PANGAEA - Publishing Network for Geoscientific & Environmental Data
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Datasets with PANGAEA technical keyword @margo
Mostrando recursos 1 - 20 de 180
Geochemical investigations of sediment profiles in the Norwegian-Greenland Sea - Voelker, Antje HL
High-, i.e. 15-140-yr-resolution climate records from sediment cores 23071, 23074, and PS2644 from the Nordic Seas were used to recon:;truct changes in the surface and deep water circulation during marine isotope stages 1-5.1, i.e. the last 82 000 yr. From this the causal links between the paleoceanographic signals and the Dansgaard-Oeschger events 1-21 revealed in 0180-ice-core records from Greenland were determined. The stratigraphy of the cores is based on the planktic 0180 curves, the minima of which were directly correlated with the GISP2-0180 record, numerous AMS 14C ages, and some ash layers.
The planktic d18O and dl3C curves of all three...
Carbon and alkenone analysis on sediment core MD97-2151 - Zhao, Meixun; Huang, Chi-Yue; Wang, Chia-Chun; Wei, Ganjian
We report 150 kyr records of U37K' sea-surface temperature (SST) and carbonate content with 150-200-year sampling resolution from the southern South China Sea (SCS) in the northern margin of the Western Pacific Warm Pool (WPWP) using IMAGES Core MD972151. The glacial/interglacial SST change is about 5 °C for Termination II (23.5 to 28.5°C) and 4°C for Termination I (24 to 28°C). The simultaneous rise of sea level and U37K' SST during Termination I suggests that sea-level change has played an important role in the SCS SST variability by influencing the exchange of tropical ocean warm surface water with the SCS...
Glacial Mediterranean sea surface tempertures based on planktonic foraminiferal assemblages - Hayes, Angela; Kucera, Michal; Kallel, Nejib; Sbaffi, Laura; Rohling, Eelco J
We present a new reconstruction of Mediterranean sea surface temperatures (SST) during the last glacial maximum (LGM). A calibration data set based on census counts of 23 species of planktonic foraminifera in 129 North Atlantic and 145 Mediterranean core top samples was used to develop summer, winter and annual average SST reconstructions using artificial neural networks (ANNs) and the revised analogue method (RAM). Prediction errors determined by cross-validation of the calibration data set ranged between 0.5 and 1.1 °C, with both techniques being most successful in predicting winter SSTs. Glacial reconstructions are based on a new, expanded data set of...
Reconstruction of sea-surface temperatures from asseblages of planktonic foraminifera - Kucera, Michal; Weinelt, Mara; Kiefer, Thorsten; Pflaumann, Uwe; Hayes, Angela; Weinelt, Martin; Chen, Min-Te; Mix, Alan C; Barrows, Timothy T; Cortijo, Elsa; Duprat, Josette; Juggins, Steve; Waelbroeck, Claire
We present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts. This approach is based on simultaneous application of a variety of transfer function techniques, which are trained on geographically constrained calibration data sets. It serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples, allowing identification of adverse effects of no-analog faunas and technique-specific bias. We have compiled new calibration data sets for the North (N=862) and South (N=321) Atlantic and the Pacific Ocean (N=1111)....
Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere - de Vernal, Anne; Eynaud, Frédérique; Henry, Maryse; Hillaire-Marcel, Claude; Londeix, Laurent; Mangin, Sylvie; Matthiessen, Jens; Marret, Fabienne; Radi, Taoufik; Rochon, André; Solignac, Sandrine; Turon, Jean-Louis
A new calibration database of census counts of organic-walled dinoflagellate cyst (dinocyst) assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the Northern Hemisphere after standardisation of taxonomy and laboratory procedures. The database comprises 940 reference data points from the North Atlantic, Arctic and North Pacific oceans and their adjacent seas, including the Mediterranean Sea, as well as epicontinental environments such as the Estuary and Gulf of St. Lawrence, the Bering Sea and the Hudson Bay. The relative abundance of taxa was analysed to describe the distribution of assemblages. The best...
