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The vertical and horizontal distribution of planktonic Foraminifera in Quaternary sediments of the Atlantic Ocean
... In past years, much attention in Russia has been given to the climatic reconstructions for the Mid-Holocene (5-6 kyr B.R; global warming ~1 °C) Eemian (120-125 kyr B.R (stage 5e); ~2 °C), Mid-Pliocene (3.3-4 Myr B.R; ~4 °C) and Last Glacial Maximum (18-20 kyr B.E; Northern Hemisphere summer warming ~-5 °C) (Barash, 1971Barash, , 1985Barash, , 1988 Barash etal., 1980 Barash etal., , 1983 Barash etal., , 1987 Velichko, 1985 Velichko, , 1988 Velichko, , 1989 Velichko et al., 1983 Velichko et al., , 1984 Velichko et al., , 1992 Velichko et al., , 1993 Borzenkova, 1988, 1990; Borzenkova, 1990 Borzenkova, , 1990a Borzenkova, , 1992). A separate list of references refers to the Russian sources. ...
Paleoclimatic reconstructions for the Mid-Holocene, Eemian, Mid-Pliocene and the Last Glacial Maximum are used to test the paleoanalog hypothesis and develop a regional climate change scenario based on a linear scaling by one parameter - the mean Northern Hemispheric temperature change with respect to present, T
NH. The empirical verification of the paleoanalog hypothesis is extended to a cold epoch for zonal means and to regional distributions of temperature in warm epochs. The best agreement among the scaled paleoanomalies from different epochs is obtained if the seasonal temperature anomalies are scaled with T
NH of the corresponding season. Preferential areas are identified where the paleoanalog hypothesis works relatively well; these areas coincide with the areas of the most pronounced warming. It is shown that the geographical distributions of the winter temperature anomalies over land in the paleodata are similar to those in the 1980–1990 period. From the three warm epochs, a paleodata-based scenario is deduced for the spatial distribution of temperature in a future climate, on the scale of continents. The conditions under which scenarios based on paleodata can be applied are discussed.
Based on paleoclimatic reconstructions of three past warm climates, Mid-Holocene, Eem ian and Mid-Pliocene, the verification of paleoanalog hypothesis is extended to regional level for both precipitation and temperature and to mean latitudinal precipitation as well. It is found that paleoanalog hypothesis holds also for zonal temperatures in cold epoch. Last Glacial Maximum.
A typical structure of regional warming and precipitation change is revealed based on the paleoclimatic data. It is shown that over land in temperate northern latitudes the current warming climate generates the similar structure. The observed increase in annual precipitation over NH extratropics agrees with the paleoscenario for precipitation.
Deep-sea cores from the Central Arctic Basin yield significant faunal and lithologic evidence of normal and low salinity cycles superimposed upon temperature fluctuations in late Cenozoic time. Lowest temperatures correspond to the upper Pleistocene (the Brunnes normal polarity epoch), whereas higher temperatures and lower salinities were recorded by planktonic foraminifera during the Matuyama reversed polarity epoch.
Biostratigraphic and lithologic correlations between cores, some with established paleomagnetic stratigraphy, supplemented by radiometric dating and oxygen isotope measurements, were used to estimate ages and sedimentation rates as well as to reconstruct the climatic and oceanographie history of the Arctic.
Ice-rafted detritus throughout the cores indicates that high latitude glaciation commenced prior to 3 million years ago. Three major climatic units may be distinguished. The sediments of unit III were deposited earlier than 2.4 million years B.P., probably during the Gauss normal polarity epoch. Lower-than-present sedimentation rates and/or corrosive deep water may account for the selective solution of the less resistant limy tests and the impoverished character of the fauna. The paucity of the fauna precludes definitive paleoclimatic reconstruction of this period; it is tentatively suggested that environments were similar to those that prevailed during the deposition of the foraminifera-rich layers of unit I. Sediments of unit II, deposited between approximately 2.4 and 0.7 million years ago, during the Matuyama epoch, are poor in both Fe and Mn oxides and in foraminifera but contain one foraminifera-rich layer. Surface water temperatures were generally higher and salinities were lower during this period than in the preceding and following epochs. It is assumed that the Arctic was free of permanent pack-ice in Matuyama time. The Brunnes cold-“warm” temperature fluctuations are represented by 4 to 6 foraminifera-rich, foraminifera-poor sequences, possibly correlative with the classic Donau, Günz, Mindel, Riss, and Würm Glacials and intervening interglacials, respectively. The former were deposited during pack-ice-covered, the latter in seasonally pack-ice-free periods.
