Atle Nesje

Holocene glacier fluctuations of Flatebreen and winter-precipitation changes in the Jostedalsbreen region, western Norvay, based on glaciolacustrine sediment records:

The history of Holocene glacier variations of Flatebreen, an independent glacier close to the SW part of the Jostedalsbreen ice cap, has been reconstructed from lacustrine sediments in the proglacial lake Jarbuvatnet. The sedimentary succession shows evidence of three maini episodes of Holocene glacier expansion. The first is recorded in the basal part of the core up to 370 cm. According to the age/depth relationship in the sediment core (based on 12 AMS radiocarbon dates), this glacier expansion episode terminated about 10200 cal. yr BP. The second major glacier phase lasted from 8400 to 8100 cal. yr BP, while the third was initiated around 4000 cal. yr BP and has continued up to the present. At 43 cm in the core, the medium silt content increases significantly, accompanied by a minor increase in the sand content. This textural change is interpreted as the first time that the tenninus of Flatebreen extended inlto an] upstream lake at 1083 m a.s.l. The age model suggests that this event took place around 800 cal. yr BP (-AD 1150), as a response to the initial ‘Little Ice Age’ glacier expansion after the ‘Mediaeval Warm Period’. By using a Holocene-inferred summer-temperature curve from central southern Norway in the exponential relationship between annual winter precipitation (snow) and ablation-season temperature at the ELA, periods of higher winter precipitation than the 1961-90 nomial in the Jostedalsbreen region are inferred for 9700-9400, 9200-8300, 8200-6500, 5700-5100, 4700-4600, 4500-4300, 3800-3000, 2100-1800, 1600-1300 and 1200-1000 cal. yr BP, and from 900 cal. yr BP to the present. The intervening periods of lower than normal winter precipitation correlate with periods of enhanced ice-rafting in the North Atlantic.

Holocene glacial and climate history of the Jostedalsbreen region, Western Norway; evidence from lake sediments and terrestrial deposits

The valleys surrounding the Jostedalsbreen ice cap were deglaciated during the latter half of the Preboreal Chronozone. At the end of the Preboreal Chronozone, however, a glacier readvance occurred. Terminal moraines were deposited by outlet valley glaciers from the Jostedalsbreen Plateau up to 1 km beyond Little Ice Age moraines. Inferred from the altitude of lateral moraines formed during this readvance and calculations of the equilibrium-line altitude (ELA) depression based on an accumulation area ratio (AAR) of 0.6, the average depression of the ELA was 325 + 75−115 m below the present. By assuming a similar precipitation pattern as at present, this suggests a mean temperature decline of about 2°C. Palynological investigations from Sygneskardet, Sunndalen, indicate that climate like the present was achieved just after 9000 BP. The Holocene climatic optimum occurred during the Atlantic Chronozone, with elm (Ulmus) stands growing at the present birch (Betula) forest limit in Sunndalen and pine (Pinus) growing at Styggevatnet to an altitude of at least 1160 m. During this period the mean summer temperature is estimated to have been at least 2.7 and 1.8°C warmer than at present, with and without the local climatic effect of Jostedalsbreen, respectively. An inferred rise of the ELA of about 400 m from the present altitude suggests that possibly no glaciers existed on the Jostedalsbreen Plateau during the Holocene climatic optimum. Vegetational changes as deduced from palynological studies, lowered tree limits and increased resedimentation in peat bogs indicate general climatic deterioration since the Late Atlantic Chronozone. A significant Alnus decline 6300 BP and a Betula expansion 5300 BP, as recorded from palynological studies of peat bogs in Sprongdalen, is interpreted to represent the initial Neoglaciation on the Jostedalsbreen Plateau. Lithostratigraphic evidence at a section in the upper part of Glomsdalen may indicate a minor Neoglacial phase close to 6000 BP. The first pronounced Neoglacial event in the Jostedalsbreen region, however, was bracketed between 3700 and 3100 BP. Sporteggbreen, the upper part lying ca. 30 m above the present regional glaciation threshold, was formed around 500 BP at the initiation of the Little Ice Age. Gelifluction at 1000 m altitude began after 3200-2800 BP. During the Medieval Period, glaciers were smaller than now. At the northwestern part of Jostedalsbreen an initial Little Ice Age glacier expansion is dated to have occurred after 890 ± 60 BP (A.D. 1030–1220). From the early 14th century, and especially from the mid-17th century, a severe climatic deterioration during the Little Ice Age is historically documented. Around Jostedalsbreen this advance culminated during the mid-18th century. Documents suggest that the western outlet glaciers from Jostedalsbreen reached their maximum Little Ice Age position some years before the longer eastern outlet valley glaciers. A typical depression of the ELA during the Little Ice Age of 100–150 m indicates a mean temperature decline from the present of ca. 0.5–1°C.

