Rock-magnetic measurements along with grain size, acid-insoluble residue (AIR), organic carbon (OC), CaCO3 and δ18O of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of India. Magnetic susceptibility (MS) values in the surficial sediments reflect the land-derived input and, in general, are the highest in terrigenous sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed by the sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin.
The down-core variations in mineral magnetic parameters reveal that the glacial sediments off the Indus are characterized by low MS values/S-ratios associated with high AIR-content, low OC/CaCO3 contents and relatively high δ18O values, while those off SW India are characterized by low MS values/high S-ratio% associated with low AIR content, and relatively high OC, CaCO3 and δ18O values. Conversely, the Early Holocene sediments of all cores are characterized by high MS values/S-ratio% associated with high AIR content, low OC, CaCO3 contents and gradually decreased δ18O values. These results imply that during the Last Glacial Maximum (LGM), the cores off northwestern India received abundant continental supply leading to the predominance of eolian/fluvial sedimentation. In the SW region the influence of hinterland flux is less evident during this period, but convective mixing associated with the NE monsoon resulted in increased productivity. During the early Holocene intense SW monsoon conditions resulted in high precipitation on land, which in turn contributed increased AIR content/MS values in the continental margin sediments. A shallow water core off Kochi further suggests that the intense SW monsoon conditions prevailed until about 5 ka. The late Holocene organic-rich sediments of the SW margin of India were, however, subjected to early diagenesis at different intervals in the cores. Therefore, caution is needed when interpreting regional climatic change from down-core changes in sediment magnetic properties. 相似文献
This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific, the oceanic region centered on the eastern Pacific warm pool, but also including the equatorial cold tongue and equatorial current system, and summarizes what is known about oceanographic influences on seabirds and cetaceans there. The eastern tropical Pacific supports on the order of 50 species of seabirds and 30 species of cetaceans as regular residents; these include four endemic species, the world’s largest populations for several others, three endemic sub-species, and a multi-species community that is relatively unique to this ecosystem. Three of the meso-scale physical features of the region are particularly significant to seabirds and cetaceans: the Costa Rica Dome for blue whales and short-beaked common dolphins, the Equatorial Front for planktivorous seabirds, and the countercurrent thermocline ridge for flocking seabirds that associate with mixed-species schools of spotted and spinner dolphins and yellowfin tuna. A few qualitative studies of meso- to macro-scale distribution patterns have indicated that some seabirds and cetaceans have species-specific preferences for surface currents. More common are associations with distinct water masses; these relationships have been quantified for a number of species using several different analytical methods. The mechanisms underlying tropical species–habitat relationships are not well understood, in contrast to a number of higher-latitude systems. This may be due to the fact that physical variables have been used as proxies for prey abundance and distribution in species–habitat research in the eastern tropical Pacific.Though seasonal and interannual patterns tend to be complex, species–habitat relationships appear to remain relatively stable over time, and distribution patterns co-vary with patterns of preferred habitat for a number of species. The interactions between seasonal and interannual variation in oceanographic conditions with seasonal patterns in the biology of seabirds and cetaceans may account for some of the complexity in species–habitat relationship patterns.Little work has been done to investigate effects of El Niño-Southern Oscillation cycles on cetaceans, and results of the few studies focusing on oceanic seabirds are complex and not easy to interpret. Although much has been made of the detrimental effects of El Niño events on apex predators, more research is needed to understand the magnitude, and even direction, of these effects on seabirds and cetaceans in space and time. 相似文献
The Eastern Flank Hydrocarbon Province borders the southeastern edge of the South Oman Salt Basin in the southern part of Oman. An intensive exploration programme by PDO over the past seven years has led to the discovery of almost 2 × 109 m3 of oil with current production of some 15000 m3/d from six fields.In stark contrast to other oil habitats of the Arabian Peninsula, the main play involves rock units and geological events ranging in age from Late Precambrian to Quaternary Times, while trap development and charging are closely related to syn-tectonic salt dissolution.The principal reservoirs and seals are poorly consolidated, Palaeozoic clastics which drape, due to salt dissolution, over residual ‘cores’ principally composed of either Lower Palaeozoic sandstones (Haima Group), or Late Proterozoic carbonates (Huqf Group), or some combination of these. Oils have been geochemically correlated with algal source rocks of the Huqf Eastern Flank. Structures are considered to have been ‘charged’ from Late Mesozoic times onwards in conjunction with progressive subsurface salt removal and the onset of maturation of local source rocks. The effectiveness of ‘charging’ along the retreating salt edge is indicated by the small percentage of dry wells.Major oil zones are found in both anticlinal and truncation traps which are commonly developed around sandstone (Haima Group) cores. Oils show a wide range of characteristics but are typically heavy, early expulsion crudes, high sulphur with little associated gas. Bacterial transformation is not uncommon.Producing reservoirs mainly occur at relatively shallow depths (600–1200 m). Primary recovery factors of around 7% reflect the high density and viscosity of the Eastern Flank crudes and have initiated interest in Enhanced Oil Recovery (EOR) techniques. Two such pilot projects, involving steam and polymer flooding, are due to commence in 1984 and, if successful, will substantially increase the reserve base of these fields. 相似文献
