Delft University of Technology a Glacial Isostatic Adjustment Model
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Delft University of Technology A glacial isostatic adjustment model for the central and northern Laurentide ice sheet based on relative sea level and GPS measurements Simon, K. M.; James, T. S.; Henton, J. A.; Dyke, A. S. DOI 10.1093/gji/ggw103 Publication date 2016 Document Version Final published version Published in Geophysical Journal International Citation (APA) Simon, K. M., James, T. S., Henton, J. A., & Dyke, A. S. (2016). A glacial isostatic adjustment model for the central and northern Laurentide ice sheet based on relative sea level and GPS measurements. Geophysical Journal International, 205(3), 1618-1636. [ggw098]. https://doi.org/10.1093/gji/ggw103 Important note To cite this publication, please use the final published version (if applicable). Please check the document version above. Copyright Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10. Geophysical Journal International Geophys. J. Int. (2016) 205, 1618–1636 doi: 10.1093/gji/ggw103 Advance Access publication 2016 March 16 GJI Geodynamics and tectonics A glacial isostatic adjustment model for the central and northern Laurentide Ice Sheet based on relative sea level and GPS measurements K.M. Simon,1,2,3 T.S. James,1,2 J.A. Henton4 and A.S. Dyke5,6 1School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada, V8P 5C2. E-mail: [email protected] 2Geological Survey of Canada - Pacific, Natural Resources Canada, Sidney, BC, Canada, V8L 4B2 3Department of Geoscience and Remote Sensing, Delft University of Technology, Delft 2628 CN, The Netherlands 4Canadian Geodetic Survey, Natural Resources Canada, Sidney, BC, Canada, V8L 4B2 5Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2 6Department of Anthropology, McGill University, Montreal, Quebec, Canada, H3A 2T4 Accepted 2016 March 10. Received 2016 March 8; in original form 2015 July 9 SUMMARY The thickness and equivalent global sea level contribution of an improved model of the central and northern Laurentide Ice Sheet is constrained by 24 relative sea level histories and 18 present-day GPS-measured vertical land motion rates. The final model, termed Laur16, is derived from the ICE-5G model by holding the timing history constant and iteratively adjusting the thickness history, in four regions of northern Canada. In the final model, the last glacial maximum (LGM) thickness of the Laurentide Ice Sheet west of Hudson Bay was ∼3.4–3.6 km. Conversely, east of Hudson Bay, peak ice thicknesses reached ∼4km.The ice model thicknesses inferred for these two regions represent, respectively, a ∼30 per cent decrease and an average ∼20–25 per cent increase to the load thickness relative to the ICE-5G reconstruction, which is generally consistent with other recent studies that have focussed on Laurentide Ice Sheet history. The final model also features peak ice thicknesses of 1.2–1.3 km in the Baffin Island region, a modest reduction relative to ICE-5G and unchanged thicknesses for a region in the central Canadian Arctic Archipelago west of Baffin Island. Vertical land motion predictions of the final model fit observed crustal uplift rates well, after an adjustment is made for the elastic crustal response to present-day ice mass changes of regional ice cover. The new Laur16 model provides more than a factor of two improvement of the fit to the RSL data (χ 2 measure of misfit) and a factor of nine improvement to the fit of the GPS data (mean squared error measure of fit), compared to the ICE-5G starting model. Laur16 also fits the regional RSL data better by a factor of two and gives a slightly better fit to GPS uplift rates than the recent ICE-6G model. The volume history of the Laur16 reconstruction corresponds to an up to 8 m reduction in global sea level equivalent compared to ICE-5G at LGM. Key words: Satellite geodesy; Sea level change; Glaciology; Dynamics of lithosphere and mantle; North America. the weight of the ice depressed the Earth’s crust and mantle so that 1 INTRODUCTION AND PREVIOUS in the vicinity of the ice sheets, relative sea level (RSL) was tens to LAURENTIDE ICE SHEET STUDIES hundreds of metres higher than at present (Walcott 1972). Following During the last glaciation, large ice sheets covered much of North deglaciation, glacial isostatic adjustment (GIA) caused the land in America, Greenland, Scandinavia and Antarctica, and at the Last regions near the former ice sheets to uplift, and relative sea level Glacial Maximum (LGM, ∼24–14 14C kyr BP), almost all of north- rapidly fell. In part owing to the great spatial lengths of shoreline ern Canada was covered by the Laurentide and Innuitian ice sheets indicating RSL history in the Canadian Arctic Archipelago, the his- (Dyke 2004). The large amount of water stored on land within the tory of postglacial sea level change in northern Canada is generally ice sheets caused globally averaged sea level to be between 120 and well recorded. 