Holocene relative sea-level changes in the Qaqortoq area, southern Greenland

We present results from an investigation of relative sea-level changes in the Qaqortoq area in south Greenland from c. 11 000 cal. yr BP to the present. Isolation and transgression sequences from six lakes and two tidal basins have been identified using stratigraphical analyses, magnetic susceptibility, XRF and macrofossil analyses. Macrofossils and bulk sediments have been dated by AMS radiocarbon dating. Maximum and minimum altitudes for relative sea level are provided from two deglaciation and marine lagoon sequences. Initially, relative sea level fell rapidly and reached present-day level at ∼9000 cal. yr BP and continued falling until at least 8800 cal. yr BP. Between 8000 and 6000 cal. yr BP, sea level reached its lowest level of around 6-8 m below highest astronomical tide (h.a.t.). At around 3750 cal. yr BP, sea level has reached above 2.7 m below h.a.t. and continued to rise slowly, reaching the present-day level between ∼2000 cal. yr BP and the present. As in the Nanortalik area further south, initial isostatic rebound caused rapid isolation of low elevation basins in the Qaqortoq area. Distinct isolation contacts in the sediments are observed. The late Holocene transgression is less well defined and occurred over a longer time interval. The late Holocene sea-level rise implies reloading by advancing glaciers superimposed on the isostatic signal from the North American Ice Sheet. One consequence of this transgression is that settlements of Palaeo-Eskimo cultures from ∼4000 cal. yr BP may have been transgressed by the sea.     

Early Holocene insect and plant remains from Jameson Land, East Greenland

Fluvial and deltaic sediments from Jameson Land in East Greenland contain the first record of the leaf beetle Phratora o f. polaris , not presently found in Greenland; the ground beetle Bembidion grapii , north of this species' present northern range limit; and the true bug Nysius gruenlandieus . In addition, there is a rather diverse flora. All of these records are in sediments of Early Holocene age. We suggest that most of these animals and plants immigrated to East Greenland in the Early Holocene by long-distance chance dispersal, mostly from northwest Europe. The environment was physiognomically similar to that of today, but Salix aretica and Cassiope tetragonu that are important dwarf shrubs today had not yet immigrated.     

Wastage features of the inland ice sheet in central South Norway

Detailed field mapping of different lateral phenomena, striae, texture and till fabric forms the basis of a reconstruction of five deglaciation phases in the east Jotunheimen-Gudbrandsdalen area, a land scape with moderate relief in the vicinity of the ice divide. During wastage, the inland ice sheet separated into several ice lobes situated in valleys enclosed by large ice-free uplands. The slope of the ice surface varied with local changes in the ice movement pattern and with the breaking of ice dams, which caused reversal of drainage from ice-dammed lakes. Non-climatic, large margianl moraines are thought to have fomed as a result of locally increased steepness of the ice surface. By tracing the deglaciation phases through two different valley systems which converge in the lake Mjøsa area, deglaciation events in the ice divide zone are correlated with marginal deposits at the front of the ice lobes.     

Late Quaternary history around Nioghalvfjerdsfjorden and Jøkelbugten, North-East Greenland

Nioghalvfjerdsfjorden in North-East Greenland is at present covered by a floating glacier. Raised marine deposits in the surrounding area contain shells of marine molluscs, bones of marine mammals and pieces of driftwood. A fairly systematic sampling of such material has been conducted, followed by extensive radiocarbon dating. We suggest that the Greenland ice sheet extended onto the shelf offshore North-East Greenland during isotope stage 2, perhaps even reaching the shelf break. During the subsequent recession of the ice sheet, the entrance of Nioghalvfjerdsfjorden had become ice-free by 9.7 cal. ka BP. The recession culminated between 7.7 and 4.5 cal. ka BP, during which time the fjord was glacier-free along its entire 80 km length. No dates younger than 4.5 cal. ka BP are available on marine material from the fjord, and it seems probable that the fjord has been continuously covered by the floating glacier since this time. The maximum glaciation was attained around AD 1900, after which thinning and recession took place. The marine limit increases from c. 40 m above sea level near the present margin of the Inland Ice to c. 65 m above sea level at the outer coast. These figures fit into the regional pattern of the marine limit for areas both to the south and north. The marine fauna comprise two bivalves, Macoma calcarea and Serripes groenlandicus, that may represent a southern element present during the Holocene temperature optimum. Remains of three taxa of southern extralimital terrestrial and limnic plants were dated to 5.1 cal. ka BP, and remains of another extralimital plant were dated to 8.8 and 8.5 cal. ka BP. The known Holocene time ranges of the willow Salix arctica and the lemming Dicrostonyx torquatus have been extended back to 8.8 and 6.4 cal. ka BP, respectively, providing minimum dates for their immigration to Greenland.     

