Many tens of terabytes of metre-resolution digital elevation data were investigated to find and map over half a million glacial landforms including those recording ice flow direction (such as drumlins), subglacial water flow (eskers and meltwater corridors) and successive ice margin positions (end moraines). This was achieved for the whole of Norway, Sweden, and Finland and glaciated parts of the Netherlands, Denmark, Germany, Poland, Lithuania, Latvia, Estonia, and Russia.
Using our observations and computational modelling we have advanced understanding of how these landforms are created, notably for drumlins and mega scale glacial lineations and for landforms arising from water drainage beneath ice sheets. We have built reconstructions combining landform data, geochronological data on timing (e.g. by radiocarbon dating) and computational ice sheet modelling for the last British-Irish Ice Sheet and for the ice sheet that covered Greenland from the last glacial, and have nearly completed this task for the former Scandinavian Ice Sheet.
For the former British-Irish Ice Sheet of the last glaciation (31 000 to 15 000 years ago) information on timing of retreat gathered on a prior project (BRITICE-CHRONO) was used on PalGlac with our tools for combining data and modelling to yield reconstructions of the changing ice extent, thickness and flow velocity through time. This is the first time a model has been tested against so much empirical data including flow direction, ice extent and timing, and this model represents the most well-constrained reconstruction of a retreating ice sheet anywhere in the world. We also modelled how the earth’s crust and its topography varied as a consequence of mass loading by this ice sheet. These sea level aspects are being used by those interested in forecasting future sea levels, relevant for low lying parts of Europe.
Our mapping of 190,000 glacial landforms recording former ice margin positions (moraines etc.) around the present day Greenland Ice Sheet was used to address an important hypothesis relevant for forecasting ice loss to year 2100, and consequent sea level rise. By combining the landforms with published dates on the timing of retreat we built maps of the retreating ice sheet at 500 year time-steps from 16,000 years ago. In order to ask whether such palaeo-history matters for future projections of mass loss from the Greenland Ice Sheet, we compared simulations accounting for this history against a simulation with no history and starting from the modern ice sheet in steady state. We found large differences, with the simulation using palaeo-history predicting the magnitude of sea level rise twice that of the simulation without prior history. This is a very important finding because it shows that more robust sea level forecasts require inclusion of prior ice sheet history over 1000s of years, and underlines the significance of improving palaeoglaciological knowledge of Earth’s ice sheets; the central aim of the PalGlac project. We conducted two field expeditions to Greenland to collect rock samples for cosmogenic dating, supporting our work to better constrain the timing of retreat of this ice sheet.
As the Scandinavian Ice Sheet grew and decayed, its patterns of ice flow and flow divides shifted and migrated. We argue that such geometrical properties are more important to capture in ice sheet modelling than just ice margin positions, which by their very nature are difficult to model; where ice tends to 0 m thickness. We pioneered a new approach to combine and steer model simulations using empirical observations of ice flow compiled from landforms such as drumlins. This work required making new comparison tools that are more statistically robust than previously adopted and devising a novel method of incorporating (calibrating) observed ice flow directions within an ice sheet model. These approaches are currently being used to build a flow-optimised reconstruction of the Scandinavian Ice Sheet that also seeks to match the geochronological data on ice margin timing.
