Premonsoonal water characteristics and circulation in the east central Arabian Sea     

V. Ramesh Babu  J. S. Sastry  V. V. Gopalakrishna  D. V. Rama Raju 《Journal of Earth System Science》1991,100(1):55-68

The hydrographic structure in the east central Arabian Sea during premonsoon period undergoes significant temporal change in the thermal field of upper 100 m, wherein temperature rises by about 0–5°C on an average from May to June. The major contribution in increasing the surface layer temperature comes from surface heat exchange processes, while the horizontal advective process tends to remove the heat from the upper layer. The geostrophic flow patterns are similar from May to June in the major part of the study area while in the coastal areas off Goa a southerly current sets in June in response to coastal upwelling.  相似文献   

Seamounts in the Central Indian Ocean Basin: indicators of the Indian plate movement     

Ranadhir Mukhopadhyay  N. H. Khadge 《Journal of Earth System Science》1990,99(3):357-365

The study of seamount parameters in the tectonically most-complicated and least-understood Indian Ocean assumes importance since their properties vary as a function of tectonic setting, physics of lithosphere, conduit geometry and chemical composition of magma. More than 100 such seamounts ranging in summit height (h) from 300 to 2870 m, are indentified in the oceanic crust between Indian continent and Mid-Indian Ridge (MIR) and South-East Indian Ridge (SEIR). Most of the minor seamounts (h > 1000) are found in the southern part of the study area. Major seamounts (h < 1000 m) are roughly distributed in two groups—the northern group on Cretaceous Oceanic Crust and southern group on Pliocene-Miocene Oceanic Crust. On an average northern group seamounts (SM 1 to 6) are taller, wider and flatter than those from the southern group. These seamounts appear to be the result of continuous growth from tapped, moving magma chamber while stress depleted magma and inconsistent Indian Plate movement during Mid-Tertiary are attributed to the origin of southern group of smaller seamounts. Distribution and morphology of seamounts as a whole indicate their formation either from Reunion hotspot or from two separate hotspots in the geological past.  相似文献   

Distribution pattern and morphochemical relationships of manganese nodules from the Central Indian Basin     

Ranadip Banerjee  Hiroyuki Miura 《Geo-Marine Letters》2001,21(1):34-41

In the Central Indian Basin manganese nodule abundance was variable in all sediment types. Mean abundance varied from 1.5 in calcareous ooze to 10.2 kg/m² in terrigenous-siliceous ooze sediments. Nodule grade and growth rates are positively correlated only up to 10 mm/My (million years), and grade shows no distinct relationship with abundance. Relationships between the morphochemical characteristics of the nodules and host sediment types are subtle. Both hydrogenetic and diagenetic nodules (with smooth and rough surfaces respectively) occur on almost all sediments, but in variable proportions. Thus, the overall distribution pattern shows that small nodules (<4-cm diameters) of lower grade (average value Ni+Cu+Co=1.21%) with smooth surfaces are more common on red clay, terrigenous, and terrigenous-siliceous ooze transition-zone sediments. By contrast, large nodules (>4-cm diameters) of higher grade (average value Ni+Cu+Co=1.80%) with rough surfaces are more prevalent on siliceous ooze, siliceous ooze-red clay, and calcareous ooze-red clay transition-zone sediments. This implies an enhanced supply of trace metals from pore waters to rough-surface nodules during early diagenesis.  相似文献   

Living planktonic foraminifera during the late summer monsoon period in the Arabian Sea     

M.V.S Guptha  Rahul Mohan  A.S Muralinath 《Marine Geology》1994,120(3-4):365-371

During the late summer monsoon living planktonic foraminifera were collected in the southeastern Arabian Sea between 3°N and 15°N by using six vertical plankton tows. Sixteen species of planktonic foraminifera were identified. Among them, Globigerinoides ruber and Globigerinoides sacculifer are the most abundant species, while the ecologically most important species Globigerina bulloides is very rare. The low abundance of G. bulloides can be explained by the warming of the surface water in combination with deepening of the mixed layer, since this species preferentially dwells in nutrient-rich upwelling waters. The population density of planktonic foraminifera ranges between 31 and 185 specimens per 10⁻³ m³. The low absolute numbers of planktonic foraminifera are similar to the numbers which were reported before from the non-upwelling areas in the Arabian Sea. The low absolute numbers and the collected foraminiferal assemblages are therefore highly indicative of the Arabian Sea non-upwelling areas. Particularly significant are the low absolute and relative numbers of the non-spinose species Globorotalia menardii and Neogloboquadrina dutertrei. The absence of these species indicate the relatively low nutrient levels in this area at the tail end of the summer monsoon period.  相似文献   

