Siv Olsson

Palaeoclimatic studies in South Shetland Islands, Antarctica, based on numerous stratigraphic variables in lake sediments

The hitherto longest found lake sediment sequence on Byers Peninsula, Livingston Island, South Shetland Islands, was analysed with respect to lithology, chronology, diatoms, Pediastrum, pollen and spores, mosses, mineralogy, and sediment chemistry. During the ca. 5000 year long development the sediments were influenced by frequent tephra fall-outs. This volcanic impact played a major role in the lakes history during two periods, 4700–4600 and 2800–2500 BP, but was of importance during the lakes entire history with considerable influence on many of the palaeoenvironmentally significant indicators. The large and complex data set was analysed and zonated with different types of multivariate analysis. This resulted in a subdivision of the sequence into 8 time periods and 21 variables. Redundancy analysis (RDA) of this data set, both without and with the tephra periods, and with 4–6 of the variables as explanatory environmental variables, reveal that climatic/environmental signals are detectable. The palaeoclimatic picture that emerged out of the tephra ‘noise’ suggests that the first 100 years were characterized by mild, humid conditions. This was followed by a less mild and humid climate until ca. 4000 BP when a gradual warming seems to have started, coupled with increased humidity. These mild and humid conditions seem to have reached an optimum slightly after 3000 BP. At ca. 2500 BP a distinct climatic deterioration occurred with colder and drier conditions and long seasons with ice cover. This arid, cold phase probably reached its optimum conditions at ca. 1500 BP, when slightly warmer conditions might have prevailed for a while. Except for the modern sample with rather mild climate, the last 1400 years seem to have been fairly arid and cold, and the effects of the frequent volcanic activity during this period is only vaguely seen in the records.

Palaeosurfaces and associated saprolites in southern Sweden

Abstract Saprolite remnants from different palaeosurfaces in southern Sweden have been analysed by XRD and SEM analyses. They represent two clearly different types. The first is a clay- and silt-rich saprolite with a kaolinite-dominated clay mineral association representative of mature saprolites and with chemically altered quartz grains. This saprolite type is associated with sub-Cambrian, sub-Jurassic and sub-Cretaceous denudation surfaces. The second type is gravelly and in a youthful stage of alteration with mainly vermiculitic clay minerals in the fine fractions. Microtextures developed on quartz grains indicate a mainly mechanical breakdown. Compared to overlying till beds this saprolite is in a more advanced stage of chemical alteration. It is not associated with any specific denudation surface. Its characteristics and thickness indicate a Plio-Pleistocene age. The saprolites represent deep weathering of the bedrock surface at different times. The weathering resulted in thin kaolinitc saprolites during the Late Proterozoic, thick kaolinitic saprolites from the latest Triassic through the Jurassic and Cretaceous, and medium thick immature saprolites from the Pliocene and onwards. The depth of the deep weathering has been decisive for the shape of the present relief and thus etch processes have been of fundamental importance in shaping the relief, even in a formerly glaciated area.

Sediment-chemistry response to land-use change and pollutant loading in a hypertrophic lake, southern Sweden

Responses to recent land-use changes and pollutant loading in the sediment of a hypertrophic lake in southern Sweden were studied by comparison of geochemical, pollen and magnetic records with historical land-use data. A chronology was constructed for the last two centuries by correlating changes in the pollen diagram to major events in the land-use history. Sediment accumulation was low (mean c. 0.2 g cm-2 yr-1) prior to 1800 AD, when less than 25% of the catchment was arable land. Reorganization of the agrarian system during the 19th century increased the annually tilled area by 300%, which accelerated soil erosion and substantially increased the accumulation of allochtonous matter in the lake. Since the turn of the century 90% of the catchment has been ploughed every year. The deposition of clastic matter in the lake has, however, decreased due to a gradual rerouting of the drainage system, which has reduced the effective catchment area by c. 85%.Authigenic vivianite (Fe3(PO4)2.8H2O) is a major P phase in the preindustrial non-sulphidic sediments, which suggests that the sediments at that time served as a fairly efficient sink for P. The arable expansion, increased manuring and, eventually, the introduction of artificial fertilizers during the 19th century led to a massive influx of nutrients, which elevated primary production in the lake. Subsequent development of bottom water anoxia around 1900, in combination with an additional pollutant burden of sulphate within the lake basin, led to major alterations of the biogeochemical cycles. The most critical change in the post-1900 sediments involved the cycling of Fe and P. The linkage between the lacustrine P and Fe cycles can explain that FeS formation was paralleled by a release of P from the sedimentary pool. This supply of P to the lake basin must have supplemented the nutrient supply by modern agriculture and contributed to recent hypertrophication. The bacterial sulphate reduction also affected the generation of alkalinity which supported a significant calcite precipitation in the post-1900 sediments.S is enriched 10-fold in the post-1900 sediments compared to preindustrial values. Along with the rise in S, soot particles derived from fossil fuel combustion appear in the sediments for the first time. Therefore, Bussj¨osj¨on is thought to be a good example of how a well-buffered, highly productive lake may respond to the pollution by sulphur from acid rain.

