Rapid reductions and millennial-scale variability in Nordic Seas sea ice cover during abrupt glacial climate changes

Constraining the past sea ice variability in the Nordic Seas is critical for a comprehensive understanding of the abrupt Dansgaard-Oeschger (D-O) climate changes during the last glacial. Here we present unprecedentedly detailed sea ice proxy evidence from two Norwegian Sea sediment cores and an East Greenland ice core to resolve and constrain sea ice variations during four D-O events between 32 and 41 ka. Our independent sea ice records consistently reveal a millennial-scale variability and threshold response between an extensive seasonal sea ice cover in the Nordic Seas during cold stadials and reduced seasonal sea ice conditions during warmer interstadials. They document substantial and rapid sea ice reductions that may have happened within 250 y or less, concomitant with reinvigoration of deep convection in the Nordic Seas and the abrupt warming transitions in Greenland. Our empirical evidence thus underpins the cardinal role of rapid sea ice decline and related feedbacks to trigger abrupt and large-amplitude climate change of the glacial D-O events.

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RECONSTRUCTING CHANGES IN SEA ICE COVER DURING MARINE ISOTOPE STAGE 11 FROM BERING SEA SEDIMENT CORES

10.1130/abs/2018nc-313273 ◽

2018 ◽

Author(s):

Natalie Thompson ◽

◽

Beth E. Caissie

Keyword(s):

Sea Ice ◽

Bering Sea ◽

Sediment Cores ◽

Ice Cover ◽

Marine Isotope Stage

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North Atlantic deep water formation and AMOC in CMIP5 models

Ocean Science ◽

10.5194/os-13-609-2017 ◽

2017 ◽

Vol 13 (4) ◽

pp. 609-622 ◽

Cited By ~ 26

Author(s):

Céline Heuzé

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

North Atlantic ◽

Deep Water ◽

Deep Convection ◽

The Arctic ◽

Subpolar Gyre ◽

Deep Water Formation ◽

Nordic Seas ◽

Water Formation

Abstract. Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turn, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecasting Arctic oceanic warming and its consequences for the global ocean circulation, cryosphere and marine life.

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Snow-ice growth: a fresh-water flux inhibiting deep convection in the Weddell Sea, Antarctica

Annals of Glaciology ◽

10.3189/172756401781818752 ◽

2001 ◽

Vol 33 ◽

pp. 45-50 ◽

Cited By ~ 14

Author(s):

V.I. Lytle ◽

S.F. Ackley

Keyword(s):

Sea Ice ◽

Thermohaline Circulation ◽

Deep Convection ◽

Ice Cover ◽

Snow Accumulation ◽

Heat Fluxes ◽

Weddell Sea ◽

Salt Flux ◽

Ice Formation ◽

Atmospheric Conditions

AbstractDuring a field experiment in July 1994, while the R.V. Nathaniel B. Palmer was moored to a drifting ice floe in the Weddell Sea, Antarctica, data were collected on sea-ice and snow characteristics. We report on the evolution of ice which grew in a newly opened lead. As expected with cold atmospheric conditions, congelation ice initially formed in the lead. Subsequent snow accumulation and large ocean heat fluxes resulted in melt at the base of the ice, and enhanced flooding of the snow on the ice surface. This flooded snow subsequently froze, and, 5 days after the lead opened, all the congelation ice had melted and 26 cm of snow ice had formed. We use measured sea-ice and snow salinities, thickness and oxygen isotope values of the newly formed lead ice to calculate the salt flux to the ocean. Although there was a salt flux to the ocean as the ice initially grew, we calculate a small net fresh-wlter input to the upper ocean by the end of the 5 day period. Similar processes of basal melt and surface snow-ice formation also occurred on the surrounding, thicker sea ice. Oceanographic studies in this region of the Weddell Sea have shown that salt rejection by sea-ice formation may enhance the ocean vertical thermohaline circulation and release heat from the deeper ocean to melt the ice cover. This type of deep convection is thought to initiate the Weddell polynya, which was observed only during the 1970s. Our results, which show that an ice cover can form with no salt input to the ocean, provide a mechanism which may help explain the more recent absence of the Weddell polynya.

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A 120 000-year record of sea ice in the North Atlantic?

Climate of the Past ◽

10.5194/cp-15-2031-2019 ◽

2019 ◽

Vol 15 (6) ◽

pp. 2031-2051 ◽

Cited By ~ 2

Author(s):

Niccolò Maffezzoli ◽

Paul Vallelonga ◽

Ross Edwards ◽

Alfonso Saiz-Lopez ◽

Clara Turetta ◽

...

