Search results for "CELL"
showing 10 items of 65972 documents
Evaluating the potential of tree-ring methodology for cross-dating of three annually laminated stalagmites from Zoolithencave (SE Germany)
2019
Abstract Three small stalagmites from Zoolithencave (southern Germany) show visible laminae, which consist of a clear and a brownish, pigmented layer pair. This potentially provides the opportunity to construct precise chronologies by counting annual laminae. The growth period of the three stalagmites was constrained by the 14C bomb peak in the youngest part of all three stalagmites and 14C-dating of a piece of charcoal in the consolidated base part of stalagmite Zoo-rez-2. These data suggest an age of AD 1970 for the top laminae and a lower age limit of AD 1973–1682 or AD 1735–1778. Laminae were counted and their thickness determined on scanned thin sections of all stalagmites. On stalagmi…
Speleothems from the Middle East: An Example of Water Limited Environments in the SISAL Database
2019
The Middle East (ME) spans the transition between a temperate Mediterranean climate in the Levant to hyper-arid sub-tropical deserts in the southern part of the Arabian Peninsula (AP), with the complex alpine topography in the northeast feeding the Euphrates and Tigris rivers which support life in the Southeastern Fertile Crescent (FC). Climate projections predict severe drying in several parts of the ME in response to global warming, making it important to understand the controls of hydro-climate perturbations in the region. Here we discuss 23 ME speleothem stable oxygen isotope (δ18Occ) records from 16 sites from the SISAL_v1 database (Speleothem Isotope Synthesis and Analysis database), …
Carbon-isotope records of the Early Jurassic (Toarcian) Oceanix Anixic Event from the Valdorbia (Umbria-Marche Apennines) and Monte Mangart (Julian A…
2009
The Toarcian oceanic anoxic event (ca 183 Ma) coincides with a global perturbation marked by enhanced organic carbon burial and a general decrease in calcium carbonate production, probably triggered by changes in the composition of marine plankton and elevated carbon dioxide levels in the atmosphere. This study is based on high-resolution sampling of two stratigraphic successions, located in Valdorbia (Umbria-Marche Apennines) and Monte Mangart (Julian Alps), Italy, which represent expressions of the Toarcian oceanic anoxic event in deep-water pelagic sediments. These successions are characterized by the occurrence of black shales showing relatively low total organic carbon concentrations (…
Isotopic seawater temperatures in the Albian Gault Clay of the Boulonnais (Paris Basin): Palaeoenvironmental implications
2016
13 pages; International audience; Oxygen isotopes were measured on several types of fossil hardparts from the Gault Clay Formation including benthic and planktonic foraminifera, belemnite guards, and fish small-teeth. Belemnites δ18O values indicate low temperatures (13.5–19.3 °C) with an increase from the Middle to Late Albian. Foraminifera provide variable δ18O values, some too low to be relevant in terms of temperature (until 42 °C). These low values probably result from a diagenetic alteration of the foraminiferal tests even though SEM observations revealed well-preserved microstructures. However, higher foraminiferal δ18O values recorded in some levels indicate temperatures in the rang…
The revolution of crossdating in marine palaeoecology and palaeoclimatology.
2019
Over the past century, the dendrochronology technique of crossdating has been widely used to generate a global network of tree-ring chronologies that serves as a leading indicator of environmental variability and change. Only recently, however, has this same approach been applied to growth increments in calcified structures of bivalves, fish and corals in the world's oceans. As in trees, these crossdated marine chronologies are well replicated, annually resolved and absolutely dated, providing uninterrupted multi-decadal to millennial histories of ocean palaeoclimatic and palaeoecological processes. Moreover, they span an extensive geographical range, multiple trophic levels, habitats and f…
Conflicting objectives in production forests pose a challenge for forest management
2017
Conflicts among different ecosystem services have been shown to be common and potentially exacerbated by management interventions. In order to improve the sustainability of natural resource use, the occurrence of these conflicts and the effects that management actions have on them need to be understood. We studied the conflicts between ecosystem services and the potential to solve them by management choices in boreal production forests. Our study area consisted of nearly 30,000 forest stands which were simulated for 50 years into the future under alternative management scenarios. The study included four ecosystem services – timber production, bilberry production, carbon storage, and pest re…
Timing and duration of European larch growing season along altitudinal gradients in the Swiss Alps.
2009
The 2007 European larch (Larix decidua Mill.) growing season was monitored along two elevational transects in the Lotschental valley in the Swiss Alps. Phenological observations and weekly microcore sampling of 28 larch trees were conducted between April and October 2007 at seven study sites regularly spaced from 1350 to 2150 m a.s.l. on northwest- and southeast-facing slopes. The developmental stages of nearly 75,000 individual cells assessed on 1200 thin sections were used to investigate the links between the trees' thermal regimes and growth phases including the beginning and ending of cell enlargement, wall thickening and maturation of the stem wood. Needles appeared approximately 3-4 w…
Accuracy of IKONOS for mapping benthic coral-reef habitats: a case study from the Puerto Morelos Reef National Park, Mexico
2012
International audience; Reefs are being threatened by global warming, natural disasters, and the increased pressure of the global population. These habitats are in urgent need of mapping at high resolution so that these threats can be quantified. Remote sensing can potentially provide such quantitative data. In this article, we attempt to map benthic coral-reef habitats at the Puerto Morelos Reef National Park in Yucatan Peninsula (Mexico) and to assess the accuracy of the technique in providing a baseline data for future monitoring of changes and evolution of the reef system. An IKONOS image was used in combination with checkpoint ground sampling and classified using a supervised maximum l…
Oxygen respiration rates of benthic foraminifera as measured with oxygen microsensors
2011
Abstract Oxygen respiration rates of benthic foraminifera are still badly known, mainly because they are difficult to measure. Oxygen respiration rates of seventeen species of benthic foraminifera were measured using microelectrodes and calculated on the basis of the oxygen fluxes measured in the vicinity of the foraminiferal specimens. The results show a wide range of oxygen respiration rates for the different species (from 0.09 to 5.27 nl cell−1 h−1) and a clear correlation with foraminiferal biovolume showed by the power law relationship: R = 3.98 10−3 BioVol0.88 where the oxygen respiration rate (R) is expressed in nl O2 h−1 and in μm3 biovolume (BioVol) (n = 44, R2 = 0.72, F = 114, p
Feeding biomechanics of Late Triassic metoposaurids (Amphibia: Temnospondyli): a 3D finite element analysis approach
2017
The Late Triassic freshwater ecosystems were occupied by different tetrapod groups including large-sized anamniotes, such as metoposaurids. Most members of this group of temnospondyls acquired gigantic sizes (up to 5 m long) with a nearly worldwide distribution. The paleoecology of metoposaurids is controversial; they have been historically considered passive, bottom-dwelling animals, waiting for prey on the bottom of rivers and lakes, or they have been suggested to be active mid-water feeders. The present study aims to expand upon the paleoecological interpretations of these animals using 3D finite element analyses (FEA). Skulls from two taxa, Metoposaurus krasiejowensis, a gigantic taxon …