Littérature scientifique sur le sujet « Andaman and nicobar »

AbstractThe Vulnerable bumphead parrotfish Bolbometopon muricatum, a highly prized fishery resource worldwide, has experienced population declines throughout its geographical range. There is limited knowledge of the distribution and abundance of, and threats to, this fish in Indian waters, particularly for the Andaman and Nicobar Islands. To assess the species’ distribution and conservation status we conducted underwater surveys across 75 sites around 51 islands and interviewed 99 fishers across the Andaman and Nicobar archipelago. We recorded a total of 59 individual B. muricatum across nine sites from the northernmost island in the Andamans (Landfall Island) to the southernmost island in the Nicobars (Great Nicobar Island). Interviews revealed that most fishers (100% in Nicobar, 94% in Middle Andaman, 62% in South Andaman) had seen B. muricatum, and knowledge of the species is highest amongst spearfishers. Generalized linear models indicated that presence of marine protected areas and high live coral cover influenced the abundance and distribution of B. muricatum. The species' density seems to be naturally low in the archipelago. We discuss our findings in the light of protecting rare and threatened species, and recommend strengthening the existing marine protected areas in these islands.

During plant exploration of Andaman and Nicobar in 2014, we were collected some interesting grass specimens from Kamorta Islands of Nicobar. After critical study and taxonomic analysis the unidentified grass species has identified as an Aira caryophyllea L. Perusals of relevant literature were revealed that, the genus Aira L. has so far not reported from Andaman and Nicobar islands. Hence, it is reported in present communication for new record to the Andaman and Nicobar Islands.

A taxonomic account of the genus Artabotrys R. Br. from the Andaman and Nicobar Islands along with a new record for India is presented. Of the three species recorded from the Andaman and Nicobar Islands, Artabotrys hexapetalus (L.f.) Bhandari is widely distributed; A. speciosus Kurz and A. nicobarianus D. Das are endemic to Andaman and Nicobar Islands, India and Artabotrys suaveolens (Bl.) Bl. is reported here as a new record for India from Great Nicobar Biosphere Reserve.

Andaman and Nicobar Islands have two different genetic groups of cattle namely Andaman local cattle and Trinket cattle. Andaman local cattle are distributed in Andaman group of Islands and Campbell Bay of Nicobar group of Islands. Andaman local cattle are non-descriptive and represent an admixture of different Indian breeds that had been brought to these islands in different phases of inhabitation and rehabilitation of migrated people. It is believed that the Andaman local cattle have the inheritance from Red Sindhi, Sahiwal and Hariana. It is unique cattle, well adapted to special type of tropical humid island climatic and environmental condition. The present study was designed to standardise the normal reference haematological and biochemical range for different age groups of Andaman local cattle which were maintained in the South Andaman and North and Middle Andaman district, Andaman and Nicobar Islands, India. In this study, haematological parameters, biochemical indices and antioxidant and oxidative stress profiles were estimated in healthy, normal physiological Andaman local cattle for different age groups. The present study results clearly indicated that the values of haematological, biochemical and antioxidant profiles were under the normal physiological range. These results of this study may serve as the reference values in which alterations due to metabolic, nutrient deficiency, physiological and health status can be compared for diagnostic and therapeutic purposes for Andaman local cattle in Andaman and Nicobar Islands and its neighbouring countries or other parts of the country with similar environmental and climatic conditions.

The damage sustained by buildings and structures in the Andaman and Nicobar islands area was due to earthquake shaking and/or giant tsunami waves. While damage on Little Andaman Island and all the Nicobar Islands was predominantly tsunami-related, damage on islands north of Little Andaman Island was primarily due to earthquake shaking even though tsunami waves and high tides were also a concern. In general, the building stock consists of a large number of traditional and non-engineered structures. Many traditional structures are made of wood, and they performed well under the intensity-VII earthquake shaking sustained along the islands. However, a number of new reinforced concrete (RC) structures suffered severe damage or even collapse. Also, extensive damage occurred to the coastal and harbor structures in the Andaman and Nicobar islands.

The genus Cycas is reviewed for Andaman and Nicobar Islands. C. andamanica, C. darshii and C. sainathii have been treated as synonyms of C. pschannae, C. spherica and C. zeylanica respectively. Records of C. darshii from Botanic garden Culcutta have been shown to described on the basis of plant under cultivation and claimed natural population in Andaman and Nicobar Islands without any supportive evidence. A taxonomic note a brief discussion on its distribution is also discussed here. Morpho-anatomical and palynological data of C. zeylanica described here is for the first time. A key to the species of Cycas from the Andaman and Nicobar Islands is also provided.

