scholarly journals Physical and Structural Characteristics of Antarctic Sea Ice

1982 ◽  
Vol 3 ◽  
pp. 113-117 ◽  
Author(s):  
A.J. Gow ◽  
S.F. Ackley ◽  
W.F. Weeks ◽  
J.W. Govoni
Keyword(s):  
Sea Ice ◽  
Structural Characteristics ◽  
Weddell Sea ◽  
The Arctic ◽  
Mcmurdo Sound ◽  
Frazil Ice ◽  
Antarctic Sea Ice ◽  
Pack Ice ◽  
Fast Ice ◽  
Ice Production

Observations during February and March 1980 of structures in 66 separate floes in Weddell Sea pack ice show widespread occurrence of frazil ice in amounts not previously reported in sea ice of comparable age and thickness in the Arctic. It is estimated that as much as 50% of the total ice production in the Weddell Sea is generated as frazil. Average floe salinities also appear higher than those of their Arctic counterparts. Comparative studies of fast ice at 28 locations in McMurdo Sound show this ice to be composed almost entirely of congelation ice that exhibits crystalline textures and orientations that are similar to those observed in Arctic fast ice. However, average fast-ice salinities in McMurdo Sound are higher than those reported for Arctic fast ice of comparable age and thickness.

scholarly journals Physical and Structural Characteristics of Antarctic Sea Ice

1982 ◽  
Vol 3 ◽  
pp. 113-117 ◽  
Author(s):  
A.J. Gow ◽  
S.F. Ackley ◽  
W.F. Weeks ◽  
J.W. Govoni
Keyword(s):  
Sea Ice ◽  
Structural Characteristics ◽  
Weddell Sea ◽  
The Arctic ◽  
Mcmurdo Sound ◽  
Frazil Ice ◽  
Antarctic Sea Ice ◽  
Pack Ice ◽  
Fast Ice ◽  
Ice Production

Observations during February and March 1980 of structures in 66 separate floes in Weddell Sea pack ice show widespread occurrence of frazil ice in amounts not previously reported in sea ice of comparable age and thickness in the Arctic. It is estimated that as much as 50% of the total ice production in the Weddell Sea is generated as frazil. Average floe salinities also appear higher than those of their Arctic counterparts. Comparative studies of fast ice at 28 locations in McMurdo Sound show this ice to be composed almost entirely of congelation ice that exhibits crystalline textures and orientations that are similar to those observed in Arctic fast ice. However, average fast-ice salinities in McMurdo Sound are higher than those reported for Arctic fast ice of comparable age and thickness.

scholarly journals Antarctic sea ice variability and trends, 1979–2010

2012 ◽  
Vol 6 (2) ◽  
pp. 931-956 ◽  
Author(s):  
C. L. Parkinson ◽  
D. J. Cavalieri
Keyword(s):  
Indian Ocean ◽  
Sea Ice ◽  
Ross Sea ◽  
Ice Cover ◽  
Weddell Sea ◽  
The Arctic ◽  
Future Research ◽  
Positive Trend ◽  
Antarctic Sea Ice ◽  
Ice Coverage

Abstract. In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has, like the Arctic, instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and Western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but differences in the magnitudes of the two trends identify regions with overall increasing ice concentrations and others with overall decreasing ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

scholarly journals Antarctic sea ice variability and trends, 1979–2010

2012 ◽  
Vol 6 (4) ◽  
pp. 871-880 ◽  
Author(s):  
C. L. Parkinson ◽  
D. J. Cavalieri
Keyword(s):  
Indian Ocean ◽  
Sea Ice ◽  
Ross Sea ◽  
Ice Cover ◽  
Weddell Sea ◽  
The Arctic ◽  
Future Research ◽  
Positive Trend ◽  
Antarctic Sea Ice ◽  
Ice Coverage

Abstract. In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has (like the Arctic) instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but the magnitudes of the two trends differ, and in some cases these differences allow inferences about the corresponding changes in sea ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

Evolution of supercooling under coastal Antarctic sea ice during winter

2011 ◽  
Vol 23 (4) ◽  
pp. 399-409 ◽  
Author(s):  
Gregory H. Leonard ◽  
Patricia J. Langhorne ◽  
Michael J.M. Williams ◽  
Ross Vennell ◽  
Craig R. Purdie ◽  
...  
Keyword(s):  
Sea Ice ◽  
Freezing Point ◽  
Circulation Pattern ◽  
Late Winter ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
The North ◽  
Antarctic Sea Ice ◽  
Ice Production

