Perceptive of the pyroxene-bearing micrometeorites and their relation to chondrites          下载免费PDF全文

N. G. Rudraswami  D. Fernandes  Agnelo De Araujo  M. Shyam Prasad  S. Taylor 《Meteoritics & planetary science》2018,53(10):2035-2050

We studied 149 pyroxenes from 69 pyroxene-bearing micrometeorites collected from deep-sea sediments of the Indian Ocean and South Pole Water Well at Antarctica, Amundsen-Scott South Pole station. The minor elements in pyroxenes from micrometeorites are present in the ranges as follows: MnO ~0.0–0.4 wt%, Al₂O₃ ~0.0–1.5 wt%, CaO ~0.0–1.0 wt%, Cr₂O₃ ~0.3–0.9 wt%, and FeO ~0.5–4 wt%. Their chemical compositions suggest that pyroxene-bearing micrometeorites are mostly related to precursors from carbonaceous chondrites rather than ordinary chondrites. The Fe/(Fe+Mg) ratio of the pyroxenes and olivines in micrometeorites shows similarities to carbonaceous chondrites with values lying between 0 and 0.2, and those with values beyond this range are dominated by ordinary chondrites. Atmospheric entry of the pyroxene-bearing micrometeorites is expected to have a relatively low entry velocity of <16 km s⁻¹ and high zenith angle (70–90°) to preserve their chemical compositions. In addition, similarities in the pyroxene and olivine mineralogical compositions between carbonaceous chondrites and cometary particles suggest that dust in the solar system is populated by materials from different sources that are chemically similar to each other. Our results on pyroxene chemical compositions reveal significant differences with those from ordinary chondrites. The narrow range in olivine and pyroxene chemical compositions are similar to those from carbonaceous chondrites, and a small proportion to ordinary chondrites indicates that dust is largely sourced from carbonaceous chondrite-type bodies.  相似文献   

Disseminated sulphides in basalts from the northern Central Indian Ridge: implications on late-stage hydrothermal activity     

Ranadip Banerjee  Dwijesh Ray 《Geo-Marine Letters》2015,35(2):91-103

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Hydrothermal signature in ferromanganese oxide coatings on pumice from the Central Indian Ocean Basin     

Niyati G. Kalangutkar  Sridhar D. Iyer  Maria B. L. Mascarenhas-Pereira  B. Nagender Nath 《Geo-Marine Letters》2015,35(3):221-235

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Trapped waves of the 27 November 1945 Makran tsunami: observations and numerical modeling   总被引：1，自引：1，他引：0  

S. Neetu  I. Suresh  R. Shankar  B. Nagarajan  R. Sharma  S. S. C. Shenoi  A. S. Unnikrishnan  D. Sundar 《Natural Hazards》2011,59(3):1609-1618

The 27 November 1945 earthquake in the Makran Subduction Zone triggered a destructive tsunami that has left important problems unresolved. According to the available reports, high waves persisted along the Makran coast and at Karachi for several hours after the arrival of the first wave. Long-duration sea-level oscillations were also reported from Port Victoria, Seychelles. On the other hand, only one high wave was reported from Mumbai. Tide-gauge records of the tsunami from Karachi and Mumbai confirm these reports. While the data from Mumbai shows a single high wave, Karachi data shows that high waves persisted for more than 7 h, with maximum wave height occurring 2.8 h after the arrival of the first wave. In this paper, we analyze the cause of these persistent high waves using a numerical model. The simulation reproduces the observed features reasonably well, particularly the persistent high waves at Karachi and the single high wave at Mumbai. It further reveals that the persistent high waves along the Makran coast and at Karachi were the result of trapping of the tsunami-wave energy on the continental shelf off the Makran coast and that these coastally-trapped edge waves were trapped in the along-shore direction within a ∼300-km stretch of the continental shelf. Sensitivity experiments establish that this along-shore trapping of the tsunami energy is due to variations in the shelf width. In addition, the model simulation indicates that the reported long duration of sea-level oscillations at Port Victoria were mainly due to trapping of the tsunami energy over the large shallow region surrounding the Seychelles archipelago.  相似文献   

TropFlux wind stresses over the tropical oceans: evaluation and comparison with other products     

B. Praveen Kumar  J. Vialard  M. Lengaigne  V. S. N. Murty  M. J. McPhaden  M. F. Cronin  F. Pinsard  K. Gopala Reddy 《Climate Dynamics》2013,40(7-8):2049-2071

In this paper, we present TropFlux wind stresses and evaluate them against observations along with other widely used daily air-sea momentum flux products (NCEP, NCEP2, ERA-I and QuikSCAT). TropFlux wind stresses are computed from the COARE v3.0 algorithm, using bias and amplitude corrected ERA-I input data and an additional climatological gustiness correction. The wind stress products are evaluated against dependent data from the TAO/TRITON, PIRATA and RAMA arrays and independent data from the OceanSITES mooring networks. Wind stress products are more consistent amongst each other than surface heat fluxes, suggesting that 10 m-winds are better constrained than near-surface thermodynamical parameters (2 m-humidity and temperature) and surface downward radiative fluxes. QuikSCAT overestimates wind stresses away from the equator, while NCEP and NCEP2 underestimate wind stresses, especially in the equatorial Pacific. QuikSCAT wind stress quality is strongly affected by rain under the Inter Tropical Convergence Zones. ERA-I and TropFlux display the best agreement with in situ data, with correlations >0.93 and rms-differences <0.012 Nm^?2. TropFlux wind stresses exhibit a small, but consistent improvement (at all timescales and most locations) over ERA-I, with an overall 17 % reduction in root mean square error. ERA-I and TropFlux agree best with long-term mean zonal wind stress observations at equatorial latitudes. All products tend to underestimate the zonal wind stress seasonal cycle by ~20 % in the western and central equatorial Pacific. TropFlux and ERA-I equatorial zonal wind stresses have clearly the best phase agreement with mooring data at intraseasonal and interannual timescales (correlation of ~0.9 versus ~0.8 at best for any other product), with TropFlux correcting the ~13 % underestimation of ERA-I variance at both timescales. For example, TropFlux was the best at reproducing westerly wind bursts that played a key role in the 1997–1998 El Niño onset. Hence, we recommend the use of TropFlux for studies of equatorial ocean dynamics.  相似文献   

