The Briksdalsbre Event: A winter precipitation-induced decadal-scale glacial advance in southern Norway in the ad 1990s and its implications

Abstract

In the ad 1990s maritime glaciers in Scandinavia started to advance as a response to positive net mass balance in the preceding years, invoking annual advance rates in the order of ~50–60 m and a total frontal advance of 285 m (at Briksdalsbreen) in less than a decade. Records from six south Norwegian glaciers with continuous, annual front measurements are used to evaluate the magnitude, duration, climatic causes, and frontal time lags involved in this mass balance perturbation and the following frontal response of glaciers in southern Norway. A climate index based on meteorological data from Bergen unequivocally demonstrates that the main cause for the large glacier advances in Scandinavia in the 1990s was high winter precipitation linked to positive NAO index in the winters of 1988/1989, 1989/1990, 1992/1993, 1994/1995, 1997/1998, and 1999/2000. Less positive (or negative) glacier mass balance years were 1990/1991, 1993/1994, 1995/1997, and 1998/1999. Between 1996/1997 and 2009, Briksdalsbreen retreated 486 m (maximum annual retreat of 145 m in 2005/2006). The main cause of the significant glacier retreat in the early twenty-first century was a combined effect of reduced winter precipitation and higher summer temperatures. The glacier advance and following retreat phase back to the pre-advance position was completed in ~20 years, and is here termed the Briksdalsbre Event. This event has relevance for the identification and interpretation of decadal to centennial Holocene glacial events recorded in lacustrine and terrestrial sequences.

Keywords

climate change climate index decadal-scale variability frontal lag time glacier variations Holocene maritime glaciers North Atlantic Oscillation (NAO)Norway reaction time

Introduction

At present, glaciers, ice caps and continental ice sheets cover approximately 10% of the Earth’s land surface and account for about three-quarters of the world’s total freshwater (Intergovernmental Panel on Climate Change (IPCC), 2007; International Glaciological Society, 2008; Meier et al., 2007; World Glacier Monitoring Service, 2008). Their fluctuations in size reflect climate change and are important to humanity for a number of reasons, including their contribution to sea-level rise (IPCC, 2007), freshwater for agriculture, industrial and domestic use, and hydroelectric power production. They can also be a natural hazard, mainly because of past and potential jökulhlaups (or GLOF; Glacial Lake Outburst Floods) from glacier- and moraine-dammed water bodies.

Glaciers grow and shrink as a response to changes in precipitation and temperature (Bamber and Payne, 2004; Dyurgerov, 2003; Kuhn, 1980; Nye, 1960). The accumulation and ablation areas are separated by the equilibrium line, where the balance between gain and loss of mass is zero at the end of the ablation season (e.g. Benn and Evans, 2010; Paterson, 1994). The glacier distribution is therefore mainly a function of accumulation-season precipitation and ablation-season temperature. In humid, maritime regions, such as western Scandinavia, the equilibrium line is at relatively low altitude, exhibits a high mass turnover and reacts strongly to atmospheric summer temperature changes and variations in winter precipitation, although other factors such as solar radiation, wind and cloudiness influence the mass and energy balance at the glacier surface (e.g. Oerlemans, 2001).

Cumulative changes in mass balance over periods of years to several decades cause volume and thickness changes that affect the flow of ice through internal deformation and basal sliding, the dynamic response leading to glacier length changes. The advance or retreat of glacier tongues forms an indirect, delayed and filtered, yet easily observed, signal of climate change. The glacier mass balance (vertical thickness or volume change), on the other hand, is a direct (not delayed) signal of annual accumulation and ablation changes (Haeberli, 1998). As a consequence, relatively short and steep glaciers, not influenced by thick debris covers, calving or surge instabilities, and with short (<10 yr) frontal time lag are considered better-suited to detect subdecadal fluctuations in climate than extensive and gentle outlet glaciers with long (several decades) time lags and response times.

