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1.
In the Arabian Sea, temporal contiguity of highly oligotrophic and eutrophic periods, along with high water temperatures, may result in unique features of bacteriaorganic matter coupling, nutrient cycling and sedimentation, which are unlike those in the classical oligotrophic and eutrophic waters. Bacteria-phytoplankton interactions are suggested to influence phytoplankton aggregation and its timing. It is also hypothesized that, within aggregates, hydrolytic ectoenzyme activity, together with condensation reactions between the hydrolysis products, produce molecular species which are not readily degraded by pelagic bacteria. Accumulation of a reservoir of such slow-to-degrade dissolved organic carbon (DOC) is proposed to be a carbon flux and energy buffer, which moderates the response of bacteria to the dramatic variations in primary production in the Arabian Sea. Use of the slow-to-degrade DOC pool during the intermonsoon could temporarily render the Arabian Sea net-heterotrophic and a source of CO2 to the atmosphere. Stored DOC is also suggested to balance the observed deficit between mesopelagic carbon demand and the sinking particulate organic carbon supply. Knowledge of the significance of bacteria in carbon storage and cycling in the Arabian Sea is needed to understand the response of the ocean’s biogeochemical state to strong physical forcing and climate change.  相似文献   

2.
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   

3.
南海北部时间系列沉降颗粒的有机地球化学特征及意义   总被引：3，自引：1，他引：3  
陈建芳 Wong  HK 《地球化学》1997,26(6):47-56
通过对南海北部用大孔径沉积物捕获器采集的时间系列沉降颗粒样品中总有机碳，总氮，氨基酸与单糖组分以及叶绿素等有机组分的分析，揭示了南海颗粒物质中有机组分的主要特征，表明沉降颗粒物质中有机质主要来自近期生长的海洋浮游生物，并进一步推断季风对南海北部沉降颗粒物质通量及有机组分具有重要的控制作用。  相似文献   

4.
Organic carbon, total nitrogen, amino acids, sugars, and chlorophyll were determined in < 1 mm fractions of the samples collected by successive large aperture time-series sediment traps (Honjo-Mark M) in northern South China Sea during September 1987 to October 1988. The ratio of C/N and the relative abundance of amino acids and sugars show that organic matter in the settling particles from northern South China Sea is derived mainly from marine plantkon (especially phytoplankton). The organic carbon fluxes in our sediment traps are lower than those in other sediment traps. But the relative contents of Corg/total particulate matter are generally similar to those in the Panama Basin, Arabian Sea and Subarctic Pacific. It is suggested that monsoon-caused changes of physical and chemical conditions in the upper euphotic layer would control the fluxes of organic matter as well as its composition and transport in northern South China Sea. This project was financially supported by both Sino-German Scientific Cooperation Program and National Natural Science Foundation of China (No. 49070269, 49776297).  相似文献   

5.
Based on Coastal Zone Color Scanner data from November 1978 through December 1981, the seasonal cycle of phytoplankton pigment in the upper part of the euphotic zone is established for the offshore Laccadive Sea. Year-round, the pigment content is low and the seasonal range is small, following the pattern of the nutrient-poor Arabian Sea to the west. Apparently, indigenous phytoplankton blooms are absent. July and August, however, were poorly studied because of cloud cover. Interannual differences during the northeast monsoon and the spring intermonsoon periods are minor. The abundant phytoplankton caused by the upwelling off India during the southwest monsoon remains essentially restricted to the shelf, but there are occasional large, zonal outbreaks into the Laccadive Sea, as well as others advected to the south of India. Visual inspection of the raw CZCS scenes for June through November 1982–1985, with almost no data until August or even September, shows such outbreaks of pigment-rich water to be common. Inspection of monthly SeaWiFS images for 1997 through part of 2001 confirms the absence of indigenous phytoplankton blooms.  相似文献   

6.
Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible, TEP concentrations were high in surface waters at 18–20°N along 64°E with concentrations well over 25 mg alginic acid equivalents I−1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial concentrations were up to 1.99 × 108 I–1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD) is estimated to be 1.017 to 4.035 g C m–2 d–1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD in the northern Arabian Sea.  相似文献   

7.
Processes and issues related to the connections between hydrography, plankton, and the flux of organic carbon to great depth are reviewed for the offshore Arabian Sea and compared with observations in similar regimes of other seas. The south-north and west-east gradients and seasonality in the Arabian Sea are emphasized, but generalizations about the area as a whole are shunned. New data include regional differences in seasonality of satellite-observed chlorophyll for two years. The rule for the depth dependence of organic flux is unclear, therefore, this should be the first priority for future investigations. While the data for supply of organic carbon by settling and demand for the depth interval 200–1,000 m in the eastern Arabian Sea are in fair agreement, this is not true for the interval between 300 and 400 m. For advancing the understanding of the generation of flux in the upper layers and the consumption at depth, very much needs to be learned about the biology of the principal species of Zooplankton and nekton. To keep the task manageable, further studies of flux should focus on only one or two subdivisions of the Arabian Sea.  相似文献   

