Mapping Shoreline Variability of Two Barrier Island Segments Along the Florida Coast     

Ravi D. Sankar  Joseph F. Donoghue  Stephen A. Kish 《Estuaries and Coasts》2018,41(8):2191-2211

Recent projections of global climate change necessitate improved methodologies that quantify shoreline variability. Updated analyses of shoreline movement provide important information that can aid and inform likely intervention policies. This paper uses the Analyzing Moving Boundaries Using R (AMBUR) technique to evaluate shoreline change trends over the time period 1856 to 2015. Special emphasis was placed on recent rates of change, during the 1994 to 2015 period of active storm conditions. Small segments, on the order of tens of kilometers, along two sandy barrier island regions on Florida’s Gulf and Atlantic coasts were chosen for this study. The overall average rate of change over the 159-year period along Little St. George Island was ??0.62?±?0.12 m/year, with approximately 65% of shoreline segments eroding and 35% advancing. During periods of storm clustering (1994–2015), retreat rates along portions of this Gulf coast barrier accelerated to ??5.49?±?1.4 m/year. Along the northern portion of Merritt Island on Florida’s Atlantic coast, the overall mean rate of change was 0.22?±?0.08 m/year, indicative of a shoreline in a state of relative dynamic equilibrium. In direct contrast with the Gulf coast shoreline segment, the majority of transects (65%) evaluated along the oceanfront of Merritt Island over the long term displayed a seaward advance. Results indicate that episodes of clustered storm activity with fairly quick return intervals generally produce dramatic morphological alteration of the coast and can delay natural beach recovery. Additionally, the data show that tidal inlet dynamics, shoreline orientation, along with engineering projects, act over a variety of spatial and temporal scales to influence shoreline evolution. Further, the trends of shoreline movement observed in this study indicate that nearshore bathymetry—the presence of shoals—wields some influence on the behavior of local segments of the shoreline.  相似文献   

Monitoring the Impact of Simulated Deep-sea Mining in Central Indian Basin     

R. Sharma  B. Nagender Nath  S. Jai Sankar 《Marine Georesources & Geotechnology》2013,31(4):339-356

Monitoring of deep-sea disturbances, naturai or man-made, has gained significance due to the associated sediment transport and for the ensuing alterations in environmental conditions. During the Indian Deep-sea Environment Experiment (INDEX), resuspension of deep-sea sediment in the Central Indian Basin (CIB) resulted in an increase and lateral movement of suspended particles, vertical mixing of sediments, changes in sedimentological, biochemical, and geochemical conditions and an overall reduction in benthic biomass. Monitoring the conditions 44 months after the experiment has shown a partial recovery of the benthic ecosystem, with indications of restoration and recolonization.  相似文献   

The longest voyage: Tectonic,magmatic, and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia     

Sankar Chatterjee  Arghya Goswami  Christopher R. Scotese 《Gondwana Research》2013,23(1):238-267