Glacier variations occur on a wide range of timescales. In the context of the Holocene, recent research in different parts of the world has recognized a large number of decadal- to millennial-scale glacier variations, which reflect global, hemispherical, regional and local climatic variations (Winkler and Matthews, 2010a). Glacier expansion during the ‘Little Ice Age’ and subsequent glacier retreat is commonly recognised as the latest centennial-scale glacier variation of a sequence of similar ‘Neoglacial’ events that have occurred during the Holocene (Matthews and Briffa, 2005; Matthews and Dresser, 2008; Nesje, 2009; Nesje et al., 2008). In many parts of the world, the maximum limits of glaciers during the ‘Little Ice Age’ event are commonly marked by prominent lateral and terminal moraines (Grove, 1988, 2004). From these limits, glaciers show a centennial trend of volume reduction and frontal retreat (Figures 1 and 2), which on a global scale has accelerated since the mid ad 1980s (International Glaciological Society, 2008; IPCC, 2007; Meier et al., 2007; World Glacier Monitoring Service, 2008). On a decadal timescale, however, glaciers in some regions of the world have experienced short-lived re-advances. In both western Scandinavia and New Zealand, for example, glaciers experienced a period of prevailing positive net mass balance and subsequent frontal advance in the 1990s (Chinn et al., 2005; Huber et al., 2005; Knight, 2006; Nesje, 2005).

Figure 1.

Short-term glacier-length changes. The number of advancing (black) and retreating (grey) glaciers around the world is plotted as stacked columns (adapted from World Glacier Monitoring Service (WGMS), 2008)

Figure 2.

Cumulative glacier front (length) and mass balance (volume) changes of glaciers around the world (adapted from WGMS, 2008)

The purpose of this article is to evaluate this decadal-scale glacier fluctuation, here termed the Briksdalsbre Event, after the location in southern Norway where it was particularly prominent and is well understood. We first describe and discuss the magnitude, duration, climatic cause(s), and frontal time lags involved in this mass balance perturbation and the following frontal response of Briksdalsbre and other glaciers in southern Norway. Second, we consider the implications of the Briksdalsbre Event for Holocene glacier and climatic variations in general.

Study glaciers and their recent length variations

The combination of high latitude and atmospheric moisture transport from the North Atlantic have led to the formation of numerous mountain glaciers and ice caps, mainly on the western side of the Scandinavian mountain range. The main bodies of ice in Scandinavia are located in southern Norway, e.g. Jostedalsbreen, Folgefonna, Hardangerjøkulen, and in Jotunheimen and Breheimen, of which Jostedalsbreen (487 km²) is the largest glacier on mainland Europe (Figure 3). The extensive observation record in Norway and elsewhere in Scandinavia (e.g. Andreassen et al., 2005; Chinn et al., 2005; Kjøllmoen, 2010; Winkler et al., 2010) is the result of the relevance of glaciers and their changes to the rural population around the glaciers and ice caps. Farmland and farmhouses destroyed by advancing glaciers, resettlements and tax reductions are reported in historical documents (Grove, 2004). At present, 98% of the hydroelectric power production and 15% of the used runoff are generated from glacierised basins (Andreassen et al., 2005).

Figure 3.

Location map of the study glaciers in southern Norway. Au, Austerdalsbreen; Bo, Bondhusbreen; Br, Briksdalsbreen; G, Gråsubreen; H, Hellstugubreen; Få, Fåbergstølsbreen; Mi, Midtdalsbreen; Ni, Nigardsbreen; Re, Rembesdalsskåka; S, Storbreen; St, Stegholtbreen; Å, Ålfotbreen. Adapted from NASA World Wind

After the glaciers reached their maximum ‘Little Ice Age’ limits – generally around the mid eighteenth century – glaciers tended to retreat gradually until the late nineteenth century (Nesje, 2009; Nesje et al., 2008). Most Norwegian glaciers experienced a rapid retreat in the twentieth century, especially between ~1930 and ~1970 (Figure 4). Subsequently, the glacier fronts were more-or-less in a stable position until c. 1990. In the 1990s, however, most maritime glaciers started to advance as a response to positive net mass balance (Figure 5), invoking annual advance rates in the order of ~50 m (Figure 6) and a total advance of up to 285 m (Briksdalsbreen; Figures 7 and 8) in less than a decade (Figure 9). The same glaciers started to retreat again after ~2000. The records from six southern Norwegian glaciers with continuous, annual front measurements are shown in Table 1 (see Figure 3 for their locations).

