Search results for "SYSTEMATICS"
showing 10 items of 6702 documents
Warming or cooling in the Pragian? Sedimentary record and petrophysical logs across the Lochkovian–Pragian boundary in the Spanish Central Pyrenees
2016
Abstract High-resolution petrophysical correlation methods were applied, for the first time, to mid-Paleozoic rocks of the Pyrenees. The methods included magnetic susceptibility measurements (MS), gamma-ray spectrometry (GRS), and alignment of MS logs using the dynamic time-warping (DTW) algorithm. Conodont biostratigraphy provided the basic framework necessary for work with the GRS and MS logs. Despite differences in the sediment patterns and accumulation/erosion rates, the logs from two selected sections in the Spanish Central Pyrenees show a striking symmetry that correlates well with the previously published logs from the Barrandian area in the Czech Republic. The high similarity betwee…
ISOTOPIC TEMPERATURES FROM THE EARLY AND MID-PLIOCENE OF THE US MIDDLE ATLANTIC COASTAL PLAIN, AND THEIR IMPLICATIONS FOR THE CAUSE OF REGIONAL MARIN…
2017
Mean seasonal extreme temperatures on the seafloor calculated from the shell d 18 Oofthescallop Placopecten clintonius from the basal part of the early Pliocene Sunken Meadow Member (Yorktown Formation) in Virginia are very similar to those from the same horizon at the latitude of Cape Hatteras in North Carolina ( ~ 210 km to the south). The lowest and highest temperatures calculated from each shell (using d 18 O seawater ¼þ 0.7 % )givemean values for winter and summer of 8.4 6 1.1 8 C( 6 1 r ) and 18.2 6 0.6 8 CinVirginia,and8.6 6 0.4 8 Cand16.5 6 1.1 8 C in North Carolina (respective median temperatures: 13.3 8 C and 12.6 8 C). Patterns of ontogenetic variation in d 18 O, d 13 C and micro…
Dietary evidence from Central Asian Neanderthals: A combined isotope and plant microremains approach at Chagyrskaya Cave (Altai, Russia).
2021
Neanderthals are known primarily from their habitation of Western Eurasia, but they also populated large expanses of Northern Asia for thousands of years. Owing to a sparse archaeological record, relatively little is known about these eastern Neanderthal populations. Unlike in their western range, there are limited zooarchaeological and paleobotanical studies that inform us about the nature of their subsistence. Here, we perform a combined analysis of carbon and nitrogen stable isotopes on bone collagen and microbotanical remains in dental calculus to reconstruct the diet of eastern Neanderthals at Chagyrskaya Cave in the Altai Mountains of Southern Siberia, Russia. Stable isotopes identify…
Venerid bivalve Venus verrucosa as a high-resolution archive of seawater temperature in the Mediterranean Sea
2021
Abstract High-resolution stable isotope data (δ18O, δ13C) were used to study growth strategies of the bivalve Venus verrucosa collected from three sites of the eastern coast of the Adriatic Sea. The principal objectives of this study were to identify the main growing season and to evaluate the potential applicability of δ18Oshell values to reconstruct the seasonal temperature variability. Calcium carbonate for oxygen and carbon isotope analyses was obtained by drilling the outer shell layer. Temporal and spatial variations in temperature and salinity values at the study sites were simulated using the 3D numerical ocean model ROMS. Annual periodicity of growth patterns was confirmed by δ18Os…
Late Holocene seasonal temperature variability of the western Scottish shelf (St Kilda) recorded in fossil shells of the bivalve Glycymeris glycymeris
2021
Abstract The North Atlantic Ocean and adjacent shelf seas play a crucial role in global climate. To better constrain long-term natural variability and marine-terrestrial linkages in this region, a network of highly resolved marine archives from the open ocean and continental shelves is needed. In recent decades, bivalve sclerochronology has emerged as a field providing such records from the mid- to high latitudes. In May 2014, dead valves and young live specimens of the bivalve Glycymeris glycymeris were collected at St Kilda, Scotland. A floating chronology spanning 187 years was constructed with fossil shells and radiocarbon dated to 3910–3340 cal yr before present (BP), with a probabilit…
Reprint of "Shell oxygen isotope values and sclerochronology of the limpet "Patella vulgata" Linnaeus 1758 from northern Iberia: Implications for the…
2017
Abstract: Understanding environmental conditions faced by hunter-fisher-gatherers during the Pleistocene and Holocene, and interpretation of subsistence strategies, social organisation and settlement patterns, are key topics for the study of past human societies. In this respect, oxygen isotope values (?18O) of mollusc shell calcium carbonate can provide important information on palaeoclimate and the seasonality of shell collection at archaeological sites. In this paper, we tested P. vulgata shells from northern Iberia as a paleoclimate archive through the study of shell oxygen isotope values and sclerochronology of modern samples. Results showed that limpets formed their shells close to is…
The ecogenetic link between demography and evolution: can we bridge the gap between theory and data?
2007
Calls to understand the links between ecology and evolution have been common for decades. Population dynamics, i.e. the demographic changes in populations, arise from life history decisions of individuals and thus are a product of selection, and selection, on the contrary, can be modified by such dynamical properties of the population as density and stability. It follows that generating predictions and testing them correctly requires considering this ecogenetic feedback loop whenever traits have demographic consequences, mediated via density dependence (or frequency dependence). This is not an easy challenge, and arguably theory has advanced at a greater pace than empirical research. Howeve…
Benefits for nurse and facilitated plants emerge when interactions are considered along the entire life-span
2019
The structure of plant communities is often influenced by facilitative interactions where ‘facilitated’ plants benefit from growing associated with ‘nurse’ plants. Facilitation has been mostly studied from the facilitated plant's perspective, and bidirectional effects between nurse and facilitated plants have received less attention. We hypothesized that reciprocal benefits in plant-plant interactions may emerge when interactions are considered along the life-span of the plants involved. Over one spring, we selected five species with similar life-form and growth strategy, and using a full factorial design, we compared different fitness components along the plants’ life-span (seedling establ…
Applicability and consequences of the integration of alternative models for CO<sub>2</sub> transfer velocity into a process-based lake mo…
2019
Abstract. Freshwater lakes are important in carbon cycling, especially in the boreal zone where many lakes are supersaturated with the greenhouse gas carbon dioxide (CO2) and emit it to the atmosphere, thus ventilating carbon originally fixed by the terrestrial system. The exchange of CO2 between water and the atmosphere is commonly estimated using simple wind-based parameterizations or models of gas transfer velocity (k). More complex surface renewal models, however, have been shown to yield more correct estimates of k in comparison with direct CO2 flux measurements. We incorporated four gas exchange models with different complexity into a vertical process-based physico-biochemical lake mo…
Summarizing the state of the terrestrial biosphere in few dimensions
2020
Abstract. In times of global change, we must closely monitor the state of the planet in order to understand the full complexity of these changes. In fact, each of the Earth's subsystems – i.e., the biosphere, atmosphere, hydrosphere, and cryosphere – can be analyzed from a multitude of data streams. However, since it is very hard to jointly interpret multiple monitoring data streams in parallel, one often aims for some summarizing indicator. Climate indices, for example, summarize the state of atmospheric circulation in a region. Although such approaches are also used in other fields of science, they are rarely used to describe land surface dynamics. Here, we propose a robust method to crea…