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101.
High-resolution mapping of large gas emitting mud volcanoes on the Egyptian continental margin (Nile Deep Sea Fan) by AUV surveys 总被引:4,自引:1,他引:3
S. Dupré G. Buffet J. Mascle J.-P. Foucher S. Gauger A. Boetius C. Marfia 《Marine Geophysical Researches》2008,29(4):275-290
Two highly active mud volcanoes located in 990–1,265 m water depths were mapped on the northern Egyptian continental slope
during the BIONIL expedition of R/V Meteor in October 2006. High-resolution swath bathymetry and backscatter imagery were
acquired with an autonomous underwater vehicle (AUV)-mounted multibeam echosounder, operating at a frequency of 200 kHz. Data
allowed for the construction of ~1 m pixel bathymetry and backscatter maps. The newly produced maps provide details of the
seabed morphology and texture, and insights into the formation of the two mud volcanoes. They also contain key indicators
on the distribution of seepage and its tectonic control. The acquisition of high-resolution seafloor bathymetry and acoustic
imagery maps with an AUV-mounted multibeam echosounder fills the gap in spatial scale between conventional multibeam data
collected from a surface vessel and in situ video observations made from a manned submersible or a remotely operating vehicle. 相似文献
102.
Regional hydrostratigraphy and groundwater flow modeling in the arsenic-affected areas of the western Bengal basin, West Bengal, India 总被引:1,自引:1,他引:1
The first documented interpretation of the regional-scale hydrostratigraphy and groundwater flow is presented for a ~21,000-km2 area of the arsenic-affected districts of West Bengal [Murshidabad, Nadia, North 24 Parganas and South 24 Parganas (including Calcutta)], India. A hydrostratigraphic model demonstrates the presence of a continuous, semi-confined sand aquifer underlain by a thick clay aquitard. The aquifer thickens toward the east and south. In the south, discontinuous clay layers locally divide the near-surface aquifer into several deeper, laterally connected, confined aquifers. Eight 22-layer model scenarios of regional groundwater flow were developed based on the observed topography, seasonal conditions, and inferred hydrostratigraphy. The models suggest the existence of seasonally variable, regional, north–south flow across the basin prior to the onset of extensive pumping in the 1970s. Pumping has severely distorted the flow pattern, inducing high vertical hydraulic gradients across wide cones of depression. Pumping has also increased total recharge (including irrigational return flow), inflow from rivers, and sea water intrusion. Consequently, downward flow of arsenic contaminated shallow groundwater appears to have resulted in contamination of previously safe aquifers by a combination of mechanical mixing and changes in chemical equilibrium. 相似文献
103.
The objective of this study is to investigate the impact of a surface data assimilation (SDA) technique, together with the
traditional four-dimensional data assimilation (FDDA), on the simulation of a monsoon depression that formed over India during
the field phase of the 1999 Bay of Bengal Monsoon Experiment (BOBMEX). The SDA uses the analyzed surface data to continuously
assimilate the surface layer temperature as well as the water vapor mixing ratio in the mesoscale model. The depression for
the greater part of this study was offshore and since successful application of the SDA would require surface information,
a method of estimating surface temperature and surface humidity using NOAA-TOVS satellites was used. Three sets of numerical
experiments were performed using a coupled mesoscale model. The first set, called CONTROL, uses the NCEP (National Center
for Environmental Prediction) reanalysis for the initial and lateral boundary conditions in the MM5 simulation. The second
and the third sets implemented the SDA of temperature and moisture together with the traditional FDDA scheme available in
the MM5 model. The second set of MM5 simulation implemented the SDA scheme only over the land areas, and the third set extended
the SDA technique over land as well as sea. Both the second and third sets of the MM5 simulation used the NOAA-TOVS and QuikSCAT
satellite and conventional upper air and surface meteorological data to provide an improved analysis. The results of the three
sets of MM5 simulations are compared with one another and with the analysis and the BOBMEX 1999 buoy, ship, and radiosonde
observations. The predicted sea level pressure of both the model runs with assimilation resembles the analysis closely and
also captures the large-scale structure of the monsoon depression well. The central sea level pressures of the depression
for both the model runs with assimilation were 2–4 hPa lower than the CONTROL. The results of both the model runs with assimilation
indicate a larger spatial area as well as increased rainfall amounts over the coastal regions after landfall compared with
the CONTROL. The impact of FDDA and SDA, the latter over land, resulted in reduced errors of the following: 1.45 K in temperature,
0.39 m s−1 in wind speed, and 14° in wind direction compared with the BOBMEX buoy observation, and 1.43 m s−1 in wind speed, 43° in wind direction, and 0.75% in relative humidity compared with the CONTROL. The impact of SDA over land
and sea compared with SDA over land only showed a further marginal reduction of errors: 0.23 K in air temperature (BOBMEX
buoy) and 1.33 m s−1 in wind speed simulations. 相似文献
104.
