A recent paper titled Geomorphological Techniques by the British Society for Geomorphology develops a technique to draw together the work of scientists who have sought to overcome a fundamental problem in glacier research: the short-time depth of the observational record. Scientists are eager to learn about the size and extent of glaciers much further into the past, and the tool they are turning to is called glacier reconstruction.
How researchers determine the size of glaciers in the past
Glacier reconstruction involves a reconstruction of past ice extent, thickness and ice flow, and dating of past ice fluctuations, with the results displayed through graphs, maps, and 2-D or 3-D renderings. Through this process, glaciologists attempt to understand what might take place in the future by learning more about how glaciers and ice sheets reacted to climate in the past.
A typical approach to glacier reconstruction may show the progression from a geomorphological map to a reconstruction of the horizontal extent of former glaciation using a flowline model and finally developing a full 3-D glacier reconstruction.
It is necessary to make a geomorphological map of the area to depict the physical features of the surface of the earth and their relation to geological structures. The type of ice-mass under consideration (ice sheet vs. mountain glacier) usually determines what methods are used for glacial geomorphological mapping. One of the major difficulties is for researchers to accurately recognize the features of what caused the landform at a specific region. This is done by looking at several lines of evidence such as glacial, periglacial (relating to or denoting an area adjacent to a glacier or ice sheet) and fluvial (of or found in a river) in order to conclude the glaciation style and size.
Challenges in glacier reconstruction
Glacier reconstruction is used all over the world; however, techniques vary and are rarely precisely described. The new research paper addresses the issue concerning the lack of a common formula for glacier reconstruction. To fill this gap, it formalizes how past glaciers are reconstructed to make it easier to compare between different studies and different regions.
Earth scientists use glacier reconstruction in North America, northern Europe and Antarctica, for example, as well as in thousands of different mountain ranges from Patagonia to Siberia. One research paper in Geomorphology by Simon Carr and Christopher Coleman used glacier reconstruction in the U.K. to investigate the recognition of past glacier extent and dynamics to better understand the climatic sensitivity of glaciers.
Glacier reconstruction includes responses to climate change such as mechanisms and processes of change, thresholds and tipping points, processes of glacier flow and magnitudes, and rates of change under different environmental scenarios.
“Glacier reconstructions not only tell us about the dimensions and dynamics of past glaciers, but are also used as indicators of past climate (i.e., they are paleoclimate proxies),” Iestyn D. Barr, author of the paper and a scientist at the School of Science and the Environment at in Manchester Metropolitan University, told GlacierHub. “This is based on the assumption that if we know the dimensions of past glaciers, we can estimate the past climatic conditions that were necessary to allow them to exist,” Barr added.
A common formula for a consistent approach
Due to the lack of a single established way of reconstructing glaciers, there can be uncertainty and debates about what different glacial landforms tell us about past glaciers. “This means that different researchers might disagree about how a particular geomorphological feature is formed which causes an inconsistent approach. There are also challenges with dating landforms—a vital step if reconstructed glaciers (and associated paleoclimate information) are to be assigned to particular period in time,’’ Barr told GlacierHub. This indicates a need to establish a common formula for glacier reconstruction.
A glacial inversion model allows for ice sheet reconstruction in terms of past size, arrangement, dynamics and retreat pattern. The origin of glacial landforms is widely debated; therefore, it is important to define the assumptions made while using this approach in order to reduce the uncertainties of glacier reconstruction.
Mountain glacier reconstruction can be made through 2-D glacier extent or 3-D geometry. For 2-D glacier extent, a selection of landforms can be used to define the size of the ice-mass. Researchers have identified one kind of landform as the most useful in mountain glacier reconstruction: These are moraines, a mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity. But when they are not present, researchers look carefully to a variety of other forms. Researchers can use techniques such as relative dating or direct dating to determine the relative age of glaciers
After this, they are ready to carry out the step of surface reconstruction. The 3-D geometry of the glacier in the past is important to establish since the following reconstruction steps rely on an accurately constrained and contoured ice surface. Generating such a surface typically follows either a cartographic approach or by implementing a flowline model (a type of numerical model that simulates ice flow along a flow line).
New advances in glacier reconstruction
The availability and quality of satellite data continues to evolve, making glacier reconstruction more efficient. “Remote sensing and GIS [geographic information system] methods has revolutionized how glaciers are reconstructed. In particular, satellite data now allows glaciers to be reconstructed over vast areas, sometimes in some of the most inaccessible parts of the world. This progress in the availability and quality (spatial resolution) of satellite data is likely to continue over coming years,” Barr told GlacierHub.
A formalized approach as provided by the new research paper provides an opportunity to compare different studies and regions more easily. A framework, used as guidance for reconstructing glaciers, in combination with the evolving quality of satellite data will make glacier reconstruction even more efficient in the future.