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Ice Core ◽

Arctic Sea Ice ◽

First Year ◽

Sea Ice Extent ◽

Nordic Seas ◽

The North ◽

Arctic Sea ◽

The North Atlantic

Abstract. Although it has been demonstrated that the speed and magnitude of the recent Arctic sea ice decline is unprecedented for the past 1450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Bromine enrichment in ice cores has been suggested to indicate the extent of newly formed sea ice areas. Despite the similarities among sea ice indicators and ice core bromine enrichment records, uncertainties still exist regarding the quantitative linkages between bromine reactive chemistry and the first-year sea ice surfaces. Here we present a 120 000-year record of bromine enrichment from the RECAP (REnland ice CAP) ice core, coastal east Greenland, and interpret it as a record of first-year sea ice. We compare it to existing sea ice records from marine cores and tentatively reconstruct past sea ice conditions in the North Atlantic as far north as the Fram Strait (50–85∘ N). Our interpretation implies that during the last deglaciation, the transition from multi-year to first-year sea ice started at ∼17.5 ka, synchronously with sea ice reductions observed in the eastern Nordic Seas and with the increase in North Atlantic ocean temperature. First-year sea ice reached its maximum at 12.4–11.8 ka during the Younger Dryas, after which open-water conditions started to dominate, consistent with sea ice records from the eastern Nordic Seas and the North Icelandic shelf. Our results show that over the last 120 000 years, multi-year sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and possibly during MIS 4, with more extended first-year sea ice during MIS 3 and MIS 5. Sea ice extent during the Holocene (MIS 1) has been less than at any time in the last 120 000 years.

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Sea ice and millennial-scale climate variability in the Nordic seas 90 kyr ago to present

Nature Communications ◽

10.1038/ncomms12247 ◽

2016 ◽

Vol 7 (1) ◽

Cited By ~ 54

Author(s):

Ulrike Hoff ◽

Tine L. Rasmussen ◽

Ruediger Stein ◽

Mohamed M. Ezat ◽

Kirsten Fahl

Keyword(s):

Climate Variability ◽

Sea Ice ◽

Nordic Seas ◽

Millennial Scale

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Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study

Climate of the Past ◽

10.5194/cp-16-2459-2020 ◽

2020 ◽

Vol 16 (6) ◽

pp. 2459-2483

Author(s):

Maria-Elena Vorrath ◽

Juliane Müller ◽

Lorena Rebolledo ◽

Paola Cárdenas ◽

Xiaoxu Shi ◽

...

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

Antarctic Peninsula ◽

Environmental Conditions ◽

Ice Core ◽

Ice Cover ◽

Atmospheric Circulation Patterns ◽

The Past ◽

Circulation Patterns ◽

Spring Sea Ice

Abstract. In the last decades, changing climate conditions have had a severe impact on sea ice at the western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with a particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 240 years and compared them to observational data, sedimentary and ice core climate archives, and results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures, and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well to satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates, the long-term model output for the past 240 years, ice core records, and reconstructed atmospheric circulation patterns such as the El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover, and, additionally, each core site reflects specific local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice-associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend carefully considering individual biomarker records to distinguish between cold sea-ice-favoring and warm sea-ice-diminishing environmental conditions.

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

Climate of the Past ◽

10.5194/cp-12-2011-2016 ◽

2016 ◽

Vol 12 (10) ◽

pp. 2011-2031 ◽

Cited By ~ 8

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.

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Deglacial sea ice variability at the continental margin off western Dronning Maud Land

10.5194/egusphere-egu2020-13950 ◽

2020 ◽

Author(s):

Juliane Müller ◽

Catalina Gebhardt ◽

Gesine Mollenhauer ◽

Ralf Tiedemann

Keyword(s):

Sea Ice ◽

Continental Margin ◽

Ice Core ◽

Physical Property ◽

Weddell Sea ◽

Geochemical Data ◽

Shelf Sediments ◽

Dronning Maud Land ◽

Oceanic Forcing ◽

Ice Conditions

Reconstructions of sea ice conditions proximal to the Antarctic coast are often hampered by a limited preservation potential of diatoms in these areas. While silica frustules are affected by opal dissolution, specific organic molecules, highly branched isoprenoids (HBIs) produced by diatoms, are well preserved in continental margin and shelf sediments and may help to overcome this gap. Here, we present biomarker and geochemical data obtained from a very well 14C-dated gravity core from the continental slope off Atka Bay in the northeastern part of the Weddell Sea. HBIs, the HBI-based PIPSO25 index (Vorrath et al., 2019), glycerol dialkyl glycerol tetraether (GDGT) proxies and phytosterols reveal highly variable sea ice conditions and water temperatures as well as primary productivity changes over the last deglacial. These biomarker records are compared to ice core data and further complemented by physical property and XRF scanning data to estimate potential linkages between oceanic forcing and ice-shelf dynamics.&#160;ReferencesVorrath, M.E., M&#252;ller, J., Esper, O., Mollenhauer, G., Haas, C., Schefu&#223;, E., and Fahl, K., 2019. Highly branched isoprenoids for Southern Ocean sea ice reconstructions: a pilot study from the Western Antarctic Peninsula. Biogeosciences, v. 16, no. 15, p. 2961-2981.