8.
A coupled physical-biological-chemical model has been developed at C-MMACS. for studying the time-variation of primary productivity and air-sea carbon-dioxide exchange in the Indian Ocean. The physical model is based on the Modular Ocean Model, Version 2 (MOM2) and the biological model describes the nonlinear dynamics of a 7-component marine ecosystem. The chemical model includes dynamical equation for the evolution of dissolved inorganic carbon and total alkalinity. The interaction between the biological and chemical model is through the Redfield ratio. The partial pressure of carbon dioxide (pCO2) of the surface layer is obtained from the chemical equilibrium equations of Penget al 1987. Transfer coefficients for air-sea exchange of CO2 are computed dynamically based on the wind speeds. The coupled model reproduces the high productivity observed in the Arabian Sea off the Somali and Omani coasts during the Southwest (SW) monsoon. The entire Arabian Sea is an outgassing region for CO2 in spite of high productivity with transfer rates as high as 80 m-mol C/m2 /day during SW monsoon near the Somali Coast on account of strong winds.  相似文献   

9.
Usingin situ data collected during 1992–1997, under the Indian programme of Joint Global Ocean Flux Study (JGOFS), we show that the biological productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability. The Arabian Sea becomes productive in summer not only along the coastal regions of Somalia, Arabia and southern parts of the west coast of India due to coastal upwelling but also in the open waters of the central region. The open waters in the north are fertilized by a combination of divergence driven by cyclonic wind stress curl to the north of the Findlater Jet and lateral advection of nutrient-rich upwelled waters from Arabia. Productivity in the southern part of the central Arabian Sea, on the other hand, is driven by advection from the Somalia upwelling. Surface cooling and convection resulting from reduced solar radiation and increased evaporation make the northern region productive in winter. During both spring and fall inter-monsoons, this sea remains warm and stratified with low production as surface waters are oligotrophic. Inter-annual variability in physical forcing during winter resulted in one-and-a-half times higher production in 1997 than in 1995.  相似文献   

10.
Data on ocean color chlorophylla (Chl a) obtained using Sea-viewing Wide Field of view Sensor (SeaWiFS), sea surface temperature (SST) by Advanced Very High Resolution Radiometer (AVHRR), and sea surface height (SSH) by TOPEX/POSEIDON were analyzed to examine the influence of Indian Ocean Dipole (IOD) on the physical and biogeochemical processes with special reference to phytoplankton primary production and air-sea fluxes of carbon dioxide in the Arabian Sea. Positive SST anomalies (SSTA) were found in the Arabian Sea (0.4 to 1.8°C) with higher values in the southwestern Arabian Sea that decreased towards north. The SSH anomalies (SSHA) and turbulent kinetic energy anomalies (TKEA) suggest decreased mixing during the IOD compared to the normal period. Chlorophylla displayed significant negative correlations with SSTA and SSHA in the Arabian Sea. Consistently, Chla showed negative anomalies (low Chl a) during the IOD period which could be due to reduced inputs of nutrients. The photic zone integrated primary production decreased by 30% during the IOD period compared to the normal whereas pCO2 levels were higher (by 10–20μatm). However, sea to air fluxes were lower by 10% during the IOD period due to prevailing weaker winds. Primary production seems to be the key process controlling the surface pCO2 levels in the Arabian Sea. In future, the influence of IOD on ecosystem structure, export production and bacterial respiration rates are to be probed throughin situ time-series observations.  相似文献   

11.
Spatial variations in aerosol optical properties as function of latitude and longitude are analysed over the Bay of Bengal and Arabian Sea during ICARB cruise period of March–May 2006 from in situ sun photometer and MODIS (Terra, Aqua) satellite measurements. Monthly mean 550 nm aerosol optical depths (AODs) over the Bay of Bengal and Arabian Sea show an increase from March to May both in spatial extent and magnitude. AODs are found to increase with latitude from 4°N to 20°N over the Bay of Bengal while over Arabian Sea, variations are not significant. Sun photometer and MODIS AODs agree well within ±1σ variation. Bay of Bengal AOD (0.28) is higher than the Arabian Sea (0.24) latitudinally. Aerosol fine mode fraction (FMF) is higher than 0.6 over Bay of Bengal, while FMF in the Arabian Sea is about 0.5. Bay of Bengal α(～1) is higher than the Arabian Sea value of 0.7, suggesting the dominance of fine mode aerosols over Bay of Bengal which is corroborated by higher FMF values over Bay of Bengal. Air back trajectory analyses suggest that aerosols from different source regions contribute differently to the optical characteristics over the Bay of Bengal and Arabian Sea.  相似文献   

