An intercomparison of Antarctic sea ice extent datasets from the US Joint Ice Center (JIC) and satellite passive microwave observations for 1979–88

US Joint Ice Center (JIC) Antarctic sea ice extent data, the longest continuous series of its kind for this part of the world, are compared with direct passive microwave-based estimates to assess their overall consistency both spatially and temporally in the period 1979–88. Using ice edge position as a proxy for ice extent, the comparison reveals close agreement in most years, in monthly averaged ice edge positions in all Antarctic regions at the time of maximum ice extent, and also in autumn and spring in the Ross and Weddell Seas. Unexpectedly, JIC relative overestimation prevails during both autumn and spring in some other areas. Previously noted differences in JIC and passive microwave total Antarctic extent in 1979–80 result mainly from problems in the Ross Sea. Reasons for the various discrepancies may lie in differences in the methods used to produce the datasets especially in spring but those in autumn seem to often arise for other reasons. It is found that the prevalent discrepancies in the Ross Sea in 1979–80 as well as those in spring in other regions from 1981 coincide with periods of ice extent change and the evolution/intensification of ice extent anomalies

Atmospheric meridional circulation impacts on contrasting winter sea ice extent in two years in the Pacific sector of the Southern Ocean

An explanation is sought for the marked variation in maximum sea ice extent observed between 2 years in the 2 areas of greatest interannual variability in winter ice extent in the South Pacific sector of the Southern Ocean. The rôle of ice recession in controlling ice extent is highlighted, and the adjustments in the near-surface atmospheric meridional circulation and air temperature that attend winter periods of ice retreat and advance are noted. Distinct meridional flow and air temperature adjustments attend periods of sea ice retreat that limit ice to higher than normal latitudes as well as ice advance to lower than normal latitudes. Ice advance leading to above-normal ice extent, for instance, takes place only when a lowering of air temperatures is accompanied by equatorward flow. A lack of warm air advection is, however, needed to adequately account for the development and maintenance of above-normal ice extent. Systematic meridional circulation changes also take place during the development and over the duration of ice extent anomalies. These are shown to emanate from adjustments of the semi-annual cycle in the extra-tropical South Pacific atmospheric circulation

The impact of winter ice retreat on Antarctic winter sea-ice extent and links to the atmospheric meridional circulation

15 years of weekly Antarctic ice extent and 10 m winds from numerical meteorological reanalyses have been used to test the hypothesis that the Antarctic final winter ice extent (FWE) is brought about by ice retreats as much as by advances, and that both are strongly affected by the meridional (north-south) component of the atmospheric circulation. This hypothesis is found to be correct and it is shown that extensive FWE fails to occur when total winter retreat is anomalously large. This is the case even in the coldest Antarctic regions. Retreats reduce the time available for advance, notably when they are substantial, with the ice cover taking up to several weeks to recover. Systematic changes in the meridional winds between retreats and advance are also detected in all regions; retreats are consistently associated with northerly winds supporting ice compaction and ice drift. The results agree with Antarctic case studies. Close similarities are found between several Antarctic and sub-Arctic regions in terms of the prevalence of retreat in some winters. its impact on the FWE and its relationship to the meridional atmospheric circulation. The study also reveals a more complex picture of the atmospheric circulation during sub-monthly ice retreats and advances. In particular, retreats in some Pacific regions are, on average, associated with anomalous anticyclonic circulations. This helps to explain why evidence of strong cyclone-ice extent relationships has not been found previously. A meteorological explanation is also sought for total retreat in winter being small in a winter of limited ice extent in the Bellingshausen Sea despite this being the mildest Antarctic region. In such cases, limited winter ice extent is attended by reduced advance caused by ice compaction due to northerly winds and waves and also anomalously high air temperatures. Reduced advance then limits opportunities for retreat to take place compared with winters with more advance and sea ice reaching lower latitudes. Overall. the results point to sub-monthly ice-atmospheric circulation interactions largely determining the winter ice extent throughout much of the Antarctic

