Svein Olaf Dahl

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.

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.

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.

Late Holocene surface ocean conditions of the Norwegian Sea (Vøring Plateau)

[1] Late Holocene sea surface ocean conditions of the eastern Norwegian Sea (Voring Plateau) are inferred from planktic stable isotopes and planktic foraminiferal assemblage changes in cores JM97-948/2A and MD952011 (66.97� N, 7.64� E). Strong covariance between the planktic stable oxygen isotopic record and abundance changes of N. pachyderma (sin) show that major changes in surface ocean conditions are reflected both in the geochemical composition of the foraminiferal tests as well as in the composition of the foraminiferal fauna. Surface ocean conditions warmer than present were common during the past 3000 years. During the so-called Medieval Warm Period, surface conditions were highly variable with marked changes in sea surface temperature. The warmest sea surface temperatures during this period occurred between 800 and 550 years BP (0 BP = AD 2000). Climatic deterioration, recorded as decreases in sea surface temperature, occurred at about 2750, 1550, 400, and 100 years BP. The cooling events at about 2750 and 1550 years BP appear to correlate with increases in ice-rafted debris in the North Atlantic. Based on the results from JM97-948/2A and MD952011, the onset of the Little Ice Age cooling trend seems to have occurred around 700–600 years BP. Faunal changes indicate two cooling events during the Little Ice Age (at 400 and 100 years BP) that correspond to decreases in Fennoscandian summer temperatures and increases in ice-rafted debris in the eastern North Atlantic. INDEX TERMS: 3030 Marine Geology and Geophysics: Micropaleontology; 4267 Oceanography: General: Paleoceanography; 4870 Oceanography: Biological and Chemical: Stable isotopes; KEYWORDS: paleoceanography, stable isotope, Holocene, micropaleontology Citation: Andersson, C., B. Risebrobakken, E. Jansen, and S. O. Dahl, Late Holocene surface ocean conditions of the Norwegian Sea (Voring Plateau), Paleoceanography, 18(2), 1044, doi:10.1029/2001PA000654, 2003.

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.

Were abrupt Lateglacial and early-Holocene climatic changes in northwest Europe linked to freshwater outbursts to the North Atlantic and Arctic Oceans?

During the Lateglacial and early Holocene, abrupt, millennial-scale climatic variations are recorded in a wide range of high-resolution proxy records from marine and terrestrial archives in NW Europe. Our review of the evidence for these rapid climate events do not show an apparent link to possible forcing factors such as long-term, orbitally induced variations in solar radiation, short-term variations in solar activity as inferred from 14C, atmospheric carbon dioxide concentration, or volcanic sulphate as recorded in the GISP2 ice-core record. There is, however, a remarkable degree of similarity with the number, duration and timing of episodes of increased flux of fresh water to the north Atlantic and Arctic Oceans from the Laurentide ice sheet and from the Baltic ice lake in SW Sweden. These freshwater outburst events occurred when continental runoff from the Laurentide ice sheet was rerouted from the Mississippi River to the Hudson River, St Lawrence River, Hudson Strait and along the Mackenzie River to the Atlantic and Arctic Oceans, and when the Baltic ice lake in SW Sweden drained to Skagerrak. Periods of increased freshwater flow to the North Atlantic and Arctic Oceans may thus provide a mechanism to explain the abrupt and significant Lateglacial and early Holocene climate events in NW Europe. The idea that freshwater outbursts might drive abrupt climate events is not new, but previous work may have underestimated the extent of support from proxy data and overestimated the influence of the Laurentide ice sheet.

Holocene glacier variations of Blåisen, Hardangerjøkulen, central Southern Norway

Abstract A 1-m-deep gully section 460 m beyond the maximum Little Ice Age marginal moraines of Blaisen, Hardangerjokulen, central southern Norway, revealed alternations of minerogenic and organic sediments. The geographical/geological settings of the dated section provides a unique on/off signal of Holocene glacier fluctuations of Blaisen. Lithostratigraphy, sediment characteristics, and radiocarbon dates from the study section indicate one period of glacier (re)advance between the late Preboreal deglaciation of the inland ice sheet and 8660 ± 100 yr B.P. A grey sand layer 56–57 cm below the surface is interpreted to be of fluvial/colluvial origin and is radiocarbon dated to about 7700 yr B.P. At 48 cm below the surface, a bluish-grey sand/silt layer is radiocarbon dated to 7590 ± 12 yr B.P. (6560–6240 B.C.) and interpreted to be glaciofluvial origin. A minor glacier oscillation postdates 1130 ± 70 yr B.P. (810–990 A.D.). The Medieval/Little Ice Age glacier advance of Blaisen beyond its modern extent occurred after 1040 ± 60 yr B.P. (960–1030 A.D.). Calculations of the modern and Little Ice Age equilibrium-line altitudes (ELAs) on Hardangerjokulen suggest an ELA depression of ca. 130 m during the Little Ice Age maximum.

Late Holocene glacier fluctuations in Bevringsdalen, Jostedalsbreen region, western Norway (ca 3200-1400 BP)

Lithostratigraphy and radiocarbon dates from a 1.3 m-deep gully section in Bevringsdalen, SW of Jostedalsbreen in western Norway, with alternating minerogenic (glacial) and peat (non-glacial) layers, demonstrate that glaciers upvalley from the site were present during the following intervals: 2595 ± 85 BP (840-700 cal. BC) to 2360 ± 80 BP (525-385 cal. BC); between 2250 ± 65 BP (395-225 cal. BC) and 2150 ± 80 BP (360-105 cal. BC); between 1740 ± 75 BP (cal. AD 205-385), and 1730 ± 75 BP (cal. AD 210-395); and subsequent to 1430 ± 45 BP (cal. AD 595-645). Detailed altitudinal fluctuations of the glaciation threshold/equilibrium line relative to the present have been reconstructed for the time interval between 1430 ± 45 BP (cal. AD 595-645) and 3180 ± 90 BP (1540-1395 cal. BC).