12.
Radiocarbon analyses were carried out in the annual bands of a 40 year old coral collected from the Gulf of Kutch (22.6°N, 70°E) in the northern Arabian Sea and in the annual rings of a teak tree from Thane (19°14′N, 73°24′E) near Bombay. These measurements were made in order to obtain the rates of air-sea exchange of CO2 and the advective mixing of water in the Gulf of Kutch. The Δ14C peak in the Thane tree occurs in the year 1964, with a value of ∼630‰, significantly lower than that of the mean atmospheric Δ14C of the northern hemisphere (∼ 1000‰). The radiocarbon time series of the coral was modelled considering the supply of carbon and radiocarbon to the gulf through air-sea exchange and advective water transport from the open Arabian Sea. A reasonable fit for the coral data was obtained with an air-sea CO2 exchange rate of 11–12 mol m−2 yr−1, and an advective velocity of 28 m yr−1 between the Arabian Sea and the Gulf of Kutch; this was based on a model generated time series for radiocarbon in the Arabian Sea. The deduced velocity (∼ 28 m yr−1) of the advective transport of water between the gulf and the Arabian Sea is much lower than the surface tidal current velocity in this region, but can be understood in terms of net fluxes of carbon and radiocarbon to the gulf to match the observed coral Δ14C time series.  相似文献   

13.
The formation and temporal variability of the oxygen minimum zone (OMZ) of the Arabian Sea is a subject of intense research. We contribute to the discussion by studying modern seawater profiles of the Indian Ocean (salinity, O2, pH, aragonite saturation, nitrate deficit, nutrients), which show that Subantarctic Mode and Antarctic Intermediate Waters (SAMW-AAIW) have a strong influence on the OMZ characteristics of the Arabian Sea. To obtain a better grasp of the range of possible OMZ variations, we studied a 50-kyr record in the NE Arabian Sea (core MD042876) from a site at 828 m water depth within the thermocline. In this core, aragonite is preserved during North Atlantic Heinrich events (HEs) and Dansgaard-Oeschger (DO) stadials, while it is absent during DO interstadials and most of the Holocene. Considering the excellent correlation between aragonite content and Sr/Ca ratio, as well as the presence of fine-grained aragonitic needles and the isotopic composition (δ13C) of carbonates in the fine fraction, we infer that essentially all aragonite originates as fine Sr-rich debris from shallow water. A comparison with other records from the NE Arabian Sea (Sr/Ca, δ15N) indicates that aragonite variability in the cores is rather controlled by OMZ intensity variations as forcing mechanism while changes in aragonite supply seem to play a minor role. The strong correlation of aragonite content with changes in millennial-scale ventilation of the Indian Ocean, as well as a comparison with modern oceanographic conditions, supports the theory that OMZ intensity variations are controlled by changes in the formation of SAMW-AAIW, and are not only due to monsoonal changes. Thus, during HEs and DO stadials, the thermocline Arabian Sea experienced a strengthened influx of O2-rich SAMW-AAIW. On the other hand, OMZ conditions during DO interstadials and the Holocene seem best explained by analogy with the present-day situation: low supply of O2 combined with elevated O2 demand controlled by monsoon-related productivity.  相似文献   

14.
从南海南部ODP184航次1143站上部合成深度190.77m共1992个样品中, 由老到新挑选了64个样品, 测试了同一样品中底栖有孔虫Uvigerina peregerina与Cibicidoides wuellerstorfi的δ18O和δ13C值, 结果表明1143站U.peregerina与C.wuellerstorfi的δ18O差值的平均值约为(0.614±0.07)×10-3, 而δ13C差值的平均值约为(0.692±0.04)×10-3.1143站U.peregerina与C.wuellerstorfi的δ18O差值与大西洋和东太平洋的标准差值0.64×10-3比较接近, 而δ13C的差值却比大西洋和东太平洋的标准差值0.9×10-3轻0.2 08×10-3, 可能是由于南沙珊瑚礁区较低的生产力缩小了沉积物与海水之间的δ13C的差异而引起的.该均衡试验为南海甚至西太平洋的古海洋学研究提供了上述2种底栖有孔虫氧碳同位素值转换的标准.   相似文献   