Figure 4.

Cumulative front variations (length changes) of seven Norwegian glaciers in the twentieth to early twenty-first centuries. Data: NVE

Figure 5.

Upper panel: The winter (Bw), summer (Bs) and net (Bn) glacier mass balance of Ålfotbreen in western Norway (data: NVE) (for location, see Figure 3) plotted versus the North Atlantic Oscillation (NAO) index (www.cru.uea.ac.uk/datapages/naoi/htm). Lower panel: Cumulative net mass balance of seven Norwegian glaciers (data: NVE)

Figure 6.

Annual front (length) variations of Briksdalsbreen (Jostedalsbreen), Midtdalsbreen (Hardangerjøkulen), and of Austerdalsbreen, Nigardsbreen, Fåbergstølsbreen and Stegholtbreen (all three eastern outlet valley glaciers from Jostedalsbreen) (data: NVE)

Figure 7.

Photographs (A-1993 to D-1997) from the advance period of Briksdalsbreen in the 1990s (see Figure 6). Photograph: Sigbjørn Myklebust

Figure 8.

Photographs (A-2001 to J-2010) of Briksdalsbreen, illustrating the frontal reatreat subsequent to the maximum position during the late 1990s. Photos: Ove Brynestad (2001–2003), Kurt Erik Nesje (2004) and Atle Nesje (2005–2010)

Figure 9.

Cumulative front (length) variations of the six glaciers in Figure 6

Table 1.

Characteristics of study glaciers

Glacier	Area (km²)^a	Elevation^a		Altitudinal			Frontal time
		Max.	Min.	Range (m)	Length (km)^a	H/L	Lag(yr)
Briksdalsbreen	11.9	1910	350	1560	6.0	0.26	3
Stegaholtbreen	15.3	1900	880	1020	7.7	0.13	6
Fåbergstølsbreen	15	1810	760	1050	7.0	0.15	5
Nigardsbreen	48	1950	355	1595	9.6	0.17	5
Austerdalsbreen	26.8	1920	390	1530	8.5	0.18	5
Midtdalsbreen	9.6	1850	1380	470	5.9	0.08	6

Adapted from Østrem et al. (1988).

Briksdalsbreen (11.94 km²) ranges in altitude from 1910 to 350 m above sea level over a distance of 6 km (Østrem et al., 1988). Briksdalsbreen experienced its ‘Little Ice Age’ maximum position around ad 1760–1765 (Nesje, 1989, 1992, 2005; Pedersen, 1976). During the ad 1930s and 1940s the glacier front retreated significantly, reaching a maximum annual retreat of 84 m in 1948 (Figure 4). The minimum twentieth-century glacier extent was reached in the early 1950s. Between 1952 and 1973 the glacier front was more-or-less in the same position. Between 1974 and 1980 the glacier front advanced 116 m. After some years of minor glacier advance since 1988, a significant glacier advance started in 1992; this culminated with an advance of 61 m in 1994, the largest annual advance recorded in the twentieth century (Winkler and Nesje, 1999). The advance period terminated in 1996, thus lasting for 5 years (Figure 6). Since 2002, Briksdalsbreen has experienced frontal retreat. Maximum rates of annual retreat occurred in 2004 and 2006, with 120 and 145 m, respectively (Figure 6).

