958 resultados para Western pacific


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In an earlier paper by two of the authors the conclusion was reached that the 33 recognized species of oxides of Mn could be separated into 3 groups: 1) those which appeared to be persistently supergene in origin, 2) those which appeared to be persistently hypogene, and 3) those which were supergene in some localities and hypogene in other localities. When that paper was written, there were available about 250 X-ray diffraction analyses of mineral specimens, also 35 complete and about 150 partial chemical analyses. The conclusions of that paper were based upon the interpretation of the geologic conditions under which these specimens occurred. Late in the preparation of that paper, it seemed worthwhile to make numerous semiquantitative analyses of specimens, largely from 9 western [U.S.A] states, selected carefully from 5 groups of geologic environments, in the hope that the frequency and percentages of some elements might be distinctive of the several geologic groups. For this purpose, 95 specimens were selected from the 5 groups, as follows: 19 specimens interpreted as supergene oxides by the geologists who collected them, 35 specimens of hypogene vein oxides, 22 specimens of Mn-bearing hot spring aprons, 9 specimens of stratified oxides, and 10 specimens of deep-sea nodules. The spectrographic analyses here recorded indicate that a group of elements - W, Ba, Sr, Be, As, Sb, Tl, and Ge - are present more commonly, and largely in higher percentages, in the hypogene oxide than in the supergene oxides and thus serve to indicate different sources of the Mn. Also, the frequency and percentages of some of these elements indicate a genetic relation of the manganese oxides in hypogene veins, hot spring aprons, and stratified deposits. The analyses indicate a declining percentage of some elements from depth to the surface in these 3 related groups and increasing percentages of some other elements. It is concluded that some of the elements in deep-sea nodules indicate that sources other than rocks decomposed on the continents, probably vulcanism on the floors of the seas, have contributed to their formation.

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Chemical analyses are presented for two Cretaceous clays from Noil Tobee, Timor. Mineralogical examination has shown that they consist principally of quartz, feldspar, illite and chlorite, together with minor amounts of montmorillonite. Both chemically and mineralogically the clays are very similar to the recent argillaceous deep-sea sediments of the Pacific and Indian Oceans, which confirms Molengraaff's theory (1921) that they are of deep-sea origin. Further confirmation of this theory is provided by comparison of the composition of micromanganese nodules, separated from one of these clays, with that of manganese nodules from the Pacific Ocean.

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We determined phosphorus (P) concentrations in Leg 138 sediment samples from Sites 844, 846, and 851, using a sequential extraction technique to identify the P associated with five sedimentary components. Total concentrations of P (sum of the five components) ranged from 4 to 35 µmol P/g sediment, with mean values relatively similar between the three sites (11, 14, and 12 for Sites 844,846, and 851, respectively). Authigenic/biogenic P was the most important component in terms of percentage of total P (about 75%), with iron-bound P (13%), adsorbed P (2%-9%), and organic P (4%) of secondary importance; detrital P was a minor P sink (1%) in these sediments. Profiles of adsorbed P and iron-bound P show decreasing concentrations with age, indicating that these components have been affected by diagenesis and reorganization of P. A peak in iron-bound P may reflect higher fluxes of hydrothermally derived Fe to eastern equatorial Pacific Ocean sediments from 11 to 8 Ma. Lower detrital P values for western Site 851 reflect a greater distance of this site from a terrigenous source area, compared to that of Sites 844 and 846. Phosphorus mass accumulation rates (P-MARs; units of µmol P/cm**2/k.y.) were calculated using total P concentrations (not including the minor and oceanically unreactive detrital P component) and sedimentation rates and dry-bulk densities averaged over time intervals of 0.5 m.y. P-MARs generally decrease from 17 Ma to the present. Eastern transect Sites 844 and 846 display a decrease in P-MARs from about 30 to 10 in the interval from 17 to 8 Ma, while western transect Site 851 is highly variable during this interval. P-MARs increase to about 45 and stay relatively high from 8 to 6 Ma, then decrease toward the present to some of the lowest values of the record (about 10). The general trend of high P-MARs at about 6 Ma and decreasing values toward the present is correlated with other geochemical and sedimentary trends through this interval and may reflect (1) a change in net sediment and P burial, (2) a reorganization of fluxes with no change of net burial, or (3) a combination of the two.

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In the GH77-1 cruise, manganese nodules were obtained from 31 stations among 37 total ones. Here are reported the preliminary results of the observation mainly done on-board. Special attention was paid to confirming the applicability of the nodule type classification tentatively established in the previous GH76-1 cruise and to delineating the pattern of the nodule distribution and clarifying its relation to the geological factors, such as topography, surface sediment types, and substrate stratigraphy. In addition, a short description of the obtained rock samples from a few stations is included in this chapter.

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Contents of free lipids in the upper layers of slightly siliceous diatomaceous oozes from the South Atlantic and of calcareous foraminiferal oozes, of coral sediments and of red clays from the western tropical Pacific amount varies from 0.014 to 0.057% of dry sediment. Their content is inversely proportional to total content of organic matter. Relative content of low-polar compounds in total amount of lipids and content of hydrocarbons, fatty acids, and sterols in the composition of these compounds can serve as an index of degree of transformation of organic matter in sediment because these compounds are resistant to various degree to microbial and hydrolytic decomposition and, consequently, are selectively preserved under conditions of biodegradation of organic compounds during oxydation-reduction processes.