Impact of benzyl butyl phthalate on shoaling behavior in Fundulus heteroclitus (mummichog) populations     

《Marine environmental research》2013

Fundulus heteroclitus preference for association with familiar conspecifics of similar body length was impacted by benzyl butyl phthalate (BBP); this was found to be a statically significant result with a p < 0.0001. When presented with equally sized shoals consisting of either large or small fish, the majority of unexposed (84%) and acetone exposed control (82%) fish selected the shoal of large fish. A small number of control fish chose either the shoal of small fish (6% and 10%) or the neutral zone (10% and 8%) where they were clear morphological outliers. Fish exposed to 0.1 mg/L BBP exposure daily for four weeks selected the shoal of small fish more often than unexposed or acetone controls (7.5- and 4.5-fold respectively). They also remained in the neutral zone and displayed agitation at levels more than twice that of control. Agitation and shoal choice disruption are quantifiable behavioral responses that support the use of F. heteroclitus as a model for detecting sub-lethal BBP exposure.  相似文献   

Observed intra-seasonal to interannual variability of the upper ocean thermal structure in the southeastern Arabian Sea during 2002–2008     

V.V. Gopalakrishna  F. Durand  K. Nisha  M. Lengaigne  T.P. Boyer  J. Costa  R.R. Rao  M. Ravichandran  S. Amrithash  L. John  K. Girish  C. Ravichandran  V. Suneel 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(6):739-754

The southeastern Arabian Sea (SEAS), located in the Indian Ocean warm pool, is a key-region of the regional climate system. It is suspected to play an important role in the dynamics of the Asian summer monsoon system. The present study reports the salient features derived from a newly harvested observational dataset consisting of repeated fortnightly XBT transects in the SEAS over the period 2002–2008. The fortnightly resolution of such a multi-year record duration is unprecedented in this part of the world ocean and provides a unique opportunity to examine the observed variability of the near-surface thermal structure over a wide spectrum, from intra-seasonal to interannual timescales. We find that most of the variability is trapped in the thermocline, taking the form of upwelling and downwelling motions of the thermal stratification. The seasonal variations are consistent with past studies and confirm the role of the monsoonal wind forcing through linear baroclinic waves (coastally-trapped Kelvin and planetary Rossby waves). Sub-seasonal variability takes the form of anomalous events lasting a few weeks to a few months and occurs at two preferred timescales: in the 30–110 day band, within the frequency domain of the Madden–Julian oscillation and in the 120–180 day band. While this sub-seasonal variability appears fairly barotropic in the offshore region, the sign of the anomaly in the upper thermocline is opposite to that in its lower part on many occasions along the coast. Our dataset also reveals relatively large interannual temperature variations of about 1 °C from 50 to 200 m depth that reflect a considerable year-to-year variability of the magnitude of both upwelling and downwelling events. This study clearly demonstrates the necessity for sustained long-term temperature measurements in the SEAS.  相似文献   

Seabed morphology and gas venting features in the continental slope region of Krishna–Godavari basin,Bay of Bengal: Implications in gas-hydrate exploration     

P. Dewangan  T. RamprasadM.V. Ramana  A. MazumdarM. Desa  F.K. Badesab 《Marine and Petroleum Geology》2010

Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, Krishna–Godavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor.  相似文献   

Image analysis of seafloor photographs for estimation of deep-sea minerals     

Rahul Sharma  S. Jai Sankar  Sudeshna Samanta  A. A. Sardar  D. Gracious 《Geo-Marine Letters》2010,30(6):617-626

Factors such as non-uniform illumination of seafloor photographs and partial burial of polymetallic nodules and crusts under sediments have prevented the development of a fully automatic system for evaluating the distribution characteristics of these minerals, necessitating the involvement of a user input. A method has been developed whereby spectral signatures of different features are identified using a software ‘trained’ by a user, and the images are digitized for coverage estimation of nodules and crusts. Analysis of >20,000 seafloor photographs was carried out along five camera transects covering a total distance of 450 km at 5,100–5,300 m water depth in the Central Indian Ocean. The good positive correlation (R² > 0.98) recorded between visual and computed estimates shows that both methods of estimation are highly reliable. The digitally computed estimates were ∼10% higher than the visual estimates of the same photographs; the latter have a conservative operator error, implying that computed estimates would more accurately predict a relatively high resource potential. The fact that nodules were present in grab samples from some locations where photographs had nil nodule coverage emphasises that nodules may not always be exposed on the seafloor and that buried nodules will also have to be accounted for during resource evaluation. When coupled with accurate positioning/depth data and grab sampling, photographic estimates can provide detailed information on the spatial distribution of mineral deposits, the associated substrates, and the topographic features that control their occurrences. Such information is critical for resource modelling, the selection of mine sites, the designing of mining systems and the planning of mining operations.  相似文献   

Comment on a paper by Sibuet et al. (2016) entitled “Thinned continental crust intruded by volcanics beneath the northern Bay of Bengal”     

《Marine and Petroleum Geology》2017

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