An apparent correspondence between geomagnetic polarity reversals and climatic changes exists.
The record of climatic changes based on paleontologie data, oxygen isotope measurements, magnetic stratigraphy, and radiometric dating indicates that the late Cenozoic major glacial-interglacial cycles were broadly synchronous throughout the world.
H. Stewart Edgell is a graduate of the University of Sydney with his doctorate in geology from Stanford University. He has spent most of his working life in the Middle East, especially in Arabia, where he has been active in oil exploration, and primarily in university teaching and research as a Professor of Geology at the Amercian University of Beirut, the UNESCO/Saudi Center for Applied Geology, Jeddah, and King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. Arabian Deserts provides a comprehensive coverage of all the deserts of Arabia largely based on the author's experience in Arabia over the last fifty years. Distinctive landforms of Arabia deserts are described, together with their geological setting and the influence of climates both past and present. The six great sand seas of Arabia are emphasized since Ar Rub' al Khali Desert forms the world's largest continuous sand desert. Sources, sedimentology, and the mechanisms of formation of these great sand deserts are examined. Distinctive sand dunes and interdunes types found in Arabia are described, classified and explained. Fluvial processes are discussed, as well as the many oases, and lake deposits formed in milder, more humid intervals. Extensive areas of black, basaltic, volcanic desert are described covering three times the area of Belgium. Ecology of Arabia and human influence on desertification are outlined. Climatic changes in the evolution of Arabian deserts during the Quaternary and their causes are explained and a chronology of climatic events during their formation is established. Audience This book will be of interest to geoscientists, especially Quaternary geologists, geomorphologists, geographers, sedimentologists interested in aeolian and fluvial processes, climatologists, coastal studies groups, desertification interest groups, and ecologists with interest in arid lands.
A framework is developed for the estimation of errors in paleotemperature reconstructions, such as those compiled by Borzenkova (Borzenkova, 1992; Borzenkova et al., 1992). Three primary sources of error are considered: (1) methodological error—the difference between the temperature inferred (method dependent) from a sample and the actual temperature when the sample was formed, (2) time-dating error—the error in temperature caused by a sample formed at a time different than intended, and (3) spatial interpolation error—the error caused by interpolating from point data to create an average or map of paleotemperatures. Each of these error sources can be the primary source of uncertainty, depending on the epoch, location, and methods applied. Preliminary error estimates are given for Borzenkova's Holocene Climatic Optimum reconstruction of the zonal-mean-annual paleotemperature distribution. For this reconstruction, methodological error is found to be the dominant source of errors at low latitudes, while spatial interpolation error is found to be the dominant source at high latitudes. This finding is due to higher expected spatial variability of temperature at high latitudes which results in an increase in spatial interpolation error with latitude relative to methodological error which is insensitive to latitude. At mid-latitudes, where the reconstruction contained a higher density of data, the temperature was found to be significantly warmer than present for the Holocene Climatic Optimum. For epochs earlier than the Quaternary, the epochs were defined by time slices that span as much as millions of years, which suggests that time-dating error could be the primary source of error for paleotemperature reconstructions which are intended to represent snapshots in time. Natural climate variability for the Cenozoic and Cretaceous over time scales of millions of years is, however, not well quantified; therefore, it remains ambiguous how to quantify errors in temperature caused by inaccurate time dating for pre-Quaternary epochs.
Studies were made of the distribution of planktonic foraminiferal tests in the sediment
layer of the upper maximum of the last continental glaciation. The sub-Arctic
thanatocoenosis type was found at that time as far south as the latitude of the Azores
in the western part of the ocean and as the latitude of the northern coasts of the Pyrenees
Peninsula in the eastern part. The same distribution is typical of coarse-grained terrigenous
material which is product of ice dispersal. Based on the above data for the time
under study, a southern boundary of floating ice is traced closing up with the boundaries
of permafrost distribution in Europe and North America. The warm-water North Atlantic
Current did not penetrate the north-eastern sector of the Atlantic.