The air-sea exchange is one of the main mechanisms maintaining the abundances of trace gases in the atmosphere. Some of these,
such as carbon dioxide and dimethyl sulphide (DMS), will have a bearing on the atmospheric heat budget. While the former facilitates
the trapping of radiation (greenhouse effect) the latter works in the opposite direction through reflectance of radiation
back into space by sulphate aerosols that form from oxidation of DMS in atmosphere. Here we report on the first measurements
made on DMS in the Bay of Bengal and the factors regulating its abundance in seawater. Phytoplankton alone does not seem to
control the extent of DMS concentrations. We find that changes in salinity could effectively regulate the extent of DMSP production
by marine phytoplankton. In addition, we provide the first ever evidence to the occurrence of DMS precursor, DMSP, in marine
aerosols collected in the boundary layer. This suggests that the marine aerosol transport of DMSP will supplement DMS gaseous
evasion in maintaining the atmospheric non-sea salt sulphur budget. 相似文献
105.
The dissolved fluoride (F−) in the Lower Ganges-Brahmaputra-Meghna (GBM) river system, Bengal basin, Bangladesh, was studied during 1991–1993 to determine
its distribution and source in the basin, and its annual flux to the Bay of Bengal. The concentration of dissolved F− varied between 2 and 11 μmol l−1 with statistically significant variations both spatially and temporally in the basin. Such variations are attributable to
the geology of the individual subbasins (Ganges, Brahmaputra and Meghna), dilution by rainwater during monsoon and groundwater
contribution to the river systems during dry season. Correlation coefficients among F− and major cations and anions suggest diverse inorganic processes responsible for regulating the concentration of F− in these river systems. However, fluorite seems to be one of the major sources of dissolved F−. The concentration of F− in the Lower GBM river system is low compared to the rivers draining Deccan Plateau and arid regions of the subcontinent,
for example, Yamuna and its tributaries. However, it is within the range of most of the other Peninsular and Himalayan rivers.
The GBM system contributes about 115×103 tonnes year−1 of dissolved F− into the Bay of Bengal, and thus accounts for about 3% of the global F− flux to the oceans annually.
Received: 19 May 1999 · Accepted: 11 October 1999 相似文献
106.
利用1998―2007年Seaflux资料结合太阳短波辐射及海面风场数据,分析了孟加拉湾海表日增温(Diurnal Warming of Sea Surface Temperature, dSST)的季节变化特征及其形成机制。结果显示,在赤道海域(5.0°N以南),dSST以年周期变化为主并呈现12月至次年5月高、6—11月低的单峰结构,在湾内(5.0°N以北),dSST则表现出显著的半年周期变化而呈现独特的春、秋季高,夏、冬季低的双峰结构。dSST空间分布形态春季呈湾中部高、四周低的态势;秋季湾口较低、湾内及赤道海域较高;夏、冬季形态基本一致均呈赤道高、湾内低的格局,但夏、冬季湾内高值中心略有不同,分别位于斯里兰卡岛东北部近海及湾西边界区。进一步分析表明,海面风速对整个研究海域的影响均较为重要,因此决定了dSST空间分布形态的季节变化。太阳短波辐射对湾内dSST季节变化的影响也较为重要,但在湾口以南至赤道大部分海域的影响较弱。 相似文献
107.
