Geophysical constraints on the Antarctic sea ice cover

Nghiem, S. V.; Rigor, Ignatius; Clemente‐Colón, P.; Neumann, Gregory A.; Li, P.P.

doi:10.1016/j.rse.2016.04.005

Cited by 59 publications

(46 citation statements)

References 64 publications

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“…A number of physical processes have been shown to contribute to differences in GCM representations of energy budgets and sea-ice in the Southern Ocean, including the abundance and brightness of clouds [Trenberth and Fasullo 2010], the representation of supercooled liquid droplets [Cesana et al 2012, McCoy et al 2015, Kay et al 2016 and the importance of regional topography and bathymetry [Nghiem et al 2016]. Here we quantify the contribution of precipitating-ice radiative effects and show that it is another important factor in modelled Antarctic sea-ice biases.…”

Section: Introductionmentioning

confidence: 76%

Improved simulation of Antarctic sea ice due to the radiative effects of falling snow

Richardson

Hong

et al. 2017

Environ. Res. Lett.

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Southern Ocean sea-ice cover exerts critical control on local albedo and Antarctic precipitation, but simulated Antarctic sea-ice concentration commonly disagrees with observations. Here we show that the radiative effects of precipitating ice (falling snow) contribute substantially to this discrepancy. Many models exclude these radiative effects, so they underestimate both shortwave albedo and downward longwave radiation. Using two simulations with the climate model CESM1, we show that including falling-snow radiative effects improves the simulations relative to cloud properties from CloudSat-CALIPSO, radiation from CERES-EBAF and sea-ice concentration from passive microwave sensors. From 50-70°S, the simulated sea-ice-area bias is reduced by 2.12 Â 10 6 km 2 (55%) in winter and by 1.17 Â 10 6 km 2 (39%) in summer, mainly because increased wintertime longwave heating restricts sea-ice growth and so reduces summer albedo. Improved Antarctic sea-ice simulations will increase confidence in projected Antarctic sea level contributions and changes in global warming driven by long-term changes in Southern Ocean feedbacks.

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Section: Introductionmentioning

confidence: 76%

Improved simulation of Antarctic sea ice due to the radiative effects of falling snow

Richardson

Hong

et al. 2017

Environ. Res. Lett.

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“…Antarctic circumpolar flow is steered by topography in areas of complex seafloor bathymetry (Emery, ; Gordon, ; Kim & Orsi, ; Orsi et al, ; Rintoul et al, ) and this bathymetrically constrained circulation is a primary control on the surface manifestation of fronts, currents, and even sea ice extent (Graham et al, ; Kim & Orsi, ; Nghiem et al, ; Orsi et al, ). In some regions of the modern Southern Ocean (e.g., Drake Passage, Macquarie Ridge, Udintsev, and Eltanin fracture zones) bathymetric steering constricts circumpolar flow to a narrow zonal band, bundling oceanographic fronts into close proximity (Orsi et al, ) and decreasing year‐on‐year variability in frontal position (Kim & Orsi, ).…”

Section: Discussionmentioning

confidence: 99%

“…This ridge steers frontal boundaries north and east across the Pacific Ocean, until the current crosses south through the Udintsev and Eltanin fracture zones and into the Amundsen Sea (Kim & Orsi, ). The topographic barrier of the Pacific‐Antarctic Ridge effectively isolates the Ross Sea sector of the Southern Ocean from the influence of warmer northern water masses, protecting the Ross Ice Shelf and supporting the seasonal development of an extensive sea ice apron (Nghiem et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Along the northern boundary of the Southern Ocean's deep, eastward‐flowing Antarctic Circumpolar Current (ACC), the Subantarctic Front (SAF) marks the southernmost limit of relatively warm subantarctic surface water (Kim & Orsi, ; Orsi, Whitworth, & Nowlin, ). The core of ACC flow is bounded to the south by the Polar Front (PF) (Kim & Orsi, ), while the southern ACC front (sACCf), defined as “the southernmost extension of a 2°C isotherm at the subsurface temperature maximum layer” (Kim & Orsi, ), determines the northern limit of winter sea ice (Nghiem et al, ). Within the polar frontal zone, nutrient‐rich upwelling stimulates primary production and the resulting diatom blooms are exported to the seafloor, accumulating in a “diatom ooze belt” that encircles the continent between ~64° and 50°S (Armand, ; Chase et al, ; Crosta et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Polar Frontal Migration in the Warm Late Pliocene: Diatom Evidence From the Wilkes Land Margin, East Antarctica

