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On the Late Saalian glaciation: A climate modeling study
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on the glaciation of the Late Saalian period (160 -140 ka) over Eurasia. The Quaternary Environment of the Eurasian North (QUEEN) project determined that during this period, the Eurasian ice sheet was substantially larger than during the entire Weichselian cycle and especially that of the Last Glacial Maximum (21 ka, LGM). The Late Saalian astronomical forcing was different than during the LGM while greenhouse gas concentrations were similar. To understand how this ice sheet could have grown so large over Eurasia during the Late Saalian, we use an Atmospherical General Circulation Model (AGCM) coupled to an oceanic mixed layer and a vegetation model to explore the influence of regional parameters, sea surface temperatures (SST) and orbital parameters on the surface mass balance (SMB) of the Late Saalian Eurasian ice sheet.

At140 ka, proglacial lakes, vegetation and simulated Late Saalian SST cool the Eurasian climate, which reduce the ablation along the southern ice sheet margins. Dust deposition on snow has the opposite effect. The presence of a Canada Basin ice-shelf during MIS6 in the Arctic Ocean, does not affect the mass balance of the ice sheet. According to geological evidence, the Late Saalian Eurasian ice sheet reached its maximum extent before 160 ka. Northern Hemisphere high latitude summer insolation shows a large insolation peak near 150 ka. The simulated climate prior to 140 ka is milder and ablation is larger along the southern margins of the Eurasian ice sheet although the mean annual SMB is positive. The Late Saalian Eurasian ice sheet may have been large enough to generate its own cooling, thus maintaining itself over Eurasia. 

Place, publisher, year, edition, pages
Stockholm: Department of Geology and Geochemistry, Stockholm University , 2009. , 53 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 335
Keyword [en]
Climate modeling, Eurasian ice sheet, Quaternary, Saalian, surface mass balance, SST
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geoscience
Identifiers
URN: urn:nbn:se:su:diva-29284ISBN: 978-91-7155-914-2 (print)OAI: oai:DiVA.org:su-29284DiVA: diva2:232193
Public defence
2009-09-14, Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Joseph Fourier, 54 rue Moliére, St-Martin d'Héres Cedex, France, 10:00 (English)
Opponent
Supervisors
Note
Joint PhD Degree between Stockholm University and Université Joseph Fourier At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Manuscript.Available from: 2009-08-30 Created: 2009-08-20 Last updated: 2009-08-21Bibliographically approved
List of papers
1. Influence of regional factors on the surface mass balance of the large Eurasian ice sheet during the peak Saalian (140 kyrs BP)
Open this publication in new window or tab >>Influence of regional factors on the surface mass balance of the large Eurasian ice sheet during the peak Saalian (140 kyrs BP)
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2009 (English)In: Global and Planetary Change, ISSN 0921-8181, Vol. 68, no 1-2, 132-148 p.Article in journal (Refereed) Published
Abstract [en]

Recent geologically-based reconstructions of the Eurasian ice sheet show that during the peak Saalian (≈ 140 kya) the ice sheet was larger over Eurasia than during the Last Glacial Maximum (LGM) at ≈ 21 kya. To address this problem we use the LMDZ4 atmospheric general circulation model to evaluate the impact on the Saalian ice sheet's surface mass balance (SMB) from proglacial lakes, dust deposition on snow, vegetation and sea surface temperatures (SST) since geological records suggest that these environmental parameters were different during the two glacial periods. Seven model simulations have been carried out. Dust deposition decreases the mean SMB by intensifying surface melt during summer while proglacial lakes cool the summer climate and reduce surface melt on the ice sheet. A simulation including both proglacial lakes and dust shows that the presence of the former parameter reduces the impact of the latter, in particular, during summer. A switch from needle-leaf to tundra vegetation affects the regional climate but not enough to significantly influence the SMB of the nearby ice margin. However, a steady-state vegetation in equilibrium with the climate should be computed to improve the boundary conditions for further evaluations of the vegetation impact on the ice sheet's SMB. Finally, changes of the SST broadly affect the regional climate with significant consequences for the SMB.

