Holocene changes in atmospheric circulation recorded in the oxygen-isotope stratigraphy of lacustrine carbonates from northern Sweden

The oxygen-isotope composition of local precipitation (d18OP) is reconstructed from carbonate lake-sediment components in a sediment core covering the last 10000 calendar years from Lake Tibetanus, a small, hydrologically open, groundwater-fed lake in the Abisko area, northern Sweden. Comparison of the d18OP history with a pollen-based palaeotemperature record from the same core clearly reveals pronounced deviations from the normally expected temporal d18OP-temperature relation (so-called ‘Dansgaard relation’) that may be a function of changing oceanicity. The transition from relatively moist, maritime conditions in the early Holo cene to a much drier climate after 6500 cal. BP is re‘ ected by major changes in forest extent and composition as recorded by pollen and plant macrofossil data. At the time of maximum in‘ uence of westerly air-mass circulation (high zonal index) c. 9500 cal. BP, brought about by high summer insolation and enhanced meridi onal pressure gradients, d18OP at Lake Tibetanus was about 2 higher than would be predicted by the modern isotope-temperature relation. The occurrence of long-term changes in d18OP-temperature relations, which are more sensitive measures of palaeoclimate than either d18OP or temperature alone, needs to be taken into account when extracting palaeoclimatic information from continental oxygen-isotope records

Holocene climate and environmental change in north-eastern Kamchatka (Russian Far East), inferred from a multi-proxy study of lake sediments

The study was supported by the Swedish Research Council through grants 621-2004-5224 and 621-2005-4444 to K.D. Bennett. A. Self and N. Solovieva acknowledge S. Brooks and V. Jones and were supported by NERC grant NE/H008160/1.A sediment record from a small lake in the north-eastern part of the Kamchatka Peninsula has been investigated in a multi-proxy study to gain knowledge of Holocene climatic and environmental change. Pollen, diatoms, chironomids and selected geochemical parameters were analysed and the sediment record was dated with radiocarbon. The study shows Holocene changes in the terrestrial vegetation as well as responses of the lake ecosystem to catchment maturity and multiple stressors, such as climate change and volcanic eruptions. Climate change is the major driving force resulting in the recorded environmental changes in the lake, although recurrent tephra deposition events also contributed. The sediment record has an age at the base of about 10,000 cal yrs BP, and during the first 400 years the climate was cold and the lake exhibited extensive ice-cover during winter and relatively low primary production. Soils in the catchment were poor with shrub alder and birches dominating the vegetation surrounding the lake. At about 9600–8900 cal yrs BP the climate was cold and moist, and strong seasonal wind stress resulted in reduced ice-cover and increased primary production. After ca. 8900 cal yrs BP the forest density increased around the lake, runoff decreased in a generally drier climate resulting in decreased primary production in the lake until ca. 7000 cal yrs BP. This generally dry climate was interrupted by a brief climatic perturbation, possibly attributed to the 8.2 ka event, indicating increasingly windy conditions with thick snow cover, reduced ice-cover and slightly elevated primary production in the lake. The diatom record shows maximum thermal stratification at ca. 6300–5800 cal yrs BP and indicates together with the geochemical proxies a dry and slightly warmer climate resulting in a high productive lake. The most remarkably change in the catchment vegetation occurred at ca. 4200 cal yrs BP in the form of a conspicuous increase in Siberian dwarf pine (Pinus pumila), indicating a shift to a cooler climate with a thicker and more long-lasting snow cover. This vegetational change was accompanied by marked shifts in the diatom and chironomid stratigraphies, which are also indicative of colder climate and more extensive ice-cover.Publisher PDFPeer reviewe

Ostracod stable isotope records from a deglacial isolation sequence in southern Sweden

A Late Weichselian sediment succession from the Kullen Peninsula, southern Sweden, was studied by means of stable carbon and oxygen isotope analyses of calcitic valves of selected ostracod taxa. The lower part of the record was deposited in a slightly brackish marginal sea close to the receding inland ice, whereas the upper part is lacustrine in origin as a result of glacio-isostatic rebound. The site was deglaciated at c. 17200 cal BP (c. 14500 C-14 BP) within the earliest ice-free area of Sweden, and the isolation took place c. 1100 cal years later. As a result of extensive input of glacial meltwater to the near-shore, shallow basin, the isotopic records predating the isolation give no clear indications of marine conditions. However, the isolation of the lake from the marginal sea is reflected by a distinct depletion of O-18 in ostracod calcite as a response to the changing isotope hydrology of the basin. The change towards a lacustrine environment also fostered a decrease in the input of minerogenic material and a related increase in organic carbon content of the sediments, which may explain a short-lasting depletion of C-13 in dissolved inorganic carbon and ostracod calcite. During the period of c. 14700-13900 cal BP a pronounced warming occurred associated with the onset of the Late Weichselian interstadial complex (Greenland Interstadial I). Based on a distinct enrichment of O-18 in ostracod calcite and applying modern spatial relations between delta(18)O of precipitation and temperature, this climatic shift involved an increase in mean annual air temperature in southernmost Sweden of at least 7 degrees C

