Australia: The Land Where Time Began

A biography of the Australian continent 

Greenland Ice Sheet – Melting at the Base Explained by the History of Iceland Hotspot

Large portions of the north-central Greenland ice sheet have been shown by ice-penetrating radar (Fahnestock et al., 2001; Oswald & Gogineni, 2012; Bell, 2014) and ice core drilling (Grinsted & Dahl-Jensen, 2002) to be melting from below. It has been argued that basal ice melt is caused by geothermal heat flux that is anomalously high (Fahnestock et al., 2001; Oswald & Gogineni, 2012; Bell, 2014; Grinsted & Dahl-Jensen, 2002) that has also influenced the development of the longest ice stream in Greenland (Fahnestock et al., 2001). In this study Rogozhina et al. estimate the geothermal flux beneath the Greenland ice sheet and identify a geothermal anomaly that is 1,200 km long and 400 km wide beneath the thick ice cover. Rogozhina et al. suggest the basal melting of the ice sheet that has been observed, is a driver of the subglacial hydrology (Bell, 2014), and controls the head of the enigmatic northeastern Greenland ice stream, that is 750 km long (Joughin et al., 2010), is explained by this anomaly. It is implied by the combined analysis of independent seismic, gravity and tectonic data (Rickers, Fichtner & Trampert, 2013; Jakovlev et al., 2012; Doubrovine, Steinberger & Torsvik, 2012; O’Neill, Müller & Steinberger, 2005) that the geothermal anomaly which crosses Greenland from west to east was formed as Greenland drifted across the Iceland mantle plume between about 80 Ma and 35 Ma. Rogozhina et al. conclude that tectonic events that predate the onset of glaciation in Greenland by many 10s of millions of years were the origin of the subglacial hydrology and dynamic features of the north central Greenland ice sheet of the present.

It is indicated by recent observations that strong regional variations in the geothermal flux (GF) dominate the thermal regime and basal melting of the ice beneath continental parts of the Greenland and Antarctic ice sheets (Fahnestock et al., 2001; Schroeder et al., 2014). Where there is high GF and there is meltwater present under the ice cover ice flows rapidly and subglacial hydrological systems develop (Kamb, 1987; Llubes, Lanseau & Remy, 2006). The GF basal melting is important because it occurs over large areas in the accumulation zone where there are no basal water sources, in spite of being small when compared to the volumes of water discharge from melting at the surface (Sørensen et al., 2011), and it affects disproportionally the overall dynamic behaviour of large sectors of the ice sheet (Fahnestock et al., 20011; Parizek, Alley & Hulbe, 2003).

It is revealed by the reconstruction by Rogozhina et al. of the thermal regime of the Greenland ice sheet (GIS) that there are more extensive areas of basal ice-melt that is GF-induced than has been recognised previously (Fahnestock et al., 2001; Oswald & Gogineni, 2012; Bell, 2014; Grinsted & Dahl-Jensen, 2002), and the possibility is introduced that a dense network of subglacial meltwater pathways is now operating beneath the ice, most of which spring from the zone affected by the history of the Iceland hotspot. It has not previously been hypothesised that melting beneath large areas of the GIS and anomalous streaming of ice in northeastern Greenland may be the result of the passage of Greenland across the Iceland plume, in spite of the aggregated evidence that has been presented in this paper. It is suggested by the geothermal anomaly that a hotspot track that is more northerly than has been proposed previously will offer a useful test for palaeoreconstructions of absolute plate motion. It is indicated by this study that there is a strong coupling between Greenland’s ice dynamics of the present, subglacial hydrology and the remote tectonic history of the North Atlantic region that has not been documented previously.

Sources & Further reading

1. Rogozhina, I., A. G. Petrunin, A. P. M. Vaughan, B. Steinberger, J. V. Johnson, M. K. Kaban, R. Calov, F. Rickers, M. Thomas and I. Koulakov (2016). "Melting at the base of the Greenland ice sheet explained by Iceland hotspot history." Nature Geosci 9(5): 366-369.