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Registros recuperados: 15
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Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene 5
Baker, Andrea; Pedentchouk, Nikolai; Routh, Joyanto; Roychoudhury, Alakendra N..
It has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the late Pleistocene. A key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions. Southern Africa's contemporary C-3 and C-4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones; however, the region is generally archive poor due to its overall semi-arid climate and high relief topography. The Mfabeni peatland, with a basal age of c. 47 k yrs calibrated before present (kcal yr BP), is one of the oldest continuous coastal peat deposits...
Tipo: Text Palavras-chave: Holocene; Pleistocene; Paleoclimatology; Southern Africa; Stable isotopes; Continental biomarkers; Peatland.
Ano: 2017 URL: https://archimer.ifremer.fr/doc/00420/53176/83104.pdf
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Cooling of the South China Sea by the Toba eruption and correlation with other climate proxies similar to 71,000 years ago 5
Huang, Cy; Zhao, M; Wang, Cc; Wei, Gj.
The Toba tephra layer has been identified in core MD972151 in the southern South China Sea (SCS), northeast of the Indonesia Toba caldera. This affords us an opportunity to directly determine a 1 degreesC cooling for ca.l kyr on the SCS following the Toba eruption (71 Ka) during the marine isotope stage 5a-4 transition, using century-scale sea surface temperature records. This cooling event in the SCS is well correlated with several coeval proxies such as increased East Asia winter monsoon intensity, increased ice-rafted detritus in the North Pacific Ocean sediments, and decreased delta O-18 in Greenland ice core. Such correlation suggests a climate change where cold climate signals originated in the Northern Hemisphere ice sheets, transferred southward by...
Tipo: Text Palavras-chave: Paleoclimatology; Ocean prediction; Volcanoclastic deposits.
Ano: 2001 URL: https://archimer.ifremer.fr/doc/00221/33202/31797.pdf
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Deep sea sedimentary analogs for the Vostok ice core 5
Mortyn, Pg; Charles, Cd; Ninnemann, Us; Ludwig, K; Hodell, Da.
Many applications of the Vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent Southern Ocean. Here we present oxygen isotopic records from high accumulation rate sites in the South Atlantic sector of the Southern Ocean, collected for the purpose of complementing the recently extended deltaD record from the Vostok ice core. The combination of several planktonic foraminiferal delta(18)O records from northern subantarctic piston cores demonstrates that all of the millennial-scale oscillations expressed in the Vostok ice core over the last 60 ky are also present in marine records. The observations also support the assumption that the millennial-scale oscillations common to both marine and ice archives...
Tipo: Text Palavras-chave: Paleoclimatology; Paleoceanography; Meteorology and atmospheric dynamics : paleoclimatology.
Ano: 2003 URL: https://archimer.ifremer.fr/doc/00226/33707/32126.pdf
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Ice-age variability from the Vostok deuterium and deuterium excess records 5
Yiou, P; Vimeux, F; Jouzel, J.
The four climatic cycles obtained from the Vostok ice core offer a unique opportunity to study the high-frequency paleoclimatic variability, i.e., on time scales smaller than 15 kyr. We focused our study on the deuterium (deltaD) and deuterium excess (d) records, which are proxies for local temperature and remote evaporation source temperature and hence give us access to spatial climatic variations. Spectral analyses of paleoclimatic records have shown that the last glacial period (110-15 kyr before present) is characterized by large and fast temperature oscillations. Examples of such variations in the Northern Hemisphere are the so-called Dansgaard-Oeschger oscillations and Heinrich events. At Vostok, these oscillations are also imprinted in the ice, with...
Tipo: Text Palavras-chave: Climate dynamics; Antarctica; Meteorology and Atmospheric Dynamics; Paleoclimatology; Paleoceanography.
Ano: 2001 URL: https://archimer.ifremer.fr/doc/00221/33219/31699.pdf
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Ice-shelf collapse from subsurface warming as a trigger for Heinrich events 5
Marcott, Shaun A.; Clark, Peter U.; Padman, Laurie; Klinkhammer, Gary P.; Springer, Scott R.; Liu, Zhengyu; Otto-bliesner, Bette L.; Carlson, Anders E.; Ungerer, Andy; Padman, June; He, Feng; Cheng, Jun; Schmittner, Andreas.
