Ice-sheet growing from the base

Freeze-on plume

Freeze-on of water at the ice-sheet bed can explain the occurrence of the large plume-shaped ice-bodies at the base.

Deep inside the ice-sheet, which for example covers the north of Greenland, layer structures have been detected in recent years using modern radar measurements. Now the occurrence of these large plume-shaped ice bodies could be explained by freeze-on of water at the ice-sheet bed.

Up to now scientists were puzzled about the formation and size of these spectacular features within the ice-sheet. The observed ice structures extend from the bed to up to half of the ice thickness, around a 1000 metres, and are up to a few tens of kilometres in length. Further, the radar images show clear evidence of folded ice layers around these ice bodies. 

Reproduction of layer structures with a computer simulation
A team of scientists from the University of Zurich, Switzerland, and the British Antarctic Survey, England, were able to reproduce such layer structures with a computer simulation by freezing on ice at the base of the ice-sheet. The study was published in Nature Communications. They demonstrate that the size and the shape of these plume structures depend upon the interplay between ice flux and basal freeze-on rates.

With a detailed ice-sheet wide analysis the team could explain that the location of the majority of the plumes match regions where water, freely running along the ice-sheet base, is expected to freeze-on.

layer structures in radar image together with simulated layer structure
layer structures in radar image together with simulated layer structure
Observed (a) and interpreted (b) layer structures in radar image together with simulated (c) layer structure for basal freeze-on. (Radar imagery from the NASA IceBridge MCoRDS L1B instrument, courtesy NASA NSIDC DAAC, NSF and CReSIS, Kansas)

Implications for ice-core studies
This new study highlights that over a rugged basal topography the ice sheet can grow from the base which has implications for the wider ice-sheet community, especially for ice-core studies, as old ice is pushed upwards from the base and folded around the ice-body. 

Literature:
Gwendolyn Leysinger Vieli, Carlos Martín, Richard C.A. Hindmarsh & Martin Lüthi: Basal freeze-on generates complex ice-sheet stratigraphy. Nature Communications. November 7, 2018. DOI: 10.1038/s41467-018-07083-3