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On the interaction between ice sheets and the large-scale atmospheric circulation over the last glacial cycle
Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The last glacial cycle (c. 115-12 kyr BP) was the most recent in a series of recurring glaciations of the subpolar continents. Massive ice sheets evolved in Eurasia and North America, which, at their maximum, were of continental scale and together lowered the global sea-level by approximately 100 m. The paleo-modelling community has focused on the last glacial maximum (LGM, ~ 20 kyr BP), leaving the longer period when the ice sheets evolved to their LGM configurations largely unexplored.

In this thesis we study the mutual interaction between the time-mean atmospheric circulation and the evolution of the Northern Hemisphere ice sheets over the build-up phase of the last glacial cycle. Experiments are conducted with coupled atmosphere-ice-sheet models and a circulation model forced by geologically consistent reconstructions of the ice-sheet topography at key stages of the glacial cycle.

The main findings from these studies are that the ice evolution in North America may have been controlled by circulation anomalies induced by the background topography in conjunction with the ice sheets themselves. A geologically consistent pre-LGM ice sheet could only be obtained when including the North American Cordillera. However, the ice sheets' influence on the local climate conditions is also found to be paramount for this configuration. We further suggest that the incipient ice sheets may have had a limited influence on the large-scale winter circulation as a result of their location relative the westerly mean flow. The LGM Laurentide Ice Sheet (LIS) was, however, different because of its continent-wide extent, and it may therefore have had a large influence on the planetary-scale circulation, especially in the Atlantic sector. We find that the planetary waves forced by the LIS were considerably larger than at earlier times, and, as a result of a more frequent planetary wave reflection over the Atlantic Ocean basin, an altered stationary wave field and a zonalised winter jet.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Meteorology, Stockholm University , 2014. , s. 49
Nyckelord [en]
Atmospheric stationary waves, coupled atmosphere-ice sheet modelling, stationary wave-ice sheet interactions
Nationell ämneskategori
Meteorologi och atmosfärforskning
Forskningsämne
atmosfärvetenskap och oceanografi
Identifikatorer
URN: urn:nbn:se:su:diva-107925ISBN: 978-91-7649-010-5 (tryckt)OAI: oai:DiVA.org:su-107925DiVA, id: diva2:752718
Disputation
2014-11-11, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.

Tillgänglig från: 2014-10-20 Skapad: 2014-10-03 Senast uppdaterad: 2014-11-18Bibliografiskt granskad
Delarbeten
1. Interactions between stationary waves and ice sheets: linear versus nonlinear atmospheric response
Öppna denna publikation i ny flik eller fönster >>Interactions between stationary waves and ice sheets: linear versus nonlinear atmospheric response
2012 (Engelska)Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 38, nr 5-6, s. 1249-1262Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This study examines the mutual interaction between topographically-forced atmospheric stationary waves and continental-scale ice sheets using a thermomechanical ice-sheet model coupled to a linear as well as a fully-nonlinear dry atmospheric primitive equation model. The focus is on how the stationary-wave induced ablation feeds back on the ice sheet. Simulations are conducted in which an embryonal ice mass, on an idealised “North American” continent, evolves to an equilibrium ice sheet. Under the coupling to the linear atmospheric model, the equilibrium ice sheet is primarily controlled by the ratio between the wavelength of the stationary waves and the zonal continental extent. When this ratio is near two, the ice sheet has its center of mass shifted far eastward and its shape is broadly reminiscent of the Laurentide ice sheet at LGM. For wavelengths comparable to the continental extent, however, the ice margin extends far equatorward on the central continent but is displaced poleward near the eastern coast. Remarkably, the coupling to the nonlinear atmospheric model yields equilibrium ice sheets that are virtually identical to the ones obtained in uncoupled simulations, i.e. a symmetric ice sheet with a zonal southern margin. Thus, the degree of linearity of the atmospheric response should control to what extent topographically-forced stationary waves can reorganise the structure of ice sheets. If the stationary-wave response is linear, the present results suggest that spatial reconstructions of past ice sheets can provide some information on the zonal-mean atmospheric circulation that prevailed.

Nyckelord
Stationary waves, ice sheets, flow-induced ablation, nonlinear topographic wave response, Laurentide ice sheet
Nationell ämneskategori
Meteorologi och atmosfärforskning Klimatforskning
Forskningsämne
atmosfärvetenskap
Identifikatorer
urn:nbn:se:su:diva-55550 (URN)10.1007/s00382-011-1004-6 (DOI)000302245900025 ()
Tillgänglig från: 2011-03-21 Skapad: 2011-03-21 Senast uppdaterad: 2019-12-12Bibliografiskt granskad
2. The North American Cordillera - an impediment to growing the Laurentide Ice Sheet
Öppna denna publikation i ny flik eller fönster >>The North American Cordillera - an impediment to growing the Laurentide Ice Sheet
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Meteorologi och atmosfärforskning
Identifikatorer
urn:nbn:se:su:diva-107751 (URN)
Tillgänglig från: 2014-09-26 Skapad: 2014-09-26 Senast uppdaterad: 2014-10-06
3. Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle
Öppna denna publikation i ny flik eller fönster >>Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle
2014 (Engelska)Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 10, nr 4, s. 1453-1471Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We present modelling results of the atmospheric circulation at the cold periods of marine isotope stage 5b (MIS 5b), MIS 4 and the Last Glacial Maximum (LGM), as well as the interglacial. The palaeosimulations are forced by ice-sheet reconstructions consistent with geological evidence and by appropriate insolation and greenhouse gas concentrations. The results suggest that the large-scale atmospheric winter circulation remained largely similar to the interglacial for a significant part of the glacial cycle. The proposed explanation is that the ice sheets were located in areas where their interaction with the mean flow is limited. However, the LGM Laurentide Ice Sheet induces a much larger planetary wave that leads to a zonalisation of the Atlantic jet. In summer, the ice-sheet topography dynamically induces warm temperatures in Alaska and central Asia that inhibits the expansion of the ice sheets into these regions. The warm temperatures may also serve as an explanation for westward propagation of the Eurasian Ice Sheet from MIS 4 to the LGM.

Nationell ämneskategori
Meteorologi och atmosfärforskning
Identifikatorer
urn:nbn:se:su:diva-106949 (URN)10.5194/cp-10-1453-2014 (DOI)000339896100012 ()
Tillgänglig från: 2014-08-29 Skapad: 2014-08-29 Senast uppdaterad: 2019-12-17Bibliografiskt granskad
4. Nonlinear stationary wave reflection as a mechanism for zonalising the LGM Atlantic winter jet
Öppna denna publikation i ny flik eller fönster >>Nonlinear stationary wave reflection as a mechanism for zonalising the LGM Atlantic winter jet
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Meteorologi och atmosfärforskning
Identifikatorer
urn:nbn:se:su:diva-107747 (URN)
Tillgänglig från: 2014-09-26 Skapad: 2014-09-26 Senast uppdaterad: 2019-12-17Bibliografiskt granskad

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Löfverström, Marcus
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