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Sample records for indian ocean based

  1. Indian Ocean analyses

    NASA Technical Reports Server (NTRS)

    Meyers, Gary

    1992-01-01

    The background and goals of Indian Ocean thermal sampling are discussed from the perspective of a national project which has research goals relevant to variation of climate in Australia. The critical areas of SST variation are identified. The first goal of thermal sampling at this stage is to develop a climatology of thermal structure in the areas and a description of the annual variation of major currents. The sampling strategy is reviewed. Dense XBT sampling is required to achieve accurate, monthly maps of isotherm-depth because of the high level of noise in the measurements caused by aliasing of small scale variation. In the Indian Ocean ship routes dictate where adequate sampling can be achieved. An efficient sampling rate on available routes is determined based on objective analysis. The statistical structure required for objective analysis is described and compared at 95 locations in the tropical Pacific and 107 in the tropical Indian Oceans. XBT data management and quality control methods at CSIRO are reviewed. Results on the mean and annual variation of temperature and baroclinic structure in the South Equatorial Current and Pacific/Indian Ocean Throughflow are presented for the region between northwest Australia and Java-Timor. The mean relative geostrophic transport (0/400 db) of Throughflow is approximately 5 x 106 m3/sec. A nearly equal volume transport is associated with the reference velocity at 400 db. The Throughflow feeds the South Equatorial Current, which has maximum westward flow in August/September, at the end of the southeasterly Monsoon season. A strong semiannual oscillation in the South Java Current is documented. The results are in good agreement with the Semtner and Chervin (1988) ocean general circulation model. The talk concludes with comments on data inadequacies (insufficient coverage, timeliness) particular to the Indian Ocean and suggestions on the future role that can be played by Data Centers, particularly with regard to quality

  2. Reevaluation of plate motion models based on hotspot tracks in the Atlantic and Indian Oceans

    SciTech Connect

    Baksi, A.K.

    1999-01-01

    Plate motion models based on hotspot tracks in the Atlantic and Indian Oceans predict minimal movement (less than a few millimeters per year) between these hotspots and their counterparts in the Pacific Ocean for the past {approximately}100 m.yr., whereas plate circuit exercises indicate relative motions of {approximately}20 mm/yr. Hotspot-based models also suggest that the Rajmahal Traps, India, were located {approximately}1,000 km away from the Kerguelen hotspot at {approximately}115 Ma, and the Deccan Traps, India, were located a similar distance from the Reunion hotspot at {approximately}65 Ma; this is at odds with conclusions derived from paleomagnetism, plate circuits, and geochemical parameters that suggest a genetic link between flood basalt provinces in India and hotspots in the Indian Ocean. These divergent views may be explained by plume action {approximately}1,000 km from its center or errors in the hotspot motion models. The latter hypothesis is scrutinized in this article by examination of the radiometric ages for hotspot tracks in the Atlantic and Indian Oceans. The {sup 40}/{sup 39}Ar step-heating data for rocks defining the tracks of the Reunion and Kerguelen hotspots in the Indian Ocean and the Great Metero and Tristan da Cunha hotspots in the Atlantic Ocean are critically reexamined. Of {approximately}35 such ages utilized for deriving plate motion models for the past 130 m.yr., at best, only three ({approximately}32, {approximately}50, and {approximately}52 Ma) in the Indian Ocean and one ({approximately}65 Ma) for the Atlantic Ocean may be treated as crystallization ages. Conclusions based on hotspot track modeling for Late Cretaceous to Eocene time are suspect, and those for the Early to Late Cretaceous period are untenable. In the absence of precise age data for the tracks of hotspots in the Atlantic and Indian Oceans, and inconsistent age progressions noted within a single volcanic chain, plate circuit models serve as the superior technique

  3. Indian Ocean Triple Junction

    SciTech Connect

    Tapscott, C.R.; Patriat, P.; Fisher, R.L.; Sclater, J.G.; Hoskins, H.; Parsons, B.

    1980-09-10

    The boundaries of three major plates (Africa, India, and Antarctica) meet in a triple junction in the Indian Ocean near 25 /sup 0/S, 70 /sup 0/E. Using observed bathymetry and magnetic anomalies, we locate the junction to within 5 km and show that it is a ridge-ridge-ridge type. Relative plate motion is N60 /sup 0/E at 50 mm/yr (full rate) across the Central Indian Ridge, N47 /sup 0/E at 60 mm/yr across the Southeast Indian Ridge, and N3 /sup 0/W at 15 mm/yr across te Southwest Indian Ridge; the observed velocity triangle is closed. Poles of instantaneous relative plate motion are determined for all plate pairs. The data in the South Atlantic and Indian oceans are consistent with a rigid African plate without significant internal deformation. Two of the ridges at the triple junction are normal midocean spreading centers with well-defined median valleys. The Southwest Indian Ridge, however, has a peculiar morphology near the triple junction, that of an elongate triangular deep, with the triple junction at its apex. The floor of the deep represents crust formed at the Southwest Indian Ridge, and the morphology is a consequence of the evolution of the triple junction and is similar to that at the Galapagos Triple Junction. Though one cannot determine with precision the stability conditions at the triple junction, the development of the junction over the last 10 m.y. can be mapped, and the topographic expressions of the triple junction traces may be detected on the three plates.

  4. Places and Bases: The Chinese Navy’s Emerging Support Network in the Indian Ocean

    DTIC Science & Technology

    2011-01-01

    fleets that sailed the Indian Ocean between 1405 and 1433, during the Ming dy- nasty.38 Zheng He’s mariners traded silk and porcelain for Arab...Lanka served as a key nexus of China’s maritime trade in the Indian Ocean along the “ Porcelain Route” (as the maritime counterpart of the Central

  5. Two flavors of the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Endo, Satoru; Tozuka, Tomoki

    2016-06-01

    The Indian Ocean Dipole (IOD) is known as a climate mode in the tropical Indian Ocean accompanied by negative (positive) sea surface temperature (SST) anomalies over the eastern (western) pole during its positive phase. However, the western pole of the IOD is not always covered totally by positive SST anomalies. For this reason, the IOD is further classified into two types in this study based on SST anomalies in the western pole. The first type (hereafter "canonical IOD") is associated with negative (positive) SST anomalies in the eastern (central to western) tropical Indian Ocean. The second type (hereafter "IOD Modoki"), on the other hand, is associated with negative SST anomalies in the eastern and western tropical Indian Ocean and positive SST anomalies in the central tropical Indian Ocean. Based on composite analyses, it is found that easterly wind anomalies cover the whole equatorial Indian Ocean in the canonical IOD, and as a result, positive rainfall anomalies are observed over East Africa. Also, due to the basin-wide easterly wind anomalies, the canonical IOD is accompanied by strong sea surface height (SSH) anomalies. In contrast, zonal wind anomalies converge in the central tropical Indian Ocean in the IOD Modoki, and no significant precipitation anomalies are found over East Africa. Also, only weak SSH anomalies are seen, because equatorial downwelling anomalies induced by westerly wind anomalies in the west are counteracted by equatorial upwelling anomalies caused by easterly wind anomalies in the east.

  6. An assessment of the diversity in scenario-based tsunami forecasts for the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Greenslade, Diana J. M.; Annunziato, Alessandro; Babeyko, Andrey Y.; Burbidge, David R.; Ellguth, Enrico; Horspool, Nick; Srinivasa Kumar, T.; Kumar, Ch. Patanjali; Moore, Christopher W.; Rakowsky, Natalja; Riedlinger, Torsten; Ruangrassamee, Anat; Srivihok, Patchanok; Titov, Vasily V.

    2014-05-01

    This work examines the extent to which tsunami forecasts from different numerical forecast systems might be expected to differ under real-time conditions. This is done through comparing tsunami amplitudes from a number of existing tsunami scenario databases for eight different hypothetical tsunami events within the Indian Ocean. Forecasts of maximum tsunami amplitude are examined at 10 output points distributed throughout the Indian Ocean at a range of depths. The results show that there is considerable variability in the forecasts and on average, the standard deviation of the maximum amplitudes is approximately 62% of the mean value. It is also shown that a significant portion of this diversity can be attributed to the different lengths of the scenario time series. These results have implications for the interoperability of Regional Tsunami Service Providers in the Indian Ocean.

  7. Precessional forced evolution of the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Wang, Yue; Jian, ZhiMin; Zhao, Ping; Chen, JunMing; Xiao, Dong

    2015-05-01

    In a transient accelerated simulation of a coupled climate model, we identified a zonal dipole-like pattern of sea surface temperature (SST) anomalies in the tropical Indian Ocean, which is forced by precessional insolation changes since 300 ka and named as the paleo-IOD (Indian Ocean Dipole). A positive paleo-IOD mean state at 23 kyr precessional band exhibits warmer and wetter conditions over the western Indian Ocean and cooler and drier conditions over the eastern tropical Indian Ocean from August to October. This zonal thermal seesaw at the sea surface can extend downward to the subsurface ocean between 60 and 80 m and accompanies stronger oceanic upwelling in the eastern tropical Indian Ocean. The associated boreal summer-autumn tropospheric circulation anomalies are characterized by anomalous ascent over the western Indian Ocean and anomalous descent over the southeastern tropical Indian Ocean, with anomalous easterlies at the surface along the equatorial Indian Ocean. The positive paleo-IOD largely originates from local air-sea interactions that are induced by the increased summer insolation, and is also contributed by the reduced boreal winter insolation through an oceanic "heat memory effect." Our simulated dipole mode index (DMI) of SST is qualitatively consistent with the paleoceanographic reconstructed DMI based on the UK37 proxy of SST at precessional band and provides a possible explanation for the in-phase precessional variation between boreal winter insolation and the UK37 proxy of SST in the eastern tropical Indian Ocean.

  8. Giant Robber Crabs Monitored from Space: GPS-Based Telemetric Studies on Christmas Island (Indian Ocean)

    PubMed Central

    Krieger, Jakob; Grandy, Ronald; Drew, Michelle M.; Erland, Susanne; Stensmyr, Marcus C.; Harzsch, Steffen; Hansson, Bill S.

    2012-01-01

    We investigated the navigational capabilities of the world's largest land-living arthropod, the giant robber crab Birgus latro (Anomura, Coenobitidae); this crab reaches 4 kg in weight and can reach an age of up to 60 years. Populations are distributed over small Indo-Pacific islands of the tropics, including Christmas Island (Indian Ocean). Although this species has served as a crustacean model to explore anatomical, physiological, and ecological aspects of terrestrial adaptations, few behavioral analyses of it exist. We used a GPS-based telemetric system to analyze movements of freely roaming robber crabs, the first large-scale study of any arthropod using GPS technology to monitor behavior. Although female robber crabs are known to migrate to the coast for breeding, no such observations have been recorded for male animals. In total, we equipped 55 male robber crabs with GPS tags, successfully recording more than 1,500 crab days of activity, and followed some individual animals for as long as three months. Besides site fidelity with short-distance excursions, our data reveal long-distance movements (several kilometers) between the coast and the inland rainforest. These movements are likely related to mating, saltwater drinking and foraging. The tracking patterns indicate that crabs form route memories. Furthermore, translocation experiments show that robber crabs are capable of homing over large distances. We discuss if the search behavior induced in these experiments suggests path integration as another important navigation strategy. PMID:23166774

  9. Indian Ocean warming modulates Pacific climate change.

    PubMed

    Luo, Jing-Jia; Sasaki, Wataru; Masumoto, Yukio

    2012-11-13

    It has been widely believed that the tropical Pacific trade winds weakened in the last century and would further decrease under a warmer climate in the 21st century. Recent high-quality observations, however, suggest that the tropical Pacific winds have actually strengthened in the past two decades. Precise causes of the recent Pacific climate shift are uncertain. Here we explore how the enhanced tropical Indian Ocean warming in recent decades favors stronger trade winds in the western Pacific via the atmosphere and hence is likely to have contributed to the La Niña-like state (with enhanced east-west Walker circulation) through the Pacific ocean-atmosphere interactions. Further analysis, based on 163 climate model simulations with centennial historical and projected external radiative forcing, suggests that the Indian Ocean warming relative to the Pacific's could play an important role in modulating the Pacific climate changes in the 20th and 21st centuries.

  10. Atlantic and Indian Oceans Pollution in Africa

    NASA Astrophysics Data System (ADS)

    Abubakar, B.

    2007-05-01

    Africa is the second largest and most populated continent after Asia. Geographically it is located between the Atlantic and Indian Oceans. Most of the Africa's most populated and industrialized cities are located along the coast of the continent facing the Atlantic and Indian Oceans, example of such cities include Casablanca, Dakar, Accra, Lagos, Luanda and Cape town all facing the Atlantic Ocean and cities like East London, Durban, Maputo, Dar-es-salaam and Mogadishu are all facing the Indian Ocean. As a result of the geographical locations of African Coastal Cities plus increase in their population, industries, sea port operations, petroleum exploration activities, trafficking of toxic wastes and improper waste management culture lead to the incessant increase in the pollution of the two oceans. NATURE OF POLLUTION OF THE ATLANTIC OCEAN i. The petroleum exploration activities going on along the coast of "Gulf of Guinea" region and Angola continuously causes oil spillages in the process of drilling, bunkering and discharging of petroleum products in the Atlantic Ocean. ii. The incessant degreasing of the Sea Ports "Quay Aprons" along the Coastal cities of Lagos, Luanda, Cape Town etc are continuously polluting the Atlantic Ocean with chemicals. iii. Local wastes generated from the houses located in the coastal cities are always finding their ways into the Atlantic Ocean. NATURE OF POLLUTION OF THE INDIAN OCEAN i. Unlike the Atlantic ocean where petroleum is the major pollutant, the Indian Ocean is polluted by Toxic / Radioactive waste suspected to have been coming from the developed nations as reported by the United Nations Environmental Programme after the Tsunami disaster in December 2004 especially along the coast of Somalia. ii. The degreasing of the Quay Aprons at Port Elizabeth, Maputo, Dar-es-Salaam and Mongolism Sea Ports are also another major source polluting the Indian Ocean. PROBLEMS GENERATED AS A RESULT OF THE OCEANS POLLUTION i. Recent report

  11. Bats of the Western Indian Ocean Islands.

    PubMed

    O'Brien, John

    2011-08-16

    The natural colonisation of many remote oceanic islands by bats, including those of the western Indian Ocean, has been facilitated by their unique capability among mammals for powered flight. In the western Indian Ocean region, only the Malagasy islands of Madagascar and the Comoros archipelago have been naturally colonised by non-volant mammals. Despite their greater potential for inter-island dispersal, and thus gene transfer, endemicity of Chiroptera in the western Indian Ocean islands is high. Given their vulnerability to stochastic and anthropogenic disturbances, greater focus needs to be placed on investigating the demographic and ecological history of bats on Western Indian Ocean islands to safeguard not only their future, but also the ecosystem functioning on these islands, for which they are undoubtedly such an integral part. Here, I summarise the taxonomic and life history information available on bats from Western Indian Ocean islands and highlight knowledge gaps and conservation issues that threaten the continued persistence of some species.

  12. Atlantic and indian oceans pollution in africa

    NASA Astrophysics Data System (ADS)

    Abubakar, Babagana

    Africa is the second largest and most populated continent after Asia. Geographically it is located between the Atlantic and Indian Oceans. Most of the Africa's most populated and industrialized cities are located along the coast of the continent facing the Atlantic and Indian Oceans, example of such cities include Casablanca, Dakar, Accra, Lagos, Luanda and Cape town all facing the Atlantic Ocean and cities like East London, Durban, Maputo, Dar-es-salaam and Mogadishu are all facing the Indian Ocean. As a result of the geographical locations of African Coastal Cities plus increase in their population, industries, sea port operations, petroleum exploration activities, trafficking of toxic wastes and improper waste management culture lead to the incessant increase in the pollution of the two oceans. NATURE OF POLLUTION OF THE ATLANTIC OCEAN i. The petroleum exploration activities going on along the coast of "Gulf of Guinea" region and Angola continuously causes oil spillages in the process of drilling, bunkering and discharging of petroleum products in the Atlantic Ocean. ii. The incessant degreasing of the Sea Ports "Quay Aprons" along the Coastal cities of Lagos, Luanda, Cape Town etc are continuously polluting the Atlantic Ocean with chemicals. iii. Local wastes generated from the houses located in the coastal cities are always finding their ways into the Atlantic Ocean. NATURE OF POLLUTION OF THE INDIAN OCEAN i. Unlike the Atlantic ocean where petroleum is the major pollutant, the Indian Ocean is polluted by Toxic / Radioactive waste suspected to have been coming from the developed nations as reported by the United Nations Environmental Programme after the Tsunami disaster in December 2004 especially along the coast of Somalia. ii. The degreasing of the Quay Aprons at Port Elizabeth, Maputo, Dar-es-Salaam and Mongolism Sea Ports are also another major source polluting the Indian Ocean. PROBLEMS GENERATED AS A RESULT OF THE OCEANS POLLUTION i. Recent report

  13. North Atlantic forcing of tropical Indian Ocean climate.

    PubMed

    Mohtadi, Mahyar; Prange, Matthias; Oppo, Delia W; De Pol-Holz, Ricardo; Merkel, Ute; Zhang, Xiao; Steinke, Stephan; Lückge, Andreas

    2014-05-01

    The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.

  14. Validation of a satellite-based cyclogenesis technique over the North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Goyal, Suman; Mohapatra, M.; Kumar, Ashish; Dube, S. K.; Rajendra, Kushagra; Goswami, P.

    2016-10-01

    Indian region is severely affected by the tropical cyclones (TCs) due to the long coast line of about 7500 km. Hence, whenever any low level circulation (LLC) forms over the Indian Seas, the prediction of its intensification into a TC is very essential for the management of TC disaster. Satellite Application Centre (SAC) of Indian Space Research Organization (ISRO), Ahmedabad, has developed a technique to predict TCs based on scatterometer-derived winds from the polar orbiting satellite, QuikSCAT and Oceansat-II. The India Meteorological Department (IMD) has acquired the technique and verified it for the years 2010-2013 for operational use. The model is based on the concept of analogs of the sea surface wind distribution at the stage of LLC or vortex (T1.0) as per Dvorak's classifications, which eventually leads to cyclogenesis (T2.5). The results indicate that the developed model could predict cyclogenesis with a probability of detection of 61% and critical success index of 0.29. However, it shows high over-prediction of the model is better over the Bay of Bengal than over Arabian Sea and during post-monsoon season (September-December) than in pre-monsoon season (March-June).

  15. Analysis of 2012 M8.6 Indian Ocean earthquake coseismic slip model based on GPS data

    NASA Astrophysics Data System (ADS)

    Maulida, Putra; Meilano, Irwan; Gunawan, Endra; Efendi, Joni

    2016-05-01

    The CGPS (Continuous Global Position System) data of Sumatran GPS Array (CGPS) and Indonesian Geospatial Agency (BIG) in Sumatra are processed to estimate the best fit coseismic model of 2012 M8.6 Indian Ocean earthquake. For GPS data processing, we used the GPS Analysis at Massachusetts Institute of Technology (GAMIT) 10.5 software and Global Kalman Filter (GLOBK) to generate position time series of each GPS stations and estimate the coseismic offset due to the Earthquake. The result from GPS processing indicates that the earthquake caused displacement northeast ward up to 25 cm in northern Sumatra. Results also show subsidence at the northern Sumatran while the central part of Sumatra show northwest direction displacement, but we cannot find whether the subsidence or the uplift signal associated to the earthquake due to the vertical data quality. Based on the GPS coseismic data, we evaluate the coseismic slip model of Indian Ocean Earthquake produced by previous study [1], [2], [3]. We calculated coseismic displacement using half-space with earthquake slip model input and compare it with the displacement produced form GPS data.

  16. Bats of the Western Indian Ocean Islands

    PubMed Central

    O'Brien, John

    2011-01-01

    Simple Summary The purpose of this paper is to review the literature pertaining to the bat faunas of the western Indian Ocean islands, particularly in light of the identification of many new species on Madagascar and the taxonomic reassignment of others, and to summarise details of their general biology, feeding ecology, reproduction and conservation. Abstract The natural colonisation of many remote oceanic islands by bats, including those of the western Indian Ocean, has been facilitated by their unique capability among mammals for powered flight. In the western Indian Ocean region, only the Malagasy islands of Madagascar and the Comoros archipelago have been naturally colonised by non-volant mammals. Despite their greater potential for inter-island dispersal, and thus gene transfer, endemicity of Chiroptera in the western Indian Ocean islands is high. Given their vulnerability to stochastic and anthropogenic disturbances, greater focus needs to be placed on investigating the demographic and ecological history of bats on Western Indian Ocean islands to safeguard not only their future, but also the ecosystem functioning on these islands, for which they are undoubtedly such an integral part. Here, I summarise the taxonomic and life history information available on bats from Western Indian Ocean islands and highlight knowledge gaps and conservation issues that threaten the continued persistence of some species. PMID:26486500

  17. Historic Tsunami in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Dominey-Howes, D.; Cummins, P. R.; Burbidge, D.

    2005-12-01

    The 2004 Boxing Day Tsunami dramatically highlighted the need for a better understanding of the tsunami hazard in the Indian Ocean. One of the most important foundations on which to base such an assessment is knowledge of tsunami that have affected the region in the historical past. We present a summary of the previously published catalog of Indian Ocean tsunami and the results of a preliminary search of archival material held at the India Records Office at the British Library in London. We demonstrate that in some cases, normal tidal movements and floods associated with tropical cyclones have been erroneously listed as tsunami. We summarise interesting archival material for tsunami that occurred in 1945, 1941, 1881, 1819, 1762 and a tsunami in 1843 not previously identified or reported. We also note the recent discovery, by a Canadian team during a post-tsunami survey following the 2004 Boxing Day Tsunami, of archival evidence that the Great Sumatra Earthquake of 1833 generated a teletsunami. Open ocean wave heights are calculated for some of the historical tsunami and compared with those of the Boxing Day Tsunami.

  18. Age of the floor of the eastern Indian ocean.

    PubMed

    Heirtzler, J R; Veevers, J V; Bolli, H M; Carter, A N; Cook, P J; Krasheninnikov, V A; McKnight, B K; Proto-Decima, F; Renz, G W; Robinson, P T; Rocker, K; Thayer, P A

    1973-06-01

    Deep sea drilling in the eastern Indian Ocean shows that the oceanic crust off Western Australia is approximately 140 million years old and becomes younger to the west; this dates the initial opening of the Indian Ocean.

  19. Variability of the southwest Indian Ocean.

    PubMed

    de Ruijter, Wilhelmus P M; Ridderinkhof, Herman; Schouten, Mathijs W

    2005-01-15

    The variability in the southwest Indian Ocean is connected to the basin-scale and global-scale ocean circulation. Two bands of enhanced variability stretch across the Southern Indian Ocean east of Madagascar around 12 degrees S and 25 degrees S, respectively. They mark the preferred routes along which anomalies, generated by varying forcing over the central basin, near the eastern boundary or in the equatorial region, propagate westward as baroclinic Rossby waves. Sea-surface height anomalies pass along the northern tip of Madagascar and are observed by satellite altimetry to propagate into the central Mozambique Channel. There, eddies are subsequently formed that propagate southward into the Agulhas retroflection region. The anomalies along the southern band trigger the formation of large dipolar vortex pairs in the separation region of the East Madagascar Current at the southern tip of the island. South of Africa these eddies and dipoles trigger the shedding of Agulhas Rings that feed the Atlantic meridional overturning circulation with warm, salty, Indian Ocean water. Interannual variability of the forcing over the Indian Ocean, such as that associated with the Indian Ocean Dipole/El Nino climate modes, propagates along these pathways and leads to associated modulations of the eddy transports into the South Atlantic.

  20. Indian Ocean and Indian summer monsoon: relationships without ENSO in ocean-atmosphere coupled simulations

    NASA Astrophysics Data System (ADS)

    Crétat, Julien; Terray, Pascal; Masson, Sébastien; Sooraj, K. P.; Roxy, Mathew Koll

    2016-10-01

    The relationship between the Indian Ocean and the Indian summer monsoon (ISM) and their respective influence over the Indo-Western North Pacific (WNP) region are examined in the absence of El Niño Southern Oscillation (ENSO) in two partially decoupled global experiments. ENSO is removed by nudging the tropical Pacific simulated sea surface temperature (SST) toward SST climatology from either observations or a fully coupled control run. The control reasonably captures the observed relationships between ENSO, ISM and the Indian Ocean Dipole (IOD). Despite weaker amplitude, IODs do exist in the absence of ENSO and are triggered by a boreal spring ocean-atmosphere coupled mode over the South-East Indian Ocean similar to that found in the presence of ENSO. These pure IODs significantly affect the tropical Indian Ocean throughout boreal summer, inducing a significant modulation of both the local Walker and Hadley cells. This meridional circulation is masked in the presence of ENSO. However, these pure IODs do not significantly influence the Indian subcontinent rainfall despite overestimated SST variability in the eastern equatorial Indian Ocean compared to observations. On the other hand, they promote a late summer cross-equatorial quadrupole rainfall pattern linking the tropical Indian Ocean with the WNP, inducing important zonal shifts of the Walker circulation despite the absence of ENSO. Surprisingly, the interannual ISM rainfall variability is barely modified and the Indian Ocean does not force the monsoon circulation when ENSO is removed. On the contrary, the monsoon circulation significantly forces the Arabian Sea and Bay of Bengal SSTs, while its connection with the western tropical Indian Ocean is clearly driven by ENSO in our numerical framework. Convection and diabatic heating associated with above-normal ISM induce a strong response over the WNP, even in the absence of ENSO, favoring moisture convergence over India.

  1. Decadal trends in Indian Ocean ambient sound.

    PubMed

    Miksis-Olds, Jennifer L; Bradley, David L; Niu, Xiaoyue Maggie

    2013-11-01

    The increase of ocean noise documented in the North Pacific has sparked concern on whether the observed increases are a global or regional phenomenon. This work provides evidence of low frequency sound increases in the Indian Ocean. A decade (2002-2012) of recordings made off the island of Diego Garcia, UK in the Indian Ocean was parsed into time series according to frequency band and sound level. Quarterly sound level comparisons between the first and last years were also performed. The combination of time series and temporal comparison analyses over multiple measurement parameters produced results beyond those obtainable from a single parameter analysis. The ocean sound floor has increased over the past decade in the Indian Ocean. Increases were most prominent in recordings made south of Diego Garcia in the 85-105 Hz band. The highest sound level trends differed between the two sides of the island; the highest sound levels decreased in the north and increased in the south. Rate, direction, and magnitude of changes among the multiple parameters supported interpretation of source functions driving the trends. The observed sound floor increases are consistent with concurrent increases in shipping, wind speed, wave height, and blue whale abundance in the Indian Ocean.

  2. Impact of Indian Ocean Dipole on the salinity budget in the equatorial Indian Ocean

    NASA Astrophysics Data System (ADS)

    DU, Y.; Zhang, Y.

    2013-12-01

    Based on ocean reanalysis data sets and observations, this study analyzes the variability of salinity and its associated ocean dynamics in the equatorial Indian Ocean (IO). The results show that significant interannual variability of salinity in boreal fall are mainly associated with the Indian Ocean dipole (IOD) events, especially the positive IOD (pIOD) events. During pIOD events, forced by anomalous easterly winds, westward current anomalies strengthen the westward advection in summer and weaken the eastward advection of Wyrtki Jets in fall. Analysis of salinity budget indicates that salinity anomalies are mainly dominated by advection, in which zonal component is the key. As the zonal current anomalies are symmetric off the equator, mean zonal salinity gradients dominate the asymmetric distribution of low-salinity advection. Low-salinity water advects to the west, shoals mixed layer, favoring SST increasing after the mature phase of pIOD. After the decay phase, low-salinity water advects across the equator to the southwestern IO, which associates with the off-equatorial anticyclonic circulations in the southern IO. When pIOD events concur with El Niño, the low-salinity water advection strengthens and advects northward and southward simultaneously after the decay phase, due to the strong off-equatorial influence from El Niño.

  3. Getting a grip on Indian Ocean monsoons

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    An improved understanding of the Indian Ocean monsoon season could help researchers to better forecast floods and the associated spread of cholera in low-lying Bangladesh.In a joint effort by the University of Colorado at Boulder, the Asian Disaster Preparedness Center, and the Bangladesh government, researchers are using a variety of monitoring and forecast modeling tools to better understand and characterize the monsoon season's active and calm periods. By studying Indian Ocean climatic conditions and probabilities that lead to regular flooding of the Bangladesh delta, researchers also can provide probabilities concerning outbreaks of cholera, an intestinal disease that infects large segments of that country's population.

  4. Estimates of upwelling rates in the Arabian Sea and the equatorial Indian Ocean based on bomb radiocarbon.

    PubMed

    Bhushan, R; Dutta, K; Somayajulu, B L K

    2008-10-01

    Radiocarbon measurements were made in the water column of the Arabian Sea and the equatorial Indian Ocean during 1994, 1995 and 1997 to assess the temporal variations in bomb 14C distribution and its inventory in the region with respect to GEOSECS measurements made during 1977-1978. Four GEOSECS stations were reoccupied (three in the Arabian Sea and one in the equatorial Indian Ocean) during this study, with all of them showing increased penetration of bomb 14C along with decrease in its surface water activity. The upwelling rates derived by model simulation of bomb 14C depth profile using the calculated exchange rates ranged from 3 to 9 m a(-1). The western region of the Arabian Sea experiencing high wind-induced upwelling has higher estimated upwelling rates. However, lower upwelling rates obtained for the stations occupied during this study could be due to reduced 14C gradient compared to that during GEOSECS.

  5. Area Handbook for the Indian Ocean Territories.

    ERIC Educational Resources Information Center

    Stoddard, Theodore L.; And Others

    This volume, one of a series of handbooks on foreign culture, is intended as a reference tool for military and other personnel requiring an objective, comprehensive, and balanced description of the Indian Ocean Territories, namely, the two republics of Meldives and Mauritius, and the two European dependencies of Seychelles and Reunion. An…

  6. Geomagnetic secular variation in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Heirtzler, J. R.; Nazarova, K.

    2003-02-01

    Annual repeat stations in Australia and in South Africa show that secular variation may change rapidly and over short geographical distances in the Indian Ocean area. Satellite models show large secular variations in the center of the Indian Ocean where there are few island geomagnetic observatories. This paper investigates marine geomagnetic measurements to see if they give more information about secular variations in this area. Between 1960 and 1988 there were more than 70 port-to-port cruises with ships towing proton precession magnetometers in the Indian Ocean. Change in field intensity from one cruise to another provides new information about the secular variation in this part of the world. Several methods were investigated to determine this change from the ship's data. Observing the change on closely parallel or crossing tracks provides an estimate of this change. These results indicate that there are short time and distance scales of secular variation in the Indian Ocean which have not been accounted for in geomagnetic field models.

  7. Coral-based history of lead and lead isotopes of the surface Indian Ocean since the mid-20th century

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Mi; Boyle, Edward A.; Suci Nurhati, Intan; Pfeiffer, Miriam; Meltzner, Aron J.; Suwargadi, Bambang

    2014-07-01

    Anthropogenic lead (Pb) from industrial activities has greatly altered the distribution of Pb in the present-day oceans, but no continuous temporal Pb evolution record is available for the Indian Ocean despite rapidly emerging industries around the region. Here, we present the coral-inferred annual history of Pb concentration and isotope ratios in the surface Indian Ocean since the mid-20th century (1945-2010). We analyzed Pb in corals from the Chagos Archipelago, western Sumatra and Strait of Singapore - which represent the central Indian Ocean via nearshore sites. Overall, coral Pb/Ca increased in the mid-1970s at all the sites. However, coral Pb isotope ratios evolve distinctively at each site, suggesting Pb contamination arises from different sources in each case. The major source of Pb in the Chagos coral appears to be India's Pb emission from leaded gasoline combustion and coal burning, whereas Pb in western Sumatra seems to be largely affected by Indonesia's gasoline Pb emission with additional Pb inputs from other sources. Pb in the Strait of Singapore has complex sources and its isotopic composition does not reflect Pb from leaded gasoline combustion. Higher 206Pb/207Pb and 208Pb/207Pb ratios found at this site may reflect the contribution of Pb from coals and ores from southern China, Indonesia, and Australia, and local Pb sources in the Strait of Singapore. It is also possible that the Pb isotope ratios of Singapore seawater were elevated through isotope exchange with natural fluvial particles considering its delta setting.

  8. Igneous Rocks of the Indian Ocean Floor.

    PubMed

    Engel, C G; Fischer, R L; Engel, A E

    1965-10-29

    Four dredge hauls from near the crest and from the eastern flank of the seismically active Mid-Indian Ocean Ridge at 23 degrees to 24 degrees S, at depths of 3700 to 4300 meters, produced only low-potassium tholeiitic basalt similar in chemical and mineralogic composition to basalts characteristic of ridges and rises in the Atlantic and Pacific oceans. A fifth haul, from a depth of 4000 meters on the lower flank of a seamount on the ocean side of the Indonesian Trench, recovered tholeiitic basalt with higher concentrations of K and Ti and slightly lower amounts of Si and Ca than the typical-oceanic tholeiite of the ridge. The last sample is vesicular, suggesting depression of the area since the basalt was emplaced. Many of the rocks dredged are variously decomposed and hydrated, but there is no evidence of important chemical modification toward conversion of the lava flows to spilite during extrusion or solidification.

  9. Igneous rocks of the Indian ocean floor

    USGS Publications Warehouse

    Engel, C.G.; Fischer, R.L.; Engel, A.E.J.

    1965-01-01

    Four dredge hauls from near the crest and from the eastern flank of the seismically active Mid-Indian Ocean Ridge at 23?? to 24??S, at depths of 3700 to 4300 meters, produced only low-potassium tholeiitic basalt similar in chemical and mineralogic composition to basalts characteristic of ridges and rises in the Atlantic and Pacific oceansA fifth haul, from a depth of 4000 meters on the lower flank of a seamount on the ocean side of the Indonesian Trench, recovered tholeiitic basalt with higher concentrations of K and Ti and slightly lower amounts of Si and Ca than the typical oceanic tholeiite of the ridgeThe last sample is vesicular, suggesting depression of the area since the basalt was emplacedMany of the rocks dredged are variously decomposed and hydrated, but there is no evidence of important chemical modification toward conversion of the lava flows to spilite during extrusion or solidification.

  10. The positive Indian Ocean Dipole-like response in the tropical Indian Ocean to global warming

    SciTech Connect

    Luo, Yiyong; Lu, Jian; Liu, Fukai; Wan, Xiuquan

    2016-02-04

    Climate models project a positive Indian Ocean Dipole (pIOD)-like SST response in the tropical Indian Ocean to global warming. By employing the Community Earth System Model (CESM) and applying an overriding technique to its ocean component Parallel Ocean Program version 2 (POP2), this study investigates the similarity and difference of the formation mechanisms for the changes in the tropical Indian Ocean during the pIOD versus global warming. Results show that their formation processes and related seasonality are quite similar; in particular, the Bjerknes feedback is the leading mechanism in producing the anomalous cooling over the eastern tropics in both cases. Some differences are also found, including that the cooling effect of the vertical advection over the eastern tropical Indian Ocean is dominated by the anomalous vertical velocity during the pIOD while it is dominated by the anomalous upper-ocean stratification under global warming. Lastly, these findings above are further examined with an analysis of the mixed layer heat budget.

  11. The positive Indian Ocean Dipole-like response in the tropical Indian Ocean to global warming

    DOE PAGES

    Luo, Yiyong; Lu, Jian; Liu, Fukai; ...

    2016-02-04

    Climate models project a positive Indian Ocean Dipole (pIOD)-like SST response in the tropical Indian Ocean to global warming. By employing the Community Earth System Model (CESM) and applying an overriding technique to its ocean component Parallel Ocean Program version 2 (POP2), this study investigates the similarity and difference of the formation mechanisms for the changes in the tropical Indian Ocean during the pIOD versus global warming. Results show that their formation processes and related seasonality are quite similar; in particular, the Bjerknes feedback is the leading mechanism in producing the anomalous cooling over the eastern tropics in both cases.more » Some differences are also found, including that the cooling effect of the vertical advection over the eastern tropical Indian Ocean is dominated by the anomalous vertical velocity during the pIOD while it is dominated by the anomalous upper-ocean stratification under global warming. Lastly, these findings above are further examined with an analysis of the mixed layer heat budget.« less

  12. An Indian Ocean precursor for Indian summer monsoon rainfall variability

    NASA Astrophysics Data System (ADS)

    Sreejith, O. P.; Panickal, S.; Pai, S.; Rajeevan, M.

    2015-11-01

    The Indian summer monsoon rainfall (ISMR) depicts large interannual variability strongly linked with El Niño-Southern Oscillation (ENSO). However, many of the El Niño years were not accompanied by deficient ISMR. The results from the study reveal the significant role of coupled air-sea interaction over the tropical Indian Ocean (IO) in modifying the ENSO-ISMR association. The IO warm water volume (WWV), a measure of heat content variations in the equatorial IO has strong influence on ISMR. A deepening (shoaling) of thermocline in the eastern equatorial IO (EEIO) during late boreal spring (April-May) accompanied by increase (decrease) in WWV anomalies weaken (enhance) the ISMR by enhancing (suppressing) the convection over EEIO resulting in the below (above) normal ISMR. Thus, the changes in the WWV anomalies in the EEIO along with ENSO conditions during boreal spring can be considered as a precursor for the performance of subsequent ISMR.

  13. Molecular based phylogenetic species recognition in the genus Pampus (Perciformes: Stromateidae) reveals hidden diversity in the Indian Ocean.

    PubMed

    Divya, P R; Mohitha, C; Rahul, G Kumar; Rajool Shanis, C P; Basheer, V S; Gopalakrishnan, A

    2017-04-01

    Pomfrets (Genus Pampus) are commercially important fishes in the Indo Pacific region. The systematics of this genus is complicated due to morphological similarities between species. The silver pomfret from Indian waters has long been considered to be Pampus argenteus. The objective of the study was to utilize the mitochondrial COI gene to establish the molecular identity of the silver pomfret distributed in Indian waters and to resolve the phylogenetic relationships among Pampus species in the world based on sequence data in the NCBI database. Seven valid Pampus species are identified in this study. The mean genetic divergence value calculated between clades representing these species was 7.9%. The mean genetic distance between the so-called Pampus argenteus from Indian waters and sequences attributed to P. argenteus from the South China Sea, where the neotype of this species was collected, was found to be greater than 12%, strongly supporting the likelihood of the Indian species being distinct. The Indian Pampus species show very close affinity to P. cinereus, with inter species differences less than 2%. The taxonomic identity of the silver pomfret in India is also discussed here, in light of molecular and morphological evidence.

  14. Warm Indian Ocean, Weak Asian Monsoon

    NASA Astrophysics Data System (ADS)

    Koll Roxy, Mathew; Ritika, Kapoor; Terray, Pascal; Murtugudde, Raghu; Ashok, Karumuri; Nath Goswami, Buphendra

    2015-04-01

    There are large uncertainties looming over the status and fate of the South Asian monsoon in a changing climate. Observations and climate models have suggested that anthropogenic warming in the past century has increased the moisture availability and the land-sea thermal contrast in the tropics, favoring an increase in monsoon rainfall. In contrast, we notice that South Asian subcontinent experienced a relatively subdued warming during this period. At the same time, the tropical Indian Ocean experienced a nearly monotonic warming, at a rate faster than the other tropical oceans. Using long-term observations and coupled model experiments, we suggest that the enhanced Indian Ocean warming along with the suppressed warming of the subcontinent weaken the land-sea thermal contrast throughout the troposphere, dampen the monsoon Hadley circulation, and reduce the rainfall over South Asia. As a result, the summer monsoon rainfall during 1901-2012 shows a significant weakening trend over South Asia, extending from Pakistan through central India to Bangladesh.

  15. Interannual variability of Indian Ocean subtropical mode water subduction rate

    NASA Astrophysics Data System (ADS)

    Ma, Jie; Lan, Jian

    2016-08-01

    The interannual variation of Indian Ocean subtropical mode water (IOSTMW) subduction rate in the Southwest Indian Ocean from 1980 to 2007 is investigated in this paper based on Simple Ocean Data Assimilation (SODA) outputs. Climatology of subduction rate exceeds 75 m/year in the IOSTMW formation area. The renewal time of permanent pycnocline water mass based on the subduction rate is calculated for each density class: 3-6 years for IOSTMW (25.8 < σ θ < 26.2 kg m-3). Subduction rate in the Southwest Indian Ocean subtropical gyre exhibits a great year-to-year variability. This interannual variations of the IOSTMW subduction rate is primarily dominated by the lateral induction term, associated with the interannual variations of strong meridional gradient of winter mixed layer depth (MLD). The slope of the mixed layer depth in the mode water is closely linked to the large variations of deep late winter MLD in the mid-latitudes and negligible variations of shallow winter MLD in lower latitudes. It is further identified that the interannual variation of late winter MLD in this area is largely controlled by the latent and sensible heat flux components. The water volume of the permanent pycnocline in the IOSTMW distribution area is also found to show a significant interannual variability, and it is well correlated with the interannual variation of subduction rate.

  16. Indian Ocean heat content changes masked by multi-decadal variability: Is the Indian Ocean warming or not?

    NASA Astrophysics Data System (ADS)

    Ummenhofer, Caroline; Biastoch, Arne; Böning, Claus

    2015-04-01

    The Indian Ocean has sustained robust surface warming in recent decades, with warming rates exceeding those of other tropical ocean basins. Significant, non-uniform trends in Indian Ocean sea surface temperatures - both in observations and projections for the 21st Century - have the potential to impact regional climate, through variations in the monsoon circulation, characteristics of Indian Ocean Dipole events, and the associated hydroclimate across the wider Indo-Pacific. However, it remains unclear what role decadal to multi-decadal variability in upper-ocean Indian Ocean thermal characteristics play in these trends. Using high-resolution ocean model hindcasts building on the ocean/sea-ice numerical Nucleus for European Modelling of the Ocean (NEMO) framework forced with atmospheric forcing fields of the Coordinated Ocean Reference Experiments (CORE), the characteristics of Indian Ocean temperature changes are explored. Sensitivity experiments, where interannual atmospheric forcing variability is restricted to thermal or wind-stress forcing only, support the interpretation of forcing mechanisms for the evolution of temperature characteristics across the Indian Ocean, focusing on the top 700m. Simulated temperature changes across the Indian Ocean in the hindcasts are consistent with those recorded in observational products, as well as ocean reanalyses. Assessment of Indian Ocean heat content since the 1950s suggests extensive (subsurface) cooling for much of the tropical Indian Ocean. The presence of substantial multi-decadal variability in its heat content further implies caution in interpreting linear trends in thermal properties, as long-term trends can be masked. The sensitivity experiments reveal that cooling trends in Indian Ocean heat content since the mid-1960s to the late 1990s are largely driven by wind-stress forcing, likely due to remote Pacific wind forcing associated with the Pacific Decadal Oscillation (PDO). As such, multi-decadal wind-forcing has

  17. Ocean atmosphere thermal decoupling in the eastern equatorial Indian ocean

    NASA Astrophysics Data System (ADS)

    Joseph, Sudheer; Ravichandran, M.; Kumar, B. Praveen; Jampana, Raju V.; Han, Weiqing

    2016-09-01

    Eastern equatorial Indian ocean (EEIO) is one of the most climatically sensitive regions in the global ocean, which plays a vital role in modulating Indian ocean dipole (IOD) and El Niño southern oscillation (ENSO). Here we present evidences for a paradoxical and perpetual lower co-variability between sea-surface temperature (SST) and air-temperature (Tair) indicating instantaneous thermal decoupling in the same region, where signals of the strongly coupled variability of SST anomalies and zonal winds associated with IOD originate at inter-annual time scale. The correlation minimum between anomalies of Tair and SST occurs in the eastern equatorial Indian ocean warm pool region (≈70°E-100°E, 5°S-5°N), associated with lower wind speeds and lower sensible heat fluxes. At sub-monthly and Madden-Julian oscillation time scales, correlation of both variables becomes very low. In above frequencies, precipitation positively contributes to the low correlation by dropping Tair considerably while leaving SST without any substantial instant impact. Precipitation is led by positive build up of SST and post-facto drop in it. The strong semi-annual response of SST to mixed layer variability and equatorial waves, with the absence of the same in the Tair, contributes further to the weak correlation at the sub-annual scale. The limited correlation found in the EEIO is mainly related to the annual warming of the region and ENSO which is hard to segregate from the impacts of IOD.

  18. Effects of Aerosols over the Indian Ocean

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Aerosols that contain black carbon both absorb and reflect incoming sunlight. Even as these atmospheric particles reduce the amount of sunlight reaching the surface, they increase the amount of solar energy absorbed in the atmosphere, thus making it possible to both cool the surface and warm the atmosphere. The images above show satellite measurements of the region studied during the Indian Ocean Experiment (INDOEX)a vast region spanning the Arabian Sea and Bay of Bengal (west to east), and from the foot of the Himalayan Mountains, across the Indian subcontinent to the southern Indian Ocean (north to south). The Aerosol images show aerosol pollution (brownish pixels) in the lower atmosphere over the INDOEX study area, as measured by the Moderate-resolution Imaging Spectroradiometer (MODIS) aboard Terra. These were composited from March 14-21, 2001. The Albedo images show the total solar energy reflected back to space, as measured by Clouds and Earth's Radiant Energy System (CERES) aboard Terra. White pixels show high values, greens are intermediate values, and blues are low. Note how the aerosols, particularly over the ocean, increase the amount of energy reflected back to space. The Atmospheric Warming images show the absorption of the black carbon aerosols in the atmosphere. Where the aerosols are most dense, the absorption is highest. Red pixels indicate the highest levels of absorption, blues are low. The Surface Cooling images show that the aerosol particles reduce the amount of sunlight reaching the surface. Dark pixels show where the aerosols exert their cooling influence on the surface (or a high magnitude of negative radiative forcing). The bright pixels show where there is much less aerosol pollution and the incoming sunlight is relatively unaffected.

  19. Biology, fishery, conservation and management of Indian Ocean tuna fisheries

    NASA Astrophysics Data System (ADS)

    Gopalakrishna Pillai, N.; Satheeshkumar, Palanisamy

    2012-12-01

    The focus of the study is to explore the recent trend of the world tuna fishery with special reference to the Indian Ocean tuna fisheries and its conservation and sustainable management. In the Indian Ocean, tuna catches have increased rapidly from about 179959 t in 1980 to about 832246 t in 1995. They have continued to increase up to 2005; the catch that year was 1201465 t, forming about 26% of the world catch. Since 2006 onwards there has been a decline in the volume of catches and in 2008 the catch was only 913625 t. The Principal species caught in the Indian Ocean are skipjack and yellowfin. Western Indian Ocean contributed 78.2% and eastern Indian Ocean 21.8% of the total tuna production from the Indian Ocean. The Indian Ocean stock is currently overfished and IOTC has made some recommendations for management regulations aimed at sustaining the tuna stock. Fishing operations can cause ecological impacts of different types: by catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, generation of marine debris, etc. Periodic reassessment of the tuna potential is also required with adequate inputs from exploratory surveys as well as commercial landings and this may prevent any unsustainable trends in the development of the tuna fishing industry in the Indian Ocean.

  20. Southwest Indian Ocean Bathymetric Compilation (swIOBC)

    NASA Astrophysics Data System (ADS)

    Jensen, L.; Dorschel, B.; Arndt, J. E.; Jokat, W.

    2014-12-01

    As result of long-term scientific activities in the southwest Indian Ocean, an extensive amount of swath bathymetric data has accumulated in the AWI database. Using this data as a backbone, supplemented by additional bathymetric data sets and predicted bathymetry, we generate a comprehensive regional bathymetric data compilation for the southwest Indian Ocean. A high resolution bathymetric chart of this region will support geological and climate research: Identification of current-induced seabed structures will help modelling oceanic currents and, thus, provide proxy information about the paleo-climate. Analysis of the sediment distribution will contribute to reconstruct the erosional history of Eastern Africa. The aim of swIOBC is to produce a homogeneous and seamless bathymetric grid with an associated meta-database and a corresponding map for the area from 5° to 39° S and 20° to 44° E. Recently, multibeam data with a track length of approximately 86,000 km are held in-house. In combination with external echosounding data this allows for the generation of a regional grid, significantly improving the existing, mostly satellite altimetry derived, bathymetric models. The collected data sets are heterogeneous in terms of age, acquisition system, background data, resolution, accuracy, and documentation. As a consequence, the production of a bathymetric grid requires special techniques and algorithms, which were already developed for the IBCAO (Jakobsson et al., 2012) and further refined for the IBCSO (Arndt et al., 2013). The new regional southwest Indian Ocean chart will be created based on these methods. Arndt, J.E., et al., 2013. The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0—A new bathymetric compilation covering circum-Antarctic waters. GRL 40, 1-7, doi: 10.1002/grl.50413, 2013. Jakobsson, M., et al., 2012. The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0. GRL 39, L12609, doi: 10.1029/2012GL052219.

  1. A Precambrian microcontinent in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Torsvik, Trond H.; Amundsen, Hans; Hartz, Ebbe H.; Corfu, Fernando; Kusznir, Nick; Gaina, Carmen; Doubrovine, Pavel V.; Steinberger, Bernhard; Ashwal, Lewis D.; Jamtveit, Bjørn

    2013-03-01

    The Laccadive-Chagos Ridge and Southern Mascarene Plateau in the north-central and western Indian Ocean, respectively, are thought to be volcanic chains formed above the Réunion mantle plume over the past 65.5 million years. Here we use U-Pb dating to analyse the ages of zircon xenocrysts found within young lavas on the island of Mauritius, part of the Southern Mascarene Plateau. We find that the zircons are either Palaeoproterozoic (more than 1,971 million years old) or Neoproterozoic (between 660 and 840 million years old). We propose that the zircons were assimilated from ancient fragments of continental lithosphere beneath Mauritius, and were brought to the surface by plume-related lavas. We use gravity data inversion to map crustal thickness and find that Mauritius forms part of a contiguous block of anomalously thick crust that extends in an arc northwards to the Seychelles. Using plate tectonic reconstructions, we show that Mauritius and the adjacent Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia. On the basis of reinterpretation of marine geophysical data, we propose that Mauritia was separated from Madagascar and fragmented into a ribbon-like configuration by a series of mid-ocean ridge jumps during the opening of the Mascarene ocean basin between 83.5 and 61 million years ago. We suggest that the plume-related magmatic deposits have since covered Mauritia and potentially other continental fragments.

  2. GEOFON, GITEWS and the Indian Ocean Tsunami Warning System

    NASA Astrophysics Data System (ADS)

    Hanka, W.; Saul, J.; Hoffmann, T. L.

    2008-12-01

    and processing software. Based on an innovative software architecture and code, the SeisComP 3 software package has evolved from the widely used SeisComP 1 and 2 packages developed earlier by GEOFON. It combines real-time data acquisition and quality control with automatic procedures to determine location, depth, magnitudes and other source parameters. Sophisticated alert and visualization tools provide a variety of front ends. The basic parameter calculation is done fully automatic by the software. Acoustic and optical alert tools are implemented to guarantee the attention of the seismic experts in the warning center. Operators can intervene and correct automatic results to accelerate the automatic processing and to improve location accuracy. Since May 2007, SeisComP 3 is being used as the primary processing software at the Indonesian Warning Center BMG for tsunami warning purposes. The current version of the software implements a newly-developed rapid and robust regional magnitude calculation. Since it installation in Indonesia in early May 2007, SeisComP 3 has provided realistic magnitude estimates allowing assessment of an earthquake's tsunami potential and possibly warning by BMG in less than 5 minutes. The SeisComP 3 earthquake monitoring system at BMG is already connected to similar systems in Germany, the Maldives and the Republic of Yemen, for exchange of seismic waveforms and earthquake parameters in real-time. Other countries in the Indian Ocean region will follow as soon as data from their seismic stations become available. There is also interconnection between the GITEWS and the Northeastern Atlantic and Mediterranean Tsunami Warning System (NEAMTWS).

  3. Seafloor topography and tectonic elements of the Western Indian Ocean.

    PubMed

    Parson, Lindsay M; Evans, Alan J

    2005-01-15

    The break-up of Gondwanaland and dispersal of several of its component continental fragments, which eventually formed the margins of the Indian Ocean, have produced an ocean basin of enormous variety, both in relief and in origin of seafloor features. The western half of the Indian Ocean alone contains every type of tectonic plate boundary, both active and fossil, and, along with some of the deepest fracture zones, the most complex mid-ocean ridge configurations and some of the thickest sedimentary sequences in the world's ocean basins. This ocean is one of the most diverse on the face of the globe. We explore the evolution of the morphology of the Indian Ocean floor, and discuss the effect of its variations, maxima and minima, on the interconnectivity of the ocean's water masses.

  4. Predecessors of the 2004 Indian Ocean Tsunami: Inferences Based on Historical, Archeological and Geological Evidence From the Indian Coast and the Andaman-Nicobar Islands

    NASA Astrophysics Data System (ADS)

    Rajendran, C.; Rajendran, K.; Machado, T.

    2007-12-01

    The 2004 tsunami is an unprecedented event in the Indian Ocean. Never in the recent or distant history of the region has such a transoceanic event of devastating proportion is known to have been reported. Obviously, apparent lack of historical references in the culturally ancient Southeast Asian region suggests rarity of such events. Therefore, a major question that has been posed since the 2004 tsunami is whether similar events have occurred in the region in the past. If there are predecessors, what is the frequency of such events? Resolving this question is of crucial importance in developing the recurrence history of megathrust earthquakes and assessing the tsunami hazard of the region. Our strategy has been to tackle this problem using historical and archeological data, combined with geological investigations in the affected regions of the Indian coast, including the Andaman- Nicobar Islands. Citations from south India on ancient tsunami include classic Tamil texts, which mention about a devastating sea surge around A.D. 950 in the southeastern coast of India. Our studies were focused on two ancient port cities on the east coast of India: Mammallapuram and Kaveripattinam, the latter being a major township during the first millennium. The 2004 tsunami had scoured Mammallapuram beach exposing the basements of older temples. We have identified a discordant sand deposit sandwiched between two bricklayers at a site where the ruins of different generations of temples have been excavated. The radiocarbon dates suggest that this was deposited during 955+/-30 yr B.P., close to the historically documented period of devastation of this site by a sea surge. Excavations at Kaveripattinam, located 200 km to the south, revealed a widely distributed occupation horizon of A.D. 8-10 century, marked by a superjacent sand layer. We suspect that this layer represents the A.D. 950- sea incursion mentioned in the in the classic Tamil texts, also in line with the archeological

  5. Impact of Indian Ocean Dipole on high-frequency atmospheric variability over the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Kug, Jong-Seong; Sooraj, K. P.; Jin, Fei-Fei; Luo, Jing-Jia; Kwon, Minho

    2009-09-01

    A strong relationship between Indian Ocean Dipole (IOD) and high-frequency (HF) atmospheric variability in the low-level zonal wind is reported in the present study. We found that the HF atmospheric variability over the Indian Ocean (IO) is strongly modulated by IOD events, that is, HF atmospheric variability becoming significantly energetic during negative IOD events. This relation still holds even after the ENSO effect is statistically removed. Our results suggest that the HF atmospheric variability is state-dependent on the IOD coupled system. Furthermore, it is demonstrated that there is a significant decadal change in this dependence. That is, the dependency of HF atmospheric activity on the IOD phase has become stronger in the recent decade.

  6. Southern Indian Ocean SST as a modulator for the progression of Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Shahi, Namendra Kumar; Rai, Shailendra; Mishra, Nishant

    2016-11-01

    This study explores the possibility of southern Indian Ocean (SIO) sea surface temperature (SST) as a modulator for the early phase of Indian summer monsoon and its possible physical mechanism. A dipole-like structure is obtained from the empirical orthogonal function (EOF) analysis which is similar to an Indian Ocean subtropical dipole (IOSD) found earlier. A subtropical dipole index (SDI) is defined based on the SST anomaly over the positive and negative poles. The regression map of rainfall over India in the month of June corresponding to the SDI during 1983-2013 shows negative patterns along the Western Ghats and Central India. However, the regression pattern is insignificant during 1952-1982. The multiple linear regression models and partial correlation analysis also indicate that the SDI acts as a dominant factor to influence the rainfall over India in the month of June during 1983-2013. The similar result is also obtained with the help of composite rainfall over the land points of India in the month of June for positive (negative) SDI events. It is also observed that the positive (negative) SDI delays (early) the onset dates of Indian monsoon over Kerala during the time domain of our study. The study is further extended to identify the physical mechanism of this impact, and it is found that the heating (cooling) in the region covering SDI changes the circulation pattern in the SIO and hence impacts the progression of monsoon in India.

  7. Interplay between the Indian Ocean Summer Monsoon and the Westerlies at Nam Co, southern Tibet, based on sedimentary lipid biomarkers within the past 24 ka cal BP

    NASA Astrophysics Data System (ADS)

    Günther, Franziska; Witt, Roman; Schouten, Stefan; Mäusbacher, Roland; Daut, Gerhard; Zhu, Liping; Xu, Baiqing; Yao, Tandong; Gleixner, Gerd

    2014-05-01

    The interplay between the Indian Ocean Summer Monsoon (IOSM) and the Westerlies influences the lake systems at the Tibetan Plateau. However, the spatio-temporal extension and intensity of these air masses in the past is still scarcely investigated, especially in the Last Glacial Maximum. We present results from a sediment core from Nam Co, one of the longest paleorecords on the Plateau enabling the investigation back to the Last Glacial Maximum. Different organic geochemical proxies are applied to reconstruct the monsoon-forced hydrological and environmental changes in different climatic periods (Last Glacial Maximum, Heinrich 1, Bølling-Ållerød, Younger Dryas, Early Holocene). Isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) are used as a temperature proxy, while the hydrogen isotopes (δD) of n-alkanes are used as a hydrological proxy. Based on the δD proxies, the aquatic signal lags the terrestrial one due to specific ecological thresholds which in addition to climatic changes can influence the aquatic organisms. Because the terrestrial vegetation reacts faster and more sensitive to changes in the monsoonal and climatic system, the δD of n-C29 and the reconstructed inflow water signal represent an appropriate IOSM proxy. In general, the interplay of the different air masses seems to be primary controlled by solar insolation. In the Interglacial, the high insolation generates a large land-ocean pressure gradient and strong monsoonal winds with the strongest IOSM occurring in the Early Holocene. In the glacial period, however, the weak insolation promotes Westerlies which may block the weaker IOSM and influence the Tibetan Plateau. Our results provide new insight into the variable IOSM and illustrate a remarkable shift in the lake system from the glacial to the interglacial period. Keywords: n-alkanes; iGDGTs; hydrogen isotopes (δD); Indian Ocean summer monsoon; temperature; precipitation; time lag; driving forces

  8. Comparative phylogeography of the western Indian Ocean reef fauna

    NASA Astrophysics Data System (ADS)

    Borsa, Philippe; Durand, Jean-Dominique; Chen, Wei-Jen; Hubert, Nicolas; Muths, Delphine; Mou-Tham, Gérard; Kulbicki, Michel

    2016-04-01

    Assessing patterns of connectivity at the community and population levels is relevant to marine resource management and conservation. The present study reviews this issue with a focus on the western Indian Ocean (WIO) biogeographic province. This part of the Indian Ocean holds more species than expected from current models of global reef fish species richness. In this study, checklists of reef fish species were examined to determine levels of endemism in each of 10 biogeographic provinces of the Indian Ocean. Results showed that the number of endemic species was higher in the WIO than in any other region of the Indian Ocean. Endemic species from the WIO on the average had a larger body size than elsewhere in the tropical Indian Ocean. This suggests an effect of peripheral speciation, as previously documented in the Hawaiian reef fish fauna, relative to other sites in the tropical western Pacific. To explore evolutionary dynamics of species across biogeographic provinces and infer mechanisms of speciation, we present and compare the results of phylogeographic surveys based on compilations of published and unpublished mitochondrial DNA sequences for 19 Indo-Pacific reef-associated fishes (rainbow grouper Cephalopholis argus, scrawled butterflyfish Chaetodon meyeri, bluespot mullet Crenimugil sp. A, humbug damselfish Dascyllus abudafur/Dascyllus aruanus, areolate grouper Epinephelus areolatus, blacktip grouper Epinephelus fasciatus, honeycomb grouper Epinephelus merra, bluespotted cornetfish Fistularia commersonii, cleaner wrasse Labroides sp. 1, longface emperor Lethrinus sp. A, bluestripe snapper Lutjanus kasmira, unicornfishes Naso brevirosris, Naso unicornis and Naso vlamingii, blue-spotted maskray Neotrygon kuhlii, largescale mullet Planiliza macrolepis, common parrotfish Scarus psicattus, crescent grunter Terapon jarbua, whitetip reef shark Triaenodon obesus) and three coastal Indo-West Pacific invertebrates (blue seastar Linckia laevigata, spiny lobster

  9. New Indian Ocean Program Builds on a Scientific Legacy

    NASA Astrophysics Data System (ADS)

    Hood, Raleigh R.; McPhaden, Michael J.; Urban, Ed

    2014-09-01

    Prior to the International Geophysical Year (1957-1958) and before the acceptance of ideas about continental drift and the emergence of the theory of plate tectonics, the Indian Ocean was viewed as one of the last great frontiers of Earth exploration. During this post-World War II era, many new technologies were emerging for sampling the ocean and atmosphere and for mapping deep-ocean topography. Yet fundamental descriptive work still remained to be done on oceanic and atmospheric circulation, marine geology, and biological and ecological variability in the Indian Ocean.

  10. Radiolarian artificial neural network based paleo sea surface water temperature and salinity changes during the last glacial cycle in the Timor Sea, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Gupta, S. M.; Malmgren, B. A.

    2015-12-01

    The western Pacific water enters into the Timor Sea (tropical Indian Ocean) by the thermohaline conveyor belt, and this region is under the influence of the SW monsoon. The higher precipitation during the monsoon rains lower the surface salinity in the north-eastern Indian Ocean towards the Bay of Bengal; whereas, the Arabian Sea remains highly saline due to higher evaporation in the region surrounding Arabian deserts. The salinity contrast in the northern Indian Ocean is very unique, and the radiolarian micro-zooplanktons living in the surface water serve a very good proxy for the monsoonal changes in the surface sea-water temperature (SST) and salinity in the geological past. We studied radiolarian faunal variation in the core MD01-2378, located at ~13oS and ~121oE (1783 m water depth), at the inlet of the thermohaline circulation into the Timor Sea. We applied the modern radiolarian based artificial neural networks (ANNs) (Gupta and Malmgren, 2009) to derive the SST and salinity during August-October for the last 140 ka (the full last glacial cycle). Based on the mean estimates of the 10 ANNs, the root mean square error in prediction (RMSEP) for SST is ~1.4oC with correlation between observed and estimated values r=0.98 (Gupta and Malmgren, 2009). Similarly, the RMSEP is 0.3 psu (r=0.94) for the salinity estimates. We derived paleo-SSTs and salinity values using modern radiolarian ANNs and the fossil radiolarian data generated from the core for the last 140-ka (Fig.1). The age model of the core is based on δ18O benthic oxygen isotope stratigraphy and 21 AMS 14C ages up to ~30-ka (Holbourn et al., 2005). Paleo SST-summer varied between 22-28.5oC, and it is in very good agreement with the δ18O benthic record of Holbourn et al. (2005) defining the Last Glacial Maximum (~24 ka) and the Eemian (~125 ka) stages. The salinity fluctuated between 34-35 psu, and compared well with oxygen isotope record representing the LGM and Eemian periods. We gratefully acknowledge

  11. Role of south Indian Ocean swells in modulating the north Indian Ocean wave climate through modelling and remote sensing

    NASA Astrophysics Data System (ADS)

    Samiksha, S. V.; Vethamony, P.; Aboobacker, V. M.; Rashmi, R.

    2012-04-01

    Implementation and validation of a third generation wave model, Wavewatch III was used to study the characteristics of the south Indian ocean swells and their propagation in the north Indian Ocean. The NCEP reanalysis wind data (2.5° x 2.5°) has been used to generate the wind waves for the entire Indian Ocean during 2006 - 2007. The modelled wave parameters have been compared with measured buoy data and with merged altimeter data. The model results show good agreement with the buoy and altimeter data. A case study is carried out to study the propagation of the swells generated at the roaring 40°S in the Indian Ocean during May 2007. The "southern swell" occurred during May 2007 has been successfully reproduced in the wave model, which confirmed by the comparison of modelled significant wave heights with the merged altimeter significant wave heights. These swells were generated in the Atlantic ocean near the southern tip of South Africa and propagated towards the north Indian Ocean. These waves touches the Madagascar region and further hits the La Reunion islands after three days thus creating numerous damages near the islands. The magnitude of the swell is around 15m near the generation area and it reduces to around 6m near the La Reunion islands while propagating towards the north Indian Ocean. Further the swell energy is spataially distributed in the northern and southern Indian Ocean. The study reveals that the swells generated in the roaring forties and propagating in the SW/SSW direction influences more to Bay of Bengal than Arabian Sea. This occurs during pre-monsoon season primarily because large scale winds are weak in the north Indian Ocean during this period and hence swells from south Indian Ocean dominates at this time. The case of "southern swell" also happened to be at the same season. Further wave parameters were extracted at few locations in the northern Indian Ocean to study the impact of May 2007 swells on the wave climate. An average of around

  12. Navy Tactical Applications Guide. Volume 5. Part 1. Indian Ocean (Red Sea/Persian Gulf) Weather Analysis and Forecast Applications. Revision.

    DTIC Science & Technology

    1985-02-01

    Tactical Applications Guide. Volume 5. Part I Indian Ocean (Red Sea/Persian Gulf) Weather Analysis and Forecast Applications . . PERFORMING ORD. REPORT...and ideaittp by hiocA nb..) Meteorological Satellite Systems Southwest Monsoon Analysis and Forecast Applications Coastal Zone Phenomena Indian Ocean...describing regional environmental analysis and forecast applications based on satellite data and conventional meteorological observations for the Indian Ocean

  13. Abyssal benthos of the central Indian Ocean

    NASA Astrophysics Data System (ADS)

    Parulekar, A. H.; Harkantra, S. N.; Ansari, Z. A.; Matondkar, S. G. P.

    1982-12-01

    Quantitative studies of the abyssal benthos (3600 to 5300 m) of the central Indian Ocean show a rich fauna and high standing crops. Density of 3 meiofaunal and 12 macrofaunal taxa are large (2175 to 15233; x = 6441 m -2) Polychaetes (41.6%), peracarid crustaceans (31.7%), ophiuroids (12.2%), echiuroid-bryozoa (9.7%), molluscs (4.8%), and agglutinating rhizopod protozoans form the macrofauna. Meiofaunal taxa are nematodes (69.4%), harpacticoid copepods (26.6%), and ostracods (4%). Meiofauna abundances are positively correlated with distance from shore, whereas the distribution and abundance of macrofauna are independent of variations in depth and distance from the shore. Ratio of macro to meiofauna in the total population is 1 to 31. The benthic standing crop is uniformly high (0.54 to 13.73 g m -2; x = 2.70 g m -2) and many times larger than previously reported for comparable depths in other oceans and from the same region. Biomass values are significantly related to distance from shore and the type of substratum. Contribution of macro and meiofauna to the total standing crop was in the ratio of 31 to 1. High benthic biomass and rich fauna are consequences of high organic production in the euphotic zone. The correlation between biomass of the total oxidizable organic matter in the water column and the benthic standing crop is statistically significant ( r = -0.64) at the P < 0.05 level. Rich fauna and high standing crop were associated with the occurrence of polymetallic nodules.

  14. Mass, heat and freshwater fluxes in the South Indian Ocean

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    1986-01-01

    Six hydrographic sections were used to examine the circulation and property fluxes in the South Indian Ocean from 10 to 32 deg S. The calculations were made by applying an inverse method to the data. In the interior of the South Indian Ocean, the geostrophic flow is generally northward. At 18 deg S, the northward interior mass flux is balanced by the southward Ekman mass flux at the surface, whereas at 32 deg S the northward interior mass flux is balanced by the southward mass flux of the Agulhas Current. There is a weak, southward mass flux of 6 x 10 to the 9th kg/s in the Mozambique Channel. The rate of water exchange between the Pacific Ocean and the Indian Ocean is dependent on the choice of the initial reference level used in the inverse calculation. The choice of 1500 m, the depth of the deep oxygen minimum, has led to a flux of water from the Pacific Ocean to the Indian Ocean at a rate of 6.6 x 10 to the 9th kg/s. Heat flux calculations indicate that the Indian Ocean is exporting heat to the rest of the world's oceans at a rate of -0.69 x 10 to the 15th W at 18 deg S and -0.25 x 10 to the 15th W at 32 deg S (negative values being southward).

  15. Heavy metal contamination in the Western Indian Ocean (a review)

    NASA Astrophysics Data System (ADS)

    Mamboya, F. A.; Pratap, H. B.; Björk, M.

    2003-05-01

    Western Indian Ocean Coast has many potential marine ecosystems such as mangrove, seagrass meadows, macroalgae, and coral reefs. It is largely unspoiled environment however, tourism and population growth in coastal urban centres, industrialization, are presenting a risk of pollutants input to the marine environment of the Western Indian Ocean. Mining, shipping and agricultural activities also input contaminants into the marine environment via runoff, vessel operations and accidental spillage. Heavy metals are among the pollutants that are expected to increase in the marine environment of the Western Indian Ocean. The increase in heavy metal pollution can pose a serious health problem to marine organism and human through food chain. This paper reviews studies on heavy metal contamination in the Western Indian Ocean. It covers heavy metal studies in the sediments, biota, particulates and seawater collected in different sites. In comparison to other regions, only few studies have been conducted in the Western Indian Ocean and are localized in some certain areas. Most of these studies were conducted in Kenyan and Tanzanian coasts while few of them were conducted in Mauritius, Somalia and Reunion. No standard or common method has been reported for the analysis or monitoring of heavy metals in the Western Indian Ocean.

  16. The Second International Indian Ocean Expedition (IIOE-2)

    NASA Astrophysics Data System (ADS)

    Cowie, Greg; Hood, Raleigh

    2015-04-01

    The International Indian Ocean Expedition (IIOE) was one of the greatest international, interdisciplinary oceanographic research efforts of all time. Planning for the IIOE began in 1959 and the project officially continued through 1965, with forty-six research vessels participating under fourteen different flags. The IIOE motivated an unprecedented number of hydrographic surveys (and repeat surveys) over the course of the expedition covering the entire Indian Ocean basin. And it was an interdisciplinary endeavor that embraced physical oceanography, chemical oceanography, meteorology, marine biology, marine geology and geophysics. The end of 2015 will mark the 50th Anniversary of the completion of the IIOE. SCOR and the IOC are working to stimulate a new phase of coordinated international research focused on the Indian Ocean for a 5-year period beginning in late 2015 and continuing through 2020. The goal is to help to organize ongoing research and stimulate new initiatives in the 2015-2020 time frame as part of a larger expedition. Several International programs that have research ongoing or planned in the Indian Ocean during this time period and many countries are planning cruises in this time frame as well. These programs and national cruises will serve as a core for the new Indian Ocean research focus, which has been dubbed "IIOE-2." The overarching goal of the IIOE-2 is to advance our understanding of interactions between geological, oceanic and atmospheric processes that give rise to the complex physical dynamics of the Indian Ocean region, and to determine how those dynamics affect climate, extreme events, marine biogeochemical cycles, ecosystems and human populations. This understanding is required to predict the impacts of climate change, pollution, and increased fish harvesting on the Indian Ocean and its nations, as well as the influence of the Indian Ocean on other components of the Earth System. New understanding is also fundamental to policy makers for

  17. The Pliocene Indian Ocean: A Unique Planktonic Foraminifer Distribution

    NASA Astrophysics Data System (ADS)

    Robinson, M. M.; Dowsett, H. J.; Stoll, D. K.

    2013-12-01

    The Indian Ocean is complex in its ocean-atmosphere interactions, most notably the Indian Monsoon, and in its circulation regime that is dictated by the surrounding continental configuration. Its relative isolation from other ocean basins and its dynamic tropical processes, ruled by variations in interannual variability, create an environment of rapid response to local climate forcings. The Indian Ocean should, therefore, be among the first regions to record geologic indicators of local responses to global climate change. Despite the wealth of global paleoclimate data available for the mid-Piacenzian, ~3.3 to 3.0 Ma, the Indian Ocean has remained a region of sparse geographic coverage in terms of microfossil analysis. This climatically relevant warm period is of particular importance due to the similarity of mid-Piacenzian climate to what is projected for the near future. In the Indian Ocean, the 3.3 to 3.0 Ma interval sits at the intersection of major regional tectonically-induced oceanic and atmospheric circulation changes and global climate reorganizations including uplift of the Tibetan Plateau, expansion of the Antarctic ice sheet, closure of the Indonesian Seaway, intensification of Northern Hemisphere glaciation, and the development of the modern east-west SST gradient in the equatorial Pacific. This was a period of intense summer monsoon activity in the Indian Ocean, leading to a reorganization of the Indian monsoon ~2.8 Ma. In an effort to characterize the surface Indian Ocean during this complex climate interval, we examined the planktonic foraminifera from ODP Sites 709, 716, 722, 747, 751, 754, 757, 758 and 763, encompassing a wide range of oceanographic conditions. Quantitative analysis of Pliocene faunas highlight the unique nature of some Indian Ocean assemblages, particularly in the Bay of Bengal where a high percentage of Sphaeroidenellopsis and Sphaeroidinella points to a thermally homogenous water column capped by a persistent shallow halocline

  18. Deciphering Detailed Plate Kinematics of the Indian Ocean: A Combined Indian-Australian-French Initiative

    NASA Astrophysics Data System (ADS)

    Vadakkeyakath, Y.; Müller, R.; Dyment, J.; Bhattacharya, G.; Lister, G. S.; Kattoju, K. R.; Whittaker, J.; Shuhail, M.; Gibbons, A.; Jacob, J.; White, L. T.; Bissessur, P. D.; Kiranmai, S.

