Holocene development of Lake Lögurinn and Eyjabakkajökull : a multi-proxy approach

Abstract: The North Atlantic region has experienced significant climate fluctuations during the Holocene. It has been shown that these fluctuations affected the terrestrial environment in Iceland, including its glaciers and ice caps. However, the full Holocene development of Icelandic glaciers, including the large Vatnajökull ice cap and its outlet glaciers, is not fully known. In this thesis, a sediment sequence covering the past 10 500 years from Lake Lögurinn in eastern Iceland has been analysed. This glacier-fed lake currently receives meltwater and sediments from Eyjabakkajökull, which is a surging outlet glacier that drains the northeastern part of Vatnajökull. Using a multi-proxy approach, proxies for glacial meltwater variability and surge periodicities of Eyjabakkajökull have been examined to infer its Holocene development. In addition, changes in sediment transport from a non-glaciated catchment adjacent to Lake Lögurinn have been analysed to reconstruct winter precipitation in the Lake Lögurinn region during the past ca. 750 years. The sediments and proxy records show a dynamic development of Eyjabakkajökull during the current interglacial. After the final phase of the last deglaciation in eastern Iceland, glacially derived sediments more or less ceased to be deposit in Lake Lögurinn between ca. 9000 and 4400 years BP (BP = calendar years before 1950 AD), which suggests that Eyjabakkajökull was much reduced in size or possibly non-existing in early and mid-Holocene. During this time, the biologic productivity in Lake Lögurinn increased. This increase is inferred to reflect a switch from glacio-lacustrine to lacustrine conditions in the lake, which likely was caused by higher temperatures both in the lake and in the ambient atmosphere. The Holocene Thermal Maximum is inferred by a period of maximum Holocene aquatic productivity, and dated to ca. 7900-7000 years BP. By 4400 years BP, glacial meltwater and sediments were again transported to Lake Lögurinn, thus marking the return of the Eyjabakkajökull glacier and the onset of Neoglaciation in eastern Iceland. The Neoglacial expansion of Eyjabakkajökull caused the glacier to begin to surge ca. 2200 years BP. During the last 1700 years, the glacier has surged at a fairly constant periodicity except for the later part of the Little Ice Age (ca. 1600-1900 AD), when the surge periodicity almost halved. This increased surge activity was likely caused by increased mass accumulation of Eyjabakkajökull, which eventually caused the glacier to reach its maximum Holocene extent since the last deglaciation. This expansion and increased surge activity may to a large extent be related to increased winter precipitation, in combination with lower annual temperatures.