The Antarctic ice sheets drain from the continent interior to the ocean via fast flowing ice streams. As the ice within these streams moves, it erodes and modifies the bed over which it travels. Some of the eroded material is trapped within the ice as mineral and rock fragments and transported into the ocean as icebergs.
As the icebergs melt, the minerals and rock fragments sink to the ocean floor as ice rafted debris. This study uniquely links lead isotope geochemistry of recently deposited ice rafted feldspars with geophysical observations over the glacial catchments and ice streams from where the feldspars originated.
The findings presented by M.J. Flowerdew and colleagues indicate that subglacial erosion of bedrock is restricted to regions where ice velocity, basal shear stresses, and bed roughness are high. Changes in the age and isotope composition of ice-rafted debris are commonly taken as evidence for the collapse or disintegration of parts of the ice sheet.
This study shows that significant variations in the chemistry and age of the ice rafted materials can instead result from changing the loci of subglacial erosion and do not necessarily correspond with episodes of major ice sheet instability.
Paper: M.J. Flowerdew et al., doi: 10.1130/G33644.1