The dominance of Neogloboquadrina pachyderma (sinistral) in 'Heinrich layers' reflects an extension of cold low salinity polar waters. The fresh water along with turbidity caused by melting icebergs may account for the low productivity during these events. In contrast, the dominance of Globigerina bulloides, N. incompta, Globorotalia scitula, Globigerinita glutinata, and Globorotalia inflata group in interglacial sediments is interpreted to reflect conditions comparable with the present day North Atlantic Current (NAC) waters in the area. Enough food and sufficient light combine to provide for pulses of algal blooms which support large populations of Foraminifera.
The relative abundance of five groups of radiolarian species (nasselarians and spumellarians) in the thanatocoenoses within the recent sediments from 64oN to the Equator is described. Four types of thanatocoenoses of Radiolarians and several subtypes are distinguished and in the broadest sense four major faunal zones can be delimited: north of 60oN, a subarctic zone, a boreal zone, a subtropical zone whose boundary runs approximately along 45oN and, south of 13oN, a tropical zone. The correlations between the faunal provinces and climatic belts are more gradual in the low and intermediate latitudes than in the high latitudes
Because no sediment of post-Eocene to Late Miocene or Pliocene age has been recovered from the central Arctic Ocean, oceanographic conditions during the middle Cenozoic are unknown. The oldest late Cenozoic sediment is glacial-marine and contains agglutinated foraminifera. A few calcareous organisms are present in the oldest late Cenozoic sediment (with an age of 2–4 Ma) but at approximately the time as deposition of lithostratigraphic unit F, sometime between 2.0 and 1.5 Ma, there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central Arctic Ocean. Many of the newly introduced species are Atlantic in origin. Preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the Arctic Ocean CCD level and this may be explained by increased circulation with the Northern Greenland Sea. Details of the change in threshold values in the Fram Strait required for the introduction of relatively warmer and carbonate-rich water into the central Arctic Ocean are unknown. There is evidence that spreading rates along the North Atlantic-Nansen Ridge System increased during the Pleistocene and this may have permitted increased circulation between the North Atlantic and the central Arctic Ocean. This important change in Arctic Ocean circulation corresponds to increased Pleistocene seasonality in the Northern Hemisphere.
During the equamarge II cruise (1988) along the Guinean continental margin (central Equatorial Atlantic) a 2.17 m long core has been sampled at 840 m water depth on the top of one of the volcanic seamounts cropping out in this area. Planktonic foraminiferal assemblages observed within the 2.13 m unconsolidated sediments indicate an age of 0.20 to 0.15 Ma, corresponding to the transition from interglacial to glacial events. Depth of deposition of the calcareous sand ranges between 150–200 m and progressively decreased during the glacial stage onset. Detailed sedimentological and micropaleontological studies, carried out on the 4 cm thick indurated core cap, indicate a deposition depth of 50–100 m, or even less. Taking into account the Pleistocene sea level fluctuations, these data suggest a rapid subsidence of the magmatic seamount since the upper most Pleistocene.RésuméPendant la campagne equamarge II (1988) le long de la marge continentale de Guinée (Atlantique équatorial), 2.17 m de sédiments ont été prélevés par carottage, par 840 m de fond au sommet d'un édifice volcanique. Les associations de Foraminifères planctoniques identifiés dans les 2.13 m de sédiments meubles, donnent un âge de 0.20 Ma à 0.15 Ma, situé à la période de transition entre un stade interglaciaire et un stade glaciaire. Il s'agit de sables carbonatés déposés sous une tranche d'eau, d'abord voisine de 150 à 200 m, puis progressivement décroissante au cours de l'instauration du refroidissement. Lors du dépôt des sédiments de la croûte phosphatée sommitale (4 cm d'épaisseur), la profondeur, d'après les données sédimentologiques et micropaléontologiques, ne dépassait pas 50 à 100 m. Compte tenu des variations eustatiques, ces observations suggèrent une subsidence rapide de l'édifice volcanique depuis le Pleistocène supérieur.
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