A Distinct Delta-C-13 Decline in Organic Lake-Sediments at the Pleistocene-Holocene Transition in Southern Sweden

Values of deltaC-13 obtained from conventional bulk sediment radiocarbon dates encompassing the Pleistocene-Holocene boundary have been compiled and plotted against C-14 age. In all, 286 lake sediment dates from southern Sweden in the range 8,000 to 13.000 BP have been evaluated. A significant decrease in deltaC-13 values, initiated shortly before 10,000 BP and amounting to 5 parts per thousand, is distinguished. This change is accompanied by increased limnic productivity, decreased erosive input and increased organic carbon content of the sediments. A probable explanation for the deltaC-13 decline in organic material is decreased importance of dissolution of silicates at the transition to the Holocene. During the Late Weichselian, extensive weathering of exposed minerogenic material with subsequent input of bicarbonate to the lake water may have caused a relative enrichment of C-13 in dissolved inorganic carbon. Furthermore, the early Holocene increase in terrestrial vegetation cover probably led to an increased supply of C-13 depleted carbon dioxide to the lake water by root respiration. Altered limnic vegetation, presumably towards increased production of phytoplankton, could also have contributed to the observed decreasing deltaC-13 trend. The importance of these processes compared to other possible influencing factors, mainly endogenic carbonate production and changes in the global carbon cycle, is discussed

Sedimentstratigrafiska och paleohydrologiska undersökningar av Fönesjön och Kalvs Mosse inom Vombslätten, centrala Skåne

This study constitutes a preliminary survey within the project "Lake and groundwater paleohydrology of the Vomb plain, southern Sweden, for quantitative paleoclimatic calibration". The aim of the study is to describe the Holocene sediment stratigraphy of the former lakes Fönesjön and Kalvsjön (Kalvs mosse), and furthermore to describe and date stratgraphical indications of climatically caused lake-level changes in the Early Holocene. The Vomb plain is a flat area situated in the south-central part of the province of Scania, South Sweden. It consists of glacifluvial deposits, mainly sand, which compose an important groundwater supply. Within the plain a number of lakes are situated, and these are entirely dependent on the supply of groundwater. The lake levels are strictly defined by the position of the water table and the groundwater flow in the surrounding permeable deposits. The two investigated lakes are kettle-holes, today completely filled with Holocene organic sediments. The stratigraphy is built up mainly by gyttja and algae gyttja with an increasing amount of minerogenic matter towards the bottom. In some places distinct layers of silt and sand occur in the lower part of the organic sediments. The Holocene sediments are resting on sand, silt, clay and clay-gyttja, deposited during the Late Weichselian. The methods used were determination of loss on ignition, pollen analysis and measurement of magnetic susceptibility. By these methods it was possible to demonstrate that some of the stratigraphical records probably were caused by climatic changes. The study was also compared with a paleohydrological reconstruction from Lake Bysjön, a nearby site which earlier has been thoroughly investigated, resulting in a detailed Holocene water-level curve. The present results show that a distinct lowering of the water table occured in the area during the zones PB and BO 1 in the Early Holocene. The water level then rose substantially during the zone BO 2, and remained high throughout the rest of the Holocene, however possibly with some minor fluctuations. The two former lakes included in this study seem to be suitable for further investigatiotls within the project, as the conditions are favourable for paleohydrological reconstructions

A Late Weichselian Stable-Isotope Stratigraphy Compared with Biostratigraphical Data - A Case-Study from Southern Sweden

Late Weichselian lake sediments from a site in southern Sweden, were analysed for stable carbon and oxygen isotopes, as well as plant macrofossils and insect remains. By comparison of independent data sets, general climatic changes were demonstrated. Lithological, chemical and stable isotope data reveal two significant climatic oscillations at ca. 12 200-12 000 and ca. 11 000-10 200 yr BP respectively. Continental climatic conditions, indicated by evaporative enrichment of O-18 in lake marl, characterise parts of the early lake history, including the Older Dryas Stadial. Distinct variations of deltaC-13 in organic material is discussed in terms of climatically induced changes in lake-water chemistry. Different types of photosynthetic assimilation of dissolved inorganic carbon is proposed as a contributing factor influencing lake marl deltaC-13. The universal application of a positive correlation between lake marl deltaO-18 and mean annual air temperature is questioned. Quantifications of mean summer and winter temperatures based on beetle analysis show a climatic optimum around 12 000 yr BP, a marked cooling around 11 000 yr BP and a strong amelioration at ca. 10 200 yr BP. These climatic events were accompanied by distinct changes in aquatic vegetation. Plant macrofossil and insect analyses indicate an open vegetation during the entire period studied. Biostratigraphical data reflecting local limnic and terrestrial vegetation and regional climate facilitate the interpretation of stable isotope data