15.
In this study, the possible linkage between summer monsoon rainfall over India and surface meteorological fields (basic fields and heat budget components) over monsoon region (30‡E-120‡E, 30‡S30‡N) during the pre-monsoon month of May and summer monsoon season (June to September) are examined. For this purpose, monthly surface meteorological fields anomaly are analyzed for 42 years (1958-1999) using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research). The statistical significance of the anomaly (difference) between the surplus and deficient monsoon years in the surface meteorological fields are also examined by Student’s t-test at 95% confidence level. Significant negative anomalies of mean sea level pressure are observed over India, Arabian Sea and Arabian Peninsular in the pre-monsoon month of May and monsoon season. Significant positive anomalies in the zonal and meridional wind (at 2 m) in the month of May are observed in the west Arabian Sea off Somali coast and for monsoon season it is in the central Arabian Sea that extends up to Somalia. Significant positive anomalies of the surface temperature and air temperature (at 2 m) in the month of May are observed over north India and adjoining Pakistan and Afghanistan region. During monsoon season this region is replaced by significant negative anomalies. In the month of May, significant positive anomalies of cloud amount are observed over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows positive anomalies over NW India and north Arabian Sea. There is overall reduction in the incoming shortwave radiation flux during surplus monsoon years. A higher magnitude of latent heat flux is also found in surplus monsoon years for the month of May as well as the monsoon season. The significant positive anomaly of latent heat flux in May, observed over southwest Arabian Sea, may be considered as an advance indicator of the possible behavior of the subsequent monsoon season. The distribution of net heat flux is predominantly negative over eastern Arabian Sea, Bay of Bengal and Indian Ocean. Anomaly between the two extreme monsoon years in post 1980 (i.e., 1988 and 1987) shows that shortwave flux, latent heat flux and net heat flux indicate reversal in sign, particularly in south Indian Ocean. Variations of the heat budget components over four smaller sectors of Indian seas, namely Arabian Sea, Bay of Bengal and west Indian Ocean and east Indian Ocean show that a small sector of Arabian Sea is most dominant during May and other sectors showing reversal in sign of latent heat flux during monsoon season.  相似文献   

16.
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   

17.
The development and propagation of a pollution gradient in the marine boundary layer over the Arabian Sea during the Intensive Field Phase of the Indian Ocean Experiment (1999) is investigated. A hypothesis for the generation of the pollution gradient is presented. Infrared satellite images show the formation of the pollution gradient as the leading edge of a polluted air mass in the marine boundary layer and also its propagation over the Arabian Sea and the northern Indian Ocean. Aerosol data measured from two research vessels over the Arabian Sea show a variation in the concentrations caused by the passage of this pollution gradient. Depth of the pollution gradient was found to be about 800 m. A numerical model was used to simulate the development of this gradient and its propagation over the ocean. Results show that its formation and structure are significantly influenced by the diurnal cycle of coastal sea-land breeze circulations along India’s west coast. Transport of aerosols and gases over the Arabian Sea in the lower troposphere from land sources appears to be through this mechanism with the other being the elevated land plume.  相似文献   

18.
THE MONSOON IN THE ARABIAN SEA:IMPLICATIONS FROM RADIOLARIAN FLUXES TO THE DEEP SEA  相似文献   

19.
A physical-biological-chemical model (PBCM) is used for investigating the seasonal cycle of air-sea carbon flux and for assessing the effect of the biological processes on seasonal time scale in the Arabian Sea (AS) and Bay of Bengal (BoB), where the surface waters are subjected to contrasting physical conditions. The formulation of PBCM is given in Swathi et al (2000), and evaluation of several ammonium-inhibited nitrate uptake models is given in Sharada et al (2005). The PBCM is here first evaluated against JGOFS data on surface pCO2 in AS, Bay of Bengal Process Studies (BoBPS) data on column integrated primary productivity in BoB, and WOCE Il data on dissolved inorganic carbon (DIC) and alkalinity (ALK) in the upper 500 meters at 9°N in AS and at 10°N in BoB in September–October. There is good qualitative agreement with local quantitative discrepancies. The net effect of biological processes on air-sea carbon flux on seasonal time scale is determined with an auxiliary computational experiment, called the abiotic run, in which the biological processes are turned off. The difference between the biotic run and abiotic run is interpreted as the net effect of biological processes on the seasonal variability of chemical variables. The net biological effect on air-sea carbon flux is found to be highest in southwest monsoon season in the northwest AS, where strong upwelling drives intense new production. The biological effect is larger in AS than in BoB, as seasonal upwelling and mixing are strong in AS, especially in the northeast, while coastal upwelling and mixing are weak in BoB.  相似文献   

20.
It is generally accepted view that the ventilation of Southern Ocean during the last deglaciation was the key factor in atmospheric CO2 rise. Further, other sites were identified, like the western equatorial Pacific, the Sub-Antarctic Atlantic and the eastern equatorial Pacific. Now there are evidences that CO2 was also released from the eastern Arabian Sea. The Arabian Sea is unique in characteristic, being land locked from the North and affected by monsoon winds and seasonal reversing circulations. Furthermore, the CO2 outgassing noticed during deglaciation makes it an interesting region to understand if the outgassing occurred from the deeper waters and hence led to any rise in deepwater \([\rm{CO}_3^{2-}]\).  相似文献   

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