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  • 11
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    Last interglacial (MIS 5e) surface circulation in the North Atlantic and Nordic seas, based on dinoflagellate cysts (2011)
    In:  [Talk] In: XVIII. INQUA-Congress, Quaternary Sciences – The View From The Mountains, 25.07.2011, Bern, Switzerland .
    Details
    Publication Date: 2012-02-23
    Description: Sediments from the last interglacial (MIS 5e) were studied for their dinoflagellate cyst (dinocyst) content from cores across the North Atlantic and Nordic seas, in order to trace changes in the interaction between the warm water masses of the northward flowing Gulf Stream/North Atlantic Drift current system and the cold water masses of the East Greenland/Labrador Current. Supported by stable isotope, IRD and planktic foraminiferal data, the qualitative and quantitative analysis of the dinocyst assemblages illustrates the stepwise development of interglacial conditions from late MIS 6 and Termination II towards a MIS 5e optimum and back to the colder MIS 5d stadial. It is shown that the development of the MIS 5e optimum occurred only late during MIS 5e in the eastern Nordic seas, as a consequence of a delayed intensification of the northernmost limb of the Gulf Stream/North Atlantic Drift. While prolonged deglacial processes presumably had hindered this northward protrusion of warm surface waters during early MIS 5e, its intensification during late MIS 5e in turn caused a reorganisation of the cold surface current system.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 12
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    The last interglacial in the northern North Atlantic and adjacent areas: evidence for a more zonal climate than during the Holocene (2011)
    Copernicus Publ.
    In:  [Talk] In: EGU General Assembly 2011, 07.04.2011, Vienna, Austria ; p. 2764 .
    Details
    Publication Date: 2012-07-06
    Description: We document climate conditions from the last interglacial optimum (LIO) or marine isotope stage 5e (MIS 5e) from terrestrial and oceanic sedimentary archives. Terrestrial climate conditions are reconstructed from pollen assemblages, whereas sea-surface temperature and salinity conditions are estimated from dinocyst assemblages and foraminiferal data (both assemblages and stable isotope composition of carbonate shells). LIO data from the eastern Canadian Arctic and northern Labrador Sea led to reconstruct much higher summer air temperature and seasurface temperature than at present by about 5°C. Data from southeastern Canada and southern Labrador Sea also suggest more thermophilic vegetation and warmer conditions although the contrast between LIO and the Holocene is of lesser amplitude. On the whole, the terrestrial and marine data sets from the northwest North Atlantic and adjacent lands suggest limited influence of southward flow from Arctic waters through the east Greenland and Labrador Currents as compared to the modern situation. The compilation of sea-surface reconstructions from the northwest and northeast North Atlantic indicate much reduced longitudinal contrasts of temperatures than at present, thus a more zonal pattern of circulation. The reconstructions also indicate a lower sea-surface salinity than at present, thus stronger stratification of upper water masses, which would be compatible with a reduced North Atlantic deep-water formation.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Talk
  • 13
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    Evaluating the role of Atlantic Water advection to the Arctic Ocean on geological, historical, and observational timescales (2014)
    IUEM
    In:  [Talk] In: ISTAS: Integrating Spatial and Temporal Scales in the Changing Arctic System, 21.10.-24.10.2014, Plouzané, France . ISTAS: Integrating Spatial and Temporal Scales in the Changing Arctic System : Towards Future Research Priorities ; Oct 21 - 24, Plouzané, IUEM ; Book of Abstracts – Plenary Session ; p. 41 .