A preliminary interpretation of two marine gravity profiles on the continental shelf margin west of Bombay (India)     

D.Gopala Rao 《Marine Geology》1976,22(1):M31-M35

Part of the gravity data collected by the U.S.C. & G.S. Ship “Oceanographer” from the continental margin west of India has been analysed. The analyses reveal a deep-lying (>8 km) crustal fracture which trends parallel to the continental margin (NW-SE) above 180 nautical miles west of Bombay.  相似文献   

Biogeochemical significance of fatty acid distribution in the coastal upwelling ecosystem off Concepción (36°S), Chile     

《Organic Geochemistry》2012

The distribution of fatty acids (FAs) in the water column and surface sediment of the coastal upwelling ecosystem off Concepción (central Chile; almost monthly from February 2007 to November 2008) was analyzed using gas chromatography–mass spectrometry. The concentration of FAs in the water column ranged from 3.4 to 67.7 μg l⁻¹ and showed higher values in surface water than in bottom water, and under upwelling vs. non-upwelling conditions. The content in surface sediment ranged from 21.6 to 328.5 μg g dw⁻¹ and had a higher abundance in February 2007, and January–March and June 2008. In surface water 16:0, 18:0 and 16:1n-7 made up ca. 47% of the FAs during the study period, while in bottom water 16:0, 18:0 and 18:1n-9 accounted for ca. 45%, and in surface sediment ca. 43% was accounted for by 14:0, 16:0, 16:1n-7 and 18:1n-7 FAs. Seasonal variability in the relative abundance of saturated and polyunsaturated FAs (PUFAs) was observed in surface water, while in bottom water and surface sediment no major temporal change in FA composition was observed. A negative exponential relationship between bacterial FAs and PUFAs from surface water and sediment suggests that bacteria may be responsible for ca. 80% of PUFA removal during sinking. We suggest that the FA composition of the surface sediment of the ocean is a consequence of rapid alteration of the FA pool by biological activity in the water column and sediment, driven by the removal of the labile fraction of FAs.  相似文献   

Implications of REE incorporation and host sediment influence on the origin and growth processes of ferromanganese nodules from Central Indian Ocean Basin     

《地学前缘(英文版)》2021,12(3)

  相似文献   

Present state of oil pollution in the northern Indian Ocean     

R. Sen Gupta  Tariq W. Kureishy 《Marine pollution bulletin》1981,12(9):295-301

A consolidated picture of oil pollution for the northern Indian Ocean is presented. Oil slicks were sighted on 5582 observations, about 83.5% of the total observations of 6689. The range of concentrations, of the floating tar balls, is 0–6.0 mg/m² in the Arabian Sea. Similarly, the oil tanker route in the Bay of Bengal has the range of 0–69.75 mg/m². North of this route, the Bay of Bengal is comparatively free from this floating tar. Mean concentrations of dissolved and dispersed hydrocarbons for 0–20 m are 32.5 and 24.1 μg kg^?1, respectively, in the Arabian Sea and the Bay of Bengal.  相似文献   

Interpretation of the 231Pa/230Th paleocirculation proxy: New water-column measurements from the southwest Indian Ocean     