Reconstruction of holocene lake-level changes in lake Xinias, central Greece

A study of past lake-level changes in Lake Xinias covering the last 40 000 years was presented in an earlier paper. In that paper, changes during the Holocene were only briefly dealt with, because of poor sedimentary representation. In this paper a supplementary transect of cores is described, in which Holocene lake-level changes are better recorded. The correlation of the cores was based on pollen and lithostratigraphic analyses, and a curve was constructed showing recorded lake-level changes. The curve from Lake Xinias was compared with an earlier compilation of lake-level changes from the Balkans, mainly from Greece. The compilation shows rising lake levels during the earlier part of the Holocene, and successively lowered levels during the later part. Most lake levels were high between about 8000 and 5500 cal. yr BP. The reconstruction from Lake Xinias indcates similar changes during the early and late Holocene. However, it differs by indicating a lowering in lake level, culminating around 7000 cal. yr BP, interrupting and dividing the period of mid-Holocene high lake-level stand. Further studies are required to show if this lowering in Lake Xinias was regionally representative and caused by climate change, or was caused by tectonic disturbance locally affecting lake level.

INTERLABORATORY CEC AND EXCHANGEABLE CATION STUDY OF BENTONITE BUFFER MATERIALS: I. Cu(II)-TRIETHYLENETETRAMINE METHOD

Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proved to be one of the most sensitive parameters for detecting changes of mineral properties such as swelling capacity and illitization in alteration experiments. Whether measured differences in CEC values of bentonite buffer samples before and after an experiment are (1) actual differences caused by clay structural changes such as illitization or (2) simply data scatter due to the different methods used by international research teams is an open question. The aim of this study was to measure the CEC of clay samples in five different laboratories using the same method and to evaluate the precision of the values measured. The Cu-trien method and four reference materials of the Alternative Buffer Material (ABM) test project in Äspö, Sweden, were chosen for this interlaboratory study. The precision of the Cu-trien method, which uses visible spectroscopy, was very good with a standard deviation of ±0.7–2.1 meq/100 g for CECs that ranged from 11 to 87 meq/100 g. For the same CEC range, analysis of Cu-trien index cations using inductively coupled plasma (mass spectrometry) and atomic absorption spectroscopy were less precise with a standard deviation of ±2.8–3.9 meq/100 g. Based on the measured precision, greater measured differences in Cu-trien CEC and exchangeable cation values of bentonite buffer samples, before and after an experiment, might be actual differences. Great care must be taken when interpreting measured CEC differences, and analytical characterization of any structural changes may be needed. Compared with results from the ‘International Soil-Analytical Exchange’ (iSE) program for soils, most absolute concentrations were much larger for the clays studied; however, for the two parameters exchangeable Ca2+ and CEC the range was similar to the iSE ring test and, most importantly, the precision was comparable. Future studies should discuss the accuracy of CEC and exchangeable cation values and compare them to alternative CEC methods in which care is taken to prevent dissolution of soluble minerals, such as calcite and gypsum.

INTERLABORATORY CEC AND EXCHANGEABLE CATION STUDY OF BENTONITE BUFFER MATERIALS: II. ALTERNATIVE METHODS

Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proven to be one of the most sensitive parameters for detecting changes in mineral properties in bentonite-alteration experiments. An interlaboratory study of CECs and exchangeable cations for three reference bentonite buffer materials that were used in the Alternative Buffer Material test (ABM) project in Äspö, Sweden, was conducted to create a suitable database. The present study focused on CEC accuracy and compared CEC methods where care was taken to prevent dissolution of soluble minerals such as calcite and gypsum. The overall quality of the CEC and exchangeable cation values measured using non-Cu-trien CEC methods were good, with CECs of 74–91±0.5–3.3 meq/100 g and exchangeable cation values of 22–61±1.2–3.9 meq/100 g Na+, 7–23±0.8–1.5 meq/100 g Mg2+, and 19–39±0.8–1.6 meq/ 100 g Ca2+. The precision was comparable to the standard Cu-trien method even for exchangeable Ca2+, although the laboratories used different solution/solid ratios and reaction-time parameters for Cu-trien which affect carbonate dissolution. The MX80 and Dep.CAN bentonite exchangeable Ca2+ values were more accurate than standard-Cu-trien values. Using the optimized methods of this study, MX80 and Dep.CAN exchangeable Ca2+ values averaged 20.2±1.6 and 38.8±1.4 meq/100 g which amounts to ~70% of the inflated Cu-trien values. A more complex analysis of the CEC data using different methods, anion analyses, and mineralogical analysis is necessary to obtain plausible and accurate CEC values. Even with a more complicated analytical procedure, the CEC and exchangeable cation values were still not accurate enough because of excess anions. Chloride, sulfate, and dolomite might have increased the exchangeable Na+, Mg2+, and Ca2+ values.

A weathered diamicton beneath Upper Weichselian sediments at Silvereke, southeastern Sweden

Abstract An at least 2 m thick, weathered, non‐glacial diamicton, buried beneath a 6 m thick Upper Weichselian glaciogenic sequence at Silvereke in SE Sweden, is composed of variously coloured angular/rhombohedral to rounded clasts set in a red or reddish‐brown matrix of clayey silty sand. The clasts (mainly local metavolcanic rock and Cambrian sandstone) are generally thoroughly weathered and would hardly survive transport, suggesting weathering after deposition. XRD‐analysis of the clay fraction of individual argillized clasts reveals an assemblage dominated by kaolin minerals, probably including halloysite. The matrix has a more complex clay mineralogy, including vermiculite. The petrography and mineralogy as well as the extensive argillization of the diamicton contrast to the composition and texture of the overlying Upper Weichselian till. Apart from small amounts of pollen, mainly Pinus, Betula and NAP, the unit is almost devoid of organic matter. Since most pollen are well‐preserved, they were proba...