Episodic iceberg-discharge events from the Hudson Strait Ice Stream (HSIS) of the Laurentide Ice Sheet, referred to as Heinrich events, are commonly attributed to internal ice-sheet instabilities, but their systematic occurrence at the culmination of a large reduction in the Atlantic meridional overturning circulation (AMOC) indicates a climate control. We report Mg/Ca data on benthic foraminifera from an intermediate-depth site in the northwest Atlantic and results from a climate-model simulation that reveal basin-wide subsurface warming at the same time as large reductions in the AMOC, with temperature increasing by approximately 2 C over a 1-2 kyr interval prior to a Heinrich event. In simulations with an ocean model coupled to a thermodynamically...
Tipo: Text Palavras-chave: Paleoceanography; Paleoclimatology; Abrupt climate change.
Ano: 2011 URL: https://archimer.ifremer.fr/doc/00227/33819/32479.pdf
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Independent tephrochronological evidence for rapid and synchronous oceanic and atmospheric temperature rises over the Greenland stadial-interstadial transitions between ca. 32 and 40 ka b2k 5
Berben, Sarah M.p.; Dokken, Trond M.; Abbott, Peter M.; Cook, Eliza; Sadatzki, Henrik; Simon, Margit H; Jansen, Eystein.
Understanding the dynamics that drove past abrupt climate changes, such as the Dansgaard-Oeschger (DO) events, depends on combined proxy evidence from disparate archives. To identify leads, lags and synchronicity between different climate system components, independent and robust chronologies are required. Cryptotephrochronology is a key geochronological tool as cryptotephra horizons can act as isochrons linking disparate and/or distant records. Here, we investigated marine sediment core MD99-2284 from the Norwegian Sea to look for previously identified Greenland ice core cryptotephra horizons and define time-parallel markers between the archives. We explored potential secondary transport and depositional mechanisms that could hamper the isochronous...
Tipo: Text Palavras-chave: Quaternary; Paleoclimatology; Paleoceanography; North Atlantic; Sedimentology; Marine cores; Ice cores; Cryptotephrochronology; DO-Events; Synchronization.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00622/73391/72606.pdf
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Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay 5
Cronin, Tm; Dwyer, Gs; Kamiya, T; Schwede, S; Willard, Da.
We present paleoclimate evidence for rapid (< 100 years) shifts of similar to 2-4 degreesC in Chesapeake Bay (CB) temperature similar to 2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (similar to 1400-1900 AD) and the Medieval Warm Period (similar to 800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between similar to450. and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous...
Tipo: Text Palavras-chave: Paleoclimatology; Holocene; Medieval Warm Period; Little Ice Age; 20th century climate; North Atlantic Oscillation.
Ano: 2003 URL: https://archimer.ifremer.fr/doc/00225/33648/32092.pdf
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New Holocene pollen records from the Brazilian Caatinga 42
MEDEIROS,VANDA B. DE; OLIVEIRA,PAULO E. DE; SANTOS,RUDNEY A.; BARRETO,ALCINA M.F.; OLIVEIRA,MARCELO A.T. DE; PINAYA,JORGE L.D..
Abstract We present two pollen diagrams from the semi-arid Caatinga of the Catimbau National Park, in Pernambuco and from a Mauritia palm forest in the Caatinga/Cerrado ecotone of southern Piauí, NE Brazil, spanning the last 10,000 cal. yrs BP and the last 1,750 cal yrs BP, respectively. These two records contain a signature of the local vegetation and permit the correlation of the pollen signal with regional climatic changes. The Catimbau record shows Zizyphus sp., a typical Caatinga taxon, in all three pollen zones indicating regional Caatinga vegetation and the predominance of local arboreal taxa adapted to high humidity from 10,000 to ca. 6,000 cal. yrs BP with a gradual tendency towards drier conditions revealed by a deposition hiatus between 6,000 to...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Paleoclimatology; Palynology; Pernambuco; Piauí; Caatinga vegetation.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652018000502011
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Oxygen isotope disequilibrium in the juvenile portion of oyster shells biases seawater temperature reconstructions 5
Huyghe, Dimitri; Emmanuel, Laurent; De Rafelis, Marc; Renard, Maurice; Ropert, Michel; Labourdette, Nathalie; Lartaud, Franck.
