Cross-cutting palaeo-ice streams in NE-Iceland reveal shifting Iceland Ice Sheet dynamics

Abstract

Ice streams are thought to have regulated the past Iceland Ice Sheet (IIS) during and following the Last Glacial Maximum (LGM) by discharging ice and sediment from the interior of the ice sheet towards the shelf edge. Previous assessments of ice streams within the IIS have produced contradictory reconstructions of ice sheet dynamics and location of ice divides. Here, we reconstruct palaeo-ice streams in NE-Iceland based on detailed mapping of streamlined subglacial bedforms (SSBs) and other glacial lineations. The morphometrics, distribution and orientation of the SSBs indicate the flow-sets of several cross-cutting palaeo-ice streams and the location and migration of ice divides, while high density and packing of SSBs possibly suggest the axial zones of the ice streams. North-trending flow-sets suggest that during maximum glaciation and ice-sheet thickness, ice flow within the study area was largely unaffected by underlying topography allowing ice to flow northwards across valleys and fjords. This ice flow direction correlates with the orientation of previously identified troughs on the north-eastern shelf and indicates that an E-W orientated ice divide was located to the south of the study area. During deglaciation and ice sheet thinning, a N-S orientated ice divide was located to the west of the study area, and palaeo-ice streams became confined to valleys and fjords, so that associated flow-sets crosscut the older ones. The absolute ages of these flow-sets are uncertain, but the simplest interpretation is that the older ones pertain to the LGM and the younger ones to the following deglaciation. This study sheds light on the dynamics and evolution of palaeo-ice streams within the IIS and highlights the importance of further efforts to understand the subglacial processes responsible for the formation of the streamlined subglacial bedforms as well as to constrain the evolution of shelf glaciation and chronology of ice stream retreat.