Abundance of picoplanktonic chroococcoid marine cyanobacteria Synechococcus was monitored weekly over the year 1998 in shallow coastal waters of the northern Levantine Basin. The ambient physical, chemical and biological variables (temperature, salinity, Secchi disk depth, total suspended sediment, nitrate, phosphate, Chl a and phytoplankton) were also measured. Synechococcus was found to be more abundant during summer and early autumn and less during winter and early spring. At the surface and 15 m depth, cell concentrations were in the range 6.4 × 103–1.5 × 105 and 3.2 × 103–1.6 × 105 cells·ml−1, respectively. Based on the Pearson product–moment correlation analysis, a highly significant correlation between Synechococcus abundance and ambient temperature was observed (n = 40, r = 0.558, P < 0.01). As Synechococcus forms blooms that usually do not last more than a week, the short time‐scale survey achieved in this study was appropriate to reveal its abundance dynamics. Several factors such as rapid changes in nutrient concentration (especially nitrate), phytoplankton, light availability, temperature, salinity, freshwater input and vertical mixing played a relevant role on the abundance of Synechococcus over the year in the highly dynamic shallow coastal waters of the Levantine Basin. 相似文献
Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments. 相似文献
Stable isotope analyses (δ13C and δ15N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ13C values of Zostera capensis and surface sediments near the salt marsh, the δ13C and δ15N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ13C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ13C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ15N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ13C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers. 相似文献
The increase in marine, land surface, atmospheric and satellite data during recent decades has led to an improved understanding of the air–sea interaction processes in the eastern tropical Pacific. This is also thanks to extensive diagnoses from conceptual and coupled ocean–atmosphere numerical models. In this paper, mean fields of atmospheric variables, such as incoming solar radiation, sea level pressure, winds, wind stress curl, precipitation, evaporation, and surface energy fluxes, are derived from global atmospheric data sets in order to examine the dominant features of the low level atmospheric circulations of the region. The seasonal march of the atmospheric circulations is presented to depict the role of radiative forcing on atmospheric perturbations, especially those dominating the atmosphere at low levels.In the tropics, the trade winds constitute an important north–south energy and moisture exchange mechanism (as part of the low level branch of the Hadley circulation), that determines to a large extent the precipitation distribution in the region, i.e., that associated with the Inter-Tropical Convergence Zone (ITCZ). Monsoonal circulations also play an important role in determining the warm season precipitation distribution over the eastern tropical Pacific through a large variety of air–sea–land interaction mechanisms. Westward traveling waves, tropical cyclones, low latitude cold air intrusions, and other synoptic and mesoscale perturbations associated with the ITCZ are also important elements that modulate the annual rainfall cycle. The low-level jets of the Gulf of California, the Intra-Americas Sea (Gulf of Mexico and Caribbean Sea) and Chocó, Colombia are prominent features of the eastern tropical Pacific low-level circulations related to sub-regional and regional scale precipitation patterns. Observations show that the Intra-Americas Low-Level Jet intensity varies with El Niño/Southern Oscillation (ENSO) phases, however its origin and role in the westward propagation and development of disturbances that may hit the eastern tropical Pacific, such as easterly waves and tropical cyclones, are still unclear. Changes in the intensity of the trade winds in the Caribbean Sea and the Gulf of Mexico (associated with eastern tropical Pacific wind jets) exert an important control on precipitation by means of wind–topography interactions. Gaps in the mountains of southern Mexico and Central America allow strong wind jets to pass over the continent imprinting a unique signal in sea surface temperatures and ocean dynamics of the eastern tropical Pacific.The warm pools of the Americas constitute an important source of moisture for the North American Monsoon System. The northeastern tropical Pacific is a region of intense cyclogenetic activity, just west of the coast of Mesoamerica. Over the oceanic regions, large-scale properties of key variables such as precipitation, moisture, surface energy fluxes and wind stress curl are still uncertain, which inhibits a more comprehensive view of the region and stresses the importance of regional field experiments. Progress has been substantial in the understanding of the ocean and atmospheric dynamics of the eastern tropical Pacific, however, recent observational evidence such as that of a shallow meridional circulation cell in that region, in contrast to the classic concept of the Hadley-type deep meridional circulation, suggests that more in situ observations to validate theories are still necessary.This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean. 相似文献