Millennial-scale climate variability during the Last Interglacial recorded in a speleothem from south-western France

A stalagmite (BDinf) recovered from an archaeological cave (Bourgeois–Delaunay, La Chaise de Vouthon) in SW France provides a rare, high-resolution, precisely dated continental palaeoclimate record covering the warmest part of the Last Interglacial (128 ± 1–121 ± 1 ka). The growth interval spans the pluvial period recorded in Soreq and Peqiin Cave speleothems (during sapropel event S5), suggesting that the eastern Mediterranean and western Europe experienced relatively wet conditions simultaneously during this part of the Last Interglacial. Stable oxygen and carbon isotope ratios from BDinf show prominent millennial-scale variations, which are interpreted respectively in terms of changes in the amount of rainfall reaching the cave and soil biological activity. The timing of the oxygen isotope changes agrees with similar excursions recorded in speleothems from Corchia Cave (Italy), where close coupling between rainfall amount and regional sea surface temperatures has been demonstrated. Three “warmer–wetter” periods are interspersed with four “cooler–drier” periods. The first “warmer–wetter” period is the most prominent, as is the case at Corchia, and coincides with the SST optimum off western Europe. This is followed by a prominent “cooler–drier” excursion (centred on ～126 ka), which can be linked to a period of increased loess deposition recorded in annually laminated lake sediments from Eifel, Germany. Although there is already ample evidence for Last Interglacial climate instability, we show for the first time that specific climatic events occurred more or less synchronously between southwestern Europe, central Mediterranean (Italy) and northern Europe (Germany).     

Effects of resuspension on benthic fluxes of oxygen,nutrients, dissolved inorganic carbon,iron and manganese in the Gulf of Finland,Baltic Sea

The effect of resuspension on benthic fluxes of oxygen (O₂), ammonium (NH₄⁺), nitrate (NO₃^?), phosphate (PO₄^3?), silicate (Si(OH)₄), dissolved inorganic carbon (DIC), total dissolved iron (Fe) and total dissolved manganese (Mn) was studied at three different stations in the Gulf of Finland (GoF), Baltic Sea during three cruises in June–July 2003, September 2004 and May 2005. The stations were situated on different bottom types in the western, central and eastern part, respectively, of the open GoF. The fluxes were measured in-situ using the autonomous Göteborg benthic lander. To simulate resuspension events, the stirring speed was increased in two of the four chambers of the lander after approximately half of the incubation time. The other two chambers were used as control chambers. Clear effects of resuspension were observed on the oxygen fluxes where an increase of the consumption was observed in 88% of the cases and on average with 59% (stdev=53). The NH₄⁺ fluxes were affected in 50% of the cases (4 out of 8 incubations) at stations with low bottom water oxygen concentrations, but in no cases where the bottom water was oxygenated (0 out of 9 incubations). The NH₄⁺ fluxes decreased by 26±27% in 2005 and by 114±19% in 2003. There was no clear effect of resuspension on the fluxes of any of the other solutes in this study. Thus, resuspension events did not play a significant role in release/uptake of NO₃^?, PO₄^3?, Si(OH)₄, DIC, Fe and Mn in GoF sediments. However, increased oxygen consumption as a result of resuspension may lead to spreading of anoxic/suboxic bottom water conditions, and thus indirectly to increased benthic release of phosphate, ammonium and iron.     

An OSL‐dated sediment sequence at Idre,west‐central Sweden,indicates ice‐free conditions in MIS 3

In central and northern Sweden, glacial sediments and landforms, formed during Early and Middle Weichselian stadials and their transition into interstadials, are often preserved in spite of having been overridden by later glacial advances. This study presents an OSL‐dated glacial stratigraphy from Idre in west‐central Sweden, expanding the area in which Middle Weichselian ice‐free conditions have been identified. Three sedimentary units were identified, with the lowermost unit consisting of glaciolacustrine sand, deposited in a stagnant water‐body. Nine OSL samples gave ages ranging from 54 to 41 ka, suggesting deposition during a deglacial phase in MIS 3. Normal faults and silt veins, formed after deposition, indicate that the area was ice‐free for a prolonged period, enabling the melting of buried stagnant ice. Above an erosional unconformity is a sediment unit characterized by gravels and sands deposited in a proximal braided‐river environment. OSL ages range from 180 to 41 ka, indicating poor sediment bleaching during deposition. We thus consider them to give a maximum age of the sedimentation, indicating deposition at or after 41 ka. The uppermost unit consists of a stacked succession of subglacial traction tills and glaciotectonite beds, representing the Late Weichselian glaciation of the area, probably during the inception phase with a wet‐based glacier regime. At the last deglaciation of the area there was extensive meltwater erosion, eroding all sedimentary units and forming a landscape with terraces and channels, and erosional remnants of the uppermost diamict as free‐standing hummocks.     

