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1.
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
2.
Selection of a set of dominant echo features to classify seafloor sediments using a multilayer perceptron neural network is
investigated at two acoustic frequencies (33 and 210 kHz). Several sets of inputs with different combinations of two, three,
four, five, and six echo features are exploited with three-layer neural networks. The performances of the networks are analyzed
to assess the most discriminating set of echo features for classification of seafloor sediments. The results of the overall
average performances reveal that backscatter strength and time spread are the two most important echo features at 33 kHz,
whereas backscatter strength has higher discriminating characteristics at 210 kHz for seafloor sediment classification. In
addition, a set of four echo features consisting of backscatter strength, time-spread, statistical skewness, and Hausdroff
dimension gives the highest success at both the acoustic frequencies. 相似文献
3.
Bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs) have potential as soil-tracing biomarkers for the extensive shelves of the Arctic Ocean. In this work these biomarkers were analysed in surface sediments along a well characterised sub-Arctic transect in the northernmost Baltic Sea from the Kalix River to the central Bothnian Bay to assess their environmental behaviour and potential for tracing the contribution of soil in this type of system. There was a high BHP diversity and enhanced total BHP concentration in the estuarine sediments, whereas a much less diverse pattern could be observed in the open bay with lower total BHP concentration. In addition, both soil marker BHPs (adenosylhopanes) and branched GDGTs were substantially more abundant in the estuarine than the open bay sediments.The index, based on the Rsoil index minus the contribution from the methylated soil marker BHPs, is suggested as a new approach for tracing soil derived organic matter (OM) in the (sub)-Arctic region. The index decreased along the transect in an off-river direction, correlating strongly with both the branched and isoprenoid tetraether (BIT) index and the stable carbon isotopic composition of the sedimentary organic carbon. These field results indicate that both the and the BIT indices have potential for tracing soil derived OM in sub-Arctic to Arctic waters. 相似文献
4.
5.
Stable isotopes of carbon and nitrogen in suspended matter and sediments from the Godavari estuary 总被引：2，自引：0，他引：2
V. V. S. S. Sarma J. Arya Ch. V. Subbaiah S. A. Naidu L. Gawade P. Praveen Kumar N. P. C. Reddy 《Journal of Oceanography》2012,68(2):307-319
Spatial distribution of the carbon and nitrogen content and their isotopic enrichment in suspended matter and sediments were
measured in the Godavari estuary to identify the sources and transformation mechanism of organic matter. Significant variability
in isotopic distribution was found over the entire length of the Godavari estuary, suggesting multiple sources of organic
matter. The mean isotopic ratios (δ13Csed −25.1 ± 0.9, δ13Csus −24.9 ± 1, δ15Nsed 8.0 ± 2 and δ15Nsus 6.5 ± 0.9‰) and elemental concentrations (Csed 0.45 ± 0.2%, Csus 0.9 ± 0.7%, Nsed 0.07 ± 0.05% and Nsus 0.16 ± 0.1%) support a predominantly terrigenous source. Significant enrichment in the isotopic ratios of δ13C from the upper to lower estuary in both suspended (−27.5 and −24.3‰, respectively) and sedimentary (−26.2 and −24.9‰, respectively)
phases indicates a decrease in the influence of terrigeneous material toward the mouth of the estuary. A significant positive
relationship exists between the δ13C of suspended and sediment, which indicates that these two organic carbon pools are likely coupled in the form of a significant
exchange between the two phases. A positive relationship exists between chlorophyll a and suspended organic matter, which may mean that a significant source of organic carbon is the in situ produced phytoplankton.
But, applying a simple mixing model to our isotopes, data yielded about 46% as the contribution of the terrestrial source
to suspended matter, which may support the excessive heterotrophic activity in the Godavari estuary reported earlier. 相似文献
6.
Critical to improving environmental governance is understanding the fit (alignment) between institutional arrangements and key ecological processes. This is particularly true for biodiversity hotpots and ecologically sensitive areas that are subject to significant impacts from human activities. Here, we have developed an innovative approach to quantify ecological-institutional alignment across an environmentally and politically complex large-scale marine social-ecological system. We mapped the trans-boundary networks of marine population dispersal corridors, and intersected these with estimates of cross-country institutional linkages related to marine management and conservation. In integrating large-scale ecological-institutional networks, we identify geopolitical fit and misfit between a region's ecological processes and its governance. We have demonstrated this approach in the Indo-West Pacific region, a global marine biodiversity hotpot in the Indo-West Pacific. We present region-specific institutional and ecological networks, highlight current challenges, and suggest future directions to refine the proposed approach to quantify alignment between ecological processes and governance arrangements. Ultimately, our method has the potential to assist management efforts in prioritizing and strengthening governance to effectively safeguard ecological processes across multiple jurisdictions. 相似文献
7.
