THE TIMING OF THE YOUNGER DRYAS GLACIER ADVANCE AND MAXIMUM IN WESTERN NORWAY - FROM CIRQUE GLACIERS TO THE INLAND ICE SHEET

(1) When did the Scandinavian Ice Sheet start to expand during the Younger Dryas (YD)?

(2) When did the Ice Sheet reach its maximum during the YD in western Norway?

(3) For how long was the Ice Sheet at its maximum?

(4) How do these ages of the inland Ice Sheet compare with the timing of the YD glacial max of smaller ice caps and cirque glaciers?

To solve these questions we have studied deposits in shallow basins located just in front of a YD ice-marginal delta in western Norway. In these records we have identified the meltwater deposits coming from the glacier and the sea level changes. Crucial in this study is the presence of the Vedde Ash Bed, dated to ca 10,300 14C yr BP - ca 12,000 ice core yr BP, that we use as a stratigraphic marker.

Short answers to the questions:

(1) Our reconstructed sea-level curve from the area shows significant glacial loading of the lithosphere already starting at ca 13,300 cal yr BP (11,600-11,500 14C yr BP) i.e. in late Allerød (AL). The AL climate in w. Norway was cool and oceanic with rel. high precipitation. The glacial build-up coincides with the Inter-Allerød Cold Period that may have increased the length of the accumulation season resulting in a reactivation of the ice sheet.

(2) In the shallow basins the deposition of silt and fine sand started, and thus the ice sheet reached its maximum, 300-400 years after the Vedde Ash fall, around 11,600-11,700 cal yr BP (10,000 14C yr BP).

(3) The ice sheet receded from its maximum position simultaneously with the increase of Betula pollen at the YD/Holocene boundary, ca 11,500 cal yr BP (10,000 14C yr BP). The duration of the YD glacial max of the Scandinavian Ice Sheet in w. Norway was only about 100-200 years.

(4) Many of the cirque glaciers in w. Norway survived through the late glacial period. However, a cirque glacier on the extreme outer coast (Kraakenes) disappeared during the AL and reformed at the AL/YD boundary. A larger ice cap (Ålfotbreen) reached its max. just before the deposition of the Vedde Ash Bed. The small cirque glaciers expanded to the max fast, the larger ice cap at Ålfotbreen at a later stage, and the advance of the Scandinavian Ice Sheet was probably aborted before it reached its equilibrium at the YD/Holocene boundary.

Bondevik, S. & Mangerud, J. 2002: A calendar age estimate of a very late Younger Dryas ice sheet maximum in western Norway. Quaternary Science Reviews 21, 1661-1676.