The advance of Briksdalsbre was the rule, rather than the exception in southern Norway. Midtdalsbreen, a NE outlet glacier from Hardangerjøkulen, experienced a similar period of glacier advance in the early 1990s that ended in 1997. The maximum annual frontal advance rate occurred in 1990 (15 m). Several eastern outlet glaciers from the Jostedalsbreen ice cap exhibited advances of variable length and duration around the same time. Austerdalsbreen advanced for seven years between 1992 and 1998 (maximum annual advance of 20 m in 1997). Nigardsbreen experienced a continuous advance between 1990 and 2000 (11 yr); its maximum annual advance occurred in 1995 (50 m). Fåbergstølsbreen experienced an advance period between 1993 and 2001; the maximum annual advance being 44 m in 1995. Finally, Stegholtbreen advanced between 1997 and 2000, experiencing the largest annual advance of 9 m in 1998 (Figures 6 and 9).

Climate index

As an indicator of winter accumulation and summer ablation and their combined effect on the glacier mass balance of the study glaciers, Nesje (2005) used records of mean winter (December–March) precipitation (Figure 10A) and mean summer (May–September) temperature (Figure 10B) at the meteorological station in Bergen (Figure 3) to produce a climate index that indicates periods favourable for glacier advance and retreat (Figure 10C). The climate index was generated by combining standardised records of mean December to March (4 months) precipitation and mean May–September (5 months) temperature in Bergen (data: met.no). The standardisation procedure was to subtract the annual mean values (X) of winter precipitation and summer temperature from the average value (X _mean) for the 1961–1990 climate normal period and divide by the standard deviation (std) of both data sets ((X−X _mean)/std). Based on the relative significance of winter balance and summer balance for the net mass balance of Nigardsbreen (the winter balance and summer balance both correlated at r = ~0.85 against the net mass balance of Nigardsbreen (Figure 11) based on mass-balance records from 1962 to 2009 (Kjøllmoen, 2010)), the climate index was given equal weight to winter precipitation and summer temperature. At more coastal glaciers, the winter precipitation has to be given more weight in the climate index than the summer temperature, whereas at inland glaciers summer temperature is given more weight than winter precipitation, as demonstrated in Figure 11.

Figure 10.

(A) Winter (October–April and December–March) precipitation in Bergen 1985–2009. (B) Summer (May–September) temperature in Bergen (Data: Climate Division, Meteorological Institute, Oslo). For location, see Figure 3. (C) Standardised values relative to the 1961–1990 climate normals for winter (December–March) precipitation and summer (May–September) temperature in Bergen ad 1985–2009. These are combined to produce an annual index for climate favourable for positive net mass balance/glacier advance (above horizontal line) and climate favourable for negative net mass balance/glacier retreat (below horizontal line). (D) The climate index for Bergen (as above), December–March precipitation in Bergen and the NAO index (www.cru.uea.ac.uk/datapages/naoi/htm) plotted together

Figure 11.

Correlation between winter (Bw)/summer (Bs) and net (Bn) mass balance at Scandinavian (including Svalbard) glaciers. Adapted from Nesje (2005)

In order to test whether the climate data from Bergen are representative for the glacier mass balance on Jostedalsbreen, the standardised climate data from Bergen (December–March precipitation and mean May–September temperature) were compared with the winter and summer balance in the accumulation and ablation seasons, respectively (Figure 12A, B). The climate index based on the Bergen winter precipitation and summer temperature records is highly correlated (r = 0.89) with the net mass balance on Nigardsbreen (Figure 12C). The December–March precipitation (standardised) and the climate index are also both highly correlated with the NAO index (December–March) (r = 0.83 and 0.67, respectively; Figure 10D).

Figure 12.

