Change and Variability in East Antarctic Sea Ice Seasonality, 1979/80–2009/10

Abstract

Recent analyses have shown that significant changes have occurred in patterns of sea ice seasonality in West Antarctica since 1979, with wide-ranging climatic, biological and biogeochemical consequences. Here, we provide the first detailed report on long-term change and variability in annual timings of sea ice advance, retreat and resultant ice season duration in East Antarctica. These were calculated from satellite-derived ice concentration data for the period 1979/80 to 2009/10. The pattern of change in sea ice seasonality off East Antarctica comprises mixed signals on regional to local scales, with pockets of strongly positive and negative trends occurring in near juxtaposition in certain regions e.g., Prydz Bay. This pattern strongly reflects change and variability in different elements of the marine “icescape”, including fast ice, polynyas and the marginal ice zone. A trend towards shorter sea-ice duration (of 1 to 3 days per annum) occurs in fairly isolated pockets in the outer pack from∼95–110°E, and in various near-coastal areas that include an area of particularly strong and persistent change near Australia's Davis Station and between the Amery and West Ice Shelves. These areas are largely associated with coastal polynyas that are important as sites of enhanced sea ice production/melt. Areas of positive trend in ice season duration are more extensive, and include an extensive zone from 160–170°E (i.e., the western Ross Sea sector) and the near-coastal zone between 40–100°E. The East Antarctic pattern is considerably more complex than the well-documented trends in West Antarctica e.g., in the Antarctic Peninsula-Bellingshausen Sea and western Ross Sea sectors.

Glacial ice and atmospheric forcing on the Mertz Glacier Polynya over the past 250 years

“…The latter would delay the onset of sea ice melt in spring in agreement with higher sea ice proxies in our record since 1960. Although based on a restricted number of data points, a reduction of sea ice proxies in the uppermost sediment sections suggests a recent tendency towards a more reduced sea ice cover in spring, which is in line with the recent analysis of the sea ice seasonality in the area using the satellite records 44 .…”

Bottom-up regulation of a pole-ward migratory predator population

“…As outlined above, the sea-ice field south of Macquarie Island has, over the past decades, trended towards increased duration (SID), extent (SIE) and concentration (SIC) and sea-ice affects female foraging behaviour and success. Most relevant to this study is that SID within the seals' feeding grounds (figure 3) has increased by up to 60 + 10 days between 1979 and 2010 [11,15,16,20]. Our analyses of the seals relationship with SID indicated inter-annual decreases (increases) in seal numbers at Macquarie Island tend to be associated with a longer (shorter) SID 3 years previous to the census.…”

“…Within the seals foraging areas (compare figures 2 and 3) the northwesterly wind vectors highlight the red-shaded area of decreased SID which largely results from advection of warm maritime air over the region; the blue area of increased SID is consistent with colder offshore southwesterly continental air flow (see wind vectors). The RS region, a known feeding ground for adult female seals from Macquarie Island (figure 3), is experiencing among the greatest SAM associated SID anomalies for the SH (figure 2 and [10,11]). …”

“…This overall expansion is essentially the sum of larger opposing SIE trends in the Ross and Bellinghausen seas [9]. For example, the Amundsen -Bellingshausen seas are presently experiencing a three month shorter ice season, whereas the Ross Sea (RS) is experiencing a two month longer season [10][11][12]. In addition, inputs to the East Antarctic ice field currently exceed losses, ice concentrations are trending higher in the mid-pack, the width of the marginal ice zone is widening and there is evidence of multi-year ice cover in the RS [10][11][12].…”

Seasonal climate summary southern hemisphere (spring 2012): warmer and drier across much of Australia, along with a new southern hemisphere sea ice extend record

“…ENSO events change the depth of the thermocline: La Niña magnifies the tilt while El Niño reduces the tilt. Statistically significant changes also exist in the seasonality of southern hemisphere sea ice (Stammerjohn et al 2012, Massom et al 2013). …”