Stabilization of glaciers terminating in closed water bodies: Evidence and broader implications

Abstract

The behavior of glaciers terminating in deep water is determined by the interaction of buoyancy, iceberg production, and the sensitivity of ice flow to subtle changes in resistance at the glacier bed. Modeling efforts assume rapid evacuation of icebergs, but some glaciers terminate in closed basins where icebergs may accumulate. Multibeam bathymetric survey of a glacial lake in Iceland that received outlet glaciers during the Little Ice Age document near parallel flow of narrow, ice fingers that extended up to 1 km beyond the grounding line. These previously unseen features apparently occurred when iceberg production exceeded iceberg melt, resulting in iceberg buttressing of the ice margin. Similar stabilization of ice flow may resolve long‐standing debates about past continental ice‐sheet behavior, including the rapid readvance of the Laurentide Ice Sheet into Lake Superior ca. 11 ka and the genesis of glacial flutes observed in the central Arctic Ocean basin.

Deglaciation of the central Barents Sea

“…We suggest that these features are formed by ploughing or pushing of sediment by advancing fingers of grounded ice at the ice front and will hereafter refer to them as ice-fingerprints. Such ice-fingers can form if the margin experiences transverse extension (Geirsdóttir et al, 2008). We suggest that the transverse extension in this case can be attributed to a slightly larger advance of the ice within the deeper tunnel valley than on the flanking bank areas.…”

Grounding‐line dynamics during the last deglaciation of Kveithola, W Barents Sea, as revealed by seabed geomorphology and shallow seismic stratigraphy

“…Similar features were described by Geirsdóttir et al . () at the front of a tidewater glacier at Lake Hvítárvatn, Iceland, and were attributed to scouring by floating yet coherent ice fingers at the tidewater glacier snout. The above interpretation implies that the highly regular/parallel MSGLs were formed at a time when the ice stream was coupled to its bed.…”

Dynamic jamming of iceberg‐choked fjords

“…At some fjords, ice mélange exists only when air and water temperatures are low enough to permit the growth of a thick sea ice matrix [Howat et al, 2010;Walter et al, 2012]. At others, a combination of high iceberg productivity and confining fjord geometry enables ice mélange to persist year round as a result of iceberg-iceberg and iceberg-bedrock contact forces [see also Geirsdóttir et al, 2008;Jakobsson et al, 2012].…”