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Landslides may cause severe destruction that affects both the individuals and functions vital for society. Minor landslides in an area with quick clay may trigger secondary slides, influencing a much greater area compared to slides in areas with no quick clay. Today’s expanding societies demand new areas for exploitation. To effectively meet this demand, there is an increased need to identify areas where quick clay may occur. Direct or indirect methods for assessing the presence of quick clay have previously been presented as well as a strategy for site investigations in quick clay areas. In this article, a methodology for mapping quick clays for the Swedish conditions with methods commonly available in this area is presented. The methodology presented in the article is structured in steps with different levels of detail and visualized with two conceptual flowcharts. Depending on the stage of planning, different types of surveys are recommended. The methodology has been applied at four sites where integrated interpretation of airborne and ground geophysical measurements as well as geotechnical investigations have been carried out. The results from two of these sites are presented here. The study reveals that all the methods used have their advantages and limitations. However, a combined use of the information provides much more accurate interpretation that can be used for a more cost-effective future planning and decision-making.

Highlights: • A first standardized and publicly available Holocene relative sea-level database for the Baltic Sea is presented. • The database holds 1099 revised data points with an estimation of vertical and chronological uncertainties. • Negative RSL tendencies prevail over the positive and complex tendencies in the Baltic Sea Basin. • Mid-Holocene RSL highstand occurred around 7.5–6.5 ka BP being consistent with the end of the final melting of the LIS. • The contribution of ice loading in the eastern Baltic Sea Basin is likely overestimated in the ICE-5G and ICE-6G_C models. Abstract: We present a compilation and analysis of 1099 Holocene relative shore-level (RSL) indicators located around the Baltic Sea including 867 relative sea-level data points and 232 data points from the Ancylus Lake and the following transitional phase. The spatial distribution covers the Baltic Sea and near-coastal areas fairly well, but some gaps remain mainly in Sweden. RSL data follow the standardized HOLSEA format and, thus, are ready for spatially comprehensive applications in, e.g., glacial isostatic adjustment (GIA) modelling. We apply a SQL database system to store the nationally provided data sets in their individual form and to map the different input into the HOLSEA format as the information content of the individual data sets from the Baltic Sea area differs. About 80% of the RSL data is related to the last marine stage in Baltic Sea history after 8.5 ka BP (thousand years before present). These samples are grouped according to their dominant RSL tendencies into three clusters: regions with negative, positive and complex (transitional) RSL tendencies. Overall, regions with isostatic uplift driven negative tendencies dominate and show regression in the Baltic Sea basin during the last marine stage. Shifts from positive to negative tendencies in RSL data from transitional regions show a mid-Holocene highstand around 7.5–6.5 ka BP which is consistent with the end of the final melting of the Laurentide Ice Sheet. Comparisons of RSL data with GIA predictions including global ICE-5G and ICE-6G_C ice histories show good fit with RSL data from the regions with negative tendencies, whereas in the transitional areas in the eastern Baltic, predictions for the mid-Holocene clearly overestimate the RSL and fail to recover the mid-Holocene RSL highstand derived from the proxy reconstructions. These results motivate improvements of ice-sheet and Earth-structure models and show the potential and benefits of the new compilation for future studies.

Climate warming and human impacts are thought to be causing peatlands to dry,\ud potentially converting them from sinks to sources of carbon. However, it is unclear\ud whether the hydrological status of peatlands has moved beyond their natural envelope.\ud Here we show that European peatlands have undergone substantial, widespread drying\ud during the last ~300 years. We analyse testate amoeba-derived hydrological\ud reconstructions from 31 peatlands across Britain, Ireland, Scandinavia and continental\ud Europe to examine changes in peatland surface wetness during the last 2000 years.\ud 60% of our study sites were drier during the period CE 1800-2000 than they have been\ud for the last 600 years; 40% of sites were drier than they have been for 1000 years; and\ud 24% of sites were drier than they have been for 2000 years. This marked recent\ud transition in the hydrology of European peatlands is concurrent with compound\ud pressures including climatic drying, warming and direct human impacts on peatlands,\ud although these factors vary between regions and individual sites. Our results suggest\ud that the wetness of many European peatlands may now be moving away from natural\ud baselines. Our findings highlight the need for effective management and restoration of\ud European peatlands.