    Details
    Publication Date: 2019-09-23
    Description: Recent observations of enhanced oceanic heat transfer into the Arctic concomitant with the rapid sea-ice decrease temptingly suggest a direct relationship between both features. However, except for marginal areas of the Arctic Ocean where warm and saline Atlantic Water (AW) reaches the surface, the majority of AW heat is presently isolated from the sea-ice cover by a cold and fresh halocline layer. No evidence has been found to suggest a weakening of the halocline across the central Arctic basins that would enhance the AW heat transfer to the surface. A more direct link between sea-ice reduction and AW inflow is, however, seen in the inflowing Barents Sea branch in both historical and observational time series. In this presentation the AW advection into the Arctic Ocean and its influence on sea-ice variability will be reviewed from a geological point of view. Records from the geologic past are of great value as the time span of modern observations and historical data is often too short to comprehend long-term trends and causes of AW variability, changes in the marginal ice zone, and the vertical structure of the Arctic water column. Paleoceanographic studies from the recent interglacial indirectly suggest that the strength of AW advection and its propagation into the Arctic interior is effective in melting sea ice in combination with other factors such as insolation, sea level, freshwater input, and upper water mass stratification. However, to date, very little paleoceanographic work in the Arctic has focused on how the strength and position of the halocline has changed during previous interglacial periods. More direct reconstructions of the Arctic’s vertical stratification in the geologic past are needed to provide a longer-term view on the stability of the halocline, and more generally, the role of Atlantic Water inflow on the stability of sea ice in the interior basins.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 14
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    Holocene versus last interglacial (MIS 5e) surface ocean conditions in the Nordic seas and northern North Atlantic (2011)
    In:  [Talk] In: 9th International Conference on Modern and Fossil Dinoflagellates, DINO9, 30.08.2011, Liverpool, Great Britain .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 15
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    A dinoflagellate cyst perspective on the surface circulation in the North Atlantic and Nordic seas during the Last Interglacial (MIS 5e) (2011)
    Centre de Villégiature Jouvence
    In:  [Talk] In: GEOTOP Annual Meeting, 06.02.2011, Orford, Quebec, Canada . Congrès annuel du GEOTOP = GEOTOP annual meeting : 4 au 6 février 2011 ; p. 67 .
    Details
    Publication Date: 2012-02-23
    Description: When looking for possible scenarios of future climate development, the last interglacial is a suitable candidate. This warm interval, know as Marine Oxygen Isotope Stage (MIS) 5e in marine sediments, lasted from ~130 000 to ~115 000 years ago, and is assumed to have been characterised by Holocene-like climatic boundary conditions. The northern North Atlantic and Nordic (Greenland, Iceland and Norwegian) seas are key areas in this context: the warm water masses that are advected into the region through the northward flowing Gulf Stream/North Atlantic Drift surface current system interact with the southward flowing polar water masses of the East Greenland/Labrador Current, and they are among the few regions were overturning and deep-water formation occurs. Changes in the sea-surface conditions in this area can therefore steer climate by influencing the Meridional Overturning Circulation, and the feedbacks this has on the atmospheric circulation. The goal of the project is to reconstruct the sea surface conditions in the northern North Atlantic and Nordic seas during MIS 5e in order to trace changes in the interaction between the warm water masses of the Gulf Stream/North Atlantic Drift current system and the cold water masses of the East Greenland/Labrador Current. This will be done by qualitative and quantitative analysis of dinoflagellate cyst assemblages, algal remains with a proven potential for paleoclimate reconstructions, in sediments from key localities across the North Atlantic and Nordic seas.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 16
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    Microfossil evidence for contrasting Holocene and last interglacial (MIS 5e) surface water conditions in the western Iceland Sea (2012)
    In:  [Talk] In: AGU Fall Meeting 2012, 05.12.2012, San Francisco, USA .
    Details
    Publication Date: 2020-11-04
    Description: PP31B-2025 Dinoflagellate cyst and planktic foraminiferal assemblages from a core in the western Iceland Sea were analysed in order to reconstruct the last interglacial (MIS 5e) surface water conditions and compare these with the Holocene climate development. The considerable dissimilarities between the assemblages from the two warm periods suggest that quite different surface water conditions existed during each of the two interglacial stages. Holocene interglacial conditions initiated around 10 ka with a subsurface warming that peaked around 7.5 ka preceding a thermal maximum in the uppermost ocean between 6.5 and 5.5 ka, followed by overall cooling. By contrast, both planktic foraminifers and dinoflagellate cysts show a last interglacial thermal optimum around 120.5 ka, following an increased influence of Atlantic (-type) waters from ~122 ka onward. A major shift of the oceanographic fronts appears to have occurred around 120 ka and marks the onset of slightly cooler conditions that persist until the return to stadial conditions around ~117 ka. This late-MIS 5e cooling in the western Nordic seas is opposite to previous observations of a late MIS 5e thermal optimum in the eastern Nordic seas. Such an opposite trend likely relates to the reorganisation of the oceanic fronts that appears to have occurred in the Nordic seas at ~120 ka. Overall, the MIS 5e assemblages are characterised by higher percentages of typical “Atlantic water” species, compared to the cooler Holocene assemblages. This implies a higher contribution of Atlantic waters in the southwestern Nordic seas, possibly due to a more northward expansion of the Irminger Current under weakened East Greenland/East Icelandic currents, during the last interglacial than during the Holocene. A reduced influence of polar waters in the southwestern Nordic seas is consistent with other evidence of relatively warm conditions during MIS 5e all around southern Greenland.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 17
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    Operational taxonomy for round, brown, spiny dinocysts from high latitudes of the Northern Hemisphere (2011)
    In:  [Poster] In: 9th International Conference on Modern and Fossil Dinoflagellates, DINO9, 30.08.2011, Liverpool, Great Britain .