130 m lower at LGM than at present (e.g. Fairbanks 1989;Yokoyama The spatial extent, flow history and chronology of the et al. 2000; Peltier & Fairbanks 2006; Austermann et al. 2013), but last North American glaciation has been constructed through 1618 C The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society. GIA of the north-central Laurentide Ice Sheet 1619 Figure 1. Regional map showing the study area and geographical place names mentioned in the text. Geographical place-name abbreviations are: BP, Boothia Peninsula; LB, Labrador; MP, Melville Peninsula; and UB, Ungava Bay. Canadian provincial and territorial abbreviations are: BC, British Columbia; AB, Alberta; SK, Saskatchewan; MB, Manitoba; ON, Ontario; QC, Quebec; NU, Nunavut; NWT, Northwest Territories. The islands of the Canadian Arctic Archipelago are shaded white. glacial-geological observations of end moraines and other ice- in accordance with the value determined from far-field sea level marginal features, flow direction indicators, glacial erratic distribu- measurements by Fairbanks (1989) and Peltier & Fairbanks (2006). tions and marine-limit and relative sea level measurements. These The model also generally well predicts sea level measurements observations indicate that growth of the Laurentide Ice Sheet (LIS) and present-day vertical and horizontal motions over Fennoscandia from its last interstadial minimum commenced approximately 30– (Peltier 2004; Argus & Peltier 2010). Based on the misfit between 27 14CkyrBP(∼35–32 cal kyr BP) at the middle to late Wis- model predictions and present-day gravity and GPS data (Lambert consinan transition (Dyke et al. 2002). The LIS reached its peak et al. 2006; Argus & Peltier 2010; Mazzotti et al. 2011;Wang extent by approximately 24–21 14CkyrBP(∼29–25 cal kyr BP), et al. 2013; Peltier et al. 2015), it has been shown that the ICE- and was confluent with the smaller Cordilleran Ice Sheet in western 5G reconstruction is too thick in the central sector of the Lauren- Canada and the Innuitian Ice Sheet to the north. Glacial flow in- tide Ice Sheet (LIS) in the region west of Hudson Bay, throughout dicators suggest that the thickest ice cover nucleated in three main Manitoba and near Yellowknife. Misfits of ICE-5G to data in North regions over an area west of Hudson Bay, Quebec-Labrador and America were similarly suggested by Braun et al.(2008)andvan Foxe Basin (Fig. 1,Dykeet al. 1982, 2002). The LIS remained at der Wal et al.(2008). Argus & Peltier (2010), additionally suggest near LGM conditions over North America until about 14 14Ckyr that the ICE-5G model reconstruction is too thin near the British BP (∼16.8 cal kyr BP). The main phase of deglaciation of the LIS Columbia–Alberta border and in southern and eastern Quebec. occurred between 14 and 7 14CkyrBP(∼16.8–7.7 cal kyr BP), A successor model to ICE-5G, ICE-6G (Argus et al. 2014; Peltier during which time there was a monotonic 90 per cent reduction in et al. 2015) has been used in recent sea level and climate modelling the area of the ice sheet complex relative to its area at LGM, in- studies (e.g. Engelhart et al. 2011; Toscano et al. 2011; Vettoretti cluding the ablation of marine-based ice in Hudson Bay between 8 & Peltier 2013). Relative to ICE-5G, Peltier et al.(2015) show that and 7 14CkyrBP(∼8.8–7.7 cal kyr BP; Dyke 2004). By 5 14Ckyr ICE-6G, with much thinner ice west of Hudson Bay, and moderately BP (∼5.9 cal kyr BP), deglaciation of North America was nearly thicker ice in western Canada and northern Quebec, provides a complete, with the exception of remnant ice persisting on Baffin better fit to GPS-measured vertical uplift rates in North America. Island. Specifically, Vettoretti & Peltier (2013) describe ICE-6G, relative to Many recent glacial isostatic adjustment studies in North Amer- ICE-5G, as being approximately 1500 m thinner in central Canada, ica have considered the global ICE-5G ice sheet reconstruction of as well as less than 1000 m thicker in both western Canada and Peltier (2004), which was developed as an update to the ICE-4G northern Quebec.