scholarly journals Warm Greenland during the last interglacial: the role of regional changes in sea ice cover

2016 ◽  
Vol 12 (10) ◽  
pp. 2011-2031 ◽  
Author(s):  
Niklaus Merz ◽  
Andreas Born ◽  
Christoph C. Raible ◽  
Thomas F. Stocker
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
Labrador Sea ◽  
Last Interglacial ◽  
Atlantic Sector ◽  
Nordic Seas ◽  
Proxy Records ◽  
Ice Retreat ◽  
Sea Ice Retreat

Abstract. The last interglacial, also known as the Eemian, is characterized by warmer than present conditions at high latitudes. This is implied by various Eemian proxy records as well as by climate model simulations, though the models mostly underestimate the warming with respect to proxies. Simulations of Eemian surface air temperatures (SAT) in the Northern Hemisphere extratropics further show large variations between different climate models, and it has been hypothesized that this model spread relates to diverse representations of the Eemian sea ice cover. Here we use versions 3 and 4 of the Community Climate System Model (CCSM3 and CCSM4) to highlight the crucial role of sea ice and sea surface temperatures changes for the Eemian climate, in particular in the North Atlantic sector and in Greenland. A substantial reduction in sea ice cover results in an amplified atmospheric warming and thus a better agreement with Eemian proxy records. Sensitivity experiments with idealized lower boundary conditions reveal that warming over Greenland is mostly due to a sea ice retreat in the Nordic Seas. In contrast, sea ice changes in the Labrador Sea have a limited local impact. Changes in sea ice cover in either region are transferred to the overlying atmosphere through anomalous surface energy fluxes. The large-scale spread of the warming resulting from a Nordic Seas sea ice retreat is mostly explained by anomalous heat advection rather than by radiation or condensation processes. In addition, the sea ice perturbations lead to changes in the hydrological cycle. Our results consequently imply that both temperature and snow accumulation records from Greenland ice cores are sensitive to sea ice changes in the Nordic Seas but insensitive to sea ice changes in the Labrador Sea. Moreover, the simulations suggest that the uncertainty in the Eemian sea ice cover accounts for 1.6 °C of the Eemian warming at the NEEM ice core site. The estimated Eemian warming of 5 °C above present day based on the NEEM δ15N record can be reconstructed by the CCSM4 model for the scenario of a substantial sea ice retreat in the Nordic Seas combined with a reduced Greenland ice sheet.

scholarly journals Warm Greenland during the last interglacial: the role of regional changes in sea ice cover

2016 ◽  
Author(s):  
Niklaus Merz ◽  
Andreas Born ◽  
Christoph C. Raible ◽  
Thomas F. Stocker
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
Labrador Sea ◽  
Last Interglacial ◽  
Atlantic Sector ◽  
Climate System Model ◽  
Nordic Seas ◽  
Ice Retreat ◽  
Sea Ice Retreat

Abstract. The last interglacial, the Eemian, is characterized by warmer than present conditions at high latitudes and is therefore often considered as a possible analogue for the climate in the near future. Simulations of Eemian surface air temperatures (SAT) in the Northern Hemisphere, however, show large variations between different climate models and it has been hypothesized that this model spread relates to diverse representations of the Eemian sea ice cover. Here we use versions 3 and 4 of the Community Climate System Model (CCSM3 and CCSM4), to highlight the crucial role of sea ice and sea surface temperatures during the Eemian, in particular for SAT in the North Atlantic sector and in Greenland. A substantial reduction in sea ice cover results in an amplified atmospheric warming and, thus, a better agreement with Eemian proxy records. Sensitivity experiments with idealized lower boundary conditions reveal that warming over Greenland is mostly due to a sea ice retreat in the Nordic Seas. In contrast, sea ice changes in the Labrador Sea have a limited local impact. Changes in sea ice cover in either region are transferred to the overlying atmosphere through anomalous surface energy fluxes. The large-scale warming simulated for the sea ice retreat in the Nordic Seas further relates to anomalous heat advection. Diabatic processes play a secondary role, yet distinct changes in the hydrological cycle are possible. Our results imply that temperature and accumulation records from Greenland ice cores are sensitive to sea ice changes in the Nordic Seas but insensitive to sea ice changes in the Labrador Sea. Moreover, our simulations suggest that the uncertainty in the Eemian sea ice cover accounts for 1.6 °C of the Eemian warming at the NEEM ice core site. The estimated Eemian warming of 5 °C above present-day based on the NEEM δ15N record can be reconstructed by the CCSM4 model for the scenario of a substantial sea ice retreat in the Nordic Seas combined with a reduced Greenland ice sheet.

