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1.
Indian Space Research Organization (ISRO) conducted the ‘Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB)’
for a two-month pre-monsoon period in 2006 with the ocean segment covering Bay of Bengal and Arabian Sea. During this campaign,
carbon monoxide (CO) was continuously monitored using a non-dispersive IR analyser. Quantifying CO in ambient air is vital
in determining the air quality of a region. Being toxic, CO is a criteria pollutant, but it is a weak green house gas. Globally,
very few measurements exist over marine atmospheres to study its temporal pattern; particularly in situ CO measurements are few over the Bay of Bengal and Arabian Sea for comparison. Present measurements indicate: (i) predominant
single peak in the diurnal pattern of CO over the marine atmosphere in contrast to the double peak over the continent, (ii)
the mean diurnal CO over the marine atmosphere showing an increasing trend towards evening hours, (iii) the amplitude of the
AN peaks over the marine atmosphere was ∼ 100 ppbv, while at a remote island site in the Indian Ocean it was ∼ 5 ppbv and
(iv) high CO values were observed close to continent and the long range transport by wind also caused CO highs. 相似文献
2.
In order to investigate how monsoons influence biogeochemical fluxes in the ocean, twelve time-series sediment traps were
deployed at six locations in the northern Indian Ocean. In this paper we present particle flux data collected during May 1986
to November 1991 and November 1987 to November 1992 in the Arabian Sea and Bay of Bengal respectively. Particle fluxes were
high during both the SW and NE monsoons in the Arabian Sea as well as in the Bay of Bengal. The mechanisms of particle production
and transport, however, differ in both the regions.
In the Arabian Sea, average annual fluxes are over 50gm-2y-1 in the western Arabian Sea and less than 27gm-2 y-1 in the central part. Biogenic matter is dominant at sites located near upwelling centers, and is less degraded during peak
flux periods. High particle fluxes in the offshore areas of the Arabian Sea are caused by injection of nutrients into the
euphotic zone due to wind-induced mixed layer deepening. In the Bay of Bengal, average annual fluxes are highest in the central
Bay of Bengal (over
50gm-2y-1) and are least in the southern part of the Bay (37gm-2y-1). Particle flux patterns coincide with freshwater discharge patterns of the Ganges-Brahmaputra river system. Opal/carbonate
and organic carbon/carbonate carbon ratios increase during the SW monsoon due to variations in salinity and productivity patterns
in the surface waters as a result of increased freshwater and nutrient input from rivers.
Comparison of S years data show that fluxes of biogenic and lithogenic particulate matter are higher in the Bay of Bengal
even though the Arabian Sea is considered to be more productive. Our results indicate that in the northern Indian Ocean interannual
variability in organic carbon flux is directly related to the strength and intensity of the SW monsoon while its transfer
from the upper layers to the deep sea is partly controlled by input of lithogenic matter from adjacent continents. 相似文献
3.
The intra-seasonal variability observed in the salinity field of the upper layers at a few locations in the east central Arabian
Sea and the northern Bay of Bengal during the summer monsoon seasons of 1977 and 1979 is documented with the aid of short
time series (1–2 weeks) of salinity measurements made from USSR and Indian ships deployed during MONSOON-77 (1977) and MONEX-79
(1979) field experiments. In the Arabian Sea a typical subsurface maxima observed beneath the mixed layer base either disappeared
or considerably weakened due to strong vertical mixing caused by the monsoonal forcing. In the northern Bay of Bengal the
salinity variability in the top 30 m water column was rapid and appeared to be influenced by large amounts of fresh water
from rain and probably from the major adjoining rivers. Some simple diagnostic calculations are presented to assess the relative
importance of various processes which control the observed salinity variability. 相似文献
4.