(A) The annual winter balance of Nigardsbreen 1985–2009 (data: NVE) plotted together with the December–March precipitation in Bergen 1985–2009 (standardised) (data: Climate Division, Meteorological Institute, Oslo). (B) Summer balance of Nigardsbreen 1985–2009 (data: NVE) plotted together with the May–September temperature index for Bergen 1985–2009 (data: Climate Division, Meteorological Institute, Oslo). (C) The Bergen climate index and the net mass balance of Nigardsbreen is highly correlated (r = 0.89)

Reaction/frontal lag times

The reaction time (e.g. Benn and Evans, 2010), equivalent to the frontal time lag (e.g. Laumann and Nesje, 2009b), referring to the time it takes for the terminus to react to a change in climate (mass balance) and the first signs of change in glacier length, was calculated for Briksdalsbreen by comparing the frontal length-variation data with the climate index using time lags of 1 … n years. The highest correlation (r = 0.56) was attained with a time lag of 3 yr (Figure 13), in close agreement with previous studies using the entire record starting in 1901 (Laumann and Nesje, 2009a,b; Nesje, 2005; Winkler and Matthews, 2010b; Winkler and Nesje, 2009; Winkler et al., 2009). A similar procedure was carried out for the other glaciers (for calculated frontal time lags, see Table 1).

Figure 13.

Correlations obtained by moving the annual front variations of Briksdalsbreen (1985–2009) relative to the climate index using different frontal time lags. The highest correlation (r = 0.56) is obtained when the frontal data is displaced by three years, which is the mean frontal time lag of Briksdalsbreen for the period 1985–2009

The reaction time or frontal time lag of a glacier is highly variable, ranging from 3–5 years at steeply sloping and short outlet valley glaciers from Jostedalsbreen (Laumann and Nesje, 2009a, b; Nesje, 2005; Nesje et al., 1995; Oerlemans, 1997, 2007) to 15–60 years on longer, more gently sloping maritime glaciers (Jóhannesson et al., 1989; Van de Wal and Oerlemans, 1995). In order to test whether short and steep outlet glaciers have a shorter frontal time lag than longer and more gently sloping glaciers, H (maximum–minimum elevation) was divided by the horizontal distance (L); the steep and short glaciers yielding higher H/L ratio than the gently sloping and longer glaciers. The data from the six glaciers included in this study yields a high negative correlation (r = −0.95) between the H/L ratios and the calculated frontal time lags (Figure 14).

Figure 14.

The altitudinal/vertical span (H, in m) divided by the length (L, in m), giving the H/L (see Table 1), plotted against the calculated mean frontal time lag (same procedure as in Figure 13) for the six glaciers included in this study (r = −0.95). This relationship demonstrates, as previously shown, that frontal time lags are shorter on short and steep glaciers than on longer and more gently sloping glaciers

The relative importance of the winter and summer glacier mass balance

Although it is well known that glaciers respond mainly to variations in both summer temperature and winter precipitation, glacier palaeorecords have, until recently, been interpreted mainly as a response to changes in summer temperature (e.g. Oerlemans, 2001, 2005). In Norwegian mass-balance studies, the ablation and accumulations seasons are approximately 1 May–30 September and 1 October–30 April, respectively (e.g. Kjøllmoen, 2004). The glacier mass balance year lasts from early October to end of September the following year. Analysis shows that the net mass balance of maritime glaciers in southern Norway, being typical accumulation-type glaciers (e.g. Benn and Evans, 2010), is mainly controlled by the winter balance (Nesje et al., 1995, 2000). At Ålfotbreen, at the extreme coast of western Norway (Figure 3), the correlation coefficients between the winter balance and the net balance and between the summer balance and the net balance (1962–2009) are 0.84 and 0.67, respectively. At the continental glaciers in Jotunheimen (Figure 3), in contrast, the correlations between the winter balance and the net balance and between the summer balance and the net balance (1962–2009) are ~0.53 and ~0.90, respectively.

Relationship to the NAO

In the extratropical Northern Hemisphere, two related major weather modes, the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO), have been related to interannual (winter-season) temperature and precipitation variability (e.g. Hurrell et al., 2003). The NAO is commonly described as the sea-level pressure difference between Iceland and the Azores, and relates to the strength of the westerly winds across the North Atlantic (e.g. Hurrell, 1995; Hurrell et al., 2003; Luterbacher et al., 2002). In a positive NAO phase, the meridional air-pressure gradient is large in winter in the North Atlantic region, bringing mild and humid winter weather in southwestern Scandinavia.

