Can North Atlantic Sea Ice Anomalies Account for Dansgaard–Oeschger Climate Signals?*

2010 ◽  
Vol 23 (20) ◽  
pp. 5457-5475 ◽  
Author(s):  
Camille Li ◽  
David S. Battisti ◽  
Cecilia M. Bitz
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Nordic Seas ◽  
Last Glacial ◽  
Ice Retreat ◽  
Climate Signals ◽  
Ice Edge ◽  
Sea Ice Edge ◽  
Sea Ice Retreat ◽  
The Last Glacial

Abstract North Atlantic sea ice anomalies are thought to play an important role in the abrupt Dansgaard–Oeschger (D–O) cycles of the last glacial period. This model study investigates the impacts of changes in North Atlantic sea ice extent in glacial climates to help provide geographical constraints on their involvement in D–O cycles. Based on a coupled climate model simulation of the Last Glacial Maximum (21 ka), the Nordic seas and western North Atlantic (broadly, south of Greenland) are identified as two plausible regions for large and persistent displacements of the sea ice edge in the glacial North Atlantic. Sea ice retreat scenarios targeting these regions are designed to represent ice cover changes associated with the cold-to-warm (stadial-to-interstadial) transitions of D–O cycles. The atmospheric responses to sea ice retreat in the Nordic seas and in the western North Atlantic are tested individually and together using an atmospheric general circulation model. The Nordic seas ice retreat causes 10°C of winter warming and a 50% increase in snow accumulation at Greenland Summit; concomitant ice retreat in the western North Atlantic has little additional effect. The results suggest that displacements of the winter sea ice edge in the Nordic seas are important for creating the observed climate signals associated with D–O cycles in the Greenland ice cores.

The impact of wintertime sea-ice retreat on convection in the Nordic Seas

2020 ◽  
Author(s):  
Yue Wu ◽  
David Stevens ◽  
Ian Renfrew ◽  
Xiaoming Zhai
Keyword(s):  
Sea Ice ◽  
Temperature Difference ◽  
North Atlantic ◽  
Nordic Seas ◽  
Convective Mixing ◽  
The North ◽  
Ice Retreat ◽  
The North Atlantic ◽  
Ice Edge ◽  
Sea Ice Retreat

<p>The Nordic Seas have a significant impact on global climate due to their role in providing dense overflows to the North Atlantic Ocean. However, the dramatic loss of sea ice in recent decades is creating a new atmosphere-ice-ocean environment where large swathes of the ocean that were previously ice-covered are now exposed to the atmosphere. Despite the largest sea-ice loss occurring in summer and autumn, the sea-ice loss in winter and spring is arguably more important for the climate system. Atmosphere-ocean coupling is the most intense in the extended winter, when convective mixing leads to water-mass modification processes, impacting the densest waters of the Atlantic Meridional Overturning Circulation. Here we focus on the marginal-ice-zone of the Nordic Seas where the air-sea temperature difference is large, promoting high heat flux events during periods of off-ice winds. We use both transient and control simulations of the coupled climate model HiGEM, which allows us to isolate the climate change response from the sea-ice retreat response. We find that wintertime sea-ice retreat leads to remarkable changes in ocean surface heat exchanges and wind energy input. As the sea ice edge retreats towards the Greenland coastline, there is a band of exposed ocean which was previously covered by ice. This exposure allows enhanced mechanical mixing by the wind and a greater loss of buoyancy from the ocean leading to deeper vertical mixing in the upper ocean. Sensible and latent heat fluxes from the ocean to the atmosphere provide the greatest loss of buoyancy. However, climate warming inhibits this process as the atmosphere warms more rapidly than the ocean which reduces the sea-air temperature difference. Further away from the retreating ice edge, toward the centre of the Greenland Sea, the upper ocean warms, resulting in a more stratified water column. As a consequence, the depth of convective mixing reduces over the deep ocean and increases over shallower regions close to the coast. This leads to changes in the formation and properties of some of the water masses that enter the North Atlantic and thus may modify the ocean circulation in the subpolar seas in response to sea-ice decline. </p>

scholarly journals The Response of the Nordic Seas to Wintertime Sea-ice Retreat

2021 ◽  
pp. 1-40
Author(s):  
Yue Wu ◽  
David P. Stevens ◽  
Ian A. Renfrew ◽  
Xiaoming Zhai
Keyword(s):  
Global Warming ◽  
Sea Ice ◽  
Climate Model ◽  
Sea Temperature ◽  
Nordic Seas ◽  
Ocean Response ◽  
Marginal Ice Zone ◽  
Ice Retreat ◽  
Ice Edge ◽  
Sea Ice Retreat