Taylor-Silva

Riesselman

2018

Paleoceanog and Paleoclimatol

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The late Pliocene is the most recent interval in Earth's history to sustain global temperatures within the range of warming predicted for the 21st century, providing an appealing analog for the changes we might encounter in the coming century. Published global reconstructions and climate models find an average +2° summer sea surface temperature anomaly relative to modern during the 3.3–3.0 Ma interval of the late Pliocene, when atmospheric CO2 concentrations last reached 400 ppm. Here we present a new diatom‐based reconstruction of Pliocene interglacial sea surface conditions from IODP Site U1361, on the East Antarctic continental rise. We find that open ocean conditions in the mid‐Pliocene became increasingly influenced by sea ice from 3.6–3.2 Ma, prior to the onset of Northern Hemisphere glaciation. This cooling trend was interrupted by a temporary southward migration of the Antarctic Polar Front, bathing U1361 in subantarctic waters during a single interglacial—marine isotope stage KM3 (3.17–3.15 Ma)—after which sea ice returned. Building on the identification of this single outlier interglacial, we have revisited earlier reconstructions to explore the response of the Southern Ocean/cryosphere system to peak late Pliocene warmth. By applying a modern chronostratigraphic framework to those low‐resolution reconstructions, we identify the same frontal migration in four other cores in the Pacific sector of the Southern Ocean, documenting a major migration of the polar front during a key interval of warm climate. These new results suggest that KM3 is a crucial interval to test ice sheet stability in the context of anthropogenic warming.

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“…Among the natural explanations are the effects of El Niño events, the Southern Annular Mode (SAM), wind patterns as well as geology, etc 11121314…”

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confidence: 99%

Increase of the Antarctic Sea Ice Extent is highly significant only in the Ross Sea

Yuan

Ding

Ludescher

et al. 2017

Sci Rep

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In the context of global warming, the question of why Antarctic sea ice extent (SIE) has increased is one of the most fundamental unsolved mysteries. Although many mechanisms have been proposed, it is still unclear whether the increasing trend is anthropogenically originated or only caused by internal natural variability. In this study, we employ a new method where the underlying natural persistence in the Antarctic SIE can be correctly accounted for. We find that the Antarctic SIE is not simply short-term persistent as assumed in the standard significance analysis, but actually characterized by a combination of both short- and long-term persistence. By generating surrogate data with the same persistence properties, the SIE trends over Antarctica (as well as five sub-regions) are evaluated using Monte-Carlo simulations. It is found that the SIE trends over most sub-regions of Antarctica are not statistically significant. Only the SIE over Ross Sea has experienced a highly significant increasing trend (p = 0.008) which cannot be explained by natural variability. Influenced by the positive SIE trend over Ross Sea, the SIE over the entire Antarctica also increased over the past decades, but the trend is only at the edge of being significant (p = 0.034).

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Geophysical constraints on the Antarctic sea ice cover

Cited by 59 publications

References 64 publications

Improved simulation of Antarctic sea ice due to the radiative effects of falling snow

Improved simulation of Antarctic sea ice due to the radiative effects of falling snow

Polar Frontal Migration in the Warm Late Pliocene: Diatom Evidence From the Wilkes Land Margin, East Antarctica

Increase of the Antarctic Sea Ice Extent is highly significant only in the Ross Sea

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