    2012-12-01

    The Indian Ocean formed as a result of the fragmentation and dispersal of East Gondwanaland since the Jurassic. The deep ocean basins in the Indian Ocean contain the imprints of this plate tectonic history, which is related with several major events such as the Kerguelen, Marion and Reunion hotspot inception and the Indo-Eurasian collision. A broad model for evolution of the Indian Ocean was proposed in the early 1980s. Subsequently, French scientists collected a large amount of magnetic data from the western and southern parts of the Indian Ocean while Indian and Australian scientists collected considerable volumes of magnetic data from the regions of Indian Ocean around their mainlands. Using these data, the Indian, French and Australian researchers independently carried out investigations over different parts of the Indian Ocean and provided improved models of plate kinematics at different sectoral plate boundaries. Under two Indo-French collaborative projects, detailed magnetic investigations were carried out in the Northwestern and Central Indian Ocean by combining the available magnetic data from conjugate regions. Those projects were complemented by additional area-specific studies in the Mascarene, Wharton, Laxmi and Gop basins, which are characterized by extinct spreading regimes. These Indo-French projects provided high resolution and improved plate tectonic models for the evolution of the conjugate Arabian and Eastern Somali basins that constrain the relative motion between the Indian-African (now Indian-Somalian) plate boundaries, and the conjugate Central Indian, Crozet and Madagascar basins that mainly constrain the relative motions of Indian-African (now Capricorn-Somalian) and Indian-Antarctic (now Capricorn-Antarctic) plate boundaries. During the same period, Australian scientists carried out investigations in the southeastern part of the Indian Ocean and provided an improved understanding of the plate tectonic evolution of the Indian

  19. Combined effects of recent Pacific cooling and Indian Ocean warming on the Asian monsoon.

    PubMed

    Ueda, Hiroaki; Kamae, Youichi; Hayasaki, Masamitsu; Kitoh, Akio; Watanabe, Shigeru; Miki, Yurisa; Kumai, Atsuki

    2015-11-13

    Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase. During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase. This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale. Here, based on model experiments, we show that the SST pattern during the hiatus explains pronounced regional anomalies of rainfall in the Asian monsoon region and thermodynamic effects due to specific humidity change are secondary. Specifically, Indo-Pacific SST anomalies cause convection to intensify over the tropical western Pacific, which in turn suppresses rainfall in mid-latitude East Asia through atmospheric teleconnection. Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.

  20. Connection of sea level height between Western Pacific and South Indian Ocean in recent decades

    NASA Astrophysics Data System (ADS)

    DU, Y.; Wang, T.; Zhuang, W.; Wang, J.

    2014-12-01

    Based on merged altimetry data and in site observations from tide gauges, we analyzed the fast increasing trend of sea surface height (SSH) in the recent two decades in the tropical Pacific and Indian Ocean. The results of analysis indicated a dynamic connection of SSH between the tropical western Pacific and the southeastern Indian Ocean. The low-frequency variations of SSH propagate westward in the tropical Pacific, enter the Indonesian Seas through the waveguide, and influence the southeastern India Ocean with the Kelvin-Rossby wave transformation. The thermal structure of upper ocean reveals the above adjustment mainly occur in the thermocline. However, the impacts from the Pacific are limited in the southeast Indian Ocean. In the central and west of the south Indian Ocean, local wind dominates the SSH changes in the last two decades. By lead-lag statistic analyses, we identified the cause of interdecadal from the interannual SSH variations. The interannual SSH variations is dominated by ENSO, forced by the anomalous wind along the equatorial Pacific. Whereas, the interdecadal SSH variations results from the off-equatorial wind stress curl, which is closely related to the Pacific Decadal Oscillation. The dynamic connections between the western Pacific and the south Indian Ocean were tested in the baroclinic Rossby wave solution and the numerical experiments based on the nonlinear reduced-gravity dynamics model.

  1. Navy Tactical Applications Guide. Volume 5. Part 1. Indian Ocean (Red Sea/Persian Gulf) Weather Analysis and Forecast Applications

    DTIC Science & Technology

    1983-06-01

    NO. Navy Tactical Applications Guide. Volume 5. Part 1 Indian Ocean (Red Sea/Persian Gulf) Weather Analysis and Forecast Applications 7...tldt It ntctf try mid Idtnlltr by block numOtr) Meteorological Satellite Systems Analysis and Forecast Applications Indian Ocean Northeast Monsoon...by block numbtr) Case studies describing regional environmental analysis and forecast applications based on satellite data and conventional

  2. Seasonal forecasting of tropical cyclogenesis over the North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Pattanaik, D. R.; Mohapatra, M.

    2016-03-01

    Over the North Indian Ocean (NIO) and particularly over the Bay of Bengal (BoB), the post-monsoon season from October to December (OND) are known to produce tropical cyclones, which cause damage to life and property over India and many neighbouring countries. The variability of frequency of cyclonic disturbances (CDs) during OND season is found to be associated with variability of previous large-scale features during monsoon season from June to September, which is used to develop seasonal forecast model of CDs frequency over the BoB and NIO based on principal component regression (PCR). Six dynamical/thermodynamical parameters during previous June-August, viz., (i) sea surface temperature (SST) over the equatorial central Pacific, (ii) sea level pressure (SLP) over the southeastern equatorial Indian Ocean, (iii) meridional wind over the eastern equatorial Indian Ocean at 850 hPa, (iv) strength of upper level easterly, (v) strength of monsoon westerly over North Indian Ocean at 850 hPa, and (vi) SST over the northwest Pacific having significant and stable relationship with CDs over BoB in subsequent OND season are used in PCR model for a training period of 40 years (1971-2010) and the latest four years (2011-2014) are used for validation. The PCR model indicates highly significant correlation coefficient of 0.77 (0.76) between forecast and observed frequency of CD over the BoB (NIO) for the whole period of 44 years and is associated with the root mean square error and mean absolute error ≤ 1 CD. With respect to the category forecast of CD frequency over BoB and NIO, the Hit score is found to be about 63% and the Relative Operating Curves (ROC) for above and below normal forecast is found to be having much better forecast skill than the climatology. The PCR model performs very well, particularly for the above and below normal CD year over the BoB and the NIO, during the test period from 2011 to 2014.

  3. Impact of an upgraded model in the NCEP Global Ocean Data Assimilation System: The tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Rahaman, Hasibur; Behringer, David W.; Penny, Stephen G.; Ravichandran, M.

    2016-11-01

    The National Centers for Environmental Prediction (NCEP) and the Indian National Centre for Ocean Information Services (INCOIS) produces global ocean analysis based on the Global Ocean Data Assimilation System (GODAS). This study shows how upgrades to the forward model simulations from MOM4p0d to MOM4p1 impact ocean analyses over the tropical Indian Ocean in GODAS. Three experiments were performed with same atmospheric forcing fields: (i) using MOM4p0d (GODAS_p0), (ii) using MOM4p1 (GODAS_p1), both using observed temperature and synthetic salinity, and (iii) using MOM4p1 (GODAS_p1S) assimilating both observed temperature and observed salinity. Validation with independent observations shows significant improvement of subsurface temperature and salinity in the new analysis using MOM4p1 versus MOM4p0d. There is also improvement in the upper ocean current of the equatorial Indian Ocean. The impact of observed salinity on the upper ocean surface current is marginal, but there is significant improvement in the subsurface current. The seasonal and inter-annual variability of the Wyrtki jet and the equatorial undercurrent is improved in GODAS_p1 versus GODAS_p0. All analyses reproduced the Indian Ocean dipole, with the GODAS_p1S simulated sea surface temperature (SST) the most accurate. The temperature inversion over the north Bay of Bengal (BoB) is reproduced only in GODAS_p1S. The mean sea level over BoB and equatorial Indian Ocean improved in GODAS_p1S as compared with AVISO observation. The combined model upgrade and assimilation of observed salinity led to reduced root-mean-square deviation and higher correlation coefficient values in the sea level anomaly (SLA) when compared with satellite observations.

  4. Decadal and interannual variability of the Indian Ocean SST

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, Lakshmi; Krishnamurthy, V.

    2016-01-01

    The variability of the Indian Ocean on interannual and decadal timescales is investigated in observations, coupled model simulation and model experiment. The Indian Ocean Dipole (IOD) mode was specifically analyzed using a data-adaptive method. This study reveals one decadal mode and two interannual modes in the sea surface temperature (SST) of the IOD. The decadal mode in the IOD is associated with the Pacific Decadal Oscillation (PDO) of the North Pacific SST. The two interannual modes are related to the biennial and canonical components of El Niño-Southern Oscillation (ENSO), consistent with previous studies. This study hypothesizes that the relation between the Indian Ocean and the North Pacific on decadal scale may be through the northerly winds from the western North Pacific. The long simulation of Community Climate System Model version 4 also indicates the presence of IOD modes associated with the decadal PDO and canonical ENSO modes. However, the model fails to simulate the biennial ENSO mode in the Indian Ocean. The relation between the Indian Ocean and North Pacific Ocean is further supported by the regionally de-coupled model experiment.

  5. Phytoplankton composition and biomass across the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Schlüter, Louise; Henriksen, Peter; Nielsen, Torkel Gissel; Jakobsen, Hans H.

    2011-05-01

    Phytoplankton composition and biomass was investigated across the southern Indian Ocean. Phytoplankton composition was determined from pigment analysis with subsequent calculations of group contributions to total chlorophyll a (Chl a) using CHEMTAX and, in addition, by examination in the microscope. The different plankton communities detected reflected the different water masses along a transect from Cape Town, South Africa, to Broome, Australia. The first station was influenced by the Agulhas Current with a very deep mixed surface layer. Based on pigment analysis this station was dominated by haptophytes, pelagophytes, cyanobacteria, and prasinophytes. Sub-Antarctic waters of the Southern Ocean were encountered at the next station, where new nutrients were intruded to the surface layer and the total Chl a concentration reached high concentrations of 1.7 μg Chl a L -1 with increased proportions of diatoms and dinoflagellates. The third station was also influenced by Southern Ocean waters, but located in a transition area on the boundary to subtropical water. Prochlorophytes appeared in the samples and Chl a was low, i.e., 0.3 μg L -1 in the surface with prevalence of haptophytes, pelagophytes, and cyanobacteria. The next two stations were located in the subtropical gyre with little mixing and general oligotrophic conditions where prochlorophytes, haptophytes and pelagophytes dominated. The last two stations were located in tropical waters influenced by down-welling of the Leeuwin Current and particularly prochlorophytes dominated at these two stations, but also pelagophytes, haptophytes and cyanobacteria were abundant. Haptophytes Type 6 ( sensuZapata et al., 2004), most likely Emiliania huxleyi, and pelagophytes were the dominating eucaryotes in the southern Indian Ocean. Prochlorophytes dominated in the subtrophic and oligotrophic eastern Indian Ocean where Chl a was low, i.e., 0.043-0.086 μg total Chl a L -1 in the surface, and up to 0.4 μg Chl a L -1 at

  6. Impacts of Indonesian Throughflow on seasonal circulation in the equatorial Indian Ocean

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Yuan, Dongliang; Zhao, Xia

    2017-03-01

    Impacts of the Indonesian Throughflow (ITF) on seasonal circulation in the equatorial eastern Indian Ocean are investigated using the ocean-only model LICOM by opening and closing ITF passages. LICOM had daily forcing from NCEP reanalysis data during 2000-2011. It can reproduce vertical profiles of mean density and buoyancy frequency of World Ocean Atlas 2013 data. The model also simulates well annual oscillation in the central Indian Ocean and semiannual oscillation in the eastern Indian Ocean of sea level anomalies (SLA) using satellite altimeter data, as well as the semiannual oscillation of surface zonal equatorial currents of Ocean Surface Current Analyses Real Time current data in the equatorial Indian Ocean. The wave decomposition method is used to analyze the propagation and reflection of equatorial long waves based on LICOM output. Wave analysis suggests that ITF blockage mainly influences waves generated from the Indian Ocean but not the Pacific Ocean, and eastern boundary reflections play an important role in semiannual oscillations of SLA and zonal current differences in the equatorial Indian Ocean associated with ITF. Reconstructed ITF-caused SLA using wave decomposition coefficient differences between closed and open ITF-passage experiments suggest both Kelvin and Rossby waves from the first baroclinic mode have comparable contributions to the semiannual oscillations of SLA difference. However, reconstructed ITF-caused surface zonal currents at the equator suggest that the first meridional-mode Rossby wave has much greater contribution than the first baroclinic mode Kelvin wave. Both reconstructed sea level and zonal currents demonstrate that the first baroclinic mode has a greater contribution than other baroclinic modes.

  7. Low-frequency sound level in the Southern Indian Ocean.

    PubMed

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Leroy, Emmanuelle C

    2015-12-01

    This study presents long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected on six widely distributed autonomous hydrophones from 47°S to 4°S and 53°E to 83°E. Daily mean power spectra (10-100 Hz) were analyzed in order to identify the main sound sources and their space and time variability. Periodic signals are principally associated with the seasonal presence of three types of blue whales and fin whales whose signatures are easily identified at specific frequencies. In the low frequencies, occurrence of winter lows and summer highs in the ambient noise levels are well correlated with iceberg volume variations at the southern latitudes, suggesting that icebergs are a major sound source, seasonally contributing to the ambient noise, even at tropical latitudes (26°S). The anthropogenic contribution to the noise spectrum is limited. Shipping sounds are only present north and west of the study area in the vicinity of major traffic lanes. Acoustic recordings from the southern sites may thus be representative of the pristine ambient noise in the Indian Ocean.

  8. Preliminary Results from an Hydroacoustic Experiment in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Royer, J.; Dziak, R. P.; Delatre, M.; Brachet, C.; Haxel, J. H.; Matsumoto, H.; Goslin, J.; Brandon, V.; Bohnenstiehl, D. R.; Guinet, C.; Samaran, F.

    2008-12-01

    We report initial results from a 14-month hydroacoustic experiment in the Indian Ocean conducted by CNRS/University of Brest and NOAA/Oregon State University. The objective was to monitor the low-level seismic activity associated with the three contrasting spreading ridges and deforming zones in the Indian Ocean. Three autonomous hydrophones, moored in the SOFAR channel, were deployed in October 2006 and recovered early 2008 by R/V Marion Dufresne, in the Madagascar Basin, and northeast and southwest of Amsterdam Island, complementing the two permanent hydroacoustic stations of the Comprehensive nuclear-Test-Ban Treaty Organization (CTBTO) located near Diego Garcia Island and off Cape Leeuwin. Our temporary network detected more than 2000 events. Inside the array, we located 592 events (compared to 49 in the NEIC earthquake catalog) with location errors less than 5 km and time error less than 2s. The hydrophone array detected on average 5 to 40 times more events per month than land-based networks. First-order observations indicate that hydroacoustic seismicity along the Southeast Indian ridge (SEIR) occurs predominantly along the transform faults. The Southwest Indian Ridge exhibits some periodicity in earthquake activity between adjacent ridge segments. Two large tectonic/volcanic earthquake swarms are observed along the Central Indian Ridge (near the triple junction) in September and December 2007. Moreover, many off ridge-axis events are also observed both south and north of the SEIR axis. Improved localization using the CTBTO records will help refine these preliminary results and further investigate extended volcanic sequences along the SEIR east of 80°E and other events outside of the temporary array. The records also display numerous vocalizations of baleen whales in the 20-40Hz bandwidth. The calls are attributed to fin whales, Antarctic blue whales and pygmy blue whales of Madagascar and Australian type. Their vocal activity is found to be highly seasonal

  9. The potential hydrothermal systems unexplored in the Southwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Suo, Yanhui; Li, Sanzhong; Li, Xiyao; Zhang, Zhen; Ding, Dong

    2017-01-01

    Deep-sea hydrothermal vents possess complex ecosystems and abundant metallic mineral deposits valuable to human being. On-axial vents along tectonic plate boundaries have achieved prominent results and obtained huge resources, while nearly 90% of the global mid-ocean ridge and the majority of the off-axial vents buried by thick oceanic sediments within plates remain as relatively undiscovered domains. Based on previous detailed investigations, hydrothermal vents have been mapped along five sections along the Southwest Indian Ridge (SWIR) with different bathymetry, spreading rates, and gravity features, two at the western end (10°-16°E Section B and 16°-25°E Section C) and three at the eastern end (49°-52°E Section D, 52°-61°E Section E and 61°-70°E Section F). Hydrothermal vents along the Sections B, C, E and F with thin oceanic crust are hosted by ultramafic rocks under tectonic-controlled magmatic-starved settings, and hydrothermal vents along the Section D are associated with exceed magmatism. Limited coverage of investigations is provided along the 35°-47°E SWIR (between Marion and Indomed fracture zones) and a lot of research has been done around the Bouvet Island, while no hydrothermal vents has been reported. Analyzing bathymetry, gravity and geochemical data, magmatism settings are favourable for the occurrence of hydrothermal systems along these two sections. An off-axial hydrothermal system in the southern flank of the SWIR that exhibits ultra-thin oceanic crust associated with an oceanic continental transition is postulated to exist along the 100-Ma slow-spreading isochron in the Enderby Basin. A discrete, denser enriched or less depleted mantle beneath the Antarctic Plate is an alternative explanation for the large scale thin oceanic crust concentrated on the southern flank of the SWIR.

  10. Indian Ocean Sea Surface Temperatures during the mid-Piacenzian

    NASA Astrophysics Data System (ADS)

    Stoll, D. K.; Robinson, M. M.; Dowsett, H. J.

    2010-12-01

    Mid-Pliocene (~3.3 to 3.0 Ma) climate is being reconstructed as part of the U.S. Geological Survey’s Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) Project. The Pliocene sea surface temperature (SST) dataset is an integral piece of PRISM’s climate reconstruction and continually evolves over time as additional data are added and refined. The Indian Ocean has in the past been a region lacking PRISM SST data coverage, while it is also a region marked with interesting climate phenomena (e.g., the Indian Ocean Dipole). Questions over the existence of these modern oceanographic elements during the mid-Piacenzian have led to increased interest in the Indian Ocean. New data analyzed by PRISM provides insight on what Indian Ocean circulation and SST may have been like ~3 million years ago. Using planktic foraminifera sampled and analyzed from Indian Ocean ODP Sites 709, 716, 754, 758, and 763, PRISM is developing new mid-Pliocene SST estimates to better understand this region’s paleoceanography.

  11. Metagenomic exploration of viruses throughout the Indian Ocean.

    PubMed

    Williamson, Shannon J; Allen, Lisa Zeigler; Lorenzi, Hernan A; Fadrosh, Douglas W; Brami, Daniel; Thiagarajan, Mathangi; McCrow, John P; Tovchigrechko, Andrey; Yooseph, Shibu; Venter, J Craig

    2012-01-01

    The characterization of global marine microbial taxonomic and functional diversity is a primary goal of the Global Ocean Sampling Expedition. As part of this study, 19 water samples were collected aboard the Sorcerer II sailing vessel from the southern Indian Ocean in an effort to more thoroughly understand the lifestyle strategies of the microbial inhabitants of this ultra-oligotrophic region. No investigations of whole virioplankton assemblages have been conducted on waters collected from the Indian Ocean or across multiple size fractions thus far. Therefore, the goals of this study were to examine the effect of size fractionation on viral consortia structure and function and understand the diversity and functional potential of the Indian Ocean virome. Five samples were selected for comprehensive metagenomic exploration; and sequencing was performed on the microbes captured on 3.0-, 0.8- and 0.1 µm membrane filters as well as the viral fraction (<0.1 µm). Phylogenetic approaches were also used to identify predicted proteins of viral origin in the larger fractions of data from all Indian Ocean samples, which were included in subsequent metagenomic analyses. Taxonomic profiling of viral sequences suggested that size fractionation of marine microbial communities enriches for specific groups of viruses within the different size classes and functional characterization further substantiated this observation. Functional analyses also revealed a relative enrichment for metabolic proteins of viral origin that potentially reflect the physiological condition of host cells in the Indian Ocean including those involved in nitrogen metabolism and oxidative phosphorylation. A novel classification method, MGTAXA, was used to assess virus-host relationships in the Indian Ocean by predicting the taxonomy of putative host genera, with Prochlorococcus, Acanthochlois and members of the SAR86 cluster comprising the most abundant predictions. This is the first study to holistically

  12. Metagenomic Exploration of Viruses throughout the Indian Ocean

    PubMed Central

    Lorenzi, Hernan A.; Fadrosh, Douglas W.; Brami, Daniel; Thiagarajan, Mathangi; McCrow, John P.; Tovchigrechko, Andrey; Yooseph, Shibu; Venter, J. Craig

    2012-01-01

    The characterization of global marine microbial taxonomic and functional diversity is a primary goal of the Global Ocean Sampling Expedition. As part of this study, 19 water samples were collected aboard the Sorcerer II sailing vessel from the southern Indian Ocean in an effort to more thoroughly understand the lifestyle strategies of the microbial inhabitants of this ultra-oligotrophic region. No investigations of whole virioplankton assemblages have been conducted on waters collected from the Indian Ocean or across multiple size fractions thus far. Therefore, the goals of this study were to examine the effect of size fractionation on viral consortia structure and function and understand the diversity and functional potential of the Indian Ocean virome. Five samples were selected for comprehensive metagenomic exploration; and sequencing was performed on the microbes captured on 3.0-, 0.8- and 0.1 µm membrane filters as well as the viral fraction (<0.1 µm). Phylogenetic approaches were also used to identify predicted proteins of viral origin in the larger fractions of data from all Indian Ocean samples, which were included in subsequent metagenomic analyses. Taxonomic profiling of viral sequences suggested that size fractionation of marine microbial communities enriches for specific groups of viruses within the different size classes and functional characterization further substantiated this observation. Functional analyses also revealed a relative enrichment for metabolic proteins of viral origin that potentially reflect the physiological condition of host cells in the Indian Ocean including those involved in nitrogen metabolism and oxidative phosphorylation. A novel classification method, MGTAXA, was used to assess virus-host relationships in the Indian Ocean by predicting the taxonomy of putative host genera, with Prochlorococcus, Acanthochlois and members of the SAR86 cluster comprising the most abundant predictions. This is the first study to holistically

  13. Seagrass ecosystems in the Western Indian Ocean.

    PubMed

    Gullström, Martin; de la Torre Castro, Maricela; Bandeira, Salomão; Björk, Mats; Dahlberg, Mattis; Kautsky, Nils; Rönnbäck, Patrik; Ohman, Marcus C

    2002-12-01

    Seagrasses are marine angiosperms widely distributed in both tropical and temperate coastal waters creating one of the most productive aquatic ecosystems on earth. In the Western Indian Ocean (WIO) region, with its 13 reported seagrass species, these ecosystems cover wide areas of near-shore soft bottoms through the 12 000 km coastline. Seagrass beds are found intertidally as well as subtidally, sometimes down to about 40 m, and do often occur in close connection to coral reefs and mangroves. Due to the high primary production and a complex habitat structure, seagrass beds support a variety of benthic, demersal and pelagic organisms. Many fish and shellfish species, including those of commercial interest, are attracted to seagrass habitats for foraging and shelter, especially during their juvenile life stages. Examples of abundant and widespread fish species associated to seagrass beds in the WIO belong to the families Apogonidae, Blenniidae, Centriscidae, Gerreidae, Gobiidae, Labridae, Lethrinidae Lutjanidae, Monacanthidae, Scaridae, Scorpaenidae, Siganidae, Syngnathidae and Teraponidae. Consequently, seagrass ecosystems in the WIO are valuable resources for fisheries at both local and regional scales. Still, seagrass research in the WIO is scarce compared to other regions and it is mainly focusing on botanic diversity and ecology. This article reviews the research status of seagrass beds in the WIO with particular emphasis on fish and fisheries. Most research on this topic has been conducted along the East African coast, i.e. in Kenya, Tanzania, Mozambique and eastern South Africa, while less research was carried out in Somalia and the Island States of the WIO (Seychelles, Comoros, Reunion (France), Mauritius and Madagascar). Published papers on seagrass fish ecology in the region are few and mainly descriptive. Hence, there is a need of more scientific knowledge in the form of describing patterns and processes through both field and experimental work

  14. Depths of Intraplate Indian Ocean Earthquakes from Waveform Modeling

    NASA Astrophysics Data System (ADS)

    Baca, A. J.; Polet, J.

    2014-12-01

    The Indian Ocean is a region of complex tectonics and anomalous seismicity. The ocean floor in this region exhibits many bathymetric features, most notably the multiple inactive fracture zones within the Wharton Basin and the Ninetyeast Ridge. The 11 April 2012 MW 8.7 and 8.2 strike-slip events that took place in this area are unique because their rupture appears to have extended to a depth where brittle failure, and thus seismic activity, was considered to be impossible. We analyze multiple intraplate earthquakes that have occurred throughout the Indian Ocean to better constrain their focal depths in order to enhance our understanding of how deep intraplate events are occurring and more importantly determine if the ruptures are originating within a ductile regime. Selected events are located within the Indian Ocean away from major plate boundaries. A majority are within the deforming Indo-Australian tectonic plate. Events primarily display thrust mechanisms with some strike-slip or a combination of the two. All events are between MW5.5-6.5. Event selections were handled this way in order to facilitate the analysis of teleseismic waveforms using a point source approximation. From these criteria we gathered a suite of 15 intraplate events. Synthetic seismograms of direct P-waves and depth phases are computed using a 1-D propagator matrix approach and compared with global teleseismic waveform data to determine a best depth for each event. To generate our synthetic seismograms we utilized the CRUST1.0 software, a global crustal model that generates velocity values at the hypocenter of our events. Our waveform analysis results reveal that our depths diverge from the Global Centroid Moment Tensor (GCMT) depths, which underestimate our deep lithosphere events and overestimate our shallow depths by as much as 17 km. We determined a depth of 45km for our deepest event. We will show a comparison of our final earthquake depths with the lithospheric thickness based on

  15. Climate variability in a coupled GCM. Part II: The Indian Ocean and monsoon

    SciTech Connect

    Latif, M.; Sterl, A.; Assenbaum, M.; Junge, M.M.; Maier-Reimer, E.

    1994-10-01

    We have investigated the seasonal cycle and the interannual variability of the tropical Indian Ocean circulation and the Indian summer monsoon simulated by a coupled ocean-atmosphere general circulation model in a 26-year integration. Although the model exhibits significant climate drift, overall, the coupled GCM simulates realistically the seasonal changes in the tropical Indian Ocean and the onset and evolution of the Indian summer monsoon. The amplitudes of the seasonal changes, however, are underestimated. The coupled GCM also simulates considerable interannual variability in the tropical Indian Ocean circulation, which is partly related to the El Nino/Southern Oscillation phenomenon and the associated changes in the Walker circulation. Changes in the surface wind stress appear to be crucial in forcing interannual variations in the Indian Ocean SST. As in the Pacific Ocean, the net surface heat flux acts as a negative feedback on the SST anomalies. The interannual variability in monsoon rainfall, simulated by the coupled GCM, is only about half as strong as observed. The reason for this is that the simulated interannual variability in the Indian monsoon appears to be related to internal processes within the atmosphere only. In contrast, an investigation based on observations shows a clear lead-lag relationship between interannual variations in the monsoon rainfall and tropical Pacific SST anomalies. Furthermore, the atmospheric GCM also fails to reproduce this lead-lag relationship between monsoon rainfall and tropical Pacific SST when run in a stand-alone integration with observed SSTs prescribed during the period 1970-1988. These results indicate that important physical processes relating tropical Pacific SST to Indian monsoon rainfall are not adequately modeled in our atmospheric GCM. Monsoon rainfall predictions appear therefore premature. 24 refs., 13 figs, 2 tabs.

  16. Indian Naval Development: Power Projection in the Indian Ocean?

    DTIC Science & Technology

    1990-12-01

    editions are obsolete SECURITY CLASSIFICATION OF THIS PAGE S/ N 0102-LF-014-6603 UNCLASSIFIED i. Approved for Public Release: Distribution is Unlimited INDIAN...8217vj !aw r ’\\ i al ,,,a.,m nnn. mil uama nnm mu Ivmunn. -nl- - -- n TABLE OF CONTENTS I. INTRODUCTION ......... .................. 1 II. INDIA-UNITED...relations with the USSR. 49 Khalilzad et al., Security in Southe-- n Asia, p. 74. 34 In bilateral relations, India felt it was not treated as seriously as

  17. PROFILE: Marine Protected Areas and Dugong Conservation Along Australia's Indian Ocean Coast

    PubMed

    Preen

    1998-03-01

    / The coastal zone of the Indian Ocean is coming under increasing pressure from human activities. Australia may be one of the few countries in this region that can afford to take adequate conservation measures in the near future. As it also has one of the longest Indian Ocean coastlines, Australia has the opportunity, and responsibility, to make a meaningful contribution to the conservation of Indian Ocean biodiversity. Threatened species, including marine turtles, inshore dolphins, and dugongs are an important component of that biodiversity. The dugong has been exterminated from several areas in the Indian Ocean, and it appears to be particularly threatened by mesh netting andhunting. Its long-term survival may depend on adequate protection in Australia, which contains the largest known Indian Ocean populations. This protection will require, in part, an appropriate system of marine protected areas (MPAs). This paper examines the adequacy of MPAs along Australia's Indian Ocean coast. Dugongs occur in two MPAs in Western Australia. The proposed expansion of the system of marine reserves is based primarily on representative samples of ecosystems from each biogeographic region. It is inadequate because it does not take into account the distribution and relative abundance of threatened species. If the conservation of biodiversity is to be maximized, the system of MPAs should incorporate both representativeness and the needs of threatened species. The level of protection provided by MPAs in Western Australia is low. Under current government policy potentially damaging activities, including commercial fishing, seismic surveys, and oil and gas drilling are permitted in protected areas.KEY WORDS: Marine protected areas; Dugongs; Western Australia; Indian Ocean; Conservation; Biodiversity

  18. Dynamics of Eddies in the Southeastern Tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Hanifah, F.; Ningsih, N. S.; Sofian, I.

    2016-08-01

    A holistic study was done on eddies in the Southeastern Tropical Indian Ocean (SETIO) using the HYbrid Coordinate Ocean Model (HYCOM) for 64 years (from 1950 to 2013). The results from the model were verified against the current and the Sea Surface Height Anomaly (SSHA) from Ocean Surface Current Analyses - Real time (OSCAR) and Archiving, Validation and Interpretation of Satellite Oceanographic Data (AVISO) respectively. The verification showed that the model simulates the condition in the area of study relatively well. We discovered that the local wind was not the only factor that contributed to the formation of eddies in the area. The difference in South Java Current (SJC) flow compared to the Indonesian Throughflow (ITF) and South Equatorial Current (SEC) flow as well as the difference in the relative velocity between the currents in the area led us to suspect that shear velocity may be responsible for the formation of eddies. The results from our model corroborated our prediction about shear velocity. Therefore, we attempted to explain the appearance of eddies in the SETIO based on the concept of shear velocity. By observing and documenting the occurrences of eddies in the area, we found that there are 8 cyclonic and 7 anticyclonic eddies in the SETIO. The distribution and frequency of the appearance of eddies varies, depending on the season.

  19. Sources of Secondary Microseisms in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Barruol, G.; Davy, C.; Fontaine, F. R.; Stutzmann, E.; Schimmel, M.

    2014-12-01

    Ocean waves activity is a major source of micro-vibrations that travel through the solid Earth, known as microseismic noise and recorded worldwide by broadband seismometers. Storms are accepted to represent an important source of noise in the ocean basins, and thus, microseisms analysis of continuous seismic records can be used to localize the noise sources in the ocean and to follow their variations in space and time. In order to locate and quantify the noise sources in the Indian Ocean, we analyzed one year (2011) of continuous data recorded by permanent seismic stations localized in the Indian Ocean. From the Rayleigh wave polarization analysis performed at each individual stations, we retrieved the number of polarized signals in the time-frequency domain and their back-azimuths. Polarization spectra show that secondary microseisms are more polarized between 6 and 10 s of period. We observe seasonal variations in the number of polarized signals with much more detections during the austral winter. On the other hand, we do not observe seasonal variations in the noise back-azimuth directions, suggesting that the dominating microseismic noise sources are always located in the southernmost Indian Ocean, except for cyclonic episodes that are restricted in space and time. Compared to the Pacific and Atlantic oceans, this Indian Ocean property can be explained by its closed geometry on the North and by the absence of large storms in the Northern part of the basin during the boreal winter. We show that the results of this polarization analysis are in good agreement with the expected source areas computed from ocean wave numerical model.

  20. Phylogeography of the small Indian civet and origin of introductions to western Indian Ocean islands.

    PubMed

    Gaubert, Philippe; Patel, Riddhi; Veron, Géraldine; Goodman, Steven M; Willsch, Maraike; Vasconcelos, Raquel; Lourenço, André; Sigaud, Marie; Justy, Fabienne; Joshi, Bheem Dutt; Fickel, Jörns; Wilting, Andreas

    2016-12-11

    The biogeographic dynamics affecting the Indian subcontinent, East and Southeast Asia during the Plio-Pleistocene has generated complex biodiversity patterns. We assessed the molecular biogeography of the small Indian civet (Viverricula indica) through mitogenome and cytochrome b + control region sequencing of 89 historical and modern samples to (i) establish a time-calibrated phylogeography across the species' native range and (ii) test introduction scenarios to western Indian Ocean islands. Bayesian phylogenetic analyses identified three geographic lineages (East Asia, sister-group to Southeast Asia and the Indian subcontinent + northern Indochina) diverging 3.2 - 2.3 Mya, with no clear signature of past demographic expansion. Within Southeast Asia, Balinese populations separated from the rest 2.6 - 1.3 Mya. Western Indian Ocean populations were assigned to the Indian subcontinent + northern Indochina lineage and had the lowest mitochondrial diversity. Approximate Bayesian computation did not distinguish between single vs multiple introduction scenarios. The early diversification of the small Indian civet was likely shaped by humid periods in the Late Pliocene - Early Pleistocene that created evergreen rainforest barriers, generating areas of intra-specific endemism in the Indian subcontinent, East and Southeast Asia. Later Pleistocene dispersals through drier conditions in South and Southeast Asia were likely, giving rise to the species' current natural distribution. Our molecular data supported the delineation of only four subspecies in V. indica, including an endemic Balinese lineage. Our study also highlighted the influence of pre-first millennium AD introductions to western Indian Ocean islands, with Indian and/or Arab traders probably introducing the species for its civet oil.

  1. The Indian Ocean tsunami and private donations to NGOs.

    PubMed

    Kim, Youngwan; Nunnenkamp, Peter; Bagchi, Chandreyee

    2016-10-01

    Non-governmental organisations (NGOs) are widely believed to raise their flag in humanitarian hotspots with a strong media presence in order to attract higher private donations. We assess this hypothesis by comparing the changes in donations between US-based NGOs with and without aid operations in the four countries most affected by the tsunami in the Indian Ocean in 2004. Simple before-after comparisons tend to support the hypothesis that 'flying the flag' helps attract higher private donations. However, performing a difference-in-difference-in-differences (DDD) approach, we find only weak indications that private donors systematically and strongly preferred NGOs with operations in the region. Extended specifications of the baseline regressions reveal that our major findings are robust. NGO heterogeneity matters in some respects, but the DDD results hold when accounting for proxies of the NGOs' reputation and experience.

  2. Source regions of stratospheric VSLS in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Quack, Birgit; Hepach, Helmke; Atlas, Elliot; Bracher, Astrid; Endres, Sonja; Arevalo-Martinez, Damian; Bange, Hermann; Lennartz, Sinikka; Steinhoff, Tobias; Booge, Dennis; Zarvasky, Alexander; Marandino, Christa; Patey, Matt; Achterberg, Eric; Dengler, Markus; Fiehn, Alina; Tegtmeier, Susann; Krüger, Kirstin

    2016-04-01

    Halogenated very-short-lived substances (VSLS), which are naturally produced in the ocean, play a significant role in present day ozone depletion, in particular in combination with enhanced stratospheric sulfate aerosol, which is also partly derived from oceanic VSLS. The decline of anthropogenic chlorine in the stratosphere within the 21st century will increase the relative importance of the natural emissions on stratospheric ozone destruction. Especially, oceanic sources and source regions of the compounds need to be better constrained, in order to improve the future prediction. During boreal summer the Asian monsoon circulation transports air masses from the Indian Ocean to the stratosphere, while the contribution of VSLS from this ocean to stratospheric halogen and sulfur is unknown. During the research cruises SO 234/2 and SO 235 in July-August 2014 onboard RV SONNE oceanic and atmospheric halogenated VSLS such as bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I) were measured in the subtropical and tropical West Indian Ocean for the first time. Here we present the oceanic sources of the halogenated compounds and their relation to other biogeochemical parameters (short- and longlived trace gases, phytoplankton and nutrients) along the cruise track, which covered coastal, upwelling and open ocean regimes and the Seychelles-Chagos thermocline ridge as important source region for stratospheric bromine.

  3. Seychelles: Petroleum potential of this Indian Ocean paradise

    SciTech Connect

    Khana, S.N.; Dillay, G.

    1986-03-24

    Seychelles archipelago consists of about 115 islands, scattered over 1.15 million sq km of the western Indian Ocean. The granitic nature of the inner group of islands makes them unique and the only example of oceanic islands of its type, indicating existence of microcontinent surrounded by oceanic crust, with banks submerged under the Indian Ocean and the raised islands exposing granite. The granite islands are surrounded by sand cays and coral islands. Mahe is about 1,300 km from Somalia, the nearest point on the African coast to the northwest; the southern tip of India lies about 2,700 km to the northeast and the northern end of Madagascar 1,000 km to the southwest. A geological evaluation of the Seychelles shelf was recently carried out to increase the understanding of this offshore sedimentary basin prior to inviting oil companies to bid for exploration.

  4. Development of a regional model for the North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Rahaman, Hasibur; Ravichandran, M.; Sengupta, Debasis; Harrison, Matthew J.; Griffies, Stephen M.

    2014-03-01

    We have developed a one-way nested Indian Ocean regional model. The model combines the National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory's (GFDL) Modular Ocean Model (MOM4p1) at global climate model resolution (nominally one degree), and a regional Indian Ocean MOM4p1 configuration with 25 km horizontal resolution and 1 m vertical resolution near the surface. Inter-annual global simulations with Coordinated Ocean-Ice Reference Experiments (CORE-II) surface forcing over years 1992-2005 provide surface boundary conditions. We show that relative to the global simulation, (i) biases in upper ocean temperature, salinity and mixed layer depth are reduced, (ii) sea surface height and upper ocean circulation are closer to observations, and (iii) improvements in model simulation can be attributed to refined resolution, more realistic topography and inclusion of seasonal river runoff. Notably, the surface salinity bias is reduced to less than 0.1 psu over the Bay of Bengal using relatively weak restoring to observations, and the model simulates the strong, shallow halocline often observed in the North Bay of Bengal. There is marked improvement in subsurface salinity and temperature, as well as mixed layer depth in the Bay of Bengal. Major seasonal signatures in observed sea surface height anomaly in the tropical Indian Ocean, including the coastal waveguide around the Indian peninsula, are simulated with great fidelity. The use of realistic topography and seasonal river runoff brings the three dimensional structure of the East India Coastal Current and West India Coastal Current much closer to observations. As a result, the incursion of low salinity Bay of Bengal water into the south-eastern Arabian Sea is more realistic.

  5. Soviet-Indian Relations and the Indian Ocean as a Zone of Peace.

    DTIC Science & Technology

    1981-12-01

    present Indian reserves, is unlikely in this century.(45] Despite these steps toward diversification , India’s economic options are hampered by the... economic or political change. Finally, some analysts were disturbed by a growing "regionalism" which contemplated denying free transit to Western...in their own backyard. Arguing along lines now familiar in North-South economic conferences, the Indian Ocean countries stated the only way the West

  6. Predictability of the Indian Ocean Dipole in the coupled models

    NASA Astrophysics Data System (ADS)

    Liu, Huafeng; Tang, Youmin; Chen, Dake; Lian, Tao

    2017-03-01

    In this study, the Indian Ocean Dipole (IOD) predictability, measured by the Indian Dipole Mode Index (DMI), is comprehensively examined at the seasonal time scale, including its actual prediction skill and potential predictability, using the ENSEMBLES multiple model ensembles and the recently developed information-based theoretical framework of predictability. It was found that all model predictions have useful skill, which is normally defined by the anomaly correlation coefficient larger than 0.5, only at around 2-3 month leads. This is mainly because there are more false alarms in predictions as leading time increases. The DMI predictability has significant seasonal variation, and the predictions whose target seasons are boreal summer (JJA) and autumn (SON) are more reliable than that for other seasons. All of models fail to predict the IOD onset before May and suffer from the winter (DJF) predictability barrier. The potential predictability study indicates that, with the model development and initialization improvement, the prediction of IOD onset is likely to be improved but the winter barrier cannot be overcome. The IOD predictability also has decadal variation, with a high skill during the 1960s and the early 1990s, and a low skill during the early 1970s and early 1980s, which is very consistent with the potential predictability. The main factors controlling the IOD predictability, including its seasonal and decadal variations, are also analyzed in this study.

  7. Forced and Unforced Changes of Indian Ocean Temperature and Land-Sea Temperature Gradient

    NASA Astrophysics Data System (ADS)

    Achutarao, K. M.; Thanigachalam, A.

    2015-12-01

    Sea surface temperature (SST) over the Indian Ocean is directly connected with circulation, winds, precipitation, humidity, etc. over India. Increased SSTs are a major consequence of climate change driven largely by anthropogenic factors. Recent literature points to weakening of the Indian Summer Monsoon possibly because of decreased land-sea temperature gradient due to faster rate of warming of the oceans compared to land regions. We examine changes in the SST over the Indian Ocean using two observational datasets; HadISST (v1.1) and ERSST (v3b). Based on trend differences between two time periods (1979-2009 and 1948-1978) we identify four regions in the Indian Ocean with different signatures of change - Bay of Bengal (BOB), Arabian Sea (AS), Southwest Indian Ocean (SWIO), and Southeast Indian Ocean (SEIO). We first quantify the extent to which the SST trends over multiple time-scales (20, 30, 50 and 100-years) are outside of the range expected from internal variability of the climate system. We make use of output data from long control run simulations from the Coupled Model Intercomparison Project Phase-5 (CMIP5) database in order to estimate the contribution of external forcings to the observed trends. Using optimal fingerprint Detection and Attribution methods we quantify the contributions of various natural and anthropogenic forcings by making use of the suite of experiments (piControl, historical, historicalNat, historicalAnt, historicalGHG, and historicalAA) from CMIP5 are used in this study. We will also address the question of what drives the observed weakening of land-ocean temperature gradients.

  8. Travel-associated diseases, Indian Ocean Islands, 1997-2010.

    PubMed

    Savini, Hélène; Gautret, Philippe; Gaudart, Jean; Field, Vanessa; Castelli, Francesco; López-Vélez, Rogelio; Lim, Poh Lian; Shaw, Marc; von Sonnenburg, Frank; Loutan, Louis; Simon, Fabrice

    2013-08-01

    Data collected by the GeoSentinel Surveillance Network for 1,415 ill travelers returning from Indian Ocean islands during 1997-2010 were analyzed. Malaria (from Comoros and Madagascar), acute nonparasitic diarrhea, and parasitoses were the most frequently diagnosed infectious diseases. An increase in arboviral diseases reflected the 2005 outbreak of chikungunya fever.

  9. Modeling the 2004 Indian Ocean Tsunami for Introductory Physics Students

    ERIC Educational Resources Information Center

    DiLisi, Gregory A.; Rarick, Richard A.

    2006-01-01

    In this paper we develop materials to address student interest in the Indian Ocean tsunami of December 2004. We discuss the physical characteristics of tsunamis and some of the specific data regarding the 2004 event. Finally, we create an easy-to-make tsunami tank to run simulations in the classroom. The simulations exhibit three dramatic…

  10. Travel-associated Diseases, Indian Ocean Islands, 1997–2010

    PubMed Central

    Gautret, Philippe; Gaudart, Jean; Field, Vanessa; Castelli, Francesco; López-Vélez, Rogelio; Lim, Poh Lian; Shaw, Marc; von Sonnenburg, Frank; Loutan, Louis; Simon, Fabrice

    2013-01-01

    Data collected by the GeoSentinel Surveillance Network for 1,415 ill travelers returning from Indian Ocean islands during 1997–2010 were analyzed. Malaria (from Comoros and Madagascar), acute nonparasitic diarrhea, and parasitoses were the most frequently diagnosed infectious diseases. An increase in arboviral diseases reflected the 2005 outbreak of chikungunya fever. PMID:23876977

  11. Sea surface height anomaly and upper ocean temperature over the Indian Ocean during contrasting monsoons

    NASA Astrophysics Data System (ADS)

    Gera, Anitha; Mitra, A. K.; Mahapatra, D. K.; Momin, I. M.; Rajagopal, E. N.; Basu, Swati

    2016-09-01

    Recent research emphasizes the importance of the oceanic feedback to monsoon rainfall over the Asian landmass. In this study, we investigate the differences in the sea surface height anomaly (SSHA) and upper ocean temperature over the tropical Indian Ocean during multiple strong and weak monsoons. Analysis of satellite derived SSHA, sea surface temperature (SST) and ocean reanalysis data reveals that patterns of SSHA, SST, ocean temperature, upper ocean heat content (UOHC) and propagations of Kelvin and Rossby waves differ during strong and weak monsoon years. During strong monsoons positive SSH, SST and UOHC anomalies develop over large parts of north Indian Ocean whereas during weak monsoons much of the north Indian Ocean is covered with negative anomalies. These patterns can be used as a standard tool for evaluating the performance of coupled and ocean models in simulating & forecasting strong and weak monsoons. The rainfall over central India is found to be significantly correlated with SSHA over the regions (Arabian Sea and West central Indian Ocean and Bay of Bengal) where SSHA is positively large during strong monsoons. The SST-SSHA correlation is also very strong over the same area. The study reveals that much convection takes place over these regions during strong monsoons. In contrast during weak monsoons, convection takes place over eastern equatorial region. These changes in SST are largely influenced by oceanic Kelvin and Rossby waves. The Rossby waves initiated in spring at the eastern boundary propagate sub-surface heat content in the ocean influencing SST in summer. The SST anomalies modulate the Hadley circulation and the moisture transport thereby contributing to rainfall over central India. Therefore oceanic Kelvin and Rossby waves influence the rainfall over central India.

  12. Basalts dredged from the Amirante ridge, western Indian ocean

    USGS Publications Warehouse

    Fisher, R.L.; Engel, C.G.; Hilde, T.W.C.

    1968-01-01

    Oceanic tholeiitic basalts were dredged from 2500 to 3000 m depth on each flank of the Amirante Ridge, 1200 km southeast of Somalia in the western Indian Ocean, by R.V. Argo in 1964. One sample, probably shed from a flow or dike in basement beneath the coralline cap, gave a wholerock KAr age of 82??16??106 years. The age is similar to those reported by others for agglomerate from Providence Reef, nearer Madagascar, and for gabbro from Chain Ridge, the southwest member of Owen Fracture Zone, nearer the Somali coast. The Amirante Cretaceous-Early Tertiary occurrence lies between the "continental" 650 ?? 106 years granites of Seychelles Archipelago and the large Precambrian "continental" block of Madagascar. Trends of major structures and distribution of the related topographic and magnetic-anomaly lineations in 7-8 ?? 106 km2of the surrounding Indian Ocean suggest that in addition to spreading of the seafloor from the seismically-active Mid-Indian Ocean Ridge-Carlsberg Ridge complex there has been, since mid-Mesozoic time, distributed left-lateral shear along 52??-54??E that has moved Madagascar at least 700 km south relative to Seychelles Bank. Measurements by other indicate the absolute movement of Madagascar has been southward as well. The emplacement of oceanic tholeiitic basalts at shallow depth, the development of volcanic topography between the sedimented Somali and Mascarene basins, and the existence of the faulted Amirante Trench and Ridge are consequences of the displacement. ?? 1968.

  13. Multidecadal variability in East African hydroclimate controlled by the Indian Ocean.

    PubMed

    Tierney, Jessica E; Smerdon, Jason E; Anchukaitis, Kevin J; Seager, Richard

    2013-01-17

    The recent decades-long decline in East African rainfall suggests that multidecadal variability is an important component of the climate of this vulnerable region. Prior work based on analysing the instrumental record implicates both Indian and Pacific ocean sea surface temperatures (SSTs) as possible drivers of East African multidecadal climate variability, but the short length of the instrumental record precludes a full elucidation of the underlying physical mechanisms. Here we show that on timescales beyond the decadal, the Indian Ocean drives East African rainfall variability by altering the local Walker circulation, whereas the influence of the Pacific Ocean is minimal. Our results, based on proxy indicators of relative moisture balance for the past millennium paired with long control simulations from coupled climate models, reveal that moist conditions in coastal East Africa are associated with cool SSTs (and related descending circulation) in the eastern Indian Ocean and ascending circulation over East Africa. The most prominent event identified in the proxy record--a coastal pluvial from 1680 to 1765--occurred when Indo-Pacific warm pool SSTs reached their minimum values of the past millennium. Taken together, the proxy and model evidence suggests that Indian Ocean SSTs are the primary influence on East African rainfall over multidecadal and perhaps longer timescales.

  14. The Nippon Foundation / GEBCO Indian Ocean Bathymetric Compilation Project

    NASA Astrophysics Data System (ADS)

    Wigley, R. A.; Hassan, N.; Chowdhury, M. Z.; Ranaweera, R.; Sy, X. L.; Runghen, H.; Arndt, J. E.

    2014-12-01

    The Indian Ocean Bathymetric Compilation (IOBC) project, undertaken by Nippon Foundation / GEBCO Scholars, is focused on building a regional bathymetric data compilation, of all publically-available bathymetric data within the Indian Ocean region from 30°N to 60° S and 10° to 147° E. One of the objectives of this project is the creation of a network of Nippon Foundation / GEBCO Scholars working together, derived from the thirty Scholars from fourteen nations bordering on the Indian Ocean who have graduated from this Postgraduate Certificate in Ocean Bathymetry (PCOB) training program training program at the University of New Hampshire. The IOBC project has provided students a working example during their course work and has been used as basis for student projects during their visits to another Laboratory at the end of their academic year. This multi-national, multi-disciplinary project team will continue to build on the skills gained during the PCOB program through additional training. The IOBC is being built using the methodology developed for the International Bathymetric Chart of the Southern Ocean (IBCSO) compilation (Arndt et al., 2013). This skill was transferred, through training workshops, to further support the ongoing development within the scholar's network. This capacity-building project is envisioned to connect other personnel from within all of the participating nations and organizations, resulting in additional capacity-building in this field of multi-resolution bathymetric grid generation in their home communities. An updated regional bathymetric map and grids of the Indian Ocean will be an invaluable tool for all fields of marine scientific research and resource management. In addition, it has implications for increased public safety by offering the best and most up-to-date depth data for modeling regional-scale oceanographic processes such as tsunami-wave propagation behavior amongst others.

  15. Ocean transport and variability studies of the South Pacific, Southern, and Indian Oceans

    NASA Technical Reports Server (NTRS)

    Church, John A.; Cresswell, G. R.; Nilsson, C. S.; Mcdougall, T. J.; Coleman, R.; Rizos, C.; Penrose, J.; Hunter, J. R.; Lynch, M. J.

    1991-01-01

    The objectives of this study are to analyze ocean dynamics in the western South Pacific and the adjacent Southern Ocean and the eastern Indian Ocean. Specifically, our objectives for these three regions are, for the South Pacific Ocean: (1) To estimate the volume transport of the east Australian Current (EAC) along the Australian coast and in the Tasman Front, and to estimate the time variability (on seasonal and interannual time scales) of this transport. (2) To contribute to estimating the meridional heat and freshwater fluxes (and their variability) at about 30 deg S. Good estimates of the transport in the western boundary current are essential for accurate estimates of these fluxes. (3) To determine how the EAC transport (and its extension, the Tasman Front and the East Auckland Current) closes the subtropical gyre of the South Pacific and to better determine the structure at the confluence of this current and the Antarctic Circumpolar Current. (4) To examine the structure and time variability of the circulation in the western South Pacific and the adjacent Southern Ocean, particularly at the Tasman Front. For the Indian Ocean: (5) To study the seasonal interannual variations in the strength of the Leeuwin Current. (6) To monitor the Pacific-Indian Ocean throughflow and the South Equatorial and the South Java Currents between northwest Australia and Indonesia. (7) To study the processes that form the water of the permanent oceanic thermocline and, in particular, the way in which new thermocline water enters the permanent thermocline in late winter and early spring as the mixed layer restratifies. For the Southern Ocean: (8) To study the mesoscale and meridional structure of the Southern Ocean between 150 deg E and 170 deg E; in particular, to describe the Antarctic frontal system south of Tasmania and determine its interannual variability; to estimate the exchanges of heat, salt, and other properties between the Indian and Pacific Oceans; and to investigate the

  16. Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Currie, J. C.; Lengaigne, M.; Vialard, J.; Kaplan, D. M.; Aumont, O.; Naqvi, S. W. A.; Maury, O.

    2013-10-01

    The Indian Ocean Dipole (IOD) and the El Niño/Southern Oscillation (ENSO) are independent climate modes, which frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled biophysical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997/1998 ENSO and IOD event. Results suggest that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. A negative influence of IOD on chlorophyll concentrations is shown in a region around the southern tip of India in fall. IOD also depresses depth-integrated chlorophyll in the 5-10° S thermocline ridge region, yet the signal is negligible in surface chlorophyll. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Yet unlike most other regions examined, the combined explanatory power of IOD and ENSO in predicting depth-integrated chlorophyll anomalies is relatively low in this region, suggestive that other drivers are important there. We show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. Our results suggest that ENSO and IOD cause significant and predictable regional re-organisation of chlorophyll via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon

  17. Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Currie, J. C.; Lengaigne, M.; Vialard, J.; Kaplan, D. M.; Aumont, O.; Naqvi, S. W. A.; Maury, O.

    2013-03-01

    The Indian Ocean Dipole (IOD) and the El Niño-Southern Oscillation (ENSO) frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled bio-physical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely-sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997-1998 ENSO and IOD event. Results show that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. IOD depresses integrated chlorophyll in the 5° S-10° S thermocline ridge region, even though the signal is negligible in surface chlorophyll. A previously-unreported negative influence of IOD on chlorophyll concentrations is also shown in a region around the southern tip of India. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Lastly, we show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. ENSO and IOD cause significant and predictable regional re-organisation of phytoplankton productivity via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets.

  18. Ocean carbon cycling in the Indian Ocean: 2. Estimates of net community production

    NASA Astrophysics Data System (ADS)

    Bates, Nicholas R.; Pequignet, A. Christine; Sabine, Christopher L.

    2006-09-01

    The spatiotemporal variability of ocean carbon cycling and air-sea CO2 exchange in the Indian Ocean was examined using inorganic carbon data collected as part of the World Ocean Circulation Experiment (WOCE) cruises in 1995. Several carbon mass balance approaches were used to estimate rates of net community production (NCP) in the Indian Ocean. Carbon transports into and out of the Indian Ocean were derived using mass transport estimates of Robbins and Toole (1997) and Schmitz (1996), and transoceanic hydrographic and TCO2 sections at 32°S and across the Indonesian Throughflow. The derived NCP rates of 749 ± 227 to 1572 ± 180 Tg C yr-1 (0.75-1.57 Pg C yr-1) estimated by carbon mass balance were similar to new production rates (1100-1800 Tg C yr-1) determined for the Indian Ocean by a variety of other methods (Louanchi and Najjar, 2000; Gnanadesikan et al., 2002). Changes in carbon inventories of the surface layer were also used to evaluate the spatiotemporal patterns of NCP. Significant NCP occurred in all regions during the Northeast Monsoon and Spring Intermonsoon periods. During the Southwest Monsoon and Fall Intermonsoon periods, the trophic status appears to shift from net autotrophy to net heterotrophy, particularly in the Arabian Sea, Bay of Bengal, and 10°N to 10°S zones.

  19. Trace elements in oceanic pelagic communities in the western Indian Ocean.

    PubMed

    Bodin, Nathalie; Lesperance, Dora; Albert, Rona; Hollanda, Stephanie; Michaud, Philippe; Degroote, Maxime; Churlaud, Carine; Bustamante, Paco

    2017-05-01

    The mineral composition of target and non-target pelagic fish caught by purse-seiners and longliners in the western-central Indian Ocean was determined. From the 10 essential elements analysed, selenium and zinc showed the highest concentrations in swordfish and blue marlin while Indian mackerel appeared as a good source of copper, iron and chrome. All catch had levels of lead and cadmium, two toxic elements, below the maximum sanitary limits. Although some concerns were raised regarding mercury concentrations in the largest species (wahoo, swordfish and blue marlin), molar ratios of mercury and selenium indicate that all oceanic pelagic fish from the western-central Indian Ocean are safe for human consumption. This study also gives insights on the relationships between the levels of essential and toxic elements in fish muscle and the size, trophic position and diet sources of the studied pelagic species.

  20. Contrasting Indian Ocean SST Variability With and Without ENSO Influence: A Coupled Atmosphere-Ocean GCM Study

    NASA Technical Reports Server (NTRS)

    Yu, Jin-Yi; Lau, K. M.

    2004-01-01

    In this study, we perform experiments with a coupled atmosphere-ocean general circulation model (CGCM) to examine ENSO's influence on the interannual sea surface temperature (SST) variability of the tropical Indian Ocean. The control experiment includes both the Indian and Pacific Oceans in the ocean model component of the CGCM (the Indo-Pacific Run). The anomaly experiment excludes ENSOs influence by including only the Indian Ocean while prescribing monthly-varying climatological SSTs for the Pacific Ocean (the Indian-Ocean Run). In the Indo-Pacific Run, an oscillatory mode of the Indian Ocean SST variability is identified by a multi-channel singular spectral analysis (MSSA). The oscillatory mode comprises two patterns that can be identified with the Indian Ocean Zonal Mode (IOZM) and a basin-wide warming/cooling mode respectively. In the model, the IOZM peaks about 3-5 months after ENSO reaches its maximum intensity. The basin mode peaks 8 months after the IOZM. The timing and associated SST patterns suggests that the IOZM is related to ENSO, and the basin- wide warming/cooling develops as a result of the decay of the IOZM spreading SST anomalies from western Indian Ocean to the eastern Indian Ocean. In contrast, in the Indian-Ocean Run, no oscillatory modes can be identified by the MSSA, even though the Indian Ocean SST variability is characterized by east-west SST contrast patterns similar to the IOZM. In both control and anomaly runs, IOZM-like SST variability appears to be associated with forcings from fluctuations of the Indian monsoon. Our modeling results suggest that the oscillatory feature of the IOZM is primarily forced by ENSO.

  1. circulation of the upper layer of the south Indian Ocean

    NASA Astrophysics Data System (ADS)

    de Ruijter, Will; Lambert, Erwin; Aguiar Gonzalez, Borja

    2016-04-01

    The south IO is characterized by high variability and mesoscale eddies. After separation the East Madagascar Current forms dipoles that continue to the south-west and connect remote (eco)systems. The Mozambique Current breaks up in eddies that move southward. They connect upstream to the Indonesian Through Flow and downstream to the Agulhas system. East of Madagascar the 'South Indian Ocean Counter Current' (SICC) flows to the east into the Leeuwin Current system while submerged eddies form a return flow to the west. Hypotheses on the coherence of these flows range from local scale frontal systems to large scale connection via the subtropical super gyre. We aim to present a coherent large-scale picture of the upper south Indian Ocean circulation, the role of the eddies as connectors and drivers of vertical exchanges that may control observed large-scale phenomena like the plankton blooms east of Madagascar.

  2. Transport of continental air to the subantarctic Indian Ocean

    NASA Technical Reports Server (NTRS)

    Balkanski, Yves J.; Jacob, Daniel J.

    1990-01-01

    The occurrence of high Rn-222 episodes (radonic storms) observed at three islands (Crozet, Kerguelen, and Amsterdam) in the subantarctic Indian Ocean is simulated using a three-dimensional chemical tracer model. The chemical tracer model is described and the simulated time series of Rn-222 concentrations at the three islands are compared to observations. The origin, seasonal frequencies, and periodicities of the storms are examined. It is found that the storms are due to fast boundary layer advection of air from South Africa, made possible by the conjunction of a subtropical high SE of Madagascar and a midlatitudes low off the southern tip of Africa. The implications of the results for the transport of continental air to the subantarctic Indian Ocean are discussed.

  3. Global environmental change issues in the western Indian ocean region

    SciTech Connect

    Gable, F.J.; Aubrey, D.G.; Gentile, J.H.

    1991-01-01

    Global climate change caused by increased atmospheric trace gas loading is expected to cause a variety of direct and indirect impacts. These impacts include rising sea levels, changes in storm climates, changes in precipitation patterns, and alterations of ocean circulation patterns. The purpose of the paper is to place into a regional context for the Western Indian Ocean region the problems arising from changes in global climate. Specifically, the paper will focus on the potential for impacts in the coastal zone, where the indirect pressures of climate change and anthropogenic forcings (e.g. pollution, dredging, coral mining) and policy (land use, coastal zone) collide.

  4. USGS scientists study sediment deposited by 2004 Indian Ocean tsunami

    USGS Publications Warehouse

    2005-01-01

    In January, U.S. Geological Survey (USGS) scientists traveled to countries on the Indian Ocean to study sediment deposited by the devastating tsunami of December 26, 2004. They hope to gain knowledge that will help them to identify ancient tsunami deposits in the geologic record—which extends much farther into the past than written records—and so compile a history of tsunamis that can be used to assess a region's future tsunami risk.

  5. Modelling of the Circulation of the Western Indian Ocean

    DTIC Science & Technology

    1988-01-01

    MODELLING OF THE CIRCULATION OF THE WESTERN INDIAN OCEAN Contract N00014-85-K-0019 Julian P. McCreary Pijush K. Kundu Nova University Oceanographic...described below. (i) Cooling of the Arabian Sea: McCreary and Kundu (1989) have just completed a modeling study of the variability in the Arabian Sea...entirely responsible for the observed annual heat gained by the Arabian Sea. (ii) The Gulf of Tehuantepec: McCreary , Lee and Enfield (1989) have

  6. N-uptake and f-ratio Characteristics of the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Prakash, S.; Ramesh, R.

    2007-05-01

    The Indian Ocean, an ideal laboratory for oceanographic studies, consists of three different biogeochemical provinces: the most productive Arabian Sea, Oligotrophic equatorial Indian Ocean and nutrient rich "HNLC" region in south. The present study investigates the N-uptake and f-ratio characteristics of these three provinces of the Indian Ocean and asses its potential role in the Global Carbon Cycle. Here we present 15N based results from the eastern Arabian Sea, equatorial Indian Ocean and the Southern Indian Ocean. The Arabian Sea, one of the most biologically productive regions of the world ocean, is driven by seasonally reversing Southwest and Northeast monsoons. Development of Noctiluca bloom during winter is well documented in literature but data available on the nitrogen uptake and f-ratios is limited. Our results of 15N based productivity from the Arabian Sea, in conjunction with earlier reported results, reveal consistent high column N-uptake and f-ratios over consecutive years during bloom conditions; mean N-uptake and f-ratio are $20.1 (± 4) mmol N m-2 d-1 and 0.86 (±0.06) respectively. Though N-uptake values are comparable with the values reported (23.2 mmol N m-2 d-1), f-ratios are significantly higher suggesting efficient utilization of available nitrate in the water column. Persistent high productivity and f-ratios over years during a bloom suggest more efficient and strong biological pump in the Arabian Sea compared to other regions of the world ocean. The increased production in the surface layer causes formation of the most severe oxygen minimum zone in this part of the world which may cause vigorous denitrification resulting in the formation of radiatively inert N2 and a potent green house gas N2O and thus can contribute significantly to the global warming. The Indian Sector of the Southern Ocean is traditionally regarded as a low productive area. Our measurements show that even though the productivity of this region is low, the f-ratio is

  7. Zoogeography of intertidal communities in the West Indian Ocean as determined by ocean circulation systems: patterns from the Tetraclita barnacles.

    PubMed

    Tsang, Ling Ming; Achituv, Yair; Chu, Ka Hou; Chan, Benny Kwok Kan

    2012-01-01

    The Indian Ocean is the least known ocean in the world with the biogeography of marine species in the West Indian Ocean (WIO) understudied. The hydrography of WIO is characterized by four distinct oceanographic systems and there were few glacial refugia formations in the WIO during the Pleistocene. We used the widely distributed intertidal barnacle Tetraclita to test the hypothesis that the distribution and connectivity of intertidal animals in the WIO are determined by the major oceanographic regime but less influenced by historical events such as Pleistocene glaciations. Tetraclita were studied from 32 locations in the WIO. The diversity and distribution of Tetraclita species in the Indian Ocean were examined based on morphological examination and sequence divergence of two mitochondrial genes (12S rDNA and COI) and one nuclear gene (histone 3, H3). Divergence in DNA sequences revealed the presence of seven evolutionarily significant units (ESUs) of Tetraclita in WIO, with most of them recognized as valid species. The distribution of these ESUs is closely tied to the major oceanographic circulation systems. T. rufotincta is distributed in the Monsoonal Gyre. T. ehsani is present in the Gulf of Oman and NW India. Tetraclita sp. nov. is associated with the Hydrochemical Front at 10°S latitude. T. reni is confined to southern Madagascan and Mauritian waters, influenced by the West Wind Drift. The endemic T. achituvi is restricted to the Red Sea. Tetraclita serrata consists of two ESUs (based on mtDNA analysis) along the east to west coast of South Africa. The two ESUs could not be distinguished from morphological analysis and nuclear H3 sequences. Our results support that intertidal species in the West Indian Ocean are associated with each of the major oceanographic circulation systems which determine gene flow. Geographical distribution is, however, less influenced by the geological history of the region.

  8. Zoogeography of Intertidal Communities in the West Indian Ocean as Determined by Ocean Circulation Systems: Patterns from the Tetraclita Barnacles

    PubMed Central

    Tsang, Ling Ming; Achituv, Yair; Chu, Ka Hou; Chan, Benny Kwok Kan

    2012-01-01

    The Indian Ocean is the least known ocean in the world with the biogeography of marine species in the West Indian Ocean (WIO) understudied. The hydrography of WIO is characterized by four distinct oceanographic systems and there were few glacial refugia formations in the WIO during the Pleistocene. We used the widely distributed intertidal barnacle Tetraclita to test the hypothesis that the distribution and connectivity of intertidal animals in the WIO are determined by the major oceanographic regime but less influenced by historical events such as Pleistocene glaciations. Tetraclita were studied from 32 locations in the WIO. The diversity and distribution of Tetraclita species in the Indian Ocean were examined based on morphological examination and sequence divergence of two mitochondrial genes (12S rDNA and COI) and one nuclear gene (histone 3, H3). Divergence in DNA sequences revealed the presence of seven evolutionarily significant units (ESUs) of Tetraclita in WIO, with most of them recognized as valid species. The distribution of these ESUs is closely tied to the major oceanographic circulation systems. T. rufotincta is distributed in the Monsoonal Gyre. T. ehsani is present in the Gulf of Oman and NW India. Tetraclita sp. nov. is associated with the Hydrochemical Front at 10°S latitude. T. reni is confined to southern Madagascan and Mauritian waters, influenced by the West Wind Drift. The endemic T. achituvi is restricted to the Red Sea. Tetraclita serrata consists of two ESUs (based on mtDNA analysis) along the east to west coast of South Africa. The two ESUs could not be distinguished from morphological analysis and nuclear H3 sequences. Our results support that intertidal species in the West Indian Ocean are associated with each of the major oceanographic circulation systems which determine gene flow. Geographical distribution is, however, less influenced by the geological history of the region. PMID:23024801

  9. Structure and characteristics of submonthly-scale waves along the Indian Ocean ITCZ

    NASA Astrophysics Data System (ADS)

    Fukutomi, Yoshiki; Yasunari, Tetsuzo

    2013-04-01

    This study examines wave disturbances on submonthly (6-30-day) timescales over the tropical Indian Ocean during Southern Hemisphere summer using Japanese Reanalysis (JRA25-JCDAS) products and National Oceanic and Atmospheric Administration outgoing longwave radiation data. The analysis period is December-February for the 29 years from 1979/1980 through 2007/2008. An extended empirical orthogonal function (EEOF) analysis of daily 850-hPa meridional wind anomalies reveals a well-organized wave-train pattern as a dominant mode of variability over the tropical Indian Ocean. Daily lagged composite analyses for various atmospheric variables based on the EEOF result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the Indian Ocean Intertropical Convergence Zone (ITCZ). The wave train is oriented in a northeast-southwest direction from Sumatra toward Madagascar. The waves have zonal wavelengths of about 3,000-5,000 km and exhibit westward and southwestward phase propagation. Individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of Sumatra into Madagascar. Meanwhile, eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern Indian Ocean. This could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern Indian Ocean along the mean monsoon westerly flow. In addition, the waves modulate the ITCZ convection. Correlation statistics show the average behavior of the wave disturbances over the tropical Indian Ocean. These statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis. The waves appear to be connected to the monsoon westerly flow. The waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon

  10. Constraints on lithospheric thermal structure for the Indian Ocean from depth and heat flow data

    NASA Technical Reports Server (NTRS)

    Shoberg, Tom; Stein, Carol A.; Stein, Seth

    1993-01-01

    Models for the thermal evolution of oceanic lithosphere are primarily constrained by variations in seafloor depth and heat flow with age. These models have been largely based on data from the Pacific and Atlantic Ocean basins. We construct seafloor age relations for the Indian Ocean which we combine with bathymetric, sediment isopach and heat flow data to derive curves for depth and heat flow versus age. Comparison of these curves with predictions from three thermal models shows that they are better fit by the shallower depths and higher heat flow for the GDH1 model, which is characterized by a thinner and hotter lithosphere than previous models.

  11. Constraints on lithospheric thermal structure for the Indian Ocean from depth and heat flow data

    NASA Astrophysics Data System (ADS)

    Shoberg, Tom; Stein, Carol A.; Stein, Seth

    1993-06-01

    Models for the thermal evolution of oceanic lithosphere are primarily constrained by variations in seafloor depth and heat flow with age. These models have been largely based on data from the Pacific and Atlantic Ocean basins. We construct seafloor age relations for the Indian Ocean which we combine with bathymetric, sediment isopach and heat flow data to derive curves for depth and heat flow versus age. Comparison of these curves with predictions from three thermal models shows that they are better fit by the shallower depths and higher heat flow for the GDH1 model, which is characterized by a thinner and hotter lithosphere than previous models.

  12. Dehydration at the Tropical Tropopause Over the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Rohs, S.; Beuermann, J.; Gensch, I.; Kraemer, M.; MacKenzie, R.; Schiller, C.; Yushkov, V. A.

    2004-05-01

    During the APE-THESEO campaign in February/March 1999 high-resolution in-situ measurements were carried out onboard the Russian M-55 Geophysica high altitude aircraft, based on the Seychelles (-4.7° N, 55.3° E) in the western Indian Ocean. In the potential temperature range from 340 - 430 K, 36 individual (quasi)-vertical profiles of temperature, the gas-phase and total water cloud particles, and ozone were obtained. The height of the tropopause and the hygropause were highly variable for the investigated period. We attribute this to short and local perturbations to the seasonal cycle. The cold point tropopause was located at a potential temperature range from 365 - 403 K. Minimum temperatures were very low (183 - 194 K), leading to saturation mixing ratios at the tropopause of 1.1 - 8.4 ppmv. The hygropause was located on average 4 K above the tropopause with water vapour mixing ratios of 1.2 - 4.1 ppmv. These very low mixing ratios are comparable to those found in previous studies in the 'fountain region' over Micronesia. For 70 % of the vertical profiles, ice saturation was found in a wide range around the tropopause. Predominantly the saturation was corroborated by concurrently detected clouds up to the altitude of the cold point, providing evidence of active dehydration. We identify three common types of vertical profiles: coincident hygropause and cold point at relatively low potential temperatures, associated with a cirrus deck; coincident hygropause and cold point at relatively high potential temperatures, associated with thin subvisible cirrus; and unsaturated, cloud-free, profiles without a pronounced relationship between hygropause and cold point. Characteristics such as extension, number density, frequency distribution of relative humidity over ice of the cirrus clouds were different for these categories which allows to infer their different origin. The low water vapour ratios and the existence of saturation support the hypothesis that the Tropical

  13. A Lost Continent in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Torsvik, T. H.; Amundsen, H.; Hartz, E. H.; Corfu, F.; Kusznir, N. J.; Gaina, C.; Doubrovine, P. V.; Steinberger, B. M.; Ashwal, L. D.; Jamtveit, B.