AbstractThe ocean response to wintertime sea-ice retreat is investigated in the coupled climate model HiGEM. We focus on the marginal ice zone and adjacent waters of the Nordic Seas, where the air-sea temperature difference can be large during periods of off-ice winds promoting high heat flux events. Both control and transient climate model ensembles are examined, which allows us to isolate the ocean response due to sea-ice retreat from the response due to climate change. As the wintertime sea-ice edge retreats towards the Greenland coastline, it exposes waters that were previously covered by ice which enhances turbulent heat loss and mechanical mixing, leading to a greater loss of buoyancy and deeper vertical mixing in this location. However, under global warming, the buoyancy loss is inhibited as the atmosphere warms more rapidly than the ocean which reduces the air-sea temperature difference. This occurs most prominently further away from the retreating ice edge, over the Greenland Sea gyre. Over the gyre the upper ocean also warms significantly, resulting in a more stratified water column and, as a consequence, a reduction in the depth of convective mixing. In contrast, closer to the coast the effect of global warming is overshadowed by the effect of the sea-ice retreat, leading to significant changes in ocean temperature and salinity in the vicinity of the marginal ice zone.

scholarly journals Transient increase in Arctic deep-water formation and ocean circulation under sea-ice retreat

2021 ◽  
pp. 1
Author(s):  
Anaïs Bretones ◽  
Kerim H. Nisancioglu ◽  
Mari F. Jensen ◽  
Ailin Brakstad ◽  
Shuting Yang
Keyword(s):  
Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Deep Water Formation ◽  
Water Formation ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Ice Edge ◽  
Sea Ice Edge ◽  
Sea Ice Retreat

AbstractWhile a rapid sea-ice retreat in the Arctic has become ubiquitous, the potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to global warming is still under debate. As deep mixing occurs in the open-ocean close to the sea-ice edge, the strength and vertical extent of the AMOC is likely to respond to ongoing and future sea-ice retreat. Here, we investigate the link between changes in Arctic sea-ice cover and AMOC strength in a long simulation with the EC-Earth-PISM climate model under the emission scenario RCP8.5. The extended duration of the experiment (years 1850-2300) captures the disappearance of summer sea ice in 2060 and the removal of winter sea ice in 2165. By introducing a new metric, the Arctic Meridional Overturning Circulation (ArMOC), we document changes beyond the Greenland-Scotland Ridge and into the central Arctic. We find an ArMOC strengthening as the areas of deep mixing move north, following the retreating winter sea-ice edge into the Nansen Basin. At the same time, mixing in the Labrador and Greenland Seas reduces and the AMOC weakens. As the winter sea-ice edge retreats further into the regions with high surface freshwater content in the central Arctic Basin, the mixing becomes shallower and the ArMOC weakens. Our results suggest that the location of deep-water formation plays a decisive role in the structure and strength of the ArMOC; however, the intermittent strengthening of the ArMOC and convection north of the Greenland-Scotland Ridge cannot compensate for the progressive weakening of the AMOC.

scholarly journals Regional seesaw between the North Atlantic and Nordic Seas during the last glacial abrupt climate events

2017 ◽  
Vol 13 (6) ◽  
pp. 729-739 ◽  
Author(s):  
Mélanie Wary ◽  
Frédérique Eynaud ◽  
Didier Swingedouw ◽  
Valérie Masson-Delmotte ◽  
Jens Matthiessen ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Sea Surface ◽  
Nordic Seas ◽  
Norwegian Sea ◽  
Surface Conditions ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial

Abstract. Dansgaard–Oeschger oscillations constitute one of the most enigmatic features of the last glacial cycle. Their cold atmospheric phases have been commonly associated with cold sea-surface temperatures and expansion of sea ice in the North Atlantic and adjacent seas. Here, based on dinocyst analyses from the 48–30 ka interval of four sediment cores from the northern Northeast Atlantic and southern Norwegian Sea, we provide direct and quantitative evidence of a regional paradoxical seesaw pattern: cold Greenland and North Atlantic phases coincide with warmer sea-surface conditions and shorter seasonal sea-ice cover durations in the Norwegian Sea as compared to warm phases. Combined with additional palaeorecords and multi-model hosing simulations, our results suggest that during cold Greenland phases, reduced Atlantic meridional overturning circulation and cold North Atlantic sea-surface conditions were accompanied by the subsurface propagation of warm Atlantic waters that re-emerged in the Nordic Seas and provided moisture towards Greenland summit.

scholarly journals 120,000 year record of sea ice in the North Atlantic

2018 ◽  
Author(s):  
Niccolò Maffezzoli ◽  
Paul Vallelonga ◽  
Ross Edwards ◽  
Alfonso Saiz-Lopez ◽  
Clara Turetta ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Arctic Sea Ice ◽  
Sea Ice Extent ◽  
Nordic Seas ◽  
Last Glacial ◽  
The North ◽  
Arctic Sea ◽  
The North Atlantic ◽  
The Last Glacial

Abstract. Although it has been demonstrated that the speed and magnitude of recent Arctic sea ice decline is unprecedented for the past 1,450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Here we present a 120 kyr record of bromine enrichment from the RECAP ice core, coastal East Greenland, and reconstruct past sea ice conditions in the North Atlantic as far north as the entrance of the Arctic Ocean (50–85° N). Bromine enrichment has been previously employed to reconstruct first-year sea ice (FYSI) in the Canadian Arctic over the last glacial cycle. We find that during the last deglaciation, the transition from multi-year sea ice (MYSI) to FYSI started at ∼ 17.6 kyr, synchronous with sea ice reductions observed in the eastern Nordic seas (Müller and Stein, 2014; Hoff et al., 2016) and with the increase of North Atlantic ocean temperature (Dokken and Jansen, 1999). FYSI reached its maximum extent at 12.4–11.8 kyr, after which open-water conditions started to dominate, as supported by sea ice records from the eastern Nordic seas and the North Icelandic shelf. Our results show that over the last 120,000 years, sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and MIS4, with decreased levels during MIS3 and the onset of the last glacial period (late-MIS5). Sea ice extent during the last 10 kyr (Holocene/MIS1) has been less than at any time in the last 120 kyr.

scholarly journals Regional seesaw between North Atlantic and Nordic Seas during the last glacial abrupt climate events

2017 ◽  
Author(s):  
Mélanie Wary ◽  
Frédérique Eynaud ◽  
Didier Swingedouw ◽  
Valérie Masson-Delmotte ◽  
Jens Matthiessen ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
Glacial Cycle ◽  
Nordic Seas ◽  
Norwegian Sea ◽  
Surface Conditions ◽  
Last Glacial ◽  
The Last Glacial

Abstract. Dansgaard-Oeschger oscillations constitute one of the most enigmatic features of the last glacial cycle. Their cold atmospheric phases have been commonly associated with cold sea-surface temperatures and expansion of sea ice in the North Atlantic and adjacent seas. Here, based on dinocyst analyses from the 48–30 ka BP interval of four sediment cores from the northern Northeast Atlantic and southern Norwegian Sea, we provide direct and quantitative evidence of a regional paradoxical seesaw pattern: cold Greenland and North Atlantic phases coincide with warmer sea-surface conditions and shorter seasonal sea-ice cover durations in the Norwegian Sea as compared to warm phases. Combined with additional paleorecords and multi-model hosing simulations, our results suggest that during cold Greenland phases, reduced Atlantic meridional overturning circulation and cold North Atlantic sea-surface conditions were accompanied by the subsurface propagation of warm Atlantic waters that re-emerged in the Nordic Seas and provided moisture towards Greenland summit.