A 14 - 0 ka record of trends and events of sea ice cover, primary production and freshwater discharge in the Beaufort Sea, Arctic Ocean

2020 ◽  
Author(s):  
Junjie Wu ◽  
Ruediger Stein ◽  
Kirsten Fahl ◽  
Nicole Syring ◽  
Jens Hefter ◽  
...  
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Beaufort Sea ◽  
Ice Cover ◽  
Sediment Flux ◽  
The Arctic ◽  
Proxy Records ◽  
Ice Retreat ◽  
Sea Ice Retreat ◽  
Natural Climate

<p>The Arctic is changing rapidly, and one of the main and most obvious features is the drastic sea-ice retreat over the past few decades. Over such time scales, observations are deficient and not long enough for deciphering the processes controlling this accelerated sea-ice retreat. Thus, high-resolution, longer-term proxy records are needed for reconstruction of natural climate variability. In this context, we applied a biomarker approach on the well-dated sediment core ARA04C/37 recovered in the southern Beaufort Sea directly off the Mackenzie River, an area that is characterized by strong seasonal variability in sea-ice cover, primary productivity and terrigenous (riverine) input. Based on our biomarker records, the Beaufort Sea region was nearly ice-free in summer during the late Deglacial to early Holocene (14 to 8 ka). During the mid-late Holocene (8 to 0 ka), a seasonal sea-ice cover developed, coinciding with a drop in both terrigenous sediment flux and primary production. Supported by multiple proxy records, two major flood events characterized by prominent maxima in sediment flux occurred near 13 and 11 ka. The former is coincident with the Younger Dryas Cooling Event probably triggered by a  freshwater outburst from the Lake Agassiz. The origin of the second (younger) one might represent a second Mackenzie flood event, coinciding with meltwater pulse IB/post-glacial flooding of the shelf and related increased coastal erosion. Here, our interpretation remains a little bit speculative, and further research is needed and also in progress.</p>

scholarly journals The Role of Northern Sea Ice Cover for the Weakening of the Thermohaline Circulation under Global Warming

2007 ◽  
Vol 20 (16) ◽  
pp. 4160-4171 ◽  
Author(s):  
A. Levermann ◽  
J. Mignot ◽  
S. Nawrath ◽  
S. Rahmstorf
Keyword(s):  
Global Warming ◽  
Sea Ice ◽  
Heat Loss ◽  
Climate Models ◽  
Thermohaline Circulation ◽  
Ice Cover ◽  
Near Surface ◽  
Ice Retreat ◽  
Sea Ice Retreat

Abstract An increase in atmospheric CO2 concentration and the resulting global warming are typically associated with a weakening of the thermohaline circulation (THC) in model scenarios. For the models participating in the Coupled Model Intercomparison Project (CMIP), this weakening shows a significant (r = 0.62) dependence on the initial THC strength; it is stronger for initially strong overturning. The authors propose a physical mechanism for this phenomenon based on an analysis of additional simulations with the coupled climate models CLIMBER-2 and CLIMBER-3α. The mechanism is based on the fact that sea ice cover greatly reduces heat loss from the ocean. The extent of sea ice is strongly influenced by the near-surface atmospheric temperature (SAT) in the North Atlantic but also by the strength of the THC itself, which transports heat to the convection sites. Consequently, sea ice tends to extend farther south for weaker THC. Initially larger sea ice cover responds more strongly to atmospheric warming; thus, sea ice retreats more strongly for an initially weaker THC. This sea ice retreat tends to strengthen (i.e., stabilize) the THC because the sea ice retreat allows more oceanic heat loss. This stabilizing effect is stronger for runs with weak initial THC and extensive sea ice cover. Therefore, an initially weak THC weakens less under global warming. In contrast to preindustrial climate, sea ice melting presently plays the role of an external forcing with respect to THC stability.