    2012-12-01

    Intra-plate magmatic activity is commonly attributed to melting associated with an upwelling mantle plume, and a dozen of hotpot volcanoes, including Reunion, and most reconstructed large igneous provinces since Pangea assembly are thought to be sourced by deep plumes from the edges of the two large low shear-wave velocity provinces at the core-mantle boundary. The Laccadives-Chagos Ridge and the Southern Mascarene Plateau are hailed as a prime example of a hotspot trail, tracking a mantle plume presently residing beneath Reunion, that was initiated with eruption of the Deccan Traps flood basalts 65.5 million years ago. We demonstrate that Mauritius lavas, formed by recent melting of the Reunion plume, contain zircon xenocrysts assimilated from Palaeoproterozoic and Neoproterozoic continental crust. This, together with plate reconstructions and crustal thickness estimates, demonstrate that Mauritius and adjacent parts of the Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia. We also show that the Chagos Bank on the Indian plate was joined to Mauritia before 41 Ma and could be underlain by continental crust. During the Precambrian, Mauritia was located between Madagascar and Southern India, but during Late Cretaceous breakup and the opening of the Mascarene Basin, a series of ridge-jumps between 83.5 and 61 Ma, possibly triggered by plumes, fragmented Mauritia into a ribbon-like configuration. These continental fragments were subsequently concealed below Reunion plume-related magmatic products, where they now reside. It is puzzling, but probably coincidental, that the Reunion hotspot trail followed continental fragments along the Southern Mascarene Plateau for the past 50 Myr: We show from absolute plate motion models that the Reunion hotspot trail is close to what is expected, but it is likely that lithospheric heterogeneities, including two major fracture zones, fossil (Cretaceous) ridges and continental lithospheric fragments

  14. Influenza A Virus on Oceanic Islands: Host and Viral Diversity in Seabirds in the Western Indian Ocean

    PubMed Central

    Lebarbenchon, Camille; Jaeger, Audrey; Feare, Chris; Bastien, Matthieu; Dietrich, Muriel; Larose, Christine; Lagadec, Erwan; Rocamora, Gérard; Shah, Nirmal; Pascalis, Hervé; Boulinier, Thierry; Le Corre, Matthieu; Stallknecht, David E.; Dellagi, Koussay

    2015-01-01

    Ducks and seabirds are natural hosts for influenza A viruses (IAV). On oceanic islands, the ecology of IAV could be affected by the relative diversity, abundance and density of seabirds and ducks. Seabirds are the most abundant and widespread avifauna in the Western Indian Ocean and, in this region, oceanic islands represent major breeding sites for a large diversity of potential IAV host species. Based on serological assays, we assessed the host range of IAV and the virus subtype diversity in terns of the islands of the Western Indian Ocean. We further investigated the spatial variation in virus transmission patterns between islands and identified the origin of circulating viruses using a molecular approach. Our findings indicate that terns represent a major host for IAV on oceanic islands, not only for seabird-related virus subtypes such as H16, but also for those commonly isolated in wild and domestic ducks (H3, H6, H9, H12 subtypes). We also identified strong species-associated variation in virus exposure that may be associated to differences in the ecology and behaviour of terns. We discuss the role of tern migrations in the spread of viruses to and between oceanic islands, in particular for the H2 and H9 IAV subtypes. PMID:25996394

  15. Influenza A virus on oceanic islands: host and viral diversity in seabirds in the Western Indian Ocean.

    PubMed

    Lebarbenchon, Camille; Jaeger, Audrey; Feare, Chris; Bastien, Matthieu; Dietrich, Muriel; Larose, Christine; Lagadec, Erwan; Rocamora, Gérard; Shah, Nirmal; Pascalis, Hervé; Boulinier, Thierry; Le Corre, Matthieu; Stallknecht, David E; Dellagi, Koussay

    2015-05-01

    Ducks and seabirds are natural hosts for influenza A viruses (IAV). On oceanic islands, the ecology of IAV could be affected by the relative diversity, abundance and density of seabirds and ducks. Seabirds are the most abundant and widespread avifauna in the Western Indian Ocean and, in this region, oceanic islands represent major breeding sites for a large diversity of potential IAV host species. Based on serological assays, we assessed the host range of IAV and the virus subtype diversity in terns of the islands of the Western Indian Ocean. We further investigated the spatial variation in virus transmission patterns between islands and identified the origin of circulating viruses using a molecular approach. Our findings indicate that terns represent a major host for IAV on oceanic islands, not only for seabird-related virus subtypes such as H16, but also for those commonly isolated in wild and domestic ducks (H3, H6, H9, H12 subtypes). We also identified strong species-associated variation in virus exposure that may be associated to differences in the ecology and behaviour of terns. We discuss the role of tern migrations in the spread of viruses to and between oceanic islands, in particular for the H2 and H9 IAV subtypes.

  16. Molecular phylogeny of the Indian Ocean Terpsiphone paradise flycatchers: undetected evolutionary diversity revealed amongst island populations.

    PubMed

    Bristol, Rachel M; Fabre, Pierre-Henri; Irestedt, Martin; Jønsson, Knud A; Shah, Nirmal J; Tatayah, Vikash; Warren, Ben H; Groombridge, Jim J

    2013-05-01

    We construct a molecular phylogeny of Terpsiphone flycatchers of the Indian Ocean and use this to investigate their evolutionary relationships. A total of 4.4 kb of mitochondrial (cyt-b, ND3, ND2, control region) and nuclear (G3PDH, MC1R) sequence data were obtained from all species, sub-species and island populations of the region. Colonisation of the western Indian Ocean has been within the last two million years and greatly postdates the formation of the older islands of the region. A minimum of two independent continent-island colonisation events must have taken place in order to explain the current distribution and phylogenetic placement of Terpsiphone in this region. While five well-diverged Indian Ocean clades are detected, the relationship between them is unclear. Short intermodal branches are indicative of rapid range expansion across the region, masking exact routes and chronology of colonisation. The Indian Ocean Terpsiphone taxa fall into five well supported clades, two of which (the Seychelles paradise flycatcher and the Mascarene paradise flycatcher) correspond with currently recognised species, whilst a further three (within the Madagascar paradise flycatcher) are not entirely predicted by taxonomy, and are neither consistent with distance-based nor island age-based models of colonisation. We identify the four non-Mascarene clades as Evolutionarily Significant Units (ESUs), while the Mascarene paradise flycatcher contains two ESUs corresponding to the Mauritius and Réunion subspecies. All six ESUs are sufficiently diverged to be worthy of management as if they were separate species. This phylogenetic reconstruction highlights the importance of sub-specific molecular phylogenetic reconstructions in complex island archipelago settings in clarifying phylogenetic history and ESUs that may otherwise be overlooked and inadvertently lost. Our phylogenetic reconstruction has identified hidden pockets of evolutionary distinctiveness, which provide a valuable

  17. Tropical cyclone activity over the Southwest Tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Burns, Jessica M.; Subrahmanyam, Bulusu; Nyadjro, Ebenezer S.; Murty, V. S. N.

    2016-08-01

    The Southwest Tropical Indian Ocean (SWTIO) is a key region for air-sea interaction. Tropical cyclones (TCs) regularly form over the SWTIO and subsurface ocean variability influences the cyclogenesis of this region. Tropical cyclone days for this region span from November through April, and peak in January and February during austral summer. Past research provides evidence for more tropical cyclone days over the SWTIO during austral summer (December-June) with a deep thermocline ridge than in austral summer with a shallow thermocline ridge. We have analyzed the Argo temperature data and HYbrid Coordinate Ocean Model (HYCOM) outputs while focusing on the austral summer of 2012/2013 (a positive Indian Ocean Dipole (IOD) year and neutral El Niño Southern Oscillation (ENSO) year) when seven named tropical cyclones developed over the SWTIO region. This study reveals that the climatic events like the IOD and ENSO influence the cyclonic activity and number of TC days over the SWTIO. We ascertain that the IOD events have linkages with the Barrier Layer Thickness (BLT) in the SWTIO region through propagating Rossby waves, and further show that the BLT variability influences the cyclonic activity in this region.

  18. Changes in local oceanographic and atmospheric conditions shortly after the 2004 Indian Ocean tsunami

    NASA Astrophysics Data System (ADS)

    Yan, Zhongzhen; Sui, Yi; Sheng, Jinyu; Tang, Danling; Lin, I.-I.

    2015-06-01

    This study examines changes in the local oceanographic and atmospheric conditions over the southern Bay of Bengal and adjacent Indian Ocean waters after the 2004 Indian Ocean tsunami based on satellite remote sensing data and atmospheric reanalysis fields. After the tsunami that occurred on 26 December 2004, the accumulated rainfall had a notably increase (600 mm per month) in January of 2005 over deep waters to the southeast of Sri Lanka. This rainfall increase after the tsunami was accompanied with cooling in the sea surface temperature (SST) (up to -2 °C). Four-day averaged SST anomalies had a noticeable increase (1-4 °C) after the tsunami over the deep waters to the southwest of the epicenter. Series of ocean atmospheric and biological variables changed successively after the change of SST. The chain of causality between the tsunami and the changes in the local atmospheric conditions is suggested.

  19. Interbasin effects of the Indian Ocean on Pacific decadal climate change

    NASA Astrophysics Data System (ADS)

    Mochizuki, Takashi; Kimoto, Masahide; Watanabe, Masahiro; Chikamoto, Yoshimitsu; Ishii, Masayoshi

    2016-07-01

    We demonstrate the significant impact of the Indian Ocean on the Pacific climate on decadal timescales by comparing two sets of data assimilation experiments (pacemaker experiments) conducted over recent decades. For the Indian Ocean of an atmosphere-ocean coupled global climate model, we assimilate ocean temperature and salinity anomalies defined as deviations from climatology or as anomalies with the area-averaged changes for the Indian Ocean subtracted. When decadal sea surface temperature (SST) trends are observed to be strong over the Indian Ocean, the equatorial thermocline uniformly deepens, and the model simulates the eastward tendencies of surface wind aloft. Surface winds strongly converge around the maritime continent, and the associated strengthening of the Walker circulation suppresses an increasing trend in the equatorial Pacific SST through ocean thermocline shoaling, similar to common changes associated with seasonal Indian Ocean warming.

  20. Haemoproteus iwa in Great Frigatebirds (Fregata minor) in the Islands of the Western Indian Ocean.

    PubMed

    Bastien, Matthieu; Jaeger, Audrey; Le Corre, Matthieu; Tortosa, Pablo; Lebarbenchon, Camille

    2014-01-01

    Blood parasites of the sub-genus Haemoproteus have been reported in seabirds, in particular in species in the Suliformes order. These parasites are transmitted by hippoboscid flies of the genus Olfersia; strong specificity has been suggested between the vector and its vertebrate host. We investigated the prevalence of Haemoproteus infection in Suliformes and hippoboscid flies in two oceanic islands of the Western Indian Ocean: Europa and Tromelin. In total, 209 blood samples were collected from great frigatebirds (Fregata minor), masked boobies (Sula dactylatra) and red-footed boobies (Sula sula). Forty-one hippoboscid flies were also collected from birds. Seventeen frigatebirds and one fly collected on Europa tested positive for the presence of Haemoproteus parasites by polymerase chain reaction. Phylogenetic analyses based on partial sequences of the Cytochrome b gene showed that parasites were closely related to Haemoproteus iwa reported from frigatebirds in the Pacific Ocean and in the Caribbean. Plasmodium was also detected in a frigatebird on Europa; however, its placement on the phylogenetic tree could not be resolved. We provide strong support for transmission of blood parasites in seabirds in the Western Indian Ocean and suggest that migrations between the Pacific and the Indian oceans could favor the large-scale distribution of Haemoproteus iwa in frigatebird populations.

  1. Dynamical response of the oceanic circulation and temperature to interdecadal variability in the surface winds over the Indian Ocean

    SciTech Connect

    Reason, C.J.C.; Allan, R.J.; Lindesay, J.A.

    1996-01-01

    A global ocean general circulation model (OGCM) is used to investigate the sensitivity of the circulation and temperature fields to observed interdecadal variability in Indian Ocean winds for the austral summer. Focus is placed on the dynamical response of the model to the imposed winds. These comprise the observed winds from COADS for the region 46{degrees}S-30{degrees}N, 17{degrees}-152{degrees}E organized into four 21-yr epochs. During the first two epochs, the southern Indian anticyclone, African monsoonal flow, and associated trades were anomalously weak, whereas during the 1963-1983 period the reverse was true. The 1942-1962 epoch appears to be a transition. The model indicates an overall decrease (increase) in the transports of the southern Indian and tropical Indian gyres for the 1900-1920, 1921-1941 cases in dynamical response to the variability in the surface winds over the Indian Ocean. Sea surface temperature (SST) perturbations in the southern Indian Ocean have the same sign as the observed anomalies but are smaller in magnitude. The model SST patterns are restricted to the southern Indian Ocean midlatitudes, whereas observations indicate anomalies throughout the Indian Ocean basin. Analysis of the streamfunction anomalies induced by the epoch winds in the model indicates that the JEBAR term is important in modulating Indian gyre transports. While it is noted that thermodynamic effects not explicitly included in the model may contribute toward the observed SST variability in certain regions and that previous model studies have shown that SST in the southern Indian Ocean is sensitive to variations in the Indonesian throughflow and the Pacific trade winds, the results lend support to the hypothesis that changes in the basin-scale ocean circulation driven by the Indian Ocean epoch winds may contribute significantly toward the observed interdecadal variability in SST in the southern regions of this ocean. 29 refs., 17 figs.

  2. Aerosol Direct Radiative Effects Over the Northwest Atlantic, Northwest Pacific, and North Indian Oceans: Estimates Based on In-situ Chemical and Optical Measurements and Chemical Transport Modeling

    NASA Astrophysics Data System (ADS)

    Bates, T. S.; Anderson, T. L.; Baynard, T.; Bond, T.; Boucher, O.; Carmichael, G.; Clarke, A.; Erlick, C.; Guo, H.; Horowitz, L.; Howell, S.; Kulkarni, S.; Maring, H.; McComiskey, A.; Middlebrook, A.; Noone, K.; O'Dowd, C. D.; Ogren, J. A.; Penner, J.; Quinn, P. K.; Ravishankara, A. R.; Savoie, D. L.; Schwartz, S. E.; Shinozuka, Y.; Tang, Y.; Weber, R. J.; Wu, Y.

    2005-12-01

    The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions. Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean during INDOEX, the Northwest Pacific Ocean during ACE-Asia, and the Northwest Atlantic Ocean during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth, and direct radiative effect of aerosols (change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Such comparisons with observations and resultant reductions in uncertainties are

  3. Surface and subsurface oceanic variability observed in the eastern equatorial Indian Ocean during three consecutive Indian Ocean dipole events: 2006 - 2008

    NASA Astrophysics Data System (ADS)

    Iskandar, I.; Mardiansyah, W.; Setiabudidaya, D.; Affandi, A. K.; Syamsuddin, F.

    2014-09-01

    8-year and 4-year long velocity time series records from the equatorial Indian Ocean successfully captured, for the first time, complete evolution of subsurface currents associated with three consecutive Indian Ocean Dipole (IOD) events in 2006 - 2008. It is found that strong eastward subsurface zonal currents in the layer between about 90 m and 150 m were observed, which were opposite to the normal conditions. Vertical structure of the zonal currents resembles that of the typical zonal currents in the equatorial Pacific with an eastward subsurface current lies beneath the surface westward currents. This vertical structure of the zonal currents was associated with anomalous easterly winds along the equatorial Indian Ocean during the maturing phase of the IOD events. In addition, subsurface temperature structures obtained from RAMA buoy network show negative temperature anomalies preceded the surface temperature evolution associated with the IOD events. The negative subsurface temperature anomaly lasted for several months before it changes into positive anomaly as the IOD terminated. The surface temperature structure indicated by the Dipole Mode Index (DMI) revealed that the 2006 IOD was a strong event, while the 2007 and 2008 events were weaker and short-lived events. The evolution of the IOD events were linked to the dynamics of oceanic equatorial wave. It is found that upwelling equatorial Kelvin waves forced by anomalous easterly wind stress play an important role in generating cooling tendency during the development and maturing phase of the IOD events. The demise of the IOD events, on the other hand, was linked to eastern-boundary-reflected Rossby waves that terminated the cooling tendency in the eastern Indian Ocean induced by the wind-forced Kelvin waves. Weakening of the zonal heat advection, then, provided a favor condition for the surface heat flux to warm the sea surface temperature in the eastern equatorial Indian Ocean.

  4. Lessons from the 2004 Indian Ocean and 2011 Tohoku Tsunamis, Developments, and Future Directions

    NASA Astrophysics Data System (ADS)

    Satake, K.

    2014-12-01

    The 2004 Indian Ocean tsunami, the worst tsunami disaster in history with 230,000 casualties, was generated by the largest earthquake (M 9.1) since the 1960 Chilean and 1964 Alaskan earthquakes, but such a giant earthquake was not anticipated in the Indian Ocean. Besides its size, lack of tsunami warning systems in the Indian Ocean and lack of knowledge about tsunami among the coastal residents enhanced the tsunami disaster, while scientific knowledge and technology for far-field tsunami warning system existed. Developments since 2004 include paleo-tsunami studies, global tsunami observations and tsunami warning and hazard mitigation systems. Tsunami deposits found in Indonesia, Thailand and India show that giant tsunamis similar to the 2004 tsunami occurred in the past. Deep ocean pressure gauges (DART system), GPS buoys and coastal tide gauges have been installed with real-time data-telemetry capability in Indian Ocean as well as the Pacific Ocean. Three regional tsunami warning centers are now in operation in India, Indonesia and Australia. The 2011 Tohoku earthquake was also generated by a giant (M 9.0) earthquake. While such an earthquake was unexpected in Japan, similar tsunamis occurred in the past and caused damage on Sanriku coast and Sendai plain. The tsunami warning, issued 3 min after the earthquake, saved many lives yet caused significant (~19,000) fatalities, partly because of underestimation of earthquake size. The insufficient tsunami hazard assessment caused the significant number of casualties and the Fukushima nuclear power plant accident. Existed coastal sea walls might have given inappropriate belief to coastal residents that they were protected from tsunami disaster. Scientific and technological developments needed for the future include estimation of probable maximum earthquake size for tsunami hazard assessment, and real-time estimation of earthquake and tsunami size based on seismic and sea level measurements. In addition, limitation of

  5. West Indian Ocean variability and East African fish catch.

    PubMed

    Jury, M; McClanahan, T; Maina, J

    2010-08-01

    We describe marine climate variability off the east coast of Africa in the context of fish catch statistics for Tanzania and Kenya. The time series exhibits quasi-decadal cycles over the period 1964-2007. Fish catch is up when sea surface temperature (SST) and atmospheric humidity are below normal in the tropical West Indian Ocean. This pattern relates to an ocean Rossby wave in one phase of its east-west oscillation. Coastal-scale analyses indicate that northward currents and uplift on the shelf edge enhance productivity of East African shelf waters. Some of the changes are regulated by the south equatorial current that swings northward from Madagascar. The weather is drier and a salty layer develops in high catch years. While the large-scale West Indian Ocean has some impact on East African fish catch, coastal dynamics play a more significant role. Climatic changes are reviewed using 200 years of past and projected data. The observed warming trend continues to increase such that predicted SST may reach 30 degrees C by 2100 while SW monsoon winds gradually increase, according to a coupled general circulation model simulation with a gradual doubling of CO(2).

  6. Nonlinear processes reinforce extreme Indian Ocean Dipole events

    NASA Astrophysics Data System (ADS)

    Ng, Benjamin; Cai, Wenju; Walsh, Kevin; Santoso, Agus

    2015-06-01

    Under global warming, climate models show an almost three-fold increase in extreme positive Indian Ocean Dipole (pIOD) events by 2100. These extreme pIODs are characterised by a westward extension of cold sea surface temperature anomalies (SSTAs) which push the downstream atmospheric convergence further west. This induces severe drought and flooding in the surrounding countries, but the processes involved in this projected increase have not been fully examined. Here we conduct a detailed heat budget analysis of 19 models from phase 5 of the Coupled Model Intercomparison Project and show that nonlinear zonal and vertical heat advection are important for reinforcing extreme pIODs. Under greenhouse warming, these nonlinear processes do not change significantly in amplitude, but the frequency of occurrences surpassing a threshold increases. This is due to the projected weakening of the Walker circulation, which leads to the western tropical Indian Ocean warming faster than the east. As such, the magnitude of SSTAs required to shift convection westward is relatively smaller, allowing these convection shifts to occur more frequently in the future. The associated changes in wind and ocean current anomalies support the zonal and vertical advection terms in a positive feedback process and consequently, moderate pIODs become more extreme-like.

  7. Nonlinear processes reinforce extreme Indian Ocean Dipole events.

    PubMed

    Ng, Benjamin; Cai, Wenju; Walsh, Kevin; Santoso, Agus

    2015-06-26

    Under global warming, climate models show an almost three-fold increase in extreme positive Indian Ocean Dipole (pIOD) events by 2100. These extreme pIODs are characterised by a westward extension of cold sea surface temperature anomalies (SSTAs) which push the downstream atmospheric convergence further west. This induces severe drought and flooding in the surrounding countries, but the processes involved in this projected increase have not been fully examined. Here we conduct a detailed heat budget analysis of 19 models from phase 5 of the Coupled Model Intercomparison Project and show that nonlinear zonal and vertical heat advection are important for reinforcing extreme pIODs. Under greenhouse warming, these nonlinear processes do not change significantly in amplitude, but the frequency of occurrences surpassing a threshold increases. This is due to the projected weakening of the Walker circulation, which leads to the western tropical Indian Ocean warming faster than the east. As such, the magnitude of SSTAs required to shift convection westward is relatively smaller, allowing these convection shifts to occur more frequently in the future. The associated changes in wind and ocean current anomalies support the zonal and vertical advection terms in a positive feedback process and consequently, moderate pIODs become more extreme-like.

  8. Winter AO/NAO modifies summer ocean heat content and monsoonal circulation over the western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Gong, Dao-Yi; Guo, Dong; Li, Sang; Kim, Seong-Joong

    2017-02-01

    This paper analyzes the possible influence of boreal winter Arctic Oscillation/North Atlantic Oscillation (AO/ NAO) on the Indian Ocean upper ocean heat content in summer as well as the summer monsoonal circulation. The strong interannual co-variation between winter 1000-hPa geopotential height in the Northern Hemisphere and summer ocean heat content in the uppermost 120 m over the tropical Indian Ocean was investigated by a singular decomposition analysis for the period 1979-2014. The second paired-modes explain 23.8% of the squared covariance, and reveal an AO/NAO pattern over the North Atlantic and a warming upper ocean in the western tropical Indian Ocean. The positive upper ocean heat content enhances evaporation and convection, and results in an anomalous meridional circulation with ascending motion over 5°S-5°N and descending over 15°-25°N. Correspondingly, in the lower troposphere, significantly anomalous northerly winds appear over the western Indian Ocean north of the equator, implying a weaker summer monsoon circulation. The off-equator oceanic Rossby wave plays a key role in linking the AO/NAO and the summer heat content anomalies. In boreal winter, a positive AO/NAO triggers a down-welling Rossby wave in the central tropical Indian Ocean through the atmospheric teleconnection. As the Rossby wave arrives in the western Indian Ocean in summer, it results in anomalous upper ocean heating near the equator mainly through the meridional advection. The AO/NAO-forced Rossby wave and the resultant upper ocean warming are well reproduced by an ocean circulation model. The winter AO/NAO could be a potential season-lead driver of the summer atmospheric circulation over the northwestern Indian Ocean.

  9. Particulate polycyclic aromatic hydrocarbons in the Atlantic and Indian Ocean atmospheres during the Indian Ocean Experiment and Aerosols99: Continental sources to the marine atmosphere

    NASA Astrophysics Data System (ADS)

    Crimmins, Bernard S.; Dickerson, Russell R.; Doddridge, Bruce G.; Baker, Joel E.

    2004-03-01

    Polycyclic aromatic hydrocarbons (PAHs), mutagenic compounds predominantly derived from combustion, have been used as markers of combustion sources to the atmosphere. Marine aerosol collected aboard the NOAA R/V Ronald Brown during the Aerosols99 and the Indian Ocean Experiment (INDOEX) projects was analyzed for PAHs to assess the continental impact of combustion-derived particulate matter on the Atlantic and Indian Ocean atmospheres. PAH concentrations in the Atlantic and southern Indian Ocean atmospheres were consistent and low, ranging from <0.45 pg/m3 for coronene to 30 pg/m3 for 9, 10-dimethylanthracene. PAH concentrations increased ten fold as the ship crossed the Intertropical Convergence Zone (ITCZ) into the northern Indian Ocean, indicating an increased anthropogenic influence. PAH concentrations over the northern Indian Ocean atmosphere were approximately an order of magnitude greater than those in the northern Atlantic Ocean atmosphere. PAH composition profiles over the northern Indian Ocean were specific to wind regimes and influenced by a combination of biomass and fossil fuel combustion. This was supported by significant correlations between select PAHs and organic carbon (OC), elemental carbon (EC), SO4-2 and K+ for particular wind regimes. Indeno[1,2,3-cd]pyrene/EC ratios used as a combustion source marker suggest that fossil fuel combustion, rather than biomass burning, is the predominant source of PAHs to the Northern Hemisphere Indian Ocean atmosphere. Interestingly, fossil fuel consumption in the Indian sub-continent is a fraction of that in Europe and the United States but the soot and PAH levels in the adjacent Northern Indian Ocean atmosphere are significantly greater than those in the Northern Atlantic atmosphere.

  10. Tropical Indian Ocean subsurface temperature variability and the forcing mechanisms

    NASA Astrophysics Data System (ADS)

    Sayantani, Ojha; Gnanaseelan, C.

    2015-05-01

    The first two leading modes of interannual variability of sea surface temperature in the Tropical Indian Ocean (TIO) are governed by El Niño Southern Oscillation and Indian Ocean Dipole (IOD) respectively. TIO subsurface however does not co-vary with the surface. The patterns of the first mode of TIO subsurface temperature variability and their vertical structure are found to closely resemble the patterns of IOD and El Niño co-occurrence years. These co-occurrence years are characterized by a north-south subsurface dipole rather than a conventional IOD forced east-west dipole. This subsurface dipole is forced by wind stress curl anomalies, driven mainly by meridional shear in the zonal wind anomalies. A new subsurface dipole index (SDI) has been defined in this study to quantify the intensity of the north-south dipole mode. The SDI peaks during December to February (DJF), a season after the dipole mode index peaks. It is found that this subsurface north-south dipole is a manifestation of the internal mode of variability of the Indian Ocean forced by IOD but modulated by Pacific forcing. The seasonal evolution of thermocline, subsurface temperature and the corresponding leading modes of variability further support this hypothesis. Positive wind stress curl anomalies in the south and negative wind stress curl anomalies in the north of 5°S force (or intensify) downwelling and upwelling waves respectively during DJF. These waves induce strong subsurface warming in the south and cooling in the north (especially during DJF) and assist the formation and/or maintenance of the north-south subsurface dipole. A thick barrier layer forms in the southern TIO, supporting the long persistence of anomalous subsurface warming. To the best of our knowledge the existence of such north-south subsurface dipole in TIO is being reported for the first time.

  11. A diffuse plate boundary model for Indian Ocean tectonics

    NASA Technical Reports Server (NTRS)

    Wiens, D. A.; Demets, C.; Gordon, R. G.; Stein, S.; Argus, D.

    1985-01-01

    It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.

  12. MORTALITY, THE FAMILY AND THE INDIAN OCEAN TSUNAMI

    PubMed Central

    Frankenberg, Elizabeth; Gillespie, Thomas; Preston, Samuel; Sikoki, Bondan; Thomas, Duncan

    2015-01-01

    Over 130,000 people died in the 2004 Indian Ocean tsunami. The correlates of survival are examined using data from the Study of the Tsunami Aftermath and Recovery (STAR), a population-representative survey collected in Aceh and North Sumatra, Indonesia, before and after the tsunami. Children, older adults and females were the least likely to survive. Whereas socio-economic factors mattered relatively little, the evidence is consistent with physical strength playing a role. Pre-tsunami household composition is predictive of survival and suggests that stronger members sought to help weaker members: men helped their wives, parents and children, while women helped their children. PMID:25866413

  13. Satellite-Based Surface Heat Budgets and Sea Surface Temperature Tendency in the Tropical Eastern Indian and Western Pacific Oceans for the 1997/98 El Nino and 1998/99 La Nina

    NASA Technical Reports Server (NTRS)

    Chou, Shu-Hsien; Chou, Ming-Dah; Chan, Pui-King; Lin, Po-Hsiung

    2002-01-01

    The 1997/98 is a strong El Nino warm event, while the 1998/99 is a moderate La Nina cold event. We have investigated surface heat budgets and sea surface temperature (SST) tendency for these two events in the tropical western Pacific and eastern Indian Oceans using satellite-retrieved surface radiative and turbulent fluxes. The radiative fluxes are taken from the Goddard Satellite-retrieved Surface Radiation Budget (GSSRB), derived from radiance measurements of the Japanese Geostationary Meteorological Satellite 5. The GSSRB covers the domain 40 deg S - 4 deg N, 90 deg E-17 deg W and a period from October 1997 to December 2000. The spatial resolution is 0.5 deg x 0.5 deg lat-long and the temporal resolution is 1 day. The turbulent fluxes are taken from Version 2 of the Goddard Satellite-based Surface Turbulent Fluxes (GSSTF-2). The GSSTF-2 has a spatial resolution of 1 deg x 1 deg lat-long over global Oceans and a temporal resolution of 1 day covering the period July 1987-December 2000. Daily turbulent fluxes are derived from the S S M (Special Sensor Microwave/Imager) surface wind and surface air humidity, and the SST and 2-m air temperature of the NCEP/NCAR reanalysis, using a stability-dependent bulk flux algorithm. The changes of surface heat budgets, SST and tendency, cloudiness, wind speed, and zonal wind stress of the 1997/98 El Nino relative to the1998/99 La Nina for the northern winter and spring seasons are analyzed. The relative changes of surface heat budgets and SST tendency of the two events are quite different between the tropical eastern Indian and western Pacific Oceans. For the tropical western Pacific, reduced solar heating (more clouds) is generally associated with decreased evaporative cooling (weaker winds), and vise versa. The changes in evaporative cooling over-compensate that of solar heating and dominate the spatial variability of the changes in net surface heating. Both solar heating and evaporative cooling offset each other to reduce

  14. Oceanic variability around Madagascar : connections to the large-scale Indian Ocean circulation and its forcing

    NASA Astrophysics Data System (ADS)

    Palastanga, V.

    2007-06-01

    The connection between the mesoscale eddy activity around Madagascar and the large-scale interannual variability in the Indian Ocean is investigated. We use the combined TOPEX/Poseidon-ERS sea surface height (SSH) data for the period 1993-2003. The SSH-fields in the Mozambique Channel and east of Madagascar exhibit a significant interannual oscillation. This is related to the arrival of large-scale anomalies that propagate westward in the band 10-15S in response to the Indian Ocean dipole (IOD) events. Positive (negative) SSH anomalies associated to a positive (negative) IOD phase induce a shift in the intensity and position of the tropical and subtropical gyres in the Indian Ocean. A weakening (strengthening) results in the intensity of the South Equatorial Current and its branches along east Madagascar. In addition, the flow through the narrows of the Mozambique Channel around 17S increases (decreases) during periods of a stronger and northward (southward) extension of the subtropical (tropical) gyre. Interaction between the currents in the narrows and southward propagating eddies from the northern Channel leads to interannual variability in the eddy kinetic energy of the central Channel in phase with the one in the SSH-field. The origin of the eddy variability along the 25S band in the Indian Ocean is also investigated. We have found that the surface circulation east of Madagascar shows an anticyclonic subgyre bounded to the south by eastward flow from southwest Madagascar and to the north by the westward flowing South Equatorial Current (SEC) between 15-20S. The shallow, eastward flow, named the South Indian Ocean Countercurrent (SICC), extends above the deep reaching, westward flowing SEC up to 95E, with its core over the latitude of the high variability band. Applying a 2-layer model reveals that regions of large vertical shear along the SICC-SEC system are baroclinically unstable. Estimates of the frequencies (3.5-6 times/year) and wavelengths (290-470 km

  15. ENSO modulation of tropical Indian Ocean subseasonal variability

    NASA Astrophysics Data System (ADS)

    Jung, Eunsil; Kirtman, Ben P.

    2016-12-01

    In this study, we use 30 years of retrospective climate model forecasts and observational estimates to show that El Niño/Southern Oscillation (ENSO) affects the amplitude of subseasonal variability of sea surface temperature (SST) in the southwest Indian Ocean, an important Tropical Intraseasonal Oscillation (TISO) onset region. The analysis shows that deeper background mixed-layer depths and warmer upper ocean conditions during El Niño reduce the amplitude of the subseasonal SST variability over Seychelles-Chagos Thermocline Ridge (SCTR), which may reduce SST-wind coupling and the amplitude of TISO variability. The opposite holds for La Niña where the shallower mixed-layer depth enhances SST variability over SCTR, which may increase SST-wind coupling and the amplitude of TISO variability.

  16. Preliminary Geochemical Results from the Mozambique Ridge, SW Indian Ocean

    NASA Astrophysics Data System (ADS)

    Jacques, G.; Werner, R.; Hauff, F.; Uenzelmann-Neben, G.; Hoernle, K.

    2015-12-01

    The Mozambique Ridge (120-140 Ma old) is a submarine plateau located in the southwest Indian Ocean. The relationship between plateau formation and the break-up of the Gondwana supercontinent is still unclear. Different models for the origin of this plateau include: 1) a continental fragment split off of Africa or Antarctica during Gondwana break-up and 2) an oceanic Large Igneous Province (LIP) formed by a mantle plume involved in Gondwana break-up. On the R/V SONNE (cruise SO232), we carried out bathymetric mapping, seismic reflection studies and rock sampling of the plateau basement, which confirmed the volcanic nature of at least the upper parts of the plateau. By reconstructing the spatial and temporal evolution in geochemistry of volcanic samples, we hope to gain new insights into the origin of the plateau. The recovered samples are mainly basaltic (SiO2 = 47-52 wt. %). On the Nb/Yb versus Th/Yb diagram, the samples overlap the field for enriched-mid-ocean-ridge basalts (EMORB) and extend towards the field for ocean island basalts (OIB). Most of the samples have relatively flat REE patterns, similar to EMORB or LIP type lavas. Initial Sr-Nd-Hf isotope ratios form tight correlations, excluding late alteration effects. The samples overlap and extend to slightly more radiogenic values than age-corrected SW Indian and South Atlantic MORB and OIB, indicating a two-component mixing between depleted (NMORB source) and enriched (OIB-type) mantle. Similar to some early Kerguelen plateau basalts, some of our samples have low Nd isotope and (Nb/La)n (< 1) ratios suggesting involvement of continental lithosphere and/or lower crust. On the 206Pb/204Pb versus 207Pb/204Pb isotope diagram, the samples extend to higher Δ7/4 than the South West Indian array, overlapping with Kerguelen lavas. Bathymetric data show numerous small cones scattered on the plateau, which are thought to represent a reactivation of volcanism after formation of the plateau basement. Moreover, seismic

  17. Indonesian throughflow nutrient fluxes and their potential impact on Indian Ocean productivity

    NASA Astrophysics Data System (ADS)

    Ayers, Jennifer M.; Strutton, Peter G.; Coles, Victoria J.; Hood, Raleigh R.; Matear, Richard J.

    2014-07-01

    The Indonesian throughflow (ITF) is a chokepoint in the upper ocean thermohaline circulation, carrying Pacific waters through the strongly mixed Indonesian Seas and into the Indian Ocean. Yet the influence of the ITF on biogeochemical fluxes into the Indian Ocean is largely unknown. This study determines the first depth- and time-resolved nitrate, phosphate, and silicate fluxes at the three main exit passages of the ITF: Lombok Strait, Ombai Strait, and Timor Passage. Nutrient flux as well as its variability with depth and time differs greatly between the passages. We estimate the effective flux of nutrients into the Indian Ocean by accounting for existing nutrients in the basin and find it largest in the upper 300-400 m. This suggests that the majority of ITF nutrient supply to the Indian Ocean is to thermocline waters, where it is likely to support new production and significantly impact Indian Ocean biogeochemical cycling.

  18. Aerosol direct radiative effects over the northwest Atlantic, northwest Pacific, and North Indian Oceans: estimates based on in-situ chemical and optical measurements and chemical transport modeling

    NASA Astrophysics Data System (ADS)

    Bates, T. S.; Anderson, T. L.; Baynard, T.; Bond, T.; Boucher, O.; Carmichael, G.; Clarke, A.; Erlick, C.; Guo, H.; Horowitz, L.; Howell, S.; Kulkarni, S.; Maring, H.; McComiskey, A.; Middlebrook, A.; Noone, K.; O'Dowd, C. D.; Ogren, J.; Penner, J.; Quinn, P. K.; Ravishankara, A. R.; Savoie, D. L.; Schwartz, S. E.; Shinozuka, Y.; Tang, Y.; Weber, R. J.; Wu, Y.

    2006-01-01

    The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions (IPCC, 2001). Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean (NIO) during INDOEX, the Northwest Pacific Ocean (NWP) during ACE-Asia, and the Northwest Atlantic Ocean (NWA) during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth (AOD), and direct radiative effect of aerosols (DRE - change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Constraining the radiative transfer

  19. Aerosol direct radiative effects over the northwest Atlantic, northwest Pacific, and North Indian Oceans: estimates based on in-situ chemical and optical measurements and chemical transport modeling

    NASA Astrophysics Data System (ADS)

    Bates, T. S.; Anderson, T. L.; Baynard, T.; Bond, T.; Boucher, O.; Carmichael, G.; Clarke, A.; Erlick, C.; Guo, H.; Horowitz, L.; Howell, S.; Kulkarni, S.; Maring, H.; McComiskey, A.; Middlebrook, A.; Noone, K.; O'Dowd, C. D.; Ogren, J.; Penner, J.; Quinn, P. K.; Ravishankara, A. R.; Savoie, D. L.; Schwartz, S. E.; Shinozuka, Y.; Tang, Y.; Weber, R. J.; Wu, Y.

    2006-05-01

    The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions (IPCC, 2001). Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean (NIO) during INDOEX, the Northwest Pacific Ocean (NWP) during ACE-Asia, and the Northwest Atlantic Ocean (NWA) during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth (AOD), and direct radiative effect of aerosols (DRE - change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Constraining the radiative transfer

  20. An extensive region of off-ridge normal-faulting earthquakes in the southern Indian Ocean

    NASA Technical Reports Server (NTRS)

    Bergman, E. A.; Nabelek, J. L.; Solomon, S. C.

    1984-01-01

    A verified prediction of the theory of plate tectonics is that the focal mechanisms of earthquakes on the mid-ocean ridge system indicate either normal faulting on ridge segments or strike-slip faulting on transform faults. A broad region in the southern Indian Ocean which differs from typical ridge and intraplate regimes has been identified. In this region a number of large off-ridge earthquakes have occurred in the last 20 years. The mechanisms for these events, where known, all involve normal faulting. Nine of these earthquakes have been studied in detail using a formal inversion technique based on matching synthetic body waves to observed seismograms.

  1. Eastern Indian Ocean microcontinent formation driven by plate motion changes

    NASA Astrophysics Data System (ADS)

    Whittaker, J. M.; Williams, S. E.; Halpin, J. A.; Wild, T. J.; Stilwell, J. D.; Jourdan, F.; Daczko, N. R.

    2016-11-01

    The roles of plate tectonic or mantle dynamic forces in rupturing continental lithosphere remain controversial. Particularly enigmatic is the rifting of microcontinents from mature continental rifted margins, with plume-driven thermal weakening commonly inferred to facilitate calving. However, a role for plate tectonic reorganisations has also been suggested. Here, we show that a combination of plate tectonic reorganisation and plume-driven thermal weakening were required to calve the Batavia and Gulden Draak microcontinents in the Cretaceous Indian Ocean. We reconstruct the evolution of these two microcontinents using constraints from new paleontological samples, 40Ar/39Ar ages, and geophysical data. Calving from India occurred at 101-104 Ma, coinciding with the onset of a dramatic change in Indian plate motion. Critically, Kerguelen plume volcanism does not appear to have directly triggered calving. Rather, it is likely that plume-related thermal weakening of the Indian passive margin preconditioned it for microcontinent formation but calving was triggered by changes in plate tectonic boundary forces.

  2. Diversity in Tsunami Forecasts in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Greenslade, Diana; Annunziato, Alessandro; Babeyko, Andrey; Burbidge, David; Ellguth, Enrico; Horspool, Nick; Kumar, Srinivasa; Kumar, Patangali; Moore, Christopher; Rakowsky, Natalja; Riedlinger, Torsten; Ruangrassamee, Anat; Srivihok, Patchanok; Titov, Vasily

    2013-04-01

    The development of the Indian Ocean Tsunami Warning and mitigation System (IOTWS) has occurred rapidly over the past few years and there are now a number of centres that perform tsunami modelling, both for risk assessment and for the provision of forecasts and warnings. The aim of this work is to determine to what extent event-specific tsunami forecasts from different numerical forecast systems differ. This will have implications for the inter-operability of the IOTWS. Forecasts from eight separate tsunami forecast systems are considered. Eight hypothetical earthquake scenarios within the Indian Ocean and ten output points at a range of depths were defined. Each forecast centre provided, where possible, time series of sea-level elevation for each of the scenarios at each location. Comparison of the resulting time series shows that the main details of the tsunami forecast, such as arrival times and characteristics of the leading waves are similar. However, there is considerable variability in the value of the maximum amplitude (hmax) for each event and, on average the standard deviation of hmax is approximately 70% of the mean. This variability is likely due to differences in the choice of numerical model and bathymetry datasets, specification of earthquake rupture mechanism, etc. This represents the range of uncertainty that exists in the real-time situation. The results suggest that it is possible that tsunami forecasts and advisories from different centres for a particular event may conflict with each other.

  3. Three years of rainfall over the Indian Ocean

    NASA Technical Reports Server (NTRS)

    Martin, David W.; Hinton, Barry B.; Auvine, Brian A.

    1993-01-01

    Monthly rain falling on the Indian Ocean is mapped for the period 1979 through 1981 by means of observations of the Nimbus-7 Scanning Multichannel Microwave Radiometer. Both stationary and mobile parts were found in the pattern of rain. The stationary part consisted of three zonal and two meridional bands. Only one, the band along and south of the equator, maintained a strong presence through all seasons. A north equatorial counterpart to this south equatorial band also was persistent, but weak. The mobile part of the pattern took the form of a wave. The locus of this wave was an eastward-tilted figure eight, which straddled the equator. The wave moved clockwise along the north loop of the figure eight, counterclockwise along the south loop. The crest of the wave crossed the equator from south to north in May or June and crossed the equator from north to south between August and October. Along its path the equatorial bands were alternately amplified and damped, and the transient bands were activated and suppressed. The effect of the bands and wave was to produce a strong 'monsoon' (annual cycle, summer peak) signature in rain falling over both the northeastern and southwestern reaches of the Indian Ocean.

  4. Pelagic ecology of the South West Indian Ocean Ridge seamounts: Introduction and overview

    NASA Astrophysics Data System (ADS)

    Rogers, A. D.

    2017-02-01

    The Indian Ocean was described by Behrman (1981) as the "Forlorn Ocean", a region neglected by science up to the late-1950s. For example, the Challenger Expedition from 1872 to 1876 largely avoided the Indian Ocean, sailing from Cape Town into Antarctic waters sampling around the Prince Edward Islands, Kerguelen Island and Crozet Islands before heading to Melbourne. From 1876 to the 1950s there were expeditions on several vessels including the Valdivia, Gauss and Planet (Germany), the Snellius (Netherlands), Discovery II, MahaBiss (United Kingdom), Albatross (Sweden), Dana and Galathea (Denmark; Behrman, 1981). There was no coordination between these efforts and overall the Indian Ocean, especially the deep sea remained perhaps the most poorly explored of the world's oceans. This situation was largely behind the multilateral effort represented by the International Indian Ocean Expedition (IIEO), which was coordinated by the Scientific Committee for Ocean Research (SCOR), and which ran from 1959-1965. Work during this expedition focused on the Arabian Sea, the area to the northwest of Australia and the waters over the continental shelves and slopes of coastal states in the region. Subsequently several large-scale international oceanographic programmes have included significant components in the Indian Ocean, including the Joint Global Ocean Flux Study (JGOFS) and the World Ocean Circulation Experiment (WOCE). These studies were focused on physical oceanographic measurements and biogeochemistry and whilst the Indian Ocean is still less understood than other large oceans it is now integrated into the major ocean observation systems (Talley et al., 2011). This cannot be said for many aspects of the biology of the region, despite the fact that the Indian Ocean is one of the places where exploitation of marine living resources is still growing (FAO, 2016). The biology of the deep Indian Ocean outside of the Arabian Sea is particularly poorly understood given the presence

  5. Factors controlling the location of compressional deformation of oceanic lithosphere in the Central Indian Ocean

    NASA Technical Reports Server (NTRS)

    Karner, Garry D.; Weissel, Jeffrey K.

    1990-01-01

    One- and two-dimensional models for the deformation by horizontal compression of an elastic plate containing a preexisting deflection were developed and analyzed in order to explain why the compressionally deformed oceanic lithosphere in the Central Indian-Ocean basin is not located where maximum levels of compressive stress in the Indo-Australian plate were predicted by Cloetingh and Wortel (1985, 1986). It is concluded from the results that the location of the deformed region is controlled by an earlier lithospheric deformation that is attributed to the emplacement of the Afanazy-Nikitin seamount group in Late Cretaceous or early Tertiary time.

  6. Combined assimilation of hydrography and TOPEX data into an Indian Ocean GCM using the adjoint method

    NASA Technical Reports Server (NTRS)

    Marotzke, T. L. J.

    1997-01-01

    To study seasonal circulation and meridional heat transport of the Indian Ocean by synthesizing dynamics with data, climatological monthly temperatures and salinities, surface heat and freshewater fluxes, and wind stresses, together with monthly ensembles of three years (93-95) of TOPEX-derived surface geostrophic velocity anomalies, are assimilated into an Indian Ocean GCM.

  7. [Post nearly Drowning Vibrio alginolyticus Septicemia Acquired in Reunion (Indian Ocean)].

    PubMed

    Gaüzère, B-A; Chanareille, P; Vandroux, D

    2016-08-01

    AbstractWe report the first case of Vibrio alginolyticus septicemia in the Indian Ocean (Reunion Island), in a patient (70-year-old-man) with multiple underlying conditions, following a nearly drowning in the lagoon of Reunion. From now on, V. alginolyticus should be considered as a possible agent of septicemia in the Indian Ocean, particularly following marine activities.

  8. Multi-genetic marker approach and spatio-temporal analysis suggest there is a single panmictic population of swordfish Xiphias gladius in the Indian Ocean.

    PubMed

    Muths, Delphine; Le Couls, Sarah; Evano, Hugues; Grewe, Peter; Bourjea, Jerome

    2013-01-01

    Genetic population structure of swordfish Xiphias gladius was examined based on 2231 individual samples, collected mainly between 2009 and 2010, among three major sampling areas within the Indian Ocean (IO; twelve distinct sites), Atlantic (two sites) and Pacific (one site) Oceans using analysis of nineteen microsatellite loci (n = 2146) and mitochondrial ND2 sequences (n = 2001) data. Sample collection was stratified in time and space in order to investigate the stability of the genetic structure observed with a special focus on the South West Indian Ocean. Significant AMOVA variance was observed for both markers indicating genetic population subdivision was present between oceans. Overall value of F-statistics for ND2 sequences confirmed that Atlantic and Indian Oceans swordfish represent two distinct genetic stocks. Indo-Pacific differentiation was also significant but lower than that observed between Atlantic and Indian Oceans. However, microsatellite F-statistics failed to reveal structure even at the inter-oceanic scale, indicating that resolving power of our microsatellite loci was insufficient for detecting population subdivision. At the scale of the Indian Ocean, results obtained from both markers are consistent with swordfish belonging to a single unique panmictic population. Analyses partitioned by sampling area, season, or sex also failed to identify any clear structure within this ocean. Such large spatial and temporal homogeneity of genetic structure, observed for such a large highly mobile pelagic species, suggests as satisfactory to consider swordfish as a single panmictic population in the Indian Ocean.

  9. The meteorology of the Western Indian Ocean, and the influence of the East African Highlands.

    PubMed

    Slingo, Julia; Spencer, Hilary; Hoskins, Brian; Berrisford, Paul; Black, Emily

    2005-01-15

    This paper reviews the meteorology of the Western Indian Ocean and uses a state-of-the-art atmospheric general circulation model to investigate the influence of the East African Highlands on the climate of the Indian Ocean and its surrounding regions. The new 44-year re-analysis produced by the European Centre for Medium range Weather Forecasts (ECMWF) has been used to construct a new climatology of the Western Indian Ocean. A brief overview of the seasonal cycle of the Western Indian Ocean is presented which emphasizes the importance of the geography of the Indian Ocean basin for controlling the meteorology of the Western Indian Ocean. The principal modes of inter-annual variability are described, associated with El Nino and the Indian Ocean Dipole or Zonal Mode, and the basic characteristics of the subseasonal weather over the Western Indian Ocean are presented, including new statistics on cyclone tracks derived from the ECMWF re-analyses. Sensitivity experiments, in which the orographic effects of East Africa are removed, have shown that the East African Highlands, although not very high, play a significant role in the climate of Africa, India and Southeast Asia, and in the heat, salinity and momentum forcing of the Western Indian Ocean. The hydrological cycle over Africa is systematically enhanced in all seasons by the presence of the East African Highlands, and during the Asian summer monsoon there is a major redistribution of the rainfall across India and Southeast Asia. The implied impact of the East African Highlands on the ocean is substantial. The East African Highlands systematically freshen the tropical Indian Ocean, and act to focus the monsoon winds along the coast, leading to greater upwelling and cooler sea-surface temperatures.

  10. Interannual variability of the Indian summer monsoon associated with the air-sea feedback in the northern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Shukla, Ravi P.; Huang, Bohua

    2016-03-01

    Using observation-based analyses, this study identifies the leading interannual pattern of the Indian summer monsoon rainfall (ISMR) independent of ENSO and examines the potential mechanisms of its formation. For this purpose, an objective procedure is used to isolate the variability of the summer precipitation associated with the contemporary ENSO state and in previous winter-spring, which influence the Indian summer monsoon (ISM) region in opposite ways. It is shown that the leading pattern of these ENSO-related monsoon rainfall anomalies reproduces some major ISMR features and well represents its connections to the global-scale ENSO features in both lower and upper troposphere. On the other hand, the leading pattern derived from the precipitation anomalies with the ENSO component removed in the ISM and surrounding region also accounts for a substantial amount of the monsoon precipitation centered at the eastern coast of the subtropical Arabian Sea, extending into both the western Indian Ocean and the Indian subcontinent. The associated atmospheric circulation change is regional in nature, mostly confined in the lower to mid troposphere centered in the Arabian Sea, with a mild connection to an opposite tendency centered at the South China Sea. Further analyses show that this regional pattern is associated with a thermodynamic air-sea feedback during early to mid summer season. Specifically, before the monsoon onset, an anomalous atmospheric high pressure over the Arabian Sea causes excessive shortwave radiation to the sea surface and increases SST in May. The warm SST anomalies peak in June and reduce the sea level pressure. The anomalous cyclonic circulation generates regional convection and precipitation, which also induces subsidence and anticyclonic circulation over the South China Sea. The combined cyclonic-anticyclonic circulation further transport moisture from the western Pacific into the Indian Ocean and causes its convergence into the Arabian Sea. As a

  11. Sources of new nitrogen in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Raes, Eric J.; Thompson, Peter A.; McInnes, Allison S.; Nguyen, Hoang Minh; Hardman-Mountford, Nick; Waite, Anya M.

    2015-08-01

    Quantifying the different sources of nitrogen (N) within the N cycle is crucial to gain insights in oceanic phytoplankton production. To understand the controls of primary productivity and the associated capture of CO2 through photosynthesis in the southeastern Indian Ocean, we compiled the physical and biogeochemical data from four voyages conducted in 2010, 2011, 2012, and 2013. Overall, higher NH4+ assimilation rates (~530 µmol m-2 h-1) relative to NO3- assimilation rates (~375 µmol m-2 h-1) suggest that the assimilation dynamics of C are primarily regulated by microbial regeneration in our region. N2 fixation rates did not decline when other source of dissolved inorganic nitrogen were available, although the assimilation of N2 is a highly energetic process. Our data showed that the diazotrophic community assimilated ~2 nmol N L-1 h-1 at relative elevated NH4+ assimilation rates ~12 nmol L-1 h-1 and NO3- assimilation rates ~6 nmol L-1 h-1. The small diffusive deep water NO3- fluxes could not support the measured NO3- assimilation rates and consequently point toward another source of dissolved inorganic NO3-. Highest NO2- values coincided consistently with shallow lower dissolved O2 layers (100-200 m; 100-180 µmol L-1). These results suggest that nitrification above the pycnocline could be a significant component of the N cycle in the eastern Indian Ocean. In our analysis we provide a conceptual understanding of how NO3- in the photic zone could be derived from new N through N2 fixation. We conclude with the hypothesis that N injected through N2 fixation can be recycled within the photic zone as NH4+ and sequentially oxidized to NO2- and NO3- in shallow lower dissolved oxygen layers.

  12. Export of dissolved inorganic nutrients to the northern Indian Ocean from the Indian monsoonal rivers during discharge period

    NASA Astrophysics Data System (ADS)

    Krishna, M. S.; Prasad, M. H. K.; Rao, D. B.; Viswanadham, R.; Sarma, V. V. S. S.; Reddy, N. P. C.

    2016-01-01

    Coastal regions are highly productive due to the nutrients largely supplied by rivers. To examine the contribution of dissolved inorganic nutrients (DIN) by Indian rivers to coastal waters, data were collected near the freshwater heads of 27 monsoonal rivers of peninsular India during three weeks in late July to mid-August, the middle of the principal runoff period of the southwest monsoon of 2011. Twelve researchers in four groups, equipped with car and portable laboratory equipment, sampled mid-stream of each estuary using mechanized boat, and filtered and partly analyzed the water in the evening. The estimated exports were 0.22 ± 0.05, 0.11 ± 0.03, and 1.03 ± 0.26 Tg yr-1 for dissolved inorganic nitrogen, phosphorus and silicate, respectively. Higher amounts of DIN reach the Bay of Bengal than the Arabian Sea due to the higher volume (∼76%) of discharge to the former. In contrast, the export of dissolved inorganic nitrogen is almost same to the Bay of Bengal (0.12 ± 0.03 Tg yr-1) and Arabian Sea (0.10 ± 0.02 Tg yr-1) principally due to the polluted Narmada and Tapti rivers in the northwest. Including input from the glacial rivers, Ganges, Brahmaputra and Indus, it is estimated that the northern Indian Ocean receives ∼1.84 ± 0.46, 0.28 ± 0.07 and 3.58 ± 0.89 Tg yr-1 of nitrate, phosphate and silicate, respectively, which are significantly lower than the earlier estimates of DIN export from the Indian rivers based on DIN measured in the mid or upstream rivers. Such low fluxes in this study were attributed to efficient retention/elimination of DIN (∼91%) before reaching the coastal ocean. Hence, this study suggests that the importance of sampling locations for estimating nutrient fluxes to the coastal ocean. Riverine DIN export of 1.84 ± 0.46 Tg yr-1 would support 12.2 ± 3.1 Tg C yr-1 of new production in coastal waters of the northern Indian Ocean that results in a removal of 12.2 ± 3.1 Tg atmospheric CO2 yr-1.

  13. Use of microwave satellite data to study variations in rainfall over the Indian Ocean

    NASA Technical Reports Server (NTRS)

    Hinton, Barry B.; Martin, David W.; Auvine, Brian; Olson, William S.

    1990-01-01

    The University of Wisconsin Space Science and Engineering Center mapped rainfall over the Indian Ocean using a newly developed Scanning Multichannel Microwave Radiometer (SMMR) rain-retrieval algorithm. The short-range objective was to characterize the distribution and variability of Indian Ocean rainfall on seasonal and annual scales. In the long-range, the objective is to clarify differences between land and marine regimes of monsoon rain. Researchers developed a semi-empirical algorithm for retrieving Indian Ocean rainfall. Tools for this development have come from radiative transfer and cloud liquid water models. Where possible, ground truth information from available radars was used in development and testing. SMMR rainfalls were also compared with Indian Ocean gauge rainfalls. Final Indian Ocean maps were produced for months, seasons, and years and interpreted in terms of historical analysis over the sub-continent.

  14. Introduction to Indian Ocean biogeochemical processes and ecological variability: Current understanding and emerging perspectives

    NASA Astrophysics Data System (ADS)

    Wiggert, Jerry D.; Hood, Raleigh R.; Naqvi, S. Wajih A.; Brink, Kenneth H.; Smith, Sharon L.

    Despite a history of exploration dating back to the classical era and its leading role as a pathway for trade and cultural exchange for the great civilizations of those times, the Indian Ocean has consistently been subject to less attention in the modern era in terms of oceanographic enquiry. The cornerstone of the Sustained Indian Ocean Biogeochemical and Ecosystem Research (SIBER) initiative has been to promote more frequent and persistent research activities that encompass the entire Indian Ocean basin and to facilitate international cooperation to realize these objectives. This volume's chapters are derived from the plenary talks given by the attendees of the first SIBER conference and are a blend of current knowledge reviews and new results. Thus this collection of papers represents an interdisciplinary contribution to the Indian Ocean literature by the leading members of the Indian Ocean research community.

  15. Reconstructing Indian Ocean Paleo-bathymetry in search of biogeographic connections

    NASA Astrophysics Data System (ADS)

    Whittaker, J. M.; Gibbons, A.; Seton, M.; Müller, D.

    2010-12-01

    Plate tectonic and geodynamic approaches can be used to constrain the spatial and temporal evolution of connections traversable by biota in the early Indian Ocean, in particular between India, Madagascar and Antarctica. Corridors that allow biota to move from one continent to another may either be continuous land-bridges or discontinuous islands that serve as ‘stepping-stones’ between major landmasses. Essentially, we need to know where there was exposed land throughout the Indian Ocean. Continental crust, Large Igneous Provinces (LIPs) and seamounts all have the potential to compose all or part of a corridor. Two key things are necessary to reconstruct accurate paleo-geographies of the Indian Ocean in the Cretaceous. The first is accurately modelling the distribution of the key tectonic elements relative to each other (i.e. accurate plate reconstructions) and the second is computing the paleo-bathymetry/topography of these features at key time intervals. Accurate plate reconstructions, based on marine geophysical data such as satellite gravity and shiptrack magnetic anomalies, are crucial for understanding the timing of separation of the major landmasses of Eastern Gondwana (India, Australia, Antarctica and Madagascar) as well as the distance between the continents and smaller LIPs and seamounts. Currently there are numerous incompatible plate kinematic models for the opening of various basins around the Indian Ocean, including the West Somali Basin, the Enderby Basin and the Bay of Bengal. We assess the alternative models in order to develop a regionally consistent model that conforms to all the available geophysical and geological data. Although they are predominantly below sealevel at the present-day, there are a number of LIPs and seamounts throughout the Indian Ocean that may have been sub-aerial in the past. We restore the location of these volcanic features based on our revised plate tectonic model and estimate their paleo-heights by incorporating

  16. Evidence of Postseismic Deformation Signal of the 2007 M8.5 Bengkulu Earthquake and the 2012 M8.6 Indian Ocean Earthquake in Southern Sumatra, Indonesia, Based on GPS Data

    NASA Astrophysics Data System (ADS)

    Alif, Satrio Muhammad; Meilano, Irwan; Gunawan, Endra; Efendi, Joni

    2016-06-01

    GPS data in southern Sumatra, Indonesia, indicate crustal deformation associated to subduction zone and inland fault of Great Sumatran Fault (GSF). We analyze these deformation characteristics using campaign and continuous GPS data available in southern Sumatra from 2006-2014. After removing the effect of GSF in southern Sumatra and coseismic displacements of 2007 Bengkulu and 2012 Indian Ocean earthquake, we find that GPS sites experienced northwest-ward direction. These GPS velocities correspond to postseismic deformation of the 2007 Bengkulu earthquake and the 2012 Indian Ocean earthquake. We analyze strain using these velocities, and we find that postseismic strains in southern Sumatra are in the range of 0.8-20 nanostrain.

  17. Ocean bottom characterestics between Iles Rodrigues and Chagos-Maldives Archepelago in western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Longhinos, Biju; Thanu Iyer, Radhakrishnan; Mohan, Karthika

    2014-05-01

    The geological and geophysical complexities in Indian ocean basin, pointed out by many earlier workers remained unresolved. Instead, taking aid from stop gap arguments, the data has been construed to follow plate tectonics format. The concept of large igneous complexes emplaced through crustal drifting ( between the India and Mozambique) during later Mesozoic to Recent fail to address geophysical characteristics exhibited here. The geophysical signatures of the sub crustal part of the ocean here resemble to that of continental regions elsewhere. Granites, greenstones and mylonized gabbro, recovered from the western Indian ocean basin, rather give Late Pre- Cambrian and Paleozoic isotopic dates. Under this light, the present paper looks into the ocean bottom characteristics of a region between iles Rodrigues and Chagos- Maldives archipelago. The region has first order curvilienar fractures, with along which the crust has displaced more than 1000m. The sea-bottom topography of the region has been modeled in Geographical Information System environment using Modified ETOPO5 provided by National Institute of Oceanography. The spatial relationship of topography with gravity and magnetic data area are analysed visually and mathematically. The detail bathymetry, gravity and magnetic data give morphology similar to that of half graben formed on a felsic crust, which later has undergone basification / eclogitization through first order fracture zones.

  18. A reduction in marine primary productivity driven by rapid warming over the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Roxy, Mathew Koll; Modi, Aditi; Murtugudde, Raghu; Valsala, Vinu; Panickal, Swapna; Prasanna Kumar, S.; Ravichandran, M.; Vichi, Marcello; Lévy, Marina

    2016-01-01

    Among the tropical oceans, the western Indian Ocean hosts one of the largest concentrations of marine phytoplankton blooms in summer. Interestingly, this is also the region with the largest warming trend in sea surface temperatures in the tropics during the past century—although the contribution of such a large warming to productivity changes has remained ambiguous. Earlier studies had described the western Indian Ocean as a region with the largest increase in phytoplankton during the recent decades. On the contrary, the current study points out an alarming decrease of up to 20% in phytoplankton in this region over the past six decades. We find that these trends in chlorophyll are driven by enhanced ocean stratification due to rapid warming in the Indian Ocean, which suppresses nutrient mixing from subsurface layers. Future climate projections suggest that the Indian Ocean will continue to warm, driving this productive region into an ecological desert.

  19. Redescriptions of Polysteganus coeruleopunctatus (Klunzinger 1870) and P. lineopunctatus (Boulenger 1903), with two new species from Western Indian Ocean.

    PubMed

    Iwatsuki, Yukio; Heemstra, Phillip C

    2015-12-21

    Five valid species in the genus Polysteganus (Pisces; Sparidae) from the Western Indian Ocean are currently known: P. baissaci Smith 1978, P. coeruleopunctatus (Klunzinger 1870), P. mascarenensis Iwatsuki & Heemstra, 2011, P. praeorbitalis (Günther 1859), and P. undulosus (Regan 1908). Although P. lineopunctatus (Boulenger 1903) has long been synonymized under P. coeruleopunctatus, both species are redescribed as valid. Two new species of Polysteganus were discovered in the course of this review. Polysteganus flavodorsalis n. sp. is described on the basis of six type specimens (143-265 mm SL) from Nazareth Bank, Mascarene Plateau, Indian Ocean, and P. cerasinus n. sp. is described based on the holotype (134 mm SL) from Saya de Malha Bank. Provisional distribution patterns of the eight valid species of Polysteganus in the Western Indian Ocean are discussed. A key to the species of Polysteganus is provided.

  20. MAGSAT anomaly profiles of the eastern Indian Ocean

    NASA Technical Reports Server (NTRS)

    Sailor, R. V. (Principal Investigator); Lazarewicz, A. R.

    1981-01-01

    Ground tracks from SEASAT were used in an effort to develop qualititative relationships between the gravity field and MAGSAT magnetic anomalies in the eastern Indian Ocean. Investigation of data quality led to analyses of the average value (over 80 vector data points, or approximately 36 km intervals) and of the standard deviation of this average, as a mean of identifying noisy portions of the data. It was discovered that the plots of the average value minus the individual (measured) point value are most useful for identifying noisy areas and data spikes. Spectrum analysis using edited (spikes removed) data show that the noise floor is less than 1 nT and the slope of the spectrum in the region of wavelengths between 1200 km and 250 km is approximately -3. Consequently the estimated resolution limit improved from approximately 360 km to approximately 250 km.

  1. Westward propagating twin gyres in the equatorial Indian Ocean

    NASA Astrophysics Data System (ADS)

    Reddy, P. Rahul Chand; Salvekar, P. S.; Deo, A. A.; Ganer, D. W.

    2004-01-01

    A reduced-gravity (1$\\frac{1}{2-layer) model forced by daily climatological winds simulates twin, anticyclonic gyres, which propagate westward on either side of the equator. The gyres form at the beginning of both the Southwest Monsoon and the Northeast monsoon in the equatorial eastern Indian Ocean, and subsequently propagate across the basin. Their existence is supported by velocity observations taken during WOCE in 1995 and by TOPEX/Poseidon sea-level observations during 1993. They are also present in the ECCO model/data product. They form at the front of a Rossby-wave packet generated by the reflection of the equatorial jet (EJ) from the eastern boundary of the basin. They are likely either Rossby solitons or result from the nonlinear interaction between the EJ and the Rossby-wave front.

  2. High-resolution Quantification of Turbulent Mixing in the North Indian Ocean During the Monsoons

    DTIC Science & Technology

    2014-09-30

    High-resolution quantification of turbulent mixing in the North Indian Ocean during the monsoons Sutanu Sarkar Department of Mechanical and...COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE High-resolution Quantification of Turbulent Mixing in the North Indian Ocean During the...the upper ocean surface of the Bay of Bengal. Understanding such processes will help improve the parametrization of momentum and heat fluxes across

  3. Magnetic Anomalies in the Enderby Basin, the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nogi, Y.; Sato, T.; Hanyu, T.

    2013-12-01

    Magnetic anomalies in the Southern indian Ocean are vital to understanding initial breakup process of Gondwana. However, seafloor age estimated from magnetic anomalies still remain less well-defined because of the sparse observations in this area. To understand the seafloor spreading history related to the initial breakup process of Gondwana, vector magnetic anomaly data as well as total intensity magnetic anomaly data obtained by the R/V Hakuho-maru and the icebreaker Shirase in the Enderby Basin, Southern Indian Ocean, are used. The strikes of magnetic structures are deduced from the vector magnetic anomalies. Magnetic anomaly signals, most likely indicating Mesozoic magnetic anomaly sequence, are obtained almost parallel to the west of WNW-ESE trending lineaments just to the south of Conrad Rise inferred from satellite gravity anomalies. Most of the strikes of magnetic structures indicate NNE-SSW trends, and are almost perpendicular to the WNW-ESE trending lineaments. Mesozoic sequence magnetic anomalies with mostly WNW-ESE strikes are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and Gunnerus Ridge. Magnetic anomalies originated from Cretaceous normal polarity superchron are found in these profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. However Mesozoic sequence magnetic anomalies are only observed in the west side of the WNW-ESE trending lineaments just to the south of Conrad Rise and not detected to the east of Cretaceous normal superchron signals. These results show that counter part of Mesozoic sequence magnetic anomalies in the south of Conrad Rise would be found in the East Enderby Basin, off East Antarctica. NNE-SSW trending magnetic structures, which are similar to those obtained just to the south of Conrad Rise, are found off East Antarctica in the East Enderby Basin. However, some of the strikes show almost E-W orientations. These suggest complicated ridge

  4. Holocene Indian Ocean Cosmic Impacts: The Megatsunami Chevron Evidence From Madagascar

    NASA Astrophysics Data System (ADS)

    Masse, W.; Bryant, E.; Gusiakov, V.; Abbott, D.; Rambolamana, G.; Raza, H.; Courty, M.; Breger, D.; Gerard-Little, P.; Burckle, L.

    2006-12-01

    The 2.6 million year Quaternary period terrestrial physical record lacks definitive crater evidence for major regional catastrophic impacts by asteroids and comets other than the 10.5-km diameter Botsumtwi structure in Ghana and the 14.0-km diameter Zhamanshin structure in Kazakhstan [1] dating between about 900 and 1100 kya. Current cosmic impact rate models suggest that an average of between 3-6 globally catastrophic impacts should have occurred on the Earth during the Quaternary, along with several additional significant regional impacts in addition to Zhamanshin and Botsumtwi. These models and data indicate that the great majority of the "missing" major impact locations would likely have occurred in poorly studied oceanic settings. Only recently have Late Quaternary and Holocene period coastal paleo-megatsunami chevron deposits been defined in the Caribbean and along the western coasts of Australia, along with the suggestion that some may have been created by oceanic cosmic impacts in distinction to those caused by landslips, eruptions, and seismic events. We investigate the possibility that many or most megatsunami chevrons occurring along the southern coast of Madagascar were caused by two or more major Holocene Indian Ocean cosmic impacts. This hypothesis is based on an initial study of the worldwide archaeological and anthropological record, and the preliminary study of satellite images of the chevrons, selected Indian Ocean deep-sea cores, sea-floor bathymetry, and physical examination of the Madagascar deposits themselves. Candidate Indian Ocean impact structures are identified and correlated with the southern Madagascar megatsunami chevron deposits. [1] Masse, W.B. 2007 The Archaeology and Anthropology of Quaternary Period Cosmic Impact. In Bobrowsky, P.T. & Rickman, H. (eds.)Comets/Asteroid Impacts and Human Society. Springer, Berlin (in press).

  5. Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean.

    PubMed

    Samaran, Flore; Stafford, Kathleen M; Branch, Trevor A; Gedamke, Jason; Royer, Jean-Yves; Dziak, Robert P; Guinet, Christophe

    2013-01-01

    Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four "acoustic populations" occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.

  6. A sea surface temperature reconstruction for the southern Indian Ocean trade wind belt from corals in Rodrigues Island (19° S, 63° E)

    NASA Astrophysics Data System (ADS)

    Zinke, Jens; Reuning, Lars; Pfeiffer, Miriam; Wassenburg, Jasper A.; Hardman, Emily; Jhangeer-Khan, Reshad; Davies, Gareth R.; Ng, Curtise K. C.; Kroon, Dick

    2016-10-01

    The western Indian Ocean has been warming rapidly over recent decades, causing a greater number of extreme climatic events. It is therefore of paramount importance to improve our understanding of links between Indian Ocean sea surface temperature (SST) variability, climate change and sustainability of tropical coral reef ecosystems. Here we present monthly resolved coral Sr / Ca records from two different locations from Rodrigues Island (63° E, 19° S) in the south-central Indian Ocean trade wind belt. We reconstruct SST based on a linear relationship with the Sr / Ca proxy with records starting from 1781 and 1945, respectively. We assess relationships between the observed long-term SST and climate fluctuations related to the El Niño-Southern Oscillation (ENSO), the Subtropical Indian Ocean Dipole Mode (SIOD) and the Pacific Decadal Oscillation (PDO) between 1945 and 2006, respectively. The reproducibility of the Sr / Ca records is assessed as are the potential impacts of diagenesis and corallite orientation on Sr / Ca-SST reconstructions. We calibrate individual robust Sr / Ca records with in situ SST and various gridded SST products. The results show that the SST record from Cabri provides the first Indian Ocean coral proxy time series that records the SST signature of the PDO in the south-central Indian Ocean since 1945. We suggest that additional records from Rodrigues Island can provide excellent records of SST variations in the southern Indian Ocean trade wind belt to unravel teleconnections with the SIOD/ENSO/PDO on longer timescales.

