Postglacial midge community change and Holocene palaeotemperaturereconstructions near treeline, southern British Columbia (Canada)

Stratigraphic analysis of fossil chironomid head capsules wasperformed at North Crater Lake and Lake of the Woods, located at treeline (2250m) in the Ashnola region of southernmost British Columbia. Priorto 10,000 yr BP, cold conditions were indicated by the lack oftemperate taxa and the presence of cold-stenotherms. The abundance anddiversity of warm-adapted taxa (e.g., Dicrotendipes,Microtendipes, Polypedilum and Cladopelma)increased rapidly after 9500 yr BP, whereas taxa indicative ofcold conditions disappeared. Beginning prior to deposition of the Mazama ash(6730 ± 40 yr BP), several warm-adapted taxa decreasedin abundance. Mid- to late-Holocene assemblages (ca. 4500yr BP to present) indicated continued cooling as revealed by afurther reduction in diversity and abundance of warm-adapted taxa atboth lakes, and the reappearance of cold-stenotherms in Lake of theWoods. Diversity changes in the cores paralleled the inferred climatic changes.Diversity was low during the late-glacial, increased in theearly-Holocene, and declined after 5400 yr BP.To quantitatively infer past climatic changes, a newweighted yphen;averaging partial-least-squares (WA-PLS)model was developed and applied to the fossil midge data. The quantitativereconstructions revealed late-glacial mean July air temperatures rangingfrom about 8 to 10°C. Summer air temperatures were highest inthe early Holocene (13 to 17°C), gradually decreasing by about3°C through the mid- to late-Holocene.     

Seasonal variations of zinc in a eutrophic lake

Depth profiles of dissolved zinc were measured monthly over one year in Lake Greifen, a eutrophic lake. The concentrations are in the range 10–40 nM and show systematic variations over time and depth. Due to the increased binding to particles and subsequent settling, concentrations of zinc in the epilimnion decrease during summer stagnation. Clear correlations between Zn and major nutrients (P, Si) are, however, not observed in the water column. No accumulation of Zn occurs in the anoxic hypolimnion. The Zn sedimentation is related to the sedimentation of algae and of manganese oxide. A mass-balance calculation shows that 87% of the Zn input is retained in the sediments of Lake Greifen.     

Evidence of NAO control on subsurface ice accumulation in a 1200 yr old cave-ice sequence, St. Livres ice cave, Switzerland

Mid-latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially interesting environmental archive. Establishing a precise chronology is, however, a prerequisite for the understanding of processes driving the cave-ice mass balance and thus allows a paleoenvironmental interpretation. At St. Livres ice cave (Jura Mountains, Switzerland), subfossil trees and organic material are abundant in the cave-ice deposit, therefore allowing the dating of individual ice layers. The dendrochronological analysis of 45 subfossil samples of Norway spruce (Picea abies (L.) Karst.) from the overhanging front of the ice outcrop as well as the dating of seven wood samples with ¹⁴C dating allowed for a reconstruction of the St. Livres cave-ice sequence and for the determination of periods of ice accumulation and ablation. Results suggest a maximal age of 1200 ± 50 ¹⁴C yr BP for the observed ice sequence and indicate the presence of four major deposition gaps dated to the 14th, 15th, mid-19th and late 19th century, which can be related with periods of positive North Atlantic Oscillation anomalies (NAO+) over the winter half-year and/or anthropogenic cave-ice abstraction. Similarly, there is evidence that periods of cave-ice accumulation as observed between AD 1877-1900 and AD 1393-1415 would correspond with phases of negative NAO indices. Cave ice represents therefore an original climate archive for the winter half-year and is complementary to other continental proxies recording preferentially summer conditions (e.g., tree rings, varves).     

Luminescence dating of historical fluvial deposits from the Danube and Ebro

The validity of optically stimulated luminescence (OSL) has been tested on known‐age (historical) fluvial deposits along the rivers Danube (Austria) and Ebro (Spain). As partial bleaching of the OSL signal prior to deposition can interfere with correct age estimates, different approaches to extracting the dose accumulated during burial are compared. Using the finite mixture model gave OSL ages that are internally as well as stratigraphically consistent and in agreement with independent age control. According to these results, fluvial deposition at the Danube River study site can be attributed to different periods ranging from Bronze Age to the 18th century A.D. Fluvial deposits of Roman age and of the late 17th or early 18th century A.D. were found at the Ebro River study site. This is consistent with the morphological subdivision of the valleys and encourages further investigation of the fluvial and archaeological history of the study areas using OSL. © 2009 Wiley Periodicals, Inc.     