scholarly journals Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

2016 ◽  
Vol 12 (12) ◽  
pp. 2241-2253 ◽  
Author(s):  
Louise C. Sime ◽  
Dominic Hodgson ◽  
Thomas J. Bracegirdle ◽  
Claire Allen ◽  
Bianca Perren ◽  
...  
Keyword(s):  
Sea Ice ◽  
Last Glacial Maximum ◽  
Heat Fluxes ◽  
Glacial Maximum ◽  
State Dependency ◽  
Last Glacial ◽  
Poleward Shift ◽  
Future Warming ◽  
Ice Edge ◽  
Sea Ice Edge

Abstract. Latitudinal shifts in the Southern Ocean westerly wind jet could drive changes in the glacial to interglacial ocean CO2 inventory. However, whilst CMIP5 model results feature consistent future-warming jet shifts, there is considerable disagreement in deglacial-warming jet shifts. We find here that the dependence of pre-industrial (PI) to Last Glacial Maximum (LGM) jet shifts on PI jet position, or state dependency, explains less of the shifts in jet simulated by the models for the LGM compared with future-warming scenarios. State dependence is also weaker for intensity changes, compared to latitudinal shifts in the jet. Winter sea ice was considerably more extensive during the LGM. Changes in surface heat fluxes, due to this sea ice change, probably had a large impact on the jet. Models that both simulate realistically large expansions in sea ice and feature PI jets which are south of 50° S show an increase in wind speed around 55° S and can show a poleward shift in the jet between the PI and the LGM. However, models with the PI jet positioned equatorwards of around 47° S do not show this response: the sea ice edge is too far from the jet for it to respond. In models with accurately positioned PI jets, a +1° difference in the latitude of the sea ice edge tends to be associated with a −0.85° shift in the 850 hPa jet. However, it seems that around 5° of expansion of LGM sea ice is necessary to hold the jet in its PI position. Since the Gersonde et al. (2005) data support an expansion of more than 5°, this result suggests that a slight poleward shift and intensification was the most likely jet change between the PI and the LGM. Without the effect of sea ice, models simulate poleward-shifted westerlies in warming climates and equatorward-shifted westerlies in colder climates. However, the feedback of sea ice counters and reverses the equatorward trend in cooler climates so that the LGM winds were more likely to have also been shifted slightly poleward.

scholarly journals Impacts of large-scale atmospheric circulation changes due to winter sea-ice retreat on Black Carbon transport and deposition to the Arctic

2016 ◽  
Author(s):  
Luca Pozzoli ◽  
Srdan Dobricic ◽  
Simone Russo ◽  
Elisabetta Vignati
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Large Scale ◽  
Southern Oscillation ◽  
The Arctic ◽  
The North ◽  
Ice Retreat ◽  
The North Atlantic Oscillation ◽  
Sea Ice Retreat

Abstract. Winter warming and sea ice retreat observed in the Arctic in the last decades determine changes of large scale atmospheric circulation pattern that may impact as well the transport of black carbon (BC) to the Arctic and its deposition on the sea ice, with possible feedbacks on the regional and global climate forcing. In this study we developed and applied a new statistical algorithm, based on the Maximum Likelihood Estimate approach, to determine how the changes of three large scale weather patterns (the North Atlantic Oscillation, the Scandinavian Blocking, and the El Nino-Southern Oscillation), associated with winter increasing temperatures and sea ice retreat in the Arctic, impact the transport of BC to the Arctic and its deposition. We found that the three atmospheric patterns together determine a decreasing winter deposition trend of BC between 1980 and 2015 in the Eastern Arctic while they increase BC deposition in the Western Arctic. The increasing trend is mainly due to the more frequent occurrences of stable high pressure systems (atmospheric blocking) near Scandinavia favouring the transport in the lower troposphere of BC from Europe and North Atlantic directly into to the Arctic. The North Atlantic Oscillation has a smaller impact on BC deposition in the Arctic, but determines an increasing BC atmospheric load over the entire Arctic Ocean with increasing BC concentrations in the upper troposphere. The El Nino-Southern Oscillation does not influence significantly the transport and deposition of BC to the Arctic. The results show that changes in atmospheric circulation due to polar atmospheric warming and reduced winter sea ice significantly impacted BC transport and deposition. The anthropogenic emission reductions applied in the last decades were, therefore, crucial to counterbalance the most likely trend of increasing BC pollution in the Arctic.