《Earth and Planetary Science Letters》2006,241(3-4):493-504

Measurements of ²³¹Pa, ²³⁰Th and ²³²Th concentrations have been made on five water-column profiles along the western margin of the Madagascar and Mascarene Basins in the southern Indian Ocean. These measurements help to fill a significant gap in the global coverage of water-column ²³²Th, ²³⁰Th and ²³¹Pa data. ²³²Th concentrations vary, but generally increase with depth, suggesting higher particle loading in deeper waters, and the presence of a significant dissolved fraction of ²³²Th. ²³⁰Th concentrations increase with depth, and profiles are similar to the average of existing data from other regions. ²³¹Pa concentrations, on the other hand, show significant depth structure, apparently reflecting the various water masses sampled at this location. The modified remnants of North Atlantic Deep Water are found at a depth of ≈ 2000 m and exhibit elevated ²³¹Pa concentrations exported from the South Atlantic. Antarctic Intermediate and Bottom Waters have lower ²³¹Pa, probably due to scavenging onto opal particles during transit from the Southern Ocean. The differences between water masses raises a question: which water mass is important in controlling the ²³¹Pa/²³⁰Th ratio in underlying sediments? A simple one-dimensional model is used to demonstrate that the ²³⁰Th and ²³¹Pa exported to sea-floor sediments last equilibrates with waters close to the seafloor (within ≈ 1000 m), rather than averaging the whole water column. These findings suggest that ²³¹Pa_xs/²³⁰Th_xs in sediments provides information primarily about deep-water masses. In this region, sedimentary records will therefore provide information about the past flow of Antarctic Bottom Water into the Indian Ocean. Interpretation of data from other regions, such as the North Atlantic where this proxy has most successfully been applied, requires careful consideration of regional oceanography and knowledge of the composition of the water masses being investigated.  相似文献   

Monsoon driven changes in phytoplankton populations in the eastern Arabian Sea as revealed by microscopy and HPLC pigment analysis   总被引：1，自引：0，他引：1  

Sushma G. Parab  S.G. Prabhu Matondkar  H. do R. Gomes  J.I. Goes 《Continental Shelf Research》2006,26(20):2538-2558

Like the rest of the Arabian Sea, the west coast of India is subject to semi-annual wind reversals associated with the monsoon cycle that result in two periods of elevated phytoplankton productivity, one during the northeast (NE) monsoon (November–February) and the other during the southwest (SW) monsoon (June–September). Although the seasonality of phytoplankton biomass in these coastal waters is well known, the abundance and composition of phytoplankton populations associated with this distinct and predictable seasonal cycle is poorly known. Here we present for the first time, the results of a study on the community structure of phytoplankton for this region, derived from HPLC pigment analysis and microscopic cell counts. Our sampling strategy allowed for large spatial and temporal coverage over regions representative of the coastal and offshore waters, and over seasons that included the NE and the SW monsoon. Monthly observations at a fixed coastal station in particular, allowed us to follow changes in phytoplankton community structure associated with the development of anoxia. Together these measurements helped establish a pattern of seasonal change of three major groups of phytoplankton: diatoms, dinoflagellates and cyanobacteria that appeared to be tightly coupled with hydrographic and chemical changes associated with the monsoonal cycle. During the SW monsoon when nitrate concentrations were high, diatoms were dominant but prymnesiophytes were present as well. By October, as nitrate fell to below detection levels and anoxic conditions began to develop on the shelf below the shallow pycnocline, both diatom and prymensiophytes declined sharply giving way to dinoflagellates. In the well oxygenated surface waters, where both nitrate and ammonium were below detection limits, pico-cyanobacterial populations became dominant.During the NE monsoon, a mixed diatom-dinoflagellate population was quickly replaced by blooms of Trichodesmium erythraeum and Noctiluca miliaris with higher amounts of zeaxanthin, β-carotene, Chl b and prasinoxanthin. Trichodesmium trichomes were noticed in the water column as early as December when nitrate concentrations became limiting. The low phytoplankton biomass and high ammonium concentrations argue that active grazing populations may be responsible for preventing diatom-dinoflagellate populations from establishing themselves to bloom proportions in the eastern Arabian Sea during the early NE monsoon. Trichodesmium continued its dominance well into May, when nutrient enrichment associated with its death and decay helped simulate the growth of both diatoms and dinoflagellates. Given that anoxic conditions are becoming more pervasive in the eastern Arabian Sea, our observations in particular, those of a shift towards dinoflagellate dominance during the development of anoxia assume particular importance.  相似文献