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Glacial geologists can reconstruct past ice-sheet thickness in a number of ways.
But this is not useful for understanding rates and magnitudes of change if we cannot put it into some kind of time-scale context.
Fortunately, we have many techniques at our disposal.
Radiocarbon dating is an essential part of the glacial geologists’ toolkit. One example of an application may be for a lake dammed by a moraine.
A radiocarbon age from the base of the sediment core gives a minimum age for moraine formation; the moraine must be older than the radiocarbon age.
Radiocarbon ages are also extensively used from marine sediment cores around the margins of ice sheets, such as the Antarctic Peninsula Ice Sheet.
Transitional Glaciomarine Sediments, those glaciomarine sediments laid down immediately after ice sheet recession and that overlie subglacial tills, provide a minimum age for ice-sheet extent at the core’s position; the ice margin was at this position before the radiocarbon age.
Cosmogenic nuclide dating in this context gives a maximum age for moraine formation; the moraine must be younger than the exposure age (unless your boulder has rolled, moved, has an inheritance, or any of the other multitude of factors that may result in an inaccurate age).
Cosmogenic nuclide dating can also be used to date trimlines and constrain past ice thickness.
We can observe modern glaciers melting; we can look at the surface of ice sheets with satellite images and calculate changes in mass balance and we can map mountain glacier recession.
Following the common practice of the w: IPCC, the zero on this figure is the mean temperature from 1961-1990. Rohde from publicly available data and is incorporated into the Global Warming Art project. Scientists reconstruction past ice sheets because they want to know how glaciers and ice sheets interact with climate and with the ocean.
Recent research shows that past ice flow was not isochronous; in fact, the last British Ice Sheet had numerous complex phases of ice flow.