    Details
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 18
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    Microfossil evidence for contrasting Holocene and last interglacial (MIS 5e) surface water conditions in the western Iceland Sea (2011)
    In:  [Poster] In: AGU Fall Meeting 2012, 05.12.2012, San Francisco, USA .
    Details
    Publication Date: 2020-11-04
    Description: PP31B-2025 Dinoflagellate cyst and planktic foraminiferal assemblages from a core in the western Iceland Sea were analysed in order to reconstruct the last interglacial (MIS 5e) surface water conditions and compare these with the Holocene climate development. The considerable dissimilarities between the assemblages from the two warm periods suggest that quite different surface water conditions existed during each of the two interglacial stages. Holocene interglacial conditions initiated around 10 ka with a subsurface warming that peaked around 7.5 ka preceding a thermal maximum in the uppermost ocean between 6.5 and 5.5 ka, followed by overall cooling. By contrast, both planktic foraminifers and dinoflagellate cysts show a last interglacial thermal optimum around 120.5 ka, following an increased influence of Atlantic (-type) waters from ~122 ka onward. A major shift of the oceanographic fronts appears to have occurred around 120 ka and marks the onset of slightly cooler conditions that persist until the return to stadial conditions around ~117 ka. This late-MIS 5e cooling in the western Nordic seas is opposite to previous observations of a late MIS 5e thermal optimum in the eastern Nordic seas. Such an opposite trend likely relates to the reorganisation of the oceanic fronts that appears to have occurred in the Nordic seas at ~120 ka. Overall, the MIS 5e assemblages are characterised by higher percentages of typical “Atlantic water” species, compared to the cooler Holocene assemblages. This implies a higher contribution of Atlantic waters in the southwestern Nordic seas, possibly due to a more northward expansion of the Irminger Current under weakened East Greenland/East Icelandic currents, during the last interglacial than during the Holocene. A reduced influence of polar waters in the southwestern Nordic seas is consistent with other evidence of relatively warm conditions during MIS 5e all around southern Greenland.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 19
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    Natural variability of the Arctic Ocean sea ice during the present interglacial (2020)
    National Academy of Sciences
    Details
    Publication Date: 2023-02-08
    Description: The impact of the ongoing anthropogenic warming on the Arctic Ocean sea ice is ascertained and closely monitored. However, its long-term fate remains an open question as its natural variability on centennial to millennial timescales is not well documented. Here, we use marine sedimentary records to reconstruct Arctic sea-ice fluctuations. Cores collected along the Lomonosov Ridge that extends across the Arctic Ocean from northern Greenland to the Laptev Sea were radiocarbon dated and analyzed for their micropaleontological and palynological contents, both bearing information on the past sea-ice cover. Results demonstrate that multiyear pack ice remained a robust feature of the western and central Lomonosov Ridge and that perennial sea ice remained present throughout the present interglacial, even during the climate optimum of the middle Holocene that globally peaked ∼6,500 y ago. In contradistinction, the southeastern Lomonosov Ridge area experienced seasonally sea-ice-free conditions, at least, sporadically, until about 4,000 y ago. They were marked by relatively high phytoplanktonic productivity and organic carbon fluxes at the seafloor resulting in low biogenic carbonate preservation. These results point to contrasted west–east surface ocean conditions in the Arctic Ocean, not unlike those of the Arctic dipole linked to the recent loss of Arctic sea ice. Hence, our data suggest that seasonally ice-free conditions in the southeastern Arctic Ocean with a dominant Arctic dipolar pattern, may be a recurrent feature under “warm world” climate.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 20
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    A global database of Holocene paleotemperature records (2020)
    Details
    Publication Date: 2023-02-08
    Description: A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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