Search results for "Paleoclima"
showing 10 items of 138 documents
Regional endothermy as a trigger for gigantism in some extinct macropredatory sharks
2017
Otodontids include some of the largest macropredatory sharks that ever lived, the most extreme case being Otodus (Megaselachus) megalodon. The reasons underlying their gigantism, distribution patterns and extinction have been classically linked with climatic factors and the evolution, radiation and migrations of cetaceans during the Paleogene. However, most of these previous proposals are based on the idea of otodontids as ectothermic sharks regardless of the ecological, energetic and body size constraints that this implies. Interestingly, a few recent studies have suggested the possible existence of endothermy in these sharks thus opening the door to a series of new interpretations. Accord…
Morphological variations of crossed-lamellar ultrastructures of Glycymeris bimaculata (Bivalvia) serve as a marine temperature proxy
2020
Abstract Bivalve shells are among the most promising archives for high-resolution seawater temperature reconstructions. However, despite major research advances in bivalve sclerochronology over the past decades, estimating water temperature from shells remains a challenging task. This is largely because the most frequently used and widely accepted temperature proxy in bivalves, i.e., the shell oxygen isotope (δ18Oshell) value, also requires knowledge of changes in δ18O of the water (δ18Owater) in which the bivalve lived, which is rarely available for ancient environments. According to a few recent studies, the size and shape of individual biomineral units (BMUs) of the shell ultrastructure …
The Eurasian Modern Pollen Database (EMPD), version 2
2020
The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land cover, and land use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil pollen found in Late Quaternary sedimentary archives throughout the Eurasian region. The EPD is in turn part of the rapidly growing Neotoma database, which is now the primary home for global palaeoecological data. This paper describes version 2 of the EMPD in which the number of samples held in the database has been increased by 60% from 4826 to…
Holocene history of Aleppo pine (Pinus halepensis Mill.) woodlands in the Ebro Basin (NE Spain). Climate-biased or human-induced?
2020
Abstract This paper reviews the past distribution of Aleppo pine woodlands in the Ebro Basin, Northeastern Iberia, from the Mesolithic to Modern times based on wood charcoal data. The aim is to detail the chronological timing and the drivers explaining the long-term presence of Aleppo pine woodlands and associated thermophilous flora. The available charcoal data support the early spread of Pinus halepensis during the Mesolithic (ca. 9000 cal BP) accompanied by Mediterranean trees and shrubs like Quercus sp. evergreen, Juniperus sp., Arbutus unedo, Pistacia lentiscus, Rhamnus/Phillyrea, Cistaceae, and Rosmarinus officinalis, as a local response to global climate change in the Early Holocene.…
Summer drought reconstruction in northeastern Spain inferred from a tree ring latewood network since 1734
2017
Drought recurrence in the Mediterranean is regarded as a fundamental factor for socio-economic development and the resilience of natural systems in context of global change. However, knowledge of past droughts has been hampered by the absence of high-resolution proxies. We present a drought reconstruction for the northeast of the Iberian Peninsula based on a new dendrochronology network considering the Standardized Evapotranspiration Precipitation Index (SPEI). A total of 774 latewood width series from 387 trees of P. sylvestris and P. uncinata were combined in an inter-regional chronology. The new chronology, calibrated against gridded climate data, reveals a robust relationship with the S…
Comparison of quantitative Holocene temperature reconstructions using multiple proxies from a northern boreal lake
2017
Four biotic proxies (plant macrofossils, pollen, chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures ( Tjul) at Lake Loitsana (northern Finland) during the Holocene. The aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest Tjul in the individual reconstructions. The reconstructed Tjul values are evaluated in relation to local-scale/site-specific processes associated with the Holocene lake development at Loitsana as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. While pollen-based temperatures follow…
Long-term summer temperature variations in the Pyrenees from detrended stable carbon isotopes
2015
Abstract Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended δ13C measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century δ13C data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater …
Up-to-date Spanish continental Neogene synthesis and paleoclimatic interpretation
1993
A synthesis of the Spanish continental Neogene is presented by designing an integrated correlative chart of the Neo" gen-e "succes"Siuns-ofthe "lberian-PeninsuIa-. -Ninemain-sedimentary-breaks-have-been -distinguished-in-most-of-the "basins. They are considered a valuable criteria for correlation as they occur in similar time intervals from basin to basin. The determined sedimentary breaks occur in the Agenian, Ramblian, Middle Aragonian, Late Aragonian, Late Vallesian, Middle Turolian, Late Turolian, Late Ruscinian-Early Villafranchian, and Villafranchian ages. The larger interior basins (Ebro, Tajo, Duero) show a fairly complete Neogene sedimentary record in which the aboye mentioned sedi…
Stable isotopes covering 96-7 ka BP from stalagmite CM (Santo Tomas Cave, Cuba)
2020
We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Stable isotope samples were micromilled at a resolution of 0.10-0.33mm, and measured using an IRMS equipped with a Gasbench. Line scans of Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records.
Late Cretaceous continental weathering evolution on the southern Atlantic margins of Africa and South America : contributions of a new geochemical tr…
2022
The late Cretaceous records a pronounced decrease in temperatures on a global scale between 90 and 65 million years that marks the first step of the progressive climatic decline ultimately leading to our modern climate mode. This first cooling step is concomitant to a major tectonic uplift of the east South American and west African margins. Relief formation on the African ans South American continent, enhancing continental weathering, can have induced a climatic cooling at a global scale through atmospheric CO2 consumption linked to silicate weathering reactions. The main objective of this project is to explore the potentially determinant impact of this tectonic uplift on the long-term coo…