Constraining landscape history and glacial erosivity using paired cosmogenic nuclides in Upernavik, northwest Greenland
The evolution of landscapes in the high Arctic is a complex process that takes place over long timescales and by multiple mechanisms.
Lee B. Corbett and colleagues investigate the age and history of the landscape in northwestern Greenland in order to understand how it has evolved over time and how effectively glaciers have shaped it. They use beryllium-10 and aluminum-26, two rare isotopes that are produced in rocks when they are exposed to bombardment by high-energy cosmic rays from space.
By quantifying the concentrations of these two isotopes, they make inferences about how much time the landscape has spent buried beneath glacial ice versus how much time it has spent exposed. Corbett and colleagues conclude that the landscape in Upernavik is very old; some locations preserve a record of almost one million years. This contrasts greatly with many other landscapes in Greenland, which date back only to about 10,000 years ago (the end of the last glacial period).
They also conclude that the land surfaces in Upernavik have been preserved beneath non-erosive glacial ice throughout many glacial periods over the course of geologic time. These so-called "ghost glaciers" cover the landscape but are incapable of eroding it, leaving behind no geologic evidence of their presence.
Article: DOI: 10.1130/B30813.1.
A cosmic trip: 25 years of cosmogenic nuclides in geology
Terrestrial cosmogenic nuclides, produced by secondary cosmic-ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere, are widely used to date surface exposure of rocks and sediments, to estimate erosion and weathering rates, and to date sediment deposition or burial.
Their use has transformed geomorphology and Quaternary geology, for the first time allowing landforms to be dated and denudation rates to be measured over soil-forming time scales. The application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry (AMS) in 1977 and increased dramatically with the measurement of in situ–produced nuclides in mineral grains near Earth's surface in the 1980s.
The past 25 years have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool. This review by Darryl E. Granger and colleagues covers the major developments of the past 25 years by comparing the state of the field in 1988 with that of today, and by identifying key advances in that period that moved the field forward.
Granger and colleagues emphasize the most commonly used in situ-produced nuclides measured by AMS for geological applications, but also discuss other nuclides where their applications overlap. Their review covers AMS instrumentation, cosmogenic nuclide production rates, the methods of surface exposure dating, measurement of erosion and weathering, and burial dating, and meteoric 10Be.
Article: DOI:10.1130/B30774.1.