Atmospheric circulation impacts on winter maximum sea ice extent in the west Antarctic Peninsula region (1979-2001)

Increasing evidence exists that the strong warming of the West Antarctic Peninsula (WAP) region since the 1950s is related to reduced sea ice that is likely to be due to changes in the atmospheric circulation. Over twenty years of sea ice extent, ice motion and reanalysed near-surface wind data are used to establish that winter ice extent in the West Antarctic Peninsula (WAP) region is largely determined by the meridional (north-south) atmospheric circulation. A remarkably strong ice extent-wind relationship is found in the WAP. No other Antarctic or comparable sub-Arctic sea ice region shows this. Ice motion data confirm wind-induced drift is crucial for extensive winter ice to occur. Reasons for winter ice extent and winds being more strongly correlated in the WAP than in other parts of the Antarctic are discussed along with implications for understanding the observed warming

Climate change in the western Antarctic Peninsula since 1945: observations and possible causes

Temperature records from stations on the west coast of the Antarctic Peninsula show a very high level of interannual variability and, over the last 50 years, larger warming trends than are seen elsewhere in Antarctica. In this paper we investigate the role of atmospheric circulation variability and sea-ice extent variations in driving these changes. Owing to a lack of independent data, the reliability of Antarctic atmospheric analyses produced in the 1950s and 1960s cannot be readily established, but examination of the available data suggests that there has been an increase in the northerly component of the circulation over the Peninsula since the late 1950s. Few observations of sea-ice extent are available prior to 1973, but the limited data available indicate that the ice edge to the west of the Peninsula lay to the north of recently observed extremes during the very cold conditions prevailing in the late 1950s. The ultimate cause of the atmospheric circulation changes remains to be determined and may lie outside the Antarctic region

Biodiversity of air-borne microorganisms at Halley station Antarctica

A study of air-borne microbial biodiversity over an isolated scientific research station on an ice-shelf in continental Antarctica was undertaken to establish the potential source of microbial colonists. The study aimed to assess: (1) whether microorganisms were likely to have a local (research station) or distant (marine or terrestrial) origin, (2) the effect of changes in sea ice extent on microbial biodiversity and (3) the potential human impact on the environment. Air samples were taken above Halley Research Station during the austral summer and austral winter over a 2-week period. Overall, a low microbial biodiversity was detected, which included many sequence replicates. No significant patterns were detected in the aerial biodiversity between the austral summer and the austral winter. In common with other environmental studies, particularly in the polar regions, many of the sequences obtained were from as yet uncultivated organisms. Very few marine sequences were detected irrespective of the distance to open water, and around one-third of sequences detected were similar to those identified in human studies, though both of these might reflect prevailing wind conditions. The detected aerial microorganisms were markedly different from those obtained in earlier studies over the Antarctic Peninsula in the maritime Antarctic

A novel Antarctic microbial endolithic community within gypsum crusts

A novel endolithic microbial habitat is described from a climatically extreme site at Two Step Cliffs, Alexander Island, Antarctic Peninsula (71°54′S, 68°13′W). Small endolithic colonies (<3 mm in diameter) are found within the translucent gypsum crust that forms on the surface of sandstone boulders. Gypsum crusts are found on ice-free rocks throughout the Antarctic and therefore offer potential colonization sites at more inhospitable locations, including sites at higher latitudes. Cyanobacterial, bacterial and fungal components were cultured from the crust material and have been identified as Chloroglea sp., Sphingomonas sp. and Verticillium sp. respectively. A non-cultured, black-pigmented fungus was also found. Cyanobacterial primary productivity is low: at depths of 1.2 and 2.5 mm within the crust, estimates of possible cell divisions per year were < 38 and four respectively. This microniche is proposed to provide protection from desiccation, rapid temperature variation and UV radiation flux while allowing penetration of photosynthetically active radiation (PAR) for utilization by phototrophs. The endolithic communities are less extensive than those of the Dry Valleys, continental Antarctica, probably owing to only recent deglaciation (<7000 year ago)