Responses of mountain ice caps in central Iceland to Holocene climate change

Abstract

A chronology of Holocene fluctuations of small outlet glaciers from the Regnabuðajökull ice cap on Hrútfell, central Iceland, allows comparison of their sensitivity with the margin of the nearby Langjökull icefield, to ascertain which frequencies of climatic variability are recorded by adjacent glaciers of different size. Dating utilised tephra layers in aeolian soils lying on, between and beneath moraine ridges. Key marker isochrones dating from the Hekla 4 tephra ( c. 3.8 ka BP) to Katla A.D. 1918 provide unequivocal bracketing ages. The stratigraphy and geochemical fingerprinting of tephras on younger moraines allows subdivision of “Little Ice Age” moraines. Five groups of moraines are identified, at c. 4.5–5.0, c. 3.0–3.5 ka BP, c. 2.0–2.5 ka BP, and from the “Little Ice Age” at c. A.D. 1700 and in the late 19th/early 20th century. These represent a Neoglacial sequence in which steep, small glaciers readvanced to similar positions during what are here termed “Little Ice Age”-type periods (LIATPs). In contrast, the nearby margins of Langjökull show evidence of a late nineteenth-century advance only, suggesting that this was the Holocene maximum for this glacier. The contrasting responses of local glaciers and the large icefield are explained by their different sizes and response times, so that the preserved moraine record is largely pre-conditioned by the glacier type. In general, the forefields of steep, fast-responding glaciers contain more complete archives of Holocene climatic changes than do the margins of the large icefields.