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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. Indian Continental Rainfall and Indian Ocean SST

    NASA Astrophysics Data System (ADS)

    Vecchi, G. A.; Harrison, D. E.

    2002-12-01

    We here explore the spatial structure of the interannual variability of southwest monsoon precipitation over the Indian subcontinent, based on gridded precipitation over the period 1982-2001, and its association to Indian Ocean sea surface temperature anomaly (SSTA) structures. We find that India is dominated by two independent regions of strong mean and variance in precipitation: the Western Ghats and the central plains region. We explore statistical relationships of precipitation anomaly in these two regions and All-India Rainfall, with SSTA in the Indian Ocean. We are able to find strong (r ~0.6-0.7) simultaneous and lead correlations between distinct Indian Ocean SSTA patterns and precipitation anomaly in the two regions, but do not find similarly strong connections with All-India rainfall. June through September (JJAS) Western Ghats precipitation (WGP) is positively correlated with JJAS western Arabian Sea SSTA, and July through September (JAS) WGP is positively correlated with June western Arabian Sea SSTA.Meanwhile, JJAS Central Plains precipitation (CPP) is negatively correlated with JJAS SSTA off the coasts of Sumatra and Java, and JAS CPP is negatively correlated with June Sumatra and Java SSTA. We are also able to find significant correlations (r ~0.5-0.7) at longer leads, in which JJAS WGP is positively correlated with SSTA in the southwest Indian Ocean in the previous northeast monsoon, and JJAS CPP is negatively correlated with SSTA in the southern Indian Ocean. The correlations between each regional precipitation index and SSTA provides stronger statistical connections that examining the Indian subcontinent as a whole. These statistical connections could possibly be used in the statistical prediction of Indian southwest monsoon precipitation. Further, examination of the dynamics controlling interannual precipitation variability in the Indian subcontinent should likely be explored independently for each of these two regions, rather than for the Indian

  3. 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

  4. Recent changes of Northern Indian Ocean summer rainfall based on CMIP5 multi-model

    NASA Astrophysics Data System (ADS)

    Yang, Yali; Du, Yan; Zhang, Yuhong; Cheng, Xuhua

    2013-06-01

    This study evaluates the simulation of summer rainfall changes in the Northern Indian Ocean (NIO) based on the fifth phase of Coupled Model Intercomparison Project (CMIP5). The historical runs of 20 CMIP5 coupled General Circulation Models (GCMs) are analyzed. The Multi-Model ensemble (MME) of the CMIP5 models well reproduces the general feature of NIO summer rainfall. For a short period 1979-2005, 14 out of 20 models show an increased trend in the mean rainfall and a similar spatial distribution to the Global Precipitation Climatology Project (GPCP) observations in MME. The increasing of the convergence in the equatorial IO results in the increase of rainfall significantly. The equatorial rainfall trend patterns seem modulated by the SST warming in the tropical Indian Ocean, which confirm the mechanism of `warmer-get-wetter' theory. For a long period 1950-2005, the trend of monsoon rainfall over India shows a decrease over the most parts of the India except an increase over the south corn er of the Indian Peninsula, due to a weakened summer monsoon circulation. The pattern is well simulated in half of the CMIP5 models. The rainfall over the north India is different for a short period, in which rainfall increases in 1979-2005, implying possible decadal variation in the NIO summer climate.

  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. Giant robber crabs monitored from space: GPS-based telemetric studies on Christmas Island (Indian Ocean).

    PubMed

    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

  7. 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

  8. Giant robber crabs monitored from space: GPS-based telemetric studies on Christmas Island (Indian Ocean).

    PubMed

    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.

  9. Internal Waves, Indian Ocean

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This photograph, taken in sunglint conditions, captures open ocean internal waves which are diffracting around shoals south of the Seychelle islands (4.5S, 55.5E) and recombining to form interference patterns. The clouds to the north of the waves cover two of the Seychelle islands: Silhouette and Mahe. Mahe is the main island of the archipelago. The small rocky island surrounded by reef around which the waves diffract is Platte Island.

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. Ocean science: Hiatus heat in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Vialard, Jérôme

    2015-06-01

    Global surface warming has slowed since the start of the twenty-first century, while Pacific heat uptake was enhanced. Analyses of ocean heat content suggest that the warm water was transferred to the Indian Ocean, through the Indonesian straits.

