Oxygen isotopes from two snow trenches from Kohnen Station, Dronning Maud Land, Antarctica from the 2012/13 field season

In low-accumulation regions, the reliability of d18O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen station, Dronning Maud Land, Antarctica. Analysing d18O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the hundred-metre scale. This data set includes the complete trench oxygen isotope record together with the meta data used in the study.

Radiocarbon ages, dose rates, water isotopic composition and hydrochemistry of samples from Komakuk Beach and Herschel Island

Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry, and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2 cal ka BP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean d18O of -29.1 per mil); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial, and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until ~11 cal ka BP during a period of low glacio-eustatic sea level. The late glacial-Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2 cal ka BP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet, ocean, and permafrost that have existed since the Late Wisconsinan.

Stable water isotope composition of precipitation from O'Higgins Station, Antarctica, 2008-2009

In order to investigate the climate variability in the northern Antarctic Peninsula region, this paper focuses on the relationship between stable isotope content of precipitation and firn, and main meteorological variables (air temperature, relative humidity, sea surface temperature, and sea ice extent). Between 2008 and 2010, we collected precipitation samples and retrieved firn cores from several key sites in this region. We conclude that the deuterium excess oscillation represents a robust indicator of the meteorological variability on a seasonal to sub-seasonal scale. Low absolute deuterium excess values and the synchronous variation of both deuterium excess and air temperature imply that the evaporation of moisture occurs in the adjacent Southern Ocean. The d18O-air temperature relationship is complicated and significant only at a (multi)seasonal scale. Backward trajectory calculations show that air-parcels arriving at the region during precipitation events predominantly originate at the South Pacific Ocean and Bellingshausen Sea. These investigations will be used as a calibration for ongoing and future research in the area, suggesting that appropriate locations for future ice core research are located above 600 m a.s.l. We selected the Plateau Laclavere, Antarctic Peninsula as the most promising site for a deeper drilling campaign.

Late Holocene climate change in central Sweden inferred from lacustrine stable isotope data

Stable isotopes (delta O-18 and delta C-13) of lacustrine carbonates (Chara spp. algae and Pisidium spp. molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (delta O-18 and delta H-2) show that Lake Blektjarnen water isotope composition is responsive to the balance between evaporation and input water (E/l ratio). A high E/l ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration probably enrich lake water in O-18 and C-13, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara delta O-18 values we infer that conditions were dry and warm between 4400 and 4000 cal. a BP, whereas more negative values indicate that conditions were wetter and probably cooler between 4000 and 3000 cal. a BP. A drier climate is inferred from more positive values between 2500 and 1000 cal. a BP. However, a successive depletion after ca. 1750 cal. a BP, also detected in several other delta O-18 records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased strength of the zonal flow.

The origin of brines underlying Lake Kinneret

Lake Kinneret (LK) is a relatively fresh water take situated in the Dead Sea Rift (DSR) Valley. The pore water (PW) in the sediments underlying LK pelagic zone have significantly higher salinity than that of the lake. The concentrations of major ion solutes (Cl, Br, Na, K, Mg) in PW from six 2.4 m to 5.1 m long sediment cores increase linearly with depth, indicating the occurrence of saline, deep seated brines. The upper part of the PW column is affected by the much fresher boundary with LK water and in most cores is characterized by gradually increasing Br/Cl and decreasing Na, Mg, K/Cl molar ratios, which tend to stabilize at about 2.0 m below the sediment surface. The 'stable' molar ratios in the deeper PW vary spatially and are supposed to represent the ratios in the deep underlying brines at each site. When plotted as Na/Cl vs. Br/Cl, the stable ratios of the northern and central part of the lake fall close to a straight line which characterizes many of the brines in the DSR Valley. However, the respective ratios in the southern part of the lake fall markedly off the DSR line. Moreover, Na/Cl and K/Cl molar ratios in the south are significantly higher than in the central and northern parts. delta Cl-37 measured in present LK water is ca. 0.0 parts per thousand. Along the PW column at the lake center, delta Cl-37 is becoming more positive with depth, reaching values of about +0.5 parts per thousand to +0.6 parts per thousand at 3 m depth. Even more positive values (+0.7 parts per thousand to +0.8 parts per thousand) are detected further north, in PW from deeper sediment layers. In contrast, in PW from the southeastern part of the lake, delta Cl-37 is becoming more negative with depth (-1.0 parts per thousand at similar to 2.6 m). It is suggested that these isotopic differences are also indicative of spatial variability in the PW brine sources. O-18 and D values in the PW of all 3 m long cores are similar and resemble the respective levels in LK. The source of H2O in 3 m deep, bed sediments is claimed to be the overlying lake water, and therefore water isotopes do not provide a clue regarding the original water isotopic composition in the underlying brines. PW from the southeast with higher K/Cl and Na/Cl but lower concentrations of these solutes, suggest leaching by meteoric water of sub-surface halite and post-halite salt formations, while the more saline PW from the northern and central parts, that have lower K/Cl and Na/Cl, and higher Br/Cl, are similar to DSR brines and represent underlying residual brines. (C) 2009 Elsevier B.V. All rights reserved.

