Search results for "atla"
showing 10 items of 1241 documents
Radiogenic isotopes: new tools help reconstruct paleocean circulation and erosion input
2001
Ocean and atmosphere circulation and continental weathering regimes have undergone great changes over thousands of years as well as tens of millions of years. During the glacial stages of the Pleistocene, ocean circulation was generally more sluggish and deep water circulation in the Atlantic had a shallower flow. At the same time, weathering on the continents was enhanced by glacial erosion, particularly in high northern latitudes, which increased the input of erosional detritus into the ocean. In addition, atmospheric pressure gradients were larger, leading to higher wind speeds and increased supply of aeolian dust to the ocean. Prior to the onset of Northern Hemisphere glaciation and pro…
Late Quaternary Variations in the South American Monsoon System as Inferred by Speleothems—New Perspectives using the SISAL Database
2019
Here we present an overview of speleothem δ18O records from South America, most of which are available in the Speleothem Isotopes Synthesis and Analysis (SISAL_v1) database. South American tropical and subtropical speleothem δ18O time series are primarily interpreted to reflect changes in precipitation amount, the amount effect, and consequently history of convection intensity variability of convergence zones such as the Intertropical Convergence Zone (ITCZ) and the South America Monsoon System (SAMS). We investigate past hydroclimate scenarios in South America related to the South American Monsoon System in three different time periods: Late Pleistocene, Holocene, and the last tw…
Holocene climate variability in north-eastern Italy: potential influence of the NAO and solar activity recorded by speleothem data
2012
Abstract. Here we present high-resolution stable isotope and lamina thickness profiles as well as radiocarbon data for the Holocene stalagmite ER 76 from Grotta di Ernesto (north-eastern Italy), which was dated by combined U-series dating and lamina counting. ER 76 grew between 8 ka (thousands of years before 2000 AD) and today, with a hiatus from 2.6 to 0.4 ka. Data from nine meteorological stations in Trentino show a significant influence of the North Atlantic Oscillation (NAO) on winter temperature and precipitation in the cave region. Spectral analysis of the stable isotope signals of ER 76 reveals significant peaks at periods of 110, 60–70, 40–50, 32–37 and around 25 a. Except for the …
Climate variability and lake ecosystem responses in western Scandinavia (Norway) during the last Millennium
2017
This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the m…
Carbon accumulation rate in a raised bog in Latvia, NE Europe, in relation to climate warming
2018
The carbon accumulation rate (CAR) over the last 180 years was estimated by measuring carbon concentrations in 1-cm layers in a fine-resolution dated and analysed peat sequence in Teiči Bog, Latvia, NE Europe. We used the Granger causality test to examine the temporal (lagged) relationships between the CAR and the historical climate variables. Our results showed that the average CAR was 192 g C m–2 yr–1 during the last 180 years and 169 g C m–2 yr–1 when excluding the acrotelm where decomposition and the stock of carbon are still not in the balance. The Granger causality test showed significant positive temporal associations between the temperature and the CAR, indicating that the temperatu…
North Atlantic Oscillation recorded in carbonate δ18O signature from Lagunillo del Tejo (Spain)
2016
Abstract Oxygen (δ18O) and carbon (δ13C) isotope compositions of authigenic carbonates measured in Lagunillo del Tejo sediment document precipitation variability during the last millennium in the Iberian Range. Modern water samples show that Lagunillo δ18O and δD plot below the Global Meteoric Water Line (GMWL). Sediment samples show a covariant trend between carbonate δ18O and δ13C, indicating that the precipitation/evaporation ratio has largely controlled the isotopic composition of this lake. This covariant trend is used to extract information about past lake level changes. Humid periods occurred around AD 1300–1450, AD 1620–1775 and AD 1950–1980, while the driest periods were concentrat…
Trilobites from the Red Fauna (latest Emsian, Devonian) of Hamar Laghdad, Morocco and their biodiversity
2018
36 pages; International audience; Trilobites are widespread in Early Devonian deposits of north Gondwana; some of the most emblematic ones were collected from the famous latest Emsian (Early Devonian) mudmound locality Hamar Laghdad in south-eastern Morocco. This locality is famous for its trilobites, especially for the conspicuous red-coloured remains of phacopid trilobites with often greenish eyes. Here, we present a taxonomic revision of the previously described trilobites from the so-called Red Fauna of Hamar Laghdad. We introduce the new taxa Harpes hamarlaghdadensis n. sp. and Morocops davidbrutoni n. sp. Phacopids dominate the trilobite assemblage from the Red Cliff at Hamar Laghdad …
Last Interglacial Iberian Neandertals as fisher-hunter-gatherers.
2020
Fruits of the sea The origins of marine resource consumption by humans have been much debated. Zilhão et al. present evidence that, in Atlantic Iberia's coastal settings, Middle Paleolithic Neanderthals exploited marine resources at a scale on par with the modern human–associated Middle Stone Age of southern Africa (see the Perspective by Will). Excavations at the Figueira Brava site on Portugal's Atlantic coast reveal shell middens rich in the remains of mollusks, crabs, and fish, as well as terrestrial food items. Familiarity with the sea and its resources may thus have been widespread for residents there in the Middle Paleolithic. The Figueira Brava Neanderthals also exploited stone pine…
Les ammonites du Pliensbachien du jebel Bou Rharraf (Haut Atlas oriental, Maroc).
2011
60 pages; International audience; L'originalité des dépôts sédimentaires et des faunes d'ammonites du jebel Bou Rharraf repose sur la présence de faciès « Ammonitico Rosso », les plus occidentaux connus pour le Pliensbachien, une forte diversité des Phylloceratida (Phylloceras, Calaiceras, Zetoceras, Partschiceras et Juraphyllites) et une disparité morphologique importante chez les Galaticeras, Miltoceras et les Tauromeniceras. Si quelques formes, telles que Miltoceras taguendoufi et Mauretaniaceras elmii nov. gen., nov. sp. ont un cachet endémique très affirmé, les faunes du Pliensbachien du Haut Atlas oriental sont classiques pour la marge sud de la Téthys occidentale. Trois genres (Callo…
Oogenesis and reproductive investment of Atlantic herring are functions of not only present but long-ago environmental influences as well
2017
Following general life history theory, immediate reproductive investment (egg mass × fecundity/body mass) in oviparous teleosts is a consequence of both present and past environmental influences. This clarification questions the frequent use of season-independent (general) fecundity formulas in marine fish recruitment studies based on body metrics only. Here we test the underlying assumption of no lag effect on gametogenesis in the planktivorous, determinate-fecundity Atlantic herring (Clupea harengus) displaying large plasticity in egg mass and fecundity, examining Norwegian summer–autumn spawning herring (NASH), North Sea autumn-spawning herring (NSAH), and Norwegian spring-spawning herri…