  15. 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

  16. Indian Ocean warming modulates Pacific climate change

    PubMed Central

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

    2012-01-01

    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. PMID:23112174

  17. 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).

  18. 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. PMID:24784218

  19. 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.

  20. 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.

  1. Indian Ocean Biogeochemical Processes and Ecological Variability

    NASA Astrophysics Data System (ADS)

    Ofori, Leslie

    2010-11-01

    The Sustained Indian Ocean Biogeochemistry and Ecosystem Research (SIBER) conference was held in 2006 in Goa, India. The goals of the workshop were to assess the known facts about basin-wide biogeochemical and ecological dynamics of the Indian Ocean, to answer major questions, and to draw a road map for future research. The AGU monograph Indian Ocean Biogeochemical Processes and Ecological Variability, edited by Jerry D. Wiggert, Raleigh R. Hood, S. Wajih A. Naqvi, Kenneth H. Brink, and Sharon L. Smith, synthesizes the talks that were presented at this conference. In this interview, Eos talks with Jerry Wiggert, assistant professor of marine science at University of Southern Mississippi, Hattiesburg.

  2. Superficial mineral resources of the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Siddiquie, H. N.; Gujar, A. R.; Hashimi, N. H.; Valsangkar, A. B.

    The sea floor of the Indian Ocean and the continental margins bordering the ocean are covered by a wide variety of terrigenous, biogenous and anthigenic mineral deposits The humid tropical climate of some of the land areas bordering the Indian Ocean accelerates weathering of the source rocks. This coupled with the large river runoff and wave and current conditions favour the formation of a variety of placer deposits. The beach and offshore placer deposits of the Indian Ocean may be some of the largest in the world. The biogenous deposits in the Indian Ocean comprise the corals on shallow banks and on the continental shelves and the oozes in the deep sea. A study of these deposits is needed to acquire a better understanding of their formation, turnover, regeneration rates and sustainable yields. The anthigenic deposits in the Indian Ocean comprise the phosphorites and the polymetallic nodules. Occurrences of phosphorite deposits have been found both along continental margins (South Africa and Western India) and around seamounts (Eastern and Western Indian Ocean). The continental margins of South Africa, East Africa, Southern Arabia, Western India and the Andamans are marked by strong upwelling and provide non-depositional environments which are conducive to the formation of phosphorite. The polymetallic nodules in the Indian Ocean cover an area of 10-15. 10 6 km 2 and the resources are estimated to be about 1.5 .10 11 tonnes. A study of over 900 chemical analyses from 350 stations shows that the deposits in most of the basins are submarginal; in the Central Indian Ocean they are paramarginal (Ni + Cu + Co > 2.4% and concentrations > 5 kg.m -2). Most of the exploration for minerals even on the continental margins of the Indian Ocean has been carried out by the developed countries from outside the region and little work has been carried out by the countries bordering the Indian Ocean. The development of capabilities within the region for exploration of the mineral

  3. 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

  4. 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.

  5. 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. PMID:15598623

  6. 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. PMID:24180757

  7. 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.

  8. 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.

  9. TRMM Based Studies of MJO Convection over the Central Indian Ocean, Maritime Continent, and Western Pacific Warm Pool

    NASA Astrophysics Data System (ADS)

    Rutledge, S. A.; Xu, W.

    2014-12-01

    The structure and organization of precipitating cloud populations related to the initiation and evolution of several MJO events have been fully investigated using data collected from the 2011-2012 DYNAMO field campaign over the Central Indian Ocean (CIO). Since DYNMO monitored the MJO behavior for only a few months, it is important to know how the DYNAMO-recorded characteristics compare to the long-term climatology, such as viewed by TRMM satellite measurements. TRMM observations are also capable of providing the regional variability of the convection as the MJO envelope propagates eastward. The objective of this study is to quantify MJO convective characteristics using 15 years of TRMM satellite measurements over three specific regions affected by the MJO including the CIO, Maritime Continent (MC), and Western Pacific (WP). TRMM data are used to quantify not only the precipitating cloud population categorized by radar echo tops and feature size (as have been previously documented), but also their convective intensity, lightning activity, precipitation structures, bulk microphysical properties, and rainfall contributions. Specifically, the radar, ice scattering (microwave), and lightning observations from TRMM are analyzed for the convective spectrum as a function of MJO stage and geographical location. Furthermore, radar characteristics of MJO events based on TRMM PR are quantitatively compared to that of the shipborne radars deployed during TOGA COARE over the WP and DYNAMO over the CIO.

