic

Following over 3 decades of gradual but uneven increases in sea ice coverage, the yearly average Antarctic sea ice extents reached a record high of 12.8 × 106 km2 in 2014, followed by a decline so precipitous that they reached their lowest value in the 40-y 1979–2018 satellite multichannel passive-microwave record, 10.7 × 106 km2, in 2017. In contrast, it took the Arctic sea ice cover a full 3 decades to register a loss that great in yearly average ice extents. Still, when considering the 40-y record as a whole, the Antarctic sea ice continues to have a positive overall trend in yearly average ice extents, although at 11,300 ± 5,300 km2⋅y−1, this trend is only 50% of the trend for 1979–2014, before the precipitous decline. Four of the 5 sectors into which the Antarctic sea ice cover is divided all also have 40-y positive trends that are well reduced from their 2014–2017 values. The one anomalous sector in this regard, the Bellingshausen/Amundsen Seas, has a 40-y negative trend, with the yearly average ice extents decreasing overall in the first 3 decades, reaching a minimum in 2007, and exhibiting an overall upward trend since 2007 (i.e., reflecting a reversal in the opposite direction from the other 4 sectors and the Antarctic sea ice cover as a whole).

scholarly journals Interannual and regional variability of Southern Ocean snow on sea ice

2006 ◽  
Vol 44 ◽  
pp. 53-57 ◽  
Author(s):  
Thorsten Markus ◽  
Donald J. Cavalieri
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Snow Depth ◽  
Critical Role ◽  
Ice Cover ◽  
Insulation Property ◽  
Regional Variability ◽  
Indirect Measure ◽  
Antarctic Sea Ice ◽  
The Antarctic

AbstractSnow depth on sea ice plays a critical role in the heat exchange between ocean and atmosphere because of its thermal insulation property. Furthermore, a heavy snow load on the relatively thin Southern Ocean sea-ice cover submerges the ice floes below sea level, causing snow-to-ice conversion. Snowfall is also an important freshwater source into the weakly stratified ocean. Snow-depth on sea-ice information can be used as an indirect measure of solid precipitation. Satellite passive microwave data are used to investigate the interannual and regional variability of the snow cover on sea ice. In this study we make use of 12 years (1992–2003) of Special Sensor Microwave/Imager (SSM/I) radiances to calculate average monthly snow depth on the Antarctic sea-ice cover. For the Antarctic sea-ice region as a whole, we find that September snow depth and sea-ice area are negatively correlated, which is not the case for individual regions. An analysis of the snow depth around Antarctica was undertaken. The results show an overall increase in snow depth for each of the five Antarctic sectors and the region as a whole, but only the Indian Ocean sector and the entire Southern Ocean show a statistically significant increase. There is a partial eastward propagation of maximum snow depths, which may be related to the Antarctic Circumpolar Wave. The overall trend and the variability of regional snow-depth distributions are also in agreement with cyclone density.

Sign in / Sign up

Export Citation Format

Share Document