Interannual and decadal variations in glacier mass balance in western Scandinavia in the late twentieth/early twenty-first centuries have been attributed to the NAO (Nesje et al., 2000). Positive NAO index winters yield above normal winter accumulation, and (if not compensated by a following warm summer), positive net mass balance on coastal glaciers in southern Norway, but in general low winter accumulation on glaciers in the Alps, and vice versa (Nesje et al., 2000; Reichert et al., 2001; Six et al., 2001). For Nigardsbreen (Jostedalsbreen) and Rôhnegletscher (Switzerland) there is a high correlation (r = 0.55) and anti-correlation (r = −0.64), respectively, between decadal variations in the NAO index and in glacier mass-balance (Reichert et al., 2001). The correlation coefficient between the December–March NAO index (www.cru.uea.ac.uk/datapages/naoi/htm) and the winter balance of Ålfotbreen and Nigardsbreen from 1962 to 2009 are 0.75 and 0.72, explaining 56 and 52% of the variability, respectively.

Implications for Holocene glacier variations and climate

The Briksdalsbre Event seems to have been comparable in scale and cause to the numerous decadal- to centennial-scale ‘Little Ice Age’-type or Neoglacial events that are now known to have occurred during the Holocene. Rates of annual glacier advance during the Briksdalsbre Event were comparable with those of the ‘Little Ice Age’ glacier expansion during the first part of the eighteenth century (Nesje, 1994; Nesje and Dahl, 2003). Historical data (e.g. Grove, 1988, 2004) show that Nigardsbreen advanced 2.8 km between ad 1710 and 1735, giving a mean annual rate of advance of 112 m/yr. Similarly, on the western side of Jostedalsbreen, Brenndalsbreen advanced 4.5 km between ad 1650 and 1700 (average advance rate of 90 m/yr) (Nesje, 1994). Nesje and Dahl (2003) and Nesje et al. (2007) inferred that this late-seventeenth/early-eighteenth century (‘Little Ice Age’) glacier advance was most probably a response to increased winter precipitation due to the prevailing positive NAO index weather mode (Luterbacher et al., 2002) rather than lower summer temperatures alone. This is also in accordance with a study of glaciers in Jotunheimen, where Rasmussen et al. (2010) calculated a ‘Little Ice Age’ precipitation anomaly relative to the 1961–1990 normal of +24 ± 22%.

Between 1996/1997 and 2009, Briksdalsbreen retreated 486 m, with a maximum annual retreat of 145 m in 2005/2006, the maximum annual retreat recorded since the frontal measurements started in 1900. In the autumn of 2009, the glacier front was 879 m behind the 1900 frontal position. The main reason for the large glacier retreat in recent later years was a combined effect of reduced winter precipitation and higher summer temperature, except for high winter precipitation in the three years 2004–2005, 2006/2007, and 2007/2008. Calving in the proglacial lake is likely to have made only a minor contribution to the retreat rate compared with the climatic effects. A similar advance and retreat was characteristic of other glaciers in western Norway not standing in water. Furthermore, the only year with significant calving at the glacier front was in the autumn of 2006, when the front was thin and low gradient (cf. Hart et al., 2011; Laumann and Nesje, 2009a, b).