A global compolation of late Holocene planktonic foraminiferal d18O - Waelbroeck, Claire; Mulitza, Stefan; Spero, Howard J; Dokken, Trond; Kiefer, Thorsten; Cortijo, Elsa
We review the different sources of uncertainty affecting the oxygen isotopic composition of planktonic foraminifera and present a global planktonic foraminifera oxygen isotope data set that has been assembled within the MARGO project for the Late Holocene time slice. The data set consists of over 2100 data from recent sediment with thorough age control, that have been checked for internal consistency. We further examine how the oxygen isotopic composition of fossil foraminifera is related to hydrological conditions, based on published results on living foraminifera from plankton tows and cultures. Oxygen isotopic values (delta18O) of MARGO recent fossil foraminifera are 0.2-0.8...
Stable isotope record of planktonic foraminifera from sediment core MD96-2085 - Chen, Min-Te; Chang, Yuan-Pin; Chang, Cheng-Chieh; Wang, Liping; Wang, Chung-Ho; Yu, Ein-Fen
A high-resolution (~4-5cm/kyr) giant piston core record (MD962085) retrieved during an IMAGES II-NAUSICAA cruise from the continental slope of the southeast Atlantic Ocean reveals striking variations in planktonic foraminifer faunal abundances and sea-surface temperatures (SST) during the past 600 000 yr. The location and high-quality sedimentary record of the core provide a good opportunity to assess the variability of the Benguela Current system and associated important features of the ocean-climate system in the southeast Atlantic. The planktonic foraminifer faunal abundances of the core are dominated by three assemblages: (1) Neogloboquadrina pachyderma (right coiling) + Neogloboquadrina dutertrei, (2) Globigerina bulloides, and...
Lithology, micropaleontology and isotope record of sediments from the Nordic Seas - Bauch, Henning A; Erlenkeuser, Helmut; Spielhagen, Robert F; Struck, Ulrich; Matthiessen, Jens; Thiede, Jörn; Heinemeier, Jan
On the basis of various lithological, mircopaleontological and isotopic proxy records covering the last 30,000 calendar years (cal kyr) the paleoenvironmental evolution of the deep and surface water circulation in the subarctic Nordic seas was reconstructed for a climate interval characterized by intensive ice-sheet growth and subsequent decay on the surrounding land masses. The data reveal considerable temporal changes in the type of thermohaline circulation. Open-water convection prevailed in the early record, providing moisture for the Fennoscandian-Barents ice sheets to grow until they reached the shelf break at ~26 cal. kyr and started to deliver high amounts of ice-rafted debris...
Age determination and stable isotope record of foraminifera of sediment core SO82_5-2 - van Kreveld, Shirley A; Sarnthein, Michael; Erlenkeuser, Helmut; Grootes, Pieter Meiert; Jung, Simon J A; Pflaumann, Uwe; Voelker, Antje HL
Surface and deepwater paleoclimate records in Irminger Sea core SO82-5 (59°N, 31°W) and Icelandic Sea core PS2644 (68°N, 22°W) exhibit large fluctuations in thermohaline circulation (THC) from 60 to 18 calendar kyr B.P., with a dominant periodicity of 1460 years from 46 to 22 calendar kyr B.P., matching the Dansgaard-Oeschger (D-O) cycles in the Greenland Ice Sheet Project 2 (GISP2) temperature record [Grootes and Stuiver, 1997, doi:10.1029/97JC00880]. During interstadials, summer sea surface temperatures (SSTsu) in the Irminger Sea averaged to 8°C, and sea surface salinities (SSS) averaged to ~36.5, recording a strong Irminger Current and Atlantic THC. During stadials, SSTsu...
Sedimentology, organic geochemistry, and stable isotopes of core PS2138-1 - Knies, Jochen; Stein, Ruediger
We studied variations in terrigenous (TOM) and marine organic matter (MOM) input in a sediment core on the northern Barents Sea margin over the last 30 ka. Using a multiproxy approach, we reconstructed processes controlling organic carbon deposition and investigated their paleoceanographic significance in the North Atlantic-Arctic Gateways. Variations in paleo-surface-water productivity are not documented in amount and composition of organic carbon. The highest level of MOM was deposited during 25-23 ka as a result of scavenging on fine-grained, reworked, and TOM-rich material released by the retreating Svalbard/Barents Sea ice sheet during the late Weichselian. A second peak of MOM...