  7. Coral reefs of the Mascarenes, Western Indian Ocean.

    PubMed

    Turner, John; Klaus, Rebecca

    2005-01-15

    The reefs of the Mascarenes differ in structure and stage of development. Mauritius is the oldest island, bound by a discontinuous fringing reef and small barrier reef, with large lagoon patch reefs. Rodrigues has nearly continuous fringing reefs bounding an extensive lagoon with deep channels and few patch reefs. Reunion, the youngest island, has short stretches of narrow fringing reefs along southwestern coasts. The islets of St Brandon are bound to the east by an extensive arc of fringing reef. Reef mapping of the Mascarenes using satellite imagery provides an estimate of 705 km2 of shallow reef habitats. These areas have been modified over geological time by changes in sea level, ocean-atmosphere disturbances and biological and chemical forcing. Further modification has resulted from historical changes in land-use patterns. Recent economic development has placed many of these reefs at risk from anthropogenic impact. The reefs of the Mascarenes have escaped mass mortality from bleaching to date, which increases their conservation significance within the wider Indian Ocean. The reefs are poorly protected. A case study shows how a geographic information system incorporating reef-habitat maps can help formulate and demonstrate Marine Protected Area boundaries.

  8. North Equatorial Indian Ocean Convection and Indian Summer Monsoon June Progression: a Case Study of 2013 and 2014

    NASA Astrophysics Data System (ADS)

    Yadav, Ramesh Kumar; Singh, Bhupendra Bahadur

    2017-02-01

    The consecutive summer monsoons of 2013 and 2014 over the Indian subcontinent saw very contrasting onsets and progressions during the initial month. While the 2013 monsoon saw the timely onset and one of the fastest progressions during the recent decades, 2014 had a delayed onset and a slower progression phase. The monthly rainfall of June 2013 was +34 %, whereas in 2014 it was -43 % of its long-period average. The progress/onset of monsoon in June is influenced by large-scale circulation and local feedback processes. But, in 2013 (2014), one of the main reasons for the timely onset and fastest progression (delayed onset and slower progression) was the persistent strong (weak) convection over the north equatorial Indian Ocean during May. This resulted in a strong (weak) Hadley circulation with strong (weak) ascent and descent over the north equatorial Indian Ocean and the South Indian Ocean, respectively. The strong (weak) descent over the south Indian Ocean intensified (weakened) the Mascarene High, which in turn strengthened (weakened) the cross-equatorial flow and hence the monsoonal circulation.

  9. Molecular phylogeny of the Robust clade (Faviidae, Mussidae, Merulinidae, and Pectiniidae): an Indian Ocean perspective.

    PubMed

    Arrigoni, Roberto; Stefani, Fabrizio; Pichon, Michel; Galli, Paolo; Benzoni, Francesca

    2012-10-01

    Recent phylogenetic analyses have demonstrated the limits of traditional coral taxonomy based solely on skeletal morphology. In this phylogenetic context, Faviidae and Mussidae are ecologically dominant families comprising one third of scleractinian reef coral genera, but their phylogenies remain partially unresolved. Many of their taxa are scattered throughout most of the clades of the Robust group, and major systematic incongruences exist. Numerous genera and species remain unstudied, and the entire biogeographic area of the Indian Ocean remains largely unsampled. In this study, we analyzed a portion of the mitochondrial cytochrome c oxidase subunit 1 gene and a portion of ribosomal DNA for 14 genera and 27 species of the Faviidae and Mussidae collected from the Indian Ocean and New Caledonia and this is the first analysis of five of these species. For some taxa, newly discovered evolutionary relationships were detected, such as the evolutionary distinctiveness of Acanthastrea maxima, the genetic overlap of Parasimplastrea omanensis and Blastomussa merleti, and the peculiar position of Favites peresi in clade XVII together with Echinopora and Montastraea salebrosa. Moreover, numerous cases of intraspecific divergences between Indian Ocean and Pacific Ocean populations were detected. The most striking cases involve the genera Favites and Favia, and in particular Favites complanata, F. halicora, Favia favus, F. pallida, F. matthaii, and F. rotumana, but divergence also is evident in Blastomussa merleti, Cyphastrea serailia, and Echinopora gemmacea. High morphological variability characterizes most of these taxa, thus traditional skeletal characteristics, such as corallite arrangement, seem to be evolutionary misleading and are plagued by convergence. Our results indicate that the systematics of the Faviidae and the Mussidae is far from being resolved and that the inclusion of conspecific populations of different geographical origin represents an unavoidable step

  10. Relocation of earthquakes at southwestern Indian Ocean Ridge and its tectonic significance

    NASA Astrophysics Data System (ADS)

    Luo, W.; Zhao, M.; Haridhi, H.; Lee, C. S.; Qiu, X.; Zhang, J.

    2015-12-01

    The southwest Indian Ridge (SWIR) is a typical ultra-slow spreading ridge (Dick et al., 2003) and further plate boundary where the earthquakes often occurred. Due to the lack of the seismic stations in SWIR, positioning of earthquakes and micro-earthquakes is not accurate. The Ocean Bottom Seismometers (OBS) seismic experiment was carried out for the first time in the SWIR 49 ° 39 'E from Jan. to March, 2010 (Zhao et al., 2013). These deployed OBS also recorded the earthquakes' waveforms during the experiment. Two earthquakes occurred respectively in Feb. 7 and Feb. 9, 2010 with the same magnitude of 4.4 mb. These two earthquakes were relocated using the software HYPOSAT based on the spectrum analysis and band-pass (3-5 Hz) filtering and picking up the travel-times of Pn and Sn. Results of hypocentral determinations show that there location error is decreased significantly by joined OBS's recording data. This study do not only provide the experiences for the next step deploying long-term wide-band OBSs, but also deepen understanding of the structure of SWIR and clarify the nature of plate tectonic motivation. This research was granted by the Natural Science Foundation of China (41176053, 91028002, 91428204). Keywords: southwest Indian Ridge (SWIR), relocation of earthquakes, Ocean Bottom Seismometers (OBS), HYPOSAT References:[1] Dick, H. J. B., Lin J., Schouten H. 2003. An ultraslow-spreading class of ocean ridge. Nature, 426(6965): 405-412. [2] Zhao M. H., et al. 2013. Three-dimensional seismic structure of the Dragon Flag oceanic core complex at the ultraslow spreading Southwest Indian Ridge (49°39' E). Geochemistry Geophysics Geosystems, 14(10): 4544-4563.

  11. Importance of the Indian Ocean for simulating rainfall anomalies over eastern and southern Africa

    NASA Astrophysics Data System (ADS)

    Goddard, Lisa; Graham, Nicholas E.

    1999-08-01

    The relative contributions of the Indian Ocean and Pacific Ocean sea surface temperatures (SSTs) to the rainfall variability over eastern central, and southern Africa during the austral spring-summer are examined. The variability of African rainfall is statistically related to both oceans, but the variability in the two oceans is also related. To separate the effects of the Indian and Pacific Oceans, a suite of numerical model simulations is presented: GOGA, the atmosphere is forced by observed SSTs globally; IOGA, the atmosphere is forced by observed SSTs only in the Indian Ocean basin; and POGA, the atmosphere is forced by observed SSTs only in the tropical Pacific basin. While the SST variability of the tropical Pacific exerts some influence over the African region, it is the atmospheric response to the Indian Ocean variability that is essential for simulating the correct rainfall response over eastern, central, and southern Africa. Analyses of the dynamical response(s) seen in the numerical experiments and in the observations indicate that the Pacific and Indian Oceans have a competing influence over the Indian Ocean/African region. This competition is related to the influence of the two oceans on the Walker circulation and the consequences of that variability on low-level fluxes of moisture over central and southern Africa. Finally, given the high correlation found between SST variability in the Indian and Pacific Oceans with the Pacific leading by ˜3 months, we speculate on an approach to long-lead dynamical climate prediction over central-east and southern Africa.

  12. Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming.

    PubMed

    Cai, Wenju; Santoso, Agus; Wang, Guojian; Weller, Evan; Wu, Lixin; Ashok, Karumuri; Masumoto, Yukio; Yamagata, Toshio

    2014-06-12

    The Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra-Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change--with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean--facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD.

  13. Oceanic crust formation in the Egeria Fracture Zone Complex (Central Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Le Minor, Marine; Gaina, Carmen; Sigloch, Karin; Minakov, Alexander

    2016-04-01

    This study aims to analyse in detail the oceanic crust fabric and volcanic features (seamounts) formed for the last 10 million years at the Central Indian Ridge between 19 and 21 latitude south. Multibeam bathymetry and magnetic data has been collected in 2013 as part of the French-German expedition RHUM-RUM (Reunion hotspot and upper mantle - Reunion's unterer mantel). Three long profiles perpendicular on the Central Indian Ridge (CIR), south of the Egeria fracture zone, document the formation of oceanic crust since 10 million years, along with changes in plate kinematics and variations in the magmatic input. We have inspected the abyssal hill geometry and orientation along conjugate oceanic flanks and within one fracture zone segment where we could identify J-shaped features that are indicators of changes in plate kinematics. The magnetic anomaly data shows a slight asymmetry in seafloor spreading rates on conjugate flanks: while a steady increase in spreading rate from 10 Ma to the present is shown by the western flank, the eastern part displays a slowing down from 5 Ma onwards. The deflection of the anti J-shaped abyssal hill lineations suggest that the left-stepping Egeria fracture zone complex (including the Egeria, Flinders and an un-named fracture zone to the southeast) was under transpression from 9 to 6 Ma and under transtension since 3 Ma. The transpressional event was triggered by a clockwise mid-ocean ridge reorientation and a decrease of its offset, whereas the transtensional regime was probably due to a counter-clockwise change in the spreading direction and an increase of the ridge offset. The new multibeam data along the three profiles reveal that crust on the eastern side is smoother (as shown by the abyssal hill number and structure) and hosts several seamounts (with age estimations of 7.67, 6.10 and 0.79 Ma), in contrast to the rougher conjugate western flank. Considering that the western flank was closer to the Reunion plume, and therefore

  14. Molecular phylogeography reveals island colonization history and diversification of western Indian Ocean sunbirds (Nectarinia: Nectariniidae).

    PubMed

    Warren, Ben H; Bermingham, Eldredge; Bowie, Rauri C K; Prys-Jones, Robert P; Thébaud, Christophe

    2003-10-01

    We constructed a phylogenetic hypothesis for western Indian Ocean sunbirds (Nectarinia) and used this to investigate the geographic pattern of their diversification among the islands of the Indian Ocean. A total of 1309 bp of mitochondrial sequence data was collected from the island sunbird taxa of the western Indian Ocean region, combined with sequence data from a selection of continental (African and Asian) sunbirds. Topological and branch length information combined with estimated divergence times are used to present hypotheses for the direction and sequence of colonization events in relation to the geological history of the Indian Ocean region. Indian Ocean sunbirds fall into two well-supported clades, consistent with two independent colonizations from Africa within the last 3.9 million years. The first clade contains island populations representing the species Nectarinia notata, while the second includes Nectarinia souimanga, Nectarinia humbloti, Nectarinia dussumieri, and Nectarinia coquereli. With respect to the latter clade, application of Bremer's [Syst. Biol. 41 (1992) 436] ancestral areas method permits us to posit the Comoros archipelago as the point of initial colonization in the Indian Ocean. The subsequent expansion of the souimanga clade across its Indian Ocean range occurred rapidly, with descendants of this early expansion remaining on the Comoros and granitic Seychelles. The data suggest that a more recent expansion from Anjouan in the Comoros group led to the colonization of Madagascar by sunbirds representing the souimanga clade. In concordance with the very young geological age of the Aldabra group, the sunbirds of this archipelago have diverged little from the Madagascar population; this is attributed to colonization of the Aldabra archipelago in recent times, in one or possibly two or more waves originating from Madagascar. The overall pattern of sunbird radiation across Indian Ocean islands indicates that these birds disperse across ocean

  15. Does the Maritime Continent region affect sea level change of the eastern Indian Ocean?

    NASA Astrophysics Data System (ADS)

    Llovel, W.; Lee, T.

    2014-12-01

    The Maritime Continent region, in particular, the Indonesian Sea, regulates the oceanic communication between the Pacific and Indian Oceans. Previous studies suggest that the freshwater transported from the South China Sea to the Indonesian Sea affects the magnitude and structure of the Indonesian throughflow, and the strong tidal mixing in the Indonesian Sea alters the time mean vertical structure of the water mass carried from the Pacific to the Indian Oceans. Sea level changes in the eastern Indian Ocean is known to be affected by those in the northwestern Pacific via coastal Kelvin wave propagation through the Indonesian Sea. However, whether the Maritime Continent region influences sea level changes in the eastern Indian Ocean has not been investigated. In this study, we used Argo floats and satellite altimeter data to study the near decadal change of sea level during the 2005-2013 period. We found that the steric sea level change in eastern Indian Ocean cannot be fully explained by either local forcing or the transmission of steric signal from the western Pacific. This implicates the potential role of the Maritime Continent region in regulating sea level changes in the eastern Indian Ocean.

  16. Population Structure of Humpback Whales from Their Breeding Grounds in the South Atlantic and Indian Oceans

    PubMed Central

    Rosenbaum, Howard C.; Pomilla, Cristina; Mendez, Martin; Leslie, Matthew S.; Best, Peter B.; Findlay, Ken P.; Minton, Gianna; Ersts, Peter J.; Collins, Timothy; Engel, Marcia H.; Bonatto, Sandro L.; Kotze, Deon P. G. H.; Meÿer, Mike; Barendse, Jaco; Thornton, Meredith; Razafindrakoto, Yvette; Ngouessono, Solange; Vely, Michel; Kiszka, Jeremy

    2009-01-01

    Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region. PMID:19812698

  17. Genome Microevolution of Chikungunya Viruses Causing the Indian Ocean Outbreak

    PubMed Central

    Schuffenecker, Isabelle; Iteman, Isabelle; Michault, Alain; Murri, Séverine; Frangeul, Lionel; Vaney, Marie-Christine; Lavenir, Rachel; Pardigon, Nathalie; Reynes, Jean-Marc; Pettinelli, François; Biscornet, Leon; Diancourt, Laure; Michel, Stéphanie; Duquerroy, Stéphane; Guigon, Ghislaine; Frenkiel, Marie-Pascale; Bréhin, Anne-Claire; Cubito, Nadège; Desprès, Philippe; Kunst, Frank; Rey, Félix A; Zeller, Hervé; Brisse, Sylvain

    2006-01-01

    Background A chikungunya virus outbreak of unprecedented magnitude is currently ongoing in Indian Ocean territories. In Réunion Island, this alphavirus has already infected about one-third of the human population. The main clinical symptom of the disease is a painful and invalidating poly-arthralgia. Besides the arthralgic form, 123 patients with a confirmed chikungunya infection have developed severe clinical signs, i.e., neurological signs or fulminant hepatitis. Methods and Findings We report the nearly complete genome sequence of six selected viral isolates (isolated from five sera and one cerebrospinal fluid), along with partial sequences of glycoprotein E1 from a total of 127 patients from Réunion, Seychelles, Mauritius, Madagascar, and Mayotte islands. Our results indicate that the outbreak was initiated by a strain related to East-African isolates, from which viral variants have evolved following a traceable microevolution history. Unique molecular features of the outbreak isolates were identified. Notably, in the region coding for the non-structural proteins, ten amino acid changes were found, four of which were located in alphavirus-conserved positions of nsP2 (which contains helicase, protease, and RNA triphosphatase activities) and of the polymerase nsP4. The sole isolate obtained from the cerebrospinal fluid showed unique changes in nsP1 (T301I), nsP2 (Y642N), and nsP3 (E460 deletion), not obtained from isolates from sera. In the structural proteins region, two noteworthy changes (A226V and D284E) were observed in the membrane fusion glycoprotein E1. Homology 3D modelling allowed mapping of these two changes to regions that are important for membrane fusion and virion assembly. Change E1-A226V was absent in the initial strains but was observed in >90% of subsequent viral sequences from Réunion, denoting evolutionary success possibly due to adaptation to the mosquito vector. Conclusions The unique molecular features of the analyzed Indian Ocean

  18. [Chikungunya virus infection in the Indian Ocean: lessons learned and perspectives].

    PubMed

    Gaüzère, B A; Gérardin, P; Vandroux, D; Aubry, P

    2012-03-01

    After a brief overview of the history of arbovirus epidemics in the Indian Ocean in XIXth and XXth centuries, a full evaluation of the chikungunya epidemic that occurred in 2005-2006 is provided including both lessons learned and future perspectives. On the positive side, the epidemic has allowed improvement of clinical and pathophysiological knowledge, epidemiological surveillance, vector control, awareness of entomology, avenues for research, and understanding of economic and societal repercussions. On the negative side, the epidemic revealed the limitations of a health care system in an island setting, need for an effective sanitary policy, low public-spiritedness, poor diffusion and understanding of public health announcements, endemization of chikungunya virus in the Indian Ocean, absence of vaccine, and global spread of tropical disease. Discussion of perspectives for future arbovirus disease outbreaks in the Indian Ocean is set against the background of climatic change, unequal socioeconomic progress, and high population growth in the Indian Ocean region.

  19. On the coherent components of low-frequency ambient noise in the Indian Ocean.

    PubMed

    Sabra, Karim G; Fried, Stephanie; Kuperman, W A; Prior, Mark

    2013-01-01

    This letter demonstrates that the dominant coherent component of low-frequency (1 Hz < f < 20 Hz) ambient noise propagating between hydrophone pairs of the same hydroacoustic station, deployed in the deep sound channel of the Indian Ocean, is directional and mainly originates from Antarctica. However, the amplitude of the peak coherent noise arrivals, obtained using a 4-month-long averaging interval, was relatively low given the small hydrophones spacing hydrophones (<2 km). Hence, extracting similar coherent arrivals between two distinct hydroacoustic stations separated instead by thousands of kilometers for noise-based acoustic thermometry purposes seems unlikely, even using a year-long averaging.

  20. Osmium isotopic evidence for ancient subcontinental lithospheric mantle beneath the kerguelen islands, southern indian ocean

    PubMed

    Hassler; Shimizu

    1998-04-17

    Upper mantle xenoliths found in ocean island basalts are an important window through which the oceanic mantle lithosphere may be viewed directly. Osmium isotopic data on peridotite xenoliths from the Kerguelen Islands, an archipelago that is located on the northern Kerguelen Plateau in the southern Indian Ocean, demonstrate that pieces of mantle of diverse provenance are present beneath the Islands. In particular, peridotites with unradiogenic osmium and ancient rhenium-depletion ages (to 1.36 x 10(9) years old) may be pieces of the Gondwanaland subcontinental lithosphere that were incorporated into the Indian Ocean lithosphere as a result of the rifting process.

  1. Tropical climate variability: interactions across the Pacific, Indian, and Atlantic Oceans

    NASA Astrophysics Data System (ADS)

    Kajtar, Jules B.; Santoso, Agus; England, Matthew H.; Cai, Wenju

    2016-06-01

    Complex interactions manifest between modes of tropical climate variability across the Pacific, Indian, and Atlantic Oceans. For example, the El Niño-Southern Oscillation (ENSO) extends its influence on modes of variability in the tropical Indian and Atlantic Oceans, which in turn feed back onto ENSO. Interactions between pairs of modes can alter their strength, periodicity, seasonality, and ultimately their predictability, yet little is known about the role that a third mode plays. Here we examine the interactions and relative influences between pairs of climate modes using ensembles of 100-year partially coupled experiments in an otherwise fully coupled general circulation model. In these experiments, the air-sea interaction over each tropical ocean basin, as well as pairs of ocean basins, is suppressed in turn. We find that Indian Ocean variability has a net damping effect on ENSO and Atlantic Ocean variability, and conversely they each promote Indian Ocean variability. The connection between the Pacific and the Atlantic is most clearly revealed in the absence of Indian Ocean variability. Our model runs suggest a weak damping influence by Atlantic variability on ENSO, and an enhancing influence by ENSO on Atlantic variability.

  2. Weakening of Spring Wyrtki Jets in the Indian Ocean during 2006-2011

    DTIC Science & Technology

    2012-04-05

    Wyrtki jets in the equatorial circulation of the Indian Ocean, it is important to monitor their variability on different timescales, which will help in...waveguide play an important role in generating eastward propagating Kelvin waves during the month of May in the equatorial Indian Ocean [Rao et al., 2010...wind forcing is the cause of the weak WJs found in our analysis of OSCAR and HYCOM results. In order to assess the importance of winds on WJs we have

  3. SST Control by Subsurface Mixing during Indian Ocean Monsoons: 1-yr Pilot Project

    DTIC Science & Technology

    2013-09-30

    public release; distribution is unlimited. SST Control by Subsurface Mixing during Indian Ocean Monsoons : 1-yr Pilot Project Emily Shroyer and James...observational basis and physical interpretation for new mixing parameterizations that will contribute to improved monsoon predictions in this sensitive...4. TITLE AND SUBTITLE SST Control by Subsurface Mixing during Indian Ocean Monsoons : 1-yr Pilot Project 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c

  4. Recent distribution of lead in the Indian Ocean reflects the impact of regional emissions.

    PubMed

    Echegoyen, Yolanda; Boyle, Edward A; Lee, Jong-Mi; Gamo, Toshitaka; Obata, Hajime; Norisuye, Kazuhiro

    2014-10-28

    Humans have injected lead (Pb) massively into the earth surface environment in a temporally and spatially evolving pattern. A significant fraction is transported by the atmosphere into the surface ocean where we can observe its transport by ocean currents and sinking particles. This study of the Indian Ocean documents high Pb concentrations in the northern and tropical surface waters and extremely low Pb levels in the deep water. North of 20°S, dissolved Pb concentrations decrease from 42 to 82 pmol/kg in surface waters to 1.5-3.3 pmol/kg in deep waters. South of 20°S, surface water Pb concentrations decrease from 21 pmol/kg at 31°S to 7 pmol/kg at 62°S. This surface Pb concentration gradient reflects a southward decrease in anthropogenic Pb emissions. The upper waters of the north and central Indian Ocean have high Pb concentrations resulting from recent regional rapid industrialization and a late phase-out of leaded gasoline, and these concentrations are now higher than currently seen in the central North Pacific and North Atlantic oceans. The Antarctic sector of the Indian Ocean shows very low concentrations due to limited regional anthropogenic Pb emissions, high scavenging rates, and rapid vertical mixing, but Pb still occurs at higher levels than would have existed centuries ago. Penetration of Pb into the northern and central Indian Ocean thermocline waters is minimized by limited ventilation. Pb concentrations in the deep Indian Ocean are comparable to the other oceans at the same latitude, and deep waters of the central Indian Ocean match the lowest observed oceanic Pb concentrations.

  5. Medieval forewarning of the 2004 Indian Ocean tsunami in Thailand

    USGS Publications Warehouse

    Jankaew, K.; Atwater, B.F.; Sawai, Y.; Choowong, M.; Charoentitirat, T.; Martin, M.E.; Prendergast, A.

    2008-01-01

    Recent centuries provide no precedent for the 2004 Indian Ocean tsunami, either on the coasts it devastated or within its source area. The tsunami claimed nearly all of its victims on shores that had gone 200 years or more without a tsunami disaster. The associated earthquake of magnitude 9.2 defied a Sumatra-Andaman catalogue that contains no nineteenth-century or twentieth-century earthquake larger than magnitude 7.9 (ref. 2). The tsunami and the earthquake together resulted from a fault rupture 1,500 km long that expended centuries' worth of plate convergence. Here, using sedimentary evidence for tsunamis, we identify probable precedents for the 2004 tsunami at a grassy beach-ridge plain 125 km north of Phuket. The 2004 tsunami, running 2 km across this plain, coated the ridges and intervening swales with a sheet of sand commonly 5-20 cm thick. The peaty soils of two marshy swales preserve the remains of several earlier sand sheets less than 2,800 years old. If responsible for the youngest of these pre-2004 sand sheets, the most recent full-size predecessor to the 2004 tsunami occurred about 550-700 years ago. ??2008 Macmillan Publishers Limited. All rights reserved.

  6. Positive Indian Ocean Dipole events precondition southeast Australia bushfires

    NASA Astrophysics Data System (ADS)

    Cai, W.; Cowan, T.; Raupach, M.

    2009-10-01

    The devastating “Black Saturday” bushfire inferno in the southeast Australian state of Victoria in early February 2009 and the “Ash Wednesday” bushfires in February 1983 were both preceded by a positive Indian Ocean Dipole (pIOD) event. Is there a systematic pIOD linkage beyond these two natural disasters? We show that out of 21 significant bushfires seasons since 1950, 11 were preceded by a pIOD. During Victoria's wet season, particularly spring, a pIOD contributes to lower rainfall and higher temperatures exacerbating the dry conditions and increasing the fuel load leading into summer. Consequently, pIODs are effective in preconditioning Victoria for bushfires, more so than El Niño events, as seen in the impact on soil moisture on interannual time scales and in multi-decadal changes since the 1950s. Given that the recent increase in pIOD occurrences is consistent with what is expected from global warming, an increased bushfire risk in the future is likely across southeast Australia.

  7. Drift pumice in the Central Indian Ocean Basin: Geochemical evidence

    NASA Astrophysics Data System (ADS)

    Pattan, J. N.; Mudholkar, A. V.; Jai Sankar, S.; Ilangovan, D.

    2008-03-01

    Abundant white to light grey-coloured pumice without ferromanganese oxide coating occurs within the Quaternary sediments of the Central Indian Ocean Basin (CIOB). Two distinct groups of pumice are identified from their geochemical composition, which allow one to define two different origins linked to two separate eruptions. One group of pumice is a dacitic type characterized by high Fe, Ti, Mg, Al and Ca with comparatively low contents of Si, rare-earth elements (∑REE, 69 ppm), Rb, Sr, U, Th, Ba, V, Nb, Sc, Mo and Co, which strongly suggest an origin from the 1883 Krakatau eruption. The other group is rhyolitic and is characterized by low contents of Fe, Ti, Mg and Ca and high Si, ∑REE content (121 ppm), Rb, Sr, U, Th, Ba, V, Nb, Mo, Co, and Sc and correlates well with the composition of the Youngest Toba Tuff (YTT) eruption of ˜74 ka from Northern Sumatra and is being reported for the first time. Therefore, correlation of the pumice to the 1883 Krakatau and YTT eruptions indicates that the pumice drifted to the CIOB and eventually sank when it became waterlogged. However, physical properties such as density, specific gravity, porosity and degree of saturation required for sinking of pumice for both 1883 Krakatau and YTT are almost similar.

  8. "Measuring by the bushel": reweighing the Indian Ocean pepper trade.

    PubMed

    Prange, Sebastian R

    2011-01-01

    Of all the oriental spices, black pepper was the most important until the eighteenth century. The historiography of the pepper trade is characterized by a strong focus on Europe in terms of both its economic significance in the ancient and medieval periods and the struggle for its control in the early modern period. This article, by contrast, seeks to situate the pepper trade firmly in its Asian contexts. It examines the Indian Ocean pepper trade from three perspectives. First, it places the trade in its supply-side context by focusing on the Malabar coast as the primary source of pepper. Second, it examines the relative importance of the different branches of Malabar's pepper trade and highlights the central role played by Muslim mercantile networks. Third, it considers the reconfiguration of these pepper networks in the sixteenth century in the face of aggressive competition from the Portuguese. In their sum, these arguments advocate the need for rethought balances of trade and a reweighted scholarly focus on the pepper trade in its global dimensions.

  9. Introduction to "Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami. Volume II."

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander B.; Geist, Eric L.; Fritz, Hermann M.; Borrero, Jose C.

    2015-12-01

    Twenty papers on the study of tsunamis and respective tsunamigenic earthquakes are included in Volume II of the PAGEOPH topical issue "Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami". The papers presented in this second of two special volumes of Pure and Applied Geophysics reflect the state of tsunami science during this time, including five papers devoted to new findings specifically in the Indian Ocean. Two papers compile results from global observations and eight papers cover Pacific Ocean studies, focusing mainly on the 2011 Tohoku earthquake and tsunami. Remaining papers in this volume describe studies in the Atlantic Ocean and Mediterranean Sea and tsunami source studies. Overall, the volume not only addresses the pivotal 2004 Indian Ocean and 2011 Tohoku tsunamis, but also examines the tsunami hazard posed to other critical coasts in the world.

  10. Ocean control of the breeding regime of the sooty tern in the southwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Jaquemet, S.; Le Corre, M.; Quartly, G. D.

    2007-01-01

    Food availability, which is often seasonal, is regarded as a key factor in the breeding success of seabirds. In oceanic tropical areas, the resources are mostly patchy and ephemeral at the surface, and the seasonality is less marked than at higher latitudes. Such a situation influences greatly the breeding strategies of the oceanic seabird species. We conducted a comparative study of the breeding phenology of the sooty tern ( Sterna fuscata) in relation to the local and regional oceanographic conditions around the four major colonies (Europa, Juan de Nova, Lys and Bird Islands) of the southwest Indian Ocean. Over the 1997-2003 period, around all the studied locations, the sea-surface temperature (SST) and the chlorophyll concentration in the Mozambique Channel and the Seychelles area showed clear seasonal differences related to the southern climate and the monsoon phenomena. The breeding activity is synchronized at each studied colony, but the timings are very different. Seasonal reproduction occurs in austral winter at Europa and Bird Island and in austral summer at Juan de Nova; at Lys Island the reproduction is non-seasonal. For the seasonal colonies, there is a large monthly change in SST just before the beginning of reproduction, which is a proxy indicating the annual phytoplankton bloom. This variation is accompanied by the development of oceanic features such as fronts that favour aggregation of prey, and may also play an important role in the presence of schools of surface tuna, which are very important for the foraging success of sooty terns. Conversely, around Lys Island the seasonal variations of the marine environment do not lead to pronounced development of oceanic structures, and consequently, the longer-lasting phytoplankton bloom could explain the non-seasonal breeding regime there. Further studies will help discern the advantages and disadvantages of seasonal and non-seasonal reproduction regime in response to unpredictable fluctuations of the

  11. Surface Deformation Caused By The 2004 Indian Ocean Tsunami Observed At Diego Garcia

    NASA Astrophysics Data System (ADS)

    Takatsuka, K.; Ohta, Y.; Miura, S.; Sato, T.; Fujii, Y.

    2008-12-01

    The large mass of water move with tsunami, and its loading causes surface deformation. Several previous researches reports about this. Nawa et al. (2007) demonstrated loading effects of the 2004 Indian Ocean tsunami observed by broadband seismometers at Syowa station, Antarctica. Yuan et al. (2005) also showed loading effects of the tsunami by broadband seismometers installed along the coastal area around the Indian Ocean. Because detections of such surface deformation give data independent of tide gauge data, the detections are important for study on tsunami source mechanisms. We report the tsunami loading effect observed by broadband seismometer at Diego Garcia, British Indian Ocean Territory and compare with synthesis calculated from the model. In this study, we analyzed seismic records at the Diego Garcia (DGAR) seismic station operated by IRIS (Incorporated Research Institutions for Seismology). The velocity records were detrended and deconvolved with the instrumental response. After the deconvolution, we applied low-pass filtering with a cut-off frequency of 10-360secnd to remove short- and long-period noises. Focusing on STS-1 record around tsunami arrival time at DGAR, significant variation shoeing longer period than expected seismic wave is prominent. For confirmation of the detection of tsunami loading effect by the broadband seismometer records, we calculated tilt change expected from tsunami source proposed by Fujii and Satake (2007). The calculation is performed by taking a convolution of the Green"fs function and the sea level variation based on the tsunami propagation. Green"fs function for surface deformation caused by loading is given by Farrell (1972). When temporal-spatial resolution of sealevel data is 5min and 18.5km, the calculation and observation show good agreement. Using higher resolution data (1min, 0.74km), amplitude of calculation is closer to observation. But agreement of phase is get worse. As future works, we plan to evaluate

  12. Mercury content in commercial pelagic fish and its risk assessment in the Western Indian Ocean.

    PubMed

    Kojadinovic, Jessica; Potier, Michel; Le Corre, Matthieu; Cosson, Richard P; Bustamante, Paco

    2006-08-01

    As top predators of pelagic food webs, large fish naturally bioaccumulate mercury (Hg). Determining Hg burdens in commercialized fish is essential considering the concern about effects of contaminants on human health and the legal thresholds that are therefore set for local consumption and/or exportation. Total Hg levels were measured in the muscular tissue of 183 fish of five commercially important species from the tropical zone of the Western Indian Ocean. All individuals were measured and sexed in order to study the impregnation of Hg with size and sex within each species. Values of Hg found in this part of the Indian Ocean were comparable to Hg in muscular tissue of the same species studied in other areas. The highest Hg levels were noted in Swordfish (Xiphias gladius) caught in waters surrounding Reunion Island (3.97+/-2.67 microg g(-1) dry weight). Following the Swordfish, in decreasing order of Hg content, were the Yellowfin Tuna (Thunnus albacares) and the Skipjack (Katsuwonus pelamis), then the Common Dolphinfish (Coryphaena hippurus) and the Wahoo (Acanthocybium solandri). In the North of the Mozambique Channel, Swordfish had higher Hg levels than Yellowfin Tunas, and Dolphinfish exhibited intermediate Hg levels. The size of a fish was a determining factor of its Hg burden, as was the species. Differences in size-normalized Hg levels were observed between the two study zones for Swordfish and Common Dolphinfish. Sex, in contrast, did not influence Hg levels suggesting that females and males have similar feeding habits. The muscular Hg levels presented here suggest that consumers of fish originating from the Western Indian Ocean should limit themselves to one Swordfish based meal per week, or one fish meal a day if they choose to eat tuna or Common Dolphinfish.

  13. Impact of eddies on surface chlorophyll in the South Indian Ocean

    NASA Astrophysics Data System (ADS)

    Dufois, François; Hardman-Mountford, Nick J.; Greenwood, Jim; Richardson, Anthony J.; Feng, Ming; Herbette, Steven; Matear, Richard

    2014-11-01

    A unique feature of the subtropical South Indian Ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies. Off Western Australia, this anomalous behavior is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients. Further off-shore, two mechanisms have been suggested to explain the eddy/chlorophyll relationship: (i) eddies originating from the Australian coast maintain their chlorophyll anomaly while propagating westward; and (ii) eddy-induced Ekman upwelling (downwelling) enhances (dampens) nutrient supply in anticyclonic (cyclonic) eddies. Here we describe the relationship between eddies and surface chlorophyll within the South Indian Ocean, and discuss possible mechanisms to explain the anomalous behavior in light of new analyses performed using satellite chlorophyll data. We show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire South Indian Ocean basin (from 20 to 28°S), particularly in winter. Using Self Organizing Maps we analyze the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity. Our analysis suggests that multiple mechanisms may underlie the observed eddy/chlorophyll relationship. Based on Argo float data, we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies. Deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer, while shallower mixing in cyclonic eddies is expected to reduce it. This could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies.

  14. Culture Based Curriculum for Young Indian Children.

    ERIC Educational Resources Information Center

    Thomas, Sharon N., Comp.

    Designed as a resource and curriculum guide for early childhood educators, this publication encompasses both American Indian sociocultural background and culture based lesson plans and activities. Indicative of its organization and scope are the comprehensive chapters devoted to discussions of: (1) the historical failure of Indian education; (2)…

  15. Fluxes of dissolved organic carbon and nitrogen to the northern Indian Ocean from the Indian monsoonal rivers

    NASA Astrophysics Data System (ADS)

    Krishna, M. S.; Prasad, V. R.; Sarma, V. V. S. S.; Reddy, N. P. C.; Hemalatha, K. P. J.; Rao, Y. V.

    2015-10-01

    Dissolved organic carbon (DOC) and nitrogen (DON) were measured in 27 major and medium monsoonal estuaries along the Indian coast during southwest monsoon in order to understand the spatial variability in their concentrations and fluxes to the northern Indian Ocean. A strong spatial variability (~20-fold) in DOC and DON was observed in the Indian monsoonal estuaries due to variable characteristics of the catchment area and volume of discharge. It is estimated that the Indian monsoonal estuaries transport ~2.37 ± 0.47 Tg (1 Tg = 1012 g) of DOC and ~0.41 ± 0.08 Tg of DON during wet period to the northern Indian Ocean. The Bay of Bengal receives 3 times higher DOC and DON (1.82 and 0.30 Tg, respectively) than the Arabian Sea (0.55 and 0.11 Tg). Catchment area normalized fluxes of DOC and DON were found to be higher in the estuaries located in the southwestern than the estuaries from other regions of India. It was attributed to relatively higher soil organic carbon, biomass carbon, and heavy rainfall in catchment areas of the rivers from the former region. It has been noticed that neither catchment area nor discharge volume of the river controls the fluxes of DOC and DON to the northern Indian Ocean. Since the total load of DOC and DON is strongly linked to the volume of discharge, alterations in the freshwater discharge due to natural or anthropogenic activities may have significant influence on organic matter fluxes to the Indian coastal waters and its impact on microbial food web dynamics needs further evaluation.

  16. Sea-air CO2 fluxes in the Indian Ocean between 1990 and 2009

    NASA Astrophysics Data System (ADS)

    Sarma, V. V. S. S.; Lenton, A.; Law, R.; Metzl, N.; Patra, P. K.; Doney, S.; Lima, I. D.; Dlugokencky, E.; Ramonet, M.; Valsala, V.

    2013-07-01

    The Indian Ocean (44° S-30° N) plays an important role in the global carbon cycle, yet remains one of the most poorly sampled ocean regions. Several approaches have been used to estimate net sea-air CO2 fluxes in this region: interpolated observations, ocean biogeochemical models, atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Indian Ocean sea-air CO2 fluxes between 1990 and 2009. Using all of the models and inversions, the median annual mean sea-air CO2 uptake of -0.37 ± 0.06 Pg C yr-1, is consistent with the -0.24 ± 0.12 Pg C yr-1 calculated from observations. The fluxes from the Southern Indian Ocean (18° S-44° S; -0.43 ± 0.07 Pg C yr-1) are similar in magnitude to the annual uptake for the entire Indian Ocean. All models capture the observed pattern of fluxes in the Indian Ocean with the following exceptions: underestimation of upwelling fluxes in the northwestern region (off Oman and Somalia), over estimation in the northeastern region (Bay of Bengal) and underestimation of the CO2 sink in the subtropical convergence zone. These differences were mainly driven by a lack of atmospheric CO2 data in atmospheric inversions, and poor simulation of monsoonal currents and freshwater discharge in ocean biogeochemical models. Overall, the models and inversions do capture the phase of the observed seasonality for the entire Indian Ocean but over estimate the magnitude. The predicted sea-air CO2 fluxes by Ocean BioGeochemical Models (OBGM) respond to seasonal variability with strong phase lags with reference to climatological CO2 flux, whereas the atmospheric inversions predict an order of magnitude higher seasonal flux than OBGMs. The simulated interannual variability by the OBGMs is weaker than atmospheric inversions. Prediction of such weak interannual variability in CO2 fluxes by atmospheric inversions

  17. Sea-air CO2 fluxes in the Indian Ocean between 1990 and 2009

    NASA Astrophysics Data System (ADS)

    Sarma, V. V. S. S.; Lenton, A.; Law, R. M.; Metzl, N.; Patra, P. K.; Doney, S.; Lima, I. D.; Dlugokencky, E.; Ramonet, M.; Valsala, V.

    2013-11-01

    The Indian Ocean (44° S-30° N) plays an important role in the global carbon cycle, yet it remains one of the most poorly sampled ocean regions. Several approaches have been used to estimate net sea-air CO2 fluxes in this region: interpolated observations, ocean biogeochemical models, atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Indian Ocean sea-air CO2 fluxes between 1990 and 2009. Using all of the models and inversions, the median annual mean sea-air CO2 uptake of -0.37 ± 0.06 PgC yr-1 is consistent with the -0.24 ± 0.12 PgC yr-1 calculated from observations. The fluxes from the southern Indian Ocean (18-44° S; -0.43 ± 0.07 PgC yr-1 are similar in magnitude to the annual uptake for the entire Indian Ocean. All models capture the observed pattern of fluxes in the Indian Ocean with the following exceptions: underestimation of upwelling fluxes in the northwestern region (off Oman and Somalia), overestimation in the northeastern region (Bay of Bengal) and underestimation of the CO2 sink in the subtropical convergence zone. These differences were mainly driven by lack of atmospheric CO2 data in atmospheric inversions, and poor simulation of monsoonal currents and freshwater discharge in ocean biogeochemical models. Overall, the models and inversions do capture the phase of the observed seasonality for the entire Indian Ocean but overestimate the magnitude. The predicted sea-air CO2 fluxes by ocean biogeochemical models (OBGMs) respond to seasonal variability with strong phase lags with reference to climatological CO2 flux, whereas the atmospheric inversions predicted an order of magnitude higher seasonal flux than OBGMs. The simulated interannual variability by the OBGMs is weaker than that found by atmospheric inversions. Prediction of such weak interannual variability in CO2 fluxes by atmospheric

  18. Rare earth abundances and Rb-Sr systematics of basalts, gabbro, anorthosite and minor granitic rocks from the Indian Ocean Ridge System, Western Indian Ocean

    USGS Publications Warehouse

    Hedge, C.E.; Futa, K.; Engel, C.G.; Fisher, R.L.

    1979-01-01

    Basalts dredged from the Mid-Indian Ocean Ridge System have rare earth, Rb, and Sr concentrations like those from other mid-ocean ridges, but have slightly higher Sr87/Sr86 ratios. Underlying gabbroic complexes are similar to the basalts in Sr87/Sr86, but are poorer K, Rb, and in rare earths. The chemical and isotopic data, as well as the geologic relations suggest a cumulate origin for the bulk of the gabbroic complexes. ?? 1979 Springer-Verlag.

  19. Earthquake source mechanisms from body-waveform inversion and intraplate tectonics in the northern Indian Ocean

    NASA Technical Reports Server (NTRS)

    Bergman, E. A.; Solomon, S. C.

    1985-01-01

    Double-couple point-source parameters for 11 of the largest intraplate earthquakes in the northern Indian Ocean during the last 20 years were determined from a formal inversion of the long-period P and SH waveforms. Two major intraplate tectonic provinces are distinguished in the northern Indian Ocean. The plate-wide stress pattern found and the high level of intraplate seismicity are probably the results of substantial resistance, along the Himalayan continental collision zone, to the continued northward motion of the western portion of the Indian plate.

  20. Circulation, stratification and seamounts in the Southwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Pollard, Raymond; Read, Jane

    2017-02-01

    Circulation in the vicinity of six seamounts along the Southwest Indian Ridge was studied as part of a multidisciplinary survey in November 2009. Examination of altimetric data shows that several of the seamounts lie in the area of slow mean westward flow between the southern tip of Madagascar (25°S) and the Agulhas Return Current (ARC) flowing eastward between 37°S and 40°S. The mean westward drift of mesoscale features was 4.1±0.9 cm s-1. Integrated between Madagascar and 37°S, this westward drift can account for 50 Sv (1 Sv=106 m3 s-1), which, added to 25 Sv of southward flow past Madagascar, is sufficient to account for the total Agulhas Current transport of 70±21 Sv. The transport of the ARC was also measured, at two longitudes, down to 2000 m. Combined with earlier crossings of the ARC in 1986 and 1995, the full depth transport of the ARC is estimated at 71-85 Sv at longitudes 40-50°E, indicating that the Agulhas Current then ARC transport continues unreduced as far as 50°E before beginning to recirculate in the Southwest Indian Ocean subtropical gyre. The primary control on the circulation near each seamount was its position relative to any mesoscale eddy at the time of the survey. Melville lay on the flank of a cyclonic eddy that had broken off the ARC and was propagating west before remerging with the next meander of the ARC. Nearby Sapmer, on the other hand, was in the centre of an anticyclonic eddy, resulting in very weak stratification over the seamount at the time of the survey. Middle of What lies most often on the northern flank of the ARC, in strong currents, but was at the time of the survey near the edge of the same eddy as Sapmer. Coral, in the Subtropical Front south of the ARC, was in waters much colder, fresher, denser and more oxygenated than all the other seamounts. Walter was close to the path of eddies propagating southwest from east of Madagascar, while Atlantis, the furthest east and north seamount, experienced the weakest eddy

  1. Phylogeography of the Crown-of-Thorns Starfish in the Indian Ocean

    PubMed Central

    Vogler, Catherine; Benzie, John; Barber, Paul H.; Erdmann, Mark V.; Ambariyanto; Sheppard, Charles; Tenggardjaja, Kimberly; Gérard, Karin; Wörheide, Gert

    2012-01-01

    Background Understanding the limits and population dynamics of closely related sibling species in the marine realm is particularly relevant in organisms that require management. The crown-of-thorns starfish Acanthaster planci, recently shown to be a species complex of at least four closely related species, is a coral predator infamous for its outbreaks that have devastated reefs throughout much of its Indo-Pacific distribution. Methodology/Principal Findings In this first Indian Ocean-wide genetic study of a marine organism we investigated the genetic structure and inferred the paleohistory of the two Indian Ocean sister-species of Acanthaster planci using mitochondrial DNA sequence analyses. We suggest that the first of two main diversification events led to the formation of a Southern and Northern Indian Ocean sister-species in the late Pliocene-early Pleistocene. The second led to the formation of two internal clades within each species around the onset of the last interglacial. The subsequent demographic history of the two lineages strongly differed, the Southern Indian Ocean sister-species showing a signature of recent population expansion and hardly any regional structure, whereas the Northern Indian Ocean sister-species apparently maintained a constant size with highly differentiated regional groupings that were asymmetrically connected by gene flow. Conclusions/Significance Past and present surface circulation patterns in conjunction with ocean primary productivity were identified as the processes most likely to have shaped the genetic structure between and within the two Indian Ocean lineages. This knowledge will help to understand the biological or ecological differences of the two sibling species and therefore aid in developing strategies to manage population outbreaks of this coral predator in the Indian Ocean. PMID:22927975

  2. Genetic structure and diversity of coffee (Coffea) across Africa and the Indian Ocean islands revealed using microsatellites

    PubMed Central

    Razafinarivo, Norosoa J.; Guyot, Romain; Davis, Aaron P.; Couturon, Emmanuel; Hamon, Serge; Crouzillat, Dominique; Rigoreau, Michel; Dubreuil-Tranchant, Christine; Poncet, Valerie; De Kochko, Alexandre; Rakotomalala, Jean-Jacques; Hamon, Perla

    2013-01-01

    Background and Aims The coffee genus (Coffea) comprises 124 species, and is indigenous to the Old World Tropics. Due to its immense economic importance, Coffea has been the focus of numerous genetic diversity studies, but despite this effort it remains insufficiently studied. In this study the genetic diversity and genetic structure of Coffea across Africa and the Indian Ocean islands is investigated. Methods Genetic data were produced using 13 polymorphic nuclear microsatellite markers (simple sequence repeats, SSRs), including seven expressed sequence tag-SSRs, and the data were analysed using model- and non-model-based methods. The study includes a total of 728 individuals from 60 species. Key Results Across Africa and the Indian Ocean islands Coffea comprises a closely related group of species with an overall pattern of genotypes running from west to east. Genetic structure was identified in accordance with pre-determined geographical regions and phylogenetic groups. There is a good relationship between morpho-taxonomic species delimitations and genetic units. Genetic diversity in African and Indian Ocean Coffea is high in terms of number of alleles detected, and Madagascar appears to represent a place of significant diversification in terms of allelic richness and species diversity. Conclusions Cross-species SSR transferability in African and Indian Ocean islands Coffea was very efficient. On the basis of the number of private alleles, diversification in East Africa and the Indian Ocean islands appears to be more recent than in West and West-Central Africa, although this general trend is complicated in Africa by the position of species belonging to lineages connecting the main geographical regions. The general pattern of phylogeography is not in agreement with an overall east to west (Mascarene, Madagascar, East Africa, West Africa) increase in genome size, the high proportion of shared alleles between the four regions or the high numbers of exclusive shared

  3. The Evolution of the Indian Ocean Triple Junction and the Finite Rotation Problem.

    DTIC Science & Technology

    1980-09-01

    Gondwanaland , J. Geophys. Res. (in press). 24 Parsons, B., and J.G. Sclater, An analysis of the variation of ocean floor bathymetry and heat flow with age, J...219-230. Norton, 1.0., and Sclater, J.G., 1978, A model for the evolution of the Indian Ocean and the breakup of Gondwanaland : Journal of Geophysical

  4. History of Antarctic glaciation: An Indian Ocean perspective

    NASA Astrophysics Data System (ADS)

    Ehrmann, W. U.; Hambrey, M. J.; Baldauf, J. G.; Barron, J.; Larsen, B.; Mackensen, A.; Wise, S. W., Jr.; Zachos, J. C.

    Legs 119 and 120 of the Ocean Drilling Program cored 16 sites on a S-N transect from the Antarctic continental shelf of Prydz Bay to the northern Kerguelen Plateau in the Indian Ocean. Thick sequences of glacigenic sediments were recovered in Prydz Bay, whereas the record on Kerguelen Plateau consists mainly of pelagic and, in part, glaciomarine sediments. This paper is a summary of the principle scientific results from the two legs that were concerned with the Cenozoic glacial and climatic history of Antarctica. It integrates a wide range of investigations, such as sedimentological studies including clay sedimentology and ice-rafted debris, studies of the oxygen isotopic composition of planktonic and benthic foraminifers, and paleontological investigations. The scientific data obtained from these cruises indicate that a long-term cooling trend started at about 52 Ma, after the thermal maximum in early Eocene time. All parameters under review indicate that there has been continental-scale ice in East Antarctica at least since earliest Oligocene time. However, the ice probably was temperate in character, whereas that of the present day is polar with the bulk of ice below the pressure melting point. The question of ice extent, specifically, whether ice had reached the Antarctic coast as early as middle and late Eocene time, is still a matter of dispute. Evidence for that is suggested by the occurrence of isolated middle Eocene sand and gravel grains and by a poorly dated, possibly upper Eocene sequence of thick massive diamictites in Prydz Bay. From Oligocene to recent time, the ice sheet experienced several major advance and retreat phases, some of them being quite rapid and short-term. However, although we did not find any clear evidence for a disappearance of the ice as postulated from other parts of Antarctica, the fragmentary nature of the stratigraphic record may hide major recessions of the ice sheet from the coast. Major increases of ice volume occurred in

  5. Multi-layer Clouds Over the South Indian Ocean

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The complex structure and beauty of polar clouds are highlighted by these images acquired by the Multi-angle Imaging SpectroRadiometer (MISR) on April 23, 2003. These clouds occur at multiple altitudes and exhibit a noticeable cyclonic circulation over the Southern Indian Ocean, to the north of Enderbyland, East Antarctica.

    The image at left was created by overlying a natural-color view from MISR's downward-pointing (nadir) camera with a color-coded stereo height field. MISR retrieves heights by a pattern recognition algorithm that utilizes multiple view angles to derive cloud height and motion. The opacity of the height field was then reduced until the field appears as a translucent wash over the natural-color image. The resulting purple, cyan and green hues of this aesthetic display indicate low, medium or high altitudes, respectively, with heights ranging from less than 2 kilometers (purple) to about 8 kilometers (green). In the lower right corner, the edge of the Antarctic coastline and some sea ice can be seen through some thin, high cirrus clouds.

    The right-hand panel is a natural-color image from MISR's 70-degree backward viewing camera. This camera looks backwards along the path of Terra's flight, and in the southern hemisphere the Sun is in front of this camera. This perspective causes the cloud-tops to be brightly outlined by the sun behind them, and enhances the shadows cast by clouds with significant vertical structure. An oblique observation angle also enhances the reflection of light by atmospheric particles, and accentuates the appearance of polar clouds. The dark ocean and sea ice that were apparent through the cirrus clouds at the bottom right corner of the nadir image are overwhelmed by the brightness of these clouds at the oblique view.

    The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously from pole to pole, and every 9 days views the entire globe between 82 degrees north and 82 degrees south latitude

  6. Front variability and surface ocean features of the presumed southern bluefin tuna spawning grounds in the tropical southeast Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nieblas, Anne-Elise; Demarcq, Hervé; Drushka, Kyla; Sloyan, Bernadette; Bonhommeau, Sylvain

    2014-09-01

    The southern bluefin tuna (SBT, Thunnus maccoyii) is an ecologically and economically valuable fish. However, surprisingly little is known about its critical early life history, a period when mortality is several orders of magnitude higher than at any other life stage, and when larvae are highly sensitive to environmental conditions. Ocean fronts can be important in creating favourable spawning conditions, as they are a convergence of water masses with different properties that can concentrate planktonic particles and lead to enhanced productivity. In this study, we examine the front activity within the only region where SBT have been observed to spawn: the tropical southeast Indian Ocean between Indonesia and Australia (10°S-20°S, 105°E-125°E). We investigate front activity and its relationship to ocean dynamics and surface features of the region. Results are also presented for the entire Indian Ocean (30°N-45°S, 20°E-140°E) to provide a background context. We use an extension of the Cayula and Cornillon algorithm to detect ocean fronts from satellite images of sea surface temperature (SST) and chlorophyll-a concentration (chl-a). Front occurrence represents the probability of occurrence of a front at each pixel of an image. Front intensity represents the magnitude of the difference between the two water masses that make up a front. Relative to the rest of the Indian Ocean, both SST and chl-a fronts in the offshore spawning region are persistent in occurrence and weak in intensity. Front occurrence and intensity along the Australian coast are high, with persistent and intense fronts found along the northwest and west coasts. Fronts in the tropical southeast Indian Ocean are shown to have strong annual variability and some moderate interannual variability. SST front occurrence is found to lead the Southern Oscillation Index by one year, potentially linked to warming and wind anomalies in the Indian Ocean. The surface ocean characteristics of the offshore

  7. Marine Science in Support for Sustainable Development of the Indian Ocean Region

    NASA Astrophysics Data System (ADS)

    Visbeck, Martin

    2014-05-01

    The Indian Ocean rim is home to a significant part of the global population. Its large heat capacity and ocean circulation responds to and regulates seasonal to multi-decadal and long term climate change. In particular the monsoon type circulation regulates rain and drought patterns over India, Africa and Southern Asia. Fishing and more recently resource extraction of energy and materials make the ocean economically important. Global trade and ocean related hazards (such as ocean warming, ocean acidification, ocean de-oxygenation, loss of biodiversity, sea level rise and earth quakes and tsunamis) have important other economic impacts on all societies. On the other hand our current scientific understanding, ability to continually observe changes in the marine environment, model all aspects of the connected ocean system and develop plausible scenarios for the Indian Ocean of the future are still in its infancy. The possibility for a decade long comprehensive Indian Ocean Study in support of providing the information needed for sustainable development of the region is explored.

  8. The Pacific and Indian Ocean Exchange: Analysis of the Imos Timor Passage and Ombai Strait Moorings

    NASA Astrophysics Data System (ADS)

    Sloyan, B.; Wijffels, S. A.; Cowley, R.

    2014-12-01

    A fundamental aspect of observing, describing, understanding and modeling the global climate and particularly the Maritime Continent, is a better knowledge of the fluxes of momentum, heat and freshwater in the ocean. The Indonesian seas are the only major low-latitude connection in the global oceans. This connection permits the transfer of Pacific waters into the Indian Ocean, known as the Indonesian Throughflow. The interaction of the Pacific and Indian basins and their modes of variability (El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD)), both through atmospheric teleconnections and the ocean link via the Indonesian Throughflow, is now being hotly pursued in the research community. We will present some initial findings from the 3-year time series (2011-2014) of the Timor Passage and Ombai Strait moorings. This mooring array is a component of the Australian Integrated Marine Observing System (IMOS), and builds on the earlier results of the INSTANT (2003-2006) observational program. The moorings comprise of velocity, temperature and salinity instruments. Observations from these moorings provide the required spatial and temporal coverage to understand ocean dynamics, the ocean's role in climate variability and change, investigate forcing of the atmosphere and ocean and assess the realism of data-assimilative ocean models and coupled ocean-atmosphere models.

  9. A 1/8° coupled biochemical-physical Indian Ocean Regional Model: Physical results and validation

    NASA Astrophysics Data System (ADS)

    Huang, Ke; Derada, Sergio; Xue, Huijie; Xiu, Peng; Chai, Fei; Xie, Qiang; Wang, Dongxiao

    2015-08-01

    A coupled physical-biochemical Indian Ocean Regional Model (IORM), based on the Navy Coastal Ocean Model (NCOM) and the Carbon Silicate Nitrogen Ecosystem (CoSiNE) model was configured with the primary objective of providing an accurate estimate of the oceanic physical state along with the biochemical processes simulated by CoSiNE to understand the variability in the Indian Ocean (IO). The model did not assimilate any data; instead, weak relaxation of temperature and salinity was implemented to keep the model stable in the long-term simulations. In this study, the skill of the IORM in simulating physical states in the IO was evaluated. Basin-scale surface circulation and cross-sectional transports were compared to observations, which demonstrated that the model replicated most of the observed features with reasonably good accuracy. Consistency and biases in the upper ocean temperature, salinity, and mixed layer depth were also analyzed. Lastly, the seasonality in the IO, its response to monsoonal forcing, and the evolution and dynamics of surface and subsurface dipole events were examined. The IORM reproduced most of the dynamic features including Ekman pumping, wave propagation, and climate variability at both annual and interannual time scales. The internal ocean dynamics and behavior of the modeled sea surface temperature anomaly (SSTA) suggest a coupled ocean/atmosphere instability that will require further research, including sensitivity experiments to realize improvements in model parameterization.

  10. Historical findings of the Russian physical oceanographers in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Koshlyakov, M. N.; Morozov, E. G.; Neiman, V. G.

    2016-12-01

    This is a review paper related to three findings of Russian physical oceanographers in the Indian Ocean. Observations in the Indian Ocean were used to investigate mesoscale eddies, subsurface equatorial undercurrent, and internal tidal waves near the Mascarene Ridge. Two surveys with measurements of temperature and salinity profiles in the Arabian Sea in 1967 made possible mapping of mesoscale eddies. Repeated moored measurements of currents in the equatorial zone between 55°E and 85°E revealed the existence of seasonal subsurface easterly Tareev undercurrent. A moored array of current and temperature recorders near the Mascarene Ridge was deployed as an antenna for internal tides. The displacements of isotherms caused by internal tides were as large as 150 m. The wave propagated to the southeast from the ridge. The review is intended to summarize the phenomena of the ocean dynamics of the Indian Ocean now when the scientific community of oceanography celebrates the 50th anniversary of the Indian Ocean expedition and plans the second Indian Ocean expedition.

  11. Productivity response to the PETM in the North Atlantic and South Indian Ocean

    NASA Astrophysics Data System (ADS)

    Sime, T.; Kanamaru-Shinn, K.; Stoll, H. M.; Shimizu, N.

    2009-12-01

    During the Paleocene Eocene Thermal Maximum (PETM), transient changes in climate and the ocean carbonate system resulted from a major release of isotopically light C into the ocean and atmosphere. We examine the productivity response of calcareous planktonic nannofossils to the dramatic climate and ecosystem changes at DSDP Site 401 in the Bay of Biscay, North Atlantic, and ODP Site 738, Southernmost Indian Ocean. We use the productivity indicator based on Sr/Ca ratios of coccoliths, which is independent of changes in sediment accumulation rate. Sr/Ca is measured in individually picked coccoliths using secondary ion mass spectrometry. At site 401, Sr/Ca ratios in coccoliths of Toweius and Coccolithus pelagicus increase during the PETM, indicating an increase in coccolithophore productivity until the PETM isotope recovery. We are working to characterize the background pre-PETM variability at this site to establish if this increase is a unique response to PETM environmental changes. Bulk sediment Sr/Ca ratios from the same depths, measured by ICP-AES, do not covary with Sr/Ca Coccolithus or Toweius but instead increases monotonically towards shallower depths. One possible explanation is a change in proportion of Sr-poor type coccoliths, such as Discoaster sp. and Zygrhab sp. Stable oxygen and carbon isotopes at site 401 exhibit extremely similar values among three different coccolith size fractions dominated by different genera, consistent with limited vital effects as observed at other sites. At ODP 738, Sr/Ca ratios in Toweius increase during the later part of the PETM and decrease by the end of the recovery, indicating a brief productivity increase. This increase is clearly beyond the background variability before the PETM or during the first part of the CIE. We are assessing whether a similar pattern is observed in Coccolithus. We will also similarly characterize productivity response to ELMO in the Equatorial Pacific and Southernmost Indian Ocean.

  12. Distichopora nitida Verrill (Cnidaria, Hydrozoa) from the Maldives, a new record from the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Scheer, Georg; Obrist, Kurt

    1986-12-01

    The stylasterid Distichopora nitida was found during dives at four localities in the South Maalhosmadulu Atoll, Maldives, Central Indian Ocean. It occurs at the reef slope in a depth of 22 48 m at the edge of grottoes. All features of the Maldive coral coincide with Boschma's (1959) description of D. nitida from the Pacific Ocean. The most important characteristics and the distribution of D. nitida were compared with those of other shallow water representatives of the genus in the Indo-Pacific. A locality of D. nitida in the western Indian Ocean, thus far anpublished, is mentioned.

  13. Dynamical analysis of the Indian Ocean climate network and its correlation with Australian Millennium Drought

    NASA Astrophysics Data System (ADS)

    Carpi, Laura; Masoller, Cristina; Díaz-Guilera, Albert; Ravetti, Martín G.

    2015-04-01

    During the period between the mid-1990s and late 2000s Australia had suffered one of the worst droughts on record. Severe rainfall deficits affected great part of southeast Australia, causing widespread drought conditions and catastrophic bushfires. The "Millennium Drought", as it was called, was unusual in terms of its severity, duration and extent, leaving important environmental and financial damages. One of the most important drivers of Australia climate variability is the Indian Ocean dipole (IOD), that is a coupled ocean and atmosphere phenomenon in the equatorial Indian Ocean. The IOD is measured by an index (DMI) that is the difference between sea surface temperature (SST) anomalies in the western and eastern equatorial Indian Ocean. Its positive phase is characterized by lower than normal sea surface temperatures in the tropical eastern coast, and higher than normal in the tropical western Indian Ocean. Extreme positive IOD (pIOD) events are associated to severe droughts in countries located over the eastern Indian Ocean, and to severe floods in the western tropical ones. Recent research works projected that the frequency of extreme pIOD events will increase significantly over the twenty-first century and consequently, the frequency of extreme climate conditions in the zones affected by it. In this work we study the dynamics of the Indian Ocean for the period of 1979-2014, by using climate networks of skin temperature and humidity (reanalysis data). Annual networks are constructed by creating links when the Pearson correlation coefficient between two nodes is greater than a specific value. The distance distribution Pd(k), that indicates the fraction of pairs of nodes at distance k, is computed to characterize the dynamics of the network by using Information Theory quantifiers. We found a clear change in the Indian Ocean dynamics and an increment in the network's similarities quantified by the Jensen-Shannon divergence in the late 1990s. We speculate that

  14. The effect of ENSO to the variability of sea surface height in western Pacific Ocean and eastern Indian Ocean and its connectivity to the Indonesia Throughflow (ITF)

    NASA Astrophysics Data System (ADS)

    Rejeki, H. A.; Munasik; Kunarso

    2017-02-01

    The differences of altimetry in the Pacific Ocean and the Indian Ocean causes the Indonesia Throughflow or commonly called ITF. The altimerty will have variation when the ENSO (El Nino Southern Oscilation) occur. The altimetry data from AVISO is used to find out how much the influence of ENSO to variations of that indicator in particular the altimetry difference between the western Pacific Ocean to the eastern Indian Ocean. When El Nino occured, the altimetry in the western Pacific Ocean will be lower than the altimetry of eastern Indian Ocean while the opposite condition occurs when the La Nina happened that the differences of altimetry in western Pacific Ocean higher than the altimetry in eastern Indian Ocean. These differences will affect the transport of ITF.

  15. Atmospheric deposition—Another source of nutrients enhancing primary productivity in the eastern tropical Indian Ocean during positive Indian Ocean Dipole phases

    NASA Astrophysics Data System (ADS)

    Siswanto, Eko

    2015-07-01

    This study used in situ and multisensor satellite data and combinations of various primary productivity (PP) and surface nitrate models to assess the contributions of upwelling and atmospheric deposition to modulating PP in the eastern tropical Indian Ocean (ETIO) during positive phases of the Indian Ocean Dipole (+IOD). Surprisingly, atmospheric deposition of nutrients from wildfires accounted for a higher portion of enhanced PP during +IODs than wind-driven nutrient upwelling. Substantial atmospheric nutrient deposition likely also maintains high PP postupwelling and postwildfire. Multiple regression analysis further supported the importance of atmospheric deposition in determining ETIO PP with a significantly large partial regression coefficient for aerosol optical thickness. It is possible that aerosols from major wildfire areas worldwide contribute nutrients that also nontrivially modulate PP in the oceans' main upwelling systems.

  16. Serological evidence for the circulation of flaviviruses in seabird populations of the western Indian Ocean.

    PubMed

    Jaeger, A; Lecollinet, S; Beck, C; Bastien, M; Le Corre, M; Dellagi, K; Pascalis, H; Boulinier, T; Lebarbenchon, C

    2016-02-01

    Birds play a central role in the epidemiology of several flaviviruses of concern for public and veterinary health. Seabirds represent the most abundant and widespread avifauna in the western Indian Ocean and may play an important role as host reservoirs and spreaders of arthropod-borne pathogens such as flaviviruses. We report the results of a serological investigation based on blood samples collected from nine seabird species from seven islands in the Indian Ocean. Using a commercial competitive enzyme-linked immunosorbent assay directed against the prototypic West Nile flavivirus, antibodies against flaviviruses were detected in the serum of 47 of the 855 seabirds tested. They were detected in bird samples from three islands and from four bird species. Seroneutralization tests on adults and chicks suggested that great frigatebirds (Fregata minor) from Europa were infected by West Nile virus during their non-breeding period, and that Usutu virus probably circulated within bird colonies on Tromelin and on Juan de Nova. Real-time polymerase chain reactions performed on bird blood samples did not yield positive results precluding the genetic characterization of flavivirus using RNA sequencing. Our findings stress the need to further investigate flavivirus infections in arthropod vectors present in seabird colonies.

  17. On the weak impact of the 26 December Indian Ocean tsunami on the Bangladesh coast

    NASA Astrophysics Data System (ADS)

    Ioualalen, M.; Pelinovsky, E.; Asavanant, J.; Lipikorn, R.; Deschamps, A.

    2007-01-01

    The 26 December 2004 Indian Ocean tsunami damaged severely most of the Gulf of Bengal's coastal areas, but the coast of Bangladesh which stands at the edge of an extraordinarily extended continental shelf. This latter feature has been built through huge discharges of river sediments along the Brahmaputra and Ganges rivers. As a result of this enormous discharge, another interesting feature of the area is the deep underwater Canyon, connected with the estuaries, running NE-SW from 25 km off the coast towards the continental slope. We investigate here how these two geological features may have modified/perturbed the Indian ocean tsunami propagation and impact on the Coast of Bangladesh. For that purpose we have realized an ensemble of numerical simulations based on Funwave Boussinesq numerical model and a validated coseismic source. It is found, at first order, that the extended shallow bathymetric profile of the continental shelf plays a key role in flattening the waveform through a defocussing process while the Canyon delays the process. The wave evolution seems to be related at first order to the bathymetric profile rather than to dynamical processes like nonlinearity, dispersion or bottom friction.

  18. Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices

    NASA Astrophysics Data System (ADS)

    Funk, C.; Hoell, A.; Shukla, S.; Bladé, I.; Liebmann, B.; Roberts, J. B.; Robertson, F. R.; Husak, G.

    2014-12-01

    In eastern East Africa (the southern Ethiopia, eastern Kenya and southern Somalia region), poor boreal spring (long wet season) rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers implement disaster risk reduction measures while guiding climate-smart adaptation and agricultural development. Building on recent research that links more frequent East African droughts to a stronger Walker circulation, resulting from warming in the Indo-Pacific warm pool and an increased east-to-west sea surface temperature (SST) gradient in the western Pacific, we show that the two dominant modes of East African boreal spring rainfall variability are tied to SST fluctuations in the western central Pacific and central Indian Ocean, respectively. Variations in these two rainfall modes can thus be predicted using two SST indices - the western Pacific gradient (WPG) and central Indian Ocean index (CIO), with our statistical forecasts exhibiting reasonable cross-validated skill (rcv ≈ 0.6). In contrast, the current generation of coupled forecast models show no skill during the long rains. Our SST indices also appear to capture most of the major recent drought events such as 2000, 2009 and 2011. Predictions based on these simple indices can be used to support regional forecasting efforts and land surface data assimilations to help inform early warning and guide climate outlooks.

  19. Ecology and Conservation Status of Indian Ocean Humpback Dolphins (Sousa plumbea) in Madagascar.

    PubMed

    Cerchio, Salvatore; Andrianarivelo, Norbert; Andrianantenaina, Boris

    2015-01-01

    The Indian Ocean humpback dolphin (Sousa plumbea) has been studied in several range states in the Southwest Indian Ocean, however little information exists on populations in Madagascar. Here, we review available literature and describe a study on S. plumbea conducted between 2004 and 2013 on the west coast of Madagascar, involving boat-based field surveys in the southwest and northwest regions, and interview surveys with local fishers from villages along most of the west coast. Field surveys in the southwest region of Anakao/St. Augustine Bay revealed low encounter rates and mean group size, and markedly declining trends in both from 1999 to 2013. Conversely, in the northwest region around Nosy Be and Nosy Iranja, encounter rates were higher, as were mean group sizes, suggesting an apparently more abundant and less impacted population. Interview surveys revealed by-catch of coastal dolphins along the entire west coast, including S. plumbea, as well as other species. Directed hunting, including drive hunts of groups of dolphins, was reported primarily in the southern regions, in the range of the Vezo Malagasy ethnicity; however, there was evidence of hunting starting in one area in the northwest, where hunting dolphins is normally considered taboo for the predominant Sakalava ethnicity. Thus, the conservation status of S. plumbea in Madagascar appears to be spatially heterogeneous, with some areas where the local population is apparently more impacted than others. Conservation measures are recommended to mitigate further decline in the southwest of Madagascar, while protecting habitat and ensuring resilience in the northwest.

  20. Heat fluxes of the Indian Ocean from a global eddy-resolving model

    NASA Astrophysics Data System (ADS)

    Garternicht, U.; Schott, F.

    1997-09-01

    The output of the global eddy-resolving ¼° ocean model of Semtner/Chervin (run by the Naval Postgraduate School, Monterey, California) has been used to study the oceanic temperature and heat flux in the Indian Ocean. The meridional heat flux in the northern Indian Ocean is at the low end of the observed values. A vertical overturning cell in the upper 500 m is the main contributor to the annual mean meridional heat flux across 5°S, whereas the horizontal gyre circulation, confined to the upper 500 m, dominates north of the equator. The change of monsoon winds is manifested in a reversal of the meridional circulation throughout the whole water column. The most notable result is a strong linear relationship of the meridional temperature flux and the zonal wind stress component north of 20°S. The model's Pacific-Indian Ocean throughflow across the section at 120°E accounts for -8.8±5.1 Sv (1 Sv≡106 m3 s-1). A strong interannual variability during the model run of 3 years shows a maximum range of 12 Sv in January/February and a minimum during March through June. The inflow from the Pacific into the Indian Ocean results in a total annual mean temperature flux of -0.9 PW (1 PW≡1015 W). In the model the temperature flux from the Pacific through the Indian Ocean to the south dominates in comparison with the input of solar heat from the northern Indian Ocean.

  1. An Analysis of the ENSO Signal in the Tropical Atlantic and Western Indian Oceans

    NASA Astrophysics Data System (ADS)

    Nicholson, Sharon E.

    1997-03-01

    This article examines the time-space evolution of the El Niño-Southern Oscillation (ENSO) signal in the tropical Atlantic and western Indian Oceans, using harmonic analysis. Composites of sea-surface temperatures (SSTs) and other variables are examined for a 24-month period beginning 6 months prior to the year of maximum warming in the Pacific (termed year 0). An ENSO signal is apparent in the Atlantic in six out of eight Pacific episodes and in the Indian Ocean in all eight episodes. Warming begins along the south-eastern Atlantic coast early in year 0, some months later elsewhere in the Atlantic and in the Indian Ocean. Maximum warming occurs in the Atlantic in October-December of year 0, but in the following January-March in the Indian Ocean.In these oceans a cold phase occurs synchronously with the first half of the Pacific episode (July of year -1 to June of year 0, in the Rasmusson-Carpenter terminology), a warm phase with the second half. Maximum cooling is 1 year prior to maximum warming in both oceans. In the Atlantic the cold phase occurs most consistently; in the Indian Ocean the warm phase occurs most consistently. There is a season-by-season reversal of SST anomalies and, to a lesser extent, pressure anomalies between the cold and warm phases. This is the basis for the biennial component of the ENSO signal.Our results indicate that the ENSO signal in African rainfall variability is a manifestation of ENSO's influence on SSTs in the Atlantic and Indian Oceans and, in turn, their influence on rainfall. The cold and warm phases correspond roughly to enhanced and reduced rainfall over the African continent, respectively. A similar reversal of rainfall anomalies is apparent season-by-season during these phases. The timing of the warming and cooling is relatively constant in the Indian Ocean. However, the onset of the warming and cooling in the south and equatorial Atlantic occurs progressively later from south to north, thus the signal propagates northward

  2. Tracking Cyclones in the Southwest Indian Ocean with an Ocean-Bottom Seismometer Network

    NASA Astrophysics Data System (ADS)

    Davy, C.; Barruol, G.; Fontaine, F. R.; Sigloch, K.; Stutzmann, E.