A large wet snow avalanche cycle in West Greenland quantified using remote sensing and in situ observations

Natural Hazards - On 11 April 2016 we observed high slushflow and wet snow avalanche activity at the environmental monitoring station Kobbefjord in W-Greenland. Snow avalanches released as a result...     

Temporal patterns in lacustrine stable isotopes as evidence for climate change during the late glacial in the Southern European Alps

We investigated oxygen and carbon isotopes of bulk carbonate and of benthic freshwater ostracods (Candona candida) in a sediment core of Lago Piccolo di Avigliana that was previously analyzed for pollen and loss-on-ignition, in order to reconstruct environmental changes during the late glacial and early Holocene. The depth–age relationship of the sediment core was established using 14 AMS ¹⁴C dates and the Laacher See Tephra. While stable isotopes of bulk carbonates may have been affected by detrital input and, therefore, only indirectly reflect climatic changes, isotopes measured on ostracod shells provide unambiguous evidence for major environmental changes. Oxygen isotope ratios of ostracod shells (δ¹⁸O_C) increased by ～6‰ at the onset of the Bølling (～14,650 cal BP) and were ～2‰ lower during the Younger Dryas (～12,850 to 11,650 cal BP), indicating a temporal pattern of climate changes similar to the North Atlantic region. However, in contrast to records in that region, δ¹⁸O_C gradually decreased during the early Holocene, suggesting that compared to the Younger Dryas more humid conditions occurred and that the lake received gradually increasing input of ¹⁸O-depleted groundwater or river water.     

Dating of soil layers in a young floodplain using iron oxide crystallinity

Dating of fluvial deposits is essential for a more quantitative understanding of landscape evolution and soil development in floodplain environments. We collected soil layers in defined depth intervals down to 60 cm along a substrate age gradient in a floodplain of the Danube River near Vienna, Austria. Depth profiles of fallout ¹³⁷Cs were used to assess short-term sedimentation, and optically stimulated luminescence (OSL) dating was used to attribute sediment deposits to time periods between the early last millennium BC and the 18th century AD. In the studied soils, the ratio of oxalate- to dithionite-extractable iron (Fe_o/Fe_d), which indicates the degree of iron oxide crystallinity, progressively decreased from ratios greater than 0.5 to values less than 0.2 with increasing soil age and proved to be a reliable indicator of soil maturity. We linked the observed Fe_o/Fe_d ratios to the radiometric and OSL ages in a chronofunction, which allows to approximately date soil layers that lack an independent age control. The soil ages calculated with this chronofunction accurately reflected their geomorphological position, resulted in consistent age trends with depth, and highlighted the active morphodynamics of the studied floodplain. The chronofunction was further validated by dating a soil profile near the studied chronosequence that contained an archaeological find dated to the La Tène period (5th to 1st century BC).     

Coupling the Xinanjiang model to a kinematic flow model based on digital drainage networks for flood forecasting

The Xinanjiang model, which is a conceptual rainfall‐runoff model and has been successfully and widely applied in humid and semi‐humid regions in China, is coupled by the physically based kinematic wave method based on a digital drainage network. The kinematic wave Xinanjiang model (KWXAJ) uses topography and land use data to simulate runoff and overland flow routing. For the modelling, the catchment is subdivided into numerous hillslopes and consists of a raster grid of flow vectors that define the water flow directions. The Xinanjiang model simulates the runoff yield in each grid cell, and the kinematic wave approach is then applied to a ranked raster network. The grid‐based rainfall‐runoff model was applied to simulate basin‐scale water discharge from an 805‐km² catchment of the Huaihe River, China. Rainfall and discharge records were available for the years 1984, 1985, 1987, 1998 and 1999. Eight flood events were used to calibrate the model's parameters and three other flood events were used to validate the grid‐based rainfall‐runoff model. A Manning's roughness via a linear flood depth relationship was suggested in this paper for improving flood forecasting. The calibration and validation results show that this model works well. A sensitivity analysis was further performed to evaluate the variation of topography (hillslopes) and land use parameters on catchment discharge. Copyright © 2009 John Wiley & Sons, Ltd.