M. Nair J. Jacob P. A. Nisha G. D. Martin K. Srinivas P. Sheeba C. M. Laluraj T. Joseph K. K. Balachandran 《Environmental Earth Sciences》2010,61(1):27-35
Temporal and spatial changes in the sediment properties of a mangrove ecosystem (Cochin, southwest coast India) are presented.
The region was freshwater dominated during monsoon (June–September) and seawater dominated during other two seasons. The system
remained eutrophic due to the high inputs of organic matter (OM) during most part of the year. The organic-rich sediments
accumulated high amount of carbohydrates (22% of OM) and proteins (11% of OM) during non-monsoon months as compared to coastal
environments. Principal component analysis showed that the biochemical properties are uniformly influenced by seasonal and
spatial variations. Higher concentrations of sediment protein over carbohydrate indicate an efficient mineralization leading
to the non-availability of aged OM in the system. The dominance of these labile components is generally indicative of the
eutrophic condition of the system. 相似文献
8.
Return period estimates of extreme sea level along the east coast of India from numerical simulations 总被引：2，自引：1，他引：1
Estimates of return periods of extreme sea level events along the coast are useful for impact assessment. In this study, a
vertically integrated 2D model was developed for the simulation of storm surges in the Bay of Bengal. The bathymetry for the
model was derived from an improved ETOPO-5 data set, which was prepared in our earlier work. The meteorological forcing for
the model was obtained from the cyclone model of Holland using the data available for 136 low-pressure systems that occurred
during 1974–2000 in the Bay of Bengal. The simulated total sea level and the surge component were obtained for each event.
The simulated peak levels showed good agreement with the observations available at few stations. The annual maxima of sea
levels, extracted from the simulations, were fitted with Gumbel distribution using r-largest annual maxima method to estimate the 5- and 50-year return periods of extreme events at 26 stations along the east
coast of India. The return periods estimated from simulated sea levels showed good agreement with those obtained from observations.
The 5- and 50-year return levels of total sea level along the east coast of India show a considerable increase from south
to north, with the 50-year return total sea levels being as high as 6.9 and 8.7 m at stations along the north eastern coast
such as Sagar Island and Chandipur, respectively. The high return levels are expected at these stations as the cyclones developed
in the Bay of Bengal generally move north or north-west, producing extreme events in the northern part, and moreover, these
stations are characterized by high tidal ranges. However, at some regions in the southern part such as Surya Lanka and Machilipatnam,
though 50-year return levels of total sea level are not very high (2.98 and 2.97 m, respectively) because of the relatively
lower tidal ranges, high return levels of surges (0.84 and 0.57 m, respectively) are found. In addition to the role of shallow
depths (5.0 and 6.1 m, respectively) at the two stations, the high return levels of surges are attributed to the effect of
geometrical configuration at Surya Lanka and width (100 km) and orientation of continental shelf at Machilipatnam. 相似文献
9.
《Marine Policy》2013
Marine protected areas (MPAs) are often managed using several management zones, each of which allows different human-uses. Decision support tools can be applied to provide advice on potential zoning configurations. However, few studies used decision support tools to systematically determine good locations for different types of zones that accommodate multiple and often conflicting objectives. Previous studies have mostly used scores to integrate multiple objectives and identify different zoning configurations or explored priority areas for each zone separately. Neither of these approaches ensure that solutions meet both biodiversity and human-use objectives. Nor do they deal with the fact that in zoning plans the whole is not the same as the sum of the parts, the importance of a site depends on how the rest of the sites are managed. The aim of this study was to identify different zoning configurations for the Raja Ampat MPA network in Eastern Indonesia that address biodiversity, sustainable fisheries and community resource access objectives. Identifying zoning configurations is particularly difficult here given the importance of protecting high biodiversity reefs and other conservation values, and the high reliance of local communities on their marine resources. Potential areas for no-take zones were identified that have a small and equitable impact across the fishing grounds of different fishing communities whilst ensuring each community has access to a ‘sustainable fishing zone’. Access to fishing grounds for each community is complicated due to marine tenure restricting where individuals can fish and reliance on traditional types of fishing vessels that restrict long distance travel. This approach for zoning was compared to three others. The first focused on identifying areas only for the no-take zone, a traditional systematic planning approach, and the second on both zones without explicitly accounting for the issue of resource access for each community. The solutions unfairly impacted particular communities. Finally, it is demonstrated how a pre-existing zoning proposal, driven by negotiation can be integrated into systematic planning. 相似文献
10.
Laurent Brodeau Bernard Barnier Anne-Marie Treguier Thierry Penduff Sergei Gulev 《Ocean Modelling》2010,31(3-4):88-104
We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 dataset of Large and Yeager (2004), used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2° × 2°) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation. 相似文献