    2014-12-01

    The French-German RHUM-RUM project deployed 57 broadband ocean-bottom seismometers (OBS) over an area of 2000 x 2000 km2 between September 2012 and December 2013, spread around La Reunion Island and along the Central and the Southwest Indian Ridges. During this period, seven tropical cyclones propagated over the OBS network, providing the unique opportunity for in situ analysis and spatio-temporal tracking of this source of secondary (i.e twice the frequency of the ocean waves) microseismic noise and pressure fluctuations induced on the seafloor. We performed spectral analysis, seafloor pressure and ground polarization analyses on the continuous OBS data, focusing on cyclone Dumile, which passed directly over the OBS network. We observe that microseisms strongly increase in amplitude in the 0.1-0.45 Hz frequency band as the cyclone approaches and propagates over the instruments, and that this noise amplitude is directly related to the distance and intensity of the cyclone. Analysis of the temporal noise variations across the network permit to locate and track the area of maximum noise amplitude, which points towards the cyclone centre with good accuracy. Polarization analyses show that cyclones generate compressional waves in the water column, which give rise to both compressional and surface waves that propagate through the solid earth. In addition to atmospheric, oceanographic and satellite observations, microseisms recorded on the seafloor may therefore be considered a means for monitoring cyclone evolution and intensity.

  3. Isotopic and geochemical provinces of the western Indian Ocean Spreading Centers

    NASA Astrophysics Data System (ADS)

    Mahoney, J. J.; Natland, J. H.; White, W. M.; Poreda, R.; Bloomer, S. H.; Fisher, R. L.; Baxter, A. N.

    1989-04-01

    Basalt glasses from the Central Indian Ridge are distinct isotopically from mid-ocean ridge basalts (MORB) of the Indian Ocean triple junction and western few hundred kilometers of the Southeast Indian Ridge. In particular, very low 206Pb/204Pb and high 87Sr/86Sr signatures, which characterize the latter region, are absent over most of the Central Indian Ridge. In turn, lavas from the unusually deep eastern 1100-1500 km of the Southwest Indian Ridge are different chemically and isotopically from those of the above areas. A rather abrupt eastern boundary to Southwest Indian Ridge-type compositions occurs at or very near the geographic triple junction. This provinciality in western Indian Ocean ridge basalts partly mirrors fundamental regional differences in the underlying mantle but, at least between the eastern Southwest Indian Ridge and the western Southeast Indian Ridge and triple junction, also may reflect variations in extent and depth of melting in a vertically zoned upper mantle. A pronounced low ɛNd, high 206Pb/204Pb, high 87Sr/86Sr anomaly exists on the Central Indian Ridge at the Marie Celeste Fracture Zone and on the adjacent ridge segment to the south. Despite the great distance (>1100 km) of Réunion Island from the ridge, this zone appears to demark a region of mantle containing substantial Réunion hotspotlike material. Several old (35-60 m.y.) Deep Sea Drilling Project basalts which erupted on the ancestral Central Indian Ridge also record a significant Réunion hotspotlike influence, whereas a 46-m.y.-old sample that formed farther from the presumed locus of the hotspot possesses isotopic values identical to many present (non-Marie Celeste area) Central Indian Ridge MORB. The variably expressed and/or heterogeneous low 206Pb/204Pb material partly responsible for the isotopic distinctiveness of Indian Ocean ridge basalts may have entered into the Indian MORB mantle as a result of continental lithospheric remobilization preceding the breakup of

  4. The Previous Occurrence of Indian Ocean Tsunami- Geological Evidence from the Southeastern Coast of India

    NASA Astrophysics Data System (ADS)

    Rajendran, C.; Srinivasalu, S.; Rajendran, K.; Kumar, S.

    2008-12-01

    The 2004 Indian Ocean tsunami is generally considered to be an event without any historical precedence. No known historical record exists on similar sized prior event of 2004 Indian Ocean tsunami magnitude. However, a closer look at the "Manimekhalai" an ancient Tamil literature from South India reveal references to a sea surge event around A.D. 1000 that may have affected the town of Pumbuhar (a ~2000 year old historical port town also known as Kaveripattinam), located at southeastern coast of India. The literary references, however, cannot be taken as historical facts unless geological evidence supports them. With this in mind, we had trenched some selected sites in the southeast Indian coastal village of Vanagiri located near Pumbuhar (Kaveripattinam). Our shallow trench sites placed roughly 1 km from present coastal margin exposed parallel laminated paleobeach facies at base of the trench overlain by relatively thick low-angle cross-bedded sand sheets sandwiched between clayey beds followed by thick soil horizon that forms the present day surface. The cross-bedded sand sheet units are bounded by fining upward transitional contact on top and an erosional contact at the bottom and is characterized by presence of heavy mineral lamination, rip-up clay clasts, contortions, occasional mud drapes and rare pottery shards. The sand sheet units are typically thick towards sea and pinches out landward forming a wedge-shaped body. The grain size and micro faunal analyses of sand sheets indicate bimodal grain size distribution and presence of foraminifera, respectively. Preliminary thermal luminescence ages obtained from the pottery shards preserved in units from below and above the sand sheets bracket age of the event between 1836+/-172 and 1017+/-168 ybp, which roughly corresponds to the age of sea surge referenced in "Manimekhalai". Further work is underway to understand geometry, fauna, lithology, age, sedimentary and chemistry of this candidate paleo tsunami deposits.

  5. Dust deposition in the eastern Indian Ocean: The ocean perspective from Antarctica to the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Grand, Maxime M.; Measures, Christopher I.; Hatta, Mariko; Hiscock, William T.; Buck, Clifton S.; Landing, William M.

    2015-03-01

    Atmospheric deposition is an important but still poorly constrained source of trace micronutrients to the open ocean because of the dearth of in situ measurements of total deposition (i.e., wet + dry deposition) in remote regions. In this work, we discuss the upper ocean distribution of dissolved Fe and Al in the eastern Indian Ocean along a 95°E meridional transect spanning the Antarctic margin to the Bay of Bengal. We use the mixed layer concentration of dissolved Al in conjunction with empirical data in a simple steady state model to produce 75 estimates of total dust deposition that we compare with historical observations and atmospheric model estimates. Except in the northern Bay of Bengal where the Ganges-Brahmaputra river plume contributes to the inventory of dissolved Al, the surface distribution of dissolved Al along 95°E is remarkably consistent with the large-scale gradients in mineral dust deposition and multiple-source regions impacting the eastern Indian Ocean. The lowest total dust deposition fluxes are calculated for the Southern Ocean (66 ± 60 mg m-2 yr-1) and the highest for the northern end of the south Indian subtropical gyre (up to 940 mg m-2 yr-1 at 18°S) and in the southern Bay of Bengal (2500 ± 570 mg m-2 yr-1). Our total deposition fluxes, which have an uncertainty on the order of a factor of 3.5, are comparable with the composite atmospheric model data of Mahowald et al. (2005), except in the south Indian subtropical gyre where models may underestimate total deposition. Using available measurements of the solubility of Fe in aerosols, we confirm that dust deposition is a minor source of dissolved Fe to the Southern Ocean and show that aeolian deposition of dissolved Fe in the southern Bay of Bengal may be comparable to that observed underneath the Saharan dust plume in the Atlantic Ocean.

  6. Operational Retrieval of aerosol optical depth over Indian subcontinent and Indian Ocean using INSAT-3D/Imager product validation

    NASA Astrophysics Data System (ADS)

    Mishra, M. K.; Rastogi, G.; Chauhan, P.

    2014-11-01

    Aerosol optical depth (AOD) over Indian subcontinent and Indian Ocean region is derived operationally for the first time from the geostationary earth orbit (GEO) satellite INSAT-3D Imager data at 0.65 μm wavelength. Single visible channel algorithm based on clear sky composites gives larger retrieval error in AOD than other multiple channel algorithms due to errors in estimating surface reflectance and atmospheric property. However, since MIR channel signal is insensitive to the presence of most aerosols, therefore in present study, AOD retrieval algorithm employs both visible (centred at 0.65 μm) and mid-infrared (MIR) band (centred at 3.9 μm) measurements, and allows us to monitor transport of aerosols at higher temporal resolution. Comparisons made between INSAT-3D derived AOD (τI) and MODIS derived AOD (τM) co-located in space (at 1° resolution) and time during January, February and March (JFM) 2014 encompasses 1165, 1052 and 900 pixels, respectively. Good agreement found between τI and τM during JFM 2014 with linear correlation coefficients (R) of 0.87, 0.81 and 0.76, respectively. The extensive validation made during JFM 2014 encompasses 215 co-located AOD in space and time derived by INSAT 3D (τI) and 10 sun-photometers (τA) that includes 9 AERONET (Aerosol Robotic Network) and 1 handheld sun-photometer site. INSAT-3D derived AOD i.e. τI, is found within the retrieval errors of τI = ±0.07 ±0.15τA with linear correlation coefficient (R) of 0.90 and root mean square error equal (RMSE) to 0.06. Present work shows that INSAT-3D aerosol products can be used quantitatively in many applications with caution for possible residual clouds, snow/ice, and water contamination.

  7. Comparison between the Coastal Impacts of Cyclone Nargis and the Indian Ocean Tsunami

    NASA Astrophysics Data System (ADS)

    Fritz, H. M.; Blount, C.

    2009-12-01

    penetrated more than 50 km inland along the Ayeyarwady delta while the maximum inundation of the Indian Ocean tsunami was 7 km at Banda Aceh. The extent of affected coast lines differs with 2 m storm surge thresholds of cyclone Nargis spanning 200 km of coastline, whereas East Africa was severely affected by the Indian Ocean tsunami at 5000 km from the epicenter. The available time window for dissemination of warnings and evacuations are significantly shorter for tsunamis than cyclones. Coastal protection in the Indian Ocean must be approached with community-based planning, education and awareness programs suited for a multi-hazard perspective. Ayeyarwady delta in Myanmar after cyclone Nargis: (a) Deforestation of mangroves for use as charcoal and land use as rice paddies; (b) Drinking water wells scoured in surf zone at Aya highlighting more than 100 m land loss due to coastal erosion.

  8. Tsunami Early Warning for the Indian Ocean Region - Status and Outlook

    NASA Astrophysics Data System (ADS)

    Lauterjung, Joern; Rudloff, Alexander; Muench, Ute; Gitews Project Team

    2010-05-01

    The German-Indonesian Tsunami Early Warning System (GITEWS) for the Indian Ocean region has gone into operation in Indonesia in November 2008. The system includes a seismological network, together with GPS stations and a network of GPS buoys additionally equipped with ocean bottom pressure sensors and a tide gauge network. The different sensor systems have, for the most part, been installed and now deliver respective data either online or interactively upon request to the Warning Centre in Jakarta. Before 2011, however, the different components requires further optimization and fine tuning, local personnel needs to be trained and eventual problems in the daily operation have to be dealt with. Furthermore a company will be founded in the near future, which will guarantee a sustainable maintenance and operation of the system. This concludes the transfer from a temporarily project into a permanent service. This system established in Indonesia differs from other Tsunami Warning Systems through its application of modern scientific methods and technologies. New procedures for the fast and reliable determination of strong earthquakes, deformation monitoring by GPS, the modeling of tsunamis and the assessment of the situation have been implemented in the Warning System architecture. In particular, the direct incorporation of different sensors provides broad information already at the early stages of Early Warning thus resulting in a stable system and minimizing breakdowns and false alarms. The warning system is designed in an open and modular structure based on the most recent developments and standards of information technology. Therefore, the system can easily integrate additional sensor components to be used for other multi-hazard purposes e.g. meteorological and hydrological events. Up to now the German project group is cooperating in the Indian Ocean region with Sri Lanka, the Maldives, Iran, Yemen, Tanzania and Kenya to set up the equipment primarily for

  9. Forcing of recent decadal variability in the Equatorial and North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Thompson, P. R.; Piecuch, C. G.; Merrifield, M. A.; McCreary, J. P.; Firing, E.

    2016-09-01

    Recent decadal sea surface height (SSH) variability across the Equatorial and North Indian Ocean (ENIO, north of 5°S) is spatially coherent and related to a reversal in basin-scale, upper-ocean-temperature trends. Analysis of ocean and forcing fields from a data-assimilating ocean synthesis (ECCOv4) suggests that two equally important mechanisms of wind-driven heat redistribution within the Indian Ocean account for a majority of the decadal variability. The first is the Cross-Equatorial Cell (CEC) forced by zonal wind stress curl at the equator. The wind stress curl variability relates to the strength and position of the Mascarene High, which is influenced by the phase of the Indian Ocean Subtropical Dipole. The second mechanism is deep (700 m) upwelling related to zonal wind stress at the equator that causes deep, cross-equatorial overturning due to the unique geometry of the basin. The CEC acts to cool the upper ocean throughout most of the first decade of satellite altimetry, while the deep upwelling delays and then amplifies the effect of the CEC on SSH. During the subsequent decade, reversals in the forcing anomalies drive warming of the upper ocean and increasing SSH, with the effect of the deep upwelling leading the CEC.

  10. Forcing of anthropogenic aerosols on temperature trends of the sub-thermocline southern Indian Ocean

    PubMed Central

    Cowan, Tim; Cai, Wenju; Purich, Ariaan; Rotstayn, Leon; England, Matthew H.

    2013-01-01

    In the late twentieth century, the sub-thermocline waters of the southern tropical and subtropical Indian Ocean experienced a sharp cooling. This cooling has been previously attributed to an anthropogenic aerosol-induced strengthening of the global ocean conveyor, which transfers heat from the subtropical gyre latitudes toward the North Atlantic. From the mid-1990s the sub-thermocline southern Indian Ocean experienced a rapid temperature trend reversal. Here we show, using climate models from phase 5 of the Coupled Model Intercomparison Project, that the late twentieth century sub-thermocline cooling of the southern Indian Ocean was primarily driven by increasing anthropogenic aerosols and greenhouse gases. The models simulate a slow-down in the sub-thermocline cooling followed by a rapid warming towards the mid twenty-first century. The simulated evolution of the Indian Ocean temperature trend is linked with the peak in aerosols and their subsequent decline in the twenty-first century, reinforcing the hypothesis that aerosols influence ocean circulation trends. PMID:23873281

  11. Metagenomic Analysis of the Indian Ocean Picocyanobacterial Community: Structure, Potential Function and Evolution

    PubMed Central

    Díez, Beatriz; Nylander, Johan A. A.; Ininbergs, Karolina; Dupont, Christopher L.; Allen, Andrew E.; Yooseph, Shibu; Rusch, Douglas B.; Bergman, Birgitta

    2016-01-01

    Unicellular cyanobacteria are ubiquitous photoautotrophic microbes that contribute substantially to global primary production. Picocyanobacteria such as Synechococcus and Prochlorococcus depend on chlorophyll a-binding protein complexes to capture light energy. In addition, Synechococcus has accessory pigments organized into phycobilisomes, and Prochlorococcus contains chlorophyll b. Across a surface water transect spanning the sparsely studied tropical Indian Ocean, we examined Synechococcus and Prochlorococcus occurrence, taxonomy and habitat preference in an evolutionary context. Shotgun sequencing of size fractionated microbial communities from 0.1 μm to 20 μm and subsequent phylogenetic analysis indicated that cyanobacteria account for up to 15% of annotated reads, with the genera Prochlorococcus and Synechococcus comprising 90% of the cyanobacterial reads, even in the largest size fraction (3.0–20 mm). Phylogenetic analyses of cyanobacterial light-harvesting genes (chl-binding pcb/isiA, allophycocyanin (apcAB), phycocyanin (cpcAB) and phycoerythin (cpeAB)) mostly identified picocyanobacteria clades comprised of overlapping sequences obtained from Indian Ocean, Atlantic and/or Pacific Oceans samples. Habitat reconstructions coupled with phylogenetic analysis of the Indian Ocean samples suggested that large Synechococcus-like ancestors in coastal waters expanded their ecological niche towards open oligotrophic waters in the Indian Ocean through lineage diversification and associated streamlining of genomes (e.g. loss of phycobilisomes and acquisition of Chl b); resulting in contemporary small celled Prochlorococcus. Comparative metagenomic analysis with picocyanobacteria populations in other oceans suggests that this evolutionary scenario may be globally important. PMID:27196065

  12. Forcing of anthropogenic aerosols on temperature trends of the sub-thermocline southern Indian Ocean.

    PubMed

    Cowan, Tim; Cai, Wenju; Purich, Ariaan; Rotstayn, Leon; England, Matthew H

    2013-01-01

    In the late twentieth century, the sub-thermocline waters of the southern tropical and subtropical Indian Ocean experienced a sharp cooling. This cooling has been previously attributed to an anthropogenic aerosol-induced strengthening of the global ocean conveyor, which transfers heat from the subtropical gyre latitudes toward the North Atlantic. From the mid-1990s the sub-thermocline southern Indian Ocean experienced a rapid temperature trend reversal. Here we show, using climate models from phase 5 of the Coupled Model Intercomparison Project, that the late twentieth century sub-thermocline cooling of the southern Indian Ocean was primarily driven by increasing anthropogenic aerosols and greenhouse gases. The models simulate a slow-down in the sub-thermocline cooling followed by a rapid warming towards the mid twenty-first century. The simulated evolution of the Indian Ocean temperature trend is linked with the peak in aerosols and their subsequent decline in the twenty-first century, reinforcing the hypothesis that aerosols influence ocean circulation trends.

  13. Metagenomic Analysis of the Indian Ocean Picocyanobacterial Community: Structure, Potential Function and Evolution.

    PubMed

    Díez, Beatriz; Nylander, Johan A A; Ininbergs, Karolina; Dupont, Christopher L; Allen, Andrew E; Yooseph, Shibu; Rusch, Douglas B; Bergman, Birgitta

    2016-01-01

    Unicellular cyanobacteria are ubiquitous photoautotrophic microbes that contribute substantially to global primary production. Picocyanobacteria such as Synechococcus and Prochlorococcus depend on chlorophyll a-binding protein complexes to capture light energy. In addition, Synechococcus has accessory pigments organized into phycobilisomes, and Prochlorococcus contains chlorophyll b. Across a surface water transect spanning the sparsely studied tropical Indian Ocean, we examined Synechococcus and Prochlorococcus occurrence, taxonomy and habitat preference in an evolutionary context. Shotgun sequencing of size fractionated microbial communities from 0.1 μm to 20 μm and subsequent phylogenetic analysis indicated that cyanobacteria account for up to 15% of annotated reads, with the genera Prochlorococcus and Synechococcus comprising 90% of the cyanobacterial reads, even in the largest size fraction (3.0-20 mm). Phylogenetic analyses of cyanobacterial light-harvesting genes (chl-binding pcb/isiA, allophycocyanin (apcAB), phycocyanin (cpcAB) and phycoerythin (cpeAB)) mostly identified picocyanobacteria clades comprised of overlapping sequences obtained from Indian Ocean, Atlantic and/or Pacific Oceans samples. Habitat reconstructions coupled with phylogenetic analysis of the Indian Ocean samples suggested that large Synechococcus-like ancestors in coastal waters expanded their ecological niche towards open oligotrophic waters in the Indian Ocean through lineage diversification and associated streamlining of genomes (e.g. loss of phycobilisomes and acquisition of Chl b); resulting in contemporary small celled Prochlorococcus. Comparative metagenomic analysis with picocyanobacteria populations in other oceans suggests that this evolutionary scenario may be globally important.

  14. The dynamic connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

    NASA Astrophysics Data System (ADS)

    Lambert, E.; Le Bars, D.; de Ruijter, W. P. M.

    2015-09-01

    East of Madagascar, wind and surface buoyancy fluxes reinforce each other, leading to frontogenesis, outcrop and an eastward along-front flow: the South Indian Ocean Countercurrent (SICC). In the east the Leeuwin Current (LC) is a unique eastern boundary current which flows poleward along Australia. It is often described as a regional coastal current forced by an off-shore meridional density gradient or a sea surface slope, yet little is known of the forcing and dynamics that control these open ocean meridional gadients. To complete this understanding, we make use of both an ocean general circulation model and a conceptual two-layer model. The SICC impinges on west Australia and adds to a sea level slope and a southward geostrophic coastal jet: the Leeuwin Current. The SICC and the LC are thus dynamically connected. An observed transport maximum of the LC around 22° S is directly related to this impingement of the SICC. The circulation of the Indonesian Throughflow (ITF) through the Indian Ocean appears to be partly trapped in the upper layer north of the outcrop line and is redirected along this outcrop line to join the eastward flow of the SICC. Shutdown of the ITF in both models strongly decreases the Leeuwin Current transport and breaks the connection between the LC and SICC. In this case, most of the SICC was found to reconnect to the internal gyre circulation in the Indian Ocean. The Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current are thus dynamically coupled.

  15. Observed subseasonal variability of heat flux and the SST response of the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Raj Parampil, Sindu; Bharathraj, G. N.; Harrison, Matthew; Sengupta, Debasis

    2016-10-01

    We develop an experimental daily surface heat flux data set based on satellite observations to study subseasonal variability (periods shorter than 90 days) in the tropical Indian Ocean. We use incoming shortwave and longwave radiation from the International Satellite Cloud Climatology Project, and sea surface temperature (SST) from microwave sensors, to estimate net radiative flux. Latent and sensible heat fluxes are estimated from scatterometer winds and near-surface air temperature and specific humidity from Atmospheric Infrared Sounder (AIRS) observations calibrated to buoy data. Seasonal biases in net heat flux are generally within 10 W m-2 of estimates from moorings, and the phases and amplitudes of subseasonal variability of heat fluxes are realistic. We find that the contribution of subseasonal changes in air-sea humidity gradients to latent heat flux equals or exceeds the contribution of subseasonal changes in wind speed in all seasons. SST responds coherently to subseasonal oscillations of net heat flux associated with active and suppressed phases of atmospheric convection in the summer hemisphere. Thus, subseasonal SST changes are mainly forced by heat flux in the northeast Indian Ocean in northern summer, and in the 15°S-5°N latitude belt in southern summer. In the winter hemisphere, subseasonal SST changes are not a one-dimensional response to heat flux, implying that they are mainly due to oceanic advection, entrainment, or vertical mixing. The coherent evolution of subseasonal SST variability and surface heat flux suggests active coupling between SST and large-scale, organized tropical convection in the summer season.

  16. Variability in tropical cyclone heat potential over the Southwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Malan, N.; Reason, C. J. C.; Loveday, B. R.

    2013-12-01

    Tropical cyclone heat potential (TCHP) has been proposed as being important for hurricane and typhoon intensity. Here, a climatology of TCHP is developed for the Southwest Indian Ocean, a basin that experiences on average 11-12 tropical cyclones per year, many of which impact on Mauritius, Reunion and Madagascar, and Mozambique. SODA data and a regional ocean model forced with the GFDL-CORE v.2b reanalysis winds and heat fluxes are used to derive TCHP values during the 1948-2007 period. The results indicate that TCHP increases through the austral summer, peaking in March. Values of TCHP above 40 kJ cm-2, suggested as the minimum needed for tropical cyclone intensification, are still present in the northern Mozambique Channel in May. A time series of TCHP spatially averaged over the Seychelles-Chagos thermocline ridge (SCTR), an important area for tropical cyclones, is presented. The model time series, which agrees well with XBT-based observations (r = 0.82, p = 0.01), shows considerable interannual variability overlaying an upward tendency that matches with an observed increase in severe tropical cyclone days in the Southwest Indian Ocean. Although an increase in severe storms is seen during 1997-2007, the increasing TCHP tendency time series after 1997 coincides with a decrease in total cyclone numbers, a mismatch that is ascribed to increased atmospheric anticyclonicity over the basin. Seasons of increased (decreased) TCHP over the SCTR appear to be associated with dry (wet) conditions over certain areas of southern and East Africa and are linked with changes in zonal wind and vertical motion in the midtroposphere.

  17. Ectoenzymatic activity in surface waters: A transect from the Mediterranean Sea across the Indian Ocean to Australia

    NASA Astrophysics Data System (ADS)

    Misic, C.; Castellano, M.; Fabiano, M.; Ruggieri, N.; Saggiomo, V.; Povero, P.

    2006-09-01

    The activities of two hydrolytic enzymes (leucine aminopeptidase and β glucosidase), belonging to the particle-bound enzymatic fraction, were measured in open-sea surface waters. Samples were collected along a transect crossing the Indian Ocean during the early NW monsoon period (November and December 2001). The latitudinal pattern of the ectoenzymatic activities highlighted a generally increasing trend of glycolysis approaching the equator, with significantly higher β glucosidase activity (0.79-3.00 nmol l -1 h -1) within the latitudinal range from 12°N to 16°S. In this area, the surface waters coming from the Indonesian Throughflow and the Bay of Bengal carry a considerable quantity of carbohydrates (38.9-41.9 μg l -1), which stimulated glycolytic activity and its cell-specific rates scaled to bacterial abundance. On the other hand, in the Central Indian Ocean, the proteolytic activity was considerable (0.91-2.03 nmol l -1 h -1), although the particulate proteins did not show significant increases and the dissolved proteinlike signal was one of the lowest of the entire transect (0.7 mg l -1 on average compared to the 1.4-1.6 mg l -1 of the adjacent areas). Therefore, in this area, the two ectoenzymes studied did not respond to the same stimulatory effect (namely the specific substrate concentrations). The time needed for the hydrolysis of macromolecules within the particulate and dissolved organic substrate fractions, although these measures are affected by a number of assumptions starting with the potential nature of the ectoenzymatic determinations, confirms these observations. The Central Indian Ocean displayed the lowest values, from 8 to 26 days for particulate and dissolved organic carbon, respectively. As observed in the equatorial areas of the Atlantic Ocean, the relevant degradation activity of the central area of the Indian Ocean Basin suggests a notable heterotrophy based on a faster turnover of organic substrates.

  18. The Indian Ocean experiment: widespread air pollution from South and Southeast Asia.

    PubMed

    Lelieveld, J; Crutzen, P J; Ramanathan, V; Andreae, M O; Brenninkmeijer, C M; Campos, T; Cass, G R; Dickerson, R R; Fischer, H; de Gouw, J A; Hansel, A; Jefferson, A; Kley, D; de Laat, A T; Lal, S; Lawrence, M G; Lobert, J M; Mayol-Bracero, O L; Mitra, A P; Novakov, T; Oltmans, S J; Prather, K A; Reiner, T; Rodhe, H; Scheeren, H A; Sikka, D; Williams, J

    2001-02-09

    The Indian Ocean Experiment (INDOEX) was an international, multiplatform field campaign to measure long-range transport of air pollution from South and Southeast Asia toward the Indian Ocean during the dry monsoon season in January to March 1999. Surprisingly high pollution levels were observed over the entire northern Indian Ocean toward the Intertropical Convergence Zone at about 6 degrees S. We show that agricultural burning and especially biofuel use enhance carbon monoxide concentrations. Fossil fuel combustion and biomass burning cause a high aerosol loading. The growing pollution in this region gives rise to extensive air quality degradation with local, regional, and global implications, including a reduction of the oxidizing power of the atmosphere.

  19. A new species of Munidopsis Whiteaves, 1874 (Crustacea: Decapoda: Anomura) from the Northwest Indian Ocean Ridge.

    PubMed

    Dong, Dong; Li, Xinzheng; Zhou, Yadong; Wang, Chunsheng

    2016-08-23

    A new species, Munidopsis militaris n. sp., from the Carlsberg Ridge, Northwest Indian Ocean Ridge is described herein. The species belongs to a group of species having a pair of epigastric spines, mesial and lateral eye-spines, abdominal tergites unarmed, five or six spines on the lateral margin of the carapace, and a denticulate carina on the distolateral margin of the P1 fixed finger. It can be distinguished from its relatives by the spinous lateral margin of the palm and dorsal carinae on the P2-4 propodus. The Munidopsis fauna of the Indian Ocean Ridge is seldom reported on; this new species is the sixth member of this genus found inhabiting the Indian Ocean Ridge.

  20. Deformation of Indian Ocean Lithosphere Implies Highly Non-linear Rheological Law for Oceanic Lithosphere

    NASA Astrophysics Data System (ADS)

    Gordon, Richard; Houseman, Gregory

    2015-04-01

    The width of diffuse oceanic plate boundaries is determined by the rheology of oceanic lithosphere. Here we apply thin viscous sheet models, which have been successfully applied to deformation in several continental deforming zones, to investigate the deformation of oceanic lithosphere in the diffuse oceanic plate boundaries between the India, Capricorn, and Australia plates. We apply kinematic boundary conditions based on the current motion between these plates. We neglect buoyancy forces due to plate thinning or thickening and assume that the thin viscous sheet has the same depth-integrated non-linear viscosity coefficient everywhere. Our initial models have only one adjustable parameter, n, the power-law exponent, with n=1, 3, 10, 30, 100. The predicted width of the deforming zone decreases with increasing n, with n ≥ 30 explaining the observations. This n-value is higher than has been estimated for continental lithosphere, and suggests that more of the strength of oceanic lithosphere lies in layers deforming by faulting or by dislocation glide than for continental lithosphere. To obtain a stress field that better fits the distribution and type of earthquake focal mechanisms in the diffuse oceanic plate boundary, we add a second adjustable parameter, representing the effect of slab-pull stretching the oceanic plate near the Sumatra trench. We show that an average velocity increment on this boundary segment of 5 mm/a (relative to the average velocity of the India and Australia plates) fits the observed distribution of fault types better than velocities of 3.3 mm/a or 10 mm/a.

  1. Atmospheric input of N, P, Fe and trace metals to north Indian Ocean

    NASA Astrophysics Data System (ADS)

    Sarin, Manmohan; Srinivas, Bikkina

    2016-04-01

    The air-sea deposition of chemical constituents to the north Indian Ocean is influenced by seasonal continental outflow during the late NE-monsoon (December-April). Our recent studies have focused on deposition of mineral dust, nutrients (N, P and Fe) and toxic trace metals to the Arabian Sea (ARS) and Bay of Bengal (BoB), two important limbs of the north Indian Ocean. The chemical composition of PM2.5 in the continental outflow to the marine atmospheric boundary layer reveals dominance of nss-SO42- (as high as 25 μg m-3) and abundance of dust varies from 3 to 20 μg m-3. A striking similarity in the temporal variability of total inorganic acidity (TIA = NO3- + nss-SO42-) and fractional solubility of aerosol-Fe (FeTot: 60 - 1145 ng m-3) provides evidence for chemical processing of mineral dust during atmospheric transport. The enhanced solubility of Fe has implications to further increase in the deposition of this micro-nutrient to ocean surface. The mass ratio of nutrients (NInorg/NTot, Norg/NTot and PInorg/nss-Ca2+) also suggests further increase in their air-sea deposition to the surface BoB. The dry-deposition flux of PInorgto BoB varies by one order of magnitude (0.5 - 5.0 μmol-P m-2 d-1; Av: 0.02 Tg P yr-1). Based on atmospheric deposition of P and Fe, C-fixation in BoB (˜1 Pg yr-1) is dominated by anthropogenic sources and that in ARS (0.3 Pg yr-1) is limited by P and Fe. This is attributed to poor fractional solubility (˜1%) of mineral dust over the Arabian Sea. However, N-fixation by diazotrophs in the two oceanic regions is somewhat similar (0.03 Pg yr-1). Our estimate of N-deposition (0.2 Tg yr-1) to the northern Indian Ocean is significantly lower than the model results (˜800 - 1200 mg-N m-2 yr-1 ≈ 5.7 - 8.6 Tg yr-1 by Duce et al. (2008); ˜4.1 Tg yr-1 by Okin et al. (2011); and ˜0.8 Tg yr-1 by Kanakidou et al. (2012). The increase in aerosol toxicity is also evident from high enrichment factors of anthropogenic trace metal (Pb, Cd, Cr, Cu and

  2. Differential heating in the Indian Ocean differentially modulates precipitation in the Ganges and Brahmaputra basins

    USGS Publications Warehouse

    Pervez, Md Shahriar; Henebry, Geoffrey M.

    2016-01-01

    Indo-Pacific sea surface temperature dynamics play a prominent role in Asian summer monsoon variability. Two interactive climate modes of the Indo-Pacific—the El Niño/Southern Oscillation (ENSO) and the Indian Ocean dipole mode—modulate the amount of precipitation over India, in addition to precipitation over Africa, Indonesia, and Australia. However, this modulation is not spatially uniform. The precipitation in southern India is strongly forced by the Indian Ocean dipole mode and ENSO. In contrast, across northern India, encompassing the Ganges and Brahmaputra basins, the climate mode influence on precipitation is much less. Understanding the forcing of precipitation in these river basins is vital for food security and ecosystem services for over half a billion people. Using 28 years of remote sensing observations, we demonstrate that (i) the tropical west-east differential heating in the Indian Ocean influences the Ganges precipitation and (ii) the north-south differential heating in the Indian Ocean influences the Brahmaputra precipitation. The El Niño phase induces warming in the warm pool of the Indian Ocean and exerts more influence on Ganges precipitation than Brahmaputra precipitation. The analyses indicate that both the magnitude and position of the sea surface temperature anomalies in the Indian Ocean are important drivers for precipitation dynamics that can be effectively summarized using two new indices, one tuned for each basin. These new indices have the potential to aid forecasting of drought and flooding, to contextualize land cover and land use change, and to assess the regional impacts of climate change.

  3. Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records (Mollusca, Gastropoda)

    PubMed Central

    Yonow, Nathalie

    2012-01-01

    Abstract Seventy species of opisthobranchs are described in this work based on collections from the Persian Gulf, Socotra, Kenya, Zanzibar, Madagascar, La Réunion, Mauritius, the Seychelles, the Maldives, and Sri Lanka. Ten species are newly recorded from the western Indian Ocean and four species are recorded in the scientific literature for the first time since their original descriptions. Two species are described as new: Cyerce bourbonica sp. n. from La Réunion and Doriopsilla nigrocerasp. n. from the Persian Gulf coast of Saudi Arabia. Chromodoris cavae is removed from its synonymy with Chromodoris tennentana and redescribed from specimens from La Réunion, while several new synonyms are proposed for some commonly occurring species. Risbecia bullockii is recorded for the second time from the Indian Ocean and assigned to its correct genus. PMID:22711992

  4. Sea-surface temperatures around the Australian margin and Indian Ocean during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Barrows, Timothy T.; Juggins, Steve

    2005-04-01

    We present new last glacial maximum (LGM) sea-surface temperature (SST) maps for the oceans around Australia based on planktonic foraminifera assemblages. To provide the most reliable SST estimates we use the modern analog technique, the revised analog method, and artificial neural networks in conjunction with an expanded modern core top database. All three methods produce similar quality predictions and the root mean squared error of the consensus prediction (the average of the three) under cross-validation is only ±0.77 °C. We determine LGM SST using data from 165 cores, most of which have good age control from oxygen isotope stratigraphy and radiocarbon dates. The coldest SST occurred at 20,500±1400 cal yr BP, predating the maximum in oxygen isotope records at 18,200±1500 cal yr BP. During the LGM interval we observe cooling within the tropics of up to 4 °C in the eastern Indian Ocean, and mostly between 0 and 3 °C elsewhere along the equator. The high latitudes cooled by the greatest degree, a maximum of 7-9 °C in the southwest Pacific Ocean. Our maps improve substantially on previous attempts by making higher quality temperature estimates, using more cores, and improving age control.

  5. A comparison of polar vortex response to Pacific and Indian Ocean warming

    NASA Astrophysics Data System (ADS)

    Li, Shuanglin

    2010-05-01

    During recent decades, the tropical Indo-Pacific Ocean has become increasingly warmer. Meanwhile, both the northern and southern hemispheric polar vortices (NPV and SPV) have exhibited a deepening trend in boreal winter. Although previous studies have revealed that the tropical Indian Ocean warming (IOW) favors an intensifying NPV and a weakening SPV, how the tropical Pacific Ocean warming (POW) influences the NPV and SPV remains unclear. In this study, a comparative analysis has been conducted through ensemble atmospheric general circulation model (AGCM) experiments. The results show that, for the Northern Hemisphere, the two warmings exerted opposite impacts in boreal winter, in that the IOW intensified the NPV while the POW weakened the NPV. For the Southern Hemisphere, both the IOW and POW warmed the southern polar atmosphere and weakened the SPV. A diagnostic analysis based on the vorticity budget revealed that such an interhemispheric difference in influences from the IOW and POW in boreal winter was associated with different roles of transient eddy momentum flux convergence between the hemispheres. Furthermore, this difference may have been linked to different strengths of stationary wave activity between the hemispheres in boreal winter.

  6. A comparison of polar vortex trend response to Pacific and Indian Ocean warming

    NASA Astrophysics Data System (ADS)

    Li, S.

    2009-12-01

    During the past decades the tropical Indo-Pacific Ocean has become warmer than before. Meanwhile, both the northern and the southern hemispheric polar vortex (NPV and SPV) exhibit a deepening trend in boreal winter-half year. Although previous studies reveal that the tropical Indian Ocean Warming (IOW) favors intensifying the NPV and weakening the SPV, how the tropical Pacific Ocean Warming (POW) influences the NPV and the SPV is unclear. In this study, a comparative analysis is conducted through ensemble atmospheric general circulation model (AGCM) experiments. The results show that, for the northern hemisphere, the two warming exert an opposite impact in boreal winter, in that the IOW intensifies the NPV while the POW weakens the NPV. For the southern hemisphere, both the IOW and POW warm the southern polar atmosphere and weaken the SPV. A diagnostic analysis based on vorticity budget reveals that such an interhemispheric different influence in boreal winter between the IOW and the POW is associated with the different roles of transient eddy momentum flux convergence. Furthermore, this difference may be linked to the different strength of stationary wave activity between the hemispheres in boreal winter.

  7. The monsoonal heat budget of the hydrosphere-atmosphere system in the Indian Ocean sector

    SciTech Connect

    Hastenrath, S.; Greischar, L. )

    1993-04-15

    The authors model the monsoon activity in the Indian Ocean basin. This system, involving the interaction of the hydrosphere and atmosphere, with interchanges of energy and heat fluxes from the sun, drives the monsoon behavior, and the role it plays in climate in that part of the world. The authors take advantage of extensive data sets available at present of temperature profiles in the Indian Ocean, of atmospheric temperature profiles, and of moisture transport, to do a more detailed modeling than was done in the past. While the data sets are not simultaneous they span a ten year period, and provide an average picture of hydrologic and atmospheric conditions on a seasonal basis.

  8. New species of hippolytid shrimps (Crustacea: Decapoda: Caridea: Hippolytidae) from a southwest Indian Ocean seamount.

    PubMed

    Nye, Verity

    2013-01-01

    Two specimens representing two hippolytid genera were sampled recently from the Coral Seamount, southwest Indian Ocean, at 732 m water depth. Lebbeus ketophilos sp. nov. and Eualus oreios sp. nov. are described and illustrated and their morphologies are compared with those of previously described species. The new species are closest in morphology to L. indicus Holthuis, 1947 and E. kinzeri Tiefenbacher, 1990 respectively. They are distinguished clearly from these and other species by a suite of morphological features. This record enhances our present knowledge of seamount biodiversity and species richness of decapod crustaceans in the Indian Ocean.

  9. Factors controlling the location of compressional deformation of oceanic lithosphere in the central Indian Ocean

    SciTech Connect

    Karner, G.D.; Weissel, J.K. )

    1990-11-10

    The compression of oceanic lithosphere in the Central Indian Ocean does not occur where recent models for the state of stress in the Indo-Australian plate predict maximum horizontal compressive stress. The Afanazy-Nikitin seamount group, which was erupted in Late Cretaceous or Early Tertiary time, is centrally located in the region where deformation is best developed. The authors suggest that critical wavelength components in the deflection caused by the emplacement of these seamounts were preferentially amplified when north-south directed compression was applied to the northern part of the Indo-Australian plate in the late Miocene. To test this hypothesis, they develop simple one- and two-dimensional models for compression of a thin elastic plate overlying an inviscid fluid, where the plate contains a preexisting deflection. The {le} 2 km peak-to-trough amplitude and 200 km average wavelength characteristics of the broad-scale crustal deformation and the observed east-west trending pattern of free-air gravity anomalies are best matched in the modeling with an applied horizontal compression of 1.5-2.0 {times} 10{sup 13} N/m, and a plate with an effective elastic thickness of 10-15 km at the time of compression. In addition, the lithosphere is particularly susceptible to deformation by horizontal compression if seawater initially filled the deflection due to seamount emplacement, but Bengal Fan sediment fills the additional deflection caused by compression. The value of effective elastic thickness determined for the deformed lithosphere is about a factor of 2 less than values obtained from flexure of comparably aged lithosphere beneath lithosphere in response to horizontal loading. They determine a north-south shortening rate of {approx}1 mm/yr from the amplitude of horizontal compression, the width of the deformed region, and the time interval over which the deformation has occurred.

  10. Diurnal Convection Peaks over the Eastern Indian Ocean over Sumatra during Different MJO Phases

    NASA Astrophysics Data System (ADS)

    Fujita, M.; Nasuno, T.; Yoneyama, K.

    2015-12-01

    The diurnal convection peak characteristics over the eastern Indian Ocean over the island of Sumatra during different phases of the Madden-Julian oscillation (MJO) were investigated. During MJO phases 2 to 3 (P2 and P3) defined by Wheeler and Hendon (2004), prominent diurnal variation in convection was observed by satellites when moderate low-level westerly winds were dominant over the eastern Indian Ocean. The diurnal convection peaks were prominent over the island of Sumatra in the evening, while migrations of the convection toward the Indian Ocean were observed in the early morning. By using the Global Positioning System around the western region offshore of Sumatra, a significant reduction in water vapor was observed from evening until midnight, compensating for the upward motion over the island. During midnight to early morning, the water vapor increased in the western offshore region as the convections migrated from the island. During P2 to P3, the atmosphere over the eastern Indian Ocean contains abundant water vapor, while the Maritime Continent is fairly well heated by solar radiation under calm conditions. This situation should be favorable for the development of two diurnal convection peaks: the evening convection over the land induced by solar radiative heating and the midnight convection over the ocean triggered by convergence of the low-level westerly wind and the land breeze.

  11. Genetic algorithm for investigating flight MH370 in Indian Ocean using remotely sensed data

    NASA Astrophysics Data System (ADS)

    Marghany, Maged; Mansor, Shattri; Shariff, Abdul Rashid Bin Mohamed

    2016-06-01

    This study utilized Genetic algorithm (GA) for automatic detection and simulation trajectory movements of flight MH370 debris. In doing so, the Ocean Surface Topography Mission(OSTM) on the Jason- 2 satellite have been used within 1 and half year covers data to simulate the pattern of Flight MH370 debris movements across the southern Indian Ocean. Further, multi-objectives evolutionary algorithm also used to discriminate uncertainty of flight MH370 imagined and detection. The study shows that the ocean surface current speed is 0.5 m/s. This current patterns have developed a large anticlockwise gyre over a water depth of 8,000 m. The multi-objectives evolutionary algorithm suggested that objects are existed on satellite data are not flight MH370 debris. In addition, multiobjectives evolutionary algorithm suggested that the difficulties to acquire the exact location of flight MH370 due to complicated hydrodynamic movements across the southern Indian Ocean.

  12. The tectonic setting of the Seychelles, Mascarene and Amirante Plateaus in the Western Equatorial Indian Ocean

    NASA Technical Reports Server (NTRS)

    Mart, Y.

    1988-01-01

    A system of marine plateaus occurs in the western equatorial Indian Ocean, forming an arcuate series of wide and shallow banks with small islands in places. The oceanic basins that surround the Seychelles - Amirante region are of various ages and reflect a complex seafloor spreading pattern. The structural analysis of the Seychelle - Amirante - Mascarene region reflects the tectonic evolution of the western equatorial Indian Ocean. It is suggested that due to the seafloor spreading during a tectonic stage, the Seychelles continental block drifted southwestwards to collide with the oceanic crust of the Mascarene Basin, forming an elongated folded structure at first, and then a subduction zone. The morphological similarity, the lithological variability and the different origin of the Seychelles Bank, the Mascarene Plateau and the Amirante Arc emphasizes the significant convergent effects of various plate tectonic processes on the development of marine plateaus.

  13. Tropical Indian Ocean surface salinity bias in Climate Forecasting System coupled models and the role of upper ocean processes

    NASA Astrophysics Data System (ADS)

    Parekh, Anant; Chowdary, Jasti S.; Sayantani, Ojha; Fousiya, T. S.; Gnanaseelan, C.

    2016-04-01

    In the present study sea surface salinity (SSS) biases and seasonal tendency over the Tropical Indian Ocean (TIO) in the coupled models [Climate Forecasting System version 1 (CFSv1) and version 2 (CFSv2)] are examined with respect to observations. Both CFSv1 and CFSv2 overestimate SSS over the TIO throughout the year. CFSv1 displays improper SSS seasonal cycle over the Bay of Bengal (BoB), which is due to weaker model precipitation and improper river runoff especially during summer and fall. Over the southeastern Arabian Sea (AS) weak horizontal advection associated with East Indian coastal current during winter limits the formation of spring fresh water pool. On the other hand, weaker Somali jet during summer results for reduced positive salt tendency in the central and eastern AS. Strong positive precipitation bias in CFSv1 over the region off Somalia during winter, weaker vertical mixing and absence of horizontal salt advection lead to unrealistic barrier layer during winter and spring. The weaker stratification and improper spatial distribution of barrier layer thickness (BLT) in CFSv1 indicate that not only horizontal flux distribution but also vertical salt distribution displays large discrepancies. Absence of fall Wyrtki jet and winter equatorial currents in this model limit the advection of horizontal salt flux to the eastern equatorial Indian Ocean. The associated weaker stratification in eastern equatorial Indian Ocean can lead to deeper mixed layer and negative Sea Surface Temperature (SST) bias, which in turn favor positive Indian Ocean Dipole bias in CFSv1. It is important to note that improper spatial distribution of barrier layer and stratification can alter the air-sea interaction and precipitation in the models. On the other hand CFSv2 could produce the seasonal evolution and spatial distribution of SSS, BLT and stratification better than CFSv1. However CFSv2 displays positive bias in evaporation over the whole domain and negative bias in

  14. Early Student Support for SST Control by Subsurface Mixing during Indian Ocean Monsoons

    DTIC Science & Technology

    2015-09-30

    Mixing during Indian Ocean Monsoons” Emily Shroyer CEOAS, Oregon State University 104 CEOAS Administration Building Corvallis, OR 97331-5503...turbulent mixing sensors (χpods), to explore the upper ocean mixed layer properties within the SLD and modification of air-sea fluxes associated with the...satellite measured OLR and TRMM data to quantify cloud cover, evaporation , and precipitation anomalies over the southwestern Bay of Bengal as related to

  15. Oceanic isoprene and DMS distributions during low-productive conditions in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Booge, Dennis; Zavarsky, Alexander; Bell, Thomas; Marandino, Christa

    2015-04-01

    measurements of isoprene concentrations in this part of the Indian Ocean. The mean measured concentrations of isoprene and DMS generally stayed at low levels of < 20 pmolL-1 and average levels of ~ 1 nmolL-1, respectively. During three 24 hour stations with 3 hourly underway sampling and 6 hourly CTD-casts, we observed that isoprene concentrations were highest in the same depth as the chlorophyll-a maximum, while DMS concentrations always peaked slightly above the chlorophyll-a maximum. During a 48h-station we performed 8 CTD stations in order to investigate isoprene and DMS diurnal cycling within the 2 days in the euphotic zone. With this analysis we contribute to a better understanding of distributions of isoprene and DMS as well as biogeochemical cycling of these volatile compounds and their possible impact on the chemistry of the atmosphere by air-sea gas exchange.

  16. El Nino Southern Oscillation (ENSO) impact on tuna fisheries in Indian Ocean.

    PubMed

    Kumar, Palanisamy Satheesh; Pillai, Gopalakrishna N; Manjusha, Ushadevi

    2014-01-01

    El Nino Southern Oscillation (ENSO) is an important driver of interannual variations in climate and ecosystem productivity in tropical regions. However, detailed information about this important phenomenon of the Indian Ocean is scarce. Consequently, the objective of this study is to improve understanding of the impact of warm event El Nino and cool event La Nina on annual tuna landings from the Indian Ocean from 1980 to 2010. In this study, maximum tuna landings were recorded during a weak El Nino year (1456054 t in 2006) and during a weak La Nina year (1243562 t in 2000), although the lowest tuna catch was followed during the strong El Nino year (1204119 t in 2009) and during a strong La Nina year (706546 t in 1988). Validation of predicted tuna landings and SST were showing a significant positive correlation (p < 0.01) was observed all the major tuna species except Southern Bluefin Tuna. Whereas the other relationships such as sea level pressure, Wind actions; Zonal Wind (U), Meridonial Wind (V), and Scalar Wind (W) are less well-defined. In contrast with principal component analysis we find that Principal Components 1 explains 75.5% of the total variance and suggest that sea surface temperature plays a major role in determining tuna availability in the region especially during warm event El Nino years; landings in Indian Ocean tend to be optimum SST 25 to 26°C in ENSO event. Our results confirm the ENSO impact on climate, tuna abundance and production in the Indian Ocean. However, among the oceanic variables SST explained the highest deviance in generalized additive models and therefore considered the best habitat predictor in the Indian Ocean followed by sea level pressure and Winds (U, V, W).

  17. Iron bacterial phylogeny and their execution towards iron availability in Equatorial Indian Ocean and coastal Arabian Sea.

    PubMed

    Rajasabapathy, Raju; Mohandass, Chellandi; Vijayaraj, Ajakkalamoole Srinivas; Madival, Varsha Vinayak; Meena, Ram Murti

    2013-01-01

    Based on distinct colony morphology, color, size, shape and certain other traits, 92 bacterial isolates were investigated to understand their managerial ability on iron from the Arabian Sea and Equatorial Indian Ocean samples. The ARDRA (amplified rDNA restriction analysis) applied to eliminate the duplication of the bacterial strains, resulted 39 different banding patterns. The 16S rRNA gene sequencing data indicate the dominancy of three phylogenetic groups, alpha-Proteobacteria (10.25%), gamma-Proteobacteria (35.89%) and Bacilli (53.84%) in these waters. Marinobacter and Bacillus were the only common genera from both of the regions. Pseudoalteromonas, Halomonas, Rheinheimera, Staphylococcus and Idiomarina were some of the other genera obtained from the Arabian Sea. Erythrobacter, Roseovarius, Sagittula and Nitratireductor were found mostly in Equatorial Indian Ocean. In addition, 16S rRNA gene sequence data of some of our iron bacterial strains belong to novel species and one isolate ASS2A could form a new genus. Close to 23% of the isolates were able to produce high affinity sets of ligands like siderophores to mediate iron transport into the cell. The current study indicated that the Equatorial Indian Ocean species were well adapted to oxidize iron as an electron acceptor and the Arabian Sea species preferably go through siderophore production.

  18. Structure and isostatic compensation of the Comorin Ridge, north central Indian Ocean

    NASA Astrophysics Data System (ADS)

    Sreejith, K. M.; Krishna, K. S.; Bansal, A. R.

    2008-11-01

    Bathymetry, gravity and magnetic data (about 9200 lkm) of the Comorin Ridge, north central Indian Ocean were investigated using the transfer function and forward model techniques to understand the mode of isostatic compensation and origin of the ridge. The ridge extends for about 500 km in NNW-SSE direction and associates with low-amplitude gravity anomalies ranging from 25 to 30 mGal compared to the ridge relief, suggesting that the anomalies are compensated at deeper depths. From Admittance analysis an Airy model or local compensation with an elastic plate thickness (Te) of about 3 km and crust thickness (t) of 15-20 km are suggested for the southern part of the Comorin Ridge (south of 5°N), whereas for the northern part a flexural plate model with an elastic thickness of about 15 km is obtained. Admittance analysis together with the results from gravity forward modelling reveal that the south part was emplaced on relatively weak oceanic crust with both surface and subsurface loading, while the north part was emplaced on the continental crust. Based on present studies and published plate kinematic models we interpret that the Comorin Ridge was evolved at about 90 Ma during the rift stage of Madagascar from the southwest of India. We have also demarcated the continent-ocean boundary (COB) west of Sri Lanka and southern tip of India, which runs across the strike of the ridge, placing the northern part of the ridge on continent and southern part on oceanic crust. On the southern part of the ridge eastern flank is steep-faulted up to 0.6 km and is controlled by the 79°E FZ and then by COB.

  19. Hydraena Kugelann, 1794 (Coleoptera, Hydraenidae) from the Seychelles, Indian Ocean, with description of a new species

    PubMed Central

    Jäch, Manfred A.; Delgado, Juan A.

    2016-01-01

    Abstract Hydraena matyoti sp. n. (Coleoptera, Hydraenidae) is described from the Seychelles, Indian Ocean. Hydraena mahensis Scott, 1913 is redescribed. The latter is here recorded from La Digue for the first time. A key to the species of the genus Hydraena Kugelann, 1794 of the Seychelles is presented. PMID:27843389

  20. RECOSCIX-WIO: Providing Scientific Information to Marine Scientists in the Western Indian Ocean Region.

    ERIC Educational Resources Information Center

    Egghe, L.; Pissierssens, P.

    1997-01-01

    Describes RECOSCIX-WIO (Regional Cooperation in Scientific Information Exchange in the Western Indian Ocean Region). Details are given on the project's history, operational structure, and communication facilities, as well as services and products including query handling and document delivery. Future plans are also discussed, including CD-ROMs and…

  1. Hydraena Kugelann, 1794 (Coleoptera, Hydraenidae) from the Seychelles, Indian Ocean, with description of a new species.

    PubMed

    Jäch, Manfred A; Delgado, Juan A

    2016-01-01

    Hydraena matyotisp. n. (Coleoptera, Hydraenidae) is described from the Seychelles, Indian Ocean. Hydraena mahensis Scott, 1913 is redescribed. The latter is here recorded from La Digue for the first time. A key to the species of the genus Hydraena Kugelann, 1794 of the Seychelles is presented.

  2. The evolution of the Indian Ocean parrots (Psittaciformes): extinction, adaptive radiation and eustacy.

    PubMed

    Kundu, S; Jones, C G; Prys-Jones, R P; Groombridge, J J

    2012-01-01

    Parrots are among the most recognisable and widely distributed of all bird groups occupying major parts of the tropics. The evolution of the genera that are found in and around the Indian Ocean region is particularly interesting as they show a high degree of heterogeneity in distribution and levels of speciation. Here we present a molecular phylogenetic analysis of Indian Ocean parrots, identifying the possible geological and geographical factors that influenced their evolution. We hypothesise that the Indian Ocean islands acted as stepping stones in the radiation of the Old-World parrots, and that sea-level changes may have been an important determinant of current distributions and differences in speciation. A multi-locus phylogeny showing the evolutionary relationships among genera highlights the interesting position of the monotypic Psittrichas, which shares a common ancestor with the geographically distant Coracopsis. An extensive species-level molecular phylogeny indicates a complex pattern of radiation including evidence for colonisation of Africa, Asia and the Indian Ocean islands from Australasia via multiple routes, and of island populations 'seeding' continents. Moreover, comparison of estimated divergence dates and sea-level changes points to the latter as a factor in parrot speciation. This is the first study to include the extinct parrot taxa, Mascarinus mascarinus and Psittacula wardi which, respectively, appear closely related to Coracopsis nigra and Psittacula eupatria.

  3. The net effect of ultraviolet radiation on atmospheric dimethylsulphide over the Southern Indian Ocean.

    PubMed

    Kniveton, Dominic R; Todd, Martin C; Sciare, Jean; Mihalopoulos, Nikos

    2005-01-15

    Dimethylsulphide (DMS) in the atmosphere may play an important role in the climate system. This study shows an inverse relationship between ultraviolet extremes and atmospheric DMS, independent of changes in wind speed, sea-surface temperature and photosynthetically active radiation, as measured at Amsterdam Island in the Southern Indian Ocean.

  4. Systematic errors in Monsoon simulation: importance of the equatorial Indian Ocean processes

    NASA Astrophysics Data System (ADS)

    Annamalai, H.; Taguchi, B.; McCreary, J. P., Jr.; Nagura, M.; Miyama, T.

    2015-12-01

    H. Annamalai1, B. Taguchi2, J.P. McCreary1, J. Hafner1, M. Nagura2, and T. Miyama2 International Pacific Research Center, University of Hawaii, USA Application Laboratory, JAMSTEC, Japan In climate models, simulating the monsoon precipitation climatology remains a grand challenge. Compared to CMIP3, the multi-model-mean (MMM) errors for Asian-Australian monsoon (AAM) precipitation climatology in CMIP5, relative to GPCP observations, have shown little improvement. One of the implications is that uncertainties in the future projections of time-mean changes to AAM rainfall may not have reduced from CMIP3 to CMIP5. Despite dedicated efforts by the modeling community, the progress in monsoon modeling is rather slow. This leads us to wonder: Has the scientific community reached a "plateau" in modeling mean monsoon precipitation? Our focus here is to better understanding of the coupled air-sea interactions, and moist processes that govern the precipitation characteristics over the tropical Indian Ocean where large-scale errors persist. A series idealized coupled model experiments are performed to test the hypothesis that errors in the coupled processes along the equatorial Indian Ocean during inter-monsoon seasons could potentially influence systematic errors during the monsoon season. Moist static energy budget diagnostics has been performed to identify the leading moist and radiative processes that account for the large-scale errors in the simulated precipitation. As a way forward, we propose three coordinated efforts, and they are: (i) idealized coupled model experiments; (ii) process-based diagnostics and (iii) direct observations to constrain model physics. We will argue that a systematic and coordinated approach in the identification of the various interactive processes that shape the precipitation basic state needs to be carried out, and high-quality observations over the data sparse monsoon region are needed to validate models and further improve model physics.

  5. Interannual variation of tropical cyclone energy metrics over North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Mohapatra, M.; Vijay Kumar, V.

    2017-03-01

    There is decreasing trend in the tropical cyclone (TC) number over the North Indian Ocean (NIO) in recent years, though there is increasing trend in the sea surface temperature (SST) which is one of the main environmental parameters for the development and intensification of TCs. Hence, a study has been performed to understand whether any trend exists in other TC parameters such as velocity flux (VF), accumulated cyclone energy (ACE) and power dissipation index (PDI). The interseasonal and interannual variations of VF, ACE and PDI for the NIO as a whole and Bay of Bengal (BOB) and Arabian Sea (AS) are analysed based on the data of 1990-2013 (24 years). Role of large scale features like El Nino southern oscillation (ENSO) and Indian Ocean dipole (IOD) have also been analyzed. The mean ACE per year for TCs [maximum sustained wind of 34 knots (kt) or more] over the NIO is about 13.1 × 104 kt2 including 9.5 × 104 kt2 over the BOB and 3.6 × 104 kt2 over the AS. The mean PDI per year for TCs over the NIO is about 10 × 106 kt3 including 3 × 106 kt3 over the AS and 7 × 106 kt3 over the BOB. The VF, ACE and PDI of TCs are significantly less over BOB during post-monsoon season (Oct.-Dec.) of El Nino years than in La Nina and normal years. The VF for TCs over the BOB during post-monsoon season is significantly less (higher) during positive (negative) IOD years. There is significant decreasing trend at 95 % level of confidence in ACE and PDI of TCs over AS during post-monsoon season and PDI over the BOB and NIO during pre-monsoon season mainly due to similar trend in average intensity of TCs and not due to trends in SST over Nino regions or IOD index.

  6. Historical seismicity near Chagos - A complex deformation zone in the equatorial Indian Ocean

    NASA Technical Reports Server (NTRS)

    Wiens, D. A.

    1986-01-01

    The historical seismicity of the Chagos region of the Indian Ocean is analyzed, using earthquake relocation methods and a moment variance technique to determine the focal mechanisms of quakes occurring before 1964. Moment variance analysis showed a thrust faulting mechanism associated with the earthquake of 1944 near the Chagos-Laccadive Ridge; a strike-slip mechanism was associated with a smaller 1957 event occurring west of the Chagos Bank. The location of the 1944 event, one of the largest intraplate earthquakes known (1.4 x 10 to the 27th dyne/cm), would imply that the Chagos seismicity is due to a zone of tectonic deformation stretching across the equatorial Indian Ocean. The possibility of a slow diffuse boundary extending west of the Central Indian Ridge is also discussed. This boundary is confirmed by recent plate motion studies which suggest that it separates the Australian plate from a single Indo-Arabian plate.

  7. Three-dimensional isoneutral potential vorticity structure in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    McCarthy, Mary C.; Talley, Lynne D.

    1999-06-01

    The three-dimensional isoneutral potential vorticity structure of the Indian Ocean is examined using World Ocean Circulation Experiment and National Oceanic and Atmospheric Administration conductivity-temperature-depth data and historical bottle data. The distribution of the potential vorticity is set by the Indian Ocean's source waters and their circulation inside the basin. The lower thermocline has a high potential vorticity signal extending westward from northwest of Australia and a low signal from the Subantarctic Mode Water in the south. The Antarctic Intermediate Water inflow creates patches of high potential vorticity at intermediate depths in the southern Indian Ocean, below which the field becomes dominated by planetary vorticity, indicating a weaker meridional circulation and weaker potential vorticity sources. Wind-driven gyre depths have lower potential vorticity gradients primarily due to same-source waters. Homogenization and western shadow zones are not observed. The β-effect dominates the effect of the Somali Current and the Red Sea Water on the potential vorticity distribution. Isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the Circumpolar Deep Water fills the basins in deep western boundary currents, indicating a strong meridional circulation north of the Antarctic Circumpolar Current. The lower-gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical Indian Ocean suggests that Rossby waves will travel ˜1.3 times faster than standard theory predicts. To the south, several pools of homogenized potential vorticity appear in the upper 2000 m of the Southern Ocean where gyres previously have been identified. South of Australia the abyssal potential vorticity structure is set by a combination of the Antarctic Circumpolar Current and the bathymetry.

  8. The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

    NASA Astrophysics Data System (ADS)

    Lambert, Erwin; Le Bars, Dewi; de Ruijter, Wilhelmus P. M.

    2016-06-01

    East of Madagascar, the shallow "South Indian Ocean Counter Current (SICC)" flows from west to east across the Indian Ocean against the direction of the wind-driven circulation. The SICC impinges on west Australia and enhances the sea level slope, strengthening the alongshore coastal jet: the Leeuwin Current (LC), which flows poleward along Australia. An observed transport maximum of the LC around 22° S can likely be attributed to this impingement of the SICC. The LC is often described as a regional coastal current that is forced by an offshore meridional density gradient or sea surface slope. However, little is known about the controls of these open-ocean gradients. The regional circulation system is embedded in the subtropical "super gyre" that connects the Indo-Pacific via the Tasman Gateway and the Indonesian passages. The Indonesian Throughflow (ITF) circulates through the Indian Ocean back into the Pacific south of Australia. This return pathway appears to be partly trapped in the upper layer north of an outcrop line. It is redirected along this outcrop line and joins the eastward flow of the SICC. To study the connection of the basin-scale and the inter-ocean-scale dynamics, we apply both an ocean general circulation model and a conceptual two-layer model. Shutdown of the ITF in the models leads to a large decrease in Leeuwin Current transport. Most of the SICC was found to then reconnect to the internal gyre circulation in the Indian Ocean. ITF, SICC and LC thus appear to be dynamically connected.

  9. An evaluation of tsunami hazard using Bayesian approach in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Yadav, R. B. S.; Tsapanos, T. M.; Tripathi, J. N.; Chopra, S.

    2013-05-01

    The present study deals with the estimation of tsunami hazard parameters (maximum regional tsunami intensity Imax, slope β-value (where, β = b / log10e) of tsunami intensity-frequency relationship and tsunami activity rate λ) in the whole Indian Ocean as well as Andaman-Sumatra-Java (ASJ) region using Bayesian statistics technique. For this purpose a reliable, homogeneous and complete tsunami catalog during the period 1797 to 2006 with tsunami intensities (Soloviev-Imamura intensity scale) I ≥ 2.0, having average wave heights H ≥ 2.83 m, is utilized. The slope (b-value) of linear tsunami intensity-frequency relationship (Log10N = a - b ∗ I) of G-R type for observed tsunami data with intensities I ≥ 2.0 is calculated as 0.41. The applied method of Bayesian statistics follow three assumptions viz. Poissonian character of tsunami events, existence of the frequency-intensity relation of G-R type with a cut-off maximum value of tsunami intensities and catalog contains rather sizable events. In this study, the maximum regional tsunami intensity (Imax) has been estimated as 5.39 ± 0.30 and 5.41 ± 0.31 for the whole Indian Ocean and ASJ regions, respectively, which is reasonably comparable to the maximum observed tsunami intensity of 5.0 for August 27, 1883 Indonesia tsunami. The slope β-value of tsunami intensity-frequency relationship is calculated as 0.81 for both the Indian Ocean and ASJ regions by Bayesian statistics theory. We have also estimated quantiles of true and apparent tsunami intensities for future time intervals of 20, 30, 40 and 50 years with confidence limits for probability levels of 50%, 60%, 70%, 80%, 90% and 95% in the Indian Ocean along with ASJ region. It is observed that the differences between true and apparent quantiles of tsunami intensities are negligible revealing that a good quality of tsunami data is used in the study. The results estimated in the present study have potential useful implications in the probabilistic tsunami

  10. Coral records of interannual, century and millenium scale climate dynamics in the tropical eastern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Abram, N. J.; Gagan, M. K.; Chappell, J.; McCulloch, M. T.; Hantoro, W. S.

    2003-04-01

    Climate in the tropical eastern Indian Ocean is dominated by the Asian monsoon but is also strongly influenced by the El Niño-Southern Oscillation (ENSO) and is the core area of activity for the Indian Ocean Dipole. We examined the interaction of these climate systems over the past 7000 years using the δ18O and Sr/Ca records of 5 modern and 33 fossil corals from the Mentawai Islands, southwest Sumatra, Indonesia. The mean δ18O and Sr/Ca values of the fossil corals define a maxima in sea surface temperature (SST) and salinity at 6.5 ka, which was followed by cooling and freshening to 4.5 ka. On the seasonal scale this cooling/freshening trend is manifest as an increase in the annual SST cycle and an increase in the frequency of Indian Ocean Dipole events. This suggests a stronger southeast Monsoon causing increased Ekman upwelling along the Sumatran coast. The fossil corals record rapid warming and drying from 4.5 to 4ka. The peak of this event corresponds to the timing of a major drought recorded in African lake levels and ice cores. The period around 2ka is characterised by rapid fluctuations in mean SST but relatively stable salinity at values close to the present day warm pool conditions. This variability in SST may reflect an increase in the strength of the ENSO system after 4ka. Changes in SST and salinity recorded by the fossil corals over the past 1000 years closely match variations in solar activity, with a distinct cool and fresh period between 0.5ka and 0.4ka that corresponds with the Sp&{uml;o}rer solar minima, as well as with high lake levels in Africa. High-resolution coral records for the past 150 years allow for a detailed examination of the interactions between the Asian Monsoon, ENSO and the Indian Ocean Dipole climate systems since 1857. This record shows that large Indian Ocean Dipole events, such as observed in 1994 and 1997, have been infrequent with only two other similar-scale events recorded since 1857. More frequent and stronger Indian

  11. Mechanisms for the Intraseasonal Variability of Tropospheric Ozone over the Indian Ocean during the Winter Monsoon

    NASA Technical Reports Server (NTRS)

    Chatfield, R. b.; Guan, H.; Thompson, A. M.; Smit, H. G. J.

    2007-01-01

    We synthesize daily sonde (vertical) information and daily satellite (horizontal) information to provide an empirical description of ozone origins over the northern Indian Ocean during the INDOEX (Indian Ocean Experiment) field campaign (February-March 1999). This area is shown to be a significant portion of the "high-ozone tropics". East-west O3 features and their flow are identified, and ozone origins are compared to other tropical regions, using water vapor as a second tracer. In the study period, multiple processes contribute to O3 column enhancements, their importance varying strongly by latitude: (1) Low-altitude O3 pollution over the northern Indian Ocean mainly originates from the Indian subcontinent and is traceable to high emission areas. Convective activity south of Sri Lanka helps direct ozone outflow from the northern Indian subcontinent. (2) Middle tropospheric O3 maxima over the northern Indian Ocean originate from various sources, often transitioning within a few hours. Convective venting of Asian pollutants can add 20-30 ppbv to the middle troposphere at 5degN-10degN, alternating with stratospheric influence. (3) A number of cases suggest that strong mixing-in of stratospheric air along the subtropical jet raised tropospheric O3 in early March by approx.40-50 ppbv, especially poleward of approx. 10degN. (4) Influences of lightning and large-scale biomass burning were not strong during this period, in contrast to the situation in Africa and the South Atlantic or locally in Southeast Asia. This work illustrates successes and limitations in approaches to synthesizing disparate information on trace-gas distributions taken from satellite retrieval products and ozonesondes.

  12. Concentrations and isotopic compositions of neodymium in the eastern Indian Ocean and Indonesian straits

    NASA Astrophysics Data System (ADS)

    Jeandel, Catherine; Thouron, Danièle; Fieux, Michèle

    1998-08-01

    Four profiles of Nd concentration and isotopic composition were determined at two stations in the eastern Indian Ocean along a north/south section between Bali and Port-Hedland and at two others in the Timor and Sumba straits. Neodymium concentrations increase with depth, between 7.2 pmol/L at the surface to 41.7 pmol/L close to the bottom. The ɛ Nd of the different water masses along the section are -7.2 ± 0.2 for the Indian Bottom Waters and -6.1 ± 0.2 for the Indian Deep Waters. The intermediate and thermocline waters are less radiogenic at st-10 than at st-20 (-5.3 ± 0.3 and -3.6 ± 0.2, respectively). In the Timor Passage and Sumba Strait, ɛ Nd of the Indonesian waters is -4.1 ± 0.2 and that of the North Indian Intermediate Waters is -2.6 ± 0.3. These distinct isotopic signals constrain the origins of the different water masses sampled in the eastern Indian Ocean. They fix the limit of the nonradiogenic Antarctic and Indian contributions to the southern part of the section whereas the northern part is influenced by radiogenic Indonesian flows. In addition, the neodymium isotopic composition suggests that in the north, deep waters are influenced by a radiogenic component originating from the Sunda Arch Slope flowing deeper than 1200 m, which was not documented previously. Mixing calculations assess the conservativity of ɛ Nd on the scale of an oceanic basin. The origin of the surprising radiogenic signal of the NIIW is discussed and could result from a remobilization of Nd sediment-hosted on the Java shelf, requiring important dissolved/particulate exchange processes. Such processes, occurring in specific areas, could play an important role in the world ocean Nd budget.

  13. Regal phylogeography: Range-wide survey of the marine angelfish Pygoplites diacanthus reveals evolutionary partitions between the Red Sea, Indian Ocean, and Pacific Ocean.

    PubMed

    Coleman, Richard R; Eble, Jeffrey A; DiBattista, Joseph D; Rocha, Luiz A; Randall, John E; Berumen, Michael L; Bowen, Brian W

    2016-07-01

    The regal angelfish (Pygoplites diacanthus; family Pomacanthidae) occurs on reefs from the Red Sea to the central Pacific, with an Indian Ocean/Rea Sea color morph distinct from a Pacific Ocean morph. To assess population differentiation and evaluate the possibility of cryptic evolutionary partitions in this monotypic genus, we surveyed mtDNA cytochrome b and two nuclear introns (S7 and RAG2) in 547 individuals from 15 locations. Phylogeographic analyses revealed four mtDNA lineages (d=0.006-0.015) corresponding to the Pacific Ocean, the Red Sea, and two admixed lineages in the Indian Ocean, a pattern consistent with known biogeographic barriers. Christmas Island in the eastern Indian Ocean had both Indian and Pacific lineages. Both S7 and RAG2 showed strong population-level differentiation between the Red Sea, Indian Ocean, and Pacific Ocean (ΦST=0.066-0.512). The only consistent population sub-structure within these three regions was at the Society Islands (French Polynesia), where surrounding oceanographic conditions may reinforce isolation. Coalescence analyses indicate the Pacific (1.7Ma) as the oldest extant lineage followed by the Red Sea lineage (1.4Ma). Results from a median-joining network suggest radiations of two lineages from the Red Sea that currently occupy the Indian Ocean (0.7-0.9Ma). Persistence of a Red Sea lineage through Pleistocene glacial cycles suggests a long-term refuge in this region. The affiliation of Pacific and Red Sea populations, apparent in cytochrome b and S7 (but equivocal in RAG2) raises the hypothesis that the Indian Ocean was recolonized from the Red Sea, possibly more than once. Assessing the genetic architecture of this widespread monotypic genus reveals cryptic evolutionary diversity that merits subspecific recognition. We recommend P.d. diacanthus and P.d. flavescens for the Pacific and Indian Ocean/Red Sea forms.

