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  • 1
    Publication Date: 2017-12-01
    Description: The motion of glacial ice is predominantly controlled by basal conditions, which include a variety of parameters such as ice rheology, temperature, water content, the presence of sediments, and topography. Soft sediment deformation has long been hypothesized to be a dominant control on the size and dynamics of temperate ice sheets such as the Laurentide Ice Sheet. The transition from hard-bedded regions (areas that lack significant sediment cover) to soft sediment areas put a limit on the maximum volume of these ice sheets. When the ice sheet margin reached soft sediment cover, it may have caused the ice sheet to surge, with global-scale climatic impacts. Current generation ice sheet models only have limited control on how sediments modify the behavior of an ice sheet. We present a model of sediment deformation that can take into account the thickness, lithology and hydrology at the base of the ice sheet using the Parallel Ice Sheet Model (PISM). We assess how changes in sediment properties affect the advance and retreat of the ice sheet, including standstills in the margin when the ice sheet becomes restricted to the hard-bedded interior areas. We apply this model to the Wisconsin Glaciation (~85-11 kyrs ago) of the Laurentide ice sheet. We show how the distribution of sediments affect its growth and retreat. We specifically focus on how the soft bedded Hudson Bay impeded the growth of the ice sheet, up to the lead up to the Last Glacial Maximum. We also investigate the relationship between Dansgaard–Oeschger and Heinrich events and the basal dynamics of the ice sheets.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 2
    Publication Date: 2017-09-11
    Description: It is not an easy task for paleoscientists to communicate the relevance of their research to policy makers and funders. However, an increase in catastrophic environmental calamities related to climate change (e.g. landslide, droughts, flooding) demands a response both in terms of policy-making and future governmental decisions. Often, climate change in the recent past was linked to major shifts in human behavior, which masks the relative contribution of humans and nature. For example, the 4.2 ka BP aridification event was so severe that it may have triggered the collapse of several large civilizations (the Old Kingdom in Egypt and the Akkadian Empire in Mesopotamia; Gibbons 1993). Compilations of long-term records of past variability can help reduce the uncertainties on past, present and future climate changes, and thus support informed societal decisions. Therefore, policymakers should (and some may argue, must) consider the long-term perspective provided by paleoscience research.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 3
    Publication Date: 2017-09-11
    Description: Three days prior to the 5th PAGES Open Science Meeting (OSM), 80 ambitious early-career scientists (PhD students and postdoctoral researchers) met in the restored village of Morillo de Tou, Spain. The remote setting in the Pyrenees, the old style buildings constructed of turbidites, and the clear and sunny weather made this place an inspiring location to discuss past climate, environment and human interactions. Despite some grumblings about cold coffee served in small cups, the conference was a high-energy affair that promoted connections.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2019-01-04
    Description: Paleo-ice sheet reconstructions are complicated by large uncertainties, particularly since it is usually only possible to infer thickness from indirect means such as the response of glacial isostatic adjustment (GIA). Recently, there has been increased attention to refining the chronology of ice sheet margins of paleo-ice sheets, and changes in relative sea level in formerly glaciated regions. Using this information, it is possible to infer the configuration of the ice sheets through time. Using the program ICESHEET (Gowan et al 2016), we reconstruct past ice sheets using a simple, though glaciologically plausible ice sheet model. The ice sheet volume is reconstructed by adjusting the basal shear stress at discrete time intervals in the region of interest until the modelled sea level is consistent with the sea level indicators. We demonstrate this technique by applying it to the Innuitian Ice Sheet. We also show the utility of the models for use in paleo-geographic reconstructions, as well as usage in paleo-climate simulations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
    Publication Date: 2019-01-04
    Description: The last interglacial (MIS 5e) was a period characterized by sea level that was up to 6-9 m above present day level, due in part to the partial collapse of the Greenland and West Antarctic Ice Sheets. Assessing the pattern of sea level change for this period is complicated due to the uncertainties in the relative contributions of these two ice sheets. In addition, past sea level is the integrated history of water load changes and associated glacial isostatic adjustment before and after the period of interest. We present a the initial results of a global ice sheet reconstruction that seeks to untangle the last interglacial ice sheet configuration. The ice sheets are reconstructed by using the program ICESHEET, which uses ice sheet margin reconstructions and estimates of basal shear stress to produce realistic ice sheet configurations. We calibrate this model by modelling glacial-isostatic adjustment with relative sea level indicators. We also investigate the role of different Earth rheology models on the global pattern of sea level change during this period. We make an assessment of how much uncertainty in the last interglacial sea level is due to the ice sheet configuration during the last glacial cycle.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 6
    Publication Date: 2019-01-04
    Description: Basal boundary conditions, such as basal geology, the presence of unconsolidated sediments, and hydrology, play a dominant role in the dynamics of ice sheets. One problem when studying existing ice sheets in Greenland and Antarctica is the lack of direct observations of these basal conditions. Studying paleo-ice sheet behaviour is advantageous in this respect, because these conditions are preserved in glacial landforms and sediments. By studying past ice sheet behaviour, we can provide analogues for modern behaviour. We investigate the role of basal geological conditions and hydrology on ice sheet dynamics using the ice sheet model PISM. We specifically focus on the North American ice sheet complex. We present datasets for this region that can be used in ice sheet models to investigate basal conditions including information on bedrock geology, the distribution of unconsolidated sediments, and the dominant grain size of the sediments. We use these datasets to investigate how they impact ice sheet dynamics with simulations over the last glacial cycle. We include a simple hydrology model that includes meltwater derived from the surface, and property changes depending on the basal geology from our datasets. Our results show that the behaviour of the ice sheet changes when there is a transition from regions with sparse sediment cover to complete sediment cover. One impact is that because ice can flow faster in regions like Hudson Bay, it can cause the Laurentide Ice Sheet to stabilize into a single continent-wide ice sheet faster than in a situation where sediments are not present. We also investigate the role of changes in basal geological conditions have in causing unstable behaviour in ice sheets.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 7