Sea-surface temperature and sea ice distribution of the Southern Ocean at the EPILOG Last Glacial Maximum - Gersonde, Rainer; Crosta, Xavier; Abelmann, Andrea; Armand, Leanne K
Based on the quantitative study of diatoms and radiolarians, summer sea-surface temperature (SSST) and sea ice distribution were estimated from 122 sediment core localities in the Atlantic, Indian and Pacific sectors of the Southern Ocean to reconstruct the last glacial environment at the EPILOG (19.5-16.0 ka or 23 000-19 000 cal yr. B.P.) time-slice. The statistical methods applied include the Imbrie and Kipp Method, the Modern Analog Technique and the General Additive Model. Summer SSTs reveal greater surface-water cooling than reconstructed by CLIMAP (Geol. Soc. Am. Map Chart. Ser. MC-36 (1981) 1), reaching a maximum (4-5 °C) in the present...
Age models and stable isotope record of sediment cores from the Atlantic Ocean - Oppo, Delia W; Fairbanks, Richard G
The high-resolution delta18O and delta13C records of benthic foraminifera from a 150,000-year long core from the Caribbean Sea indicate that there was generally high delta13C during glaciations and low delta13C during interglaciations. Due to its 1800-m sill depth, the properties of deep water in the Caribbean Sea are similar to those of middepth tropical Atlantic water. During interglaciations, the water filling the deep Caribbean Sea is an admixture of low delta13C Upper Circumpolar Water (UCPW) and high delta13C Upper North Atlantic Deep Water (UNADW). By contrast, only high delta13C UNADW enters during glaciations. Deep ocean circulation changes can influence atmospheric...
Age determination of North Atlantic sediment cores - Bard, Edouard; Fairbanks, Richard G; Maurice, Pierre; Duprat, Josette; Moyes, Jean; Duplessy, Jean-Claude
Coupled measurements of delta18O and accelerator mass spectrometry (AMS) 14C in a particular species of planktonic foraminifera may be used to calculate sea-level estimates for the last deglaciation. Of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth, which can be provided by delta18O measurements of modern shells (core tops, plankton tows). Isotopic (delta18O, AMS-14C dating) and faunal records (transfer function sea surface temperature) were obtained from two cores in the North Atlantic at about 37°N. The locations were chosen to obtain high sedimentation rate records removed from the major ice-melt discharge areas...
Stable isotope record of sediment cores from the North Atlantic - Duplessy, Jean-Claude; Labeyrie, Laurent D; Arnold, Maurice; Paterne, Martine; Duprat, Josette; van Weering, Tjeerd CE
Abrupt and short climate changes, such as the Younger Dryas, punctuated the last glacial-to-interglacial transition (Ruddiman and McIntyre, 1981 doi:10.1016/0031-0182(81)90097-3; Duplessy et al., 1981 doi:10.1016/0031-0182(81)90096-1; Oeschger et al. 1984; Broecker et al., 1985 doi:10.1038/315021a0). Broecker et al. (1988 doi:10.1029/PA003i001p00001) proposed that these may have been caused by an interruption of thermohaline circulation as inputs of glacial meltwater freshened the surface waters of the North Atlantic. The finding (Fairbanks, 1989 doi:10.1038/342637a0) that meltwater discharge was minimal during the Younger Dryas, however, led to the suggestion that the surface-water salinity drop might have been caused instead by changes in the freshwater budget...
Stable carbon and oxygen isotope ratios of benthic foraminifera - Curry, William B; Duplessy, Jean-Claude; Labeyrie, Laurent D; Shackleton, Nicholas J
Carbon isotopic measurements on the benthic foraminiferal genus Cibicidoides document that mean deep ocean delta13C values were 0.46 per mil lower during the last glacial maximum than during the Late Holocene. The geographic distribution of delta13C was altered by changes in the production rate of nutrient-depleted deep water in the North Atlantic. During the Late Holocene, North Atlantic Deep Water, with high delta13C values and low nutrient values, can be found throughout the Atlantic Ocean, and its effects can be traced into the southern ocean where it mixes with recirculated Pacific deep water. During the glaciation, decreased production of North...
Foraminiferal faunal estimates of paleotemperature: Circumventing the no-analog problem yields cool ice age tropics - Mix, Alan C; Morey, Ann E; Pisias, Nicklas G; Hostetler, Steven W
The sensitivity of the tropics to climate change, particularly the amplitude of glacial-to-interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no-analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods. A new calibration strategy developed here, which uses past variability of species to define robust faunal assemblages, solves the no-analog problem and reveals ice age cooling of 5° to 6°C in the equatorial current systems of the Atlantic and eastern Pacific...