对MADE KYUN河三角洲海底斜坡所在区域地形地貌、地层岩性等进行阐述分析,结合调查资料确定了斜坡坡体组成与特征:该斜坡坡体主要为淤泥、淤泥质黏土,厚度6~9m。基于GEO-SLOPE软件的SLOPE/W模块计算斜坡稳定性安全系数并确定最危险滑动面,利用BING软件的Herschel-Bulkley模型、双线型模型对最危险滑动面的滑移距离进行模拟预测。数值分析结果表明:在考虑孔隙水压力的情况下,4种计算方法得到的稳定性系数均有所下降,M-P法计算得到的斜坡稳定性安全系数为0.606,处于不稳定状态;2种模型计算得到的滑移距离分别为207和213m,峰值滑移速率分别为7.80和9.33m/s,会对较大范围的海底管道等海底设施造成破坏性影响。 相似文献
108.
The Penglai 9-1 (PL9-1) oil field, which contains China's third largest offshore oil accumulation (in-place reserves greater than 2.28 × 108 ton or 1.49 × 109 bbl), was found in shallow reservoirs (700–1700 m, 2297–5577 ft) within the most active fault zone in east China. The PL9-1 field contains two oil-bearing series, the granite intrusions in Mesozoic (Mz) and both the sandstone reservoirs in Neogene Guantao (Ng) and Neogene Minghuazhen (Nm) Formation. The origins of the PL9-1 field, both in terms of source rock intervals and generative kitchens, were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples. The Mesozoic granite intrusions, which hold more than 80% of the oil reserves in the field, were charged in the west by oil generated from the third member (Es3) of the Shahejie Formation in the Bodong depression. The Neogene reservoirs of the PL9-1 field were charged in the west by oil generated from the third member (Es3) of the Shahejie Formation in the Bodong depression and in the south by oil generated from the first member (Es1) of the Shahejie Formation in the Miaoxibei depression. Interactive contact between the large fan delta and the mature source rocks residing in the Es3 Formation of the Bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the PL9-1 field, which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east China. 相似文献
109.
The signatures of mesoscale eddies induced surface and subsurface changes have not been comprehensively quantified for the Bay of Bengal (BoB) region. This study quantifies the statistical properties and three-dimensional (3D) eddy structures in the BoB. To accomplish this, the satellite altimetry data combined with automated eddy detection and tracking algorithm is used. Horizontal distribution of surface characteristics of eddies is analyzed by using 24 years (1993–2016) of AVHRR infrared satellite sea surface temperature (SST) and 7 years (2010–2016) of sea surface salinity (SSS) of SMOS satellite data. Surface eddy centric composite analysis reveals the existence of warm (cold) and diverse SSS anomalies for anticyclonic (cyclonic) eddies. During winter, it is important to note that the eddy induced SST and SSS anomalies show the dipole patterns show opposite phases for the cyclonic and anticyclonic eddies. Observed diploe structures are consistent with the eddy rotation and background large-scale meridional gradient of temperature and salinity fields. The 3D structure of eddies is investigated by using the ARMOR3D and Argo float profiles. The horizontal distribution of temperature and salinity anomalies from ARMOR3D signify the monopole structure of eddies in the subsurface layers. Further, the analysis of composite averages of 241 (200) Argo temperature profiles indicates the core of anticyclonic (cyclonic) eddies centered at about ∼140 m (∼100 m). However, salinity profiles depict the existence of core at ∼65 m (∼50 m). This study have practical relevance to a variety of stakeholders and finds profound importance in the validation of eddy-resolving ocean models for the BoB region. 相似文献
110.
The influence of the tropical Indo-Pacific Ocean heat content on the onset of the Bay of Bengal summer monsoon(BOBSM) onset was investigated using atmospheric data from the NCEP and ocean subsurface temperature data from the Japan Metorology Agency(JMA).Results showed that the onset time of the BOBSM is highly related to the tropical Pacific upper ocean heat content(HC),especially in the key region of the western Pacific warm pool(WPWP),during the preceding winter and spring.When the HC anomalies in the WPWP are positive(negative),the onset of the BOBSM is usually early(late).Accompanied by the variation of the convection activity over the WPWP,mainly induced by the underlying ocean temperature anomalies,the Walker circulation becomes stronger or weaker.This enhances or weakens the westerly over the tropical Indian Ocean flowing into the BOB in the boreal spring,which is essential to BOBSM onset.The possible mechanism of influence of cyclonic/anti-cyclonic circulation over the northwestern tropical Pacific on BOBSM onset is also discussed. 相似文献