Dynamics and retreat of the Late Weichselian Kongsfjorden ice stream, NW Svalbard

Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsfjordhallet area, NW Svalbard, have provided new insight on configuration, dynamics, and deglaciation of the Late Weichselian Kongsfjorden ice stream. The minimum Late Weichselian ice surface elevation in Kongsfjorden was >449 m a.s.l. indicating considerably thicker ice and a steeper surface gradient than earlier suggested. For the adjacent inter-ice stream area an even steeper surface slope is reconstructed. The glacial landforms, as well as the surface exposure ages of erratic boulders at different elevations, suggest a gradual lowering of the ice surface. Deglaciation of the higher elevations was probably underway by 20.0 ka. At ca 16.6 ka a large moraine complex ('the Kongsfjorden moraine') was deposited close to the fjord mouth. The shape of the moraines, the steep ice surface gradient, as well as the correlation to fine laminated clay lacking ice rafted debris deposited in the trough beyond the moraine suggest that ice dynamics switched from ice-stream behaviour to a slower flowing outlet (tidewater) glacier. A Younger Dryas or Early Holocene advance of local valley glaciers is shown by moraine lobes cross-cutting the Late Weichselian lateral moraines.