V. V. S. S. Sarma M. Dileep Kumar M. Gauns M. Madhupratap 《Journal of Earth System Science》2000,109(4):471-479
The variability in partial pressure of carbon dioxide (pCO2) and its control by biological and physical processes in the mixed layer (ML) of the central and eastern Arabian Sea during
inter-monsoon, northeast monsoon, and southwest monsoon seasons were studied. The ML varied from 80–120 m during NE monsoon,
60–80 m and 20–30 m during SW- and inter-monsoon seasons, respectively, and the variability resulted from different physical
processes. Significant seasonal variability was found in pCO2 levels. During SW monsoon, coastal waters contain two contrasting regimes; (a) pCO2 levels of 520–685 μatm were observed in the SW coast of India, the highest found so far from this region, driven by intense
upwelling and (b) low levels of pCO2 (266 μatm) were found associated with monsoonal fresh water influx. It varied in ranges of 416–527 μatm and 375–446 μatm
during inter- and NE monsoon, respectively, in coastal waters with higher values occurring in the north. The central Arabian
Sea pCO2 levels were 351–433, 379–475 and 385–432 μatm during NE-inter and SW monsoon seasons, respectively. The mixed layer pCO2 relations with temperature, oxygen, chlorophylla and primary production revealed that the former is largely regulated by physical processes during SW- and NE monsoon whereas
both physical and biological processes are important in inter-monsoon. Application of Louanchiet al (1996) model revealed that the mixing effect is the dominant during monsoons, however, the biological effect is equally significant
during SW monsoon whereas thermodynamics and fluxes influence during inter-monsoons. 相似文献
5.
6.
Particulate organic carbon (POC) was measured for 77 water samples collected over a 3000 m water column along 88° E in the
central Bay of Bengal. The POC values varied from 80 to 895 μg per litre at the surface and 171 to 261 μg per litre at 2000
m. The POC decreased with increasing water depth at all the stations. Deep water concentrations of POC were higher than those
reported from other oceanic waters. Distribution of POC was not influenced by water masses. The POC was not significantly
correlated with chlorophylla. 相似文献
7.
Particulate organic carbon (POC) of 161 water samples collected from 8 depths (surface to 1000 m) at 21 stations was measured. The POC concentrations ranged from 154 to 554 ¼g per litre at the surface and decreased in the upper 300 m water column. At greater depths (> 300 m), POC concentrations increased and were similar (145 to 542 ¼g1?1) to those observed at surface. Deep water POC maximum was embedded within the oxygen minimum layer and was also associated with high phosphate-phosphorus. The POC contents increased, whereas oxygen decreased as the distance away from the shore increased. Phytoplankton biomass was a major source of POC. The observed pattern of POC is discussed with respect to some physicochemical and biological factors. 相似文献
8.
S. K. Sasamal 《Journal of Earth System Science》1990,99(3):367-381
Bay of Bengal is well known for less saline waters in the surface layer of northern Indian Ocean. High saline waters of the
Bay are considered as an influx from the Arabian Sea within a depth range of 200 to 900 m. Some of the recent observations
in the western Bay of Bengal have shown salinity values higher than those reported earlier (35-2 × 10−3). Such values are explained on the basis of regional climatology suggesting their local formation on the shallow continental
shelf during pre-monsoon months and their subsequent distribution along the coast. 相似文献
9.
We combined a surface irradiance model with a non-spectral photosynthesisirradiance model to estimate the daily, average rate
of mixed-layer primary production in the Arabian Sea for the 15th day of months at the end of the northeast monsoon, the southwest
monsoon, and the fall and spring inter-monsoons. Our model experiment uses climatologies of cloud cover, mixed-layer thickness,
and satellite ocean-color observations of phytoplankton biomass.
Modelled surface radiation is at an annual maximum in May beneath nearly cloud-free skies just prior to the summer solstice.
The model estimate of surface radiation diminishes through the southwest monsoon over most of the northern Arabian Sea to
an annual minimum in August due to intense cloudiness.