  14. Observational Studies on Association between Eastward Equatorial Jet and Indian Ocean Dipole

    DTIC Science & Technology

    2010-01-01

    School sponsored this re- search. References Chang, P., T. Yamagata, P. Schopf, S. K. Behera , J. Carton, W. S. Kessler, G. Meyers, T. Qu, F. Schott...J. Atmos. Oceanic Technol., 24, 688–701. Rao, A. S., S. K. Behera , Y. Masumoto and T. Yamagata (2002): Interannual variability in the subsurface...T., S. K. Behera , J.-J. Luo, S. Masson, M. Jury and S. A. Rao (2004): Coupled ocean-atmosphere variability in the tropical Indian Ocean. p. 189–212

  15. Variability of The Southwest Indian and Atlantic Oceans and Connexions To Atmospheric Anomalies

    NASA Astrophysics Data System (ADS)

    Fauchereau, N.; Trzaska, S.; Richard, Y.; Roucou, P.

    Sea-Surface-Temperature variability in the Southern Indian and Atlantic Oceans is in- vestigated using Empirical Orthogonal Functions analysis over the 1950-1999 period. It reveals a significant pattern of co-variability between the SouthWest Indian and SouthWest Atlantic Oceans (roughly located in the Southwestern branches of the sub- tropical gyres and their retroflection regions). The robustness of this mode is assessed through correlation between box-averaged indices and composite analysis. This mode is phase-locked on the Austral Summer (november to january) and is associated with significant anomalies in the SLP field. A discussion on the potential mechanisms in- volved in such Ocean Atmosphere anomalies is given and attention is devoted to their impact on the precipitation anomalies over Southern America and mainly Southern Africa. Relations to the SST - atmosphere patterns of variability recently described by Behera et Yamagata (2001. Geophysical Research Letters, 28, 2, 327-330) for the Indian Ocean and Venegas et al (1997. Journal of Climate, 19, 2904-2920) for the Atlantic Ocean is also discussed.

  16. Plate kinematics and passive margin development in the southern Indian Ocean

    SciTech Connect

    Coffin, M.F.; Royer, J.Y.; Sclater, J.G. ); Cande, S.C. ); Schlich, R. ); Symonds, P.A. ); Kelts, K. ); Wise, S.W. )

    1990-05-01

    The development of the Indian Ocean began in the Middle to Late Jurassic with the breakup of Gondwanaland. Marine magnetic anomalies and limited Deep Sea Drilling Project and Ocean Drilling Program core samples have been used to date the crust. Fracture zone trends interpreted from satellite (Seasat and Geosat) altimetry and marine seismic, gravity, and magnetic data have been combined with crustal dates to product kinematic models of plate movements. Between Jurassic and Late Cretaceous time the plate tectonic evolution of the Indian Ocean is poorly known. Mesozoic marine magnetic anomalies offshore eastern Africa Antarctica, and Western Australia document plate motions during the interval; however, extensive areas of oceanic crust from which no anomalies have been identified and a dearth of fracture zones prevent detailed links with the much better defined plate kinematic synthesis of the past 80 m.y. The passive margins of the southern Indian Ocean flank eastern Africa, Madagascar, Antarctica, and Australia. Simple and pure shear models have been proposed to account for these margins' development but compelling evidence for a unique rifting mechanism has yet to be presented for any part of the margins. Each margin contains rifted and sheared sectors of markedly different structural style. Prerift sedimentary sections typically document a rift phase lasting several tens of millions of years before breakup occurred. Synrift sequences commonly contain evidence of volcanic activity. Variations in sediment supply and type, as well as variations in climate have resulted in widely differing postrift sedimentary sequences along the margins.

  17. Geochemical variability of MORBs along slow to intermediate spreading Carlsberg-Central Indian Ridge, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Ray, D.; Misra, S.; Banerjee, R.

    2013-07-01

    We present new major and ICP-MS trace element data from the Carlsberg Ridge MORBs from two different locations (i.e., 3°35'N/64°05'E and 3°41'N/64°09'E). Using this data we reassess the intra-ridge geochemical variations of the Carlsberg Ridge- Central Indian Ridge MORBs. Trace element contents of the Carlsberg Ridge MORBs are similar to the Rodriguez Triple Junction MORBs [e.g., LIL and REE spidergrams and (La/Sm)N ratio etc.]; both closely resemble the average N-MORB. However, the MORBs from the northern- and southern Central Indian Ridge, significantly vary in composition from the average N- and E-MORBs. Most Carlsberg Ridge- Central Indian Ridge MORBs show significantly less fractionation in FeOt, in the MgO-CaO-FeOt diagram, compared to those of the Mid Atlantic- and East Pacific Rise MORBs. Furthermore, the depleted LREE and nearly flat HREE patterns of the Carlsberg Ridge-Central Indian Ridge MORBs (along with their low compatible trace element (Ni, Cr, Sr) variability compared with the increasing incompatible trace element (Y, Zr) contents in the log-log plots, as well as their increasing incompatible trace element ratios) favor partial melting dominated processes for their petrogenetic evolution. Our (Sr, Nd, Pb) isotope data review shows that the Carlsberg Ridge-Central Indian Ridge MORBs are derived from a depleted mantle source that was variously contaminated by continental crust, perhaps during the third stage of Gondwana break up between 155 and 135 Ma. Such contamination could also have occurred later during the strike slip movement along a mega fracture (a member of the Davie Transform Faults in the Somali Basin that broke Gondwanaland into the East and West Gondwanas). The 208Pb/204Pb versus 206Pb/204Pb plot of above mentioned MORBs suggests that the depleted mantle source of the Rodriguez Triple Junction MORBs was contaminated by ˜21% lower continental crust, whereas the mantle source of the Central Indian Ridge MORBs was contaminated by

  18. A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals.

    PubMed

    Roquet, Fabien; Williams, Guy; Hindell, Mark A; Harcourt, Rob; McMahon, Clive; Guinet, Christophe; Charrassin, Jean-Benoit; Reverdin, Gilles; Boehme, Lars; Lovell, Phil; Fedak, Mike

    2014-01-01

    The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20-140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate.

  19. The relationship between Arabian Sea upwelling and Indian Monsoon revisited in a high resolution ocean simulation

    NASA Astrophysics Data System (ADS)

    Yi, Xing; Hünicke, Birgit; Tim, Nele; Zorita, Eduardo

    2017-03-01

    Studies based on sediment records, sea-surface temperature and wind suggest that upwelling along the western coast of Arabian Sea is strongly affected by the Indian summer Monsoon. We examine this relationship directly in an eddy-resolving global ocean simulation STORM driven by atmospheric reanalysis over the last 61 years. With its very high spatial resolution (10 km), STORM allows us to identify characteristics of the upwelling system. We analyse the co-variability between upwelling and meteorological and oceanic variables from 1950 to 2010. The analysis reveals high interannual correlations between coastal upwelling and along-shore wind-stress (r = 0.73) as well as with sea-surface temperature (r = -0.83). However, the correlation between the upwelling and the Monsoon is small. We find an atmospheric circulation pattern different from the one that drives the Monsoon as the main modulator of the upwelling variability. In spite of this, the patterns of temperature anomalies that are either linked to Arabian Sea upwelling or to the Monsoon are spatially quite similar, although the physical mechanisms of these links are different. In addition, no long-term trend is detected in our modelled upwelling in the Arabian Sea.

  20. Molecular phylogeny of the spiny lobster genus Palinurus (Decapoda: Palinuridae) with hypotheses on speciation in the NE Atlantic/Mediterranean and SW Indian Ocean.

    PubMed

    Groeneveld, Johan C; Gopal, Keshni; George, Ray W; Matthee, Conrad A

    2007-10-01

    Sequence data derived from the mitochondrial DNA 16S rRNA and COI genes were used to determine the phylogenetic relationships among six Palinurus spiny lobster species. Three species (P. charlestoni, P. elephas, and P. mauritanicus) occur in the northeastern Atlantic/Mediterranean, and the others (P. barbarae, P. delagoae and P. gilchristi) inhabit the southwestern Indian Ocean. Parsimony and model based phylogenetics strongly supported the monophyly of the genus. A combined parsimony analysis based on 1001bp and 274 parsimony informative characters recovered the most resolved phylogeny with >70% bootstrap support for associations among species. The Atlantic P. charlestoni consistently clusters nested within the Indian Ocean clade, and the mtDNA sequence divergence between the two most distant species is 8.24%. If the northward collision of Africa with Eurasia in the Miocene caused the final physical separation between the Atlantic and Indian Ocean taxa, then the Palinurus mtDNA (COI and 16S combined) evolved no faster than 0.18% (lower bound) to 0.36% (upper bound) per lineage per million years. The six extant species occur in the pathways of the North Atlantic and South Indian Ocean gyres, and hypotheses on their radiation are developed relative to the strengthening of boundary currents in the Miocene and life history traits congruent with survival in strong ocean currents.

  1. Vertical Distribution of Bacterial Communities in the Indian Ocean as Revealed by Analyses of 16S rRNA and nasA Genes.

    PubMed

    Jiang, Xuexia; Jiao, Nianzhi

    2016-09-01

    Bacteria play an important role in the marine biogeochemical cycles. However, research on the bacterial community structure of the Indian Ocean is scarce, particularly within the vertical dimension. In this study, we investigated the bacterial diversity of the pelagic, mesopelagic and bathypelagic zones of the southwestern Indian Ocean (50.46°E, 37.71°S). The clone libraries constructed by 16S rRNA gene sequence revealed that most phylotypes retrieved from the Indian Ocean were highly divergent from those retrieved from other oceans. Vertical differences were observed based on the analysis of natural bacterial community populations derived from the 16S rRNA gene sequences. Based on the analysis of the nasA gene sequences from GenBank database, a pair of general primers was developed and used to amplify the bacterial nitrate-assimilating populations. Environmental factors play an important role in mediating the bacterial communities in the Indian Ocean revealed by canonical correlation analysis.

  2. Observed correlations between aerosol and cloud properties in an Indian Ocean trade cumulus regime

    DOE PAGES

    Pistone, Kristina; Praveen, Puppala S.; Thomas, Rick M.; ...

    2016-04-27

    There are many contributing factors which determine the micro- and macrophysical properties of clouds, including atmospheric vertical structure, dominant meteorological conditions, and aerosol concentration, all of which may be coupled to one another. In the quest to determine aerosol effects on clouds, these potential relationships must be understood. Here we describe several observed correlations between aerosol conditions and cloud and atmospheric properties in the Indian Ocean winter monsoon season.In the CARDEX (Cloud, Aerosol, Radiative forcing, Dynamics EXperiment) field campaign conducted in February and March 2012 in the northern Indian Ocean, continuous measurements were made of atmospheric precipitable water vapor (PWV)more » and the liquid water path (LWP) of trade cumulus clouds, concurrent with measurements of water vapor flux, cloud and aerosol vertical profiles, meteorological data, and surface and total-column aerosol from instrumentation at a ground observatory and on small unmanned aircraft. We present observations which indicate a positive correlation between aerosol and cloud LWP only when considering cases with low atmospheric water vapor (PWV < 40 kg m–2), a criterion which acts to filter the data to control for the natural meteorological variability in the region.We then use the aircraft and ground-based measurements to explore possible mechanisms behind this observed aerosol–LWP correlation. The increase in cloud liquid water is found to coincide with a lowering of the cloud base, which is itself attributable to increased boundary layer humidity in polluted conditions. High pollution is found to correlate with both higher temperatures and higher humidity measured throughout the boundary layer. A large-scale analysis, using satellite observations and meteorological reanalysis, corroborates these covariations: high-pollution cases are shown to originate as a highly polluted boundary layer air mass approaching the observatory from a

  3. Observed correlations between aerosol and cloud properties in an Indian Ocean trade cumulus regime

    NASA Astrophysics Data System (ADS)

    Pistone, Kristina; Praveen, Puppala S.; Thomas, Rick M.; Ramanathan, Veerabhadran; Wilcox, Eric M.; Bender, Frida A.-M.

    2016-04-01

    There are many contributing factors which determine the micro- and macrophysical properties of clouds, including atmospheric vertical structure, dominant meteorological conditions, and aerosol concentration, all of which may be coupled to one another. In the quest to determine aerosol effects on clouds, these potential relationships must be understood. Here we describe several observed correlations between aerosol conditions and cloud and atmospheric properties in the Indian Ocean winter monsoon season.In the CARDEX (Cloud, Aerosol, Radiative forcing, Dynamics EXperiment) field campaign conducted in February and March 2012 in the northern Indian Ocean, continuous measurements were made of atmospheric precipitable water vapor (PWV) and the liquid water path (LWP) of trade cumulus clouds, concurrent with measurements of water vapor flux, cloud and aerosol vertical profiles, meteorological data, and surface and total-column aerosol from instrumentation at a ground observatory and on small unmanned aircraft. We present observations which indicate a positive correlation between aerosol and cloud LWP only when considering cases with low atmospheric water vapor (PWV < 40 kg m-2), a criterion which acts to filter the data to control for the natural meteorological variability in the region.We then use the aircraft and ground-based measurements to explore possible mechanisms behind this observed aerosol-LWP correlation. The increase in cloud liquid water is found to coincide with a lowering of the cloud base, which is itself attributable to increased boundary layer humidity in polluted conditions. High pollution is found to correlate with both higher temperatures and higher humidity measured throughout the boundary layer. A large-scale analysis, using satellite observations and meteorological reanalysis, corroborates these covariations: high-pollution cases are shown to originate as a highly polluted boundary layer air mass approaching the observatory from a northwesterly

  4. Observed correlations between aerosol and cloud properties in an Indian Ocean trade cumulus regime

    SciTech Connect

    Pistone, Kristina; Praveen, Puppala S.; Thomas, Rick M.; Ramanathan, Veerabhadran; Wilcox, Eric M.; Bender, Frida A.-M.

    2016-04-27

    There are many contributing factors which determine the micro- and macrophysical properties of clouds, including atmospheric vertical structure, dominant meteorological conditions, and aerosol concentration, all of which may be coupled to one another. In the quest to determine aerosol effects on clouds, these potential relationships must be understood. Here we describe several observed correlations between aerosol conditions and cloud and atmospheric properties in the Indian Ocean winter monsoon season.

    In the CARDEX (Cloud, Aerosol, Radiative forcing, Dynamics EXperiment) field campaign conducted in February and March 2012 in the northern Indian Ocean, continuous measurements were made of atmospheric precipitable water vapor (PWV) and the liquid water path (LWP) of trade cumulus clouds, concurrent with measurements of water vapor flux, cloud and aerosol vertical profiles, meteorological data, and surface and total-column aerosol from instrumentation at a ground observatory and on small unmanned aircraft. We present observations which indicate a positive correlation between aerosol and cloud LWP only when considering cases with low atmospheric water vapor (PWV < 40 kg m–2), a criterion which acts to filter the data to control for the natural meteorological variability in the region.

    We then use the aircraft and ground-based measurements to explore possible mechanisms behind this observed aerosol–LWP correlation. The increase in cloud liquid water is found to coincide with a lowering of the cloud base, which is itself attributable to increased boundary layer humidity in polluted conditions. High pollution is found to correlate with both higher temperatures and higher humidity measured throughout the boundary layer. A large-scale analysis, using satellite observations and meteorological reanalysis, corroborates these covariations: high-pollution cases are shown to originate as a highly polluted boundary layer air mass approaching the

  5. A high-resolution, absolute-dated deglacial speleothem record of Indian Ocean climate from Socotra Island, Yemen

    NASA Astrophysics Data System (ADS)

    Shakun, Jeremy D.; Burns, Stephen J.; Fleitmann, Dominik; Kramers, Jan; Matter, Albert; Al-Subary, Abdulkarim

    2007-07-01

    Stalagmite M1-5 from Socotra Island, Yemen in the northwest Indian Ocean provides a robust, high-resolution paleoclimate record from ˜ 27.4-11.1 ka based on 717 stable isotope and 28 230Th measurements. Variations in M1-5 oxygen isotope ratios ( δ18O) are interpreted to be primarily driven by an amount effect related to changes in the mean position and/or intensity of convection of the intertropical convergence zone, the island's only source of precipitation. The M1-5 δ18O time series is strongly correlated to the Greenland ice cores, similar to an older Socotra speleothem deposited from 53-40 ka [S.J. Burns, D. Fleitmann, A. Matter, J. Kramers, A. Al-Subbary, Indian Ocean climate and an absolute chronology over Dansgaard/Oeschger events 9 to 13, Science 301 (2003) 1365-1367], indicating that a North Atlantic-Indian Ocean cold-dry/warm-wet teleconnection persisted through the end of the last glacial period. Peak aridification occurred at ˜ 23 ka and a gradual increase in moisture thereafter was interrupted by an abrupt drying event at ˜ 16.4 ka, perhaps related to Heinrich event 1. Indian Ocean rainfall increased dramatically during the Bølling period and then decreased continuously and gradually through the Allerød and Younger Dryas. The Holocene began abruptly with increased precipitation at 11.4 ka and was followed by a major but short-lived drying during the Preboreal Oscillation at ˜ 11.2 ka. M1-5 is highly correlated to the Dongge Cave record from 15.5-11 ka, suggesting much of the Indian Ocean monsoon region responded similarly to the major climate changes of the last deglaciation. The transitions into the Younger Dryas and to a lesser extent the Bølling are remarkably gradual in M1-5, as they are in all other Asian speleothem records, occurring over several centuries. These gradual transitions are in striking contrast to high-resolution records from around the North Atlantic basin where the transitions are extremely abrupt and generally occur in

  6. Submarine structure of Reunion Island (Indian Ocean) inferred from gravity

    NASA Astrophysics Data System (ADS)

    Gailler, L.; Lénat, J.

    2008-12-01

    La Reunion is a large (diameter: 220 km; height: 7 km), mostly immerged (97%) oceanic volcanic system. New land and marine gravity data are used to study the structure of its submarine part. The gravity models are interpreted jointly with the published geology interpretations and compared with magnetic models. This allows us to derive a new model of the shallow and internal structure of the submarine flanks. Recent cruises have collected high quality gravity, magnetic and multi-beam swath bathymetry data over the submarine flanks of La Réunion and the surrounding oceanic plate. A new Bouguer anomaly map has been computed for a reduction density of 2.67.103 kg m-3. A magnetic anomalies map covering the same area has been also built. Studies based on bathymetric and acoustic data have previously shown the presence of different types of submarine features: a coastal shelf, huge bulges built by debris avalanches and sediment deposits, erosion canyons, volcanic constructions near the coast, isolated seamounts offshore, and elongate volcanic ridges on the Mascarene plate. On the new Bouguer anomaly map, all these features are associated with negative anomalies. They have been modeled using 2 3/4 D modeling techniques. The short wavelength anomalies over the coastal shelf area can be explained by piles of low density layers. This suggests that they are mostly built by hyaloclastites which are generally characterized by lower densities than lava flows. The voluminous debris avalanche deposits which formed the huge Submarine Bulges to the east, north, west, and south of the island have also been modeled as low density formations. Each bulge is modeled with an overall density less than 2.67.103 kg m-3, in order to account for its long wavelength anomaly. Some shorter wavelength features are superimposed on these long wavelength negative anomalies. They probably represent heterogeneities within the bulges. Some shallow ones can be associated with observed surface geological

  7. The ocean floor morphostructure of the Bay of Bengal (Indian Ocean) and the problem of its origin

    NASA Astrophysics Data System (ADS)

    Illarionov, V. K.; Boyko, A. N.; Udintsev, G. B.

    2016-05-01

    This study is based on the geological and geophysical data obtained in the Bay of Bengal and adjacent part of the Mid-Indian Ocean Basin by different Russian scientific and industrial institutions in the 1980s and 1990s. The results of the more recent foreign investigations are also involved. The analysis of the collected data provided a new insight into the geological structure and evolution of the region indicating that a large dry-land area—the Bengal elevation—existed in the Cretaceous at the location of the present-day Bay of Bengal. During the Cretaceous, the geological evolution of this area was controlled by epicontinental sedimentation and active volcanism. In the Late Cretaceous, progressive submersion with the inception of the Central Basin took place in the region. The subsidence of the basement was accompanied by active differentiated tectonic movements in the southern part of the Bay of Bengal. As a result, the basement experienced fragmentation into blocks with the formation of horst and graben structures. The horst relics eventually submerged to the current depths in the Late Miocene-Pliocene. The maximal amplitude of basement submersion within the bay is more than 11 km.

  8. More-frequent extreme northward shifts of eastern Indian Ocean tropical convergence under greenhouse warming

    PubMed Central

    Weller, Evan; Cai, Wenju; Min, Seung-Ki; Wu, Lixin; Ashok, Karumuri; Yamagata, Toshio

    2014-01-01

    The Intertropical Convergence Zone (ITCZ) in the tropical eastern Indian Ocean exhibits strong interannual variability, often co-occurring with positive Indian Ocean Dipole (pIOD) events. During what we identify as an extreme ITCZ event, a drastic northward shift of atmospheric convection coincides with an anomalously strong north-minus-south sea surface temperature (SST) gradient over the eastern equatorial Indian Ocean. Such shifts lead to severe droughts over the maritime continent and surrounding islands but also devastating floods in southern parts of the Indian subcontinent. Understanding future changes of the ITCZ is therefore of major scientific and socioeconomic interest. Here we find a more-than-doubling in the frequency of extreme ITCZ events under greenhouse warming, estimated from climate models participating in the Coupled Model Intercomparison Project phase 5 that are able to simulate such events. The increase is due to a mean state change with an enhanced north-minus-south SST gradient and a weakened Walker Circulation, facilitating smaller perturbations to shift the ITCZ northwards. PMID:25124737

  9. More-frequent extreme northward shifts of eastern Indian Ocean tropical convergence under greenhouse warming.

    PubMed

    Weller, Evan; Cai, Wenju; Min, Seung-Ki; Wu, Lixin; Ashok, Karumuri; Yamagata, Toshio

    2014-08-15

    The Intertropical Convergence Zone (ITCZ) in the tropical eastern Indian Ocean exhibits strong interannual variability, often co-occurring with positive Indian Ocean Dipole (pIOD) events. During what we identify as an extreme ITCZ event, a drastic northward shift of atmospheric convection coincides with an anomalously strong north-minus-south sea surface temperature (SST) gradient over the eastern equatorial Indian Ocean. Such shifts lead to severe droughts over the maritime continent and surrounding islands but also devastating floods in southern parts of the Indian subcontinent. Understanding future changes of the ITCZ is therefore of major scientific and socioeconomic interest. Here we find a more-than-doubling in the frequency of extreme ITCZ events under greenhouse warming, estimated from climate models participating in the Coupled Model Intercomparison Project phase 5 that are able to simulate such events. The increase is due to a mean state change with an enhanced north-minus-south SST gradient and a weakened Walker Circulation, facilitating smaller perturbations to shift the ITCZ northwards.

  10. Vertical profiles of optical and microphysical particle properties above the northern Indian Ocean during CARDEX 2012

    NASA Astrophysics Data System (ADS)

    Höpner, F.; Bender, F. A.-M.; Ekman, A. M. L.; Praveen, P. S.; Bosch, C.; Ogren, J. A.; Andersson, A.; Gustafsson, Ö.; Ramanathan, V.

    2016-01-01

    A detailed analysis of optical and microphysical properties of aerosol particles during the dry winter monsoon season above the northern Indian Ocean is presented. The Cloud Aerosol Radiative Forcing Experiment (CARDEX), conducted from 16 February to 30 March 2012 at the Maldives Climate Observatory on Hanimaadhoo island (MCOH) in the Republic of the Maldives, used autonomous unmanned aerial vehicles (AUAV) to perform vertical in situ measurements of particle number concentration, particle number size distribution as well as particle absorption coefficients. These measurements were used together with surface- based Mini Micro Pulse Lidar (MiniMPL) observations and aerosol in situ and off-line measurements to investigate the vertical distribution of aerosol particles.Air masses were mainly advected over the Indian subcontinent and the Arabian Peninsula. The mean surface aerosol number concentration was 1717 ± 604 cm-3 and the highest values were found in air masses from the Bay of Bengal and Indo-Gangetic Plain (2247 ± 370 cm-3). Investigations of the free tropospheric air showed that elevated aerosol layers with up to 3 times higher aerosol number concentrations than at the surface occurred mainly during periods with air masses originating from the Bay of Bengal and the Indo-Gangetic Plain. This feature is different compared to what was observed during the Indian Ocean Experiment (INDOEX) conducted in winter 1999, where aerosol number concentrations generally decreased with height. In contrast, lower particle absorption at the surface (σabs(520 nm) = 8.5 ± 4.2 Wm-1) was found during CARDEX compared to INDOEX 1999.Layers with source region specific single-scattering albedo (SSA) values were derived by combining vertical in situ particle absorption coefficients and scattering coefficients calculated with Mie theory. These SSA layers were utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for 550 nm for dry

  11. Analysis of Coseismic Fault Slip Models of the 2012 Indian Ocean Earthquake: Importance of GPS Data for Crustal Deformation Studies

    NASA Astrophysics Data System (ADS)

    Gunawan, Endra; Maulida, Putra; Meilano, Irwan; Irsyam, Masyhur; Efendi, Joni

    2016-12-01

    Based on continuous GPS data, we analyze coseismic deformation due to the 2012 Indian Ocean earthquake. We use the available coseismic slip models of the 2012 earthquake, derived from geodetic and/or seismic waveform inversion, to calculate the coseismic displacements in the Andaman-Nicobar, Sumatra and Java. In our analysis, we employ a spherical, layered model of the Earth and we find that Java Island experienced coseismic displacements up to 8 mm, as also observed by our GPS network. Compared to coseismic offsets measured from GPS data, a coseismic slip model derived from multiple observations produced better results than a model based on a single type of observation.

  12. Interaction of the Reunion hotspot and the Central Indian Ridge near Rodrigues Island (Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Dyment, J.; Hémond, C.; Bissessur, D.; Scientific Party, Cruises Magofond 2; Gimnaut Scientific Party, Cruise; Knox11RR Scientific Party, Cruise

    2009-04-01

    Reunion hotspot is often viewed as a typical intraplate hotspot, which can be traced back along the southern Mascarene Plateau and the Chagos - Laccadive Ridge to the Deccan flood basalt, caused by the inception of a mantle plume head by the Indian lithosphere. The Rodrigues Ridge, an E-W trending structure more than 600 km-long and 2500 m-high above the seafloor, and small volcanic features that extend it up to the Central Indian Ridge axis at 19°S, do not fit well into this scheme and more probably correspond to the manifestation of an interaction of the Reunion hotspot with the Central Indian Ridge. In this talk we present bathymetric, geophysical and geochemical evidences for such a ridge-hotspot interaction as provided by the analysis of data and samples collected by cruises Magofond 2 of R/V Marion Dufresne (IPEV, France), Gimnaut of R/V L'Atalante with deep-sea submersible Nautile (IFREMER, France), and KNOX11RR of R/V Revelle (Scripps Institution of Oceanography, USA). The reality of the ridge hotspot interaction is substantiated by the shallow bathymetry and the "hot" morphology of the Central Indian Ridge, as well as the presence of volcanic ridges - the Rodrigues, Three Magi and Gasitao ridges - which exhibit isotopic signatures intermediate between those of the Reunion hotspot and MORB. The few age determinations obtained on the Rodrigues Ridge and its eastern extension suggest synchronous pulses of activity on the hotspot and the region of interaction with the spreading centre: the first pulse, between 12 and 8 Ma, corresponds to the shield volcano building of Mauritius Island and the formation of the Rodrigues Ridge, whereas the second pulse, since about 2 Ma, results in the building of Reunion Island, the formation of Rodrigues Island, Three Magi and Gasitao ridges close to the Central Indian Ridge. These pulses are further confirmed by the detailed evolution of the ridge segmentation of the Central Indian Ridge for the last 10 Ma, deciphered from

  13. Evaluation of CMIP5 models on sea surface salinity in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Fathrio, Ibnu; Manda, Atsuyoshi; Iizuka, Satoshi; Kodama, Yasu-Masa; Ishida, Sachinobu

    2017-01-01

    Prior to future climate assessment of the 5th Coupled Model Intercomparison (CMIP5) experiments, how well CMIP5 models simulates present climate should be examined. Sea surface salinity (sss) play important role in ocean stratification and indirectly affects air sea interaction. However, few studies have been carried out to evaluate sss in CMIP5 models. In this study, performance of CMIP5 models in simulating sss in Indian Ocean was examined with respect to the observation. Our results showed that multi model ensemble (MME) mean of CMIP5 models displayed annual and seasonal salinity bias in three regions i.e. Western Indian Ocean (WIO), Bay of Bengal (BOB) and Southeastern Indian Ocean (SEIO). CMIP5 models overestimate sss in BOB about 1.5 psu and underestimated sss in WIO and SEIO about 0.4 psu. Biases in WIO and BOB were mainly attributed to bias in precipitation. CMIP5 models overestimated (underestimated) precipitation in WIO (BOB) with greater bias found during Boreal summer to winter. Meanwhile, advection process was responsible for negative SSS bias in SEIO.

  14. A new dipole index of the salinity anomalies of the tropical Indian Ocean.

    PubMed

    Li, Junde; Liang, Chujin; Tang, Youmin; Dong, Changming; Chen, Dake; Liu, Xiaohui; Jin, Weifang

    2016-04-07

    With the increased interest in studying the sea surface salinity anomaly (SSSA) of the tropical Indian Ocean during the Indian Ocean Dipole (IOD), an index describing the dipole variability of the SSSA has been pursued recently. In this study, we first use a regional ocean model with a high spatial resolution to produce a high-quality salinity simulation during the period from 1982 to 2014, from which the SSSA dipole structure is identified for boreal autumn. On this basis, by further analysing the observed data, we define a dipole index of the SSSA between the central equatorial Indian Ocean (CEIO: 70°E-90°E, 5°S-5°N) and the region off the Sumatra-Java coast (SJC: 100°E-110°E, 13°S-3°S). Compared with previous SSSA dipole indices, this index has advantages in detecting the dipole signals and in characterizing their relationship to the sea surface temperature anomaly (SSTA) dipole variability. Finally, the mechanism of the SSSA dipole is investigated by dynamical diagnosis. It is found that anomalous zonal advection dominates the SSSA in the CEIO region, whereas the SSSA in the SJC region are mainly influenced by the anomalous surface freshwater flux. This SSSA dipole provides a positive feedback to the formation of the IOD events.

  15. Indian Ocean sea surface temperature variability and change since 1960s: forcing and process

    NASA Astrophysics Data System (ADS)

    Han, W.; Meehl, G. A.; Hu, A.

    2005-12-01

    Indian Ocean sea surface temperature (SST) variability and change since 1960s are investigated using global coupled models,the Community Climate System Model version 3 (CCSM3) and parallel climate model (PCM). Results from the CCSM3 and a series of PCM experiments are analyzed in order to understand the roles played by internal variability, human-induced warming, and external forcing in causing the SST variations. To consolidate the model results, the simple Ocean model Data Assimilation (SODA) products are also analyzed. The results suggest that the SST in both the south and north Indian Ocean (IO) has an increasing trend. Overlying on this trend is decadal variability. Consistent with previous studies, the warming trend results mainly from the human-induced increased green house gases, which increase downward longwave fluxes. Interestingly, warming of the upper tropical and subtropical basins is accomanied by cooling in higher-latitudes in the Antarctic Circumpolar Current (ACC) region, which results from the reduced southward heat transports by weakened the subtropical cells (STCs). This colder, ACC water can enter the IO via deep layers in the south and then shoals upward to the thermocline layer in the tropical Indian Ocean, causing a distinct vertical structrure: with warming in the near surface and below the thermocline and cooling in the thermocline. The SST decadal variability, however, is caused primarily by external forcing, due to a combined effect of surface heat flux and lateral heat transport. Internal variability of the coupled system also plays a role.

  16. Causes for the reversal of North Indian Ocean decadal sea level trend in recent two decades

    NASA Astrophysics Data System (ADS)

    Srinivasu, U.; Ravichandran, M.; Han, Weiqing; Sivareddy, S.; Rahman, H.; Li, Yuanlong; Nayak, Shailesh

    2017-03-01

    Using satellite and in-situ observations, ocean reanalysis products and model simulations, we show a distinct reversal of the North Indian Ocean (NIO, north of 5°S) sea level decadal trend between 1993-2003 and 2004-3013, after the global mean sea level rise is removed. Sea level falls from 1993 to 2003 (Period I) but rises sharply from 2004 to 2013 (Period II). Steric height, which is dominated by thermosteric sea level of the upper 700 m, explains most of the observed reversal, including the spatial patterns of sea level change. The decadal change of surface turbulent heat flux acts in concert with the change of meridional heat transport at 5°S, with both being driven by decadal change of surface winds over the Indian Ocean, to cause sea level fall during Period I and rise during Period II. While the effect of surface net heat flux is consistent among various data sets, the uncertainty is larger for meridional heat transport, which shows both qualitative and quantitative differences amongst different reanalyses. The effect of the Indonesian Throughflow on heat content and thus thermosteric sea level is limited to the South Indian Ocean, and has little influence on the NIO. Our new results point to the importance of surface winds in causing decadal sea level change of the NIO.

  17. A new dipole index of the salinity anomalies of the tropical Indian Ocean

    PubMed Central

    Li, Junde; Liang, Chujin; Tang, Youmin; Dong, Changming; Chen, Dake; Liu, Xiaohui; Jin, Weifang

    2016-01-01

    With the increased interest in studying the sea surface salinity anomaly (SSSA) of the tropical Indian Ocean during the Indian Ocean Dipole (IOD), an index describing the dipole variability of the SSSA has been pursued recently. In this study, we first use a regional ocean model with a high spatial resolution to produce a high-quality salinity simulation during the period from 1982 to 2014, from which the SSSA dipole structure is identified for boreal autumn. On this basis, by further analysing the observed data, we define a dipole index of the SSSA between the central equatorial Indian Ocean (CEIO: 70°E-90°E, 5°S-5°N) and the region off the Sumatra-Java coast (SJC: 100°E-110°E, 13°S-3°S). Compared with previous SSSA dipole indices, this index has advantages in detecting the dipole signals and in characterizing their relationship to the sea surface temperature anomaly (SSTA) dipole variability. Finally, the mechanism of the SSSA dipole is investigated by dynamical diagnosis. It is found that anomalous zonal advection dominates the SSSA in the CEIO region, whereas the SSSA in the SJC region are mainly influenced by the anomalous surface freshwater flux. This SSSA dipole provides a positive feedback to the formation of the IOD events. PMID:27052319

  18. A new dipole index of the salinity anomalies of the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Li, Junde; Liang, Chujin; Tang, Youmin; Dong, Changming; Chen, Dake; Liu, Xiaohui; Jin, Weifang

    2016-04-01

    With the increased interest in studying the sea surface salinity anomaly (SSSA) of the tropical Indian Ocean during the Indian Ocean Dipole (IOD), an index describing the dipole variability of the SSSA has been pursued recently. In this study, we first use a regional ocean model with a high spatial resolution to produce a high-quality salinity simulation during the period from 1982 to 2014, from which the SSSA dipole structure is identified for boreal autumn. On this basis, by further analysing the observed data, we define a dipole index of the SSSA between the central equatorial Indian Ocean (CEIO: 70°E-90°E, 5°S-5°N) and the region off the Sumatra-Java coast (SJC: 100°E-110°E, 13°S-3°S). Compared with previous SSSA dipole indices, this index has advantages in detecting the dipole signals and in characterizing their relationship to the sea surface temperature anomaly (SSTA) dipole variability. Finally, the mechanism of the SSSA dipole is investigated by dynamical diagnosis. It is found that anomalous zonal advection dominates the SSSA in the CEIO region, whereas the SSSA in the SJC region are mainly influenced by the anomalous surface freshwater flux. This SSSA dipole provides a positive feedback to the formation of the IOD events.

  19. Drying of Indian subcontinent by rapid Indian Ocean warming and a weakening land-sea thermal gradient.

    PubMed

    Roxy, Mathew Koll; Ritika, Kapoor; Terray, Pascal; Murtugudde, Raghu; Ashok, Karumuri; Goswami, B N

    2015-06-16

    There are large uncertainties looming over the status and fate of the South Asian summer monsoon, with several studies debating whether the monsoon is weakening or strengthening in a changing climate. Our analysis using multiple observed datasets demonstrates a significant weakening trend in summer rainfall during 1901-2012 over the central-east and northern regions of India, along the Ganges-Brahmaputra-Meghna basins and the Himalayan foothills, where agriculture is still largely rain-fed. Earlier studies have suggested an increase in moisture availability and land-sea thermal gradient in the tropics due to anthropogenic warming, favouring an increase in tropical rainfall. Here we show that the land-sea thermal gradient over South Asia has been decreasing, due to rapid warming in the Indian Ocean and a relatively subdued warming over the subcontinent. Using long-term observations and coupled model experiments, we provide compelling evidence that the enhanced Indian Ocean warming potentially weakens the land-sea thermal contrast, dampens the summer monsoon Hadley circulation, and thereby reduces the rainfall over parts of South Asia.

  20. An ancient slab visible from the transition zone to the deep mantle beneath the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Sandvol, E. A.; Skobeltsyn, G.; Turkelli, N.; Polat, G.; Yetirmishli, G.; Godoladze, T.; Mellors, R. J.; Gok, R.

    2014-12-01

    Ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia including some that subducted before the end of the Mesozoic Era. It is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the southern hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle transition zone to the core-mantle boundary region - with striking similarities to past and current images of the Farallon slab. Based on the image and additional geoscientific observations, we postulate that the structure is an oceanic plate that sank into the mantle along a 7000-km intra-oceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era, perhaps beginning prior to 200 Ma. Slab material still trapped in the transition zone is positioned near the former edge of East Gondwana ca. 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents. If our interpretation is correct, the slab likely represents the first of its kind with extensive transition zone stagnation (exceeding 100 million years) followed by eventual penetration into the lower mantle. It suggests that some slabs may sink through the mantle much slower than previously believed and may reside intact in the shallow mantle if left undisturbed by subsequent subduction episodes. We postulate other dynamic mechanisms that may be involved and a potential link to Indian Ocean MORB chemistry. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-675725

  1. An ancient slab visible from the transition zone to the deep mantle beneath the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Simmons, N. A.; Myers, S.; Johannesson, G.; Matzel, E.; Grand, S.

    2015-12-01

    Ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia including some that subducted before the end of the Mesozoic Era. It is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the southern hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle transition zone to the core-mantle boundary region - with striking similarities to past and current images of the Farallon slab. Based on the image and additional geoscientific observations, we postulate that the structure is an oceanic plate that sank into the mantle along a 7000-km intra-oceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era, perhaps beginning prior to 200 Ma. Slab material still trapped in the transition zone is positioned near the former edge of East Gondwana ca. 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents. If our interpretation is correct, the slab likely represents the first of its kind with extensive transition zone stagnation (exceeding 100 million years) followed by eventual penetration into the lower mantle. It suggests that some slabs may sink through the mantle much slower than previously believed and may reside intact in the shallow mantle if left undisturbed by subsequent subduction episodes. We postulate other dynamic mechanisms that may be involved and a potential link to Indian Ocean MORB chemistry. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-675725

  2. Atmospheric response to Indian Ocean Dipole forcing: changes of Southeast China winter precipitation under global warming

    NASA Astrophysics Data System (ADS)

    Zhang, Ling; Sielmann, Frank; Fraedrich, Klaus; Zhi, Xiefei

    2016-05-01

    To investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the subsequent winter precipitation in Southeast China (SEC), observed fields of monthly precipitation, sea surface temperature (SST) and atmospheric circulation are subjected to a running and a maximum correlation analysis. The results show a significant change of the relevance of IOD for the early modulation of SEC winter precipitation in the 1980s. After 1980, positive correlations suggest prolonged atmospheric responses to IOD forcing, which are linked to an abnormal moisture supply initiated in autumn and extended into the subsequent winter. Under global warming two modulating factors are relevant: (1) an increase of the static stability has been observed suppressing vertical heat and momentum transports; (2) a positive (mid-level) cloud-radiation feedback jointly with the associated latent heating (apparent moisture sink Q2) explains the prolongation of positive as well as negative SST anomalies by conserving the heating (apparent heat source Q1) in the coupled atmosphere-ocean system. During the positive IOD events in fall (after 1980) the dipole heating anomalies in the middle and lower troposphere over the tropical Indian Ocean are prolonged to winter by a positive mid-level cloud-radiative feedback with latent heat release. Subsequently, thermal adaptation leads to an anticyclonic anomaly over Eastern India overlying the anomalous cooling SST of the tropical Eastern Indian Ocean enhancing the moisture flow from the tropical Indian Ocean through the Bay of Bengal into South China, following the northwestern boundary of the anticyclonic circulation anomaly over east India, thereby favoring abundant precipitation in SEC.

  3. Atmospheric response to Indian Ocean Dipole forcing: changes of Southeast China winter precipitation under global warming

    NASA Astrophysics Data System (ADS)

    Zhang, Ling; Sielmann, Frank; Fraedrich, Klaus; Zhi, Xiefei

    2017-03-01

    To investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the subsequent winter precipitation in Southeast China (SEC), observed fields of monthly precipitation, sea surface temperature (SST) and atmospheric circulation are subjected to a running and a maximum correlation analysis. The results show a significant change of the relevance of IOD for the early modulation of SEC winter precipitation in the 1980s. After 1980, positive correlations suggest prolonged atmospheric responses to IOD forcing, which are linked to an abnormal moisture supply initiated in autumn and extended into the subsequent winter. Under global warming two modulating factors are relevant: (1) an increase of the static stability has been observed suppressing vertical heat and momentum transports; (2) a positive (mid-level) cloud-radiation feedback jointly with the associated latent heating (apparent moisture sink Q2) explains the prolongation of positive as well as negative SST anomalies by conserving the heating (apparent heat source Q1) in the coupled atmosphere-ocean system. During the positive IOD events in fall (after 1980) the dipole heating anomalies in the middle and lower troposphere over the tropical Indian Ocean are prolonged to winter by a positive mid-level cloud-radiative feedback with latent heat release. Subsequently, thermal adaptation leads to an anticyclonic anomaly over Eastern India overlying the anomalous cooling SST of the tropical Eastern Indian Ocean enhancing the moisture flow from the tropical Indian Ocean through the Bay of Bengal into South China, following the northwestern boundary of the anticyclonic circulation anomaly over east India, thereby favoring abundant precipitation in SEC.

  4. Seasonal Variability of Salt Transport During the Indian Ocean Monsoons

    DTIC Science & Technology

    2011-08-27

    influence of precipitation (P), evaporation (E), river runofT(R), advection and mixing [Wijffels et al, 1992; Han and McCreary , 2001; Prasad and...enced by water circulation and ocean-atmosphere coupled interactions such as the Maddcn- Julian Oscillation (MJO) [Joseph and Freeland, 2005]. As a...1997; Schott and McCreary , 2001]. The Somali Current also flows northward into the AS. During this season too, the humid southwesterly winds from the

  5. Southwestern limits of Indian Ocean Ridge mantle and the origin of low Pb-206/Pb-204 mid-ocean ridge basalt - Isotope systematics of the central Southwest Indian Ridge (17 deg - 50 deg E)

    NASA Astrophysics Data System (ADS)

    Mahoney, J.; Le Roex, A. P.; Peng, Z.; Fisher, R. L.; Natland, J. H.

    1992-12-01

    The isotopic characteristics of the Indian Ocean Ridge midocean ridge basalts (MORBs) and of the Atlantic and the Pacific MORBs (north of 25 deg S) were determined in order to estimate the southwestern limits of the Indian Ocean Ridge mantle and the origin of low Pb-206/Pb-204 MORB. In view of the possible importance of a Marion-type mantle along portions of the ridge, lavas from several Marion Island, Prince Edward Island, and Funk Seamount were also analyzed isotopically. The isotopic results include analyses of fields for the Indian Ocean triple junction area, the entire Central Indian and southern Carlsberg ridges, for several oceanic islands, and Pacific and/or North Atlantic MORBs.

  6. Performance report of the RHUM-RUM ocean bottom seismometer network around La Réunion, western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Stähler, S. C.; Sigloch, K.; Hosseini, K.; Crawford, W. C.; Barruol, G.; Schmidt-Aursch, M. C.; Tsekhmistrenko, M.; Scholz, J.-R.; Mazzullo, A.; Deen, M.

    2016-02-01

    RHUM-RUM is a German-French seismological experiment based on the sea floor surrounding the island of La Réunion, western Indian Ocean (Barruol and Sigloch, 2013). Its primary objective is to clarify the presence or absence of a mantle plume beneath the Reunion volcanic hotspot. RHUM-RUM's central component is a 13-month deployment (October 2012 to November 2013) of 57 broadband ocean bottom seismometers (OBS) and hydrophones over an area of 2000 × 2000 km2 surrounding the hotspot. The array contained 48 wideband OBS from the German DEPAS pool and 9 broadband OBS from the French INSU pool. It is the largest deployment of DEPAS and INSU OBS so far, and the first joint experiment. This article reviews network performance and data quality: of the 57 stations, 46 and 53 yielded good seismometer and hydrophone recordings, respectively. The 19 751 total deployment days yielded 18 735 days of hydrophone recordings and 15 941 days of seismometer recordings, which are 94 and 80 % of the theoretically possible yields. The INSU seismic sensors stand away from their OBS frames, whereas the DEPAS sensors are integrated into their frames. At long periods (> 10 s), the DEPAS seismometers are affected by significantly stronger noise than the INSU seismometers. On the horizontal components, this can be explained by tilting of the frame and buoy assemblage, e.g. through the action of ocean-bottom currents, but in addition the DEPAS intruments are affected by significant self-noise at long periods, including on the vertical channels. By comparison, the INSU instruments are much quieter at periods > 30 s and hence better suited for long-period signals studies. The trade-off of the instrument design is that the integrated DEPAS setup is easier to deploy and recover, especially when large numbers of stations are involved. Additionally, the wideband sensor has only half the power consumption of the broadband INSU seismometers. For the first time, this article publishes response

  7. Evaluating 20th century warming trends with modern Porites corals from the western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Pfeiffer, M.; Zinke, J.; Dullo, W.-C.; Cahyarini, S. Y.

    2009-04-01

    Recent studies suggest that instrumental records of sea surface temperature (SST) are unreliable prior to 1965 due to changes in the measurement procedures. Thompson et al. (2008) identified an artificial cool bias of up to 0.3˚ C in global mean SSTs between 1945 and the mid-1960s. Geochemical parameters in skeletons of massive corals can be used to infer past changes in climate on seasonal to centennial time scales. The Sr/Ca ratio of coral aragonite is a widely used tool for deriving high-resolution proxy records of past sea surface temperatures. Application of the Sr/Ca paleothermometer relies on the assumption that coral Sr/Ca varies predictably with temperature and that seawater Sr/Ca is invariant on millennial timescales due to the long residence time of Sr and Ca in the ocean. In contrast, the oxygen isotope ratios (^18O) of coral aragonite vary in response to temperature and changes in the ^18O of seawater, the latter depending on the freshwater balance. Thus, coral ^18O may be used as a record of past sea surface temperatures only at sites were ^18O seawater variations are negligible. SST in the western tropical Indian Ocean closely follows global mean temperature trends (Funk et al., 2008). Here we present a set of Porites coral Sr/Ca and/or oxygen isotope records from the tropical Indian Ocean covering the past 120-336 years (Seychelles, Chagos Archipelago). We computed a composite sea surface temperature record for the Western Indian Ocean using ^18O (Seychelles) and Sr/Ca (Chagos). This record clearly follows instrumental SST trends in the Western tropical Indian Ocean, except in the 1945-1965 interval, were instrumental SST data show a pronounced cooling not evident in the coral proxy index (the linear correlation coefficient between the coral index and instrumental SST is r=0.86 if we omit the most problematic time period from 1945 to 1960). However, the coral index follows the global land surface air temperature trend, which is free of systematic

  8. Calls reveal population structure of blue whales across the southeast Indian Ocean and the southwest Pacific Ocean

    PubMed Central

    Balcazar, Naysa E.; Tripovich, Joy S.; Klinck, Holger; Nieukirk, Sharon L.; Mellinger, David K.; Dziak, Robert P.; Rogers, Tracey L.

    2015-01-01

    For effective species management, understanding population structure and distribution is critical. However, quantifying population structure is not always straightforward. Within the Southern Hemisphere, the blue whale (Balaenoptera musculus) complex is extremely diverse but difficult to study. Using automated detector methods, we identified “acoustic populations” of whales producing region-specific call types. We examined blue whale call types in passive acoustic data at sites spanning over 7,370 km across the southeast Indian Ocean and southwest Pacific Ocean (SWPO) from 2009 to 2012. In the absence of genetic resolution, these acoustic populations offer unique information about the blue whale population complex. We found that the Australian continent acts as a geographic boundary, separating Australia and New Zealand blue whale acoustic populations at the junction of the Indian and Pacific Ocean basins. We located blue whales in previously undocumented locations, including the far SWPO, in the Tasman Sea off the east coast of Australia, and along the Lau Basin near Tonga. Our understanding of population dynamics across this broad scale has significant implications to recovery and conservation management for this endangered species, at a regional and global scale. PMID:26989263

  9. Calls reveal population structure of blue whales across the southeast Indian Ocean and the southwest Pacific Ocean.

    PubMed

    Balcazar, Naysa E; Tripovich, Joy S; Klinck, Holger; Nieukirk, Sharon L; Mellinger, David K; Dziak, Robert P; Rogers, Tracey L

    2015-11-24

    For effective species management, understanding population structure and distribution is critical. However, quantifying population structure is not always straightforward. Within the Southern Hemisphere, the blue whale (Balaenoptera musculus) complex is extremely diverse but difficult to study. Using automated detector methods, we identified "acoustic populations" of whales producing region-specific call types. We examined blue whale call types in passive acoustic data at sites spanning over 7,370 km across the southeast Indian Ocean and southwest Pacific Ocean (SWPO) from 2009 to 2012. In the absence of genetic resolution, these acoustic populations offer unique information about the blue whale population complex. We found that the Australian continent acts as a geographic boundary, separating Australia and New Zealand blue whale acoustic populations at the junction of the Indian and Pacific Ocean basins. We located blue whales in previously undocumented locations, including the far SWPO, in the Tasman Sea off the east coast of Australia, and along the Lau Basin near Tonga. Our understanding of population dynamics across this broad scale has significant implications to recovery and conservation management for this endangered species, at a regional and global scale.

  10. Pelagic cephalopods in the western Indian Ocean: New information from diets of top predators

    NASA Astrophysics Data System (ADS)

    Ménard, Frédéric; Potier, Michel; Jaquemet, Sébastien; Romanov, Evgeny; Sabatié, Richard; Cherel, Yves

    2013-10-01

    Using a combination of diverse large predatory fishes and one seabird, we collected information on the cephalopod fauna of the western Indian Ocean. We analyzed the stomach contents of 35 fishes representing ten families (Xiphiidae, Istiophoridae, Scombridae, Carangidae, Coryphaenidae, Alepisauridae, Dasyatidae, Carcharhinidae, Alopiidae and Sphyrnidae) and of the sooty tern Onychoprion fuscata of the Mozambique Channel from 2000 to 2010. Both fresh and accumulated beaks were used for identifying cephalopod prey. Cephalopods were important prey for twelve predators; swordfish Xiphias gladius had the highest cephalopod proportion; sooty tern (O. fuscata) and bigeye tuna (Thunnus obesus) had high proportions too. We recovered 23 cephalopod families and identified 38 species. Ten species from four Teuthida families (Ommastrephidae, Onychoteuthidae, Histioteuthidae and Ancistrocheiridae) and two Octopoda families (Argonautidae and Bolitaenidae) occurred very frequently in the stomach contents, while Sepiida were rare. Ommastrephidae were the most cephalopod food sources: the purpleback flying squid Sthenoteuthis oualaniensis was the most prevalent prey by far, Ornithoteuthis volatilis was important for eleven predators and few but large specimens of the neon flying squid Ommastrephes bartramii were recovered in the stomachs of swordfish in the Indian South Subtropical Gyre province only. Predators' groups were identified based on cephalopod prey composition, on depth in which they forage, and on prey size. Surface predators' diets were characterized by lower cephalopod diversity but greater average numbers of cephalopod prey, whereas the deep-dwelling predators (swordfish and bigeye tuna) preyed on larger specimens than surface predators (O. fuscata or yellowfin tunas Thunnus albacares). Our findings emphasized the usefulness of a community of marine predators to gain valuable information on the biology and the distribution of the cephalopod forage fauna that are

  11. Growth response of a deep-water ferromanganese crust to evolution of the Neogene Indian Ocean

    USGS Publications Warehouse

    Banakar, V.K.; Hein, J.R.

    2000-01-01

    A deep-water ferromanganese crust from a Central Indian Ocean seamount dated previously by 10Be and 230Th(excess) was studied for compositional and textural variations that occurred throughout its growth history. The 10Be/9Be dated interval (upper 32 mm) yields an uniform growth rate of 2.8 ?? 0.1 mm/Ma [Frank, M., O'Nions, R.K., 1998. Sources of Pb for Indian Ocean ferromanganese crusts: a record of Himalayan erosion. Earth Planet. Sci. Lett., 158, pp. 121-130.] which gives an extrapolated age of ~ 26 Ma for the base of the crust at 72 mm and is comparable to the maximum age derived from the Co-model based growth rate estimates. This study shows that Fe-Mn oxyhydroxide precipitation did not occur from the time of emplacement of the seamount during the Eocene (~ 53 Ma) until the late Oligocene (~ 26 Ma). This paucity probably was the result of a nearly overlapping palaeo-CCD and palaeo-depth of crust formation, increased early Eocene productivity, instability and reworking of the surface rocks on the flanks of the seamount, and lack of oxic deep-water in the nascent Indian Ocean. Crust accretion began (older zone) with the formation of isolated cusps of Fe-Mn oxide during a time of high detritus influx, probably due to the early-Miocene intense erosion associated with maximum exhumation of the Himalayas (op. cit.). This cuspate textured zone extends from 72 mm to 42 mm representing the early-Miocene period. Intense polar cooling and increased mixing of deep and intermediate waters at the close of the Oligocene might have led to the increased oxygenation of the bottom-water in the basin. A considerable expansion in the vertical distance between the seafloor depth and the CCD during the early Miocene in addition to the influx of oxygenated bottom-water likely initiated Fe-Mn crust formation. Pillar structure characterises the younger zone, which extends from 40 mm to the surface of the crust, i.e., ~ 15 Ma to Present. This zone is characterised by > 25% higher

  12. 2nd Radio and Antenna Days of the Indian Ocean (RADIO 2014)

    NASA Astrophysics Data System (ADS)

    2014-10-01

    It was an honor and a great pleasure for all those involved in its organization to welcome the participants to the ''Radio and Antenna Days of the Indian Ocean'' (RADIO 2014) international conference that was held from 7th to 10th April 2014 at the Sugar Beach Resort, Wolmar, Flic-en-Flac, Mauritius. RADIO 2014 is the second of a series of conferences organized in the Indian Ocean region. The aim of the conference is to discuss recent developments, theories and practical applications covering the whole scope of radio-frequency engineering, including radio waves, antennas, propagation, and electromagnetic compatibility. The RADIO international conference emerged following discussions with engineers and scientists from the countries of the Indian Ocean as well as from other parts of the world and a need was felt for the organization of such an event in this region. Following numerous requests, the Island of Mauritius, worldwide known for its white sandy beaches and pleasant tropical atmosphere, was again chosen for the organization of the 2nd RADIO international conference. The conference was organized by the Radio Society, Mauritius and the Local Organizing Committee consisted of scientists from SUPELEC, France, the University of Mauritius, and the University of Technology, Mauritius. We would like to take the opportunity to thank all people, institutions and companies that made the event such a success. We are grateful to our gold sponsors CST and FEKO as well as URSI for their generous support which enabled us to partially support one PhD student and two scientists to attend the conference. We would also like to thank IEEE-APS and URSI for providing technical co-sponsorship. More than hundred and thirty abstracts were submitted to the conference. They were peer-reviewed by an international scientific committee and, based on the reviews, either accepted, eventually after revision, or rejected. RADIO 2014 brought together participants from twenty countries spanning

  13. Impact of prolonged La Niña events on the Indian Ocean with a special emphasis on southwest Tropical Indian Ocean SST

    NASA Astrophysics Data System (ADS)

    Singh, P.; Chowdary, J. S.; Gnanaseelan, C.

    2013-01-01

    This study examines the mechanisms governing the teleconnections associated with the long-lived La Niña variability in the tropical Indian Ocean (TIO) sea surface temperature (SST) anomalies using observational and reanalysis products. Two long-lived La Niña events (1973 to 1976 and 1998 to 2001) are observed in the recent years, one falling before and the other after the mid 1970's climatic shift. The winter (boreal) and spring (November to April) TIO SST is highly influenced by long-lived La Niña forcing. Climatic shift in mid 1970s contributes to the changes in TIO SST pattern during these two long-lived La Niña events. Surface heat flux variations due to long-lived La Niña contribute to the SST changes except in the southwest TIO. The upwelling favorable local surface wind stress curl and upwelling Rossby waves originating from the east are the dominant mechanisms responsible for the La Niña related winter time SST cooling over the southwest TIO. Long-lived La Niña induced surface wind anomalies enhance the fall Wyrtki Jet in the equatorial Indian Ocean resulting large scale anomalous heat transport. Local SST cooling reduces convection and contributes to the low rainfall over southwest TIO and the northern parts of Madagascar Island.

  14. Present-day zonal wind influences projected Indian Ocean Dipole skewness

    NASA Astrophysics Data System (ADS)

    Ng, Benjamin; Cai, Wenju

    2016-11-01

    A prominent feature of the Indian Ocean Dipole (IOD) is its positive skewness, where positive phases tend to be stronger in amplitude than the negative phase. Positive IOD events are associated with devastating floods over parts of East Africa and India, while Australia and Indonesia experience dry conditions. Under greenhouse warming, climate models project a weakening of the positive IOD skewness, but their simulation of present-day skewness is too weak. Here we show that this bias and the projected skewness change are related to the simulation of the climatological zonal wind in the central equatorial Indian Ocean. In particular, models with overly weak present-day westerlies, which is a common model bias, generate overly weak present-day skewness and a smaller projected reduction in skewness. Improving the ability of models in simulating stronger westerly winds may lead to stronger present-day simulated skewness and a larger skewness reduction in a warmer climate.

  15. Feeding ecology of silky sharks Carcharhinus falciformis associated with floating objects in the western Indian Ocean.

    PubMed

    Filmalter, J D; Cowley, P D; Potier, M; Ménard, F; Smale, M J; Cherel, Y; Dagorn, L

    2016-12-14

    The silky shark Carcharhinus falciformis is commonly associated with floating objects, including fish aggregating devices (FADs), in the Indian Ocean. While the motives for this associative behaviour are unclear, it does make them vulnerable to capture in the tuna purse seine fishery that makes extensive use of FADs. Here, the diet of 323 C. falciformis, caught at FADs in the Indian Ocean, was investigated to test the hypothesis that trophic benefits explain the associative behaviour. A high proportion of stomachs with fresh contents (57%) suggested that extensive feeding activity occurred while associated with FADs. Multiple dietary indices showed that typical non-associative prey types dominated, but were supplemented with fishes typically found at FADs. While the trophic benefits of FAD association may be substantial, our results suggest that associative behaviour is not driven solely by feeding.

  16. A new species of Saurida (Pisces: Synodontidae) from the Mascarene Plateau, Western Indian Ocean.

    PubMed

    Russell, Barry C

    2015-04-16

    A new species of lizardfish, Saurida tweddlei n.sp., from the Mascarene Plateau, Western Indian Ocean, is described and figured. The new species is characterised by the following combination of characters: dorsal fin with 12-13 rays; pectorals with 14-15 rays; lateral-line scales 53-55; transverse scale rows above lateral line 4½, below lateral line 5½; pectoral fins moderately long (extending to or just beyond a line from origin of pelvic fins to origin of dorsal fin); 2 rows of teeth on outer palatines; 0-3 teeth on vomer; tongue with about 4-5 rows of teeth posteriorly; caudal peduncle compressed (depth greater than width); stomach and intestine pale whitish. A key to the species of Saurida of the Western Indian Ocean is provided.

  17. [Dengue fever in the Reunion Island and in South Western islands of the Indian Ocean].

    PubMed

    D'Ortenzio, E; Balleydier, E; Baville, M; Filleul, L; Renault, P

    2011-09-01

    South Western islands of the Indian Ocean are permanently threatened by dengue fever outbreaks. On the Reunion Island, two dengue outbreaks were biologically documented (1977-1978 and 2004). And since July 2004 there has been an inter-epidemic period for the island with sporadic cases and clusters. Between January 1, 2007 and October 5, 2009, the epidemiologic surveillance system detected five confirmed autochthonous cases, five confirmed imported cases (South-East Asia), and 71 probable cases. All the five autochthonous confirmed cases occurred in Saint-Louis during two consecutive clusters. In other South Western islands of the Indian Ocean, several dengue fever outbreaks have been reported. Importation of dengue virus from South-East Asia is a major risk for a new outbreak on the island. The introduction of a new serotype could lead to the emergence of new and severe clinical forms, including dengue hemorrhagic fever.

  18. The Influence of Indian Ocean Atmospheric Circulation on Warm Pool Hydroclimate During the Holocene Epoch

    NASA Technical Reports Server (NTRS)

    Tierney, J.E.; Oppo, D. W.; LeGrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.

    2012-01-01

    Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September-November (SON) season is important for hydroclimate in Borneo. The preeminence of the SON season suggests that a seasonally lagged relationship between the Indian monsoon and Indian Ocean Walker circulation influences IPWP hydroclimatic variability during the Holocene.

  19. Sea level and coral atolls: Late holocene emergence in the Indian Ocean

    SciTech Connect

    Woodroffe, C. ); McLean, R. ); Polach, H.; Wallensky, E. )

    1990-01-01

    The Cocos (keeling) Islands in the eastern Indian Ocean were visited by Charles Darwin, who described geomorphological evidence that he considered supported his subsidence theory of coral-reef development. However, several other accounts of the reef islands have questioned Darwin's interpretation, and have suggested that a conglomerate platform that underlies most of the reef islands may indicate recent emergence of the atoll. Radiocarbon ages on corals from this conglomerate platform, reported here, indicate that it formed in the late Holocene. Fossil in situ microatolls above present upper coral growth limits, the elevation of associated beachrock, and the morphological similarity of the conglomerate platform to the present reef-flat deposits indicate a late Holocene sea level above the present relative to the atoll. The atoll has undergone at least 0.5 m of emergence since about 3000 yr B.P. This represents the first radiometrically dated evidence of Holocene emergence from islands in the eastern or central Indian Ocean.

  20. Introduction to "Tsunami Science: Ten Years After the 2004 Indian Ocean Tsunami. Volume I"

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander B.; Geist, Eric L.; Fritz, Hermann M.; Borrero, Jose C.

    2015-03-01

    Twenty-two papers on the study of tsunamis are included in Volume I of the PAGEOPH topical issue "Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami." Eight papers examine various aspects of past events with an emphasis on case and regional studies. Five papers are on tsunami warning and forecast, including the improvement of existing tsunami warning systems and the development of new warning systems in the northeast Atlantic and Mediterranean region. Three more papers present the results of analytical studies and discuss benchmark problems. Four papers report the impacts of tsunamis, including the detailed calculation of inundation onshore and into rivers and probabilistic analysis for engineering purposes. The final two papers relate to important investigations of the source and tsunami generation. Overall, the volume not only addresses the pivotal 2004 Indian Ocean (Sumatra) and 2011 Japan (Tohoku) tsunamis, but also examines the tsunami hazard posed to other critical coasts in the world.

  1. The distribution of pelagic sound scattering layers across the southwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Boersch-Supan, Philipp H.; Rogers, Alex D.; Brierley, Andrew S.

    2017-02-01

    Shallow and deep scattering layers (SLs) were surveyed with split-beam echosounders across the southwest Indian Ocean (SWIO) to investigate their vertical and geographical distribution. Cluster analysis was employed to objectively classify vertical backscatter profiles. Correlations between backscatter and environmental covariates were modelled using generalized additive mixed models (GAMMs) with spatial error structures. Structurally distinct SL regimes were found across the Subantarctic Front. GAMMs indicated a close relationship between sea surface temperature and mean volume backscatter, with significantly elevated backscatter in the subtropical convergence zone. The heterogeneous distribution of scattering layer biota reflects the biogeographic zonation of the survey area and is likely to have implications for predator foraging and carbon cycling in the Indian Ocean.

  2. The effect of zonal gradients of sea surface temperature on the Indian Ocean winter monsoon

    NASA Technical Reports Server (NTRS)

    Cohen, C.

    1981-01-01

    Several global climate simulations by the 7-layer, 8 x 10 GISS climate model were designed to test the contributions of various surface boundary conditions to the global climate. The model was run with the sun fixed at a perpetual January. In a comparison of run #5, in which realistic January surface boundary conditions were used, with run #4, which was the same except that a zonally symmetric climatological January sea surface temperature (SST) field was used, one of the results was that run #5 provided a better simulation of the Indian Ocean monsoon. A further comparison of the wind fields over the Indian Ocean that were generated by these two model runs is presented.

  3. Seasonal water mass distribution in the Indonesian throughflow entering the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Coatanoan, C.; Metzl, N.; Fieux, M.; Coste, B.

    1999-09-01

    A multiparametric approach is used to analyze the seasonal properties of water masses in the eastern Indian Ocean. The data were measured during two cruises of the Java Australia Dynamic Experiment (JADE) program carried out during two opposite seasons: August 1989 (SE monsoon) and February-March 1992 (NW monsoon). These cruises took place at the end of a La Niña event and during an El Niño episode, respectively. Seven sources have been identified in the studied region for the 200-800 m layer: the Subtropical Indian Water, the Indian Central Water, the modified Antarctic Intermediate Water, the Indonesian Subsurface Water, the Indonesian Intermediate Water, the Arabian Sea-Persian Gulf Water (AS-PGW), and the Arabian Sea-Red Sea Water (AS-RSW). The selected tracers are potential temperature, salinity and oxygen with mass conservation and positive mixing coefficients as constraints. The analysis indicates the proportion of each water source along the Australia-Bali section and into the Indonesian channels. Although no large changes are observed for Indonesian waters, significant seasonal variations are found for the southern and northern Indian Ocean water. During the NW monsoon, the contribution of the AS-RSW increases at the entrance of the Indonesian archipelago whereas the contribution of the south Indian waters decreases in the northwest Australia basin. In a complementary study, nutrients are introduced into the multiparametric analysis in order to more clearly separate the signature of the north Indian waters (AS-PGW, AS-RSW) and to provide supplementary information on the biological history of the water masses, which is compared to large-scale primary production estimates.

  4. Relation between tropical cyclone heat potential and cyclone intensity in the North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Jangir, B.; Swain, D.; Udaya Bhaskar, T. V. S.

    2016-05-01

    Ocean Heat Content (OHC) plays a significant role in modulating the intensity of Tropical Cyclones (TC) in terms of the oceanic energy available to TCs. TC Heat Potential (TCHP), an estimate of OHC, is thus known to be a useful indicator of TC genesis and intensification. In the present study, we analyze the role of TCHP in intensification of TCs in the North Indian Ocean (NIO) through statistical comparisons between TCHP and Cyclone Intensities (CI). A total of 27 TCs (20 in the Bay of Bengal, and 7 in the Arabian Sea) during the period 2005-2012 have been analyzed using TCHP data from Global Ocean Data Assimilation System (GODAS) model of Indian National Center for Ocean Information Services and cyclone best track data from India Meteorological Department. Out of the 27 cyclones analyzed, 58% (86%) in the Bay (Arabian Sea) have negative correlation and 42% (14%) cyclones have positive correlation between CI and TCHP. On the whole, more than 60% cyclones in the NIO show negative correlations between CI and TCHP. The negative percentage further increases for TCHP leading CI by 24 and 48 hours. Similar trend is also seen with satellite derived TCHP data obtained from National Remote Sensing Center and TC best track data from Joint Typhoon Warming Centre. Hence, it is postulated that TCHP alone need not be the only significant oceanographic parameter, apart from sea surface temperature, responsible for intensification and propagation of TCs in the NIO.

  5. Solubility of iron and other trace elements over the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Heimburger, A.; Losno, R.; Triquet, S.

    2013-03-01

    The fraction of soluble aerosols that is deposited on the open ocean is vital for phytoplankton growth. It is believed that a large proportion of this dissolved fraction is bioavailable for marine biota and thus plays an important role in primary production, especially in HNLC oceanic areas where this production is limited by micronutrient supply. There is still much uncertainty surrounding the solubility of atmospheric particles in global biogeochemical cycles and it is not well understood. In this study, we present the solubilities of seven elements (Al, Ce, Fe, La, Mn, Nd, Ti) in rainwater on Kerguelen Islands, in the middle of the Southern Indian Ocean. The solubilities exhibit high values, generally greater than 70%, and Ti remains the least soluble element. Because the Southern Indian Ocean is remote from its dust sources, only the fraction of smaller aerosols reaches Kerguelen Islands after undergoing several cloud and chemical processes during their transport resulting in a drastic increase in solubility. Finally, we deduced an average soluble iron deposition flux of 23 μg m-2 d-1 (0.4 μmol m-2 d-1) for the studied oceanic area, taking into account a~median iron solubility of 82% ± 18%.

  6. Air-Sea Interaction Studies of the Indian and Pacific Oceans

    DTIC Science & Technology

    2014-09-30

    tasks: Task 1: Air- Sea Interactions Impacting the North Arabian Sea Circulation Task 2: Satellite Observations of Flow Encountering Abrupt...resolution SAR data will allow monitoring of ocean processes in the North Arabian Sea circulation region due to current and/or meteorological forcing at a...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Air- Sea Interaction Studies of the Indian and Pacific

  7. Estimation of the Barrier Layer Thickness in the Indian Ocean Using Aquarius Salinity

    DTIC Science & Technology

    2014-07-08

    derived from satellite measurements using a multilinear regression model (MRM) within the Indian Ocean. Sea surface salinity ( SSS ) from the recently...surface salinity ( SSS ), sea surface temperature (SST), and sea surface height anomalies (SSHA). Three regions where the BLT variability is most...mechanisms are important for sustaining the BLT variability in each of the selected regions. Sensitivity tests show that SSS is the primary driver of

  8. Drifter Studies of the Western Pacific, Indian Ocean and Arabian Sea

    DTIC Science & Technology

    2015-09-30

    Arabian Sea Principal Investigator: Dr. Luca Centurioni The Scripps Institution of Oceanography, 0213 La Jolla, CA 92093-0213 Email...in the Indian Ocean and in the Arabian Sea to improve the dynamical knowledge and predictability of the near-surface circulation in these regions and...have an impact on the boundary current observed on the east side of Palau? 3) Can the island rule provide a plausible explanation for observations of

  9. Changes in erosion and ocean circulation recorded in the Hf isotopic compositions of North Atlantic and Indian Ocean ferromanganese crusts

    USGS Publications Warehouse

    Piotrowski, Alexander M.; Lee, Der-Chuen; Christensen, John N.; Burton, Kevin W.; Halliday, Alex N.; Hein, James R.; Günther, Detlef

    2000-01-01

    High-resolution Hf isotopic records are presented for hydrogenetic Fe–Mn crusts from the North Atlantic and Indian Oceans. BM1969 from the western North Atlantic has previously been shown to record systematically decreasing Nd isotopic compositions from about 60 to ∼4 Ma, at which time both show a rapid decrease to unradiogenic Nd composition, thought to be related to the increasing influence of NADW or glaciation in the northern hemisphere. During the Oligocene, North Atlantic Hf became progressively less radiogenic until in the mid-Miocene (∼15 Ma) it reached +1. It then shifted gradually back to an ϵHf value of +3 at 4 Ma, since when it has decreased rapidly to about −1 at the present day. The observed shifts in the Hf isotopic composition were probably caused by variation in intensity of erosion as glaciation progressed in the northern hemisphere. Ferromanganese crusts SS663 and 109D are from about 5500 m depth in the Indian Ocean and are now separated by ∼2300 km across the Mid-Indian Ridge. They display similar trends in Hf isotopic composition from 20 to 5 Ma, with the more northern crust having a composition that is consistently more radiogenic (by ∼2 ϵHf units). Paradoxically, during the last 20 Ma the Hf isotopic compositions of the two crusts have converged despite increased separation and subsidence relative to the ridge. A correlatable negative excursion at ∼5 Ma in the two records may reflect a short-term increase in erosion caused by the activation of the Himalayan main central thrust. Changes to unradiogenic Hf in the central Indian Ocean after 5 Ma may alternatively have been caused by the expanding influence of NADW into the Mid-Indian Basin via circum-Antarctic deep water or a reduction of Pacific flow through the Indonesian gateway. In either case, these results illustrate the utility of the Hf isotope system as a tracer of paleoceanographic changes, capable of responding to subtle changes in erosional regime not readily resolved

  10. The Central Sudetes Rheic Ocean Ophiolites: Quantifying the spatial and temporal extent of the Indian Ocean-Dupal mantle signature

    NASA Astrophysics Data System (ADS)

    band, Ade R.; Barry, Tiffany; Murphy, Brendan; Saunders, Andrew

    2014-05-01

    The Indian Ocean-Dupal (Dupal herein) mantle signature is documented to be an integral component in the formation of the Carboniferous Palaeo-Tethys ophiolites. Spatially associated with the Palaeo-Tethys Ocean, the Rheic Ocean separated Laurussia and Gondwana after its conception during the latest Cambrian until closure during the Devonian-Carboniferous Variscan-Alleghanian orogeny. The age and location of Rheic Ocean ophiolites preserved within the Variscide belt offers an insight into the spatial and temporal extent, and also the origin of the Dupal mantle signature. The Central Sudetes Ophiolites consist of the low metamorphic grade, partially dismembered Nowa Ruda, Braszowice and Ślęża mafic/ultramafic bodies of Lower Silesia, Poland. Geochemical analysis of extrusive and hypabyssal lithologies indicate that despite the majority of samples exhibiting characteristics compatible with formation within a SSZ setting (Th and LILE enrichment, Ta and Nb depletion), a significant MORB suite is also present. MORB offer an opportunity to isotopically fingerprint the underlying mantle source region, thus offering an insight into the chemistry of the southern hemisphere mantle at c. 420-400 Ma. Utilising the robust Hf-Nd systematics this study has succeeded in documenting the mantle domain from which the eastern Rheic Ocean was sourced whilst simultaneously constraining the timing and nature of a previous melt extraction event.