For decades, bivalve shells have constituted one of the most common supports for paleoclimatic archives based on stable isotope approaches. In this work, we conducted chemical marking and recapture techniques to study the fluctuation of δ18O values of oyster shells of the species Magallana gigas reared in natural environment in Normandy (France) for two years. The results were compared to the continuous monitoring of temperature and salinity and monthly records of seawater δ18O. Isotopic measurements were performed on the hinge area that regroups the whole life of the oysters. Here we demonstrate that oysters mineralized their shells with no significant growth breaks during the two-years experiment, even at temperatures below 6 °C. The results confirm that...
Tipo: Text Palavras-chave: Stable isotopes; Paleoclimatology; Sclerogeochemistry; Sclerochronology; Kinetic isotope effect.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00624/73622/73038.pdf
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Oxygen isotope/salinity relationship in the northern Indian Ocean 5
Delaygue, G; Bard, E; Rollion, C; Jouzel, J; Stievenard, M; Duplessy, Jc; Ganssen, G.
We analyze the surface sigma O-18 - salinity relationships of the Bay of Bengal and the Arabian Sea, in the northern Indian Ocean, known for their contrasting hydrological conditions. New measurements of these tracers show a very low sigma O-18 - salinity slope associated with the strong dilution in the Bay of Bengal, but a slope more typical of this latitude in the Arabian Sea. Although this region is marked by a complex monsoonal regime, numerical modeling using a box model and a general circulation model is able to capture the sigma O-18 - salinity slope and its geographical variation. Both models clearly show that the low sigma O-18 - salinity slope is due to the evaporation-minus-precipitation balance, with an important contribution of the continental...
Tipo: Text Palavras-chave: Indian Ocean; Ocean/atmosphere interactions; Paleoclimatology; Stable isotopes.
Ano: 2001 URL: https://archimer.ifremer.fr/doc/00221/33225/31800.pdf
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Palynological analysis of a late Holocene core from Santo Antônio da Patrulha, Rio Grande do Sul, Southern Brazil 42
Macedo,Renato B.; Souza,Paulo A.; Bauermann,Soraia G.; Bordignon,Sérgio A.L..
A sedimentar core collected at Santo Antônio da Patrulha, Rio Grande do Sul State, southmost Brazil, was submitted to pollen analysis to provide the vegetational history of this region, and the paleoecological and paleoclimatic changes. A total of 98 taxa of palynomorphs was identified from 35 subsamples. Three radiocarbonic datings were obtained along a section of 115 cm depth, including the basal age of 4730 ± 50 yr BP. Pollen diagrams and cluster analysis were performed based on palynomorphs frequencies, demonstrating five distinct phases (SAP-I to SAP-V), which reflected different paleoecological conditions. The predominance of plants associated with grasslands in the phase SAP-I suggests warm and dry climate conditions. A gradual increasing of...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Palynology; Paleoecology; Paleoclimatology; Atlantic rainforest; Late Holocene; Rio Grande do Sul State.
Ano: 2010 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652010000300020
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Phase lag between Intertropical Convergence Zone migration and subtropical monsoon onset over the northwestern Indian Ocean during Marine Isotopic Substage 6.5 (MIS 6.5) 5
Malaize, B.; Joly, C.; Venec-peyre, M. -t.; Bassinot, F.; Caillon, N.; Charlier, K..
High-resolution faunal and isotopic analyses of foraminifera were performed on core MD96-2073 (10 degrees 94'N, 52 degrees 62'E, 3142 m depth), located close to Socotra Island in the upwelling area of the Somali Basin ( NW Indian Ocean). This work focuses on Marine Isotopic Stage 6.5 in order to reconstruct paleo-upwelling changes and their links with the Arabian Sea summer monsoon and the migration of the Intertropical Convergence Zone (ITCZ). Correspondence and cluster analyses of planktonic foraminiferal abundances, partly controlled by temperature and water mass productivity, together with an upwelling intensification index, show the occurrence of a strong upwelling between 176 and 165 ka. This upwelling intensification responds to a northward...