In agreement with previous ship-based measurements, the photosynthesis-irradiance model predicts that the mixed-layer primary
production in the Arabian Sea is extremely seasonal, and peaks annually during the southwest monsoon to the north-west of
the atmospheric Findlater Jet and along the coast of Somalia. Northern Arabian Sea maxima predicted for both the summer and
winter monsoons are separated by periods of low mixed-layer primary production, the fall and spring inter-monsoons. The annual
cycles of modelled mixed-layer primary production differ by region in the Arabian Sea due to varying monsoon influence and
circulation dynamics. 相似文献
10.
Evidence for anisotropy in the super-thick sedimentary basin under the northern Bay of Bengal is presented. Surface wave group
velocity data given by Brune and Singh (1986) is better fit by an anisotropic model than an isotropic one. This lends support
to the hypothesis that the mid-crustal rocks are metasediments and that the section of sediments and metasediments is more
than 20 km thick. 相似文献
11.
Numerical Modelling of Storm Surge in the Head Bay of Bengal Using Location Specific Model 总被引:1,自引:1,他引:1
The head Bay of Bengal region, which covers part of Orissa and west Bengal in India as well as Bangladesh, is one of the most vulnerable regions of extreme sea levels associated with severe tropical cyclones which cause extensive damage. There has been extensive loss of life and property due to extreme events in this region. Shallow nature of the Bay, presence of Ganga-Brahmaputra-Meghna deltaic system and high tidal range are responsible for storm surges in this region. In view of this a location specific fine resolution numerical modelis developed for the simulation of storm surges. To represent mostof the islands and rivers in this region a 3km grid resolution is adopted. Several numerical experiments are carried out to compute the storm surges using the wind stress forcings representative of 1974, 1985, 1988, 1989, 1991, 1994 and 1999 cyclones, which crossed this region. The model computed surges are in good agreement with the available observations/estimates. 相似文献
12.
S. W. A. Naqvi 《Journal of Earth System Science》1994,103(2):279-300
Recent information on some consequences of the acute mid-water oxygen deficiency in the Arabian Sea, especially on carbon-nitrogen
cycling, is reviewed. An evaluation of published estimates of water column denitrification rate suggests an overall rate in
the vicinity of 30Tg Ny-1, but the extent of benthic contribution remains unknown. A decoupling of denitrification from primary production, unique
to the Arabian Sea, is revealed by nitrite, electron transport system (ETS) activity and bacterial production data. Results
of both enzymatic and microbiological investigations strongly point to a major role of organic carbon other than that sinking
from surface layers in supporting denitrification. Although denitrification is associated with an intermediate nepheloid layer,
it seems unlikely that the excess carbon comes with particles re-suspended along the continental margins and transported quasi-horizontally
into the ocean interior; instead, the particle maximum may directly reflect a higher bacterial abundance. It is proposed that
denitrification may be predominantly fuelled by the dissolved organic matter. 相似文献
13.
A special feature of the Bay of Bengal circulation is its seasonal variation in response to the monsoonal winds. In the case
of the Bay of Bengal, observationally very little is known about the large scale circulation. Theoretically, the problem of
driving the circulation in the Bay of Bengal is more complex than that in other basins because of the presence of large quantities
of fresh water discharge from Ganga-Brahmaputra-Meghna river systems, and also because the atmospheric driving forces even
within a season are highly variable with frequent occurrences of tropical disturbances. Exploring the nature of the circulation
in the Bay of Bengal is a problem of great importance in itself as well as for the critical role this region plays in the
genesis of tropical disturbances which are the main source of large scale rainfall over the northern part of the Indian subcontinent.
The surface circulation of the Bay of Bengal may, therefore, help in understanding the variation of rainfall over time scales
ranging from the subseasonal to the interannual.
Keeping this in view, an attempt was made towards the development of an oceanic climatological circulation model for the Bay
of Bengal, which explains the seasonal variability of the currents. The model is fully non-linear and vertically integrated,
with realistic basin geometry. The treatment of coastal boundaries involves a procedure leading to a realistic curvilinear
representation of the western and eastern sides of the Bay of Bengal. This coastal representation has the advantage of taking
into account the finer resolution in the shallow regions of the northern Bay.
