CRYONUS

Spotlight Studies

Summaries of published articles that use the iceTEA tools.


Rates of past ice sheet thinning in Antarctica

11th March 2019

Satellite measurements show us that the Antarctic Ice Sheet is losing ice and, most notably, getting thinner in many places. Predicting how these changes will continue into the future requires advanced computer models that can simulate ice sheet behaviour over 100s to 1000s of years. To improve the accuracy of these models we can test their performance at reproducing past ice sheet changes that are recorded from geological data. Cosmogenic-nuclide surface-exposure dating is a technique that can tell us how long a rock has been exposed at the Earth’s surface. As an ice sheet gets thinner it deposits rocks on mountains emerging from the icerocks on the upper slopes will be exposed before rocks on the lower slopes. By dating the time of exposure with surface-exposure dating it is possible to calculate how quickly the ice sheet thinned in the past.

Small et al. compiled existing surface-exposure data from across the Antarctic continent. While some of this data had previously been used to calculate thinning rates, much of it had not. By compiling all the useful data they were able to produce the first continent-wide database of past Antarctic Ice Sheet thinning rates. The rates were produced using the Estimate Linear Rate tool MATLAB code. This compilation shows us that thinning rates in the pastduring a time when the ice sheet was shrinking from its maximum extent at the last ice ageare similar to rates observed by satellites today. Additionally, the locations where rapid thinning is recorded in the past appear to broadly match locations where rapid thinning occurs today. These estimates of past ice sheet thinning will next be used to help constrain computer models that are simulating changes in the size and behaviour of the Antarctic Ice Sheet since the last ice age.

 

Example thinning rates generated using the Estimate Linear Rate iceTEA tool. Weighted Least Squares linear regression was performed within a Monte Carlo framework, shown here for two vertical sample transects (A and B; Sites 1 and 9). The resulting distribution of modelled thinning rates is then calculated (C and D), at 68% (dashed vertical lines) and 95% (dotted vertical lines) confidence. The mean rate (labelled here as ‘best-fit’) and median rate are shown as blue and red vertical lines, respectively. Note, the mean, median and probability range is much larger at Site 9 (Maish Nunatak).

 

Computed rates of past thinning (circles) are shown against modern thinning rates and present-day ocean temperatures at 500 m depth (produced using Quantarctica GIS package). The rates of past thinning are similar to those observed today, implying that modern thinning has the potential to be sustained for some time into the future.

 

Reference

Small, D., Bentley, M.J., Jones, R.S., Pittard, M.L. and Whitehouse, P.L., 2019. Antarctic ice sheet palaeo-thinning rates from vertical transects of cosmogenic exposure ages. Quaternary Science Reviews, 206, 65-80. [DOI: 10.1016/j.quascirev.2018.12.024]