AbstractHere we describe the evolution through winter of a layer of in situ supercooled water beneath the sea ice at a site close to the McMurdo Ice Shelf. From early winter (May), the temperature of the upper water column was below its surface freezing point, implying contact with an ice shelf at depth. By late winter the supercooled layer was c. 40 m deep with a maximum supercooling of c. 25 mK located 1–2 m below the sea ice-water interface. Transitory in situ supercooling events were also observed, one lasting c. 17 hours and reaching a depth of 70 m. In spite of these very low temperatures the isotopic composition of the water was relatively heavy, suggesting little glacial melt. Further, the water's temperature-salinity signature indicates contributions to water mass properties from High Salinity Shelf Water produced in areas of high sea ice production to the north of McMurdo Sound. Our measurements imply the existence of a heat sink beneath the supercooled layer that extracts heat from the ocean to thicken and cool this layer and contributes to the thickness of the sea ice cover. This sink is linked to the circulation pattern of the McMurdo Sound.

Structural characteristics and development of sea ice in the western Ross Sea

1993 ◽  
Vol 5 (1) ◽  
pp. 63-75 ◽  
Author(s):  
M. O. Jeffries ◽  
W. F. Weeks
Keyword(s):  
Sea Ice ◽  
Internal Structure ◽  
Ross Sea ◽  
Ice Cores ◽  
Arctic Sea Ice ◽  
Weddell Sea ◽  
The Arctic ◽  
Ice Thickness ◽  
Pack Ice ◽  
Western Ross Sea

The internal structure of ice cores from western Ross Sea pack ice floes showed considerable diversity. Snow-ice formation made a small, but significant contribution to ice growth. Frazil ice was common and its growth clearly occurred during both the pancake cycle and deformation events. Congelation ice was also common, in both its crystallographically aligned and non-aligned varieties. Platelet ice was found in only one core next to the Drygalski Ice Tongue, an observation adding to the increasing evidence that this unusual ice type occurs primarily in coastal pack ice near ice tongues and ice shelves. The diverse internal structure of the floes indicates that sea ice development in the Ross Sea is as complex as that in the Weddell Sea and more complex than in the Arctic. The mean ice thickness at the ice core sites varied between 0.71 m and 1.52 m. The thinnest ice generally occurred in the outer pack ice zone. Regardless of latitude, the ice thickness data are further evidence that Antarctic sea ice is thinner than Arctic sea ice.

scholarly journals Development of Sea Ice in the Weddell Sea

1989 ◽  
Vol 12 ◽  
pp. 92-96 ◽  
Author(s):  
M.A. Lange ◽  
S.F. Ackley ◽  
P. Wadhams ◽  
G.S. Dieckmann ◽  
H. Eicken
Keyword(s):  
Sea Ice ◽  
Coastal Region ◽  
Ice Cores ◽  
Arctic Basin ◽  
Major Elements ◽  
Weddell Sea ◽  
The Arctic ◽  
Frazil Ice ◽  
Sea Ice Edge ◽  
Eastern Weddell Sea

We report on the development and physical properties of sea ice in the central and eastern Weddell Sea. The investigations were part of the Winter Weddell Sea Project 1986, which extended over the months of July through December. Major elements of the glaciological part of this study included continuous shipborne observations of sea-ice conditions and occasional helicopter reconnaissance flights, extensive measurements of snow and ice thicknesses at daily ice stations, and detailed analyses of sampled ice cores from each ice station. Textural investigations of the sampled ice revealed the dominance of frazil ice in the central Weddell Sea and the occurrence of an additional ice class, called platelet ice, together with the commonly known frazil and congelation ice in the coastal region of the eastern Weddell Sea. These results, in combination with the visual ice observations, reveal two major mechanisms for sea-ice generation in the Antarctic, which were not sufficiently well accounted for in previous investigations. In the central Weddell Sea, a cycle of pancake-ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea-ice edge. In the coastal waters, the growing sea-ice cover consists, to a considerable degree, of ice platelets which are formed in the underlying water column in front of the ice-shelf edges. Thus, congelation-ice growth, which is mainly controlled by atmospheric, thermodynamic forcing, seems to be of less importance in the central and south-eastern Weddell Sea than, for example, in the Arctic Basin.

