Cosmogenic 36Cl exposure ages reveal a 9.3 ka BP glacier advance and the Late Weichselian-Early Holocene glacial history of the Drangajökull region, northwest Iceland

Skafti Brynjólfsson, Anders Schomacker, Ólafur Ingólfsson, Jakob K. Keiding

Publikation: Bidrag til tidsskriftArtikelForskningpeer review

24 Citationer (Scopus)

Abstrakt

We present twenty-four new cosmogenic isotope (36Cl) surface exposure ages from erratic boulders, moraine boulders and glacially eroded bedrock that constrain the late Weichselian to Holocene glacial history of the Drangajökull region, northwest Iceland. The results suggest a topographically controlled ice sheet over the Vestfir{eth}ir (Westfjords) peninsula during the last glaciation. Cold based non-erosive sectors of the ice sheet covered most of the mountains while fjords and valleys were occupied with erosive, warm-based ice.Old36Cl exposure ages from highlands and mountain plateaux (L8; 76.5 ka and H1; 41.6 ka) in combination with younger erratic boulders (L7; 26.2 and K1-K4; 15.0-13.8 ka) superimposed on such surfaces suggest the presence of non-erosive ice over uplands and plateaux in the Vestfir{eth}ir peninsula during the last glaciation. Glacially scoured terrain and erratic boulders yielding younger exposure ages (L1-L6; 11.3-9.1 ka and R1, R6-R7; 10.6-9.4 ka) in the lowland areas indicate that the valleys and fjords of the Vestfir{eth}ir peninsula were occupied by warm-based, dynamic ice during the last glaciation.The deglaciation of mountain Leirufjall by 26.2 ka BP suggests that ice thinning and deglaciation of some mountains and plateaux preceded any significant lateral retreat of the ice sheet. Subsequently this initial ice thinning was followed by break-up of the shelf based ice sheet off Vestfir{eth}ir about 15 ka BP. Hence, the new exposure ages suggest a stepwise asynchronous deglaciation on land, following the shelf break-up with some valleys and most of the highlands, ice free by 14-15 ka BP.The outermost moraine at the mouth of Leirufjörour is dated to 9.3 ka BP, and we suggest the moraine to be formed by a glacier re-advance in response to a cooler climate forced by the reduced Atlantic Meridional Overturning Circulation at around 9.3 ka BP. A system of moraines proximal to the 9.3 ka moraine in Leirufjör{eth}ur as well as a 9.4 ka deglaciation age in the coastal area of Reykjarfjör{eth}ur suggest that an extensive ice cap persisted over the eastern Vestfiroir peninsula at least until c. 9 ka BP.

OriginalsprogEngelsk
Sider (fra-til)140-157
Antal sider18
TidsskriftQuaternary Science Reviews
Vol/bind126
DOI
StatusUdgivet - 15 okt. 2015

Programområde

  • Programområde 5: Natur og klima

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