Abrupt mid-twentieth-century decline in Antarctic sea-ice extent from whaling records

Mare, William K. de la

doi:10.1038/37956

Cited by 218 publications

(30 citation statements)

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“…The period spanning the last 30 yr during which sea ice cover slightly expanded in the Southern Ocean might follow a large melting that may have happened before 1979 (e.g. de la Mare, 1997Mare, , 2009Cavalieri et al, 2003;Curran et al, 2003;Cotté and Guinet, 2007;Goosse et al, 2009b). This suggests that multidecadal variability in the Southern Ocean is large, but the available data do not allow a quantitative estimation of its value.…”

Section: Zunz Et Al: Cmip5 1979-2005 Southern Ocean Sea Icementioning

confidence: 71%

How does internal variability influence the ability of CMIP5 models to reproduce the recent trend in Southern Ocean sea ice extent?

2013

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Abstract.Observations over the last 30 yr have shown that the sea ice extent in the Southern Ocean has slightly increased since 1979. Mechanisms responsible for this positive trend have not been well established yet. In this study we tackle two related issues: is the observed positive trend compatible with the internal variability of the system, and do the models agree with what we know about the observed internal variability? For that purpose, we analyse the evolution of sea ice around the Antarctic simulated by 24 different general circulation models involved in the 5th Coupled Model Intercomparison Project (CMIP5), using both historical and hindcast experiments. Our analyses show that CMIP5 models respond to the forcing, including the one induced by stratospheric ozone depletion, by reducing the sea ice cover in the Southern Ocean. Some simulations display an increase in sea ice extent similar to the observed one. According to models, the observed positive trend is compatible with internal variability. However, models strongly overestimate the variance of sea ice extent and the initialization methods currently used in models do not improve systematically the simulated trends in sea ice extent. On the basis of those results, a critical role of the internal variability in the observed increase of sea ice extent in the Southern Ocean could not be ruled out, but current models results appear inadequate to test more precisely this hypothesis.

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Section: Zunz Et Al: Cmip5 1979-2005 Southern Ocean Sea Icementioning

confidence: 71%

How does internal variability influence the ability of CMIP5 models to reproduce the recent trend in Southern Ocean sea ice extent?

2013

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“…In contrast to the Arctic, the overall extent of Antarctic sea ice has increased slightly since satellite observations first became available in 1979. Indirect evidence from methanesulphonic acid measurements in ice‐sheet cores (Curran et al ., ; Abram et al ., ) and from historical whaling records (de la Mare, , ) indicate a decline in sea ice between the 1950s and 1970s (but see Ackley et al ., ).…”

Section: Exposure: Observed and Predicted Change In Physical Habitatsmentioning

confidence: 99%

Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota

Constable

Melbourne-Thomas

Corney

et al. 2014

Global Change Biology

456

372

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Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed.

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“…Summer ice edge has been estimated using historical whaling records [de la Mare, 1997Mare, , 2009], but there are concerns over the reliability of this approach [Ackley et al, 2003], and they do not provide a continuous record to the present day. Several geophysical regional reconstructions have been published in recent years [Curran et al, 2003;Abram et al, 2010;Murphy et al, 2014;Sinclair et al, 2014;Thomas and Abram, 2016], all of which report statistically significant local changes in sea ice cover, but these reconstructions have not previously been compared with simulated variability or forced response.…”

Section: Introductionmentioning

confidence: 99%

Century‐scale perspectives on observed and simulated Southern Ocean sea ice trends from proxy reconstructions

et al. 2016

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Since 1979 when continuous satellite observations began, Southern Ocean sea ice cover has increased, whilst global coupled climate models simulate a decrease over the same period. It is uncertain whether the observed trends are anthropogenically forced or due to internal variability, or whether the apparent discrepancy between models and observations can be explained by internal variability. The shortness of the satellite record is one source of this uncertainty, and a possible solution is to use proxy reconstructions, which extend the analysis period but at the expense of higher observational uncertainty. In this work, we evaluate the utility for change detection of 20th century Southern Ocean sea ice proxies. We find that there are reliable proxies for the East Antarctic, Amundsen, Bellingshausen and Weddell sectors in late winter, and for the Weddell Sea in late autumn. Models and reconstructions agree that sea ice extent in the East Antarctic, Amundsen and Bellingshausen Seas has decreased since the early 1970s, consistent with an anthropogenic response. However, the decrease is small compared to internal variability, and the change is not robustly detectable. We also find that optimal fingerprinting filters out much of the uncertainty in proxy reconstructions. The Ross Sea is a confounding factor, with a significant increase in sea ice since 1979 that is not captured by climate models; however, existing proxy reconstructions of this region are not yet sufficiently reliable for formal change detection.

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Abrupt mid-twentieth-century decline in Antarctic sea-ice extent from whaling records

Cited by 218 publications

References 1 publication

How does internal variability influence the ability of CMIP5 models to reproduce the recent trend in Southern Ocean sea ice extent?

How does internal variability influence the ability of CMIP5 models to reproduce the recent trend in Southern Ocean sea ice extent?

Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota

Century‐scale perspectives on observed and simulated Southern Ocean sea ice trends from proxy reconstructions

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