The tectonic evolution of the Indian plate, which started in Late Jurassic about 167 million years ago (~ 167 Ma) with the breakup of Gondwana, presents an exceptional and intricate case history against which a variety of plate tectonic events such as: continental breakup, sea-floor spreading, birth of new oceans, flood basalt volcanism, hotspot tracks, transform faults, subduction, obduction, continental collision, accretion, and mountain building can be investigated. Plate tectonic maps are presented here illustrating the repeated rifting of the Indian plate from surrounding Gondwana continents, its northward migration, and its collision first with the Kohistan–Ladakh Arc at the Indus Suture Zone, and then with Tibet at the Shyok–Tsangpo Suture. The associations between flood basalts and the recurrent separation of the Indian plate from Gondwana are assessed. The breakup of India from Gondwana and the opening of the Indian Ocean is thought to have been caused by plate tectonic forces (i.e., slab pull emanating from the subduction of the Tethyan ocean floor beneath Eurasia) which were localized along zones of weakness caused by mantle plumes (Bouvet, Marion, Kerguelen, and Reunion plumes). The sequential spreading of the Southwest Indian Ridge/Davie Ridge, Southeast Indian Ridge, Central Indian Ridge, Palitana Ridge, and Carlsberg Ridge in the Indian Ocean were responsible for the fragmentation of the Indian plate during the Late Jurassic and Cretaceous times. The Réunion and the Kerguelen plumes left two spectacular hotspot tracks on either side of the Indian plate. With the breakup of Gondwana, India remained isolated as an island continent, but reestablished its biotic links with Africa during the Late Cretaceous during its collision with the Kohistan–Ladakh Arc (~ 85 Ma) along the Indus Suture. Soon after the Deccan eruption, India drifted northward as an island continent by rapid motion carrying Gondwana biota, about 20 cm/year, between 67 Ma to 50 Ma; it slowed down dramatically to 5 cm/year during its collision with Asia in Early Eocene (~ 50 Ma). A northern corridor was established between India and Asia soon after the collision allowing faunal interchange. This is reflected by mixed Gondwana and Eurasian elements in the fossil record preserved in several continental Eocene formations of India. A revised India–Asia collision model suggests that the Indus Suture represents the obduction zone between India and the Kohistan–Ladakh Arc, whereas the Shyok-Suture represents the collision between the Kohistan–Ladakh arc and Tibet. Eventually, the Indus–Tsangpo Zone became the locus of the final India–Asia collision, which probably began in Early Eocene (~ 50 Ma) with the closure of Neotethys Ocean. The post-collisional tectonics for the last 50 million years is best expressed in the evolution of the Himalaya–Tibetan orogen. The great thickness of crust beneath Tibet and Himalaya and a series of north vergent thrust zones in the Himalaya and the south-vergent subduction zones in Tibetan Plateau suggest the progressive convergence between India and Asia of about 2500 km since the time of collision. In the early Eohimalayan phase (~ 50 to 25 Ma) of Himalayan orogeny (Middle Eocene–Late Oligocene), thick sediments on the leading edge of the Indian plate were squeezed, folded, and faulted to form the Tethyan Himalaya. With continuing convergence of India, the architecture of the Himalayan–Tibetan orogen is dominated by deformational structures developed in the Neogene Period during the Neohimalayan phase (~ 21 Ma to present), creating a series of north-vergent thrust belt systems such as the Main Central Thrust, the Main Boundary Thrust, and the Main Frontal Thrust to accommodate crustal shortening. Neogene molassic sediment shed from the rise of the Himalaya was deposited in a nearly continuous foreland trough in the Siwalik Group containing rich vertebrate assemblages. Tomographic imaging of the India–Asia orogen reveals that Indian lithospheric slab has been subducted subhorizontally beneath the entire Tibetan Plateau that has played a key role in the uplift of the Tibetan Plateau. The low-viscosity channel flow in response to topographic loading of Tibet provides a mechanism to explain the Himalayan–Tibetan orogen. From the start of its voyage in Southern Hemisphere, to its final impact with the Asia, the Indian plate has experienced changes in climatic conditions both short-term and long-term. We present a series of paleoclimatic maps illustrating the temperature and precipitation conditions based on estimates of Fast Ocean Atmospheric Model (FOAM), a coupled global climate model. The uplift of the Himalaya–Tibetan Plateau above the snow line created two most important global climate phenomena—the birth of the Asian monsoon and the onset of Pleistocene glaciation. As the mountains rose, and the monsoon rains intensified, increasing erosional sediments from the Himalaya were carried down by the Ganga River in the east and the Indus River in the west, and were deposited in two great deep-sea fans, the Bengal and the Indus. Vertebrate fossils provide additional resolution for the timing of three crucial tectonic events: India–KL Arc collision during the Late Cretaceous, India–Asia collision during the Early Eocene, and the rise of the Himalaya during the Early Miocene.  相似文献   

A new atlas of temperature and salinity for the North Indian Ocean   总被引：2，自引：0，他引：2  

A CHATTERJEE  D SHANKAR  S S C SHENOI  G V REDDY  G S MICHAEL  M RAVICHANDRAN  V V GOPALKRISHNA  E P RAMA RAO  T V S UDAYA BHASKAR  V N SANJEEVAN 《Journal of Earth System Science》2012,121(3):559-593

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Geological Characterization of the Miocene–Pliocene Succession in the Semliki Basin,Uganda: Implications for Hydrocarbon Exploration and Drilling in the East African Rift System     

Mutebi  Stephen  Sen  Souvik  Sserubiri  Tonny  Rudra  Arka  Ganguli  Shib Sankar  Radwan  Ahmed E. 《Natural Resources Research》2021,30(6):4329-4354

Natural Resources Research - The Albertine Graben, an active sedimentary petroliferous basin, has gained global attention as the unexplored areas are recently being targeted for hydrocarbon...  相似文献   

Determination of Mercury in Thirty‐three International Stream Sediment and Soil Reference Samples by Direct Mercury Analyser     

Nitish Kumar Roy  Surya Sankar Bose 《Geostandards and Geoanalytical Research》2008,32(3):331-335

