Twin 5-month seasonal forecast experiments are performed to predict the September 2018 mean and minimum ice extent using the fully coupled Navy Earth System Prediction Capability (ESPC). In the control run, ensemble forecasts are initialized from the operational US Navy Global Ocean Forecasting System (GOFS) 3.1 but do not assimilate ice thickness data. Another set of forecasts are initialized from the same GOFS 3.1 fields but with sea ice thickness derived from CryoSat-2 (CS2). The Navy ESPC ensemble mean September 2018 minimum sea ice extent initialized with GOFS 3.1 ice thickness was over-predicted by 0.68 M km2 (5.27 M km2) vs the ensemble forecasts initialized with CS2 ice thickness that had an error of 0.40 M km2 (4.99 M km2), a 43% reduction in error. The September mean integrated ice edge error shows a 18% improvement for the Pan-Arctic with the CS2 data vs the control forecasts. Comparison against upward looking sonar ice thickness in the Beaufort Sea reveals a lower bias and RMSE with the CS2 forecasts at all three moorings. Ice concentration at these locations is also improved, but neither set of forecasts show ice free conditions as observed at moorings A and D.

The emperor penguin (Aptenodytes forsteri) is highly dependent on sea ice conditions, and future climate change may affect its distribution and numbers. Most studies on the demography and population dynamics of emperor penguins in relation to sea ice characteristics were conducted at a single colony (Pointe Géologie). Several non-exclusive hypotheses have been proposed to explain the dramatic decline of this colony, including changes in sea ice conditions, predation, flipper banding and human disturbance. Here, we report and analyse updated long-term trends in numbers of breeding pairs made at two colonies (Pointe Géologie and Haswell Island) where counts are comparable. Similar changes were observed for both colonies and paralleled changes in sea ice extent. At Pointe Géologie and Haswell Island, populations declined similarly and later growth rates were also similar since the early 1990s for Haswell and early 1980s for Pointe Géologie. The magnitude of the decline was similar between both colonies when numbers of breeding pairs were assessed. This study suggests that a common large-scale environmental factor has probably negatively affected both colonies.

The emperor penguin (Aptenodytes forsteri) is extremely dependent on the extent and stability of sea ice, which may make the species particularly susceptible to environmental change. In order to appraise the stability of the emperor penguin populations at six colonies in the western Ross Sea, we used linear regression analysis to evaluate chick abundance trends (1983–2005) and Pearson's r correlation to assess their relation to two local and two large-scale climate variables. We detected only one significant abundance trend; the Cape Roget colony increased from 1983 to 1996 (n = 6). Higher coefficients of variation in chick abundances at smaller colonies (Cape Crozier, Beaufort Island, Franklin Island) suggest that such colonies occupy marginal habitat, and are more susceptible to environmental change. We determined chick abundance to be most often correlated with local Ross Sea climate variables (sea ice extent and sea surface temperature), but not in consistent patterns across the colonies. We propose that chick abundance is most impacted by fine scale sea ice extent and local weather events, which are best evaluated by on-site assessments. We did not find sufficient evidence to reject the hypothesis that the overall emperor penguin population in the Ross Sea was stable during this period.

The land-fast ice and the platelet ice layer off Adélie Land are inhabited by a dense and diversified diatom community. Along with Bacillariophyceae, Archaeomonadaceae sensu Deflandre are present and relatively abundant. These modern siliceous nanostructures are similar to the nanofossils described by geologists in marine sediments from upper Cretaceous to Pliocene, Pleistocene and recently in Holocene and modern sediments, and are probably related to chrysophyte cysts. The two most abundant taxa were Achaeomonas cf areolata Deflandre and Litheusphaerella cf spectabilis Deflandre. The other taxa were not common. Despite the taxonomic uncertainty of immature forms, the diversity of archaeomonads was high. Three new species of Archaeomonas are described. The morphology of A. cf areolata is highly variable, showing a possible diversification over geologic time. Litheusphaerella cf spectabilis also shows some differences between fossil and modern specimens. Recent studies confirm that archaeomonads are extant in diverse marine water bodies and recent sediments. There is growing evidence that these siliceous structures represent possible reliable proxies of sea ice extent, even if their presence in geologic time is not always linked exclusively to sea ice. Further studies are needed to elucidate the exact origin of these cysts and their real taxonomic affinities.

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.