[1] Previous studies have shown strong contrasting trends in annual sea ice duration and in monthly sea ice concentration in two regions of the Southern Ocean: decreases in the western Antarctic Peninsula/southern Bellingshausen Sea (wAP/sBS) region and increases in the western Ross Sea (wRS) region. To better understand the evolution of these regional sea ice trends, we utilize the full temporal (quasi-daily) resolution of satellite-derived sea ice data to track spatially the annual ice edge advance and retreat from 1979 to 2004. These newly analyzed data reveal that sea ice is retreating 31 ± 10 days earlier and advancing 54 ± 9 days later in the wAP/sBS region (i.e., total change over , whereas in the wRS region, sea ice is retreating 29 ± 6 days later and advancing 31 ± 6 days earlier. Changes in the wAP/sBS and wRS regions, particularly as observed during sea ice advance, occurred in association with decadal changes in the mean state of the Southern Annular Mode (SAM; negative in the 1980s and positive in the 1990s) and the high-latitude response to El Niño-Southern Oscillation (ENSO). In general, the high-latitude ice-atmosphere response to ENSO was strongest when -SAM was coincident with El Niño and when +SAM was coincident with La Niña, particularly in the wAP/sBS region. In total, there were 7 of 11 -SAMs between 1980 and 1990 and the 7 of 10 +SAMs between 1991 and 2000 that were associated with consistent decadal sea ice changes in the wAP/sBS and wRS regions, respectively. Elsewhere, ENSO/SAMrelated sea ice changes were not as consistent over time (e.g., western Weddell, Amundsen, and eastern Ross Sea region), or variability in general was high (e.g., central/ eastern Weddell and along East Antarctica).

The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 28C increase in the annual mean temperature and a 68C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.68C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in icedependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients extending along the WAP and the presence of monitoring systems, field stations and long-term research programmes make the region an invaluable observatory of climate change and marine ecosystem response.

The climate of the western shelf of the Antarctic Peninsula (WAP) is undergoing a transition from a cold-dry polar-type climate to a warm-humid sub-Antarctic-type climate. Using three decades of satellite and field data, we document that ocean biological productivity, inferred from chlorophyll a concentration (Chl a), has significantly changed along the WAP shelf. Summertime surface Chl a (summer integrated Chl a approximately 63% of annually integrated Chl a) declined by 12% along the WAP over the past 30 years, with the largest decreases equatorward of 63 degrees S and with substantial increases in Chl a occurring farther south. The latitudinal variation in Chl a trends reflects shifting patterns of ice cover, cloud formation, and windiness affecting water-column mixing. Regional changes in phytoplankton coincide with observed changes in krill (Euphausia superba) and penguin populations.

[1] This bi-polar analysis resolves ice edge changes on space/time scales relevant for investigating seasonal iceocean feedbacks and focuses on spatio-temporal changes in the timing of annual sea ice retreat and advance over 1979/ 80 to 2010/11. Where Arctic sea ice decrease is fastest, the sea ice retreat is now nearly 2 months earlier and subsequent advance more than 1 month later (compared to 1979/80), resulting in a 3-month longer summer ice-free season. In the Antarctic Peninsula and Bellingshausen Sea region, sea ice retreat is more than 1 month earlier and advance 2 months later, resulting in a more than 3-month longer summer icefree season. In contrast, in the western Ross Sea (Antarctica) region, sea ice retreat and advance are more than 1 month later and earlier respectively, resulting in a more than 2 month shorter summer ice-free season. Regardless of trend magnitude or direction, and at latitudes mostly poleward of 70 (N/S), there is strong correspondence between anomalies in the timings of sea ice retreat and subsequent advance, but little correspondence between advance and subsequent retreat. These results support a strong ocean thermal feedback in autumn in response to changes in spring sea ice retreat. Further, model calculations suggest different net ocean heat changes in the Arctic versus Antarctic where autumn sea ice advance is 1 versus 2 months later. Oceanatmosphere changes, particularly in boreal spring and austral autumn (i.e., during $March-May), are discussed and compared, as well as possible inter-hemispheric climate connections. Citation: Stammerjohn, S., R. Massom, D. Rind, and D. Martinson (2012), Regions of rapid sea ice change: An interhemispheric seasonal comparison, Geophys. Res. Lett., 39, L06501,

Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or ongoing, possibly unstable response to a past climate anomaly. Lengthening satellite records appear incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000-2016 near Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of ~4 between cool and warm extremes via a non-linear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice shelf thinning and retreat of the grounding line, which readvanced during a post-2011 cool phase. Those observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The non-linear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high.

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Over the past 37 years, satellite records show an increase in Antarctic sea ice cover that is most pronounced in the period of sea ice growth. This trend is dominated by increased sea ice coverage in the western Ross Sea, and is mitigated by a strong decrease in the Bellingshausen and Amundsen seas. The trends in sea ice areal coverage are accompanied by related trends in yearly duration. These changes have implications for ecosystems, as well as global and regional climate. In this review, we summarise the research to date on observing these trends, identifying their drivers, and assessing the role of anthropogenic climate change. Whilst the atmosphere is thought to be the primary driver, the ocean is also essential in explaining the seasonality of the trend patterns. Detecting an anthropogenic signal in Antarctic sea ice is particularly challenging for a number of reasons: the expected response is small compared to the very high natural variability of the system; the observational record is relatively short; and the ability of global coupled climate models to faithfully represent the complex Antarctic climate system is in doubt.