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Landfast ice zoning from SAR imagery

10.5194/egusphere-egu2020-22541 ◽

2020 ◽

Author(s):

Valeria Selyuzhenok ◽

Denis Demchev ◽

Thomas Krumpen

Keyword(s):

Time Series ◽

Sea Ice ◽

Ice Cover ◽

Arctic Sea Ice ◽

The Arctic ◽

Ice Drift ◽

Landfast Ice ◽

Sea Ice Drift ◽

Ice Conditions ◽

Sar Imagery

Landfast sea ice is a dominant sea ice feature of the Arctic coastal region. As a part of Arctic sea ice cover, landfast ice is an important part of coastal ecosystem, it provides functions as a climate regulator and platform for human activity. Recent changes in sea ice conditions in the Arctic have also affected landfast ice regime. At the same time, industrial interest in the Arctic shelf seas continue to increase. Knowledge on local landfast ice conditions are required to ensure safety of on ice operations and accurate forecasting.&#160; In order to obtain a comprehensive information on landfast ice state we use a time series of wide swath SAR imagery.&#160; An automatic sea ice tracking algorithm was applied to the sequential SAR images during the development stage of landfast ice cover. The analysis of resultant time series of sea ice drift allows to classify homogeneous sea ice drift fields and timing of their attachment to the landfast ice. In addition, the drift data allows to locate areas of formation of grounded sea ice accumulation called stamukha. This information &#1089;an be useful for local landfast ice stability assessment. The study is supported by the Russian Foundation for Basic Research (RFBR) grant 19-35-60033.

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Multiproxy climate and sea ice reconstruction of the industrial era at the Western Antarctic Peninsula

10.5194/egusphere-egu2020-525 ◽

2020 ◽

Author(s):

Maria-Elena Vorrath ◽

Paola Cárdenas ◽

Lorena Rebolledo ◽

Xiaoxu Shi ◽

Juliane Müller ◽

...

Keyword(s):

Sea Ice ◽

Antarctic Peninsula ◽

System Analysis ◽

Ice Cover ◽

Weddell Sea ◽

Water Masses ◽

Western Antarctic Peninsula ◽

Climate Conditions ◽

Ice Conditions ◽

Bransfield Basin

Recent changes and variability in climate conditions leave a significant footprint on the distribution and properties of sea ice, as it is sensitive to environmental variations. We investigate the rapidly transforming region of the Western Antarctic Peninsula (WAP) focusing on the conditions and development of sea ice in the pre-satellite era. For this study on past sea ice cover we apply the novel proxy IPSO25 (Ice Proxy for the Southern Ocean with 25 carbon atoms; Belt et al., 2016). Three sampling sites were selected to cover areas near the Antarctic mainland, in the Bransfield Basin (2000 m depth) and the deeper shelf under an oceanographic frontal system. Analysis of short cores (multicores) resolving the last 200 years (based on 210Pbex dating) focused on geochemical bulk parameters, biomarkers (highly branched isoprenoids, GDGTs, sterols) and diatoms. These results are compared to multiple climate archives and modelled data. This multiproxy based approach provides insights on changes in spring sea ice cover, primary production regimes, subsurface ocean temperature (SOT based on TEXL86) and oceanographic as well as atmospheric circulation patterns. While environmental proxies preserved in two cores near the coast and in the Bransfield Basin reflect the properties of water masses from the Bellingshausen Sea and Weddell Sea, respectively, data from the third core at the deeper shelf depict mixed signals of both water masses. Our study reveals clear evidence for warm and cold periods matching with ice core records and other marine sediment data at the WAP. We observe a general decrease in SOT and an increase in sea ice cover overprinted by high decadal fluctuations. Trends in SOT seem to be decoupled from atmospheric temperatures in the 20th century, and this is supported by previous studies (e.g. Barbara et al., 2013), and may be related to the Southern Annual Mode. We consider numerical modelling of sea ice conditions, sea surface temperature and SOT for further support of our findings.&#160;References:Barbara, L., Crosta, X., Schmidt, S. and Mass&#233;, G.: Diatoms and biomarkers evidence for major changes in sea ice conditions prior the instrumental period in Antarctic Peninsula, Quat. Sci. Rev., 79, 99&#8211;110, doi:10.1016/j.quascirev.2013.07.021, 2013.Belt, S. T., Smik, L., Brown, T. A., Kim, J. H., Rowland, S. J., Allen, C. S., Gal, J. K., Shin, K. H., Lee, J. I. and Taylor, K. W. R.: Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25, Nat. Commun., 7, 1&#8211;10, doi:10.1038/ncomms12655, 2016.

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