A Piston Corer for Lacustrine and Marine Sediments

A piston corer for lacustrine and marine sediments is described. The sampler can core up to 6 m of sediments and can easily be handled by three persons both from ice and rafts in water depths to at least 60 m.

Holocene glacier and climate variations in western Norway: Evidence for early Holocene glacier demise and multiple Neoglacial events

Lithostratigraphic and paleobotanical studies suggest that the Jostedalsbreen ice cap probably disappeared during the early Holocene Hypsithermal interval (ca. 8000-6000 B.P.) and re-formed about 5300 B.P. The equilibrium-line altitude was lower than the modern mean equilibrium-line altitude between 2595 ±85 and 2360 ±80 B.P., between 2250 ±65 and 2150 ±80 B.P., between 1740 ±75 and 1730 ±75 B.P., between 1430 ±45 and 1270 ±60 B.P., and subsequent to 890 ±60 B.P. The outlet valley glaciers reached their maximum Neoglacial extent during the Little Ice Age in the middle of the eighteenth century.

Is the North Atlantic Oscillation reflected in Scandinavian glacier mass balance records

The North Atlantic Oscillation (NAO) is one of the modes of climate variability in the North Atlantic region. The atmospheric circulation during the winter season in this region commonly displays a strong meridional (north-south) pressure contrast, with low air pressure (cyclone) centred close to Iceland and high air pressure (anticyclone) near the Azores. This pressure gradient drives the mean surface winds and the mid-latitude winter storms from west to east across the North Atlantic, bringing mild moist air to northwest Europe. The NAO index is based on the difference of normalised sea-level pressures (SLP) between Ponta Delgada, Azores and Stykkisholmur, Iceland. The SLP anomalies at these stations are normalised by division of each monthly pressure by the long-term (1865-1984) standard deviation. Interannual atmospheric climate variability in northwest Europe, especially over Great Britain and western Scandinavia has, during the last decades, been attributed mainly to the NAO, causing variations in the winter weather over the northeast North Atlantic and the adjacent land areas. A comparison between the NAO index and the winter (December-March) precipitation between ad 1864 and 1995 in western Norway shows that these are strongly linked (correlation coefficient 0.77). Variations in the NAO index are also reflected in the mass balance records of glaciers in western Scandinavia. The NAO index is best correlated with mass balance data from maritime glaciers in southern Norway (e.g. Alfotbreen R 2 ! 0.51). The record of Holocene (last ca. 11 500 cal. yr) glacier variations of maritime glaciers in western Scandinavia is thus a proxy of pre-instrumental NAO variations. Copyright  2000 John Wiley & Sons, Ltd.

THE LAST ICE SHEET IN NORTH-WEST SCOTLAND: RECONSTRUCTION AND IMPLICATIONS

Recent models of the last Scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation. This proposition has been investigated on 140 mountains over an area of 10,000 km2 in NW Scotland. Outside the limits of the later Loch Lomond Readvance in this area there is evidence for a single high-level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris. This limit occurs at altitudes ranging from 425 to 450 m in the Outer Hebrides to >950 m on the mainland, and is best developed on lithologies that resisted breakdown after ice-sheet downwastage. Interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by: (1) joint-depth and Schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit; (2) a much greater representation of gibbsite (a pre-Late Devensian weathering product) in the clay fraction of soils above the limit; (3) cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit; (4) the sharpness of the limit at some sites and its regular decline along former ice flowlines; and (5) shear stress calculations based on the inferred altitude and gradient of the former ice surface. Reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from >900 m to ca. 550 m at the north coast. Independent dispersion centres fed broad ice streams that occupied major troughs. On Skye an ice dome >800 m deflected the northwestwards movement of mainland ice, but the mountains of Rum were over-ridden by mainland ice up to an altitude of ca. 700 m. The Outer Hebrides supported an independent ice cap that was confluent with mainland ice in the Minches. Extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative, and suggests that low-gradient ice streams extended across the Hebridean Shelf offshore. Wider implications of this research are: (1) that blockfields and other periglacial weathering covers are not all of the same age or significance, depending on the resistance of different lithologies to frost weathering; (2) that the contrasting degree of glacial modification in the Western and Eastern Highlands of Scotland may reflect a former cover of predominantly warm-based ice in the former and predominantly cold-based ice in the latter; and (3) that the approach and techniques developed in this study have potential application for constraining ice-sheet models, not only in areas peripheral to the main centres of ice accumulation in Britain and Ireland, but also in other mountain areas where nunataks protruded through warm-based Late Pleistocene ice masses.