    Publication Date: 2019-03-18
    Description: The ice–substrate interface is an important boundary condition for ice sheet modelling. The substrate affects the ice sheet by allowing sliding through sediment deformation and accommodating the storage and drainage of subglacial water. We present three datasets on a 1 : 5 000 000 scale with different geological parameters for the region that was covered by the ice sheets in North America, including Greenland and Iceland. The first dataset includes the distribution of surficial sediments, which is separated into continuous, discontinuous and predominantly rock categories. The second dataset includes sediment grain size properties, which is divided into three classes: clay, silt and sand, based on the dominant grain size of the fine fraction of the glacial sediments. The third dataset is the generalized bedrock geology. We demonstrate the utility of these datasets for governing ice sheet dynamics by using an ice sheet model with a simulation that extends through the last glacial cycle. In order to demonstrate the importance of the basal boundary conditions for ice sheet modelling, we changed the shear friction angle to account for a weaker substrate and found changes up to 40 % in ice thickness compared to a reference run. Although incorporation of the ice–bed boundary remains model dependent, our dataset provides an observational baseline for improving a critical weakness in current ice sheet modelling.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2018-09-12
    Description: We use the three-dimensional Parallel Ice Sheet Model (PISM) to simulate Northern Hemisphere ice sheets evolution through the last glacial-interglacial cycle. The simulation is driven by the NGRIP δ18O index combined with climate forcing at two time slices, the Last Glacial Maximum (LGM) and present day (PD). In order to investigate the sensitivity of the ice sheets to the atmospheric forcing, atmospheric output from nine climate models from the Paleoclimate Modeling Intercomparison Project Phase III (PMIP3) are used to force the ice sheet model with the same set-up. The results show large diversity in simulated ice sheets between different models. By comparing the atmospheric forcing, we found that summer surface air temperature pattern resembles the ice sheet extent pattern at the LGM, which shows great sensitivity to summer surface air temperature. This implies that careful constrains on climate output is essential for simulating reliable glacial-interglacial Northern Hemisphere ice sheets. The ablation process is of vital importance for high-latitude Northern Hemisphere ice sheets. Besides, the absent nonlinear interactions between ice sheet and atmosphere and ocean, which have different signals regionally, also contribute to the mismatches between simulated ice sheets and geological evidences. Hence, we highlight the needs for coupling an ice sheet model to GCM to take into account these missing processes.
    Type: Article , NonPeerReviewed
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  • 9
    Publication Date: 2018-03-12
    Description: Paleo-ice sheet reconstructions are complicated by large uncertainties, particularly since it is usually only possible to infer thickness from indirect means such as the response of glacial isostatic adjustment (GIA). GIA itself has large uncertainties with respect to the rheological structure of the Earth, and it is possible to get multiple possible best fitting ice sheet configurations using different Earth models. Usually the best geological constraints for paleo-ice sheets are ice margin location, via dating methods and geomorphological features. Using the program ICESHEET (Gowan et al 2016), it is possible to exploit this knowledge and create glaciologically consistent ice sheet reconstructions for use in GIA modeling. We demonstrate this by applying them to the North American Laurentide and Innuitian ice sheets, and show that it is possible to have an ice sheet that has a much lower profile than other GIA constrained reconstructions such as ICE-6G, GLAC-1 and ANU. A lower profile ice sheet has profound implications for past climate reconstructions, including radically different atmospheric and Atlantic Ocean circulation at the Last Glacial Maximum. Such a reconstruction is better able to fit geological constraints in the near field, but are at odds with global sea level reconstructions that require much larger ice volume. We discuss possible solutions to this issue. Another benefit of ICESHEET is that it does not require climatic information, since the ice thickness is adjusted by changing a spatially and temporarily variable basal shear stress parameter. Using these reconstructions in climate models do not face the circularity of dynamic ice sheet models that require a climatic input that was often derived from a-priori ice sheet reconstructions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 10
    Publication Date: 2018-04-23
    Description: Proglacial lakes have an important impact on the dynamics of ice sheets by imposing a marine-like boundary condition to the ice margin. At the ice-ocean interface the ice sheet is know to have a complex dynamical behavior. These processes can include the formation of ice shelves that can buttress glaciers, increase subglacial melting, reduce basal friction and calving of icebergs. Such processes also act at the boundaries at ice-marginal lakes, which arose along the ice margins of past continental ice sheets. Some of these lakes spanned several hundreds of kilometers. We have implemented a module into the Parallel Ice Sheet Model (PISM) to study the impacts of proglacial lakes on the ice dynamics. This model dynamically updates the lake basins by filling all depressions of the domain until they overflow. This simple approach does not calculate a water budget and therefore does not rely on an advanced and computationally expensive hydrology model. The lake boundaries are treated in a similar way as a marine boundary. We test this model by reconstructing the evolution of the North American ice sheets by using a transient climate forcing for the last glacial cycle. These reconstructions are then compared to geological records, such as ice margins and paleo-lake shorelines.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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