Kristian Schoning

Reconstructed water tables from two ombrotrophic mires in eastern central Sweden compared with instrumental meteorological data

Water-level changes for the last 125 years were reconstructed from two ombrotrophic mires in eastern central Sweden using testate amoebae assemblages. The reconstructed water tables show the same overall pattem with high water tables during the 1950s and 1960s and low water levels from the 1970s until present. The similarity in the two records supports the hypothesis that water-table changes in the ombrotrophic mires of this area are driven by climate change. Correlation of decadal means of reconstructed iV l water levels and instrumental meteorological data was performed to examine the relationship between water table and climatic variability. The results show that the reconstructed water tables are correlated with changes in mean annual temperature (p < 0.05). This contrasts with similar data for other parts of Europe where correlations have been found with summer or annual precipitation and temperature. We A suggest that low rainfall in this area of Sweden makes the peatlands more susceptible to changing temperaHOLOCENE ture and that the lack of a response to precipitation is a function of low rainfall variability over the comRESEARCH parison period. The results show that mire surface wetness responses to climate change are spatially PAPER variable and greater attention should be given to understanding this variability if more accurate palaeoclimatic inferences are to be drawn from longer Holocene records.

An event stratigraphy for the Last Glacial–Holocene transition in eastern middle Sweden: results from investigations of varved clay and terrestrial sequences

This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the tim ...

Early Holocene deglaciation chronology in Västergötland and Närke, southern Sweden — biostratigraphy, clay varve, 14C and calendar year chronology

This thesis outlines an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. Events are short-lived occurrences that have left traces in the geological record and w ...

The long-term fate of permafrost peatlands under rapid climate warming.

Permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, climate warming and permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to recent rapid warming. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms.

Age, geochemistry and distribution of the mid-Holocene Hekla-S/Kebister tephra

The middle Holocene Hekla-S/Kebister tephra originates in the Hekla volcanic system on SW Iceland. The distal distribution of the tephra includes the Faroe Islands, Shetland and Central Sweden, indicating a main dispersal towards the east. The chemical composition of the tephra follows the pattern of other major eruptions of Hekla, and ratios between selected oxides may in some cases allow separation from other major Holocene tephras from Hekla. Tephra from the Plinian phase dominates in eastern sites, while tephra also from later phases is found in the Faroe sites. Wiggle-matching of radiocarbon dates around the tephra in a Swedish peat-bog suggests an age around 3720 cal. yr BP (3750—3700 cal. yr BP), which is in accordance with previous attempts to date this tephra. This is within a period with significant climate changes in NW Europe and opens possibilities for exact comparisons of peat and lake sediment records from different geographical areas.

Calcareous fossils and radiocarbon dating of the saline phase of the Yoldia Sea stage

Abstract The content of calcareous fossils (molluscs, foraminifera, and ostracods) in clay‐varve sites from eastern central Sweden and the northwestern Baltic Sea is presented. The sequences were deposited during the brackish phase of the Yoldia Sea stage. The faunal composition (four foraminiferal and four ostracod taxa) suggests arctic to boreal conditions, high meltwater influx and a brackish water influence during at least 100 clay‐varve years. AMS dates of foraminifera and the mollusc Portlandia (Yoldia) arctica indicate that the reservoir age of the Yoldia Sea may have been as great as 1000 to 1500 years. Evidence for immigration of ostracod species which today are considered arctic relicts in the Baltic Sea, is given for the first time from Yoldia Sea deposits. Wastegard, S. & Schoming, K., 1997: Calcareous fossils and radiocarbon dating of the saline phase of the Yoldia Sea stage. GFF, Vol. 119 (Pt. 3, September), pp. 245–248. Stockholm. ISSN 1103–5897.

Ostracod assemblages in late Quaternary varved glaciomarine clay of the Baltic Sea Yoldia stage in eastern middle Sweden

Abstract Four cored sites in eastern middle Sweden have been analysed for their content of calcareous fossils. The investigated sediments consist of late Quaternary varved clay deposited during the Baltic Sea Yoldia stage. Four regional palaeoecological units, A–D, have been established. Unit A reflects ice-proximal conditions, unit B optimal conditions for the benthic fauna and unit C the termination of a saline phase. In unit C oxygen deficiency might have occurred. In the fourth unit, D, no fossils were found. The fauna recorded is poor in taxa and indicates a weak marine influence. The salinity was higher in the western part of the investigated area due to the proximity to the inlet of marine water. The meltwater influx was high and the salinity probably fluctuated considerably. The ostracod Cytheromorpha macchesneyi (Brady and Crosskey) is reported for the first time in Quaternary deposits from northwestern Europe and indicates that a connection could have existed between the Baltic and the White Sea in Late Glacial times.

Palaeohydrography and marine conditions in the south-western part of the Vänern basin during the Younger Dryas and Early Preboreal

Abstract A clay-sequence from Lake Götesjön in the south-western part of the Lake Vänern basin has been investigated with respect to the foraminiferal and ostracod faunas and δ18Oc and δ13Cc. The sequence covers the middle/late Younger Dryas and the early part of the Preboreal chronozones. The conditions were severe during the Younger Dryas due to sea ice cover and a proximal position to the ice. The faunal assemblages indicate arctic glaciomarine conditions with a reduced salinity and the marine conditions ceased at c. 9700 14C-years BP. In the late Younger Dryas an increased ice retreat raised the salinity of the bottomwater. This was due to the formation of reaction currents with marine water entering the basin at the bottom as a response to a surface freshwater flowing out from the basin. A period with improved marine conditions is recorded in the Early Preboreal. The transition from the Younger Dryas to the Preboreal is recorded as a lowering in the δ18Oc due to increased input of meltwater and higher δ13Cc as a consequence of a more intensive mixing of water masses and a less extensive sea ice cover. The Vedde Ash is found in the lower part of the sequence and AMS radiocarbon datings of bivalves suggest a marine reservoir age in the area of 800–900 years during the Younger Dryas. The final drainage of the Baltic Ice Lake had only limited effects on the marine environment in the south-western part of the Vänern basin.