Timing of the first drainage of the Baltic Ice Lake synchronous with the onset of Greenland Stadial 1

Glacial varves can give significant insights into recession and melting rates of decaying ice sheets. Moreover, varve chronologies can provide an independent means of comparison to other annually resolved climatic archives, which ultimately help to assess the timing and response of an ice sheet to changes across rapid climate transitions. Here we report a composite 1257‐year‐long varve chronology from southeastern Sweden spanning the regional late Allerød–late Younger Dryas pollen zone. The chronology was correlated to the Greenland Ice‐Core Chronology 2005 using the time‐synchronous Vedde Ash volcanic marker, which can be found in both successions. For the first time, this enables secure placement of the Lateglacial Swedish varve chronology in absolute time. Geochemical analysis from new varve successions indicate a marked change in sedimentation regime accompanied by an interruption of ice‐rafted debris deposition synchronous with the onset of Greenland Stadial 1 (GS‐1; 12 846 years before AD 1950). With the support of a simple ice‐flow/calving model, we suggest that slowdown of sediment transfer can be explained by ice‐sheet margin stabilization/advance in response to a significant drop of the Baltic Ice Lake level. A reassessment of chronological evidence from central‐western and southern Sweden further supports the hypothesis of synchronicity between the first (penultimate) catastrophic drainage of the Baltic Ice Lake and the start of GS‐1 in Greenland ice‐cores. Our results may therefore provide the first chronologically robust evidence linking continental meltwater forcing to rapid atmosphere–ocean circulation changes in the North Atlantic.     

Probability of combined high sea levels and large rains in Malmö, Sweden,southern Öresund

Observations of sea level and precipitation in Malmö, Sweden in the southeastern part of the sound Öresund have been used to estimate the probabilities of local compound events of high sea level and large daily and hourly rains. There are observations of sea level and daily rains extending back to 1930. The observations of short‐term rainfall are from 1980 and onwards. Most large rainfalls come in the summer, while the highest sea levels are in the autumn and in the winter. The highest observed sea level is about 130 cm above mean sea level, and the largest daily rain is close to 100 mm. However, the highest sea level observed during a day with rainfall corresponding to the 1‐year rain is less than 60 cm. The highest sea level observed during an hour with 1‐year hourly rainfall is 30 cm. From the statistics of daily rains, hourly rains and sea level, extreme values for each of them have been computed. For events with frequency higher than one per four years the probabilities of combined events sea level – rainfall are determined directly from the observations. For more rare events, marginal distributions of sea level and rainfall are determined. Copulas and conditional probabilities are used. When the sea level exceeds 20 cm above mean sea level, daily rains exceeding 10 mm are almost independent of the sea level and so are hourly rains exceeding 5 mm. It is extremely rare that large rains occur when the sea level is very high. The combination of 1‐year rainfall and the 1‐year sea level has a return period of more than 200 years.     

Spatial variation of wetlands and flux of dissolved organic carbon in boreal headwater streams

In order to investigate the relation between water chemistry and functional landscape elements, spatial data sets of characteristics for 68 small (0·2–1·5 km²) boreal forest catchments in western central Sweden were analysed in a geographical information system (GIS). The geographic data used were extracted from official topographic maps. Water sampled four times at different flow situations was analysed chemically. This paper focuses on one phenomenon that has an important influence on headwater quality in boreal, coniferous forest streams: generation and export of dissolved organic carbon (DOC). It is known that wetland cover (bogs and fens) in the catchment is a major source of DOC. In this study, a comparison was made between a large number of headwater catchments with varying spatial locations and areas of wetlands. How this variation, together with a number of other spatial variables, influences the DOC flux in the streamwater was analysed by statistical methods. There were significant, but not strong, correlations between the total percentages of wetland area and DOC flux measured at a medium flow situation, but not at high flow. Neither were there any significant correlations between the percentage of wetland area connected to streams, nor the percentage of wetland area within a zone 50 m from the stream and the DOC flux. There were, however, correlations between catchment mean slope and the DOC flux in all but one flow situations. This study showed that, considering geographical data retrieved from official sources, the topography of a catchment better explains the variation in DOC flux than the percentage and locations of distinct wetland areas. This emphasizes the need for high‐resolution elevation models accurate enough to reveal the sources of DOC found in headwater streams. Copyright © 2007 John Wiley & Sons, Ltd.     

