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

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

Low-frequency and high-frequency changes in temperature and effective humidity during the Holocene in south-central Sweden: implications for atmospheric and oceanic forcings of climate

An integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes. Here we report a 10,000 year quantitative record of annual mean temperature (T-ann), based on pollen-climate transfer functions and pollen-stratigraphical data from Lake Flarken, south-central Sweden. The pollen-based temperature reconstruction is compared with a reconstruction of effective humidity, as reflected by a delta(18)O record obtained on stratigraphy of lacustrine carbonates from Lake Igelsjon, c. 10 km from Lake Flarken, which gives evidence of pronounced changes in effective humidity. The relatively low T-ann, and high effective humidity as reflected by a low evaporation/inflow ratio suggest a maritime early Holocene climate (10,000-8,300 cat year BP), seemingly incompatible with the highly seasonal solar insolation configuration. We argue that the maritime climate was due to the stronger-than-present zonal flow, enhanced by the high early Holocene sea-surface temperatures in the North Atlantic. The maritime climate mode was disrupted by the abrupt cold event at 8,200 cat year BP, followed at 8,000 cat year BP by a stable Holocene Thermal Maximum. The latter was characterized by T-ann values about 2.5 degrees C higher than at present and markedly dry conditions, indicative of stable summertime anti-cyclonic circulation, possibly corresponding with modern blocking anticyclonic conditions. The last 4,300 year period is characterized by an increasingly cold, moist, and unstable climate. The results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability, generality, and interpretability of the palaeoclimatic results. Further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial-scale climate dynamics

Stable carbon isotope composition of terrestrial leaves: inter- and intraspecies variability, cellulose and whole-leaf tissue difference, and potential for climate reconstruction

Stable carbon isotope analysis of terrestrial plant leaves preserved in Quaternary lake sediments has the potential to provide high-resolution reconstructions of past climatic conditions. Preferably, delta(13)C measurements should be made on a single leaf component, e.g. cellulose, but this approach is often precluded by limited leaf availability. Previous work suggests that reliable palaeoclimatic information also may be derived from delta(13)C measurements on whole-leaf tissue, given a similar degree of leaf decomposition between samples. Leaf delta(13)C data for 12 Scandinavian species of dwarf-shrubs, shrubs and trees, and a comparison of delta(13)C data on recent and late Holocene Salix herbacea leaves, revealed that the delta(13)C signal registered by holocellulose is largely reflected by measurements on whole-leaf tissue. Holocellulose was found to be consistently enriched in C-13, although this delta(13)C offset was smaller for subfossil leaves. This supports the use of delta(13)C measurements on whole-leaf tissue for climate reconstruction, at least for leaves preserved in soft, late Holocene sediments with minimal diagenetic effects. Leaf carbon and nitrogen data on fresh leaves of the same 12 Scandinavian species, and corresponding data on late Holocene Salix herbacea leaves, suggest that the leaf C:N ratio is a suitable indicator of the degree of leaf decomposition. Copyright (C) 2003 John Wiley Sons, Ltd