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.

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 Phytoplankton distribution in unusually low sea ice cover over the Pacific Arctic

2012 ◽  
Vol 9 (11) ◽  
pp. 4835-4850 ◽  
Author(s):  
P. Coupel ◽  
H. Y. Jin ◽  
M. Joo ◽  
R. Horner ◽  
H. A. Bouvet ◽  
...  
Keyword(s):  
Sea Ice ◽  
Marine Ecosystem ◽  
Environmental Parameters ◽  
Arctic Basin ◽  
Ice Cover ◽  
Phytoplankton Distribution ◽  
The Pacific ◽  
Ice Retreat ◽  
Sea Ice Retreat ◽  
The Impact

Abstract. A large part of the Pacific Arctic basin experiences ice-free conditions in summer as a result of sea ice cover steadily decreasing over the last decades. To evaluate the impact of sea ice retreat on the marine ecosystem, phytoplankton in situ observations were acquired over the Chukchi shelf and the Canadian basin in 2008, a year of high melting. Pigment analyses and taxonomy enumerations were used to characterise the distribution of main phytoplanktonic groups. Marked spatial variability of the phytoplankton distribution was observed in summer 2008. Comparison of eight phytoplankton functional groups and 3 size-classes (pico-, nano- and micro-phytoplankton) also showed significant differences in abundance, biomass and distribution between summer of low ice cover (2008) and heavy ice summer (1994). Environmental parameters such as freshening, stratification, light and nutrient availability are discussed as possible causes to explain the observed differences in phytoplankton community structure between 1994 and 2008.

scholarly journals Role of Eurasian Snow Cover in Linking Winter‐Spring Eurasian Coldness to the Autumn Arctic Sea Ice Retreat

2019 ◽  
Vol 124 (16) ◽  
pp. 9205-9221 ◽  
Author(s):  
Ruonan Zhang ◽  
Chenghu Sun ◽  
Renhe Zhang ◽  
Weijing Li ◽  
Jinqing Zuo
Keyword(s):  
Sea Ice ◽  
Snow Cover ◽  
Arctic Sea Ice ◽  
Eurasian Snow Cover ◽  
Eurasian Snow ◽  
Arctic Sea ◽  
Ice Retreat ◽  
Sea Ice Retreat

scholarly journals Consistent Changes in the Sea Ice Seasonal Cycle in Response to Global Warming

2011 ◽  
Vol 24 (20) ◽  
pp. 5325-5335 ◽  
Author(s):  
Ian Eisenman ◽  
Tapio Schneider ◽  
David S. Battisti ◽  
Cecilia M. Bitz
Keyword(s):  
Sea Ice ◽  
Northern Hemisphere ◽  
Surface Albedo ◽  
Climate Models ◽  
Climate Model ◽  
Ice Cover ◽  
Climate Forcing ◽  
Sea Ice Extent ◽  
Ice Retreat ◽  
Sea Ice Retreat

Abstract The Northern Hemisphere sea ice cover has diminished rapidly in recent years and is projected to continue to diminish in the future. The year-to-year retreat of Northern Hemisphere sea ice extent is faster in summer than winter, which has been identified as one of the most striking features of satellite observations as well as of state-of-the-art climate model projections. This is typically understood to imply that the sea ice cover is most sensitive to climate forcing in summertime, and previous studies have explained this by calling on factors such as the surface albedo feedback. In the Southern Hemisphere, however, it is the wintertime sea ice extent that retreats fastest in climate model projections. Here, it is shown that the interhemispheric differences in the model projections can be attributed to differences in coastline geometry, which constrain where sea ice can occur. After accounting for coastline geometry, it is found that the sea ice changes simulated in both hemispheres in most climate models are consistent with sea ice retreat being fastest in winter in the absence of landmasses. These results demonstrate that, despite the widely differing rates of ice retreat among climate model projections, the seasonal structure of the sea ice retreat is robust among the models and is uniform in both hemispheres.

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