Tipo: Text Palavras-chave: Paleoclimatology; Foraminifera; Isotopes; Indian monsoon; ITCZ; Sapropels; Upwelling.
Ano: 2006 URL: https://archimer.ifremer.fr/doc/00234/34487/33433.pdf
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Population ecology and shell chemistry of a phytal ostracode species (Loxoconcha matagordensis) in the Chesapeake Bay watershed 5
Vann, Cd; Cronin, Tm; Dwyer, Gs.
Population ecology and shell chemistry were studied in the phytal ostracode Loxoconcha matagordensis (Swain 1955) collected from Zostera marina seagrass beds in the Chesapeake Bay to provide seasonal constraints on shell secretion time for paleothermometry. Population density and age structure were defined by two main breeding cycles that occurred between 01 to 15 June and 02 to 16 August 2001. The time interval between breeding cycles was similar to2 months and total juvenile standing crop increased almost three-fold between the first and second breeding cycles. Dark brown over-wintered adults comprised the majority of the population between March and April 2001, while newly secreted translucent adults were predominant between June and September. Seasonal...
Tipo: Text Palavras-chave: Ostracoda; Paleoclimatology; Ecology; Minor elements; Holocene; Seagrass.
Ano: 2004 URL: https://archimer.ifremer.fr/doc/00229/33995/32356.pdf
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Reconstruction of full glacial environments and summer temperatures from Lago della Costa, a refugial site in Northern Italy 5
Samartin, Stephanie; Heiri, Oliver; Kaltenrieder, Petra; Kühl, Norbert; Tinner, Willy.
Vegetation and climate during the last ice age and the Last Glacial Maximum (LGM, similar to 23,000-19,000 cal BP) were considerably different than during the current interglacial (Holocene). Cold climatic conditions and growing ice-sheets during the last glaciation radically reduced forest extent in Europe to a restricted number of so-called "refugia", mostly located in the southern part of the continent. On the basis of paleobotanical analyses the Euganian Hills (Colli Euganei) in northeastern Italy have previously been proposed as one of the northernmost refugia of temperate trees (e.g. deciduous Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Abies alba, Fagus sylvatica, Carpinus and Castanea) in Europe. In this study we provide the first...
Tipo: Text Palavras-chave: Chironomids; Refugia; Vegetation; Northern Italy; Mediterranean; Climate; Last Glacial; LGM; Heinrich events; Paleoecology; Paleoclimatology.
Ano: 2016 URL: https://archimer.ifremer.fr/doc/00421/53234/54773.pdf
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Recording of ocean-climate changes during the last 2,000 years in a hypoxic marine environment off northern Chile (23°S) 97
ORTLIEB,LUC; ESCRIBANO,RUBEN; FOLLEGATI,RENZO; ZUÑIGA,OSCAR; KONG,ISMAEL; RODRIGUEZ,LUIS; VALDES,JORGE; GUZMAN,NURY; IRATCHET,PAOLA.
Atmosphere-ocean interactions are particularly strong along the Chile-Peru coast and largely account for the extreme aridity of the Atacama Desert. Near the center of the driest part of this coastal desert, we found that the embayment Bahía Mejillones constitutes an unusually favorable setting for the formation and subsequent preservation of a sedimentary record of the successive oceanographic conditions of the last few thousand years. This work deals with relative abundance of various bio-indicators, including fish scales, foraminifers and phytoplankton, with a centimetre-scale resolution, in several gravity cores taken from 80 to 120 m depth, in a low-oxygen environment. We use this information to document ocean-climate changes at decadal to centennial...
Tipo: Journal article Palavras-chave: Bioindicators; Paleoceanography; Paleoclimatology; Northern-Chile; Low-oxygen sediments.
Ano: 2000 URL: http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2000000200002
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