Hydrogeochemical characterization of Seehausen territory - Bremen

The aim of this thesis is to provide a geochemical characterization of the Seehausen territory (a neighborhood) of Bremen, Germany. In this territory it is hosted a landfill of dredged sediments coming both from Bremerhaven (North See) and Bremen harbor (directly on the river Weser). For this reason this work has been focused also on possible impacts of the landfill on the groundwaters (shallow and deep aquifer). The Seehausen landfill uses the dewatering technique to manage the dredged sediments: incoming sediments are put into dewatering fields until they are completely dried (it takes almost a year). Then they are randomly sampled and analyzed: if the pollutants content is acceptable, sediments are treated with other materials and used instead of raw material for embankment, bricks, etc., otherwise they are disposed in the landfill. During this work it has been made a study of the natural geology and hydrogeology of the whole area of interest, especially because it is characterized by ancient natural salt deposits. Then, together with the Geological Survey of Bremen and the Harbor Authority of Bremen there have been identified all useful piezometers for a monitoring net around the landfill. During the sampling campaign there have been collected data of the principal anions and cations, physical parameters and stable water isotopes. Data analysis has been focused particularly on Cl, Na, SO4 and EC because these parameters might be helpful to attribute geochemical trends to the landfill or to a natural background. Furthermore dataloggers have been installed for a month in some piezometers and EC, pressure, dissolved oxygen and temperature data have been collected. Finally there has been made a deep comparison between current and historical data (1996 – 2011) and between old interpolation maps and current ones in order to see time trends of the aquifer geochemistry.

Natural tracer profiles across argillaceous formations

Argillaceous formations generally act as aquitards because of their low hydraulic conductivities. This property, together with the large retention capacity of clays for cationic contaminants, has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste. In several countries, programmes are under way to characterise the detailed transport properties of such formations at depth. In this context, the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large-scale and long-term transport behaviour of these formations. Here, tracer-profile data, obtained by various methods of pore-water extraction for nine sites in central Europe, are compiled. Data at each site comprise some or all of the conservative tracers: anions (Cl(-), Br(-)), water isotopes (delta(18)O, delta(2)H) and noble gases (mainly He). Based on a careful evaluation of the palaeo-hydrogeological evolution at each site, model scenarios are derived for initial and boundary pore-water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites, using transport parameters derived from laboratory or in situ tests. The comprehensive results from this project have been reported in Mazurek et al. (2009). Here the results for three sites are presented in detail, but the conclusions are based on model interpretations of the entire data set. In essentially all cases, the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles. Transport by advection has a negligible influence on the observed profiles at most sites, as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data. The advantages and disadvantages of different conservative tracers are also assessed. The anion Cl(-) is well suited as a natural tracer in aquitards, because its concentration varies considerably in environmental waters. It can easily be measured, although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue. The stable water isotopes are also well suited, but they are more difficult to measure and their values generally exhibit a smaller relative range of variation. Chlorine isotopes (delta(37)Cl) and He are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence. It is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion, leading to relatively sharp changes of boundary conditions, can be considered as a pre-requisite to obtain well-interpretable tracer signatures. On the other hand, gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation.

The Effects of Joint ENSO-Antarctic Oscillation Forcing on the McMurdo Dry Valleys, Antarctica

Stable oxygen analyses and snow accumulation rates from snow pits sampled in the McMurdo Dry Valleys have been used to reconstruct variations in summer temperature and moisture availability over the last four decades. The temperature data show a common interannual variability, with strong regional warmings occurring especially in 1984/85, 1995/96 and 1990/91 and profound coolings during 1977/78, 1983/84, 1988/89, 1993/94, and 1996/97. Annual snow accumulation shows a larger variance between sites, but the early 1970s, 1984, 1997, and to a lesser degree 1990/91 are characterized overall by wetter conditions, while the early and late 1980s show low snow accumulation values. Comparison of the reconstructed and measured summer temperatures with the Southern Oscillation Index (SOI) and the Antarctic Oscillation (AAO) yield statistically significant correlations, which improve when phaserelationships are considered. A distinct change in the phase relationship of the correlation is observed, with the SOI-AAO leading over the temperature records by one year before, and lagging by one year after 1988. These results suggest that over the last two decades summer temperatures are influenced by opposing El Niho Southern Oscillation and AAO forcings and support previous studies that identified a change in the Tropical-Antarctic teleconnection between the 1980s and 1990s.

Tracer profiles across argillaceous formations: A tool to constrain transport processes.

The spatial distributions of non-reactive natural tracers (anions, stable water isotopes, noble gases) in pore water of clay-rich formations were studied at nine sites. Regular curved profiles were identified in most cases. Transport modeling considering diffusion, advection and available constraints on the paleo-hydrogeological evolution indicates generally that diffusion alone can explain the observations, whereas a marked advective component would distort the profiles and so is not consistent with the data.

Age model and stable oxygen isotope mean values of ice core SZ99 from Akademii Nauk ice cap on Severnaya Zemlya

Between 1999 and 2001, a 724 m long ice core was drilled on Akademii Nauk, the largest glacier on Severnaya Zemlya, Russian Arctic. The drilling site is located near the summit. The core is characterized by high melt-layer content. The melt layers are caused by melting and even by rain during the summer. We present high-resolution data of density, electrical conductivity (dielectrical profiling), stable water isotopes and melt-layer content for the upper 136 m (120 m w.e.) of the ice core. The dating by isotopic cycles and electrical conductivity peak identification suggests that this core section covers approximately the past 275 years. Singularities of volcanogenic and anthropogenic origin provide well-defined additional time markers. Long-term temperatures inferred from 12 year running mean averages of d18O reach their lowest level in the entire record around 1790. Thereafter the d18O values indicate a continuously increasing mean temperature on the Akademii Nauk ice cap until 1935, interrupted only by minor cooling episodes. The 20th century is found to be the warmest period in this record.