Paleoclimatic implications based on equilibrium-line altitude depressions of reconstructed Younger Dryas and Holocene cirque glaciers in inner Nordfjord, western Norway

Abstract Relative to a present cirque glacier in innner Nordfjord, western Norway, equilibrium-line altitude (ELA) depressions for reconstructed cirque glaciers formed during the Younger Dryas (11,000–10,000 yr B.P.), the Erdalen Event (9100±200 yr B.P.) and the Little Ice Age (mid-18th century) are calculated by the use of accumulation-area ratio (AAR), and compared to the corresponding values for plateau glaciers. The temperature-precipitation ELA (TP-ELA), as reflected by plateau glaciers, gives considerably larger ELA depressions than use of the temperature-precipitation-wind ELA (TPW-ELA) for cirque glaciers. ELA depressions during the Younger Dryas, Erdalen Event and the Little Ice Age thus strongly indicate that cirque glaciers are much more sensitive to changes in winter precipitation than plateau glaciers. The difference in ELA depressions of contemporaneous plateau and cirque glaciers during the Younger Dryas, Erdalen Event and the Little Ice Age suggests that winter precipitation was reduced to 59±7, 71±6 and 88±7% compared to present values. Taken into account the reduced winter precipitation, the corresponding mean ablation-season temperature depressions were probably 4.3±0.3, 3.0± 0.2 0.3 and 1.4± 0.3 0.2 ° C , respectively.

Holocene mean July temperature and winter precipitation in western Norway inferred from palynological and glaciological lake-sediment proxies

Reconstructions of mean July temperature (Tjul) and winter precipitation (Pw) for the last 11/500 years on the Folgefonna peninsula are presented. Tjul was reconstructed using pollen-climate transfer functions and Pw was reconstructed based on the exponential relationship between mean solid winter precipitation and ablation-season temperature at the equilibrium-line altitude (ELA) with a reconstructed former ELA, using Tjul as the proxy for ablation-season temperature. The reconstructions from the Folgefonna peninsula suggest that the early Holocene was relatively cool and dry until c. 8000 cal. yr BP, followed by a warm and humid mid-Holocene until c. 4000 cal. yr BP with inferred Tjul above 12°C and Pw reaching as high as 225% of the present day. Subsequent to c. 4000 cal. yr BP a reduction is seen in both inferred Tjul and Pw with large fluctuations during the last 500 years. In addition, new calculations of Pw from two glaciers (Hardangerjøkulen and Jostedalsbreen) in southern Norway are presented. The results show that Pw varied in phase at all glaciers, probably as a response to the same climate forcing factor. During the early Holocene a major shift is suggested between winds from the west and the east.

Lateglacial and Holocene glacier fluctuations and climate variations in western Norway: A review

Abstract Evidence from terminal moraines, palynological data and tree limits suggests that considerable climatic changes occurred in western Norway from Lateglacial (about 14 ka BP) up to the present. The most significant climatic changes took place around the Younger Dryas (11-10 ka BP), the Erdalen event (9.1 ± 0.2 ka BP) and the Little Ice Age (mid 18th century). Lithostratigraphic and paleobotanical studies suggest that the Jostedalsbre ice cap, and possibly most of the west Norwegian glaciers, disappeared during the early Holocene Hypsithermal interval (ca. 8-6 ka BP) and was reformed about 5 ka BP. From about 2.5 ka BP the equilibrium-line altitude (ELA) fluctuated around modern levels. The modern glaciers in western Norway reached their maximum Neoglacial extent during the Little Ice Age, when the ELA was depressed 100–150 m.

Reconstruction of former glacier equilibrium-line altitudes based on proglacial sites: an evaluation of approaches and selection of sites

Abstract Various approaches are used to record variations in glacier activity and equilibrium-line altitudes (ELAs) based on proglacial sites (lacustrine and terrestrial). These approaches are based on a conceptual model of glacier-meltwater induced sedimentation in which the minerogenic (nonorganic) component of the sediments is related to the occurrence of a glacier in the catchment. The principal coupling to former glacier activity and ELAs is common for these approaches. However, different methods and techniques may complement each other, and both possibilities and limitations are demonstrated. Site selection for reconstructing variations in glacier activity/ELAs is evaluated and critical factors are discussed. Rerouting of glacier meltwater streams across local watersheds in combination with proglacial sites gives a distinct on/off signal for former glacier activity/ELAs. Together with representative lateral moraines of known age, local watersheds are important for calibrating reconstructed glacier activity/ELAs based on a chain of proglacial lakes. Based on the ‘modern analogue principle’, various proxies can record whenever glaciers existed in a catchment. In a chain of proglacial lakes with different sensitivity to record variations in glacier activity/ELAs, these proxies can be calibrated against independent records. For one-site approaches, however, variations in glacier activity/ELAs depend on the interpretation and sensitivity of the proxies used.