COUNTING ATOMS TO PLACE HUMAN IMPACTS IN A GEOLOGIC CONTEXT
Since the 1990s, measurements of cosmogenic nuclides in river sediment have been used to compare contemporary rates of sediment export with background rates of sediment generation - important data for understanding the global flux of sediment and sediment-associated nutrients to deltas and the world’s oceans as well as estimating the filling rates of reservoirs. Where Anthropocene rates of sediment export have been measured, they typically exceed geologic rates of sediment generation by several times. Global compilations and many regional studies show average basin slope is a reasonable proxy for long-term erosion rates providing a simple, calibrated means to estimate rates needed to establish regulatory limits for sediment when it is considered a pollutant.
Since the 1980s, a variety of different nuclides have been used to determine the history of now-vanished glaciers and ice sheets mostly by dating moraines. Recently, in light of rapid, human-induced climate change, cosmogenic nuclides have been used to understand better the sensitivity of ice sheets to past periods of warmth. Measurements of Be-10 and Al-26 in marine sediment cores, ice-bound cobbles, and rock recovered from under ice have been used to argue both for and against the long-term stability of the Greenland and Antarctic Ice Sheets. Such data, once we are better able to interpret it, could well allow us to see into the past and determine how Earth’s ice sheets responded to past periods of exceptional warmth – our likely future.