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961.
The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related
annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted
for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface
regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing
due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent
studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating
along the west coast of India.
The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary
current. Local wind-driving is also important to the coastal circulation off western India during the southwest monsoon but
not during the northeast monsoon when a strong (approximately 7 × 106m3/sec) current moves poleward against weak winds. This current is driven by a pressure gradient which forms along this coast
during the northeast monsoon due to either thermohaline-forcing or due to the arrival of Kelvin waves from the Bay of Bengal.
The present speculation about flow of bottom water (deeper than about 3500 m) in the Arabian Sea is that it moves northward
and upwells into the layer of North Indian Deep Water (approximately 1500–3500m). It is further speculated that the flow in
this layer consists of a poleward western boundary current and a weak equatorward flow in the interior. It is not known if
there is an annual cycle associated with the deep and the bottom water circulation. 相似文献
962.
The paper presents the evolution of the geographic environment imposed by sea-level changes in selected sites of the Aegean Sea region during the Upper Holocene. The changes are due, mainly, to paroxysmic phases of the actual neotectonic evolution and to differential—in time and space—block movements, and emerged or submerged coasts. The reconstitution of these coasts is presented and, in some cases, natural harbor morphology is revealed. The use and evolution of these sites is discussed. Other sites concern coastal or inland ancient settlements or constructions affected by submersion by the sea, by the rise of the groundwater table, or by uplift movements. A general discussion on engineering measures to be applied for protection of the antiquities affected by these geographic changes closes the presentation. 相似文献
963.
We have modeled the distribution of nine toxic metals in the surface sediments from 163 stations in the Venice lagoon using published data. Three entrances from the Adriatic Sea control the circulation in the lagoon and divide it into three basins. We assume, for purposes of modeling, that Porto Marghera at the head of the Industrial Zone area is the single source of toxic metals in the Venice lagoon. In a standing body of lagoon water, concentration of pollutants at distancex from the source (C
0) may be given byC=C
0e–kx wherek is the rate constant of dispersal. We calculatedk empirically using concentrations at the source, and those farthest from it, that is the end points of the lagoon. Averagek values (ppm/km) in the lagoon are: Zn 0.165, Cd 0.116, Hg 0.110, Cu 0.105, Co 0.072, Pb 0.058, Ni 0.008, Cr (0.011) and Fe (0.018 percent/km), and they have complex distributions. Given thek values, concentration at source (C
0), and the distancex of any point in the lagoon from the source, we have calculated the model concentrations of the nine metals at each sampling station. Tides, currents, floor morphology, additional sources, and continued dumping perturb model distributions causing anomalies (observed minus model concentrations). Positive anomalies are found near the source, where continued dumping perturbs initial boundary conditions, and in areas of sluggish circulation. Negative anomalies are found in areas with strong currents that may flush sediments out of the lagoon. We have thus identified areas in the lagoon where higher rate of sediment removal and exchange may lessen pollution. 相似文献
964.
Radon-222 activity levels have been measured at deck level in regions of the Arabian Sea, Indian Ocean, and Bay of Bengal during the summer monsoon periods of 1973, 1977, and 1979, as part of the Monex programme. The aim of the measurements was to find the source regions of the monsoon air and the variations in its composition under different synoptic conditions. The radon data confirm that the monsoon air is predominantly of southern-hemisphere origin, with a small continental component. The continental component, as indicated by radon values, increases at higher latitudes and seems to vary with different circulation patterns in the synoptic scale. The use of radon as a tracer in monsoon studies is thus demonstrated. 相似文献
965.
东海陆架盆地岩石密度与磁性 总被引:9,自引:0,他引:9
本文在东海陆架盆地20口钻井160块岩心标本物测定和17口钻井密度测井的基础上,通过整理、分析、统计,给出了东海陆架盆地的岩石密度和磁性特征。 相似文献
966.
运用David A.White,1988介绍的方法,编制东海陆架盆地西湖凹陷和瓯江凹陷油气成藏组合图。通过图件编制的启示,对两个凹陷成藏主要特征和控制油气规律提出了一些新认识,并确定有利勘探区和勘探对象。 相似文献
967.
T. Spencer 《地球表面变化过程与地形》1995,20(1):49-64
Coral islands formed of largely unconsolidated sands only a few metres above sea level are thought to be particularly vulnerable to sea-level rise consequent upon global warming. However, scenarios which predict catastrophic flooding and loss of island area need reassessment, particularly in the light of the continued downwards revision of projected rates of future sea-level rise. Revised questions concern the interactions between reef growth and sea-level change, biophysical constraints on coral growth, and the importance to reef systems of potential changes in the magnitude, frequency and location of tropical cyclones and hurricanes. It is clear that most reefs have the growth potential to meet even the highest of future sea-level rise scenarios, but too little is known about physiological and physical constraints to reef growth to adequately evaluate the importance of these two factors in constraining this potential at the present time. Future sea-level rise in the tropical oceans, and coral reef responses, will take place against a backdrop of inter-regional differences in Holocene sea levels, resulting from the varying interaction of eustatic and hydro-isostatic processes. These differences have generated varying constraints on the development of modern reefs and varying inherited topographies upon which future sea-level changes will be superimposed. These controls are particularly important in assessing differences in vulnerability to future sea-level rise for reef islands in the Pacific Ocean and the Caribbean Sea. 相似文献
968.
Rock salt is approximately 1000 times more soluble than limestone and thus displays high rates of geomorphic evolution. Cave stream channel profiles and downcutting rates were studied in the Mount Sedom salt diapir, Dead Sea rift valley, Israel. Although the area is very arid (mean annual rainfall ≈ 50 mm), the diapir contains extensive karst systems of Holocene age. In the standard cave profile a vertical shaft at the upstream end diverts water from a surface channel in anhydrite or clastic cap rocks into the subsurface route in the salt. Mass balance calculations in a sample cave passage yielded downcutting rates of 0–2 mm s?1 during peak flood conditions, or about eight orders of magnitude higher than reported rates in any limestone cave streams. However, in the arid climate of Mount Sedom floods have a low recurrence interval with the consequence that long-term mean downcutting rates are lower: an average rate of 8·8 mm a?1 was measured for the period 1986–1991 in the same sample passage. Quite independently, long-term mean rates of 6·2mm a?1 are deduced from 14C ages of driftwood found in upper levels of 12 cave passages. These are at least three orders of magnitude higher than rates established for limestone caves. Salt cave passages develop in two main stages: (1) an early stage characterized by high downcutting rates into the rock salt bed, and steep passage gradients; (2) a mature stage characterized by lower downcutting rates, with establishment of a subhorizontal stream bed armoured with alluvial detritus. In this mature stage downcutting rates are controlled by the uplift rate of the Mount Sedom diapir and changes of the level of the Dead Sea. Passages may also aggrade. These fast-developing salt stream channels may serve as full-scale models for slower developing systems such as limestone canyons. 相似文献
969.
970.
从贝丘遗址看绳纹人与环境的相互关系 总被引:1,自引:0,他引:1
介绍了自本世纪70年代末以来,日本学者在绳纹时代的考古研究中开辟的一个新领域,即通过分析贝丘遗址和周围的自然环境去认识绳纹的环境变化及绳纹人与环境的关系。同时提出了笔者关于绳纹时代人与环境关系的一个模式。 相似文献