scholarly journals Estimation of Thin Ice Thickness and Detection of Fast Ice from SSM/I Data in the Antarctic Ocean

2007 ◽  
Vol 24 (10) ◽  
pp. 1757-1772 ◽  
Author(s):  
Takeshi Tamura ◽  
Kay I. Ohshima ◽  
Thorsten Markus ◽  
Donald J. Cavalieri ◽  
Sohey Nihashi ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ross Sea ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Coastal Current ◽  
Antarctic Ocean ◽  
Coastal Polynya ◽  
Fast Ice ◽  
Ice Production ◽  
The Antarctic

Abstract Antarctic coastal polynyas are important areas of high sea ice production and dense water formation, and thus their detection including an estimate of thin ice thickness is essential. In this paper, the authors propose an algorithm that estimates thin ice thickness and detects fast ice using Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) data in the Antarctic Ocean. Detection and estimation of sea ice thicknesses of <0.2 m are based on the SSM/I 85- and 37-GHz polarization ratios (PR85 and PR37) through a comparison with sea ice thicknesses estimated from the Advanced Very High Resolution Radiometer (AVHRR) data. The exclusion of data affected by atmospheric water vapor is discussed. Because thin ice and fast ice (specifically ice shelves, glacier tongues, icebergs, and landfast ice) have similar PR signatures, a scheme was developed to separate these two surface types before the application of the thin ice algorithm to coastal polynyas. The probability that the algorithm correctly distinguishes thin ice from thick ice and from fast ice is ∼95%, relative to the ice thicknesses estimated from AVHRR. Although the standard deviation of the difference between the thin ice thicknesses estimated from the SSM/I algorithm and AVHRR is ∼0.05 m and thus not small, the estimated ice thicknesses from the microwave algorithm appear to have small biases and the accuracies are independent of region and season. A distribution map of thin ice occurrences derived from the SSM/I algorithm represents the Ross Sea coastal polynya being by far the largest among the Antarctic coastal polynyas; the Weddell Sea coastal polynyas are much smaller. Along the coast of East Antarctica, coastal polynyas frequently form on the western side of peninsulas and glacier tongues, downstream of the Antarctic Coastal Current.

scholarly journals Study of the Impact of Ice Formation in Leads upon the Sea Ice Pack Mass Balance Using a New Frazil and Grease Ice Parameterization

2015 ◽  
Vol 45 (8) ◽  
pp. 2025-2047 ◽  
Author(s):  
Alexander V. Wilchinsky ◽  
Harold D. B. S. Heorton ◽  
Daniel L. Feltham ◽  
Paul R. Holland
Keyword(s):  
Sea Ice ◽  
Mass Balance ◽  
Ice Crystals ◽  
The Arctic ◽  
Ice Formation ◽  
Frazil Ice ◽  
Marginal Seas ◽  
Ice Production ◽  
The Impact ◽  
Ice Pack

AbstractLeads are cracks in sea ice that often form because of deformation. During winter months, leads expose the ocean to the cold atmosphere, resulting in supercooling and the formation of frazil ice crystals within the mixed layer. Here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the Los Alamos sea ice model (CICE). The frazil ice module considers an initial cooling of leads followed by a steady-state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice. The grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice. Simulations of the sea ice cover in the Arctic and Antarctic are performed and compared to a model that treats leads the same as the open ocean. The processes of ice formation in the new module slow down the refreezing of leads, resulting in a longer period of frazil ice production. The fraction of frazil-derived sea ice increases from 10% to 50%, corresponding better to observations. The new module has higher ice formation rates in areas of high ice concentration and thus has a greater impact within multiyear ice than it does in the marginal seas. The thickness of sea ice in the central Arctic increases by over 0.5 m, whereas within the Antarctic it remains unchanged.

scholarly journals Spatio-temporal variability and decadal trends of snowmelt processes on Antarctic sea ice observed by satellite scatterometers

2019 ◽  
Author(s):  
Stefanie Arndt ◽  
Christian Haas
Keyword(s):  
Time Series ◽  
Sea Ice ◽  
Weddell Sea ◽  
Passive Microwave ◽  
The Arctic ◽  
Signal Frequency ◽  
Onset Date ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Perennial Ice