Recent Trends in Rainfall-Runoff Characteristics in the Alzette River Basin, Luxembourg

The effects of rainfall structure and atmosphericcirculation variability on streamflow in the AlzetteRiver basin (Grand Duchy of Luxembourg, Europe) wereinvestigated. Evidence is presented regarding the local-scalesensitivity of the Alzette River basin to large-scalechanges in atmospheric circulation. Since the1950s, there has been a marked increase in thecontribution of the westerly component of atmosphericcirculation to rainfall. These changes in atmosphericcirculation are on a par with an increase in rainfallintensity and duration, which has induced a significantincrease in the winter maximum daily storm flow in theAlzette River basin since the 1970s.     

Social Change, Ecology and Climate in 20th-Century Greenland

Two great transitions, from seal hunting to codfishing, then from cod fishing to shrimp, affectedpopulation centers of southwest Greenland during the20th century. These economic transitionsreflected large-scale shifts in the underlying marineecosystems, driven by interactions between climate andhuman resource use. The combination of climaticvariation and fishing pressure, for example, provedfatal to west Greenland's cod fishery. We examine thehistory of these transitions, using data down to thelevel of individual municipalities. At this level,the uneven social consequences of environmental changeshow clearly: some places gained, while others lost. Developments in 20th-century Greenland resemblepatterns of human-environment interactions in themedieval Norse settlements, suggesting some generalpropositions relevant to the human dimensions ofclimatic change.     

Toxic metal contamination in the lateral lakes of the Coeur d'Alene River valley, Idaho

 The 11 lateral lakes of Coeur d'Alene River valley in northern Idaho have received heavy metal contamination from over a century of upstream mining. The lateral lakes lie within the flood plain of the Coeur d'Alene River, and in their bottom sediments is preserved a stratigraphic record of the upstream mining operations. To characterize the contaminated sediments in the lateral lakes, sampling techniques, including the Livingston piston corer and the Huttenen freeze box, have been developed by Quaternary geologists to preserve the vertical stratigraphy in the samples. From 26 cm to over 55 cm of undisturbed tailing sediments, commonly with “varve-like” features, have been found in each of the lateral lakes, with maximum concentrations by weight of lead at 3.8%, zinc at 3.4%, arsenic at 340 mg/kg, cadmium at 120 mg/kg and mercury at 7 mg/kg. The contamination in the lakes appears to be restricted to the shallow subsurface and heavy metal concentrations generally drop to background levels within a meter of depth. Received: 22 May 1998 · Accepted: 21 September 1998     

A rate‐dependent cohesive crack model based on anisotropic damage coupled to plasticity

In quasi‐brittle material the complex process of decohesion between particles in microcracks and localization of the displacement field into macrocracks is limited to a narrow fracture zone, and it is often modelled with cohesive crack models. Since the anisotropic nature of the decohesion process in separation and sliding is essential, it is particularly focused in this paper. Moreover, for cyclic and dynamic loading the unloading, load reversal (including crack closure) and rate dependency are essential features that are included in a new model. The modelling of degradation is based on a ‘localized’ version of anisotropic continuum damage coupled to inelasticity. The concept of strain energy equivalence between the states in the effective and nominal settings is adopted in order to define the free energy of the interface. The proposed fracture criterion is of the Mohr type, with a smooth transition of the failure and kinematics (slip and dilatation) characteristics between tension and shear. The chosen potential, of the Lemaitre‐type, for evolution of the dissipative processes is additively decomposed into plastic and damage parts, and non‐associative constitutive equations are obtained. The constitutive equations are integrated by applying the backward Euler rule and by using Newton iteration. The proposed model is assessed analytically and numerically and a typical calibration procedure for concrete is proposed. Copyright © 2006 John Wiley & Sons, Ltd.     

X-ray emission from the W UMa system TZ Bootis

HEAO-B (Einstein) satellite measurements with the Imaging Proportional Counter revealed the W UMa binary system TZ Bootis as an X-ray source. It is estimated that the luminosity ratioL _x/L_vof this system is about 10^–3.8 indicating that TZ Bootis is in the transition region between A- and W-type W UMa systems.