Mercury was determined in thirty‐three international stream sediment and soil reference samples (eleven Chinese soils, GSS‐1 to GSS‐11; twelve Chinese stream sediments, GSD‐1A to GSD‐12; four Canadian stream sediments STSD‐1 to STSD‐4; South African stream sediments, SARM‐42, SARM‐46 and SARM‐47; Japanese stream sediments, JSd‐1 to JSd‐3) by direct mercury analyser. Samples were taken in 500 μl quartz boats, placed in an auto sampler and processed (drying time 60 s at 300 °C; decomposition time 120 s at 850 °C; waiting time 45 s). The instrument was calibrated in the low (0‐50 ng) and high ranges (50‐500 ng) with two reference materials GSS‐5 and GXR‐2 (USGS). Using the calibration line, reference samples were analysed for Hg. The results of the determinations agreed with the recommended values of RMs in all cases except JSd‐1. The RSD calculated for the RMs was found to be within 20%. The detection limit was 1 ng g^?1.  相似文献   

Optimum sampling interval for evaluating ferromanganese nodule resources in the central Indian Ocean     

P. Jauhari  V. Kodagali  S. Sankar 《Geo-Marine Letters》2001,21(3):176-182

A study to estimate manganese nodule abundance (weight of nodules in kg/m²) was carried out in a small area of the abyssal plains covering a one-degree square block in the central Indian Basin. Abundance was assessed at various intervals by progressively reducing the grid spacing. Sampling the corners of the 1° survey block (approximately110-km spacing), i.e., four stations with 5-7 free-fall operations (sampling locations) in each case, indicated a nodule abundance of 3.50 kg/m². By reducing the sampling spacing to four grid units (0.5° survey blocks) and sampling the entire block at eight stations (25 locations), the average abundance of the block was 3.36 kg/m². Further reduction of the grid to 0.25° survey blocks and sampling in 16 grid units (70 sampling locations) increased the abundance to 4.41 kg/m². For 64 grid units in the one-degree block (sampling in 0.125° survey blocks), a substantially higher value was recorded, i.e., 5.31 kg/m² or about 1.5 times the abundance obtained at a 1° spacing. Adding 25 more stations in 0.0625° survey blocks (intervals of sampling locations approximately 500 m) resulted in a negligible change in abundance, the average value of the one-degree block being 5.23 kg/m². These data demonstrate that, for estimating nodule resources in the region, it is important to adopt a close-grid sampling strategy, so that areas with lower abundance can be relinquished and areas with higher abundance can be confidently identified. To ascertain exact nodule abundance for mine-track selection, it may be sufficient to restrict detailed grid surveys to areas with marked variations in topography and nodule abundance, rather than carrying out such detailed (albeit less cost effective) surveys at a very narrow spacing (0.0625°) over the entire pioneer area.  相似文献   

Palaeo-path investigation of the lower Ajay River (India) using archaeological evidence and applied remote sensing     

Suvendu Roy  Abhay Sankar Sahu 《国际地球制图》2016,31(9):966-984

Numerous palaeochannels, oxbow lakes and elongated sediment fills in Eastern India, particularly along the lower Ajay River, provide a record of channel shifting during the Late Quaternary. Proper characterization of these features is useful for discussing the dynamic evolution of the river system in the Ajay-Damodar Interfluve region. Remote sensing data, archaeological evidence and sedimentology aid in reconstructing the geomorphic history of the lower Ajay River. Archaeological studies help in calculating the rate and direction of channel migration. The channel migration rate varies from 0.32 to 3.41 m/year in the study area. Bouguer gravity anomalies suggest that the rate of channel migration may be controlled by the density variations of the basement rocks. Furthermore, neotectonics activity played a significant role in the migration of Ajay River towards north-east direction.  相似文献   

Identification of new Landslides from High Resolution Satellite Data Covering a Large Area Using Object-Based Change Detection Methods     

Tapas R. Martha  P. Kamala  Josna Jose  K. Vinod Kumar  G. Jai Sankar 《Journal of the Indian Society of Remote Sensing》2016,44(4):515-524

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Origin of the Deccan Trap flows at Mahabaleshwar inferred from Nd and Sr isotopic and chemical evidence     

J. Mahoney  J.D. Macdougall  G.W. Lugmair  A.V. Murali  M. Sankar Das  K. Gopalan 《Earth and Planetary Science Letters》1982,60(1):47-60

The Deccan flows at Mahabaleshwar are divisible into a lower and an upper group, based on Nd and Sr isotopic ratios, which define two correlated trends. This distinction is supported by incompatible element ratios and bulk compositions. The data reflect contamination in a dynamic system of magmas from an LIL-depleted,ε_JUV ≥ +8 mantle by two different negative ε_JUV endmembers, one undoubtedly continental crust, the other either continental crust or enriched mantle. The depleted mantle source, anomalously high in (⁸⁷Sr/⁸⁶Sr), may have been in the subcontinental lithosphere or a region of rising Indian Ocean MORB mantle.  相似文献