Abstract. The timing and intensity of snowmelt processes on sea ice are key drivers determining the seasonal sea-ice energy and mass budgets. In the Arctic, satellite passive microwave and radar observations have revealed a trend towards an earlier snowmelt onset during the last decades, which is an important aspect of Arctic amplification and sea ice decline. Around Antarctica, snowmelt on perennial ice is weak and very different than in the Arctic, with most snow surviving the summer. Here we compile time series of snowmelt-onset dates on seasonal and perennial Antarctic sea ice from 1992 to 2014/15 using active microwave observations from European Remote Sensing Satellite (ERS-1/2), Quick Scatterometer (QSCAT) and Advanced Scatterometer (ASCAT) radar scatterometers. We define two snowmelt transition stages: A weak backscatter rise indicating the initial warming and metamorphism of the snowpack (pre-melt), followed by a rapid backscatter rise indicating the onset of thaw-freeze cycles (snowmelt). Results show large interannual variability with an average pre-melt onset date of 29 November and melt onset of 10 December, respectively, on perennial ice, without any significant trends over the study period, consistent with the small trends of Antarctic sea ice extent. There was a latitudinal gradient from early snowmelt onsets in mid-November in the northern Weddell Sea to late (end-December) or even absent snowmelt conditions in the southern Weddell Sea. We show that QSCAT Ku-band (13.4 GHz signal frequency) derived pre-melt and snowmelt onset dates are earlier by 25 and 11 days, respectively, than ERS and ASCAT C-band (5.6 GHz) derived dates. This offset has been considered when constructing the time series. Snowmelt onset dates from passive microwave observations (37 GHz) are later by 13 and 5 days than those from the scatterometers, respectively. Based on these characteristic differences between melt onset dates observed by different microwave wavelengths, we developed a conceptual model which illustrates how the evolution of seasonal snow temperature profiles affects different microwave bands with different penetration depths. These suggest that future multi-frequency active/passive microwave satellite missions could be used to resolve melt processes throughout the vertical snow column.

scholarly journals A comparison of East Antarctic sea-ice motion derived using drifting buoys and remote sensing

2001 ◽  
Vol 33 ◽  
pp. 139-144 ◽  
Author(s):  
P. Heil ◽  
C.W. Fowler ◽  
J. A. Maslanik ◽  
W. J. Emery ◽  
I. Allison
Keyword(s):  
Sea Ice ◽  
Microwave Radiometer ◽  
Correlation Method ◽  
Weddell Sea ◽  
The Arctic ◽  
Antarctic Sea Ice ◽  
Spatial Coverage ◽  
Surface Patterns ◽  
Buoy Measurements ◽  
Drifting Buoys

AbstractResults of East Antarctic (20−160° E) sea-ice motion derived from drifting buoys (collected in eight selected years between 1985 and 1997) are compared with sea-ice motion derived from sequential images from the 37 and 85.5 GHz channels of the Scanning Multichannel Microwave Radiometer (SMMR, 1979−87) and the Special Sensor Microwave/Imager (SSM/I, 1987−97). For the latitudes of interest, buoys yield velocity fields at 2 hourly resolution/while SMMR and SSM/I provide daily data. The spatial coverage of the drifting buoys is relatively sparse compared to the complete coverage of the southern sea-ice zone by SMMR and SSM/I, but the accuracy of the buoy position is better than ±280 m, while the resolution for the 85.5 GHz channel is only about 12.5 km, and about 25 km for the 37 GHz channel. The buoy measurements represent point motion, equal to the velocity of an individual ice floe, while the satellite data derived via the maximum cross-correlation method represent the motion of surface patterns within a gridcell. Comparison of the mean distributions of daily velocity derived from the datasets shows that while the broad-scale velocity patterns agree, the magnitude of the satellite-derived sea-ice velocities is significantly lower (typically by 40% or less) than the velocities derived from buoy measurements. This is in contrast with previous studies for the Arctic Ocean and the Weddell Sea, Antarctica. To elucidate differences in the velocity magnitude, individual trajectories from a number of drift regimes off East Antarctica are directly compared. Discrepancies between the two datasets are discussed with regard to the difference in spatial resolution of the data, the data-collection and −processing methods and the observed region.

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