Keyword
surface mass balance, Eurasian ice sheet, Saalian, proglacial lakes, dust, SST, vegetation
National Category
Climate Research
Identifiers
urn:nbn:se:su:diva-29298 (URN)10.1016/j.gloplacha.2009.03.021 (DOI)000269401100012 ()
Projects
ANR IDEGLACEANR PICC
Available from: 2009-08-21 Created: 2009-08-20 Last updated: 2014-05-20Bibliographically approved
2. Sensitivity of the Late Saalian (140 kyrs BP) and LGM (21 kyrs BP) Eurasian ice sheet surface mass balance to vegetation feedbacks
Open this publication in new window or tab >>Sensitivity of the Late Saalian (140 kyrs BP) and LGM (21 kyrs BP) Eurasian ice sheet surface mass balance to vegetation feedbacks
2009 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, L08704Article in journal (Refereed) Published
Abstract [en]

This work uses an atmospheric general circulation model (AGCM) asynchronously coupled to an equilibrium vegetation model to investigate whether vegetation feedbacks could be one of the reasons why the Late Saalian ice sheet (140 kyrs BP) in Eurasia was substantially larger than the Last Glacial Maximum (LGM, 21 kyrs BP) Eurasian ice sheet. The modeled vegetation changes induce a regional cooling for the Late Saalian while they cause a slight regional warming for LGM. As a result, ablation along the margins of the Late Saalian ice sheet is significantly reduced, leading to an increased surface mass balance, while there are no significant mass balance changes observed from vegetation feedbacks at LGM.

Keyword
vegetation modeling, Late Saalian, Quaternary, climate, ice sheet, surface mass balance
National Category
Climate Research
Identifiers
urn:nbn:se:su:diva-29299 (URN)10.1029/2009GL037200 (DOI)000265534000002 ()
Projects
ANR IDEGLACEExplora Doc Rohnes AlpesLavoisier Cotutelle - FranceThe Bert Bolin Centre for Climate Research
Available from: 2009-08-21 Created: 2009-08-20 Last updated: 2016-03-01Bibliographically approved
3. The Late Saalian surface ocean (140 ka): sensitivity of the Late Saalian Eurasian ice sheet to sea surface conditions
Open this publication in new window or tab >>The Late Saalian surface ocean (140 ka): sensitivity of the Late Saalian Eurasian ice sheet to sea surface conditions
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

This work focuses on the Late Saalian (140 ka) and LGM (21 ka) Eurasian ice sheets surface mass balance (SMB) sensitivity to changes in sea surface temperatures (SST). Since no global Late Saalian SST compilations exist, we test the sensitivity of the Late Saalian climate using an AGCM forced with two data-based LGM SST reconstructions. Furthermore, an attempt to reconstruct the Late Saalian SST is performed using an AGCM coupled to a mixed-layer ocean. The resulting Late Saalian SST are cooler than the LGM SST in the Northern Hemisphere and warmer in the Southern. The winter sea ice extends to 40◦ N in both North Atlantic and Pacific oceans. Changes in SST affect the SMB of the Eurasian ice sheet during both glaciations although the Late Saalian ice sheet is less sensitive to the prescribed SST changes than the LGM.

Keyword
Sea surface conditions, Late Saalian, Eurasian ice sheet, Climate modelling, Quaternary
National Category
Climate Research Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:su:diva-29300 (URN)
Projects
ANR IDEGLACEThe Bert Bolin Center for Climate ResearchExplora Doc (Rhones Alpes)Lavoisier Cotutelle
Available from: 2009-08-21 Created: 2009-08-20 Last updated: 2010-01-14Bibliographically approved
4. The role of an Arctic ice shelf in the climate of the last glacial maximum of MIS 6 (140 ka)
Open this publication in new window or tab >>The role of an Arctic ice shelf in the climate of the last glacial maximum of MIS 6 (140 ka)
2010 (English)In: Quaternary Science Reviews, ISSN 0277-3791, Vol. 29, no 25-26, 3590-3597 p.Article in journal (Refereed) Published
Abstract [en]

