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During the early Holocene abrupt climate variations caused significant glacier variations in Norway. The largest early-Holocene glacier re-advances occurred ∼11 200, 10 500, 10 100, 9700, 9200 and 8400-8000 cal. yr BP. Increased freshwater input to the North Atlantic and Arctic Oceans has been suggested as one of the most likely mechanism to explain some of the abrupt and significant early-Holocene climatic events in NW Europe. During and after the 8.2 ka event, several glaciers had re-advances either as a response to colder summer temperature or higher winter precipitation. The studied Norwegian glaciers melted away at least once during the early-/mid-Holocene. The period with the most contracted glaciers was between 6500 and 6000 cal. yr BP. Subsequent to ∼6000 cal. yr BP the glaciers started to advance and the periods with the most extensive glaciers were at ∼5600, 4400, 3200, 2000, 1600 cal. yr BP, and during the 'Little Ice Age'. Most Norwegian glaciers attained their maximum 'Little Ice Age' extent during the mid 18th century.
Periods with overall less glacier activity were apparently around 5000, 4000, 3000, and 1000 cal. yr BP. Cumulative glacier length variations in southern Norway, based on marginal moraines dated by lichenometry and historic evidence, show an overall retreat from the mid-18th century until the 1930s and 1940s. Maritime outlet glaciers with short response time (<10-15 years) started to advance in the mid-1950s, whereas larger outlet glaciers with longer frontal time lag (>15-20 years) continued their retreat to the 1970s and 1980s. However, in the 1990s maritime glaciers started to advance as a response to higher winter accumulation. After 2000 several of the observed glaciers have retreated remarkably fast (annual frontal retreat >100 m) mainly as a response to high summer temperatures.
The general glacier retreat during the early Holocene and the Neoglacial advances after 6000 cal. yr BP are in line with orbital forcing, due to decrease of Northern Hemisphere summer solar insolation. Solar activity and volcanic eruptions in addition to regional weather modes, such as the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO), played a significant role with respect to decadal and multi-decadal climate variability and glacier-size variations.
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