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  • 1
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    Sensitivity of atmospheric forcing on Northern Hemisphere ice sheets during the last glacial-interglacial cycle using output from PMIP3 (2017)
    Copernicus
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    Publication Date: 2017-08-30
    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.
    Print ISSN: 1814-9340
    Electronic ISSN: 1814-9359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
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    ICESHEET 1.0: a program to produce paleo-ice sheet reconstructions with minimal assumptions (2016)
    Copernicus
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    Publication Date: 2016-05-03
    Description: We describe a program that produces paleo-ice sheet reconstructions using an assumption of steady-state, perfectly plastic ice flow behaviour. It incorporates three input parameters: ice margin, basal shear stress and basal topography. Though it is unlikely that paleo-ice sheets were ever in complete steady-state conditions, this method can produce an ice sheet without relying on complicated and unconstrained parameters such as climate and ice dynamics. This makes it advantageous to use in glacial-isostatic adjustment ice sheet modelling, which are often used as input parameters in global climate modelling simulations. We test this program by applying it to the modern Greenland Ice Sheet and Last Glacial Maximum Barents Sea Ice Sheet and demonstrate the optimal parameters that balance computational time and accuracy.
    Print ISSN: 1991-959X
    Electronic ISSN: 1991-9603
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
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    Geology datasets in North America, Greenland and surrounding areas for use with ice sheet models (2019)
    Copernicus
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    Publication Date: 2019-03-12
    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 (https://doi.org/10.1594/PANGAEA.895889, Gowan et al., 2018b).
    Print ISSN: 1866-3508
    Electronic ISSN: 1866-3516
    Topics: Geosciences
    Published by Copernicus
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  • 4
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    Geology datasets of North America for use with ice sheet models (2018)
    Copernicus
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    Publication Date: 2018-11-22
    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 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 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 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. Changes in ice thickness by up to 40 % relative to a reference simulation happened when the shear friction angle was reduced to account for a weaker substrate. These datasets provide a basis to improve the basal boundary conditions in ice sheet models. Gowan, E. J., Niu, L., Knorr, G., and Lohmann, G., 2018. Geology datasets of North America for use with ice sheet models, link to datafiles. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.895889
    Electronic ISSN: 1866-3591
    Topics: Geosciences
    Published by Copernicus
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  • 5
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    Centennial- to millennial-scale monsoon changes since the last deglaciation linked to solar activities and North Atlantic cooling (2020)
    Copernicus
    Details
    Publication Date: 2020-02-14
    Description: Rapid monsoon changes since the last deglaciation remain poorly constrained due to the scarcity of geological archives. Here we present a high-resolution scanning X-ray fluorescence (XRF) analysis of a 13.5 m terrace succession on the western Chinese Loess Plateau (CLP) to infer rapid monsoon changes since the last deglaciation. Our results indicate that Rb∕Sr and Zr∕Rb are sensitive indicators of chemical weathering and wind sorting, respectively, which are further linked to the strength of the East Asian summer monsoon (EASM) and the East Asian winter monsoon (EAWM). During the last deglaciation, two cold intervals of the Heinrich event 1 and Younger Dryas were characterized by intensified winter monsoon and weakened summer monsoon. The EAWM gradually weakened at the beginning of the Holocene, while the EASM remained steady till 9.9 ka and then grew stronger. Both the EASM and EAWM intensities were relatively weak during the Middle Holocene, indicating a mid-Holocene climatic optimum. Rb∕Sr and Zr∕Rb exhibit an antiphase relationship between the summer and winter monsoon changes on a centennial timescale during 16–1 ka. Comparison of these monsoon changes with solar activity and North Atlantic cooling events reveals that both factors can lead to abrupt changes on a centennial timescale in the Early Holocene. During the Late Holocene, North Atlantic cooling became the major forcing of centennial monsoon events.
    Print ISSN: 1814-9324
    Electronic ISSN: 1814-9332
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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