An inverse approach to the course of the ‘Little Ice Age’ glacier advance and the following deglaciation at Austerdalsisen, eastern Svartisen, northern Norway

Abstract

The course of the ‘Little Ice Age’ (LIA) in Scandinavia is characterized by large glacier advances that started at about AD 1300 and culminated at about AD 1750. The end of the LIA is marked as an unprecedented and ongoing glacier retreat that accelerated from the early 20th century. The course of the LIA is here presented based on fluctuations of Austerdalsisen, the largest valley outlet glacier draining the Austre Svartisen (Østisen) ice cap, Nordland, northern Norway. During the LIA glacierization, Austerdalsisen separated into two branches, and relative to the present glacier terminus, a western valley glacier advanced more than 4 km, whereas a SE valley glacier advanced about 3 km. At present, meltwater from Austerdalsisen drains towards SE. If the glacier obtains a critical magnitude, however, most of the meltwater is drained westwards across a higher overflow gap. Based on radiocarbon-dated lake sediments, distal proglacial glaciolacustrine/glaciofluvial sediments and historical observations, the course and chronology of the deglaciation following the LIA glacier maximum at Austerdalsisen are established. Because of high sedimentation rates due to low local bedrock resistance to glacier erosion beneath Austerdalsisen, however, cores from distal glacier-fed lakes covering the entire LIA/Holocene are hard to retrieve. Hence, an inverse approach to reconstruct the entire course of the LIA glacierization at Austerdalsisen is performed by suggesting little input of glacier-meltwater-induced sediments to the SE distal glacier-fed lake Litl Røvatnet, whenever Austerdalsisen rerouted meltwater westwards. If the terminus of Austerdalsisen was near the critical magnitude threshold, regular glacier lake outburst floods (GLOFs) towards SE occurred.