The paper explores the key factors relevant to the development of micro and small businesses in the Andaman and Nicobar Islands. This study specifically focused on the relevant factors from the islands' perspectives. This study used primary sources of data collected in the South Andaman Islands (Andaman and Nicobar Islands), and the obtained data were analyzed using SPSS. The findings of the study proved that tourism business and marine and wood-based businesses have huge potential in the Andaman Islands. The study's findings highlighted the significance of subsidies and incentives for island promotion and sustainable development, which could be accomplished through capital investment, as well as transportation subsidies, which are critical for new and existing businesses on islands. Cargo transportation from the mainland to islands is the primary mode of sea transportation and the only mode between island regions. Under this situation, the Andaman and Nicobar Islands totally rely on manufacturing or service businesses as a lifeline. Hence, micro- and small businesses will play a vital role in employment generation, production, investments, and the growth of a small business. As a result, the administration of the islands should implement appropriate policy measures based on the relevant factors in the islands' region. The local administration needs to support and provide easy access to finance, transportation, and other facilities for small businesses in the Andaman and Nicobar Islands.

A new species of Habenaria (Orchidaceae), H. rangatensis is described from stunted evergreen forest of Middle Andamans, Andaman & Nicobar Islands, India. This new species is morphologically similar to Habenaria acuifera but differ in certain characters, which are discussed below. A detailed description and photographs are provided for identification of the present novel species.

Sediments can be considered geological archives as they record and preserve the signatures of ancient geological events affecting source areas. This primitive provenance signal is modified by physical and chemical processes during transport and deposition. The present thesis is devoted to highlight the importance of heavy minerals analysis on modern sediments to refine classical provenance models, unraveling sediment sources, transport conditions, diagenetic processes and recycling phenomena. In the first part of the thesis a classification of surface textures observed on detrital heavy mineral grains in sands and sandstones is proposed in order to enhance data reproducibility among operators and to implement the use of high-resolution heavy-mineral data in studies on sediment-generation, provenance and diagenesis. Different stages of progressive weathering are collected in numerous color tables for visual comparison. They are specifically devised to systematically collect valuable information for paleoclimatic or diagenetic interpretation during routine grain-counting operations under the microscope. This catalog (Andò et al., 2012) represents a useful subsidiary tool to reveal the different degrees of weathering for diverse minerals in modern sands of equatorial Africa, and to identify post-depositional modifications of detrital assemblages in buried orogenic sediments of the Bengal Basin. These data, integrated with the concentration of heavy minerals in each sample, provide the fundamental clue to quantify the degree of heavy-mineral depletion caused by either pre-depositional or post-depositional processes (useful to understand the development of secondary porosity and to assess the potential of water and hydrocarbon reservoirs). The second part of the thesis focuses on two regional studies on compositional variability, provenance and long-distance trasport of terrigenous sediments from Barbados Island (Limonta et al., in prep.) and Indo-Burma-Andaman-Nicobar Ridge (Garzanti et al., 2013a). Subduction complexes large enough to be exposed subaerially and to become significant sources of terrigenous detritus are formed by tectonic accretion above trenches choked with thick sections of remnant-ocean turbidites. They thus need to be connected along strike to a large Alpine-type or Andean-type orogen, where huge volumes of orogenic detritus are produced and conveyed via a major fluvio-deltaic system to the deep sea (Ingersoll et al., 2003). We investigated sediment generation and recycling in the Indo-Burman-Andaman-Nicobar subduction complex, representing the archetype of such settings in the eastern prolongation of the Himalayan collisional system. “Subduction Complex Provenance” is composite, and chiefly consists of detritus recycled from largely turbiditic parent rocks (Recycled Clastic Provenance), with local supply from ultramafic and mafic rocks of forearc lithosphere (Ophiolite Provenance) or recycled paleovolcanic to neovolcanic sources (Volcanic Arc Provenance; Garzanti et al., 2007). In order to specifically investigate the effect of recycling, we characterized the diverse detrital signatures of Cenozoic sandstones deposited during subsequent stages of “soft” and “hard” Himalayan collision and exposed from Bangladesh to the Andaman Islands, and discuss the reasons for compositional discrepancies between parent sandstones and their recycled daughter sands. A companion study was carried out with the same methodologies, rationale and goals on Barbados Island. Also modern Barbados sands are largely multicyclic, reflecting mixing in various proportions of detritus from the basal Scotland Formation (sandstones and mudrocks), their stratigraphic and tectonic cover, the Oceanic Formation (quartzose turbidites and deep-water biogenic oozes including radiolarites), and from the Pleistocene calcarenite and reef caps, as well as from volcanic layers ultimately derived from the Lesser Antilles. Mixing of detritus recycled from orogen-derived turbidites transported long distance with detritus from oceanic mèlange, pelagic sediments and younger calcareous cap rocks and in addition volcaniclastic products thus redefines the diagnostic mark of Subduction Complex Provenance as quite distinct from the original definition by Dickinson and Suczek (1979).

