Environmental impacts of the Norse settlement: palaeoenvironmental data from Myvatnssveit, northern Iceland

Lawson, I. T., Gathorne‐Hardy, F. J., Church, M. J., Newton, A. J., Edwards, K. J., Dugmore, A. J. & Einarsson, Á. 2007 (January): Environmental impacts of the Norse settlement: palaeoenvironmental data from Mývatnssveit, northern Iceland. Boreas, Vol. 36, pp. 1–19. Oslo. ISSN 0300–9483. The first stratigraphically continuous pollen profile spanning the Norse and Medieval periods from the archaeologically‐rich Mvatnssveit region of northern Iceland is presented. Detailed analyses were made of the tephra, sediment characteristics, pollen and chironomids of a 3 kyr sediment sequence from Helluvastjörn, a small, shallow lake. The pollen data show a steady decline in the percentage abundance of tree birch (Betula pubescens) pollen between the Norse settlement (landnám, c. AD 870) and c. AD 1300, a pattern that contrasts with the abrupt fall in birch pollen percentages immediately following the Norse colonization at almost all previously studied sites in Iceland. Some lines of evidence suggest that the gradual birch decline could be a result of reworking of soil pollen, but independent evidence suggests that this may not necessarily be the case. The pollen record indicates that birch woodland was replaced by acidophilic taxa (notably Empetrum nigrum and Sphagnum), again contrasting with the more usual pattern of Poaceae expansion seen in post‐landnám pollen diagrams from mires close to farm sites. Chironomid and Pediastrum accumulation data show that the limnic environment became more productive immediately after landnám, probably because of anthropogenic disturbance. An increase in sedimentation rate after landnám appears initially to have been caused by increased lake productivity, while reworked inorganic soil materials became a significant contributor to the sediments after c. AD 1200. The data suggest that the impact of settlement on terrestrial vegetation may have been more variable than previously thought, while freshwater ecosystems experienced significant and rapid change.     

The pre-Landnám fauna of Iceland: a palaeontological contribution

The origins of the Icelandic biota are discussed with particular reference to recent work on Coleopteran (beetle) and Trichopteran (caddis fly) fossils from deposits which are earlier than the arrival of man (Landnám) in the country. The hypothesis of survival through Pleistocene glaciations in refugia is discounted in favour of immigration on ice floes during Late Glacial/Early Holocene deglaciation. Consideration of the nature of the insect fauna and the extent of Late Glacial ice sheets, with the evidence from ocean circulation patterns, suggests a source area in the fjords of south-west Norway. The model is applicable to the origins of the biota on all the North Atlantic islands, east of the Davis Strait.     

Quaternary changes in level of the upper Taylor Glacier, Antarctica: implications for paleoclimate and East Antarctic Ice Sheet dynamics

Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. ³He and ¹⁰Be exposure age dating (from Brook et al . 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma.     

Age and extent of the Scandinavian ice sheet in northwest Russia

The last glacial maximum (LGM) of the Scandinavian ice sheet in the Arkhangelsk region has been identified morphologically as ridges and hummocks in an otherwise flat topography. Stratigraphically the limit is marked by the presence of till above Mikhulinian (last interglacial) sediments inside the ridges and by the absence of till outside the ridges. During the LGM, ice flowed into the region from the north and northwest forming a lobe in the Dvina-Vaga depression. The continuation northward, northeast of Arkhangelsk, is still somewhat uncertain, but evidence suggests that the outer margin of the Scandinavian ice sheet was situated in the Mezen drainage basin. Luminescence and radiocarbon dates suggest that the maximum position was attained after some 17 ka ago, and that deglaciation started close to 15 ka ago. This age for the maximum position is younger than the maximum position in the western peripheral areas of the Scandinavian ice sheet. This may be accounted for by initial ice build-up in the west followed by a successive migration of the ice divide(s) to the east as ice growth continued. Deglaciation was either by lateral retreat or isolation of dead ice masses causing areal downwasting.     

Origin of quartz cements in some sandstones from the Jurassic of the Inner Moray Firth (UK)

The extent of quartz cementation in shallow marine sandstones of the Brora Arenaceous Formation (Oxfordian) is closely related to the occurrence and abundance of Rhaxella perforata sponge spicules. Three cement morphologies are identified, chalcedonic quartz, microquartz and mesoquartz. Chalcedonic quartz forms matrix-supported cements which preserve moulds of Rhaxella spicules. Chalcedonic quartz crystals have inequant development of crystal faces, on average 0·1 μm in diameter, and are the first formed cement and reveal homogeneous dark grey tones on the SEM-CL/BEI. Microquartz forms 5–10 μm diameter crystals, which commonly grow on chalcedonic quartz substrates and show various grey tones under SEM-CL/BEI. Mesoquartz crystals grow in optical continuity with their host grains, have >20 μm a-axial diameter crystals, and exhibit distinctly zoned luminescence. Although no opaline silica is preserved, the quartz cement is interpreted to have formed from an opaline precursor. Detrital quartz has an average δ¹⁸O composition of + 12·2‰ and mesoquartz (syntaxial overgrowth) has an average δ¹⁸O composition of +20·0‰. Estimates of the δ¹⁸O compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types; mixtures of the two give consistently higher δ¹⁸O compositions than mesoquartz, the higher estimate being +39·2‰. From oxygen isotope data the formation of quartz, microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71°C in marine derived pore waters. Organic and inorganic maturation data constrain the upper temperature limit to less than 60°C.     

Mudslides Developed on Waitemata Group Rocks, Tawharanui Peninsula, North Auckland

On Tawharanui Peninsula mudslides occur in soils developed on Waitemata Group flysch similar to that underlying much of the Auckland metropolitan area. Mudslides are shallow soil failures with a bowlshaped source area, an elongated track, and an accumulation zone. Movement may continue for decades to centuries. Modelling suggests that failure of saturated soils occurs along a basal surface defined by the regolith / bedrock contact; rates of movement and time of initiation have not been established. Reactivation or increased mobility of mudslides due to climatic change represents an increased hazard for infrastructure in Auckland City.     

Breeding biology of dark-bellied brent geese Branta b. bernicla in Taimyr in 1990 in the absence of arctic foxes and under favourable weather conditions

In combination with observations in spring staging and wintering grounds in western Europe, a detailed etho-ecological study of nesting dark-bellied brent geese Branta b. bernicla in western Taimyr, Krasnoyarsk, Russia, was made in 1990. Most brent geese arrived on the breeding grounds from 14–19 June and started nesting within a few days. In the study area 264 nests of breeding brent geese were found, mainly on islands but also along small rivers on the mainland. The mean clutch size was 3.0 and 80% of the eggs hatched. Time budget studies showed that incubating females spent on average 138 minutes per 24 hours on feeding. Despite favourable weather conditions and a low density of arctic foxes, only about one-third of the mature birds in the study area bred. In the autumn an intermediate breeding success of 20% juveniles was recorded in the wintering areas. This was probably due to the relatively poor condition in which the brent geese left their spring staging areas.     

Insects in amber

Amber is fossilized resin that has exquisitely preserved many insects that otherwise would not be represented in the fossil record. The insects and other inclusions give us an insight into what terrestrial life and the environment was like millions of years ago.