Paleoclimatic implications of an early Holocene glacier advance on Disko Island, West Greenland

The paper describes studies of glacial deposits and raised beaches on the island of Disko. West Greenland. Two stades in the glacial history are defined, the Godhavn stade, which represents the last major glaciation on Disko, and the Disko stade, which defines a Preboreal readvance. During the Godhavn stade, only eastern and southern Disko were affected by the extended Inland Ice, while glaciation on western and northern Disko was local in character. In connection with the deglaciation, the sea transgressed to the marine limit at c. 9,250-9,000 BP. Immediately before, tentatively culminating around 9,300 BP, a significant readvance of glaciers on eastern Disko occurred. The marine limit rises on a transect from northwest to southeast across Disko from 60 m a.s.l. to 90 m. The paper discusses changes in equilibrium line altitude (ELA) during the deglaciation, and explains the Disko stade readvance in terms of variations in upper-air wind conditions.     

Weichselian in central South Norway: the Gudbrandsdal Interstadial and the following glaciation.

Present knowledge of sub-till sediments found in the valleys in the Mid-Gudbrandsdal area and the stratigraphy of the overlying basal tills is summarized. The existence of widespread waterlain sediments which are thought to have been depostied in a cold ice-free period of Middle/Early Weichselilan age, the Gudbradnsdal Interstadial, gives evidence of surprisingly modest ice erosion during the last ice age, even in valleys close to the highest mountains. Judging by the nearly total evacuation of older deposits from the tributaries, the ice-free period seems to have lasted for a long time, with very strong slope processes. Huge quantities of proglacial sandur sediments accumulated in the main valleys indicate that the last inland ice sheet grew slowly. By comprehensive analyses the authors have succeeded in correlating the overlying tills with four regional glacial phases of the last ice age reconstructed mainly through analyses of striae. It is found that the conservation of the sediments, as well as the distribution of different tills, was dependent on the relative location of the ice divide.     

Regressions and transgressions of the Baltic basin reflected by a new high-resolution deglacial and postglacial lithostratigraphy for Arkona Basin sediments (western Baltic Sea)

Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several distinct reflectors. The physical, sedimentological, mineralogical and geochemical properties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS ¹⁴C data and biostratigraphic information were gathered. Based on this multi‐proxy approach, seven lithostratigraphic units (AI, AII, B to F) were distinguished. These consist of fine‐grained clay, silt and mud, and are separated from each other by thin basin‐wide traceable sandy layers (S_ab‐S_ef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain‐size fraction >63μm. In addition, some of the quartz‐grain‐dominated sandy layers cause the strong reflection lines recorded in seismoacoustic profiles. The sandy layers are interpreted to reflect enhanced hydrodynamic energy induced by episodes of basin‐wide water‐level low‐stand conditions. These low stands resulted from water‐level drops that occurred frequently during the Baltic Sea's history and presumably affected the entire Baltic basin. The thick fine‐grained units AI, AII to F, in which coarser material is absent, represent water‐level high‐stands. We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and after the Billingen‐1 regression, respectively. We assign the most prominent sandy layer S_ab to the final drainage of the Baltic Ice Lake (Billingen‐2), whereas the sandy layers between units B, C., D and E are related to the Yoldia Sea and Ancylus Lake regressions of the Baltic Sea's history. The uppermost fine‐grained unit F with its high organic carbon content contains marine sediments deposited after the Littorina Transgression. The macroscopically well‐visible sediment colour change from reddish/brown‐to‐grey, previously interpreted as a regional stratigraphic boundary, varies from core to core. It has been shown by our new data that this colour change has a diagenetic origin, and thus does not represent a stratigraphic boundary. Previous subdivisions therefore have to be revised.     

