Search results for "Arctic"
showing 10 items of 565 documents
Gulf of Maine shells reveal changes in seawater temperature seasonality during the Medieval Climate Anomaly and the Little Ice Age
2011
article i nfo In this study, we use subannually resolved oxygen isotope values of fossil (dead-collected) and modern (live- caught) bivalve shells (Arctica islandica L.) from the northwestern Atlantic (Gulf of Maine, USA) to reconstruct past seasonal changes in seawater temperature. Our results indicate decreased seasonal temperature amplitude of about 1.6 °C (or ∼21%) during Medieval times (ca. AD 1033-1062) compared to shells from the early Little Ice Age (ca. AD 1321-1391) and during the late 19th century (AD 1864-1886). Additionally, seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the Gulf of Maine during the 11th century compared to summers and …
Dicarbonylchloro(pentabenzylcyclopentadienyl)ruthenium as Racemization Catalyst in the Dynamic Kinetic Resolution of Secondary Alcohols
2009
Dicarbonylchloro(pentabenzylcyclopentadienyl)ruthenium has been prepared and its structure confirmed by X-ray analysis. This complex shows excellent catalytic activity and modest stability against air in racemization reactions of secondary alcohols. In Candida antarctica lipase B (CAL-B) catalyzed dynamic kinetic resolution (DKR) of 1-phenyl- and 1-(furan-2-yl)ethanol compounds, the new complex shows improved performance as an alcohol racemization catalyst in comparison with its well-known pentaphenylcyclopentadienyl analogue, hitherto considered as the leading catalyst candidate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
A Revision of theniveaGroup of the Shore-Fly GenusDitrichophoraCresson (Diptera: Ephydridae)
2010
ABSTRACT Species of the nivea group (genus Ditrichophora Cresson) are revised. The group now includes four species of which one, D. gulkana (Alaska and Mongolia), is newly described. The group is now known to have a Holarctic distribution with two species, D. gulkana and D. nivea, being the first reported from the Nearctic Region. Another Asian species, D. brunnicosa, previously placed in Diclasiopa, is transferred to this group (genus Ditrichophora) and is also reported from Mongolia. To facilitate identification of these rare species, we have included diagnoses of the tribe, genus, and species group and have also provided an annotated key to Holarctic genera of the tribe Discocerinini and…
Lipid-rich zooplankton subsidise the winter diet of benthivorous Arctic charr (Salvelinus alpinus) in a subarctic lake
2013
Summary Generalist fish species commonly act as important links between littoral and pelagic habitats and food-web compartments in lakes. However, diet and habitat links may depend significantly on seasonal availability of, and qualitative differences between, littoral and pelagic prey and on fish size. Despite increasing interest in food-web dynamics, little is known about the seasonal changes in, or qualitative differences between, littoral and pelagic trophic pathways supporting generalist fish species in high-latitude lakes. We used stomach contents together with analyses of stable carbon and nitrogen isotopes and fatty acids to study the winter and summer diet of generalist Arctic char…
Where are you from, stranger? The enigmatic biogeography of North African pond turtles (Emys orbicularis)
2014
Abstract The European pond turtle (Emys orbicularis) is a Nearctic element in the African fauna and thought to have invaded North Africa from the Iberian Peninsula. All North African populations are currently identified with the subspecies E. o. occidentalis. However, a nearly range-wide sampling in North Africa used for analyses of mitochondrial and microsatellite DNA provides evidence that only Moroccan populations belong to this taxon, while eastern Algerian and Tunisian pond turtles represent an undescribed distinct subspecies. These two taxa are most closely related to E. o. galloitalica with a native distribution along the Mediterranean coast of northern Spain through southern France …
Revision of the genusXyalaspisHartig, 1843 (Hymenoptera: Figitidae: Anacharitinae) in the Western Palaearctic
2015
ABSTRACT A revision of Xyalaspis Hartig, 1843 (Hymenoptera: Anacharitinae) in the Western Palaearctic region is given. Xyalaspis spinigera Reinhard, 1860 and Xyalaspis subulifera (Thomson, 1862) are synonymized with Xyalaspis laevigata Hartig, 1843 and Xyalaspis rugosa Hartig, 1843 respectively, and their distribution areas are extended. A new species Xyalaspis pseudolaevigata n. sp. is described from France. One species previously assigned to the genus Xyalaspis, X. laevis (Hedicke, 1914), is transferred to Aegilips Haliday, 1835. Diagnostic characters are illustrated and data about biology, distribution and morphological variability of the studied species are presented and discussed. A ke…
<strong>Revision of the Western Palaearctic species of the genus <em>Dinotrema</em> Foerster, 1862 (Hymenoptera, Braconidae, Alysii…
2014
The first comprehensive revision of the Western Palaearctic species of the genus Dinotrema Foerster, 1862 is provided. 174 species of this genus are redescribed and illustrated. Ten species are described as new, viz, D. acompressum sp. nov., D. cahitum sp. nov., D. collybiae sp. nov., D. digitatum sp. nov., D. glabrideum sp. nov., D. helote sp. nov., D. lepiotae sp. nov., D. norwegicum sp. nov., D. oxybellum sp. nov. and D. torpi sp. nov. The following new combinations are suggested: Dinotrema adventum (Fischer), comb. nov., D. aurelianum (Fischer), comb. nov., D. cetiusmonte (Fischer), comb. nov., D. converginerve (Fischer), comb. nov., D. intermissum (Fischer), comb. nov., D. leptocorne (…
Effect of organic matrices on the determination of the trace element chemistry (Mg, Sr, Mg/Ca, Sr/Ca) of aragonitic bivalve shells (<i>Arctica …
2010
The element chemistry of biogenic carbonates can provide important data on past environments. However, the Sr/Ca and Mg/Ca ratios as well as the Mg and Sr concentrations of biological carbonates, especially aragonitic bivalves often depart from apparent thermodynamic equilibrium. When measured in situ by means of LA-ICP-MS, the Mg concentration is often substantially enriched (two- to threefold) near the organic-rich, annual growth lines. To test the hypothesis that some organic components exert a major influence on the skeletal metal content, the element chemistry of different shell components (insoluble organic matrix, IOM; dissolved CaCO3 and soluble organics, SOM) of Arctica islandica w…
Coralline algal growth-increment widths archive North Atlantic climate variability
2011
Over the past decade coralline algae have increasingly been used as archives of paleoclimate information. Encrusting coralline algae, which deposit annual growth increments in a high Mg-calcite skeleton, are amongst the longest-lived shallow marine organisms. In fact, a live-collected plant has recently been shown to have lived for at least 850 years based on radiometric dating. While a number of investigations have successfully used geochemical information of coralline algal skeletons to reconstruct sea surface temperatures, less attention has been paid to employ growth increment widths as a temperature proxy. Here we explore the relationship between growth and environmental parameters in …
Accurate increment identification and the spatial extent of the common signal in fiveArctica islandicachronologies from the Fladen Ground, northern N…
2009
[1] The creation of networks of shell-based chronologies which can provide regionally extensive high-resolution proxies for the marine environment depends on the spatial extent of the common environmental signal preserved in the shell banding and on the reliability of the dating model. Here Arctica islandica chronologies from five neighboring sites in the North Sea are compared, and the strength of the common environmental signal across distances up to 80 km is analyzed using statistical techniques derived from dendrochronology. The signal is found to be coherent across these distances. In a linked study, chronologies based on one of the same sites but constructed by two different research …