Long‐term change of daily and multi‐daily precipitation in southern Sweden

Daily rain series from southern Sweden with records dating back to the 1870s have been analysed to investigate the trends of daily and multi‐day precipitation of different return periods with emphasis on the extremes. Probabilities of extreme storms were determined as continuously changing values based on 25 years of data. An extra set of data was used to investigate changes in Skåne, the southernmost peninsula of Sweden. Another 30‐year data set of more than 200 stations of a dense gauge network in Skåne was used to investigate the relation between very large daily rainfall and annual precipitation. The annual precipitation has increased significantly all over southern Sweden due to increased winter precipitation. There is a trend of increasing maximum annual daily precipitation at only one station, where the annual maximum often occurs in winter. The number of events with a short return period is increasing, but the number of more extreme events has not increased. Daily and multi‐daily design storms of long return periods determined from extreme value analysis with updating year by year are not higher today than during the last 100 years. The largest daily storms are not related to stations with annual rainfall but seem to occur randomly. Copyright © 2013 John Wiley & Sons, Ltd.     

U–Pb ID-TIMS dating of igneous and metaigneous rocks from the El-Sibai area: time constraints on the tectonic evolution of the Central Eastern Desert,Egypt

This paper presents new ID-TIMS U–Pb zircon and titanite ages from the El-Sibai gneiss complex in the Eastern Desert of Egypt. The zircon data support previous studies, indicating that the protoliths of the gneissic (oldest) units in the area were emplaced during the East African orogeny, and do not represent an older pre-Neoproterozoic, reworked cratonic basement. The crystallization ages of three compositionally distinct orthogneiss protoliths are c. 685, 682 and 679 Ma, respectively. A U–Pb titanite age from one orthogneiss overlaps with the protolith age, indicating that the gneisses did not undergo post-magmatic high-temperature metamorphism. The gneissic textures of the rocks are therefore interpreted to reflect syn-emplacement deformation. This, and evidence for static amphibolite facies metamorphism in country-rock metavolcanics, lead us to conclude that the gneisses of El-Sibai do not represent an exhumed middle crustal gneiss dome, but are part of the island arc affined allochthon into which they were emplaced synchronously with NW-ward nappe translation. We also report ages from rocks cross-cutting the gneisses and the surrounding island arc affined assemblages that yield the hitherto youngest robust pre-Cretaceous intrusive ages in the Eastern Desert. The dated rocks are an anorthosite and a cross-cutting syenogranite giving ages of c. 541 and 540 Ma, respectively. We consider this late magmatic pulse to be anorogenic, most likely reflecting a separate extensional event involving asthenospheric upwelling and decompression melting of the mantle.     

From registration to visualization of geological data with MO2GEO: applications of the FieldModule,interpolation methods,and computer visualization

The registration and screen visualization of geological data are basic steps in modelling of 3D structures and geoscientific processes. Therefore, a standardized coding of geological field observations is reasonable to enable an independent modelling approach. The field module of MO2GEO provides diverse standards for data coding and was tested in the frame of a mapping project. The visualization of profiles and the construction of cross-sections improve the database for a variety of interpolation methods. The subsequently developed 3D models, constructed with diverse modelling tools, can be visualized and serve as the base for diverse applied scientific projects.     

Visualizing the temporal development of thermo-radiative features on ground-based thermographs

In urban microclimate research, ground-based thermography is used to gain insight into the spatial distribution of surface temperatures of various materials. Taking snapshots over a certain time span helps experts to observe the temporal thermo-radiative behavior of the monitored surface elements and therefore supports decisions on possible optimizations, e.g., improving the thermal comfort in a neighborhood. Appropriate visualization techniques facilitate decision-making and are thus crucial in the optimization process. In this study, we present a tool that eases the extraction of thermo-radiative features from multi-temporal thermographs taken from a monitored scene. Assisted by our tool, users can identify, choose, and register thermo-radiative features for each time step according to their individual research needs. The features’ temporal development is then visualized using a directed graph that encodes topological events as well as each feature’s size and summarizing statistics. To enhance this summary, a comprehensive animated sequence emphasizes the spatiotemporal behavior of the most significant thermo-radiative features. Salient developments are visually embedded and highlighted in the original infrared images, which are blended in an animation from time step to time step. Since we enable the user to interact with the data in a flexible way, noisy and low resolution image data sets can also be processed.