Search results for "Paleoclima"

Distribution and ecology of the Globigerinoides ruber — Globigerinoides elongatus morphotypes in the Azores region during the late Pleistocene-Holoce…

2018

Abstract Globigerinoides ruber is the dominant taxon in the North Atlantic Subtropical Gyre, nowadays limited to the north by the Azores Current. It is highly sensitive to recent and late Pleistocene Azores Front Current System variability. In this study, we analyse the distribution of five individual morphotypes of the G. ruber – G. elongatus plexus (G. ruber s.s., G. ruber cyclostoma type, G. elongatus, G. elongatus cf.1, G. elongatus pyramidical type) and G. ruber kummerform gr. in a core (ATA13-OF-KT1) collected southwest of the Azores islands and located in a strategical position near the present-day boundary of the Subtropical Gyre/Azores Front Current System (STG/AFCS). Micropaleonto…

The significance of dropstones in a tropical lacustrine setting, eastern Cameros Basin (Late Jurassic–Early Cretaceous, Spain)

2004

International audience; Outsized clasts (mainly white quartzite pebbles) are found in carbonate deposits of the Enciso Group exposed on the northern border of the Cameros rift basin (Late Jurassic – Early Cretaceous, northern Spain). In the Arnedillo section, all the stones are enclosed in micrite, which was assumed deposited in littoral to open lacustrine environments, with minor inputs of deltaic sandstones. The clasts are found in fine-grained lacustrine sediments either as isolated stones or as loosely packed elongated clusters occasionally associated with quartz sands and gravels. The mean size of the clasts is 40 mm (range: 3 – 100 mm); they are polished, well-rounded, and lack any fa…

The transport history of two Saharan dust events archived in an Alpine ice core

2005

Mineral dust from the Saharan desert can be transported across the Mediterranean towards the Alpine region several times a year. When coinciding with snowfall, the dust can be deposited on Alpine glaciers and then appears as yellow or red layers in ice cores. Two such significant dust events were identified in an ice core drilled at the high-accumulation site Piz Zupó in the Swiss Alps (46°22' N, 9°55' E, 3850 m a.s.l.). From stable oxygen isotopes and major ion concentrations, the events were approximately dated as October and March 2000. In order to link the dust record in the ice core to the meteorological situation that led to the dust events, a novel methodology based on b…

Signatures terrigène et volcanique des bassins sédimentaires : implications stratigraphiques et paléoclimatiques

2018

Potential Interactions between Climate and Prehistoric Populations in Southern Morocco: Insights from Archaeological and Paleoclimatic Evidence

2022

Southern Morocco contains a rich archaeological record: engraving, painted rocks, and funerary monuments. This pre-historic and proto-historical heritage offers valuable information about the environmental context of pre-historic settlements. However, the Southern Moroccan archaeological record suffers from dating scarcity. And hence, the difficulty in establishing a reliable chronology. Most of the archaeological sites date from 7000 to 1000 years BP and are marked by a transition period from a humid to dry climate during the late Holocene. The relatively drier conditions likely resulted in adopting a new lifestyle characterized by cattle ranching, agriculture, and animal domestication. Ho…

Comparative sclerochronology of modern and mid-Pliocene (c. 3.5Ma) Aequipecten opercularis (Mollusca, Bivalvia): an insight into past and future clim…

2009

Records of environment contained within the accretionarily deposited tissues of fossil organisms afford a means of detailed reconstruction of past climates and hence of rigorous testing of numerical climate models. We identify the environmental factors controlling oxygen and carbon stable-isotopic composition, and microgrowth-increment size, in the shell of modern examples of the Queen Scallop, Aequipecten opercularis. This understanding is then applied in interpretation of data from mid-Pliocene A. opercularis from eastern England. On the basis of oxygen-isotope evidence we conclude that winter minimum seafloor temperature was similar to present values (typically 6–7 °C) in the adjacent so…

Climate change at the 4.2 ka BP termination of the Indus valley civilization and Holocene south Asian monsoon variability

2003

[1] Planktonic oxygen isotope ratios off the Indus delta reveal climate changes with a multi-centennial pacing during the last 6 ka, with the most prominent change recorded at 4.2 ka BP. Opposing isotopic trends across the northern Arabian Sea surface at that time indicate a reduction in Indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south Asia. The 4.2 ka event is coherent with the termination of urban Harappan civilization in the Indus valley. Thus, drought may have initiated southeastward habitat tracking within the Harappan cultural domain. The late Holocene drought cycles following the 4.2 ka BP event vary between 200 and 800 y…

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 …

Eurhomalea exalbida (Bivalvia): A reliable recorder of climate in southern South America?

2012

Abstract Due to the lack of suitable high-resolution archives, regional and continental-scale climate dynamics of southern South America are not well understood. Shells of the long-lived, shallow-marine bivalve mollusk, Eurhomalea exalbida (Dillwyn), are likely to contain information on the past water temperatures. As yet, however, no rigorous calibration study has been presented so that growth history traits and the reliability of shell oxygen isotope-based temperature estimates remain unknown. Shell growth patterns and oxygen isotope ratios of four young specimens of E. exalbida from the Falkland Islands (Southwest Atlantic) were analyzed and cross-calibrated with environmental parameters…

Tarbellastraea (Scleractinia): A new stable isotope archive for Late Miocene paleoenvironments in the Mediterranean

2008

Abstract Geochemical proxy records of sea surface temperature (SST) or sea surface salinity (SSS) variability on intra- and interannual time-scales in corals from geological periods older than Pleistocene are extremely rare due to pervasive diagenetic alteration of coralline aragonite. Very recently, however, stable isotope data (δ18O, δ13C) from specimens of Porites of Late Miocene age (10 Ma) have been shown to preserve original environmental signatures. In this paper we describe new finds of the zooxanthellate corals Porites and Tarbellastraea in exceptional aragonite preservation from the island of Crete in sediments of Tortonian (∼ 9 Ma) and Early Messinian (∼ 7 Ma) age. Systematic, co…