  10. 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…

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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 and applying an overriding technique to its ocean component (version 2 of the Parallel Ocean Program), this study investigates the similarities and differences 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, wind-thermocline-SST feedback is the leading mechanism in producing the anomalous cooling over the eastern tropics in both cases. Some differences are also found, including the fact that the cooling effect of the vertical advection over the eastern tropical Indian Ocean is dominated by the anomalous vertical velocity during the pIOD but by the anomalous upper-ocean stratification under global warming. These findings are further examined through an analysis of the mixed layer heat budget.

  14. Aldabra Islands, Seychelle Archipelago, Indian Ocean

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The Aldabra Islands, two coral atolls of the Seychelle Archipelago (9.5S, 46.5E) in the Indian Ocean, because of their remotness, have a rare ecosystem almost completely untouched by outside influences. About 10 % of the plant and animal life is unique to the atolls and therefore, development of the area has been barred. Assumption, the smaller atoll has a small aircraft runway to support occasional environmental or scientific survey teams.

  15. Pirate attacks affect Indian Ocean climate research

    NASA Astrophysics Data System (ADS)

    Smith, Shawn R.; Bourassa, Mark A.; Long, Michael

    2011-07-01

    Pirate attacks in the Gulf of Aden and the Indian Ocean off the coast of Somalia nearly doubled from 111 in 2008 to 217 in 2009 [International Maritime Bureau, 2009, International Maritime Bureau, 2010]. Consequently, merchant vessel traffic in the area around Somalia significantly decreased. Many of these merchant vessels carry instruments that record wind and other weather conditions near the ocean surface, and alterations in ship tracks have resulted in a hole sized at about 2.5 million square kilometers in the marine weather-observing network off the coast of Somalia. The data void exists in the formation region of the Somali low-level jet, a wind pattern that is one of the main drivers of the Indian summer monsoon. Further, a stable, multidecadal record has been interrupted, and consequently, long-term analyses of the jet derived from surface wind data are now showing artificial anomalies that will affect efforts by scientists to identify interannual to decadal variations in the climate of the northwestern Indian Ocean.

  16. The Indian ocean experiment: aerosol forcing obtained from satellite data

    NASA Astrophysics Data System (ADS)

    Rajeev, K.; Ramanathan, V.

    The tropical Indian Ocean provides an ideal and unique natural laboratory to observe and understand the role of anthropogenic aerosols in climate forcing. Since 1996, an international team of American, European and Indian scientists have been collecting aerosol, chemical and radiation data from ships and surface stations, which culminated in a multi-platform field experiment conducted during January to March of 1999. A persistent haze layer that spread over most of the northern Indian Ocean during wintertime was discovered. The layer, a complex mix of organics, black carbon, sulfates, nitrates and other species, subjects the lower atmosphere to a strong radiative heating and a larger reduction in the solar heating of the ocean. We present here the regional distribution of aerosols and the resulting clear sky aerosol radiative forcing at top-of-atmosphere (TOA) observed over the Indian Ocean during the winter months of 1997, 1998 and 1999 based on the aerosol optical depth (AOD) estimated using NOAA14-AVHRR and the TOA radiation budget data from CERES on board TRMM. Using the ratio of surface to TOA clear sky aerosol radiative forcing observed during the same period over the Indian Ocean island of Kaashidhoo (Satheesh and Ramanathan, 2000), the clear sky aerosol radiative forcing at the surface and the atmosphere are discussed. The regional maps of AVHRR derived AOD show abnormally large aerosol concentration during the winter of 1999 which is about 1.5 to 2 times larger than the AOD during the corresponding period of 1997 and 1998. A large latitudinal gradient in AOD is observed during all the three years of observation, with maximum AOD in the northern hemisphere. The diurnal mean clear sky aerosol forcing at TOA in the northern hemisphere Indian Ocean is in the range of -4 to -16 Wm -2 and had large spatio-temporal variations while in the southern hemisphere Indian Ocean it is in the range of 0 to -6Wm -2. The importance of integrating in-situ data with satellite

  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. 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.

  19. 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.

  20. 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.