This thesis is a descriptive study of problem representations of climate-induced human mobility in policy. Two cases which are severely impacted by climate change have been selected for the analysis: Kiribati and Andaman and Nicobar Islands. Policies of these cases are analysed through a qualitative text analysis following the methodological approach “What’s the Problem Represented to Be?”. A particular focus is given to the issue of “planned relocations” as this is a form of human movement that is, per definition, driven by policy. The analysis found negative representations of human mobility to be present in both cases, but also positive representations in the case of Kiribati. Planned relocations were represented as something necessary and difficult by both the cases, but a substantial difference concerned the intended length of such movements. Lastly, this study highlights the need for further research on policy engagement in climate-induced human mobility.

Tsunami hazards were greatly underestimated along the coasts of countries bordering the northeastern Indian Ocean until the occurrence of the 26 December 2004, Mw 9.2 earthquake and its ensuing tsunami. Sourced off the coast of northern Sumatra, on the plate boundary between the Indo-Australian and Eurasian plates, the rupture of the 2004 earthquake propagated ~1300 km northward. The magnitude of this earthquake and the reach of its tsunami exceeded all known precedents, based on instrumental and historic records. The coseismic deformational and post-tsunami depositional features facilitated opportunities to conduct tsunami geology studies along the coasts of countries bordering the Indian Ocean. Several questions are being posed, the answers of which have implications for tsunami hazard assessment. How did this plate boundary behave prior to and after the great earthquake? Was the 2004 earthquake the first of its kind on the Sumatra-Andaman plate boundary? If it had a predecessor, when did it occur and was it a true predecessor in terms of its rupture dimensions and tsunamigenic potential? What types of depositional evidence are preserved and how can we use them to develop the history of past tsunamigenic earthquakes? Researchers are exploring the affected regions and using the imprints left by the 2004 event, to address these questions. There are two components to this study: one, a seismotectonic analysis of the region from the perspective of plate driving forces and their relative roles in the interseismic and post-seismic phases. This study uses global data catalogs like the NEIC PDE (National Earthquake Information Centre Preliminary Determination of Epicenters) and the Global Centroid Moment Tensor (CMT) solutions for earthquake source parameters to understand the along-strike variations in seismicity patterns before and after the 2004 earthquake. The 2004 experience was unprecedented in South Asia. Unaffected by tsunami hazards in the past, tsunami geology is a nascent field for most South Asian researchers. Very little background field data is available on the deformational features of great earthquakes along this plate boundary and the depositional characteristics of extreme coastal surges, such as tsunamis and storms. Where do we begin our search for evidence of past tsunamigenic earthquakes? How best can we use the 2004 tsunami and its deposits as a proxy? What problems are encountered in the interpretations? This thesis addresses these questions in part and presents observations from the Andaman Islands (the ~400 km, northern segment of the Sumatra-Andaman subduction zone) and the southeast coast of India, towards developing a reliable database of tsunami geology for 2004-type events. The premise is that regions affected by the 2004 earthquake are more likely to conserve signatures from older events. Based on the stratigraphic context of the proxy and quality of age estimates, this work presents evidence for past earthquake related deformation and tsunami deposition. In this work we use deformational and depositional features from the Andaman Islands, falling within the 2004 rupture zone and from one location on the Tamil Nadu coast of India (Kaveripattinam). From a perceptive understanding of the features related to tectonic deformation of the Sumatra-Andaman subduction zone, we have selected the Andaman segment that demonstrates explicit evidence for deformation and tsunami deposition through geomorphological and stratigraphic features, which are key to our exploration. A gist of each chapter is given below. The introduction (chapter 1) presents the background, motivation and scope of this work and the organization of this thesis, also summarizing the contents of each chapter. Chapter 2 provides a review of literature on subduction zone earthquakes and updates on tsunami geology, to place this study in the global context. The next two chapters discuss the seismotectonics of the Sumatra-Andaman plate boundary, the important earthquakes and their source processes. In chapter 3 we discuss the Andaman segment (from 10–15° N), characterized by relatively lower level seismicity, but distinctive, as it falls within the northern limit of the 2004 rupture. The deformational and depositional features here are better exposed due to availability of land straddling the hinge line separating the areas of 2004 uplift and subsidence. Here, the pre-2004 earthquakes used to occur along a gently dipping subducting slab, up to a depth of about 40 km. Post-2004, the earthquakes moved up-dip, extending also to the outer-rise and outer-ridge regions, expressing post-earthquake