Mountain glaciers respond to climate change by rapidly advancing or receding as global temperatures have spiked upward and downward numerous times throughout geological history. Those changes in glacier extent control hydrology, sediment transport, and deposition in rivers downstream.
The sedimentary record in glaciated catchments therefore is an important archive with that can help unravel past climate changes but, unlike rivers, whose flow is controlled entirely by land surface topography, glaciers are able to flow uphill and across ridgelines - a process called "transfluence." Glacier advance and recession can result in drainage capture by transfluent ice flow, and so change catchment drainage areas and hydrological budgets.
Because glacial-drainage capture often occurs in alpine environments where ice caps straddle range divides, researchers created a 3-D glacier model of ice flow during the last glaciation in adjacent catchments in the Southern Alps of New Zealand and found that glacial-drainage capture is a more important control on hydrology and the sedimentary record than climate change alone.
They found that during the Last Glacial Maximum, the effective drainage area of the Ashburton catchment increased to 160% of the interglacial value with drainage capture, driving an increase in discharge exceeding that resulting from glacier recession.
These results from New Zealand demonstrate how scientists can use the sedimentary record to investigate past climate change both in this mid-latitude Southern Hemisphere location and in glaciated settings worldwide.
Citation: Ann V. Rowan, Mitchell A. Plummer, Simon H. Brocklehurst, Merren A. Jones and David M. Schultz, 'Drainage capture and discharge variations driven by glaciation in the Southern Alps, New Zealand', GEOLOGY doi: 10.1130/G33829.1