Latest Pleistocene and Holocene alpine glacier fluctuations in Scandinavia

Abstract

During the early Holocene abrupt, decadal to centennial-scale climate variations caused significant glacier variations in Norway. Increased freshwater inflow to the North Atlantic and Arctic Oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant Lateglacial and early Holocene climatic events in NW Europe. The largest early Holocene glacier readvances occurred ∼11,200, 10,500, 10,100, 9700, 9200 and 8400–8000 cal. yr BP. The studied Norwegian glaciers apparently melted away at least once during the early/mid-Holocene. The period with the most contracted glaciers in Scandinavia was between 6600 and 6000 cal. yr BP. Subsequent to ∼6000 cal. yr BP the glaciers started to advance and the most extensive glaciers existed at about ∼5600, 4400, 3300, 2300, 1600 cal. yr BP, and during the ‘Little Ice Age’. Times with overall less glacier activity were apparently around 5000, 4000, 3000, 2000, and 1200 cal. yr BP. It has been proposed that several glacier advances occurred in Scandinavia (including northern Sweden) at ∼8500–7900, 7400–7200, 6300–6100, 5900–5800, 5600–5300, 5100–4800, 4600–4200, 3400–3200, 3000–2800, 2700–2000, 1900–1600, 1200–1000, and 700–200 cal. yr BP. Glaciers in northern Sweden probably reached their greatest ‘Little Ice Age’ extent between the 17th and the beginning of the 18th centuries. Evidence for early Holocene glacier advances in northern Scandinavia, however, has been questioned by more recent, multi-disciplinary studies. The early to mid-Holocene glacier episodes in northern Sweden may therefore be questioned.

Most Norwegian glaciers attained their maximum ‘Little Ice Age’ extent during the mid-18th century. 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–40s. Subsequently, most Norwegian glaciers retreated significantly. Maritime outlet glaciers with short frontal time lags (<10–15 years) started to advance in the mid-1950s, whereas long outlet glaciers with longer frontal time lags (>15–20 years) continued their retreat to the 1970s and 1980s. However, maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s. After 2000 several of the observed glaciers have retreated remarkably fast (annual frontal retreat > 100 m) mainly due 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 the decrease of Northern Hemisphere summer solar insolation and the increase in winter insolation. In addition, regional weather modes, such as the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO), play a significant role with respect to decadal and multi-decadal climate variability.

Introduction

In the North Atlantic region, significant, high-frequency climate fluctuations have been recorded during the Lateglacial and the early Holocene (for proxies and key references, see Table 1). These climatic changes, causing significant variations in marginal/frontal position of the Scandinavian ice sheet, occurred at a time of maximum summer solar insolation in the Northern Hemisphere and they cannot therefore be explained by orbital forcing. The cause(s) of these climatic fluctuations must therefore be sought in the ocean/atmosphere climate system. Increased freshwater discharge from the vanishing Laurentide and Eurasian ice sheets to the North Atlantic and Arctic Oceans has been suggested as an important mechanism to explain the abrupt and significant Lateglacial and early Holocene climatic events in NW Europe (Clarke et al., 2003, Nesje et al., 2004, and references therein).

Strong climatic gradients across Scandinavia and its location in relation to North Atlantic cyclone tracks and the Arctic atmospheric and oceanic polar fronts make detailed reconstruction of Lateglacial and Holocene glacier and climatic fluctuations in Scandinavia of special interest. Data from this region may therefore provide important information relevant to the present debate about the magnitude, timing, and possible cause(s) of Lateglacial and Holocene glacier and climate variations (e.g. Kutzbach and Guetter, 1986, Davis and Osborn, 1988, Karlén and Kuylenstierna, 1996).

Climate changes cause responses to the cryosphere (Bamber and Payne, 2004). Our understanding of past glacier fluctuations has greatly improved during the last decades. High-resolution reconstructions of past climate variations have enabled better understanding of climate–glacier relationships. Cumulative glacier length variations have been used to model global temperature variations during the last centuries (Oerlemans, 2005). Equilibrium-line altitude reconstructions have been shown to be useful when investigating long-term accumulation-season precipitation anomalies in Scandinavia (Nesje et al., 2008). Glacier records are therefore taken into account when discussing long-term, regional and global climate trends (e.g. Moberg et al., 2005a). Significant progress has been made in the use of lacustrine sediments in proglacial lakes used in reconstructing upstream glacier variations (e.g. Dahl et al., 2003). Monitoring present changes in glacier mass balance and length variations of glaciers in response to a changing climate is of great importance (e.g. IPCC, 2007). Mass-balance measurements provide a direct (no time delay) signal of climate change that causes variations in accumulation and ablation. Glacier length is commonly easily measured, but the length records provide an indirect, filtered, and delayed signal of climate change. Despite the fact that glacier retreat is mentioned in many climate change assessments, the number of systematic studies of long glacier length records is rather few. Some glaciers, such as Storglaciären (northern Sweden), Storbreen (Jotunheimen) and Nigardsbreen (Jostedalsbreen) have been studied in great detail. The World Glacier Monitoring Service (www.geo.unizh.ch/wgms/) collects data and maintains a database on glacier mass balance and glacier length variations around the world.

The aim of the present paper is to compile, assess and evaluate evidence of Lateglacial and Holocene glacier fluctuations in Scandinavia (Fig. 1) as deduced from ice-marginal features, marginal moraines, proglacial terrestrial and lacustrine sites, especially new information that has become available since the review paper published by Karlén (1988). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)