  11. Can Indian Ocean SST variability impact TC activity in the South Pacific? A Spatial Analysis

    NASA Astrophysics Data System (ADS)

    Magee, Andrew D.; Verdon-Kidd, Danielle C.; Kiem, Anthony S.

    2015-04-01

    Tropical Cyclones (TCs) represent a significant natural hazard to the 15 island nations and 2.7 million inhabitants of the South Pacific, accounting for 76% of reported disasters in the region since 1950. This vast area, dominated by the coupled ocean-atmosphere interactions of the South Pacific fuels the highly variable nature of TCs (both spatially and temporally), leading to difficulties in planning for and responding to these extreme events. While it is well known that the El Niño/Southern Oscillation (ENSO) plays a significant role in modulating the background state on which TCs form, there are other large-scale climate drivers operating on annual timescales or longer within the South Pacific (e.g. ENSO Modoki and the Interdecadal Pacific Oscillation) and outside the Pacific Basin (e.g. the Indian Ocean Dipole and the Southern Annular Mode) that may also influence TC formation. In response to this issue, the impact of these large-scale climate drivers upon the spatial characteristics of tropical cyclogenesis is assessed for the South Pacific region (5o-35oS, 145oE-130oW) over a 67-year period (1945-2011). It is shown, that in addition to the impact of 'Pacific-centric' climate drivers, eastern Indian Ocean sea surface temperatures significantly impact the spatial characteristics of tropical cyclogenesis in the South Pacific. In particular, warming (cooling) in the eastern Indian Ocean is found to result in an eastward (westward) shift in the average location of tropical cyclogenesis in the South Pacific (up to 712km between extreme phases). One mechanism that may account for this east/west modulation of TC activity in the South Pacific is the propagation of warmer water from the Timor Sea through the Coral Sea to the Pacific, resulting in a strengthening of the Pacific Warm Pool and associated meteorological characteristics connected with tropical cyclogenesis. Understanding how other large-scale climate modes interact with Indian Ocean processes is important

  12. Results from a 14-month hydroacoustic monitoring of the three mid-oceanic ridges in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Royer, J.-Y.; Dziak, R. P.; Delatre, M.; Chateau, R.; Brachet, C.; Haxel, J. H.; Matsumoto, H.; Goslin, J.; Brandon, V.; Bohnenstielh, D. R.

    2009-04-01

    From October 2006 to January 2008, an hydroacoustic experiment in the Indian Ocean was carried out by the CNRS/University of Brest and NOAA/Oregon State University to monitor the low-level seismic activity associated with the three contrasting spreading ridges and deforming zones in the Indian Ocean. Three autonomous hydrophones were moored in the SOFAR channel by R/V Marion Dufresne for 14 months in the Madagascar Basin, and northeast and southwest of Amsterdam Island, complementing the two permanent hydroacoustic stations of the Comprehensive nuclear-Test-Ban Treaty Organization (CTBTO) located near Diego Garcia Island and off Cape Leeuwin. The three instruments successfully collected 14 month of continuous acoustic records. Combined with the records from the permanent stations, the array detected 1780 acoustic events consisting mostly of earthquake generated T-waves, but also of iceberg tremors from Wilkes Land, Antarctica. Within the triangle defined by the temporary array, the three ridges exhibit contrasting seismicity patterns. Along the Southeast Indian ridge (SEIR), the 272 acoustic events (vs 24 events in the NEIC catalog) occur predominantly along the transform faults ; only one ridge segment (76˚E) displays a continuous activity for 10 months. Along the Central Indian Ridge (CIR), seismicity is distributed along fracture zones and ridge segments (269 events vs 45 NEIC events), with two clusters of events near the triple junction (24-25S) and south of Marie-Celeste FZ (18.5S). Along the Southwest Indian Ridge (SWIR), the 222 events (vs 31 NEIC events) are distributed along the ridge segments with a larger number of events west of Melville FZ and a cluster at 58E. The immediate vicinity of the Rodrigues triple junction shows periods of quiescence and of intense activity. Some large earthquakes (Mb>5) near the triple junction (SEIR and CIR) seem to be preceded by several acoustic events that may be precursors. Finally, off-ridge seismicity is mostly

  13. Brevibacterium oceani sp. nov., isolated from deep-sea sediment of the Chagos Trench, Indian Ocean.

    PubMed

    Bhadra, Bhaskar; Raghukumar, Chandralata; Pindi, Pavan Kumar; Shivaji, Sisinthy

    2008-01-01

    Two bacterial strains, designated BBH5 and BBH7(T), were isolated from a deep-sea sediment sample collected from the Chagos Trench of the Indian Ocean (1 degrees 06' S 7 degrees 31' E). Based on their 16S rRNA gene sequence similarity (99.9%), level of DNA-DNA relatedness (93%) and a number of similar phenotypic characteristics, the two strains are identified as representing the same species. Their phylogenetically nearest neighbours, based on 16S rRNA gene sequence similarity values (97.9-98.4%), were identified as Brevibacterium iodinum, Brevibacterium epidermidis, Brevibacterium linens and Brevibacterium permense. However, strains BBH5 and BBH7(T) could be distinguished from the above four species by a number of phenotypic characteristics, and levels of DNA-DNA relatedness between the two new isolates and these Brevibacterium species were 35-42%. Therefore, strains BBH5 and BBH7(T) are considered to represent a novel species of the genus Brevibacterium, for which the name Brevibacterium oceani sp. nov. is proposed. The type strain is BBH7(T) (=LMG 23457(T) =IAM 15353(T)).

  14. Reduction of the Powerful Greenhouse Gas N2O in the South-Eastern Indian Ocean

    PubMed Central

    Raes, Eric J.; Bodrossy, Levente; Van de Kamp, Jodie; Holmes, Bronwyn; Hardman-Mountford, Nick; Thompson, Peter A.; McInnes, Allison S.; Waite, Anya M.

    2016-01-01

    Nitrous oxide (N2O) is a powerful greenhouse gas and a key catalyst of stratospheric ozone depletion. Yet, little data exist about the sink and source terms of the production and reduction of N2O outside the well-known oxygen minimum zones (OMZ). Here we show the presence of functional marker genes for the reduction of N2O in the last step of the denitrification process (nitrous oxide reductase genes; nosZ) in oxygenated surface waters (180–250 O2 μmol.kg-1) in the south-eastern Indian Ocean. Overall copy numbers indicated that nosZ genes represented a significant proportion of the microbial community, which is unexpected in these oxygenated waters. Our data show strong temperature sensitivity for nosZ genes and reaction rates along a vast latitudinal gradient (32°S-12°S). These data suggest a large N2O sink in the warmer Tropical waters of the south-eastern Indian Ocean. Clone sequencing from PCR products revealed that most denitrification genes belonged to Rhodobacteraceae. Our work highlights the need to investigate the feedback and tight linkages between nitrification and denitrification (both sources of N2O, but the latter also a source of bioavailable N losses) in the understudied yet strategic Indian Ocean and other oligotrophic systems. PMID:26800249

  15. Origin of carbonaceous aerosols over the tropical Indian Ocean: Biomass burning or fossil fuels?

    SciTech Connect

    Novakov, T.; Andreae, M.O.; Gabriel, R.; Kirchstetter, T.; Mayol-Bracero, O.L.; Ramanathan, V.

    2000-08-26

    We present an analysis of the carbon, potassium and sulfate content of the extensive aerosol haze layer observed over the tropical Indian Ocean during the Indian Ocean Experiment (INDOEX). The black carbon (BC) content of the haze is as high as 17% of the total fine particle mass (the sum of carbonaceous and soluble ionic aerosol components) which results in significant solar absorption. The ratio of black carbon to organic carbon (OC) (over the Arabian Sea and equatorial Indian Ocean) was a factor of 5 to 10 times larger than expected for biomass burning. This ratio was closer to values measured downwind of industrialized regions in Japan and Western Europe. These results indicate that fossil fuel combustion is the major source of carbonaceous aerosols, including black carbon during the events considered. If the data set analyzed here is representative of the entire INDOEX study then fossil fuel emissions from South Asia must have similarly contributed to aerosols over the whole study region. The INDOEX ratios are substantially different from those reported f or some source regions of South Asia, thus raising the possibility that changes in composition of carbonaceous aerosol may occur during transport.

  16. Weakening of spring Wyrtki jets in the Indian Ocean during 2006-2011

    NASA Astrophysics Data System (ADS)

    Joseph, Sudheer; Wallcraft, Alan J.; Jensen, Tommy G.; Ravichandran, M.; Shenoi, S. S. C.; Nayak, Shailesh

    2012-04-01

    Beginning in 2006, the Indian Ocean experienced climatologically anomalous conditions due to large-scale coupled air-sea interactions that influenced the surface circulation of the equatorial Indian Ocean. Here we present evidence from observations as well as a general circulation model to demonstrate that spring Wyrtki jets (WJ) were weak during the past 6 years and were even reversed to westward flow during 2008. We note that this weakening coincided with uniformly high sea level as well as positive east to west gradient anomalies along the equatorial Indian Ocean during the month of May each year, starting in 2006. The weakened jets occur in conjunction with the latitude of zero zonal wind (LUZ) being close to the equator during these years, resulting in weaker than normal zonal winds along the equator from 2006 and onward. We find that starting in 2006, the normal tendency of westward propagation of the annual harmonic mode switches to eastward propagation, coherent with the wind forcing. In comparison to the annual harmonic component of the zonal current, the weak WJs are mainly associated with the semiannual harmonic WJs, as evident from an amplitude reduction of that mode by at least 0.3 m s-1 during the post-2005 period. Our analysis demonstrates that the variance explained by the semiannual harmonic is reduced to half (30-40%) at the core of the WJ in 2006 and later years in comparison with earlier years when it was 70-80%.

  17. Descriptions of four new species of Thysanophrys (Scorpaeniformes: Platycephalidae) from the Western Indian Ocean.

    PubMed

    Knapp, Leslie W

    2013-01-17

    Four new species of Thysanophrys are described from the Western Indian Ocean (WIO). T. rarita, known from a single specimen taken off Somalia, is provisionally placed in Thysanophrys and is distinguished by its color pattern and number of preocular and suborbital spines. T. tricaudata is described from three specimens taken at SCUBA stations off southwestern Sri Lanka. They differ from other western Indian Ocean (WIO) Thysanophrys in color pattern, lack of ocular flaps, number of dorsal fin spines and scale counts. The remaining two new species are somewhat similar to the widespread Indo-Pacific species, T. chiltonae Schultz (1966). T. randalli is described from specimens taken at the Amirante Islands and Mauritius. It may also be widespread in the Indo-Pacific, but differs from T. chiltonae in nasal spine structure, color pattern, type of iris lappet margin, and in having a much shorter maximum size. T. springeri also appears to be a smaller species than T. chiltonae and, aside from one record off Djibouti, is restricted to Red Sea. It also differs from T. chiltonae in color pattern, in having fewer pectoral rays and fewer scale rows between the second dorsal-fin insertion and the lateral line. Although T. chiltonae is relatively common in the northern Indian Ocean, it does not appear to have entered the Red Sea.

  18. Maculabatis ambigua sp. nov., a new whipray (Myliobatiformes: Dasyatidae) from the Western Indian Ocean.

    PubMed

    Last, Peter R; Bogorodsky, Sergey V; Alpermann, Tilman J

    2016-08-18

    A new whipray, Maculabatis ambigua sp. nov., described from material collected from the Red Sea and off Zanzibar (Tanzania), is probably more widespread in the northwestern Indian Ocean. It has been confused with other Indian Ocean whiprays of the genus Maculabatis (formerly Himantura in part) i.e. M. gerrardi and M. randalli. Maculabatis ambigua sp. nov. was first distinguished from these species by molecular analysis, and subsequently by a combination of morphological characters, i.e. disc shape, coloration, morphometrics and squamation. Molecular data suggest that it is most closely related to the morphologically similar M. gerrardi, which occurs further east in the Indian Ocean (Oman to Indonesia) and North-West Pacific (north to Taiwan). The dorsal disc of M. gerrardi typically has a full or partial coverage of white spots (usually present at least on the posterior disc), whereas M. ambigua sp. nov. is plain coloured. Maculabatis randalli, which occurs in the Persian and Arabian Gulfs, is plain coloured, but has a longer disc relative to its width, more acute and longer snout, longer head and larger intergill width, wider internasal distance, and a narrower secondary denticle band in adults. Maculabatis ambigua sp. nov. is relatively common in the shallow, soft-sedimentary habitats of the southern Red Sea from where it is taken as low-value or discarded bycatch of trawl fisheries. It is a medium-sized whipray with a maximum confirmed size of 840 mm disc width.

  19. Diversity and distribution of avian haematozoan parasites in the western Indian Ocean region: a molecular survey.

    PubMed

    Ishtiaq, Farah; Beadell, Jon S; Warren, Ben H; Fleischer, Robert C

    2012-02-01

    The genetic diversity of haematozoan parasites in island avifauna has only recently begun to be explored, despite the potential insight that these data can provide into the history of association between hosts and parasites and the possible threat posed to island endemics. We used mitochondrial DNA sequencing to characterize the diversity of 2 genera of vector-mediated parasites (Plasmodium and Haemoproteus) in avian blood samples from the western Indian Ocean region and explored their relationship with parasites from continental Africa. We detected infections in 68 out of 150 (45·3%) individuals and cytochrome b sequences identified 9 genetically distinct lineages of Plasmodium spp. and 7 lineages of Haemoproteus spp. We found considerable heterogeneity in parasite lineage composition across islands, although limited sampling may, in part, be responsible for perceived differences. Two lineages of Plasmodium spp. and 2 lineages of Haemoproteus spp. were shared by hosts in the Indian Ocean and also on mainland Africa, suggesting that these lineages may have arrived relatively recently. Polyphyly of island parasites indicated that these parasites were unlikely to constitute an endemic radiation and instead probably represent multiple colonization events. This study represents the first molecular survey of vector-mediated parasites in the western Indian Ocean, and has uncovered a diversity of parasites. Full understanding of parasite community composition and possible threats to endemic avian hosts will require comprehensive surveys across the avifauna of this region.

  20. Indian Ocean Small Island States: Indicators of Dangerous Anthropogenic Influences of Climate Change?

    NASA Astrophysics Data System (ADS)

    Mills, W. B.; Heidel, K.; Chung, C.

    2005-12-01

    This study focuses on both the climatic and non-climatic stresses that affect Small Island Developing States (SIDS) in the Indian Ocean. SIDS are independent developing nations that are located in the Indian, Atlantic, and Pacific Oceans. For this project four SIDS in the Indian Ocean have been studied: Comoros, Seychelles, Mauritius, and the Maldives. A general characteristic of these SIDS is that they have been little studied in the past, they have limited modern infrastructure, and hold the perception that environmental conditions on their islands are worsening at an accelerated pace. These SIDS are all densely populated, with populations per island between 90,000 to 1,200,000. The population growth rate is also high. This study has examined major environmental issues faced by all of these islands, including natural hazards (such as volcanic eruptions,tropical cyclones, and tsunamis), and climate related changes (such as warming, precipitation changes, and sea level rise). Comparisons between impacts of climate change, natural hazards, and population and tourism were made. It was concluded that the Maldives, due to such features as being a very low-lying island group, are now showing effects of climate related changes such as sea level rise, and that in the future it is likely that climatic stresses will compete with population growth as the major stressor on all of the islands.

  1. The South Indian Ocean Countercurrent: a return pathway of the Indonesian Throughflow?

    NASA Astrophysics Data System (ADS)

    Lambert, Erwin; leBars, Dewi; de Ruijter, Will

    2014-05-01

    The South Indian Ocean Counter Current (SICC) is associated with a thermal front embedded in a broad eastward flow across the subtropical Indian Ocean and feeds into the poleward Leeuwin Current (LC). Previous studies have shown that the LC and SICC are sensitive to variations of the inflow of Pacific water through the Indonesian Passages (ITF). These subtropical countercurrents, of which the SICC is an example, are characterized by high eddy activity and theoretical work has shown the non-linear nature of their dynamics. That has motivated us to investigate the inertial response to the ITF of the IO circulaion. Analysis of two global eddy resolving model runs with the Indonesian Passages open and closed showed that the full 15 Sv of the ITF flows through the Mozambique Channel but only 10 Sv ends up in the Agulhas Current. This suggests that the SICC-LC system forms part of the return pathway of the ITF to the Pacific. Using the Hallberg Isopycnal Model we have investigated the combined effect of ITF, wind- and buoyancy forcing on the Indian Ocean circulation in the inertial boundary layer regime.

  2. Reduction of the Powerful Greenhouse Gas N2O in the South-Eastern Indian Ocean.

    PubMed

    Raes, Eric J; Bodrossy, Levente; Van de Kamp, Jodie; Holmes, Bronwyn; Hardman-Mountford, Nick; Thompson, Peter A; McInnes, Allison S; Waite, Anya M

    2016-01-01

    Nitrous oxide (N2O) is a powerful greenhouse gas and a key catalyst of stratospheric ozone depletion. Yet, little data exist about the sink and source terms of the production and reduction of N2O outside the well-known oxygen minimum zones (OMZ). Here we show the presence of functional marker genes for the reduction of N2O in the last step of the denitrification process (nitrous oxide reductase genes; nosZ) in oxygenated surface waters (180-250 O2 μmol.kg(-1)) in the south-eastern Indian Ocean. Overall copy numbers indicated that nosZ genes represented a significant proportion of the microbial community, which is unexpected in these oxygenated waters. Our data show strong temperature sensitivity for nosZ genes and reaction rates along a vast latitudinal gradient (32°S-12°S). These data suggest a large N2O sink in the warmer Tropical waters of the south-eastern Indian Ocean. Clone sequencing from PCR products revealed that most denitrification genes belonged to Rhodobacteraceae. Our work highlights the need to investigate the feedback and tight linkages between nitrification and denitrification (both sources of N2O, but the latter also a source of bioavailable N losses) in the understudied yet strategic Indian Ocean and other oligotrophic systems.

  3. Relationship between Prevailing Oceanographic conditions on the fishing operations in the Northern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Moazzam Khan, Muhammad

    2014-05-01

    Marked seasonality in fishing operation and catch composition was observed in the Northern Indian Ocean. These variations are more pronounced and noticeable in case of trawling for fish and shrimp as well as in the surface gillnetting for tuna and large pelagics. Although oceanographic conditions of the Northern Indian Ocean has been studied comprehensively, some facets of these are not well understood especially their relation with the fish distribution and abundance. Important oceanographic factors especially migration of oxygen minimum layer towards coastal areas after the cessation of South-West Monsoon seems to the most important factor responsible for the seasonal variation in the fishing intensity and species composition. Distribution and abundance of some of the commercially important marine animals especially billfishes was observed to be associated with the physical features of the area especially their abundance was noticed along continental margin and on the ridges in the Arabian Sea. The paper describes seasonal variation in abundance and catch composition of various fishing operations in the Indian Ocean and relates its to prevailing oceanographic conditions. Fishermen traditional knowledge about the seasonality of these conditions is also documented in the paper.

  4. Nutrient characteristics of the water masses and their seasonal variability in the eastern equatorial Indian Ocean.

    PubMed

    Sardessai, S; Shetye, Suhas; Maya, M V; Mangala, K R; Prasanna Kumar, S

    2010-01-01

    Nutrient characteristics of four water masses in the light of their thermohaline properties are examined in the eastern Equatorial Indian Ocean during winter, spring and summer monsoon. The presence of low salinity water mass with "Surface enrichments" of inorganic nutrients was observed relative to 20 m in the mixed layer. Lowest oxygen levels of 19 microM at 3 degrees N in the euphotic zone indicate mixing of low oxygen high salinity Arabian Sea waters with the equatorial Indian Ocean. The seasonal variability of nutrients was regulated by seasonally varying physical processes like thermocline elevation, meridional and zonal transport, the equatorial undercurrent and biological processes of uptake and remineralization. Circulation of Arabian Sea high salinity waters with nitrate deficit could also be seen from low N/P ratio with a minimum of 8.9 in spring and a maximum of 13.6 in winter. This large deviation from Redfield N/P ratio indicates the presence of denitrified high salinity waters with a seasonal nitrate deficit ranging from -4.85 to 1.52 in the Eastern Equatorial Indian Ocean.

  5. Geologic impacts of the 2004 Indian ocean tsunami on Indonesia, Sri Lanka, and the Maldives

    USGS Publications Warehouse

    Richmond, B.M.; Jaffe, B.E.; Gelfenbaum, G.; Morton, R.A.

    2006-01-01

    The December 26, 2004 Indian Ocean tsunami was generated by a large submarine earthquake (magnitude ???9.1) with an epicenter located under the seafloor in the eastern Indian Ocean near northern Sumatra, Indonesia. The resulting tsunami was measured globally and had significant geologic impacts throughout the Indian Ocean basin. Observations of tsunami impacts, such as morphologic change, sedimentary deposits, and water-level measurements, are used to reconstruct tsunamogenic processes. Data from Sumatra, Sri Lanka, and the Maldives provide a synoptic view of tsunami characteristics from a wide range of coastal environments both near- and far-field from the tsunami origin. Impacts to the coast as a result of the tsunami varied depending upon the height of the wave at impact, orientation of the coast with regard to direction of wave approach, and local topography, bathymetry, geology, and vegetation cover. Tsunami deposits were observed in all the countries visited and can be generally characterized as relatively thin sheets (<80 cm), mostly of sand. ?? 2006 Gebru??der Borntraeger.

  6. Air-sea interactions during tropical cyclone in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Rashmi, R.; Vethamony, P.; Aboobacker, V. M.

    2012-04-01

    Estimation of air-sea momentum flux during tropical cyclone is one of the most important fields of study in wind - wave modeling and prediction. A number of studies suggested that the Charnock coefficient depends on the sea state. The Charnock coefficient (α) is firstly considered as a constant 0.0144 (Charnock, 1955). Toba et al. (1990) suggested that α increases with the wave age (β) based on the observations of mostly young waves in a wave flume, while Donelan (1990), Johnson et al. (1998), Lange et al. (2004), showed that α decreases with the wave age β. Moon et al. (2004) studied the effect of surface waves on Charnock coefficient under tropical cyclones and pointed out that the Charnock coefficient is mainly determined by two parameters: the wave age and the wind speed. Also there is a strong correlation between drag coefficient (Cd) and wave age (β) for each wind speed. When the wind speed is higher than 30 m/s, Cd will increase with β, otherwise Cd will decrease with increasing β. Amorocho et al. (1980) showed that three regions exist in the development of the wind stress: (i) a lower region in which the wind waves have not begun to break, for which drag coefficient (Cd) is approximately constant; (ii) a transitional region after the onset of breakers, for which Cd varies non-linearly with U10; (iii) a limiting region for which Cd tends again toward a constant value, and corresponds to a condition of breaker saturation. The three regions described above can be classified as 'low roughness', 'transitional', and 'high roughness', respectively. Wavewatch III model was used to study the air sea interaction during tropical cyclone in the Indian Ocean. ECMWF winds (2.5° x 2.5°) have been used for forcing the wave model. Air-sea momentum data was obtained by simulating wave fields of tropical cyclones during 1996 in the Indian Ocean. The wave parameters from the model results have been compared with measured buoy data and with merged altimeter data. The

  7. Observed correlations between aerosol and cloud properties in an Indian Ocean trade cumulus regime

    NASA Astrophysics Data System (ADS)

    Pistone, K.; Praveen, P. S.; Thomas, R. M.; Ramanathan, V.; Wilcox, E.; Bender, F. A.-M.

    2015-10-01

    There are many contributing factors which determine the micro- and macrophysical properties of clouds, including atmospheric structure, dominant meteorological conditions, and aerosol concentration, all of which may be coupled to one another. In the quest to determine aerosol effects on clouds, these potential relationships must be understood, as changes in atmospheric conditions due to aerosol may change the expected magnitude of indirect effects by altering cloud properties in unexpected ways. Here we describe several observed correlations between aerosol conditions and cloud and atmospheric properties in the Indian Ocean winter monsoon season. In the CARDEX (Cloud, Aerosol, Radiative forcing, Dynamics EXperiment) field campaign conducted in February and March 2012 in the northern Indian Ocean, continuous measurements of atmospheric precipitable water vapor and the liquid water path (LWP) of trade cumulus clouds were made, concurrent with measurements of water vapor flux, cloud and aerosol vertical profiles, meteorological data, and surface and total-column aerosol. Here we present evidence of a positive correlation between aerosol and cloud LWP which becomes clear after the data are filtered to control for the natural meteorological variability in the region. We then use the aircraft and ground observatory measurements to explore the mechanisms behind the observed aerosol-LWP correlation. We determine that increased boundary-layer humidity lowering the cloud base is responsible for the observed increase in cloud liquid water. Large-scale analysis indicates that high pollution cases originate with a highly-polluted boundary layer air mass approaching the observatory from a northwesterly direction. This polluted mass exhibits higher temperatures and humidity than the clean case, the former of which may be attributable to heating due to aerosol absorption of solar radiation over the subcontinent. While high temperature conditions dispersed along with the high

  8. A ~25 ka Indian Ocean monsoon variability record from the Andaman Sea

    USGS Publications Warehouse

    Rashid, H.; Flower, B.P.; Poore, R.Z.; Quinn, T.M.

    2007-01-01

    Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ18O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ18O of seawater (δ18Osw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ∼3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ18Osw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ18Osw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.

  9. Rajella paucispinosa n. sp., a new deep-water skate (Elasmobranchii, Rajidae) from the western Indian Ocean off South Mozambique, and a revised generic diagnosis.

    PubMed

    Weigmann, Simon; Stehmann, Matthias F W; Thiel, Ralf

    2014-08-08

    A new species of the widely in temperate and tropical latitudes distributed skate genus Rajella is described based on an almost adult male specimen from the western Indian Ocean off South Mozambique. The holotype of R. paucispinosa n. sp. was caught during cruise 17 of RV 'Vityaz' along the deep western Indian Ocean in 1988/89. It is the northernmost record of a Rajella specimen in the western Indian Ocean. The new species is the 18th valid species of the genus and the fifth species in the western Indian Ocean. It differs from its congeners in the small maximal total length of about 50 cm and only few thorns on the dorsal surface. The new species has only two thorns on each orbit, one nuchal thorn, one right scapular thorn (left one not detectable, abraded), and one median row of tail thorns. Other species of Rajella typically have half rings of thorns on orbital rims, a triangle of thorns on nape-shoulder region, and at least three rows of tail thorns. Another conspicuous feature of the new species is the almost completely white dorsal and ventral coloration. 

  10. The NOW regional coupled model: Application to the tropical Indian Ocean climate and tropical cyclone activity

    NASA Astrophysics Data System (ADS)

    Samson, G.; Masson, S.; Lengaigne, M.; Keerthi, M. G.; Vialard, J.; Pous, S.; Madec, G.; Jourdain, N. C.; Jullien, S.; Menkes, C.; Marchesiello, P.

    2014-09-01

    This paper presents the NOW regional coupled ocean-atmosphere model built from the NEMO ocean and WRF atmospheric numerical models. This model is applied to the tropical Indian Ocean, with the oceanic and atmospheric components sharing a common ¼° horizontal grid. Long experiments are performed over the 1990-2009 period using the Betts-Miller-Janjic (BMJ) and Kain-Fritsch (KF) cumulus parameterizations. Both simulations produce a realistic distribution of seasonal rainfall and a realistic northward seasonal migration of monsoon rainfall over the Indian subcontinent. At subseasonal time scales, the model reasonably reproduces summer monsoon active and break phases, although with underestimated rainfall and surface wind signals. Its relatively high resolution results in realistic spatial and seasonal distributions of tropical cyclones, but it fails to reproduce the strongest observed cyclone categories. At interannual time scales, the model reproduces the observed variability associated with the Indian Ocean Dipole (IOD) and the delayed basin-wide warming/cooling induced by the El Niño Southern Oscillation (ENSO). The timing of IOD occurrence in the model generally matches that of the observed events, confirming the influence of ENSO on the IOD development (through the effect of lateral boundary conditions in our simulations). Although the KF and BMJ simulations share a lot in common, KF strongly overestimates rainfall at all time scales. KF also overestimates the number of simulated cyclones by a factor two, while simulating stronger events (up to 55 m s-1) compared to BMJ (up to 40 m s-1). These results could be related to an overly active cumulus parameterization in KF.

  11. Mesozoic Sequence Magnetic Anomalies in the South of Corad Rise, the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nogi, Y.; Ikehara, M.; Nakamura, Y.; Kameo, K.; Katsuki, K.; Kawamura, S.; Kita, S.

    2009-04-01

    The Southern Indian Ocean is key area for understanding the fragmentation process of the Gondwana. However, tectonic history in the Southern Indian Ocean still remains less well-defined because of the sparse observations in this area. The R/V Hakuho-maru cruise KH-07-4 Leg3 were conducted to understand the tectonic history related to the Gondwana breakup in the Southern Indian Ocean between Cape Town, South Africa, and off Lutzow-Holm Bay, Antarctica. Total intensity and vector geomagnetic field measurements as well as swath bathymetry mapping were collected during the cruise. Magnetic anomaly data have been collected along WNW-ESE trending inferred from satellite gravity anomalies just to the south of Conrad Rise. We have also collected magnetic anomaly data along NNE-SSW trending lineaments from satellite gravity anomaly data between the south of the Conrad Rise and off Lutzow-Holm Bay. Magnetic anomalies with amplitude of about 500 nT, originating from normal and reversed magnetization of oceanic crust are detected along the WNW-ESE trending structures just to the south of Conrad Rise. Those magnetic anomalies most likely indicate Mesozoic magnetic anomaly sequence, Mesozoic sequence magnetic anomalies with amplitude of about 300 nT are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and off Lutzow-Holm Bay. Oceanic crusts formed during Cretaceous normal polarity superchron are found in both profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. These suggest the extinct spreading axes in the south of Conrad Rise and the two different seafloor spreading systems were active around Cretaceous normal polarity superchron between the south of the Conrad Rise and off Lutzow-Holm Bay. These provide new constraints for the fragmentation process of the Gondwana.

  12. Methods for monitoring hydroacoustic events using direct and reflected T waves in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Hanson, Jeffrey A.; Bowman, J. Roger

    2006-02-01

    The recent installation of permanent, three-element hydrophone arrays in the Indian Ocean offshore Diego Garcia and Cape Leeuwin, Australia, provides an opportunity to study hydroacoustic sources in more detail than previously possible. We developed and applied methods for coherent processing of the array data, for automated association of signals detected at more than one array, and for source location using only direct arrivals and using signals reflected from coastlines and other bathymetric features. During the 286-day study, 4725 hydroacoustic events were defined and located in the Indian and Southern oceans. Events fall into two classes: tectonic earthquakes and ice-related noise. The tectonic earthquakes consist of mid-ocean ridge, trench, and intraplate earthquakes. Mid-ocean ridge earthquakes are the most common tectonic events and often occur in clusters along transform offsets. Hydroacoustic signal levels for earthquakes in a standard catalog suggest that the hydroacoustic processing threshold for ridge events is one magnitude below the seismic network. Fewer earthquakes are observed along the Java Trench than expected because the large bathymetric relief of the source region complicates coupling between seismic and hydroacoustic signals, leading to divergent signal characteristics at different stations. We located 1843 events along the Antarctic coast resulting from various ice noises, most likely thermal fracturing and ice ridge forming events. Reflectors of signals from earthquakes are observed along coastlines, the mid-Indian Ocean and Ninety East ridges, and other bathymetric features. Reflected signals are used as synthetic stations to reduce location uncertainty and to enable event location with a single station.

  13. Pronounced warming in the Indian and Pacific sectors of the Southern Ocean during the 1970s

    NASA Astrophysics Data System (ADS)

    Turney, Chris; Fogwill, Chris; Palmer, Jonathan; van Sebille, Erik; Thomas, Zoë; McGlone, Matt; Richardson, Sarah; Wilmshurst, Janet; Fenwick, Pavla; Carter, Lionel; Jones, Richard; Harsch, Melanie; Wilson, Kerry-Jayne; Clark, Graeme; Marzinelli, Ezequiel; Rogers, Tracey; Rainsley, Eleanor; Ciasto, Laura; Waterman, Stephanie; Antarctic Expedition 2013-2014 Members, Australasian

    2015-04-01

    Occupying some 20% of the world's ocean surface, the Southern Ocean is home to a diverse and unique biota and plays a fundamental role in global oceanic circulation, climate variability, Antarctic ice sheet stability and carbon cycling. Significant warming has been observed over recent decades, most prominently in the Antarctic Circumpolar Current (ACC). The mechanism(s) behind this warming, however, remain uncertain. Here, we integrate historic ocean and atmospheric observations and climate-sensitive tree growth on subantarctic islands from the northern limit of the ACC to extend historic and satellite measurements to produce a unique proxy record of temperature across 4˚ of latitude in the southwest Pacific. We demonstrate a hitherto unobserved abrupt warming during the 1970s that is unprecedented over the past 130 years, coincident with a significant decline in marine vertebrate populations and wider warming across the Indian Ocean. Comparison between our reconstruction and high-resolution ocean modelling provides a possible mechanism, suggesting warmer waters resulted from a poleward migration of the subtropical and ACC fronts. Projected increases in the strength of westerly winds are likely to continue the fronts' migration, driving warming in the Southern Ocean (>50˚S), with significant impacts on biota.

  14. Community structure across a large-scale ocean productivity gradient: Marine bird assemblages of the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Hyrenbach, K. David; Veit, Richard R.; Weimerskirch, Henri; Metzl, Nicolas; Hunt, George L., Jr.

    2007-07-01

    Our objective was to understand how marine birds respond to oceanographic variability across the Southern Indian Ocean using data collected during an 16-day cruise (4-21 January 2003). We quantified concurrent water mass distributions, ocean productivity patterns, and seabird distributions across a heterogeneous pelagic ecosystem from subtropical to sub-Antarctic waters. We surveyed 5155 km and sighted 15,606 birds from 51 species, and used these data to investigate how seabirds respond to spatial variability in the structure and productivity of the ocean. We addressed two spatial scales: the structure of seabird communities across macro-mega scale (1000 s km) biogeographic domains, and their coarse-scale (10 s km) aggregation at hydrographic and bathymetric gradients. Both seabird density and species composition changed with latitudinal and onshore-offshore gradients in depth, water temperature, and chlorophyll-a concentration. The average seabird density increased across the subtropical convergence (STC) from 2.4 birds km -2 in subtropical waters to 23.8 birds km -2 in sub-Antarctic waters. The composition of the avifauna also differed across biogeographic domains. Prions ( Pachyptila spp.) accounted for 57% of all sub-Antarctic birds, wedge-tailed shearwaters ( Puffinus pacificus) accounted for 46% of all subtropical birds, and Indian Ocean yellow-nosed albatross ( Thallasarche carteri) accounted for 32% of all birds in the STC. While surface feeders were the most abundant foraging guild across the study area, divers were disproportionately more numerous in the sub-Antarctic domain, and plungers were disproportionately more abundant in subtropical waters. Seabird densities were also higher within shallow shelf-slope regions, especially in sub-Antarctic waters, where large numbers of breeding seabirds concentrated. However, we did not find elevated seabird densities along the STC, suggesting that this broad frontal region is not a site of enhanced aggregation.

  15. Ocean feedback to pulses of the Madden-Julian Oscillation in the equatorial Indian Ocean.

    PubMed

    Moum, James N; Pujiana, Kandaga; Lien, Ren-Chieh; Smyth, William D

    2016-10-19

    Dynamical understanding of the Madden-Julian Oscillation (MJO) has been elusive, and predictive capabilities therefore limited. New measurements of the ocean's response to the intense surface winds and cooling by two successive MJO pulses, separated by several weeks, show persistent ocean currents and subsurface mixing after pulse passage, thereby reducing ocean heat energy available for later pulses by an amount significantly greater than via atmospheric surface cooling alone. This suggests that thermal mixing in the upper ocean from a particular pulse might affect the amplitude of the following pulse. Here we test this hypothesis by comparing 18 pulse pairs, each separated by <55 days, measured over a 33-year period. We find a significant tendency for weak (strong) pulses, associated with low (high) cooling rates, to be followed by stronger (weaker) pulses. We therefore propose that the ocean introduces a memory effect into the MJO, whereby each event is governed in part by the previous event.

  16. Ocean feedback to pulses of the Madden–Julian Oscillation in the equatorial Indian Ocean

    PubMed Central

    Moum, James N.; Pujiana, Kandaga; Lien, Ren-Chieh; Smyth, William D.

    2016-01-01

    Dynamical understanding of the Madden–Julian Oscillation (MJO) has been elusive, and predictive capabilities therefore limited. New measurements of the ocean's response to the intense surface winds and cooling by two successive MJO pulses, separated by several weeks, show persistent ocean currents and subsurface mixing after pulse passage, thereby reducing ocean heat energy available for later pulses by an amount significantly greater than via atmospheric surface cooling alone. This suggests that thermal mixing in the upper ocean from a particular pulse might affect the amplitude of the following pulse. Here we test this hypothesis by comparing 18 pulse pairs, each separated by <55 days, measured over a 33-year period. We find a significant tendency for weak (strong) pulses, associated with low (high) cooling rates, to be followed by stronger (weaker) pulses. We therefore propose that the ocean introduces a memory effect into the MJO, whereby each event is governed in part by the previous event. PMID:27759016

  17. Biogeography and diversification of hermit spiders on Indian Ocean islands (Nephilidae: Nephilengys).

    PubMed

    Kuntner, Matjaž; Agnarsson, Ingi

    2011-05-01

    The origin of the terrestrial biota of Madagascar and, especially, the smaller island chains of the western Indian Ocean is relatively poorly understood. Madagascar represents a mixture of Gondwanan vicariant lineages and more recent colonizers arriving via Cenozoic dispersal, mostly from Africa. Dispersal must explain the biota of the smaller islands such as the Comoros and the chain of Mascarene islands, but relatively few studies have pinpointed the source of colonizers, which may include mainland Africa, Asia, Australasia, and Madagascar. The pantropical hermit spiders (genus Nephilengys) seem to have colonized the Indian Ocean island arc stretching from Comoros through Madagascar and onto Mascarenes, and thus offer one opportunity to reveal biogeographical patterns in the Indian Ocean. We test alternative hypotheses on the colonization route of Nephilengys spiders in the Indian Ocean and simultaneously test the current taxonomical hypothesis using genetic and morphological data. We used mitochondrial (COI) and nuclear (ITS2) markers to examine Nephilengys phylogenetic structure with samples from Africa, southeast Asia, and the Indian Ocean islands of Madagascar, Mayotte, Réunion and Mauritius. We used Bayesian and parsimony methods to reconstruct phylogenies and haplotype networks, and calculated genetic distances and fixation indices. Our results suggest an African origin of Madagascar Nephilengys via Cenozoic dispersal, and subsequent colonization of the Mascarene islands from Madagascar. We find strong evidence of gene flow across Madagascar and through the neighboring islands north of it, while phylogenetic trees, haplotype networks, and fixation indices all reveal genetically isolated and divergent lineages on Mauritius and Réunion, consistent with female color morphs. These results, and the discovery of the first males from Réunion and Mauritius, in turn falsify the existing taxonomic hypothesis of a single widespread species, Nephilengys borbonica

  18. Understanding Predictability of the MJO Initiation over the Tropical Indian Ocean Using Stochastic Ensemble of a Coupled Atmosphere-Ocean Model

    NASA Astrophysics Data System (ADS)

    Chen, Shuyi; Savarin, Ajda; Curcic, Milan; Judt, Falko

    2015-04-01

    One of the most challenging problems in prediction of Madden-Julian Oscillation (MJO) is the initiation of large-scale convection over the equatorial Indian Ocean. The Dynamics of MJO (DYNAMO) field campaign in 2011-12 has provided unprecedented in situ observations to advance our understanding of MJO initiation. It is evident that the complex multiscale interaction among convective cloud systems and their large-scale environment on time scales from hours to months is a key contributing factor. Two new science hypotheses on MJO initiation have emerged based on DYNAMO observations. First, dry air intrusions associated with synoptic-scale wave-like disturbances from subtropical Indian Ocean play an important role in 1) alternating deep convection from ITCZ to equatorial convection during the onset of MJO initiation and 2) favoring eastward propagation of MJO convection by entraining dry air into the equatorial region to the west by the Rossby-wave like gyres. Second, convective cloud systems and convective cold pools are sensitive to the large-scale water vapor distribution and air-sea fluxes. The boundary layer recovery time from the cold pools can affect the re-development of convection. The cold pool recovery time vary from a few hours during the convective active phases of MJO to more than 30 hrs during the suppressed phase, which indicating the upscaling effects of convective systems on MJO may be important for the evolution of MJO. The predictability of convective cloud systems and their up-scaling influence on MJO have not been studied systematically. Although the predictability of individual convective cloud systems is likely to be less than 1-2 days, the predictability of MJO initiation over the Indian Ocean should be much longer if the large-scale atmosphere and ocean processes are dominant factors. To address the question of convective upscaling and dry air intrusions on the MJO initiation, numerical experiments using the Coupled Model (coupled WRF

  19. Atmospheric electric conductivity measurements over the Indian Ocean during the Indian Antarctic Expedition in 1996-1997

    NASA Astrophysics Data System (ADS)

    Deshpande, C. G.; Kamra, A. K.

    2002-11-01

    The atmospheric electric conductivity measurements made over the Indian Ocean with a Gerdien's apparatus mounted aboard MV Polarbird during the XVI Indian Scientific Expedition in 1996-1997 are reported. Simultaneous three-hourly measurements of aerosol concentrations of 13-1000 nm size and some meteorological parameters are also reported. Latitudinal variation of conductivity along the cruise route shows a minimum at ˜28°S. Further, the variations in conductivity in the 10°N-20°S and 60°-70°S latitudinal belts show opposite trends on the outward and return cruises, which fall near to the onset and withdrawal phases of the northeast monsoon season, respectively. The results are explained on the basis of the well-known northward shift of the subsidence leg of the southern Hadley cell and of the position of the Intertropical Convergence Zone during the months of March-April in this region and the observations of the cyclonic systems near the continent of Antarctica during the period of outward cruise.

  20. 10Be application to soil development on Marion Island, southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Haussmann, N.; Aldahan, A.; Boelhouwers, J.; Possnert, G.

    2010-04-01

    Marion Island, located in the southern Indian Ocean, constitutes the summit of an active shield volcano. It is a small terrestrial environment where glacially abraded bedrock became exposed c × 10 kyr ago. These conditions provide an interesting possibility for the assessment of 10Be accumulation rates and their application to soil erosion studies on the island. 10Be concentrations were measured in precipitation, soil profiles and an Azorella selago cushion plant. The data reveal a 10Be precipitation flux several times higher than model prediction. Estimation of the 10Be accumulation based on the soil inventory suggests a span between 2000 and 7000 yr. This time span is not in accordance with the accepted notion that the island was covered with ice about 10,000 yr ago and suggests either removal of 10Be from the soil profile, an overestimated Holocene 10Be-flux or a delayed soil development history. Our results provide new data on 10Be concentrations from the sub-Antarctic islands and contribute towards enlarging the southern-hemisphere 10Be database.

  1. Uniting and networking the magnetic community in the northern Indian Ocean region - MAGNIO - a new initiative

    NASA Astrophysics Data System (ADS)

    Arora, Kusumita

    2015-04-01

    The North Indian Ocean (NIO) - a region of sparse data coverage - is a prime location for the measurement and study of variations of the geomagnetic field, where the effects of the Equatorial Electrojet (EEJ) and Solar quiet (Sq) currents as well as lithospheric configuration, are yet to be delineated. Ground based measurements of magnetic variations with a time resolution of one minute or better in the NIO region would provide an ideal window of opportunity to augment satellite measurements (SWARM). As the dip equator passes through the NIO, the magnetic field here can be subject to rapid change. Therefore it is felt that forging collaborative scientific links between the scientists and stakeholder communities of these nations is vital. In recognition of the significance of a regional initiative, the International Council of Science (ICSU) has awarded the MAGNIO project to the International Union of Geodesy and Geophysics (IUGG), to undertake activities necessary to put further medium and long term endeavors in place. The MAGNIO proposal aims to bring all NIO magnetic observatories and organisations using magnetic data together, along with relevant stakeholders. The line of action to be adopted for the fulfillment of MAGNIO objectives is presented. Critical issues of trust development, communication establishment, internet usage, role of mentors and policymankers, which could construct the requisite links to bring about such a collaborration and take it forward are discussed.

  2. Indian Ocean Climate event brings floods to East Africa's lakes and the Sudd Marsh

    NASA Astrophysics Data System (ADS)

    Birkett, Charon; Murtugudde, Ragu; Allan, Tony

    During an El Niño, the expected rainfall increase over most of the Lake Victoria catchment area is ˜15-25%. However, due to anomalous warming of the western equatorial Indian Ocean during 1997, strong convection developed over parts of the Horn and eastern Africa. This resulted in a much larger 20-160% precipitation excess during the “short rainy” season. Satellite radar altimetry data reveals that not only did Lake Victoria rise by ˜1.7 m, but that the rainfall event similarly affected lakes Tanganyika, Malawi and Turkana. In addition, the seasonal level minima of the Sudd marshes and Lakes T'ana and Nasser continue to increase. Such a rainfall event will have severe, long-term consequences for the natural surface flows and storages along the White Nile. Based on the hydrological impacts of the historic 1961 East Africa event, we can expect the current high levels of Lake Victoria to be maintained for the remainder of this decade. In addition, we anticipate a major expansion of the permanent swamp regions of the Sudd marshes over the forthcoming seasons. Blue Nile flows, further enhanced by the above-average 1998 rainfall season, can also be expected to remain high, at least until early 1999.

  3. Understanding the origin of black carbon in the atmospheric brown cloud over the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Stone, Elizabeth A.; Lough, Glynis C.; Schauer, James J.; Praveen, P. S.; Corrigan, C. E.; Ramanathan, V.

    2007-11-01

    Atmospheric particulate matter samples were collected at two Maldives climate observatories from 30 August 2004 to 21 January 2005. This time period encompassed both wet and dry seasons, which correspond to low and high aerosol loadings. High aerosol loadings were observed in the northern sampling site in Hanimaadhoo, caused by long-range transport from south and Southeast Asia, whereas the southern sampling site, Gan, was not subject to as much continental inflow. The polluted period began in mid-November and lasted through the remainder of the sampling period. Fine particulate matter during this time was characterized by relatively high concentrations of aerosol mass and elemental carbon. Concentrations of water-soluble potassium, sulfate, levoglucosan, polyaromatic hydrocarbons, aliphatic diacids, aromatic diacids, and trace metals increased over the clean, transition, and polluted dry season. Organic speciation suggested that significant secondary organic aerosol formation occurred during the polluted dry season, meaning that traditional methods of source identification relying on fixed elemental and organic carbon ratios between source and receptors are not sufficient. Well-studied molecular markers for combustion sources were not adequate in fully attributing elemental carbon over the northern Indian Ocean to specific sources. Further source profiling of south and Southeast Asian biofuels and fossil fuels is recommended. A receptor-based positive matrix factorization model was applied to fine particulate matter trace metal measurements and showed that biofuel burning and fossil fuel combustion were equally important sources of elemental carbon during the polluted dry season.

  4. Chelidoperca stella, a new species of perchlet (Perciformes: Serranidae) from the Andaman Sea, eastern Indian Ocean.

    PubMed

    Matsunuma, Mizuki; Motomura, Hiroyuki

    2016-03-16

    A new species of serranid fish, Chelidoperca stella, is described on the basis of five specimens from the Andaman Sea in the eastern Indian Ocean. The species can be readily distinguished from all valid congeners by having fewer pored lateral-line scales (34 or 35 vs. 40-45 in the latter) and the pelvic fin white with several small yellow spots (vs. spots absent). The species is also characterized by having relatively high counts of small serrae on the posterior margins of the preopercle (33-43 serrae), interopercle (7-10) and subopercle (18-28), despite the small body size (51.7-61.8 mm SL). Although Chelidoperca stella resembles C. margaritifera in having 2.5 scale rows between lateral line and the sixth dorsal-fin spine base, a relatively wider interorbital region, and the interorbital scales not reaching a vertical through the orbit anterior margin, but differs by having the above-mentioned diagnostic characters plus a slightly shorter longest anal-fin soft ray [17.4-18.7 (mean 18.1) % SL vs. 22.6-26.4 (24.4) % SL in C. margaritifera].

  5. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean: Ancient Slab Beneath the Indian Ocean

    DOE PAGES

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; ...

    2015-11-14

    In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along anmore » extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.« less

  6. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean: Ancient Slab Beneath the Indian Ocean

    SciTech Connect

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-14

    In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.

  7. Amirante Basin, western Indian Ocean: Possible impact site of the Cretaceous/Tertiary extinction bolide?

    NASA Astrophysics Data System (ADS)

    Hartnady, C. J. H.

    1986-05-01

    If an impact event caused the mass extinctions and geochemical anomalies at the Cretaceous/Tertiary boundary, it probably occurred in an oceanic area. However, no convincing impact site has yet been discovered. Whereas Late Cretaceous magnetic lineations in other oceans show no obvious signs of disturbance at the Tertiary boundary, the end-Cretaceous African plate boundary in the Indian Ocean provides evidence of major tectonic reorganization at or shortly after magnetostratigraphic chron C29r. Immediately south of the microcontinental Seychelles Bank, the Amirante Basin has a roughly circular shape of about 300 km diameter, is partially ringed by enigmatic “arc” and “trench” structures, and is located within oceanic crust of Late Cretaceous age. It is therefore a possible impact site. Extensive chaotic slump structures apparently exist at the appropriate level on the East African continental margin, and they may indicate its proximity to the mega-earthquake focus and/or giant tsunamis in the Somali Basin. By triggering readjustments along the Indian-African and Antarctic-African plate boundaries and thus altering the regional balance of driving forces, the impact may have affected plate motions.

  8. Intraseasonal Variability of the Equatorial Indian Ocean Observed from Sea Surface Height, Wind, and Temperature Data

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    2007-01-01

    The forcing of the equatorial Indian Ocean by the highly periodic monsoon wind cycle creates many interesting intraseasonal variabilities. The frequency spectrum of the wind stress observations from the European Remote Sensing Satellite scatterometers reveals peaks at the seasonal cycle and its higher harmonics at 180, 120, 90, and 75 days. The observations of sea surface height (SSH) from the Jason and Ocean Topography Experiment (TOPEX)/Poseidon radar altimeters are analyzed to study the ocean's response. The focus of the study is on the intraseasonal periods shorter than the annual period. The semiannual SSH variability is characterized by a basin mode involving Rossby waves and Kelvin waves traveling back and forth in the equatorial Indian Ocean between 10(deg)S and 10(deg)N. However, the interference of these waves with each other masks the appearance of individual Kelvin and Rossby waves, leading to a nodal point (amphidrome) of phase propagation on the equator at the center of the basin. The characteristics of the mode correspond to a resonance of the basin according to theoretical models. The theory also calls for similar modes at 90 and 60 days.

  9. High connectivity of the crocodile shark between the Atlantic and Southwest Indian Oceans: highlights for conservation.

    PubMed

    da Silva Ferrette, Bruno Lopes; Mendonça, Fernando Fernandes; Coelho, Rui; de Oliveira, Paulo Guilherme Vasconcelos; Hazin, Fábio Hissa Vieira; Romanov, Evgeny V; Oliveira, Claudio; Santos, Miguel Neves; Foresti, Fausto

    2015-01-01

    Among the various shark species that are captured as bycatch in commercial fishing operations, the group of pelagic sharks is still one of the least studied and known. Within those, the crocodile shark, Pseudocarcharias kamoharai, a small-sized lamnid shark, is occasionally caught by longline vessels in certain regions of the tropical oceans worldwide. However, the population dynamics of this species, as well as the impact of fishing mortality on its stocks, are still unknown, with the crocodile shark currently one of the least studied of all pelagic sharks. Given this, the present study aimed to assess the population structure of P. kamoharai in several regions of the Atlantic and Indian Oceans using genetic molecular markers. The nucleotide composition of the mitochondrial DNA control region of 255 individuals was analyzed, and 31 haplotypes were found, with an estimated diversity Hd = 0.627, and a nucleotide diversity π = 0.00167. An analysis of molecular variance (AMOVA) revealed a fixation index ΦST = -0.01118, representing an absence of population structure among the sampled regions of the Atlantic Ocean, and between the Atlantic and Indian Oceans. These results show a high degree of gene flow between the studied areas, with a single genetic stock and reduced population variability. In panmictic populations, conservation efforts can be concentrated in more restricted areas, being these representative of the total biodiversity of the species. When necessary, this strategy could be applied to the genetic maintenance of P. kamoharai.

  10. High Connectivity of the Crocodile Shark between the Atlantic and Southwest Indian Oceans: Highlights for Conservation

    PubMed Central

    da Silva Ferrette, Bruno Lopes; Mendonça, Fernando Fernandes; Coelho, Rui; de Oliveira, Paulo Guilherme Vasconcelos; Hazin, Fábio Hissa Vieira; Romanov, Evgeny V.; Oliveira, Claudio; Santos, Miguel Neves; Foresti, Fausto

    2015-01-01

    Among the various shark species that are captured as bycatch in commercial fishing operations, the group of pelagic sharks is still one of the least studied and known. Within those, the crocodile shark, Pseudocarcharias kamoharai, a small-sized lamnid shark, is occasionally caught by longline vessels in certain regions of the tropical oceans worldwide. However, the population dynamics of this species, as well as the impact of fishing mortality on its stocks, are still unknown, with the crocodile shark currently one of the least studied of all pelagic sharks. Given this, the present study aimed to assess the population structure of P. kamoharai in several regions of the Atlantic and Indian Oceans using genetic molecular markers. The nucleotide composition of the mitochondrial DNA control region of 255 individuals was analyzed, and 31 haplotypes were found, with an estimated diversity Hd = 0.627, and a nucleotide diversity π = 0.00167. An analysis of molecular variance (AMOVA) revealed a fixation index ΦST = -0.01118, representing an absence of population structure among the sampled regions of the Atlantic Ocean, and between the Atlantic and Indian Oceans. These results show a high degree of gene flow between the studied areas, with a single genetic stock and reduced population variability. In panmictic populations, conservation efforts can be concentrated in more restricted areas, being these representative of the total biodiversity of the species. When necessary, this strategy could be applied to the genetic maintenance of P. kamoharai. PMID:25689742

  11. Controls on 231Pa/230Th in the Indian Ocean: Circulation or Productivity?

    NASA Astrophysics Data System (ADS)

    Thomas, A. L.; Henderson, G. M.; McCave, N.

    2004-12-01

    (231Paxs/230Thxs)0 ratios in marine sediments are a potential proxy of palaeoproductivity and/or past ocean circulation. Studies in the Atlantic have demonstrated the particular potential of this proxy to assess the rate of past circulation AƒAøAøâ_sA¬Aøâ,¬Å" an important environmental variable which is otherwise difficult to reconstruct {[1, 2]}. In this study, we present new water-column and sediment data from the western Indian Ocean to improve understanding of the controls on (231Paxs/230Thxs)0 and test the use of this proxy. The Indian Ocean differs from the Atlantic because deep waters forming in the Southern Ocean and transported into the basin have high rather than low Pa and Th concentrations [3]. The ability to reconstruct past rates of flow into the Indian Ocean would be a powerful new use of Pa/Th, but no data presently exist to test this application. Water samples (10 litre), surface sediments, and a 5.5m Kasten core were collected on the Charles Darwin cruise CD154 from the area East of Madagascar. The down-core record, from10°S extends to 150 ka, and is coupled with a stable isotope stratigraphy and a sortable silt record. Water and sediment samples were analysed for isotopes of Pa, Th and U on a Nu Instruments MC-ICP-MS. The water-column dataset (26 samples) indicate that Pa concentrations are high in NADW transported into the Indian Ocean from the Atlantic, while opal scavenging has lowered Pa concentrations in deeper water masses. Sedimentary 230Th data indicate that there has been significant sediment focusing and that sediment mass fluxes are low. Preliminary sedimentary Pa/Th data show little relation to the sortable silt record. Ongoing Pa/Th and Ba data will complete this downcore record and allow comparison of a Pa/Th record with independent proxies of current speed and productivity in the same core. [1] E.F. Yu, et al, Nature 379, 689-694, 1996. [2] J.F. McManus, et al, Nature 428, 834-837, 2004. [3] M. M. Rutgers van der Loeff

  12. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-01

    Ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.

  13. Osmium isotopic constraints on the nature of the DUPAL anomaly from Indian mid-ocean-ridge basalts.

    PubMed

    Escrig, S; Capmas, F; Dupré, B; Allègre, C J

    2004-09-02

    The isotopic compositions of mid-ocean-ridge basalts (MORB) from the Indian Ocean have led to the identification of a large-scale isotopic anomaly relative to Pacific and Atlantic ocean MORB. Constraining the origin of this so-called DUPAL anomaly may lead to a better understanding of the genesis of upper-mantle heterogeneity. Previous isotopic studies have proposed recycling of ancient subcontinental lithospheric mantle or sediments with oceanic crust to be responsible for the DUPAL signature. Here we report Os, Pb, Sr and Nd isotopic compositions of Indian MORB from the Central Indian ridge, the Rodriguez triple junction and the South West Indian ridge. All measured samples have higher (187)Os/(188)Os ratios than the depleted upper-mantle value and Pb, Sr and Nd isotopic compositions that imply the involvement of at least two distinct enriched components in the Indian upper-mantle. Using isotopic and geodynamical arguments, we reject both subcontinental lithospheric mantle and recycled sediments with oceanic crust as the cause of the DUPAL anomaly. Instead, we argue that delamination of lower continental crust may explain the DUPAL isotopic signature of Indian MORB.

  14. Bythaelurus tenuicephalus n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the western Indian Ocean.

    PubMed

    Kaschner, Carina Julia; Weigmann, Simon; Thiel, Ralf

    2015-09-07

    A new dwarf deep-water catshark, Bythaelurus tenuicephalus, is described based on one adult and one juvenile male specimen from off Tanzania and Mozambique in the western Indian Ocean. The new species differs from its congeners by its slender head and snout, which is only slightly bell-shaped in dorsoventral view without distinct lateral indention. All other Bythaelurus species have distinctly bell-shaped snouts with a strong lateral indention anterior to outer nostrils. Compared to its congeners in the western Indian Ocean, B. tenuicephalus n. sp. also has broader claspers in adult males (base width 2.1% TL vs. 1.5-1.8% TL). It further differs from B. clevai by attaining a smaller maximum size and having a color pattern of fewer and smaller blotches, larger oral papillae, a shorter snout, and broader claspers without knob-like apex and with a smaller envelope and a subtriangular (vs. subrectangular) exorhipidion. Compared to B. hispidus, the new species has a longer snout, a longer dorsal-caudal space, broader clasper without knob-like apex, and fewer vertebral centra. In contrast to B. lutarius, B. tenuicephalus attains a smaller maximum size and has a blotched (vs. largely plain) coloration, numerous (vs. lacking) oral papillae, shorter anterior nasal flaps, a longer caudal fin, a shorter pelvic anal space, and shorter and broader claspers.

  15. Two new species of Cabillus (Perciformes: Gobiidae) and the first record of Cabillus macrophthalmus from the Western Indian Ocean.

    PubMed

    Kovačić, Marcelo; Bogorodsky, Sergey V

    2013-01-01

    Two new species of the gobiid genus Cabillus, C. nigromarginatus sp. nov. and Cabillus nigrostigmus sp. nov. are described. Cabillus nigromarginatus (from Rodrigues, Western Indian Ocean) is distinguished from congeners by having 18-20 pectoral-fin rays; predorsal area naked; two scales with enlarged ctenii ventrally and dorsally at the caudal-fin base; head with anterior and posterior oculoscapular, and preopercular canals, with pores σ, λ, κ, ω, α, β, ρ, ρ1, ρ2 and γ, δ, ε respectively; the body with four midline lateral blotches, with two or three of them expanding upwards in dorsal saddles; a dark triangular blotch at caudal-fin base; and predorsal with pigmentation at lateral edges forming a rectangle. Cabillus nigrostigmus (from the Red Sea) is distinguished from its congeners by having 19 pectoral-fin rays; transverse scale series 7; nape scaled, median predorsal scales 7; body depth 5.8-6.0 in SL; snout length 1.5-1.9 in eye diameter; caudal-peduncle depth in its length 2.4-2.5; a broad dark brown bar below first dorsal fin beginning anteriorly at the level of fourth spine of the first dorsal fin; elongate black blotch along posterior half of first dorsal fin extending into the sixth spine and adjacent membranes; and midlateral black spot at the end of caudal peduncle followed by S-shaped dark bar. Cabillus macrophthalmus is recorded for the first time in the Western Indian Ocean (Red Sea and Seychelles) and redescribed.

  16. Geochemistry and mineralogy of REY-rich mud in the eastern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Yasukawa, Kazutaka; Liu, Hanjie; Fujinaga, Koichiro; Machida, Shiki; Haraguchi, Satoru; Ishii, Teruaki; Nakamura, Kentaro; Kato, Yasuhiro

    2014-10-01

    Deep-sea sediments in parts of the Pacific Ocean were recently found to contain remarkably high concentrations of rare-earth elements and yttrium (REY) of possible economic significance. Here we report similar REY-rich mud in a core section from Deep Sea Drilling Project Site 213 in the eastern Indian Ocean. The sediments consist mainly of siliceous ooze, with subordinate zeolitic clay that contains relatively high REY concentrations. The maximum and average total REY (ΣREY) contents of this material are 1113 and 629 ppm, respectively, which are comparable to those reported from the Pacific Ocean. The REY-rich mud at Site 213 shows enrichment in heavy rare-earth elements, negative Ce anomalies, and relatively low Fe2O3/ΣREY ratios, similar to those in the Pacific Ocean. In addition, the major-element composition of the Indian Ocean REY-rich mud indicates slight enrichment in lithogenic components, which probably reflects a contribution from southern African eolian dust. A volcaniclastic component from neighboring mid-ocean ridges or intraplate volcanoes is also apparent. Elemental compositions and X-ray diffraction patterns for bulk sediment, and microscopic observation and elemental mapping of a polished thin section, demonstrate the presence of phillipsite and biogenic apatite, such as fish debris, in the REY-rich mud. The strong correlation between total REY content and apatite abundance implies that apatite plays an important role as a host phase of REY in the present deep-sea sediment column. However, positive correlations between ΣREY and elements not present in apatite (e.g., Fe2O3, MnO, and TiO2) imply that the REY-rich mud is not formed by a simple mixture of REY-enriched apatite and other components.

  17. Evolution of the lithosphere in the Indian Ocean from combined earthquake and ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Ma, Zhitu; Dalton, Colleen A.

    2017-01-01

    Rayleigh wave dispersion extracted from ambient seismic noise has been widely used to image crustal and uppermost mantle structure. Applications of this approach in continental settings are abundant, but there have been relatively few studies within ocean basins. By cross-correlating ambient noise recorded at broadband seismic stations around the Indian Ocean, we demonstrate the feasibility of extracting high-quality, long-period (10-30 mHz) Rayleigh waves that traverse the entire ocean basin. High-quality Rayleigh wave cross-correlation functions can be obtained from stacking waveforms over less than 2 years at land stations and less than 4 years at island stations. We show that adding the dispersion information extracted from ambient noise to a global earthquake data set can improve the resolution of phase velocity maps by about 20% in the northern Indian Ocean, where the station distribution is the best. We find that a plate cooling model with a potential temperature of 1450°C and plate thickness of 125 km can fit both the seismic observations and seafloor topography. The Seychelles-Mascarene Plateau is characterized by anomalously slow velocity at 30 mHz. The inclusion of ambient noise data in the tomographic inversion shifts the slow velocity anomaly into better agreement with the topographic relief, allowing us to estimate its crustal thickness and confirm that the plateau's elevation is supported by thick crust. The 10 and 20 mHz phase velocity maps show a strong asymmetry across the Central Indian Ridge that is best explained by eastward asthenospheric flow emanating from nearby hot spots.

  18. Indian Ocean radiocarbon: Data from the INDIGO 1, 2, and 3 cruises

    SciTech Connect

    Sepanski, R.J.

    1991-01-01

    This document presents {sup 14}C activities (expressed in the internationally adopted {Delta}{sup 14}C scale) from water samples taken at various locations and depths in the Indian and Southern oceans through the Indien Gaz Ocean (INDIGO) project. These data were collected as part of the INDIGO 1, INDIGO 2, and INDIGO 3 cruises, which took place during the years 1985, 1986, and 1987, respectively. These data have been used to estimate the penetration of anthropogenic CO{sub 2} in the Indian and Southern oceans. The document also presents supporting data for potential temperature, salinity, density (sigma-theta), {delta}{sup 13}C, and total CO{sub 2}. All radiocarbon measurements have been examined statistically for quality of sample counts and stability of counting efficiency and background. In addition, all data have been reviewed by the Carbon Dioxide Information Analysis Center and assessed for gross accuracy and consistency (absence of obvious outliers and other anomalous values). These data are available free of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of this document and a magnetic tape containing machine-readable files. This document provides sample listing of the Indian Ocean radiocarbon data as they appear on the magnetic tape, as well as a complete listing of these data in tabular form. This document also offers retrieval program listings, furnishes information on sampling methods and data selection, defines limitations and restrictions of the data, and provides reprints of pertinent literature. 13 refs., 4 tabs.

  19. Controls on ferromanganese crust composition and reconnaissance resource potential, Ninetyeast Ridge, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Hein, James R.; Conrad, Tracey; Mizell, Kira; Banakar, Virupaxa K.; Frey, Frederick A.; Sager, William W.

    2016-04-01

    A reconnaissance survey of Fe-Mn crusts from the 5000 km long (~31°S to 10°N) Ninetyeast Ridge (NER) in the Indian Ocean shows their widespread occurrence along the ridge as well as with water depth on the ridge flanks. The crusts are hydrogenetic based in growth rates and discrimination plots. Twenty samples from 12 crusts from 9 locations along the ridge were analyzed for chemical and mineralogical compositions, growth rates, and statistical relationships (Q-mode factor analysis, correlation coefficients) were calculated. The crusts collected are relatively thin (maximum 40 mm), and those analyzed varied from 4 mm to 32 mm. However, crusts as thick as 80 mm can be expected to occur based on the age of rocks that comprise the NER and the growth rates calculated here. Growth rates of the crusts increase to the north along the NER and with water depth. The increase to the north resulted from an increased supply of Mn from the oxygen minimum zone (OMZ) to depths below the OMZ combined with an increased supply of Fe at depth from the dissolution of biogenic carbonate and from deep-sourced hydrothermal Fe. These increased supplies of Fe increased growth rates of the deeper-water crusts along the entire NER. Because of the huge terrigenous (rivers, eolian, pyroclastic) and hydrothermal (three spreading centers) inputs to the Indian Ocean, and the history of primary productivity, Fe-Mn crust compositions vary from those analyzed from open-ocean locations in the Pacific. The sources of detrital material in the crusts change along the NER and reflect, from north to south, the decreasing influence of the Ganga River system and volcanic arcs located to the east, with increasing influence of sediment derived from Australia to the south. In addition, weathering of NER basalt likely contributed to the aluminosilicate fraction of the crusts. The southernmost sample has a relatively large detrital component compared to other southern NER crust samples, which was probably

  20. Growth and Construction of Oceanic Crust at Atlantis Bank, Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Schwartz, J. J.; John, B. E.; Cheadle, M. J.; Miranda, E. A.; Grimes, C. B.; Wooden, J. L.; Dick, H. J.

    2005-12-01

    Magmatic zircon is a common accessory mineral in oceanic crustal rocks including gabbro, oxide gabbro, diabase and felsic veins. Its presence in these rocks provides an exceptional opportunity to document crustal growth processes at slow-spreading mid-ocean ridges. We present nineteen Pb/U zircon SHRIMP-RG ion probe ages of lower crustal rocks collected by manned submersible, ROV, dredging and ODP drilling from a 20 x 30 km2 area of Atlantis Bank, Southwest Indian Ridge, which allow us to constrain the growth and construction of oceanic crust. Weighted average 206Pb/238U ages of these samples range from 10.7 to 13.9 Ma, with errors of 0.1-0.6 m.y. (<1 - 4%). At least 75% of these gabbros accreted within error of the predicted sea-surface magnetic age, whereas up to 25% are between 700,000 and 2.5 m.y. older. In one sample, we identified zircon with inherited cores as much as 1.5 m.y. older than their corresponding rims. There is no observable correlation between age and lithology, and the anomalously old samples are not from any specific part of Atlantis Bank; they appear to be randomly distributed amongst the non-anomalous age samples and come from various structural depths. We consider two models to explain the presence of these anomalously old rocks: i) a stochastic intrusion model whereby magma was intruded at different spatial locations within the rift valley as the plates spread apart, resulting in the entrapment of older lower crust by subsequent intrusions; and/or ii) a model in which some gabbroic bodies originally crystallized at depths of ~5-18 km below the base of the crust in a thick, cold, axial lithosphere and were subsequently uplifted along flow-lines and intruded by shallow-level magmas during the creation of Atlantis Bank. In this model, the difference in time between the Pb/U zircon crystallization age and the magnetic age is a proxy for the depth at which zircon crystallized (assuming a constant mantle upwelling rate during the construction of

  1. Constraints of subducted slabs under the Indian Ocean on the northward motion of India from Gondwanaland towards Eurasia

    NASA Astrophysics Data System (ADS)

    Suppe, John; Lin, Chris D. J.; Wu, Jonny; Kanda, Ravi V. S.

    2013-04-01

    We find an extensive swath of slabs in the lower mantle under the Indian Ocean at depths of 1000-2200km, with shallower slabs to the north under India and Eurasia at ~200-1500km. These slabs closely correspond to the well-known track that India has travelled northward from Gondwanaland toward its collision with Eurasia, viewed in the Indo-Atlantic moving hotspot reference frame, and account for a significant proportion of the predicted loss of the Ceno- and Neo-Tethyan Oceans since ~140Ma. Our work is based on our methodology of [1] mapping subducted slabs in global tomography (MITP08, Li et al. 2008) as 3D mid-slab surfaces in the Gocad environment, [2] quantitatively unfolding these surfaces to the surface of the earth in a spherical Earth model, minimizing changes in area and distortion, and [3] incorporating them into Gplates global plate tectonic reconstructions (http://www.earthbyte.org). These unfolded subducted slabs provide substantial quantitative constraints for the original location and extent of India and Greater India and for the nature and history of Ceno- and Neo-Tethys. We observe a distinct discontinuity in amplitude of p- and s-wave velocity anomalies between the higher-amplitude Neo-Tethyan slabs to the north under India and the Middle East and the lower-amplitude Ceno-Tethyan slabs under the central Indian Ocean, which is in agreement with a predicted large ~100Ma discontinuity in age-at-subduction between Neo- and Ceno-Tethys in existing plate-tectonic models (e.g. Müller et al., 2008; Seton et al, 2012). We present a plate tectonic reconstruction that incorporates these mapped slab constraints, with the implication that a substantial fraction of the Tethyan Ocean (~3000km) subducted southward under India at an early stage in the northward motion of India from Gondwanaland.

  2. Genetic Isolation among the Northwestern, Southwestern and Central-Eastern Indian Ocean Populations of the Pronghorn Spiny Lobster Panulirus penicillatus

    PubMed Central

    Abdullah, Muhamad Fadry; Alimuddin; Muththalib, Mohamed; Salama, Adnan Jameel; Imai, Hideyuki

    2014-01-01

    The pronghorn spiny lobster Panulirus penicillatus is a highly valuable species which is widely distributed in Indo-West Pacific and Eastern Pacific regions. Mitochondrial DNA control region sequences (566–571 bp) were determined to investigate the population genetic structure of this species in the Indian Ocean. In total, 236 adult individuals of Panulirus penicillatus were collected from five locations in the Indian Ocean region. Almost all individuals had a unique haplotype. Intrapopulation haplotype (h) and nucleotide (π) diversities were high for each locality, ranging from h = 0.9986–1.0000 and π = 0.031593–0.043441. We observed distinct genetic isolation of population located at the northwestern and southwestern edge of the species range. Gene flow was found within localities in the central and eastern region of the Indian Ocean, probably resulting from an extended planktonic larval stage and prevailing ocean currents. PMID:24865488

  3. Genetic isolation among the northwestern, southwestern and central-eastern Indian Ocean populations of the pronghorn spiny lobster Panulirus penicillatus.