The model is forced by the monthly mean wind stress derived from 30 years (1950–79) of Comprehensive Oceanographic Atmospheric
Data Sets (COADS). Special emphasis is given to the southern open boundary condition for the model. For this purpose, sensitivity
experiments have been performed with six open boundary conditions and a comparative study of the results has been made. These
sensitivity tests for the open boundary condition will help the development of a suitable coupled ocean-atmosphere model for
this region. The model-generated main features are in general agreement with the known climatological circulation of the Bay
of Bengal. 相似文献
14.
孟加拉湾由于陆源物质大量输入产生稀释效应,使碳酸盐含量表现为冰期时减小、间冰期时增大的“大西洋型”旋回。通过对该区四支活塞岩芯的有孔虫溶解指数、浮游有孔虫沉积通量、CaCO3 沉积通量和 >16 0 μm粗组分沉积通量的分析发现,研究区碳酸盐溶解作用强烈,表现出冰期减弱而间冰期增强的总趋势,且溶解作用滞后于浮游有孔虫壳的氧同位素旋回,尤以氧同位素 4、5期的高溶解度情况与印度洋和太平洋氧同位素 5期晚期至 4期为CaCO3溶解高峰一致。因此,孟加拉湾地区的CaCO3 旋回是大西洋型稀释作用与太平洋型溶解作用两者叠加的产物. 相似文献
15.
K. Gopala Reddy G. Bharathi A. Ravi Kumar M. V. Subrahmanyam K. Muni Krishna 《Journal of Earth System Science》2003,112(2):267-281
Time series measurements of radiative fluxes were made onboard INS Sagardhwani (SD) in the south Bay of Bengal near DS3 (13‡N
and 87‡E) during the BOBMEX field experiment. An inter-comparison experiment conducted at DS3 showed that the radiative fluxes
measured by Kipp and Zonen, Albedo meter and net Pyrgeometer onboard SD and by Eppley radiometers onboard ORV Sagar Kanya
(SK) are well matched. It may be mentioned that the measurements showed consistency and good agreement between SD and SK ships,
even though no Gimbal mounting was used for radiation instruments onboard SD.
The main aim of the experiment was collection of high quality radiation data during the monsoon period, which can give an
insight into the nature of the ocean-atmosphere coupling. The data on the four radiative fluxes collected on SD are averaged
at 5 minute intervals and then hourly and daily averages have been computed. The hourly shortwave albedo and the atmospheric
transmission factor are also computed and the variation of albedo in relation to the solar altitude and the transmissivity
factor (TF) are studied. The mean albedo over the south Bay of Bengal under clear, partly cloudy and overcast skies are found
to be 0.05, 0.07 and 0.2 respectively. 相似文献
16.
THE MONSOON IN THE ARABIAN SEA:IMPLICATIONS FROM RADIOLARIAN FLUXES TO THE DEEP SEA 相似文献
17.
Bruce A. Warren 《Journal of Earth System Science》1994,103(2):301-314
The setting of the Arabian Sea is reviewed in order to examine which of the circumstances causing large oxygen depletion in
the ocean are responsible for the suboxic layer (concentrations < 0.1 ml 1−1) in the northern thermocline there. The wind field forces circulations that restrict but do not exclude exchange with the
south, and a recent box-model interpretation of trichlorofluoromethane measurements indicates a modest throughflow for the
layer of about 5 × 106m3s
−1.The associated oxygen-flux divergence is roughly consistent with biochemical determinations of local oxygen-consumption rates,
both approaches giving values (3–6 pl 1−1 sτ-1) that are modest in comparison with estimates elsewhere in the world ocean. Despite the high mean-annual surface productivity
in the region (nearly 1gCm−2 day−1), it seems plausible that too little of this particulate matter is consumed at thermocline depths to cause an inflated oxygen
demand there. Since the layer is neither an isolated pool, nor a sluggish backwater, nor a conspicuous oxygen sink, the suboxic
concentrations must be due (as earlier proposed) to the low concentration in the water entering the layer from the south.