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Sand and sandstone compositions from different types of basins reflect provenance terranes governed by plate tectonics. One hundred and one thin sections of Upper Miocene to Holocene sand-sized material were examined from DSDP/IPOD Sites in the North Pacific Ocean and the Bering Sea. The Gazzi-Dickinson point-counting method was used to establish compositional characteristics of sands from different tectonic settings. Continental margin forearc sands from the western North America continental margin arc system are clearly different from backarc/marginal-sea sands from the Aleutian intraoceanic arc system. The forearc sands have average QFL percentages of 29-42-29, LmLvLst percentages of 32-34-34, 3 Fmwk%M and 0.82 P/F. Aleutian backarc sands have average QFL percentages of 8-22-69. LmLvLst percentages of 9-85-6, 0.5 Fmwk%M and 0.96 P/F. A trend of increasing QFL%Q and decreasing LmLvLst%Lv westward in the backarc region of the Aleutian Ridge reflects the influence of the Asiatic continental margin. Aleutian backarc sands without continental influence have average QFL percentages of 1-20-79, LmLvLst percentages of 1-98-1, 0 Fmwk%M and 0.99 P/F. Of the continental margin forearc samples, sands on the Astoria Fan (west of the Oregon-Washington trench) contain the highest LmLvLst%Lv and lowest P/F; sands from mixed transform-fault and trench settings (Delgada Fan and Gulf of Alaska samples) have slightly higher Qp/Q (0.03); and sands from the Pacific-Juan de Fuca-North America triple junction have the highest Fmwk%M. Delgada Fan and Gulf of Alaska sands have average QFL percentages of 27-38-35, LmLvLst percentages of 37-26-37, 2 Fmwk%M and 0.86 P/F. Astoria Fan sands have average QFL percentages of 35-41-24, LmLvLst percentages of 30-47-23, 3 Fmwk%M and 0.74 P/F. The triple-junction sands have average QFL percentages of 28-59-13, LmLvLst percentages of 25-26-49, 9 Fmwk%M and 0.87 P/F. The petrologic data from the modern ocean basins examined in this study can provide useful analogs for interpretation of ancient oceanic sequences. Our data suggest some refinements of, but generally substantiate, existing petrologic models relating sandstone composition to tectonic setting.

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Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18-15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5-1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.

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Aim The spread of non-indigenous species in marine ecosystems world-wide is one of today's most serious environmental concerns. Using mechanistic modelling, we investigated how global change relates to the invasion of European coasts by a non-native marine invertebrate, the Pacific oyster Crassostrea gigas. Location Bourgneuf Bay on the French Atlantic coast was considered as the northern boundary of C. gigas expansion at the time of its introduction to Europe in the 1970s. From this latitudinal reference, variations in the spatial distribution of the C. gigas reproductive niche were analysed along the north-western European coast from Gibraltar to Norway. Methods The effects of environmental variations on C. gigas physiology and phenology were studied using a bioenergetics model based on Dynamic Energy Budget theory. The model was forced with environmental time series including in situ phytoplankton data, and satellite data of sea surface temperature and suspended particulate matter concentration. Results Simulation outputs were successfully validated against in situ oyster growth data. In Bourgneuf Bay, the rise in seawater temperature and phytoplankton concentration has increased C. gigas reproductive effort and led to precocious spawning periods since the 1960s. At the European scale, seawater temperature increase caused a drastic northward shift (1400 km within 30 years) in the C. gigas reproductive niche and optimal thermal conditions for early life stage development. Main conclusions We demonstrated that the poleward expansion of the invasive species C. gigas is related to global warming and increase in phytoplankton abundance. The combination of mechanistic bioenergetics modelling with in situ and satellite environmental data is a valuable framework for ecosystem studies. It offers a generic approach to analyse historical geographical shifts and to predict the biogeographical changes expected to occur in a climate-changing world.

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The following paper considers the question, where to office property? In doing so, it focuses, in the first instance, on identifying and describing a selection of key forces for change present within the contemporary operating environment in which office property functions. Given the increasingly complex, dynamic and multi-faceted character of this environment, the paper seeks to identify only the primary forces for change, within the context of the future of office property. These core drivers of change have, for the purposes of this discussion, been characterised as including a range of economic, demographic and socio-cultural factors, together with developments in information and communication technology. Having established this foundation, the paper proceeds to consider the manner in which these forces may, in the future, be manifested within the office property market. Comment is offered regarding the potential future implications of these forces for change together with their likely influence on the nature and management of the physical asset itself. Whilst no explicit time horizon has been envisioned in the preparation of this paper particular attention has been accorded short to medium term trends, that is, those likely to emerge in the office property marketplace over the coming two decades. Further, the paper considers the question posed, in respect of the future of office property, in the context of developed western nations. The degree of commonality seen in these mature markets is such that generalisations may more appropriately and robustly be applied. Whilst some of the comments offered with respect to the target market may find application in other arenas, it is beyond the scope of this paper to explicitly consider highly heterogeneous markets. Given also the wide scope of this paper key drivers for change and their likely implications for the commercial office property market are identified at a global level (within the above established parameters). Accordingly, the focus is necessarily such that it serves to reflect overarching directions at a universal level (with the effect being that direct applicability to individual markets - when viewed in isolation on a geographic or property type specific basis – may not be fitting in all instances)