The Effect of a Large Freshwater Perturbation on the Glacial North Atlantic Ocean Using a Coupled General Circulation Model

2006 ◽  
Vol 19 (17) ◽  
pp. 4436-4447 ◽  
Author(s):  
C. D. Hewitt ◽  
A. J. Broccoli ◽  
M. Crucifix ◽  
J. M. Gregory ◽  
J. F. B. Mitchell ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Quasi Equilibrium ◽  
Last Glacial ◽  
Proxy Records ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial

Abstract The commonly held view of the conditions in the North Atlantic at the last glacial maximum, based on the interpretation of proxy records, is of large-scale cooling compared to today, limited deep convection, and extensive sea ice, all associated with a southward displaced and weakened overturning thermohaline circulation (THC) in the North Atlantic. Not all studies support that view; in particular, the “strength of the overturning circulation” is contentious and is a quantity that is difficult to determine even for the present day. Quasi-equilibrium simulations with coupled climate models forced by glacial boundary conditions have produced differing results, as have inferences made from proxy records. Most studies suggest the weaker circulation, some suggest little or no change, and a few suggest a stronger circulation. Here results are presented from a three-dimensional climate model, the Hadley Centre Coupled Model version 3 (HadCM3), of the coupled atmosphere–ocean–sea ice system suggesting, in a qualitative sense, that these diverging views could all have occurred at different times during the last glacial period, with different modes existing at different times. One mode might have been characterized by an active THC associated with moderate temperatures in the North Atlantic and a modest expanse of sea ice. The other mode, perhaps forced by large inputs of meltwater from the continental ice sheets into the northern North Atlantic, might have been characterized by a sluggish THC associated with very cold conditions around the North Atlantic and a large areal cover of sea ice. The authors’ model simulation of such a mode, forced by a large input of freshwater, bears several of the characteristics of the Climate: Long-range Investigation, Mapping, and Prediction (CLIMAP) Project’s reconstruction of glacial sea surface temperature and sea ice extent.

Reconstruction of sea-surface temperature, salinity, and sea-ice cover in the northern North Atlantic during the last glacial maximum based on dinocyst assemblages

2000 ◽  
Vol 37 (5) ◽  
pp. 725-750 ◽  
Author(s):  
Anne de Vernal ◽  
Claude Hillaire-Marcel ◽  
Jean-Louis Turon ◽  
Jens Matthiessen
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Last Glacial Maximum ◽  
North Atlantic ◽  
Ice Cover ◽  
Glacial Maximum ◽  
Sea Surface ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Past sea-surface conditions over the northern North Atlantic during the last glacial maximum were examined from the study of 61 deep-sea cores. The last glacial maximum time slice studied here corresponds to an interval between Heinrich layers H2 and H1, and spanning about 20-16 ka on a 14C time scale. Transfer functions based on dinocyst assemblages were used to reconstruct sea-surface temperature, salinity, and sea-ice cover. The results illustrate extensive sea-ice cover along the eastern Canadian margins and sea-ice spreading, only during winter, over most of the northern North Atlantic. On the whole, much colder winter prevailed, despite relatively mild conditions in August (10-15°C at most offshore sites), thus suggesting a larger seasonal contrast of temperatures than today. Lower salinity than at present is reconstructed, especially along the eastern Canadian and Scandinavian margins, likely because of meltwater supply from the surrounding ice sheets. These reconstructions contrast with those established by CLIMAP on the basis of planktonic foraminifera. These differences are discussed with reference to the stratigraphical frame of the last glacial maximum, which was not the coldest phase of the last glacial stage. The respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses, which was apparently much more stratified than at present in the northern North Atlantic, thus preventing deep-water formation.

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