The Briksdalsbre Event has similar relevance for the identification and interpretation of earlier Neoglacial events since the deglaciation of the Weichselian ice sheet about 10 000 cal. yr BP (Bakke et al., 2010; Matthews and Dresser, 2008; Nesje, 2009). Knowledge and understanding of such events in southern Norway is based largely on distal (downstream) lacustrine and terrestrial sedimentary sequences (e.g. Bakke et al., 2005a, b, 2010; Dahl et al., 2003; Hormes et al., 2009; Matthews and Dresser, 2008; Matthews and Karlén, 1992; Matthews et al., 2000, 2005; Nesje, 2009; Nesje et al., 1991, 2000; Shakesby et al., 2007). In particular, it has been a problem to interpret and directly relate thin minerogenic layers to previous, short-lived glacial episodes in the upstream catchment. Recent Holocene glacier reconstructions from distal glacier-fed lakes based on multiproxy approaches that take into account the inorganic sedimentation directly related to the glacier(s) in the catchment indicate that a number of short-lived glacial episodes, similar in magnitude and duration to the Briksdalsbre Event, have occurred in Norway during the late Holocene (e.g. Bakke et al., 2010; Matthews and Dresser, 2008; Nesje, 2009).

A close exponential relationship between temperature and precipitation at the ELA of ten Norwegian glaciers, ranging from maritime to continental climates, was established by O. Liestøl and published in Sissons (1979). On the basis of climatic reconstructions involving winter precipitation estimates from the ‘Liestøl equation’, it appears that winter precipitation, rather than summer temperature, was the main cause of many of these Neoglacial events (e.g. Bakke et al., 2010; Dahl and Nesje, 1996; Matthews et al., 2005; Nesje et al., 2001). This is in accord with the underlying causes of the Briksdalbre Event, emphasising the value of this event as an analogue for understanding these earlier events.

Summary and conclusions

During the Briksdalsbre Event, maritime glaciers in Scandinavia started to advance in the ad 1990s because of positive net mass balance in the preceding years, invoking annual advance rates in the order of ~50–60 m. Briksdalsbreen itself underwent a total frontal advance of 285 m in less than a decade. This was followed by a retreat of 486 m between 1996/1997 and 2009, with a maximum annual retreat of 145 m in 2005/2006.

Frontal records from six southern Norwegian glaciers were used to assess the magnitude, duration, climatic causes, and frontal time lags involved in this mass balance perturbation and following frontal advance. A comparison with meteorological data from Bergen demonstrates that the main reason for the glacier advances in Scandinavia in the 1990s was high winter precipitation (positive climate index and positive NAO index in 1988/1989, 1989/1990, 1992/1993, 1994/1995, 1997/1998, and 1999/2000). Between 1989/1990 and 1994/1995 (7 years) the mean annual December–March precipitation was 1192 mm, which is 160% of the 1961–1990 normal (= 100%). Less positive (or negative) mass balance years were recorded in 1990/1991, 1993/1994, 1995/1997, and 1998/1999. The reason for the large glacier retreat in later years is a combined effect of reduced winter precipitation and higher summer temperature (with the exception of high winter precipitation in the three years 2004/2005, 2006/2007, and 2007/2008).

It has been a challenge to interpret and directly relate thin minerogenic layers in distal glacier-fed lakes and in sections along glacial meltwater streams (where peat is intercalated with thin minerogenic layers) to previous, short-lived glacial episodes in the catchment. Recent Holocene glacier reconstructions from distal glacier-fed lakes based on multiproxy approaches that take into account the inorganic sedimentation directly related to the glacier(s) in the catchment indicate that a number of short-lived glacial episodes, similar in magnitude and duration to the Briksdalsbre event, have occurred in Norway during the late Holocene. The Briksdalsbre Event is therefore considered to be an analogue for the numerous decadal- to centennial-scale ‘Little Ice Age’-type or Neoglacial events that are now known to have occurred during the Holocene. Although these earlier events were undoubtedly influenced by summer temperature variations, it seems they were predominantly driven by variations in winter precipitation.

Footnotes

Acknowledgements

The meteorological and glacier data were provided by The Meteorological Office (met.no) and Norwegian Water Resources and Energy Directorate (NVE), respectively. Jane Ellingsen drafted some of the figures. To these we acknowledge our sincere thanks. This is publication no. A 324 from the Bjerknes Centre for Climate Research and Jotunheimen Research Expeditions Contribution No. 181.

This study has received funding from Department of Earth Science, University of Bergen and the Bjerknes Centre for Climate Research.

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