That depletion in turn seems due to moderate consumption as the water travels the very long trajectories from its zone of
sea-surface renewal (Lats. 40–50°S). Although large seasonal variations are expected in both throughflow volume transport
and surface productivity (suggesting comparable changes in consumption rate), the volume of the suboxic layer seems big enough
to buffer the oxygen levels there against any very noticeable overall variability. 相似文献
18.
S. W. A. Naqvi T. Yoshinari J. A. Brandes A. H. Devol D. A. Jayakumar P. V. Narvekar M. A. Altabet L. A. Codispoti 《Journal of Earth System Science》1998,107(4):367-378
Measurements of15N/14N in dissolved molecular nitrogen (N2), nitrate (NO
3
−
) and nitrous oxide (N2O) and18O/16O in N2O [expressed as δ15N and δ18O, relative to atmospheric N2 and oxygen (O2), respectively] have been made in water column at several locations in the Arabian Sea, a region with one of the thickest
and most intense O2 minima observed in the open ocean. Microbially-mediated reduction of NO
3
−
to N2 (denitrification) in the oxygen minimum zone (OMZ) appears to greatly affect the natural isotopic abundances. The δ15N of NO
3
−
increases from 6‰ in deep waters (2500 m) to 15‰ within the core of the denitrifying layer (250–350 m); the δ15N of N2 concurrently decreases from 0.6‰ to 0.20‰ Values of the isotopic fractionation factor (ε) during denitrification estimated
using simple advection-reaction and diffusion-reaction models are 22‰ and 25‰, respectively. A strong decrease in δ15N of NO
3
−
is observed from ∼ 200m (> 11‰) to 80m (∼ 6‰); this is attributed to the input of isotopically light nitrogen through nitrogen
fixation. Isotopic analysis of N2O reveals extremely large enrichments of both15N and18O within the OMZ, presumably due to the preferential reduction of lighter N2O to N2. However, isotopically light N2O is observed to accumulate in high concentrations above the OMZ indicating that the N2O emitted to the atmosphere from this region cannot be very heavy. The isotope data from the intense upwelling zone off the
southwest coast of India, where some of the highest concentrations of N2O ever found at the sea surface are observed, show moderate depletion of15N, but slight enrichment of18O relative to air. These results suggest that the ocean-atmosphere exchange cannot counter inputs of heavier isotopes (particularly18O) associated with the stratospheric back flux, as proposed by previous workers. This calls for additional sources and/or
sinks of N2O in the atmosphere. Also, the N2O isotope data cannot be explained by production through either nitrification or denitrification, suggesting a possible coupling
between the two processes as an important mechanism of N2O production. 相似文献
19.
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
20.
U. C. Mohanty N. V. Sam S. Das A. N. V. Satyanarayana 《Journal of Earth System Science》2003,112(2):147-163
Convective activity is one of the major processes in the atmosphere influencing the local and large-scale weather in the tropics.
The latent heat released by the cumulus cloud is known to drive monsoon circulation, which on the other hand supplies the
moisture that maintains the cumulus clouds. An investigation is carried out on the convective structure of the atmosphere
during active and suppressed periods of convection using data sets obtained from the Bay of Bengal and Monsoon Experiment
(BOBMEX). The cumulus convection though being a small-scale phenomenon, still influences its embedding environment by interaction
through various scales. This study shows the variation in the kinematic and convective parameters during the transition from
suppressed to active periods of convection. Convergence in the lower levels and strong upward vertical velocity, significant
during active convection are associated with the formation of monsoon depressions. The apparent heat source due to latent
heat release and the vertical transport of the eddy heat by cumulus convection, and the apparent moisture sink due to net
condensation and vertical divergence of the eddy transport of moisture, are estimated through residuals of the thermodynamic
equation and examined in relation to monsoon activity during BOBMEX. 相似文献