ISOTOPE RECORDS FROM MONGOLIAN AND ALPINE ICE CORES AS CLIMATE INDICATORS

The link between long term changes in the isotopic composition of precipitation and surface air temperature at a given location is of exceptional importance for paleoclimatic studies, as ahs been demonstrated by many recent publications based on the isotope records from polar ice cores. By means of direct comparison with instrumental data, this paper evaluates the potential of the deuterium and oxygen-18 records from two continental glaciers for monitoring climatic trends. The isotopic data presented characterize climatically contrasted enviroments. The records from the Swiss glacier show distinct seasonal variations. Oxygen-18 is fairly well correlated with the instrumental record of atmospheric temperature; the seasonal differences in deuterium excess reflect nearness to the oceanic moisture source. By contrast, the isotope data from the Mongolian site show poor correlation with atmospheric temperature. The seasonal variations in deuterium excess, with higher values during summer time, indicate that precipitation largely originates from re-evaporated continental moisture sources. In both cases however, the correlation with temperature is significantly improved by the elimination of values derived from years where major changes in seasonal distribution and/or snow loss obviously have occurred, thereby distoring the isotopic ratios for that particular year. Depending on the site selected for study, the stable isotope composition of ice cores should therefore be viewed not only as a proxy for atmospheric temperature, but also as an additional hydrometeorological parameter and source indicator for atmospheric moisture.     

Late Quaternary development of the southern sector of the Greenland Ice Sheet, with particular reference to the Qassimiut lobe

The evolution of the southern Greenland Ice Sheet is interpreted from a synthesis of geological data and palaeoclimatic information provided by the ice-sheet cores. At the Last Glacial Maximum the ice margin would have been at the shelf break and the ice sheet was fringed by shelf ice. Virtually all of the present ice-free land was glaciated. The initial ice retreat was controlled by eustatic sea level rise and was mainly by calving. When temperatures increased, melt ablation led to further ice-margin retreat and areas at the outer coast and mountain tops were deglaciated. Retreat was interrupted by a readvance during the Neria stade that may correlate with the Younger Dryas cooling. The abrupt temperature rise at the Younger Dryas-Holocene transition led to a fast retreat of the ice margin, and after ∼9 ka BP the ice sheet was smaller than at present. Expansion of the ice cover began in the Late Holocene, with a maximum generally during the Little Ice Age. The greatest changes in ice cover occurred in lowland areas, i.e. in the region of the Qassimiut lobe. The date of the historical maximum advance shows considerable spatial variability and varies between AD 1600 and the present. Local anomalous readvances are seen at possibly 7-8 ka and at c. 2 ka BP. A marked relative sea level rise is seen in the Late Holocene; this is believed to reflect a direct glacio-isostatic response to increasing ice load.     

Near-shore Baltic Ice Lake deposits in Fakse Bugt, southeast Denmark

Shallow seismic, sedimentological and macrofossil data and AMS radiocarbon dates on terrestrial plant remains from submarine deposits in Fakse Bugt in the southwestern part of the Baltic Sea are presented. The sediments were deposited near the shore of the Baltic Ice Lake, mostly in barrier-lagoon environments, during two highstand episodes dated to around 12.5–12.2 ¹⁴C ka BP and 10.6–10.3 ka BP. Coastal sediments from the highstands indicate maximum water levels of 13–15 m and 13 m below present sea level, respectively. During the first episode Salix polaris was widespread in the land area, and during the second episode Dryas octopetala and Betula nana were the most common woody plants. During the lowstand episode Betula pubescens woods dominated. The flora and fauna of the Baltic Ice Lake were rather diverse, reflecting the long and increasing distance to the margin of the Fennoscandian Ice Sheet. Calcium-carbonate-rich, mesotrophic water characterized the Baltic Ice Lake in Fakse Bugt.