Rosqvist G.C.,University of Stockholm |
Leng M.J.,University of Leicester |
Leng M.J.,British Geological Survey |
Goslar T.,Adam Mickiewicz University |
And 10 more authors.
Quaternary Science Reviews | Year: 2013
Here we present δ;18Odiatom data from two high-latitude lakes; one has short residence time and a water isotopic composition (δ18Olake) that fluctuate due to seasonal variations in precipitation and temperature, and the other has δ18Olake that is influenced by longer lake water residence times and evaporation. The δ18Odiatom records reveal common responses to precipitation forcing over the past millennium. Relatively wet summers are inferred from δ18Odiatom between 1000 and 1080 AD, 1300 and 1440 AD, and during the early 19th century, coincided with periods of high cloud cover inferred from tree-ring carbon isotopes, and other data for high Arctic Oscillation index. While relatively dry summers with increasing influence of winter snow are indicated between 1600 and 1750 AD. The co-response between carbon isotopes in trees and oxygen isotopes in diatoms strengthens the relationship between cloud cover and precipitation and the hypothesis that these changes were the result of significant regional shifts in atmospheric circulation. © 2012 Elsevier Ltd. Source
Finsinger W.,French National Center for Scientific Research |
Finsinger W.,University Utrecht |
Schoning K.,Geological Survey of Sweden |
Hicks S.,University of Oulu |
And 5 more authors.
Journal of Quaternary Science | Year: 2013
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 <1 year in the most recent part), the potential to determine cause-effect (or lead-lag) relationships between environmental changes and biotic responses is limited by proxy-specific incorporation processes below the actively growing Sphagnum surface. Nevertheless, what emerges is that mire development was closely related to water-table changes rather than to summer temperature and that water-table decreases were associated with increasing peat-accumulation rates and more abundant mire vegetation. A rapid fen-to-bog transition occurred within a few years around AD 1960 when the water table decreased beyond the historical minimum, supporting the notion that mires can rapidly shift into bogs in response to allogenic factors. © 2012 John Wiley & Sons, Ltd. Source
Michalska D.,Adam Mickiewicz University |
Czernik J.,Poznan Radiocarbon Laboratory
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2015
Lime mortars as a mixture of binder and aggregate may contain carbon of various origins. If the mortars are made of totally burnt lime, radiocarbon dating of binder yields the real age of building construction. The presence of carbonaceous aggregate has a significant influence on the 14C measurements results and depending on the type of aggregate and fraction they may cause overaging. Another problem, especially in case of hydraulic mortars that continue to be chemically active for a very long time, is the recrystallization usually connected with rejuvenation of the results but also, depending on local geological structures, with so called reservoir effect yielding apparent ages. An attempt in separating the binder from other carbonaceous components successfully was made for samples from Israel by Nawrocka-Michalska et al. (2007). The same preparation procedure, after taking into account the petrographic composition, was used for samples coming from Poland, Nawrocka et al. (2009). To verify the procedure used previously for non-hydraulic samples determination an experimental tests on carbonaceous mortars with crushed bricks from Novae in Bulgaria were made. Additionally, to identify different carbonaceous structures and their morphology, a cathodoluminescence and scanning electron microscope with electron dispersive spectrometer were applied. The crushed bricks and brick dust used in mortars production process have been interpreted as an alternative use to other pozzolanic materials. The reaction between lime and pozzolanic additives take place easily and affects the rate and course of carbonates decomposition in orthophosphric acid, during the samples pretreatment for dating. The composition of the Bulgarian samples together with influence of climate conditions on mortar carbonates do not allow for making straightforward conclusions in chronology context, but gives some new guidelines in terms of hydraulic mortars application for dating. This work has mainly methodological character, illustrating the special preparation methods used for mortars with complicated (in context of radiocarbon dating) petrographic composition. The local geology combined with finding sources of raw materials for the production of mortars is important issue in final interpretation of the 14C measurement results. © 2015 Elsevier B.V. All rights reserved. Source
Rozanski K.,AGH University of Science and Technology |
Klisch M.A.,AGH University of Science and Technology |
Wachniew P.,AGH University of Science and Technology |
Gorczyca Z.,AGH University of Science and Technology |
And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2010
Two water-based oxygen-isotope geothermometers (calcite-cellulose and silica-cellulose) were tested using well-dated intervals of laminated sediment retrieved from Lake Gościaz, a small hardwater lake in central Poland. Five sections spanning ca. 90-200years of deposition were selected and subsampled at approximately decadal resolution to characterize relatively stable climatic and hydrologic conditions during the middle of the Younger Dryas cold period, the rapid environmental changes that occurred at the Younger Dryas-Preboreal (YD-PB) boundary, and three subsequent periods of relative stability during the early, middle and late Holocene. The two geothermometers are based on the premise that aquatic cellulose δ18O serves as a direct proxy for lakewater δ18O, thereby allowing resolution of temperature signals in δ18O records obtained from co-existing authigenic calcite or diatom silica. Qualitatively consistent results from the calcite-cellulose geothermometer were obtained for all five intervals, clearly showing the expected low epilimnion water temperatures in the mid-YD, rapid warming during the YD-BP transition and maximum temperatures during the early Holocene, followed by slightly lower temperatures during the middle and late Holocene. Results from the silica-cellulose geothermometer also showed lower temperatures during the YD than the late Holocene, although insufficient diatom silica for analysis was present in the intervening intervals. The calcite-cellulose geothermometer yielded consistently higher estimates of epilimnion temperatures than the silica-cellulose thermometer in the YD and late Holocene intervals, and unrealistically high values throughout the Holocene. We speculate that the calcite-cellulose geothermometer is influenced by kinetic effects during rapid carbonate precipitation, which offsets temperature-dependent fractionation and thus leads to high temperature estimates. In contrast, the silica-cellulose geothermometer may be affected by the production of diatom silica early in the spring, prior to seasonal warming and isotopic enrichment of the epilimnion, thus generating low temperature estimates. © 2010 Elsevier Ltd. Source
Esmeijer-Liu A.J.,University Utrecht |
Kurschner W.M.,University of Oslo |
Lotter A.F.,University Utrecht |
Verhoeven J.T.A.,University Utrecht |
And 2 more authors.
Water, Air, and Soil Pollution | Year: 2012
In this study, we test whether the δ 13C and δ 15N in a peat profile are, respectively, linked to the recent dilution of atmospheric δ 13CO 2 caused by increased fossil fuel combustion and changes in atmospheric δ 15N deposition. We analysed bulk peat and Sphagnum fuscum branch C and N concentrations and bulk peat, S. fuscum branch and Andromeda polifolia leaf δ 13C and δ 15N from a 30-cm hummocklike peat profile from an Aapa mire in northern Finland. Statistically significant correlations were found between the dilution of atmospheric δ 13CO 2 and bulk peat δ 13C, as well as between historically increasing wet N deposition and bulk peat δ 15N. However, these correlations may be affected by early stage kinetic fractionation during decomposition and possibly other processes. We conclude that bulk peat stable carbon and nitrogen isotope ratios may reflect the dilution of atmospheric δ 13CO 2 and the changes in δ 15N deposition, but probably also reflect the effects of early stage kinetic fractionation during diagenesis. This needs to be taken into account when interpreting palaeodata. There is a need for further studies of δ 15N profiles in sufficiently old dated cores from sites with different rates of decomposition: These would facilitate more reliable separation of depositional δ 15N from patterns caused by other processes. © Springer Science+Business Media B.V. 2011. Source