    PubMed

    Abdullah, Muhamad Fadry; Alimuddin; Muththalib, Mohamed; Salama, Adnan Jameel; Imai, Hideyuki

    2014-05-26

    The pronghorn spiny lobster Panulirus penicillatus is a highly valuable species which is widely distributed in Indo-West Pacific and Eastern Pacific regions. Mitochondrial DNA control region sequences (566-571 bp) were determined to investigate the population genetic structure of this species in the Indian Ocean. In total, 236 adult individuals of Panulirus penicillatus were collected from five locations in the Indian Ocean region. Almost all individuals had a unique haplotype. Intrapopulation haplotype (h) and nucleotide (π) diversities were high for each locality, ranging from h = 0.9986-1.0000 and π = 0.031593-0.043441. We observed distinct genetic isolation of population located at the northwestern and southwestern edge of the species range. Gene flow was found within localities in the central and eastern region of the Indian Ocean, probably resulting from an extended planktonic larval stage and prevailing ocean currents.

  4. Quantitative Analysis of the Distribution of cis-Eicosenoic Acid Positional Isomers in Marine Fishes from the Indian Ocean.

    PubMed

    Senarath, Samanthika; Yoshinaga, Kazuaki; Nagai, Toshiharu; Yoshida, Akihiko; Beppu, Fumiaki; Jayasinghe, Chamila; Devadawson, Chandravathany; Gotoh, Naohiro

    2017-02-01

    This study investigated the occurrence and distribution of cis-eicosenoic acid (c-20:1) positional isomers in fishes from the Indian Ocean and compared to those from the Pacific and Atlantic Ocean. Lipids were extracted from the edible part of the fish and then methylated. The eicosenoic acid methyl ester fraction was separated from total fatty acid methyl esters by reversed-phase HPLC and quantitatively analyzed using a GC-FID fitted with the SLB-IL111 highly polar GC column. c14-20:1 was used as an internal standard. The results indicated that the highest levels of c-20:1 positional isomers were found in fishes from the Pacific Ocean (saury, 166.95±12.4 mg/g of oil), followed by the Atlantic Ocean (capelin, 162.7±3.5 mg/g of oil), and lastly in fishes from the Indian Ocean (goatfish, 34.39 mg/g of oil). With only a few exceptions, the most abundant 20:1 positional isomer found in fishes of the Indian and Atlantic Ocean was the c11-20:1 isomer (>50%) followed by the c13-20:1 isomer (<25%). Unusually, the c7-20:1 isomer was predominantly found in a few fishes such as the tooth ponyfish, longface emperor, and commerson's sole. The c9, c5, and c15-20:1 isomers were the least occurring in fishes from the Indian and Atlantic Ocean. In contrast, the c9-20:1 isomer was the principal isomer identified in fishes from the Pacific Ocean. The results revealed that the content and distribution of c-20:1 positional isomers varied among fishes in different oceans. The data presented in the current study are the first to report on the distribution of c-20:1 positional isomers in fishes from the Indian Ocean.

  5. Sediment distribution on the inner continental shelf off Khao Lak (Thailand) after the 2004 Indian Ocean tsunami

    NASA Astrophysics Data System (ADS)

    Feldens, P.; Schwarzer, K.; Sakuna, D.; Szczuciński, W.; Sompongchaiyakul, P.

    2012-10-01

    The coastline of Khao Lak (Thailand) was heavily damaged by the 2004 Indian Ocean tsunami. Onshore tsunami deposits and satellite images, which show large amounts of sediment transported offshore, indicate that the seafloor was impacted by tsunami run-up and backwash. In this study, high-resolution maps of sediment distribution patterns and the geological development of the seafloor are presented. These maps are based on multibeam, side-scan sonar and seismic profiling surveys offshore Khao Lak. Paleoreefs, with associated boulder fields and sandy sediment dominate the inner continental shelf. Patches of fine-grained (silt to fine sand) sediments exist in water depths of less than 15 m. The sediment distribution pattern is stable between 2008 and 2010, apart from small shifts regarding the boundaries of the fine-grained sediment patches. In one sediment core and several grab samples an event layer was documented, situated below a cover of modern sediments which is only a few cm thick. The event-layer is traced down to 18 m water depth. It consists mostly of sand and contains compounds of terrigenous origin. It is interpreted as a 2004 Indian Ocean tsunami deposit. However, over large areas of the study-site, the impact of the tsunami is hardly identifiable by seafloor morphology or sediment distribution.

  6. Hygroscopic properties of different aerosol types over the Atlantic and Indian Oceans

    NASA Astrophysics Data System (ADS)

    Maßling, A.; Wiedensohler, A.; Busch, B.; Neusüß, C.; Quinn, P.; Bates, T.; Covert, D.

    2003-01-01

    Hygroscopic properties of atmospheric particles were studied in the marine tropospheric boundary layer over the Atlantic and Indian Oceans during two consecutive field studies: the Aerosols99 cruise (Atlantic Ocean) from 15 January to 20 February 1999, and the INDOEX cruise (Indian Ocean Experiment) from 23 February to 30 March 1999. The hygroscopic properties were compared to optical and chemical properties, such as absorption, chemical inorganic composition, and mass concentration of organic and elemental carbon, to identify the influence of these parameters on hygroscopicity. During the two field studies, four types of aerosol-sampling instruments were used on board the NOAA (Northern Organization Atlantic Administration) Research Vessel Ronald H Brown: Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA), seven-stage cascade impactor, two-stage cascade impactor, and Particle Soot Absorption Photometer (PSAP). The HTDMA was used to determine the hygroscopic properties of atmospheric particles at initial dry sizes (Dp) of 50, 150, and 250 nm and at relative humidities (RH) of 30, 55, 75, and 90%. The HTDMA data provide insight into the mixing state of the aerosol in terms of its hygroscopic behavior. Simultaneously, a seven-stage cascade impactor (3 in the sub-µm size range) was used to determine the molar composition of the major inorganic ions such as ammonium and sulfate ions. A two-stage cascade impactor (1 in the sub-µm size range, 1 in the sup-µm size range) was used to determine the mass concentration of organic and elemental carbon. The PSAP was used (at a wavelength of 565 nm) to measure the light absorption coefficient of the aerosol. During the two field studies, air masses of several different origins passed the ship's cruise path. The air mass back-trajectory analysis revealed marine air masses as well as air masses with continental influence from Africa, India, or Arabia. The occurrence of different air masses was classified into special

  7. Convective Lofting Links Indian Ocean Air Pollution to Paradoxical South Atlantic Ozone Maxima

    NASA Technical Reports Server (NTRS)

    Chatfield, Robert B.; Guan, Hong; Thompson, Anne M.; Witte, Jacquelyn C.

    2003-01-01

    We describe a broad resolution of the "Atlantic Paradox" concerning the seasonal and geographic distribution of tropical tropospheric ozone. We describe periods of significant maximum tropospheric O3 for Jan.-April, 1999, exploiting satellite estimates and SHADOZ (Southern Hemisphere Additional Ozonesondes). Trajectory analyses connecting sondes and Total Tropospheric Ozone (TTO)O3 maps suggest a complex influence from the Indian Ocean: beginning with mixed combustion sources, then low level transport, cumulonimbus venting, and finally high-level transport to the west, with possible mixing over Africa. For the Jan.- March highest column-O3 periods in the Atlantic, distinct sounding peaks trace to specific NO sources, especially lightning, while in the same episodes, recurring every 30 or 60 days, more diffuse buildups of Indian-to-Atlantic pollution make important contributions.

  8. Convective lofting links Indian Ocean air pollution to paradoxical South Atlantic ozone maxima

    NASA Technical Reports Server (NTRS)

    Chatfield, R. B.; Guan, H.; Thompson, A. M.; Witte, J. C.

    2005-01-01

    We describe a broad resolution of the Atlantic Parado concerning the seasonal and geographic distribution, of tropical tropospheric ozone. We highlight periods of significant maximum tropospheric O3 for Jan.- April, 1999, exploiting satellite estimates and SHADOZ (Southern Hemisphere Additional Ozonesondes). Trajectory analyses connecting sondes and Total Tropospheric Ozone (TTO) maps suggest a complex influence from the Indian Ocean: beginning with mixed combustion sources, then low level transport, cumulonimbus venting, possible stratospheric input, and finally high-level transport to the west, with possible mixing over Africa. For the Jan.-March highest column-O3 periods in the Atlantic, distinct sounding peaks trace to specific NO sources, especially lightning, while in the same episodes, recurring every 20-50 days, more diffuse buildups of Indian-to-Atlantic pollution make important contributions.

  9. Convective lofting links Indian Ocean air pollution to paradoxical South Atlantic ozone maxima

    NASA Astrophysics Data System (ADS)

    Chatfield, R. B.; Guan, H.; Thompson, A. M.; Witte, J. C.

    2004-03-01

    We describe a broad resolution of the ``Atlantic Parado'' concerning the seasonal and geographic distribution of tropical tropospheric ozone. We highlight periods of significant maximum tropospheric O3 for Jan.-April, 1999, exploiting satellite estimates and SHADOZ (Southern Hemisphere Additional Ozonesondes). Trajectory analyses connecting sondes and Total Tropospheric Ozone (TTO) maps suggest a complex influence from the Indian Ocean: beginning with mixed combustion sources, then low level transport, cumulonimbus venting, possible stratospheric input, and finally high-level transport to the west, with possible mixing over Africa. For the Jan.-March highest column-O3 periods in the Atlantic, distinct sounding peaks trace to specific NO sources, especially lightning, while in the same episodes, recurring every 20-50 days, more diffuse buildups of Indian-to-Atlantic pollution make important contributions.

  10. Analyses of MAGSAT tracks crossing the study region in the Indian Ocean

    NASA Technical Reports Server (NTRS)

    Sailor, R. V.; Lazarewicz, A. R. (Principal Investigator)

    1981-01-01

    Progress in software development and in preliminary analysis of MAGSAT tracks crossing the Indian Ocean is reported. Tracks crossing the Java Trench, Broken Ridge, the Southeast Indian Ridge, and the Ninetyeast Ridge show that magnetic anomalies correlate with some of these features. Preliminary study of anomaly profiles indicates that tracks of anomaly data (the observations minus a core field model) have a power spectrum decreasing as the inverse square of the spatial frequency. An apparent noise floor of about one to two gammas rms is reached at wavelengths of about 360 km, corresponding to approximately 10 samples of the decimated Investigator tape data at a sampling rate of approximately 4.9 sec/sample.

  11. Role of the oceanic channel in the relationships between the basin/dipole mode of SST anomalies in the tropical Indian Ocean and ENSO transition

    NASA Astrophysics Data System (ADS)

    Zhao, Xia; Yuan, Dongliang; Yang, Guang; Zhou, Hui; Wang, Jing

    2016-12-01

    The relationships between the tropical Indian Ocean basin (IOB)/dipole (IOD) mode of SST anomalies (SSTAs) and ENSO phase transition during the following year are examined and compared in observations for the period 1958-2008. Both partial correlation analysis and composite analysis show that both the positive (negative) phase of the IOB and IOD (independent of each other) in the tropical Indian Ocean are possible contributors to the El Niño (La Niña) decay and phase transition to La Niña (El Niño) about one year later. However, the influence on ENSO transition induced by the IOB is stronger than that by the IOD. The SSTAs in the equatorial central-eastern Pacific in the coming year originate from subsurface temperature anomalies in the equatorial eastern Indian and western Pacific Ocean, induced by the IOB and IOD through eastward and upward propagation to meet the surface. During this process, however the contribution of the oceanic channel process between the tropical Indian and Pacific oceans is totally different for the IOB and IOD. For the IOD, the influence of the Indonesian Throughflow transport anomalies could propagate to the eastern Pacific to induce the ENSO transition. For the IOB, the impact of the oceanic channel stays and disappears in the western Pacific without propagation to the eastern Pacific.

  12. Search strategy in a complex and dynamic environment (the Indian Ocean case)

    NASA Astrophysics Data System (ADS)

    Loire, Sophie; Arbabi, Hassan; Clary, Patrick; Ivic, Stefan; Crnjaric-Zic, Nelida; Macesic, Senka; Crnkovic, Bojan; Mezic, Igor; UCSB Team; Rijeka Team

    2014-11-01

    The disappearance of Malaysia Airlines Flight 370 (MH370) in the early morning hours of 8 March 2014 has exposed the disconcerting lack of efficient methods for identifying where to look and how to look for missing objects in a complex and dynamic environment. The search area for plane debris is a remote part of the Indian Ocean. Searches, of the lawnmower type, have been unsuccessful so far. Lagrangian kinematics of mesoscale features are visible in hypergraph maps of the Indian Ocean surface currents. Without a precise knowledge of the crash site, these maps give an estimate of the time evolution of any initial distribution of plane debris and permits the design of a search strategy. The Dynamic Spectral Multiscale Coverage search algorithm is modified to search a spatial distribution of targets that is evolving with time following the dynamic of ocean surface currents. Trajectories are generated for multiple search agents such that their spatial coverage converges to the target distribution. Central to this DSMC algorithm is a metric for the ergodicity.

  13. Asthenosphere rheology inferred from observations of the 2012 Indian Ocean earthquake.

    PubMed

    Hu, Yan; Bürgmann, Roland; Banerjee, Paramesh; Feng, Lujia; Hill, Emma M; Ito, Takeo; Tabei, Takao; Wang, Kelin

    2016-10-20

    The concept of a weak asthenospheric layer underlying Earth's mobile tectonic plates is fundamental to our understanding of mantle convection and plate tectonics. However, little is known about the mechanical properties of the asthenosphere (the part of the upper mantle below the lithosphere) underlying the oceanic crust, which covers about 60 per cent of Earth's surface. Great earthquakes cause large coseismic crustal deformation in areas hundreds of kilometres away from and below the rupture area. Subsequent relaxation of the earthquake-induced stresses in the viscoelastic upper mantle leads to prolonged postseismic crustal deformation that may last several decades and can be recorded with geodetic methods. The observed postseismic deformation helps us to understand the rheological properties of the upper mantle, but so far such measurements have been limited to continental-plate boundary zones. Here we consider the postseismic deformation of the very large (moment magnitude 8.6) 2012 Indian Ocean earthquake to provide by far the most direct constraint on the structure of oceanic mantle rheology. In the first three years after the Indian Ocean earthquake, 37 continuous Global Navigation Satellite Systems stations in the region underwent horizontal northeastward displacements of up to 17 centimetres in a direction similar to that of the coseismic offsets. However, a few stations close to the rupture area that had experienced subsidence of up to about 4 centimetres during the earthquake rose by nearly 7 centimetres after the earthquake. Our three-dimensional viscoelastic finite-element models of the post-earthquake deformation show that a thin (30-200 kilometres), low-viscosity (having a steady-state Maxwell viscosity of (0.5-10) × 10(18) pascal seconds) asthenospheric layer beneath the elastic oceanic lithosphere is required to produce the observed postseismic uplift.

  14. Asthenosphere rheology inferred from observations of the 2012 Indian Ocean earthquake

    NASA Astrophysics Data System (ADS)

    Hu, Yan; Bürgmann, Roland; Banerjee, Paramesh; Feng, Lujia; Hill, Emma M.; Ito, Takeo; Tabei, Takao; Wang, Kelin

    2016-10-01

    The concept of a weak asthenospheric layer underlying Earth’s mobile tectonic plates is fundamental to our understanding of mantle convection and plate tectonics. However, little is known about the mechanical properties of the asthenosphere (the part of the upper mantle below the lithosphere) underlying the oceanic crust, which covers about 60 per cent of Earth’s surface. Great earthquakes cause large coseismic crustal deformation in areas hundreds of kilometres away from and below the rupture area. Subsequent relaxation of the earthquake-induced stresses in the viscoelastic upper mantle leads to prolonged postseismic crustal deformation that may last several decades and can be recorded with geodetic methods. The observed postseismic deformation helps us to understand the rheological properties of the upper mantle, but so far such measurements have been limited to continental-plate boundary zones. Here we consider the postseismic deformation of the very large (moment magnitude 8.6) 2012 Indian Ocean earthquake to provide by far the most direct constraint on the structure of oceanic mantle rheology. In the first three years after the Indian Ocean earthquake, 37 continuous Global Navigation Satellite Systems stations in the region underwent horizontal northeastward displacements of up to 17 centimetres in a direction similar to that of the coseismic offsets. However, a few stations close to the rupture area that had experienced subsidence of up to about 4 centimetres during the earthquake rose by nearly 7 centimetres after the earthquake. Our three-dimensional viscoelastic finite-element models of the post-earthquake deformation show that a thin (30-200 kilometres), low-viscosity (having a steady-state Maxwell viscosity of (0.5-10) × 1018 pascal seconds) asthenospheric layer beneath the elastic oceanic lithosphere is required to produce the observed postseismic uplift.

  15. Wake Vortices and Tropical Cyclogenesis Downstream of Sumatra over the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Fine, Caitlin Marie

    A myriad of processes acting singly or in concert may contribute to tropical cyclogenesis, including convectively coupled waves, breakdown of the inter-tropical convergence zone (ITCZ), or upper-level troughs. This thesis investigates the role that topographic effects from the island of Sumatra may play in initiating tropical cyclogenesis (TC genesis) in the eastern Indian Ocean. If easterly flow is split by the mountains of Sumatra, counter-rotating lee vortices may form downstream. Because Sumatra straddles the equator, though the wake vortices rotate in opposite directions, they will both be cyclonic when winds are easterly upon Sumatra, and may intensify further into tropical cyclones. The phenomenon of crossequatorial cyclone pairs, or "twin" tropical cyclones, in the Indian Ocean originating from Sumatra was first noted by Kuettner (1989). TC genesis appears to be particularly favored during the pre-onset phase of the Madden Julian Oscillation (MJO), when easterly flow encroaches upon Sumatra and the resulting cyclonic wake vortices encounter convectively coupled waves and enhanced moisture associated with the MJO in the Indian Ocean. Operational analysis data from the Year of Tropical Convection (YOTC) and Dynamics of the Madden Julian Oscillation (DYNAMO) campaigns were used to evaluate the impacts of Sumatra's topography upon the flow. The YOTC data encompass two years, from May 2008 to April 2010, while the special observing period of DYNAMO was conducted from October to December 2011. This research also presents three case studies of twin tropical cyclones west of Sumatra in the Indian Ocean, which were all determined to originate from Sumatran wake vortices and occurred between October and December of 2008, 2009, and 2011. Multiple cyclonic wake vortices and vorticity streamers were observed downstream of Sumatra during periods of easterly flow, most frequently between October and December. Froude numbers calculated for the region upstream of Sumatra

  16. Linking geological evidence from the Eurasian suture zones to a regional Indian Ocean plate tectonic model

    NASA Astrophysics Data System (ADS)

    Gibbons, A.; Aitchison, J.; Müller, R.; Whittaker, J.

    2012-12-01

    We present a revised regional plate tectonic model for the Indian Ocean from the Late Jurassic to present, which assimilates both marine geophysical data constraining the seafloor spreading history as well as a variety of geological observations from the Eurasian collision zone. This model includes relative motion between Greater India, Sri Lanka, West Australia, East Antarctica, East Madagascar, the Seychelles and Argoland, a continental sliver which began migrating towards Eurasia in the Late Jurassic, forming the northern margins of Greater India and western Australia. Recently collected data offshore northwest Australia suggest that the majority of Greater India reached only halfway along the West Australian margin in an Early Mesozoic reconstruction, bounded by the Wallaby-Zenith Fracture Zone. The revised geometries and relative motion histories redefine the timing and nature of collisional events, as well as the history of back-arc basins and intra-oceanic arcs, such as the Kohistan-Ladakh intra-oceanic arc in northwest India and Pakistan. Abundant ophiolites have been identified throughout the Yarlung-Tsangpo Suture Zone, between the Indian-Himalaya and Tibet, several have boninitic compositions and almost all date to either the Mid Jurassic or late Early Cretaceous. Further evidence suggests that an intra-oceanic arc collided with Greater India before colliding with Eurasia. Our model features a transform boundary running north of East Africa, which initiated an oceanic arc following short-lived compression between the western and central Mesotethys in the Late Jurassic, coinciding with the initial motion of Argoland. The arc developed through extension and ophiolite generation until at least the mid-Cretaceous and consumed a narrow thinned sliver of West Argoland between ~120-65 Ma. The arc remained active in the same position until its eventual collision with Greater India ~55 Ma. The eastern portion of the intra-oceanic arc accreted to eastern Eurasia

  17. Seafloor seismicity, Antarctic ice-sounds, cetacean vocalizations and long-term ambient sound in the Indian Ocean basin

    NASA Astrophysics Data System (ADS)

    Royer, J.-Y.; Chateau, R.; Dziak, R. P.; Bohnenstiehl, D. R.

    2015-08-01

    This paper presents the results from the Deflo-hydroacoustic experiment in the Southern Indian Ocean using three autonomous underwater hydrophones, complemented by two permanent hydroacoustic stations. The array monitored for 14 months, from November 2006 to December 2007, a 3000 × 3000 km wide area, encompassing large segments of the three Indian spreading ridges that meet at the Indian Triple Junction. A catalogue of 11 105 acoustic events is derived from the recorded data, of which 55 per cent are located from three hydrophones, 38 per cent from 4, 6 per cent from five and less than 1 per cent by six hydrophones. From a comparison with land-based seismic catalogues, the smallest detected earthquakes are mb 2.6 in size, the range of recorded magnitudes is about twice that of land-based networks and the number of detected events is 5-16 times larger. Seismicity patterns vary between the three spreading ridges, with activity mainly focused on transform faults along the fast spreading Southeast Indian Ridge and more evenly distributed along spreading segments and transforms on the slow spreading Central and ultra-slow spreading Southwest Indian ridges; the Central Indian Ridge is the most active of the three with an average of 1.9 events/100 km/month. Along the Sunda Trench, acoustic events mostly radiate from the inner wall of the trench and show a 200-km-long seismic gap between 2 °S and the Equator. The array also detected more than 3600 cryogenic events, with different seasonal trends observed for events from the Antarctic margin, compared to those from drifting icebergs at lower (up to 50°S) latitudes. Vocalizations of five species and subspecies of large baleen whales were also observed and exhibit clear seasonal variability. On the three autonomous hydrophones, whale vocalizations dominate sound levels in the 20-30 and 100 Hz frequency bands, whereas earthquakes and ice tremor are a dominant source of ambient sound at frequencies <20 Hz.

  18. Reconstruction of the coastal impact of the Indian Ocean tsunami on December 26, 2004

    NASA Astrophysics Data System (ADS)

    Eriksson, L. Y.; Skelton, A.; Mård Karlsson, J.

    2015-12-01

    The aim of this study is to reconstruct the coastal impact of the Indian Ocean tsunami on coastal areas of Thailand based on amateur videos. The purpose of such reconstructions is to provide quantitative data needed to verify computer simulations of tsunamis which are used to guide mitigation efforts during the critical time interval following a potentially tsunamigenic earthquake. More than ten years have passed since the tsunami catastrophe in Thailand 2004, and there are almost no visible signs left from the damage it caused. Many of the buildings in Thailand were rebuilt precisely as they were before the catastrophe. This allowed us to use amateur videos made a decade ago, during the tsunami to estimate tsunami height, direction and velocity. We also made an analogue experiment in a lab at Stockholm University to examine how the tsunami was affected entering a narrow passage (e.g. a street). The results of this study is an overview of tsunami height data and velocity. Our tsunami height results show an average and standard deviation of (6.8+/-0.1 m) and are remarkably uniform across the 100 km x 100 km study area although the height is increasing slightly on its way north. Tsunami velocity is also increasing on its way north while the velocity is decreasing on its way east. Based on these observations, which are unexpected because the velocity and height are more powerful in the northern parts which are further away from the epicentre than the southern parts of the study area, we interpret that this is a result of that the southern parts are shielded by the northern parts of Sumatra. Our analogue experiment showed that tsunami height and velocity are essentially unaffected by entering a narrow passage (e.g. a street) perpendicular to the beach. This indicates that measurements done in this environment are indeed reliable because it avoids the influence of back flow as the tsunami hits a barrier.

  19. Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM

    NASA Astrophysics Data System (ADS)

    Benedict, James J.; Pritchard, Michael S.; Collins, William D.

    2015-12-01

    The superparameterized Community Atmosphere Model (SPCAM) is used to investigate the impact and geographic sensitivity of positive Indian Ocean Dipole (+IOD) sea-surface temperatures (SSTs) on Madden-Julian oscillation (MJO) propagation. The goal is to clarify potentially appreciable +IOD effects on MJO dynamics detected in prior studies by using a global model with explicit convection representation. Prescribed climatological October SSTs and variants of the SST distribution from October 2006, a +IOD event, force the model. Modest MJO convection weakening over the Maritime Continent occurs when either climatological SSTs, or +IOD SST anomalies restricted to the Indian Ocean, are applied. However, severe MJO weakening occurs when either +IOD SST anomalies are applied globally or restricted to the equatorial Pacific. MJO disruption is associated with time-mean changes in the zonal wind profile and lower moist static energy (MSE) in subsiding air masses imported from the Subtropics by Rossby-like gyres. On intraseasonal scales, MJO disruption arises from significantly smaller MSE accumulation, weaker meridional advective moistening, and overactive submonthly eddies that mix drier subtropical air into the path of MJO convection. These results (1) demonstrate that SPCAM reproduces observed time-mean and intraseasonal changes during +IOD episodes, (2) reaffirm the role that submonthly eddies play in MJO propagation and show that such multiscale interactions are sensitive to interannual SST states, and (3) suggest that boreal fall +IOD SSTs local to the Indian Ocean have a significantly smaller impact on Maritime Continent MJO propagation compared to contemporaneous Pacific SST anomalies which, for October 2006, resemble El Niño-like conditions.

  20. New data regarding distribution of cattle ticks in the south-western Indian Ocean islands

    PubMed Central

    2013-01-01

    Recent studies have produced new insight into the origin and distribution of some cattle ticks in the south-western Indian Ocean islands. Rhipicephalus appendiculatus, introduced from Tanzania in 2002, is now well established on Grande Comore but has not yet reached the other islands of the archipelago (Mohéli, Anjouan and Mayotte). Only one of the two clades identified in Africa has settled so far. Amblyomma variegatum, which was not supposed to be able to persist in the Antananarivo region (1300 m) nor in other Malagasy regions of high altitude without regular introductions of ticks by infested cattle, is now endemic as a general rule up to 1600 m although other regions of lower altitude (1400 m) are still free of the tick. This species remains confined in a small area of the west coast on La Reunion Island. On the contrary, Hyalomma dromedarii could not settle on Madagascar where it was introduced in 2008 and Rhipicephalus evertsi evertsi is not yet present in Grande Comore despite regular introductions by infested cattle from Tanzania. A phylogeographic approach has been carried out at an intra-specific level for A. variegatum. This study has led to the identification of two main lineages, one covering all species distribution and one restricted to East Africa and the Indian Ocean area. These two lineages are in sympatry in Madagascar where a high genetic diversity has been described, whereas a lower genetic diversity is observed on other islands. These results seem to agree with the historical data concerning the introduction of the tick in the Indian Ocean area. PMID:24016261

  1. New data regarding distribution of cattle ticks in the south-western Indian Ocean islands.

    PubMed

    Stachurski, Frédéric; Tortosa, Pablo; Rahajarison, Patrick; Jacquet, Stéphanie; Yssouf, Amina; Huber, Karine

    2013-09-09

    Recent studies have produced new insight into the origin and distribution of some cattle ticks in the south-western Indian Ocean islands. Rhipicephalus appendiculatus, introduced from Tanzania in 2002, is now well established on Grande Comore but has not yet reached the other islands of the archipelago (Mohéli, Anjouan and Mayotte). Only one of the two clades identified in Africa has settled so far. Amblyomma variegatum, which was not supposed to be able to persist in the Antananarivo region (1300 m) nor in other Malagasy regions of high altitude without regular introductions of ticks by infested cattle, is now endemic as a general rule up to 1600 m although other regions of lower altitude (1400 m) are still free of the tick. This species remains confined in a small area of the west coast on La Reunion Island. On the contrary, Hyalomma dromedarii could not settle on Madagascar where it was introduced in 2008 and Rhipicephalus evertsi evertsi is not yet present in Grande Comore despite regular introductions by infested cattle from Tanzania. A phylogeographic approach has been carried out at an intra-specific level for A. variegatum. This study has led to the identification of two main lineages, one covering all species distribution and one restricted to East Africa and the Indian Ocean area. These two lineages are in sympatry in Madagascar where a high genetic diversity has been described, whereas a lower genetic diversity is observed on other islands. These results seem to agree with the historical data concerning the introduction of the tick in the Indian Ocean area.

  2. An Analysis of an Eddy-Resolving Global Ocean Model in the Tropical Indian Ocean

    DTIC Science & Technology

    1990-09-01

    Ocean circulation. The seasonally-reversing Somali Current is simulated by the model, and includes seasonai undercurrents and a tvo-gyre system during...undercurrents and a two-gyre system during the southwest monson. Westward-flow occ,, rs beneath the Southwest Monsoon Current during June and July. The...25 F. THE SOMALI CURRENT SYSTEM ....................................... 28 G. THROUGHFLOW IN THE

  3. Future projection of mean and variability of the Asian Summer Monsoon and Indian Ocean Climate systems

    SciTech Connect

    Annamalai, H.

    2014-09-15

    The overall goal of this project is to assess the ability of the CMIP3/5 models to simulate the Indian-Ocean monsoon systems. The PI along with post-docs investigated research issues ranging from synoptic systems to long-term trends over the Asian monsoon region. The PI applied diagnostic tools such as moist static energy (MSE) to isolate: the moist and radiative processes responsible for extended monsoon breaks over South Asia, precursors in the ENSO-monsoon association, reasons for the drying tendency over South Asia and the possible effect on tropical Indian Ocean climate anomalies influencing certain aspects of ENSO characteristics. By diagnosing various observations and coupled model simulations, we developed working hypothesis and tested them by carrying out sensitivity experiments with both linear and nonlinear models. Possible physical and dynamical reasons for model sensitivities were deduced. On the teleconnection front, the ability of CMIP5 models in representing the monsoon-desert mechanism was examined recently. Further more, we have applied a suite of diagnostics and have performed an in depth analysis on CMIP5 integrations to isolate the possible reasons for the ENSO-monsoon linkage or lack thereof. The PI has collaborated with Dr. K.R. Sperber of PCMDI and other CLIVAR Asian-Australian monsoon panel members in understanding the ability of CMIP3/5 models in capturing monsoon and its spectrum of variability. The objective and process-based diagnostics aided in selecting models that best represent the present-day monsoon and its variability that are then employed for future projections. Two major highlights were an invitation to write a review on present understanding monsoons in a changing climate in Nature Climate Change, and identification of an east-west shift in observed monsoon rainfall (more rainfall over tropical western Pacific and drying tendency over South Asia) in the last six decades and attributing that shift to SST rise over the tropical

  4. Metonymic objects, cultural practices and narrative repair: Sri Lankan responses to the Indian Ocean tsunami.

    PubMed

    Cassim, Shemana; Stolte, Ottilie; Hodgetts, Darrin

    2015-07-01

    The 2004 Indian Ocean tsunami resulted in a tragic loss of life and immense suffering. This article explores the ways in which a group of people from Sri Lanka worked to address the disruption to their life narratives caused by the loss of loved ones. We go beyond a focus on 'talk' in narrative research in health psychology to explore the importance of material objects in sustaining continued bonds with the deceased. This article provides an alternative to the tendency in mainstream psychology to pathologise grief and highlights the importance of culturally patterned responses to disaster.

  5. Evolution of the eastern Indian Ocean since the Late Cretaceous - Constraints from Geosat altimetry

    NASA Technical Reports Server (NTRS)

    Royer, Jean-Yves; Sandwell, David T.

    1989-01-01

    A model of the tectonic evolution of the eastern Indian Ocean from the Late Cretaceous to the present is constructed. Reinterpretations of seafloor magnetic anomalies are used to place constraints on spreading rates and the timing of major reorganizations. Vertical deflection profiles from 22 repeat cycles of Geosat altimeter data are used to determine the tectonic fabric associated with fracture zones. The Geosat data place constraints on paleospreading directions. Consideration is given to the implications of the model for the relative motions between India, Australia, and Antarctica.

  6. Modeling Salinity Exchanges Between the Equatorial Indian Ocean and the Bay of Bengal

    DTIC Science & Technology

    2016-06-01

    of high-salinity water from the equatorial Indian Ocean into the Bay of Bengal during the northeast monsoon, although it is weaker than during the...southwest monsoon. On average, salt is transported into the Bay of Bengal between 83°E and 95°E, and low-salinity water flows southward near the...that a strong subsurface current with a speed of about 1 m s–1 intrudes into the Bay of Bengal beneath southward-flowing low-salinity water during the

  7. Q-structure beneath the north and central Indian Ocean from the inversion of observed Love and Rayleigh wave attenuation data

    NASA Astrophysics Data System (ADS)

    Singh, D. D.

    80 km is estimated beneath the Arabian Fan, and the Indian Ocean off Ninetyeast Ridge and across Ninetyeast Ridge, respectively. The base of the lithosphere is identified as the depth at which there is a significant increase in the Qβ-1 value, which attains its maximum value in the asthenosphere. The thinning of Indian lithosphere beneath the Arabian Fan suggests high temperature below Moho depth (60 km from surface) which has caused a high-attenuation zone at this shallow depth.

  8. Hydrothermal circulation and subsidence of ocean basins : a case study from the South-East Indian Ocean

    NASA Astrophysics Data System (ADS)

    Louis, G. B.; Jean, F.; James, C. R.; Cinthia, L.; Delphine, A.

    2003-12-01

    The South-East Indian Ridge (SEIR) flanks between 105° E and 130° E are characterized by anomalously low subsidence rates, less than about 280 m/ sqrt(Ma) [Hayes and Kane, JGR, 1994]. While individual estimates of the upper mantle temperature variations below the SEIR axis may vary significantly from one study to the other, all geophysical (axial morphology, seismology and geoid) and geochemical (major and trace elements systematics) evidence is compatible with variations of less than about 100° C. Such a temperature anomaly is not sufficient to fully explain the observed anomalously low subsidence rates, using the present available models for the thermal evolution of the lithosphere. Ad hoc explanations, such as, for instance, variations in mantle thermal parameters cannot be readily rejected, but are not completely satisfactory because they cannot be supported by direct estimates. In contrast, of direct evidence is the lack of sedimentation that characterizes the flanks of the SEIR and the fact, recognized from heat flow data, that in absence of sediment cover, seawater penetrates into the ocean crust and plays a key role in the mechanisms of heat transfer through the seafloor. Although it is now widely accepted that seawater may penetrate massively into poorly sedimented off-axis crust, the contribution of water circulation to the seafloor subsidence rate has only been considered so far near crestal areas, but not at the scale of tens of millions years. We thus propose a simple model which assumes, at first approximation, that seawater penetrates into highly permeable off-axis crust to a depth H below the seafloor and maintains the temperature equal to Tc at that depth (Note : H may depend on age crust). Assuming that hydrothermal circulation is active over large periods (of tens of Ma, for instance), the subsidence rate is controlled by Tm-Tc. The model thus predicts that variations in the hydrothermal regime, by affecting Tc, may affect the subsidence rate

  9. A new deepwater legskate, Sinobatis kotlyari n. sp. (Rajiformes, Anacanthobatidae) from the southeastern Indian Ocean on Broken Ridge.

    PubMed

    Stehmann, Matthias F W; Weigmann, Simon

    2016-11-10

    Sinobatis kotlyari n. sp. is described, based on the nearly adult 331 mm TL holotype male from 1400 m depth in the southeastern Indian Ocean at Broken Ridge. The new species is assigned to Sinobatis due to mainly characters of its clasper and cranium fontanelle distinguishing it from congeners and other anacanthobatid skates with clasper features known. It further differs from its morphologically closest congener, S. borneensis, which is only known from the northwestern Pacific Ocean, e.g. in larger maturing size, longer snout and head, the absence of a snout filament and skin fold on tail, a longer caudal fin, and in colouration. The two congeners known from the eastern Indian Ocean, S. bulbicauda and S. cae-rulea, mature at much larger size, grow to larger maximum size and differ in numerous morphometric and meristic           characters, as well as in colouration. The type locality appears to be very remote as compared with other Indian Ocean legskates, which have primarily been found on continental and insular slopes.

  10. Coral record of southeast Indian Ocean marine heatwaves with intensified Western Pacific temperature gradient

    NASA Astrophysics Data System (ADS)

    Zinke, J.; Hoell, A.; Lough, J. M.; Feng, M.; Kuret, A. J.; Clarke, H.; Ricca, V.; Rankenburg, K.; McCulloch, M. T.

    2015-10-01

    Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threatening the integrity and functional diversity of coral reefs. Here we demonstrate the role of inter-ocean coupling in amplifying thermal stress on reefs in the poorly studied southeast Indian Ocean (SEIO), through a robust 215-year (1795-2010) geochemical coral proxy sea surface temperature (SST) record. We show that marine heatwaves affecting the SEIO are linked to the behaviour of the Western Pacific Warm Pool on decadal to centennial timescales, and are most pronounced when an anomalously strong zonal SST gradient between the western and central Pacific co-occurs with strong La Niña's. This SST gradient forces large-scale changes in heat flux that exacerbate SEIO heatwaves. Better understanding of the zonal SST gradient in the Western Pacific is expected to improve projections of the frequency of extreme SEIO heatwaves and their ecological impacts on the important coral reef ecosystems off Western Australia.

  11. Polychlorinated naphthalenes in the air over the equatorial Indian Ocean: Occurrence, potential sources, and toxicity.

    PubMed

    Huang, Yumei; Li, Jun; Xu, Yue; Xu, Weihai; Zhong, Guangcai; Liu, Xiang; Zhang, Gan

    2016-06-15

    Monitoring of marine polychlorinated naphthalenes (PCNs) is crucial, as they are considered persistent organic pollutants (POPs) by the Stockholm Convention. Data on PCNs in marine environment are scarce. In this study, 19 air samples were collected during a cruise in the equatorial Indian Ocean on board the Chinese research vessel Shiyan I from 4/2011 to 5/2011. PCN concentration of these air samples ranged from 0.033 to 2.56pgm(-3), with an average of 0.518pgm(-3), equal to or lower than the values reported for other oceans, seas, and lakes worldwide. Tri- and tetra-CNs were the main homologues in most samples. Reemission of Halowax mixtures and incineration processes were the major sources of atmospheric PCNs in the study area. The PCN-corresponding toxic equivalency values ranged from 0 to 0.190fgm(-3) (average: 0.038fgm(-3)), falling in the low end of global range.

  12. Continuous transport of Pacific-derived anthropogenic radionuclides towards the Indian Ocean

    PubMed Central

    Pittauer, Daniela; Tims, Stephen G.; Froehlich, Michaela B.; Fifield, L. Keith; Wallner, Anton; McNeil, Steven D.; Fischer, Helmut W.

    2017-01-01

    Unusually high concentrations of americium and plutonium have been observed in a sediment core collected from the eastern Lombok Basin between Sumba and Sumbawa Islands in the Indonesian Archipelago. Gamma spectrometry and accelerator mass spectrometry data together with radiometric dating of the core provide a high-resolution record of ongoing deposition of anthropogenic radionuclides. A plutonium signature characteristic of the Pacific Proving Grounds (PPG) dominates in the first two decades after the start of the high yield atmospheric tests in 1950’s. Approximately 40–70% of plutonium at this site in the post 1970 period originates from the PPG. This sediment record of transuranic isotopes deposition over the last 55 years provides evidence for the continuous long-distance transport of particle-reactive radionuclides from the Pacific Ocean towards the Indian Ocean. PMID:28304374

  13. Continuous transport of Pacific-derived anthropogenic radionuclides towards the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Pittauer, Daniela; Tims, Stephen G.; Froehlich, Michaela B.; Fifield, L. Keith; Wallner, Anton; McNeil, Steven D.; Fischer, Helmut W.

    2017-03-01

    Unusually high concentrations of americium and plutonium have been observed in a sediment core collected from the eastern Lombok Basin between Sumba and Sumbawa Islands in the Indonesian Archipelago. Gamma spectrometry and accelerator mass spectrometry data together with radiometric dating of the core provide a high-resolution record of ongoing deposition of anthropogenic radionuclides. A plutonium signature characteristic of the Pacific Proving Grounds (PPG) dominates in the first two decades after the start of the high yield atmospheric tests in 1950’s. Approximately 40–70% of plutonium at this site in the post 1970 period originates from the PPG. This sediment record of transuranic isotopes deposition over the last 55 years provides evidence for the continuous long-distance transport of particle-reactive radionuclides from the Pacific Ocean towards the Indian Ocean.

  14. Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013

    PubMed Central

    Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain

    2016-01-01

    In-situ measurement of the upper ocean velocity discloses significant abnormal behaviors of two Wyrtki Jets (WJs) respectively in boreal spring and fall, over the tropical Indian Ocean in 2013. The two WJs both occurred within upper 130 m depth and persisted more than one month. The exceptional spring jet in May was unusually stronger than its counterpart in fall, which is clearly against the previous understanding. Furthermore, the fall WJ in 2013 unexpectedly peaked in December, one month later than its climatology. Data analysis and numerical experiments illustrate that the anomalous changes in the equatorial zonal wind, associated with the strong intra-seasonal oscillation events, are most likely the primary reason for such anomalous WJs activities. PMID:27436723

  15. Radiocesium monitoring in Indonesian waters of the Indian Ocean after the Fukushima nuclear accident.

    PubMed

    Suseno, Heny; Wahono, Ikhsan Budi; Muslim

    2015-08-15

    As data on anthropogenic radionuclide concentrations (i.e., (134)Cs and (137)Cs) in Indonesian marine environments including the Indian Ocean are scarce, offshore monitoring has been performed in the West Sumatra and South Java Seas. The activity concentration of (137)Cs ranges from below minimum detectable activity (MDA) to 0.13Bqm(-3) in the surface seawater of the South Java Sea and from lower than MDA to 0.28Bqm(-3) in the surface seawater of the West Sumatra Sea. The concentrations of (137)Cs in the surface seawater of the West Sumatra and South Java Seas are lower than the estimation of (137)Cs concentration in the subsurface waters owing to the input of the North Pacific Ocean via the Indonesian Throughflow (ITF). The concentrations of (134)Cs in the sampling locations were lower than MDA. These results have indicated that these Indonesian marine waters have not yet been influenced by the Fukushima radioactive release.

  16. Why does near ridge extensional seismicity occur primarily in the Indian Ocean?

    NASA Technical Reports Server (NTRS)

    Stein, Seth; Cloetingh, Sierd; Wortel, Rinus; Wiens, Douglas A.

    1987-01-01

    It is argued that though thermoelastic stresses provide a low level background in all plates, the data favoring their contributing significantly to the stress field and seismicity in the young oceanic lithosphere may be interpreted in terms of stresses resulting from individual plate geometry and local boundary effects. The dramatic concentration of extensional seismicity in the Central Indian Ocean region is shown to be consistent with finite element results for the intraplate stress incorporating the effects of the Himalayan collision and the various subduction zones. Most of the data for both ridge-parallel extension and depth stratification are provided by earthquakes in this area, and it is suggested that these effects may be due more to the regional stress.

  17. Coral record of southeast Indian Ocean marine heatwaves with intensified Western Pacific temperature gradient.

    PubMed

    Zinke, J; Hoell, A; Lough, J M; Feng, M; Kuret, A J; Clarke, H; Ricca, V; Rankenburg, K; McCulloch, M T

    2015-10-23

    Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threatening the integrity and functional diversity of coral reefs. Here we demonstrate the role of inter-ocean coupling in amplifying thermal stress on reefs in the poorly studied southeast Indian Ocean (SEIO), through a robust 215-year (1795-2010) geochemical coral proxy sea surface temperature (SST) record. We show that marine heatwaves affecting the SEIO are linked to the behaviour of the Western Pacific Warm Pool on decadal to centennial timescales, and are most pronounced when an anomalously strong zonal SST gradient between the western and central Pacific co-occurs with strong La Niña's. This SST gradient forces large-scale changes in heat flux that exacerbate SEIO heatwaves. Better understanding of the zonal SST gradient in the Western Pacific is expected to improve projections of the frequency of extreme SEIO heatwaves and their ecological impacts on the important coral reef ecosystems off Western Australia.

  18. Contribution of seasonal presence of cetaceans, earthquakes, drifting icebergs and anthropogenic activity to the ambient noise level in the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves

    2015-04-01

    Assessing the ambient sound level in the oceans is essential for a better understanding of the interactions between the ecosystem and anthropogenic activities. Ambient noise studies conducted in the North Pacific and Atlantic oceans, have shown that since the 60's oceanic noise level increases with the ship traffic, even if potential impacts of shipping noise on the ecosystem is not yet fully understood. However long-term acoustic records for the Indian Ocean are still limited. Here we present long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected at 5 widely distributed autonomous hydrophones. The data consist of single hydrophone spectra (10-100 Hz in 1-Hz bins) averaged using Welch's method over 200 s. Spectral probability distributions of the ambient sound level are analyzed in order to identify the main sound sources and their geographical and time variability. The mean sound level within the array is 10 to 20 dB lower than in other oceans, revealing a weaker influence of shipping on the Southern Indian Ocean noise budget. Seismic events are evenly distributed in time and space and mostly contribute to the general low-frequency background noise. Periodic signals are mainly associated with the seasonal presence of 3 types of blue whales and fin whales whose signatures are easily identified at target frequencies. Winter lows and summer highs of the ambient noise levels are also well correlated with ice volume variations. Icebergs are found to be a major sound source, strongly contributing to seasonal variations even at northernmost sites of the array. Although anthropogenic factors do not seem to dominate the noise spectrum, shipping sounds are present north and east of the array. Observed higher sound levels are consistent with the proximity of major traffic lanes.

  19. Significant influence of the boreal summer monsoon flow on the Indian Ocean response during dipole events

    NASA Astrophysics Data System (ADS)

    Raghavan, Krishnan; Panickal, Swapna

    2010-05-01

    A majority of positive Indian Ocean Dipole (IOD) events in the last 50-years were accompanied by enhanced summer-monsoon circulation and above-normal precipitation over central-north India. Given that IODs peak during boreal-autumn following the summer-monsoon season, this study examines the role of the summer-monsoon flow on the Indian Ocean (IO) response using a suite of ocean model experiments and supplementary data-diagnostics. The present results indicate that if the summer-monsoon Hadley-type circulation strengthens during positive-IOD events, then the strong off-equatorial south-easterly winds over the northern flanks of the intensified Australian High can effectively promote upwelling in the south-eastern tropical Indian Ocean and amplify the zonal-gradient of the IO heat-content response. While it is noted that a strong-monsoon cross-equatorial flow by itself may not generate a dipole-like response, a strengthening (weakening) of monsoon easterlies to the south-of-equator during positive-IOD events tends to reinforce (hinder) the zonal-gradient of the upper-ocean heat-content response. The findings show that an intensification of monsoonal-winds during positive-IOD periods produces nonlinear amplification of easterly wind-stress anomalies to the south-of-equator due to the nonlinear dependence of wind-stress on wind-speed. It is noted that such an off-equatorial intensification of easterlies over SH enhances upwelling in the eastern IO off Sumatra-Java; and the thermocline shoaling provides a zonal pressure-gradient which drives anomalous eastward equatorial under-currents (EUC) in the sub-surface. Furthermore, the combination of positive-IOD and stronger-than-normal monsoonal flow favors intensification of shallow transient meridional-overturning circulation in the eastern IO; and enhances the feed of cold subsurface off-equatorial waters to the EUC. References: P. Swapna and R. Krishnan 2008: Geophy. Res. Lett. 35, L14S04, doi: 10.1029/ 2008GL033430 R

  20. Argo profiles nonlinear feedback processes associated with the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Cai, W.; Qiu, Y.

    2012-12-01

    A well-known feature of the Indian Ocean Dipole (IOD) is its positive skewness, with cold sea surface temperature (SST) anomalies over the east pole (IODE) exhibiting a larger amplitude than warm SST anomalies. Several mechanisms have been proposed for this asymmetry, but due to a lack of observations, the role of various processes remains contentious. Using Argo profiles and other newly available data, we provide an observation-based assessment of the IOD skewness. Firstly, the role of a nonlinear dynamical heating process is re-affirmed, which reinforces IODE cold anomalies but damps IODE warm anomalies. This reinforcing effect is greater than the damping effect, further contributing to the skewness. Secondly, the existence of a thermocline-temperature feedback asymmetry, whereby IODE cold anomalies induced by a shoaling thermocline are greater than warm anomalies associated with a deepening thermocline, is the primary forcing of the IOD skewness. This thermocline-temperature feedback asymmetry is a part of the nonlinear Bjerknes-like positive feedback loop involving winds, SST, and the thermocline, all displaying a consistent asymmetry with a stronger response when IODE SST anomalies are anomalously cool. The asymmetry is enhanced by a nonlinear barrier layer response, showing a greater thinning associated with IODE cold anomalies than a thickening associated with IODE warm anomalies. Finally, in response to IODE cool anomalies, rainfall and evaporative heat loss reduce, and incoming shortwave radiation increases, damping the SST anomalies. The damping increases with IODE cold anomalies. Thus, the IOD skewness is generated in spite of a greater damping effect of the SST-cloud-radiation feedback process.

  1. Tide Gauge Observations of 2004-2007 Indian Ocean Tsunamis from Sri Lanka and Western Australia

    NASA Astrophysics Data System (ADS)

    Pattiaratchi, Charitha B.; Sarath Wijeratne, E. M.

    2009-02-01

    Tide gauge data collected from Sri Lanka (three stations) and Western Australia (eleven stations) during the Indian Ocean tsunamis, which occurred in December 2004, March 2005, July 2006, and September 2007, and incorporated five tsunamis, were examined to determine tsunami behaviour during these events. During the December 2004 tsunami, maximum wave heights of 3.87 m and 1.75 m were recorded at Colombo (Sri Lanka) and Bunbury (Western Australia), respectively. The results indicated that although the relative magnitudes of the tsunamis varied, the tsunami behaviour at each station was similar. This was due to the effect of the local and regional topography. At all tide gauges, the spectral energy corresponding to periods between 20 and 85 minutes increased during the tsunami. The sea-level data obtained from the west and south coasts of Sri Lanka (Colombo and Kirinda) indicated the importance of wave reflections from the Maldives Island chain, which produced the maximum wave two to three hours after the arrival of the first wave. In contrast, Trincomalee on the east coast did not show evidence of a reflected wave. Similarly, along the west coast of Australia, the highest waves occurred 15 hours after the arrival of the first wave. Here, based on travel times, we postulated that the waves were reflected from the Mascarene Ridge and/or the Island of Madagascar. Reflected waves were not present in the 2006 tsunami, where the primary waves propagated away from topographic features. One of the main influences of the tsunami was to set up oscillations at the local resonance frequency. Because Sri Lanka and Western Australia have relatively straight coastlines, these oscillations were related to the fundamental period of the shelf oscillation. For Colombo, this corresponded to 75-minute period, whereas in Geraldton and Busselton (Australia), the four-hour period was most prominent; at Jurien Bay and Fremantle, the resonance period was 2.7 hours.

  2. Kocuria subflava sp. nov., isolated from marine sediment from the Indian Ocean.

    PubMed

    Jiang, Zhao; Zhang, Wei-Hua; Yuan, Chang-Guo; Chen, Jia-Yang; Cao, Li-Xiang; Park, Dong-Jin; Xiao, Min; Kim, Chang-Jin; Li, Wen-Jun

    2015-12-01

    A novel Gram-staining positive, catalase-positive, oxidase-negative, aerobic, non-motile coccus, designated strain YIM 13062(T), was isolated from a marine sediment sample collected from the Indian Ocean. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM 13062(T) belongs to the genus Kocuria, and is closely related to Kocuria polaris NBRC 103063(T) (97.8 % similarity), Kocuria rosea NBRC 3768(T) (97.6 % similarity) and Kocuria carniphila JCM 14118(T) (97.4 % similarity). The strain grew optimally at 28 °C, pH 8.0 and in the presence of 2-4 % (w/v) NaCl. Cell-wall peptidoglycan type was Lys-Ala3 (type A3α). The major isoprenoid quinones were MK-6(H2) and MK-7(H2). The polar lipids of strain YIM 13062(T) consisted of diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), one unidentified phospholipid (PL), one unidentified aminophospholipid (APL), two unidentified aminolipids (AL) and four unidentified lipids (L). Major fatty acids of the novel isolate were anteiso-C15:0, iso-C14:0 and C18:1 2OH. The genomic DNA G+C content of strain YIM 13062(T) was 68.0 mol%. The level of DNA-DNA relatedness between strain YIM 13062(T) and K. polaris NBRC 103063(T), K. rosea NBRC 3768(T), K. carniphila JCM 14118(T) were 53.2, 48.8 and 42.6 %, respectively. On the basis of genotypic and phenotypic data, it is apparent that strain YIM 13062(T) represents a novel species of the genus Kocuria, for which the name Kocuria subflava sp. nov. is proposed. The type strain is YIM 13062(T) (=CGMCC 4.7252(T)=KCTC 39547(T)).

  3. Identification of a bacterial pathogen associated with Porites white patch syndrome in the Western Indian Ocean.

    PubMed

    Séré, Mathieu G; Tortosa, Pablo; Chabanet, Pascale; Quod, Jean-Pascal; Sweet, Michael J; Schleyer, Michael H

    2015-09-01

    Porites white patch syndrome (PWPS) is a coral disease recently described in the Western Indian Ocean. This study aimed to isolate and identify potential pathogens associated with PWPS utilizing both culture and nonculture screening techniques and inoculation trials. A total of 14 bacterial strains (those dominant in disease lesions, absent or rare in healthy tissues and considered potential pathogens in a previous study) were cultured and used to experimentally inoculate otherwise healthy individuals in an attempt to fulfil Henle-Koch's postulates. However, only one (P180R), identified as closely related (99-100% sequence identity based on 1.4 kb 16S RNA sequence) to Vibrio tubiashii, elicited signs of disease in tank experiments. Following experimental infection (which resulted in a 90% infection rate), the pathogen was also successfully re-isolated from the diseased tissues and re-inoculated in healthy corals colonies, therefore fulfilling the final stages of Henle-Koch's postulates. Finally, we report that PWPS appears to be a temperature-dependent disease, with significantly higher tissue loss (anova: d.f. = 2, F = 39.77, P < 0.01) occurring at 30 °C [1.45 ± 0.85 cm(2) per day (mean ± SE)] compared to ambient temperatures of 28 and 26 °C (0.73 ± 0.80 cm(2) per day (mean ± SE) and 0.51 ± 0.50 cm(2) per day (mean ± SE), respectively).

  4. A climatological model of North Indian Ocean tropical cyclone genesis, tracks and landfall

    NASA Astrophysics Data System (ADS)

    Wahiduzzaman, Mohammad; Oliver, Eric C. J.; Wotherspoon, Simon J.; Holbrook, Neil J.

    2016-12-01

    Extensive damage and loss of life can be caused by tropical cyclones (TCs) that make landfall. Modelling of TC landfall probability is beneficial to insurance/re-insurance companies, decision makers, government policy and planning, and residents in coastal areas. In this study, we develop a climatological model of tropical cyclone genesis, tracks and landfall for North Indian Ocean (NIO) rim countries based on kernel density estimation, a generalised additive model (GAM) including an Euler integration step, and landfall detection using a country mask approach. Using a 35-year record (1979-2013) of tropical cyclone track observations from the Joint Typhoon Warning Centre (part of the International Best Track Archive Climate Stewardship Version 6), the GAM is fitted to the observed cyclone track velocities as a smooth function of location in each season. The distribution of cyclone genesis points is approximated by kernel density estimation. The model simulated TCs are randomly selected from the fitted kernel (TC genesis), and the cyclone paths (TC tracks), represented by the GAM together with the application of stochastic innovations at each step, are simulated to generate a suite of NIO rim landfall statistics. Three hindcast validation methods are applied to evaluate the integrity of the model. First, leave-one-out cross validation is applied whereby the country of landfall is determined by the majority vote (considering the location by only highest percentage of landfall) from the simulated tracks. Second, the probability distribution of simulated landfall is evaluated against the observed landfall. Third, the distances between the point of observed landfall and simulated landfall are compared and quantified. Overall, the model shows very good cross-validated hindcast skill of modelled landfalling cyclones against observations in each of the NIO tropical cyclone seasons and for most NIO rim countries, with only a relatively small difference in the percentage of

  5. Modeling Reef Fish Biomass, Recovery Potential, and Management Priorities in the Western Indian Ocean

    PubMed Central

    McClanahan, Timothy R.; Maina, Joseph M.; Graham, Nicholas A. J.; Jones, Kendall R.

    2016-01-01

    Fish biomass is a primary driver of coral reef ecosystem services and has high sensitivity to human disturbances, particularly fishing. Estimates of fish biomass, their spatial distribution, and recovery potential are important for evaluating reef status and crucial for setting management targets. Here we modeled fish biomass estimates across all reefs of the western Indian Ocean using key variables that predicted the empirical data collected from 337 sites. These variables were used to create biomass and recovery time maps to prioritize spatially explicit conservation actions. The resultant fish biomass map showed high variability ranging from ~15 to 2900 kg/ha, primarily driven by human populations, distance to markets, and fisheries management restrictions. Lastly, we assembled data based on the age of fisheries closures and showed that biomass takes ~ 25 years to recover to typical equilibrium values of ~1200 kg/ha. The recovery times to biomass levels for sustainable fishing yields, maximum diversity, and ecosystem stability or conservation targets once fishing is suspended was modeled to estimate temporal costs of restrictions. The mean time to recovery for the whole region to the conservation target was 8.1(± 3SD) years, while recovery to sustainable fishing thresholds was between 0.5 and 4 years, but with high spatial variation. Recovery prioritization scenario models included one where local governance prioritized recovery of degraded reefs and two that prioritized minimizing recovery time, where countries either operated independently or collaborated. The regional collaboration scenario selected remote areas for conservation with uneven national responsibilities and spatial coverage, which could undermine collaboration. There is the potential to achieve sustainable fisheries within a decade by promoting these pathways according to their social-ecological suitability. PMID:27149673

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

    NASA Astrophysics Data System (ADS)

    Kalangutkar, Niyati G.; Iyer, Sridhar D.; Mascarenhas-Pereira, Maria B. L.; Nath, B. Nagender

    2015-06-01

    Mineralogical and elemental analyses of 20 ferromanganese (FeMn)-coated pumice samples from the Central Indian Ocean Basin (CIOB) indicate that todorokite is the major mineral phase, whereas vernadite occurs only rarely. Based on major, trace and rare earth elements (REEs) as well as Ce anomalies, the sources of the FeMn oxides were identified to be either hydrogenous, hydrothermal-plume fallout, diagenetic or a combination of these. Plots of Fe/Mn vs. Ce or Co reveal a distinct demarcation of the diagenetic, hydrogenous and plume fallout samples. Five samples are interpreted to be of hydrothermal origin because these show negative Ce anomalies and low Co/Zn ratios (0.5 to 1.1), and are masked by diagenesis. The relative contributions of hydrogenous, hydrothermal and diagenetic inputs were assessed in terms of ternary mixing patterns using REE mass balance equations. Furthermore, the hypothetical Ce anomaly (Ce/Ce*) was calculated using ternary mixing calculations for hydrogenous, hydrothermal and diagenetic end-members to ascertain the input to FeMn oxides on the pumice samples. This revealed a distinction between hydrogenous and hydrothermal components but diagenetic and plume fallout components could not be distinguished because this scheme comprises a three end-member calculation. A conservative estimate indicates the hydrothermal component to vary between 24% and 72%. The growth rates of the oxides, as estimated from published empirical methods, range between 3 and 47 mm/106 years. Fe/Mn ratios yielded a maximum age of 5-7 Ma and a minimum of 0.04-0.1 Ma. This suggests that the commencement of accretion of the FeMn oxides generally precedes the age of the Krakatau 1883 eruption, which is commonly considered as being the prime source of pumice to the CIOB. This is the first evidence of hydrothermal influence in the formation of FeMn oxides on CIOB pumice.

  7. Magnetic Anomalies in the South of Corad Rise, the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nogi, Y.; Ikehara, M.; Nakamura, Y.; Kameo, K.; Katsuki, K.; Kawamura, S.; Kita, S.

    2008-12-01

    Seafloor age estimated from magnetic anomalies in the Southern Indian Ocean are vital to understanding the fragmentation process of the Gondwana, but the seafloor age still remain less well-defined because of the sparse observations in this area. To understand the seafloor spreading history related to the Gondwana breakup, total intensity and vector geomagnetic field measurements as well as swath bathymetry mapping were conducted during the R/V Hakuho-maru cruise KH-07-4 Leg3 in the Southern Indian Ocean between Cape Town, South Africa, and off Lützow-Holm Bay, Antarctica. Magnetic anomaly data have been collected along WNW-ESE trending structures of unknown origin inferred from satellite gravity anomalies just to the south of Conrad Rise. We have also collected magnetic anomaly data along NNE-SSW trending lineaments from satellite gravity anomaly data between the south of the Conrad Rise and off Lützow-Holm Bay. Magnetic anomalies with amplitude of about 500 nT, originating from normal and reversed magnetization of oceanic crust, are detected along the WNW-ESE trending structures just to the south of Conrad Rise. These magnetic anomalies possibly belong to Mesozoic magnetic anomaly sequence and this shows the part of the oceanic crust just to the south of the Conrad Rise formed before the long Cretaceous normal polarity superchron although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. Magnetic anomalies with amplitude of about 300 nT are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and off Lützow-Holm Bay, and most likely indicate Mesozoic magnetic anomaly sequence. These suggest the extinct spreading axes in the south of Conrad Rise and complicated seafloor spreading history in this area.

  8. Seasonal and intraseasonal biogeochemical variability in the thermocline ridge of the southern tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Resplandy, L.; Vialard, J.; LéVy, M.; Aumont, O.; Dandonneau, Y.

    2009-07-01

    The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) time series shows high variability of surface chlorophyll at seasonal and intraseasonal time scales in the oligotrophic southern tropical Indian Ocean thermocline ridge called the Seychelles-Chagos thermocline ridge (SCTR). The SCTR is characterized by an open ocean upwelling due to local Ekman pumping, which annually maintains the mixed layer (ML) shallow and is responsive to atmospheric forcing and in particular to the Madden-Julian Oscillation (MJO) at an intraseasonal time scale. Here we present an overview of SCTR biogeochemistry and investigate the physical processes driving the response observed at seasonal and intraseasonal time scales. Using satellite observations and biophysical ocean simulations, we show that seasonal and intraseasonal SeaWiFS signals (in austral winter and during MJO events, respectively) correspond to wind-induced mixing episodes. During such episodes, entrainment fertilizes the ML and allows phytoplankton production. Increased surface production is compensated by a decrease in the subsurface due to light limitation, leading to no significant change in integrated biomass and carbon export. Satellite observations and model results support the conclusion that the biogeochemical response to MJO is highly dependent on interannual variability of thermocline depth. Following Indian Ocean Dipole events, deepened nutrient-rich waters prevent nutrient input into the ML, decreasing the biogeochemical response to MJO. These results shed light on the physical processes at work in the strong surface temperature response to MJO in this region and suggest that entrainment cooling can play a role in the temperature signature to the MJO but is highly modulated by basin-scale interannual variability.

  9. Advances in earthquake and tsunami sciences and disaster risk reduction since the 2004 Indian ocean tsunami

    NASA Astrophysics Data System (ADS)

    Satake, Kenji

    2014-12-01

    The December 2004 Indian Ocean tsunami was the worst tsunami disaster in the world's history with more than 200,000 casualties. This disaster was attributed to giant size (magnitude M ~ 9, source length >1000 km) of the earthquake, lacks of expectation of such an earthquake, tsunami warning system, knowledge and preparedness for tsunamis in the Indian Ocean countries. In the last ten years, seismology and tsunami sciences as well as tsunami disaster risk reduction have significantly developed. Progress in seismology includes implementation of earthquake early warning, real-time estimation of earthquake source parameters and tsunami potential, paleoseismological studies on past earthquakes and tsunamis, studies of probable maximum size, recurrence variability, and long-term forecast of large earthquakes in subduction zones. Progress in tsunami science includes accurate modeling of tsunami source such as contribution of horizontal components or "tsunami earthquakes", development of new types of offshore and deep ocean tsunami observation systems such as GPS buoys or bottom pressure gauges, deployments of DART gauges in the Pacific and other oceans, improvements in tsunami propagation modeling, and real-time inversion or data assimilation for the tsunami warning. These developments have been utilized for tsunami disaster reduction in the forms of tsunami early warning systems, tsunami hazard maps, and probabilistic tsunami hazard assessments. Some of the above scientific developments helped to reveal the source characteristics of the 2011 Tohoku earthquake, which caused devastating tsunami damage in Japan and Fukushima Dai-ichi Nuclear Power Station accident. Toward tsunami disaster risk reduction, interdisciplinary and trans-disciplinary approaches are needed for scientists with other stakeholders.

  10. Planktonic foraminiferal biogeography in the Indian sector of the Southern Ocean: Contribution from CPR data

    NASA Astrophysics Data System (ADS)

    Meilland, Julie; Fabri-Ruiz, Salomé; Koubbi, Philippe; Monaco, Claire Lo; Cotte, Cédric; Hosie, Graham W.; Sanchez, Sophie; Howa, Hélène

    2016-04-01

    Within the framework of the Scientific Committee on Antarctic Research (SCAR) Southern Ocean-Continuous Plankton Recorder (SO-CPR) Survey, the oceanic regions around Crozet and Kerguelen Islands were investigated in February-March 2013. Living planktonic Foraminifera (LPF) were collected in the upper mixed layer with a CPR along a 2160 nautical mile sea transect that crossed main hydrological fronts in the Indian sector of the Southern Ocean. In the SO-CPR database, mean total abundances of Foraminifera occurring during late austral summer are highly variable at an inter-annual scale, from 10 to 250 ind.m-3, representing 10-40% of the total zooplankton abundance, respectively. In the Southern Ocean, major inter-annual changes in zooplankton community structure were already reported. In this study, we describe the large scale distributional pattern of individual planktonic foraminiferal species living in near-surface waters of the Indian sector of the Southern Ocean, and we attempt to explain why major spatial variability in relative species abundances occurs during a late austral summer. In February-March 2013, LPF total abundances recorded between 42.86°S and 56.42°S ranged from 0 to a maximum of 258 ind.m-3. In the Open Ocean Zone, the LPF community was composed of four major species (Globigerinita uvula, Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globigerina bulloides). Generally, LPF total abundances are supposed to mirror primary production induced by hydrological fronts or induced by topography near Crozet and Kerguelen Islands. However, during late austral summer 2013, high foraminiferal abundances in the upper mixed layer did not always match the pattern of near-surface primary production (high Chl-a concentration areas delineated from satellite imagery). Low LPF standing stocks in late austral summer in the Southern Ocean contrasted with the presence of high densities of heavily silicified diatoms. This suggests that the late bloom

  11. A study of biases in simulation of the Indian Ocean basin mode and its capacitor effect in CMIP3/CMIP5 models

    NASA Astrophysics Data System (ADS)

    Tao, Weichen; Huang, Gang; Hu, Kaiming; Gong, Hainan; Wen, Guanhuan; Liu, Lin

    2016-01-01

    Based on 15 Coupled Model Intercomparison Project (CMIP) phase 3 (CMIP3) and 32 CMIP phase 5 (CMIP5) models, a detailed diagnosis was carried out to understand what compose the biases in simulation of the Indian Ocean basin mode (IOBM) and its capacitor effect. Cloud-radiation-SST (CRS) feedback and wind-evaporation-SST (WES) feedback are the two major atmospheric processes for SST changes. Most CMIP models simulate a stronger CRS feedback and a weaker WES feedback. During boreal fall of the El Niño/Southern Oscillation developing year and the following spring, there are weak biases of suppressed rainfall anomalies over the Maritime Continent and anomalous anticyclone over South Indian Ocean. Most CMIP models simulate reasonable short wave radiation (SWR) and weaker latent heat flux (LHF) anomalies. This leads to a weak bias of atmospheric processes. During winter, however, the rainfall anomalies are stronger due to west bias, and the anomalous anticyclone is comparable to observations. As such, most models simulate stronger SWR and reasonable LHF anomalies, leading to a strong bias of atmospheric processes. The thermocline feedback is stronger in most models. Though there is a deep bias of climatology thermocline, most models capture reasonable sea surface height-induced SST anomalies. Therefore, the effect of oceanic processes offset the weak bias of atmospheric processes in spring, and the tropical Indian Ocean warming persists into summer. However, anomalous northwest Pacific (NWP) anticyclone is weaker due to weak and west bias of the capacitor effect. The unrealistic western Pacific SST anomalies in models favor the westward extension of Rossby wave from the Pacific, weakening the effect of Kelvin wave from the Indian Ocean. Moreover, the western Pacific warming forces the NWP anticyclone move farther north than observations, suggesting a major forcing from the Pacific. Compared to CMIP3, CMIP5 models simulate the feedbacks more realistically and display

  12. Coarse fraction fluctuations in pelagic carbonate sediments from the tropical Indian Ocean: A 1500-kyr record of carbonate dissolution

    NASA Astrophysics Data System (ADS)

    Bassinot, Franck C.; Beaufort, Luc; Vincent, Edith; Labeyrie, Laurent D.; Rostek, Frauke; Müller, Peter J.; Quidelleur, Xavier; Lancelot, Yves

    1994-08-01

    Appendix Table Al Is available with entire article onmicrofiche. Order from the American Geophysical Union, 2000Florida Avenue, N.W., Washington, D.C. 20009. DocumentP94-001; $2.50. Payment must accompany order.We examined coarse fraction contents of pelagic carbonates deposited between 2000-and 3700-m water depth in the tropical Indian Ocean using Ocean Drilling Program (ODP) sites 722 (Owen Ridge, Arabian Sea) and 758 (Ninetyeast Ridge, eastern equatorial Indian Ocean), and four giant piston cores collected by the French R/V Marion Dufresne during the SEYMAMA expedition. Over the last 1500 kyr, coarse fraction records display high-amplitude oscillations with an irregular wavelength on the order of ˜500 kyr. These oscillations can be correlated throughout the entire equatorial Indian Ocean, from the Seychelles area eastward to the Ninetyeast Ridge, and into the Arabian Sea. Changes in grain size mainly result from changes in carbonate dissolution as evidenced by the positive relationship between coarse fraction content and a foraminiferal preservation index based on test fragmentation. The well-known "mid-Bruhes dissolution cycle"represents the last part of this irregular long-term dissolution oscillation. The origin of this long-term oscillation is still poorly understood. Our observations suggest that it is not a true cycle (it has an irregular wavelength) and we propose that it may result from long-term changes in Ca++flux to the ocean. Sites 722 and 758 δ18O records provide a high-resolution stratigraphy that allows a detailed intersite comparison of the two coarse fraction records over the last 1500 kyr. Site 722 (2030 m) lies above the present and late Pleistocene lysocline. The lysocline shoaled to the position of site 758 (2925 m) only during the interglacial intervals that occurred between about 300 and 500 ka (Peterson and Prell, 1985a). Despite these supralysoclinal positions of the two sites, short-term changes in coarse fraction contents are

  13. Integrated bio-magnetostratigraphy of ODP Site 709 (equatorial Indian Ocean).

    NASA Astrophysics Data System (ADS)

    Villa, Giuliana; Fioroni, Chiara; Florindo, Fabio

    2015-04-01

    Over the last decade, calcareous nannofossil biostratigraphy of the lower Eocene-Oligocene sediments has shown great potential, through identification of several new nannofossil species and bioevents (e.g. Fornaciari et al., 2010; Bown and Dunkley Jones, 2012; Toffanin et al., 2013). These studies formed the basis for higher biostratigraphic resolution leading to definition of a new nannofossil biozonation (Agnini et al., 2014). In this study, we investigate the middle Eocene-lower Oligocene sediments from ODP Hole 709C (ODP Leg 115) by means of calcareous nannofossils and magnetostratigraphy. Ocean Drilling Program (ODP) Site 709 was located in the equatorial Indian Ocean and biostratigraphy has been investigated in the nineties (Okada, 1990; Fornaciari et al., 1990) while paleomagnetic data from the Initial Report provided only a poorly constrained magnetostratigraphic interpretation, thus the cored succession was dated only by means of biostratigraphy. Our goal is to test