We present a record of peatland development in relation to climate changes and human activities from the Palomaa mire, a remote site in northern Finland. We used fine-resolution and continuous sampling to analyse several proxies including pollen (for vegetation on and around the mire), testate amoebae (TA; for mire-wetness changes), oxygen and carbon isotopes from Sphagnum cellulose (δ18O and δ13C; for humidity and temperature changes), peat-accumulation rates and peat-colour changes. In spite of an excellent accumulation model (30 14C dates and estimated standard deviation of sample ages

The aim of this thesis was to reconstruct humidity variability in central Sweden during the late Holocene. A multi-proxy approach was used to infer humidity changes as recorded in a lake and a mire. Age-models were constructed based on radiocarbon dating and the Askja-1875 tephra. Stable isotopes (δ18O and δ13C) on Chara spp encrustations and Pisidium spp mollusc shells and carbon content were analysed in the lake record, whereas peat stratigraphy, humification, testate amoebae assemblages, C/N ratio and stable isotopes (δ13C and δ15N) were analysed in the mire record. Stable isotopes (δ2H and δ18O) on lake water showed that Lake Blektjarnen responded to changes in the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate during which evaporation and atmospheric equilibration likely enrich lake water in 18O and 13C, respectively, and vice versa for a low E/I ratio. The relatively high Chara δ18O and δ13C values between ca 4400 and 4000 cal yr BP thus suggest relatively dry and likely warm conditions, whereas depleted values suggest wetter and probably cooler conditions between ca 4000 and 3000 cal yr BP. Again, drier and probably warmer conditions were inferred from the relatively enriched δ18O values between ca 2500 and 1000 cal yr BP, and depleted δ18O values were recorded between ca 1000 and 50 cal yr BP indicating wetter and likely cooler conditions. The results from the mire mainly indicated vegetation succession, however, the changes inferred at ca 2600 and 1000 cal yr BP could have been triggered by climate change. This study shows that the proxies responded sensitively to humidity changes in the investigated archives allowing for reconstruction of climate change in central Sweden during late Holocene.

Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrop ...

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.

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.

This thesis focuses on responses in raised bogs to changes in the effective humidity during the Holocene. Raised bogs are terrestrial deposits that can provide contiguous records of past climate changes. Information on and knowledge about past changes in climate is crucial for our understanding of natural climate variability. Analyses on different spatial and temporal scales have been conducted on a number of raised bogs in south-central Sweden in order to gain more knowledge about Holocene climate variability.Peatlands are useful as palaeoenvironmental archives because they develop over the course of millennia and provide a multi-faceted contiguous outlook on the past. Peat humification, a proxy for bog surface wetness, has been used to reconstruct palaeoclimate. In addition measurements of carbon and nitrogen on sub-recent peat from two bogs have been performed. The chronologies have been constrained by AMS radiocarbon dates and tephrochronology and by SCPs for the sub-recent peat.A comparison between a peat humification record from Varmland, south-central Sweden, and a dendrochronological record from Jamtland, north-central Sweden, indicates several synchronous changes between drier and wetter climate. This implies that changes in hydrology operate on a regional scale.In a high resolution study of two bogs in Uppland, south-central Sweden, C, N and peat humification have been compared to bog water tables inferred from testate amoebae and with meteorological data covering the last 150 years. The results indicate that peat can be subjected to secondary decomposition, resulting in an apparent lead in peat humification and C/N compared to biological proxies and meteorological data.Several periods of wetter conditions are indicated from the analysis of five peat sequences from three bogs in Varmland. Wetter conditions around especially c. 4500, 3500, 2800 and 1700-1000 cal yr BP can be correlated to several other climate records across the North Atlantic region and Scandinavia, indicating wetter and/or cooler climatic conditions at these times. Frequency analyses of two bogs indicate periodicities between 200 and 400 years that may be caused by cycles in solar activity.

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.

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 ...

A clay-sequence from Lake Gotesjon in the south-western part of the Lake Vanern 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 highe...

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 marine benthic fauna and the δ 18 Oc of foraminifers and ostracods from six sites situated on a west-east transect through central Sweden have been analysed in order to estimate the palaeosalinity and palaeocirculation in this shallow-marine environment. The measurements have been undertaken on material from the early Preboreal, when the Baltic Basin was in contact with the North Sea through straits in central Sweden. The δ 18 Oc values have a more negative value towards the east, indicating decreasing salinity. This was the result of limited possibilities for marine water to penetrate into the Baltic Basin and the mixing with freshwater from the melting Fennoscandian ice-sheet. Four water masses existed in the area: a surface layer of freshwater, marine water from the North Sea, brackish-marine intermediate water on the Swedish west coast and brackish Yoldia Sea water in the Baltic Basin. The chronology is based on radiocarbon dates of marine fossils and, at one site, on the occurrence of the Vedde Ash (10 400-10 300 14 C yr BP). This is the first record from marine settings in Sweden. Copyright  2001 John Wiley & Sons, Ltd. Journal of Quaternary Science

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.

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.