During the last decade, Arctic icebreaker and nuclear submarine expeditions have revealed large-scale Pleistocene glacial erosion on the Lomonosov Ridge, Chukchi Borderland and along the Northern Alaskan margin indicating that the glacial Arctic Ocean hosted large Antarctic-style ice shelves. Dating of sediment cores indicates that the most extensive and deepest ice grounding occurred during Marine Isotope Stage (MIS) 6. The precise extents of Pleistocene ice shelves in the Arctic Ocean are unknown but seem comparable to present existing Antarctic ice shelves. How would an Antarctic-style ice shelf in the MIS 6 Arctic Ocean influence the Northern Hemisphere climate? Could it have impacted on the surface mass balance (SMB) of the MIS 6 Eurasian ice sheet and contributed to its large southward extent? We use an Atmospheric General Circulation Model (AGCM) to investigate the climatic impacts of both a limited MIS 6 ice shelf covering portions of the Canada Basin and a fully ice shelf covered Arctic Ocean. The AGCM results show that both ice shelves cause a temperature cooling of about 3 °C over the Arctic Ocean mainly due to the combined effect of ice elevation and isolation from the underlying ocean heat fluxes stopping the snow cover from melting during summer. The calculated SMB of the ice shelves are positive. The ice front horizontal velocity of the Canada Basin ice shelf is estimated to ≈ 1 km yr−1 which is comparable to the recent measurements of the Ross ice shelf, Antarctica. The existence of a large continuous ice shelf covering the entire Arctic Ocean would imply a mean annual velocity of icebergs of ≈12 km yr−1 through the Fram Strait. Our modeling results show that both ice shelf configurations could be viable under the MIS 6 climatic conditions. However, the cooling caused by these ice shelves only affects the Arctic margins of the continental ice sheets and is not strong enough to significantly influence the surface mass balance of the entire MIS 6 Eurasian ice sheet.

Keyword
Arctic ice shelf, Marine Isotope Stage 6, atmospheric modeling, climate
National Category
Climate Research Geology
Identifiers
urn:nbn:se:su:diva-29301 (URN)10.1016/j.quascirev.2010.06.023 (DOI)000284724400018 ()
Available from: 2009-08-21 Created: 2009-08-20 Last updated: 2014-05-20Bibliographically approved
5. The Late Saalian period (160 - 140 ka): insight on an unusual glaciation
Open this publication in new window or tab >>The Late Saalian period (160 - 140 ka): insight on an unusual glaciation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This work focuses on the climate evolution over the Late Saalian period (160 - 140 ka) over Eurasia. At this time, the Eurasian ice sheet was larger and higher than during the Last Glacial Maximum. June insolation over the high latitudes presents a large fluctuation over this period: two glacial minima toward 160 and 140 ka and a large insolation peak toward 150 ka. From the geological evidence chronology, it seems clear that the large Eurasian ice sheet already reached its maximum extent at 160 ka. To understand how this ice sheet could survive the 150 ka June insolation maximum, we use several numerical models to simulate the evolution of the vegetation cover, the surface ocean temperatures and finally the evolution of the Late Saalian climate over the three time slices 140, 150 and 160 ka. Results show that the Late Saalian climate variations are dominated by orbital forcings, responding to a large eccentricity enhancing the precession effect especially at 140 ka. From 160 to 150 ka, the surface ocean exhibits open water conditions in the North At- lantic during summer while sea surface temperature at 140 ka are clearly colder with a large sea ice extent reaching 40◦ N in both the North Atlantic and the North Pacific. This corresponds to a milder climate before 140 ka inducing a larger positive surface mass balance despite the 150 ka insolation peak because of larger precipitation rates. On the contrary, the drastic cooling caused by the astronomical forcing at 140 ka leads to a drier climate cancelling ablation and reducing the accumulation over the ice sheet.

Identifiers
urn:nbn:se:su:diva-29302 (URN)
Available from: 2009-08-21 Created: 2009-08-20 Last updated: 2010-01-14Bibliographically approved

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