relaxation [Andrade and Rajendran, 2011]. The southern Nicobar segment (5–10° N) differs from the Andaman segment in its style of deformation and seismic productivity. The decreasing obliquity of convergence, the likely influence of a subducting ocean ridge on the subducting plate and the character of the subducting oceanic plate make this segment distinctly different. In chapter 4 we present an analysis of its seismotectonic environment based on the well-constrained focal mechanisms of historic and recent earthquakes. We report that left-lateral strike-slip faulting on near N-S oriented faults control the deformation and the style of faulting is consistent to ~80 km within the subducting slab [Rajendran, K. et al., 2011]. The 11 April 2012 sequence of earthquakes on the subducting oceanic plate, between the Sumatra Trench and the Ninety East Ridge are the more recent among the oceanic intraplate earthquakes that demonstrate the reactivation of N-S oriented fossil fractures. The limited availability of land and the 2004 coseismic deformation dominated by subsidence, followed by prolonged waterlogging makes exploration difficult in the Nicobar segment. Thus, we focus on the Andaman Islands for deformational and depositional evidence, using observations that can be corroborated through multiple proxies and depositional environments that are not prone to other coastal surges, such as cyclones and storms. The criteria for selection of sites, evaluation of deposits and determination of limiting ages are discussed in chapters 5 through 9. In chapter 5 we discuss different types of coastal environments and their response to high-energy sea surges. We also give a brief review of the comparative analyses of storm and tsunami deposits, a highly debated issue and then discuss important characteristics of these two deposits, using examples from the 2004 tsunami and the 2011 Thane cyclone that affected parts of the Tamil Nadu coast. An important component of tsunami geology is the ability to identify and select datable material from tsunami deposits and chose an appropriate method for dating (chapter 6). The types of material used vary from peat layers, peat-rich soil, gastropod shells, wood, charcoal, organic remains such as bones, coral fragments, pottery sherds and buried soil. Techniques such as AMS Carbon-14 and Thermoluminescence are commonly used with appropriate calibrations and corrections. In addition to the dates generated in this study (based on wood and shell dates) we use some previous dates from the entire stretch of the rupture within the Indian Territory and assign a relative grading to these ages, based on the quality criterion evolved in this study. We believe that this is the first attempt to segregate age data obtained from coastal deposits, and assign them a specific quality grading based on their environment of deposition and the type of material dated. Chapter 7 presents results of our investigations in the Andaman Islands, which cover ~30% of the rupture area. A coseismically subsided mangrove from Rangachanga (Port Blair, east coast of South Andaman) led us to a former subsidence during AD 770–1040, which we believe is the most convincing evidence for a previous tectonic event. Data based on inland deposits of coral and organic debris yielded a younger age in the range of AD 1480–1660. Both these dates fall in the age brackets reported from other regions of this plate boundary (mainly Sumatra) as well as distant shores of Sri Lanka, Thailand and mainland India. To understand the nature of distant deposits, we present observations from Kaveripattinam, an ancient port city on the east coast of India, where a high-energy sea surge deposit, found 1 km inland is attributed to a paleotsunami. The inland location of this archeological site at an elevation of 2 m and characteristics of the deposit that help discriminate it from typical storm deposition provide clinching evidence in favor of a 1000-year old regional tsunami (chapter 8). In chapter 9 we discuss the results of our study. We evaluate the nature of deformation/deposition and the calibrated age data in the context of their environments. Ages based on the organic material associated with coral debris (at Hut Bay and Interview Island) and the remains of mangrove roots, 1 m below the present ground level (at Port Blair) are considered as reliable estimates, due to their sheltered inland location and the in situ root horizon used for dating. Age data from Kaveripattinam is also considered reliable, based on its inland location beyond the reach of storm surges, sediment characteristics typical of tsunami deposition and ages based on multiple methods and samples. The age data based on the sites presented in this thesis are more conclusive about the 800 to 1100 AD and 1250 to 1450 AD tsunamis, and the former is represented from regions closer to the 2004 source as well as distant shores reached by its tsunami. Chapter 10 presents our conclusions and the scope for future studies. We present this as the first study of its kind in the northeastern Bay of Bengal, wherein the coseismic vertical coastal deformation features along an interplate subduction boundary and a variety of tsunami deposits are used to categorize depositional environments and ages of paleoearthquakes and tsunamis. To our knowledge, this is the first study of its kind where the effects of a recent tsunami have been used to evaluate paleodeposits based on their respective environments of occurrence. Our results have implications for tsunami geology studies in coastal regions prone to tsunami hazard.