Antarctic Sea Ice Expansion Research Articles

Present-day and future Antarctic ice sheet climate and surface mass balance in the Community Earth System Model

We present climate and surface mass balance (SMB) of the Antarctic ice sheet (AIS) as simulated by the global, coupled ocean–atmosphere–land Community Earth System Model (CESM) with a horizontal resolution of $${\sim }1^\circ$$ in the past, present and future (1850–2100). CESM correctly simulates present-day Antarctic sea ice extent, large-scale atmospheric circulation and near-surface climate, but fails to simulate the recent expansion of Antarctic sea ice. The present-day Antarctic ice sheet SMB equals $$2280 \pm 131$$ $$\mathrm {Gt\,year^{-1}}$$ , which concurs with existing independent estimates of AIS SMB. When forced by two CMIP5 climate change scenarios (high mitigation scenario RCP2.6 and high-emission scenario RCP8.5), CESM projects an increase of Antarctic ice sheet SMB of about 70 $$\mathrm {Gt\,year^{-1}}$$ per degree warming. This increase is driven by enhanced snowfall, which is partially counteracted by more surface melt and runoff along the ice sheet’s edges. This intensifying hydrological cycle is predominantly driven by atmospheric warming, which increases (1) the moisture-carrying capacity of the atmosphere, (2) oceanic source region evaporation, and (3) summer AIS cloud liquid water content.

Obliquity Control On Southern Hemisphere Climate During The Last Glacial.

Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent.

A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated?

Abstract. Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one-third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably smaller and statistically indistinguishable from zero. Here, we show that much of the increase in the reported trend occurred due to the previously undocumented effect of a change in the way the satellite sea ice observations are processed for the widely used Bootstrap algorithm data set, rather than a physical increase in the rate of ice advance. Specifically, we find that a change in the intercalibration across a 1991 sensor transition when the data set was reprocessed in 2007 caused a substantial change in the long-term trend. Although our analysis does not definitively identify whether this change introduced an error or removed one, the resulting difference in the trends suggests that a substantial error exists in either the current data set or the version that was used prior to the mid-2000s, and numerous studies that have relied on these observations should be reexamined to determine the sensitivity of their results to this change in the data set. Furthermore, a number of recent studies have investigated physical mechanisms for the observed expansion of the Antarctic sea ice cover. The results of this analysis raise the possibility that much of this expansion may be a spurious artifact of an error in the processing of the satellite observations.

Recent Antarctic sea ice trends in the context of Southern Ocean surface climate variations since 1950

This study compares the distribution of surface climate trends over the Southern Ocean in austral summer between 1979–2011 and 1950–1978, using a wide variety of data sets including uninterpolated gridded marine archives, land station data, reanalysis, and satellite products. Apart from the Antarctic Peninsula and adjacent regions, sea surface temperatures and surface air temperatures decreased during 1979–2011, consistent with the expansion of Antarctic sea ice. In contrast, the Southern Ocean and coastal Antarctica warmed during 1950–1978. Sea level pressure (SLP) and zonal wind trends provide additional evidence for a sign reversal between the two periods, with cooling (warming) accompanied by stronger (weaker) westerlies and lower (higher) SLP at polar latitudes in the early (late) period. Such physically consistent trends across a range of independently measured parameters provide robust evidence for multidecadal climate variability over the Southern Ocean and place the recent Antarctic sea ice trends into a broader context.

Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded1, with record extent2 in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica’s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends4, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

Ungulate diversity and precipitation history since the Last Glacial Maximum in the Western Cape, South Africa

This study reviews the precipitation history of the winter and year-round rainfall zones in the Western Cape (South Africa) in light of its fossil ungulate communities. Fossil sequences spanning the Last Glacial Maximum (LGM) and Lateglacial through the Holocene document a decline in ungulate richness through time. Based on the observed relationship between ungulate community richness and annual precipitation in Southern and East Africa, this implies increased effective precipitation during the LGM-Lateglacial at sites located in both the winter and year-round rainfall zones. These results are consistent with other lines of paleoenvironmental evidence from the winter rainfall zone, although they contradict records from the year-round rainfall zone that have been interpreted as reflecting aridity. A critical review of these records suggests that the patterns interpreted in terms of aridity can be explained by other mechanisms, including vegetation change. Current evidence is consistent with paleoclimatic models indicating that altered rainfall patterns during the LGM-Lateglacial were primarily related to the position of westerly frontal systems, which were displaced northward due to the expansion of Antarctic sea ice. Seasonal migration of these systems resulted in an expanded winter rainfall zone across much of southwestern Africa, but perhaps with some summer rains reaching the southern coast.

Occurrence of whale barnacles in Nerja Cave (Málaga, southern Spain): Indirect evidence of whale consumption by humans in the Upper Magdalenian

A total of 167 plates of two whale barnacle species (Tubicinella majorLamarck, 1802 and Cetopirus complanatusMörch, 1853) have been found in the Upper Magdalenian layers of Nerja Cave, Mina Chamber (Maro, Málaga, southern Spain). This is the first occurrence of these species in a prehistoric site. Both species are specific to the southern right whale Eubalena australis, today endemic in the Southern Hemisphere. Because of Antarctic sea-ice expansion during the Last Glacial Period, these whales could have migrated to the Northern Hemisphere, and reached southern Spain. Whale barnacles indicate that maritime-oriented forager human groups found stranded whales on the coast and, because of the size and weight of the large bones, transported only certain pieces (skin, blubber and meat) to the caves where they were consumed.

Antarctic sea ice and the control of Pleistocene climate instability

A hypothesis is presented for the origin of Pleistocene climate instability, based on expansion of Antarctic sea ice and associated changes in the oceans' salinity structure. The hypothesis assumes that thermohaline overturning is dominated by the reconfigured conveyor of Toggweiler and Samuels [1993b], in which deepwater upwelling is restricted to high southern latitudes. The reconfigured conveyor is shown to be potentially stabilized in an “on” mode by precipitation at high southern latitudes and potentially destabilized into “on” and “off” modes by the counteracting influence of Antarctic sea ice. The mechanism is clarified by the use of a hydraulic analogue. We hypothesize that this mechanism accounts for dominant patterns of thermohaline overturning and climate instability between Pleistocene warm and cold periods. The hypothesis is shown to be consistent with a range of paleoceanographic evidence and to potentially account for details of observed rapid climate changes during glacial and interglacial periods, including aspects of interhemispheric timing.

Pack-Ice Drift off East Antarctica and some Implications

Three satellite-tracked data buoys were deployed between 70° and 80°E south of 65°S in February-March 1985. These buoys were subsequently trapped within the expanding seasonal sea ice and drifted with the ice. The buoys measured air temperature and pressure, and water temperatures to 100 m depth. Data from the buoys are used to describe the ice drift and environment within the winter sea-ice zone in this region, both north and south of the Antarctic Divergence. Additional preliminary data from a further six buoys deployed in the same area in March 1987 are also presented. Besides providing information on the broad-scale drift of the ice in the Prydz Bay region, data from the buoys have shown: (i) the important role that ice drift plays in determining the autumn and winter expansion of Antarctic sea ice; (ii) the highly mobile nature of the ice, even hundreds of kilometres from the ice edge; (iii) the role that ocean-bottom topography has in determining ice drift over the continental shelf; and (iv) the modifying influence that an ice cover has on regional climate. A qualitative assessment is made of the relative importance of the major forces driving the ice, although the data are insufficient for a detailed study of the ice dynamics.