  1. Climatic Influences on Indian and Pacific Ocean Heat Waves

    NASA Astrophysics Data System (ADS)

    Scannell, H. A.; England, M. H.; Sen Gupta, A.

    2014-12-01

    Large-scale ocean heat waves can be extremely damaging for both ecosystem functioning and fishery productivity. Unlike terrestrial heat waves, little work has been done to understand the dynamics of heat waves in sea surface temperature (SST). New high spatial and temporal resolution SST products now make it possible to investigate regions of persistent extreme anomalies in SST. Here we characterize the properties of Indian and Pacific Ocean heat waves and investigate how they are modulated by the dominant modes of Indo-Pacific climate variability. In particular, we investigate the influence of El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) in preconditioning ocean heat waves. For the purposes of this study we define heat waves based on an index of cumulative SST 1ºC above the annual maximum with a geographic extent on the order of 105 square kilometers. We examine the prevalence of ocean heat waves during different phases of ENSO and the IOD, and explore the oceanic and atmospheric processes that give rise to these events.

  2. 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.

  3. 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.

  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. 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

  6. 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.

  7. 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

  8. 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

  9. Tropical Indian Ocean Variability Driving Southeast Australian Droughts

    NASA Astrophysics Data System (ADS)

    Ummenhofer, C. C.; England, M. H.; McIntosh, P. C.; Meyers, G. A.; Pook, M. J.; Risbey, J. S.; Sen Gupta, A.; Taschetto, A. S.

    2009-04-01

    Variability in the tropical Indian Ocean has widespread effects on rainfall in surrounding countries, including East Africa, India and Indonesia. The leading mode of tropical Indian Ocean variability, the Indian Ocean Dipole (IOD), is a coupled ocean-atmosphere mode characterized by sea surface temperature (SST) anomalies of opposite sign in the east and west of the basin with an associated large-scale atmospheric re-organisation. Earlier work has often focused on the positive phase of the IOD. However, we show here that the negative IOD phase is an important driver of regional rainfall variability and multi-year droughts. For southeastern Australia, we show that it is actually a lack of the negative IOD phase, rather than the positive IOD phase or Pacific variability, that provides the most robust explanation for recent drought conditions. Since 1995, a large region of Australia has been gripped by the most severe drought in living memory, the so-called "Big Dry". The ramifications for affected regions are dire, with acute water shortages for rural and metropolitan areas, record agricultural losses, the drying-out of two of Australia's major river systems and far-reaching ecosystem damage. Yet the drought's origins have remained elusive. For Southeast Australia, we show that the "Big Dry" and other iconic 20th Century droughts, including the Federation Drought (1895-1902) and World War II drought (1937-1945), are driven by tropical Indian Ocean variability, not Pacific Ocean conditions as traditionally assumed. Specifically, a conspicuous absence of characteristic Indian Ocean temperature conditions that are conducive to enhanced tropical moisture transport has deprived southeastern Australia of its normal rainfall quota. In the case of the "Big Dry", its unprecedented intensity is also related to recent above-average temperatures. Implications of recent non-uniform warming trends in the Indian Ocean and how that might affect ocean characteristics and climate in

  10. 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.

  11. 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).

  12. A dipole mode in the tropical Indian Ocean.

    PubMed

    Saji, N H; Goswami, B N; Vinayachandran, P N; Yamagata, T

    1999-09-23

    For the tropical Pacific and Atlantic oceans, internal modes of variability that lead to climatic oscillations have been recognized, but in the Indian Ocean region a similar ocean-atmosphere interaction causing interannual climate variability has not yet been found. Here we report an analysis of observational data over the past 40 years, showing a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies. The spatio-temporal links between sea surface temperatures and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air-sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Niño/Southern Oscillation. The discovery of this dipole mode that accounts for about 12% of the sea surface temperature variability in the Indian Ocean--and, in its active years, also causes severe rainfall in eastern Africa and droughts in Indonesia--brightens the prospects for a long-term forecast of rainfall anomalies in the affected countries. PMID:16862108

  13. Future change of the Indian Ocean basin-wide and dipole modes in the CMIP5

    NASA Astrophysics Data System (ADS)

    Chu, Jung-Eun; Ha, Kyung-Ja; Lee, June-Yi; Wang, Bin; Kim, Byeong-Hee; Chung, Chul Eddy

    2014-07-01

    The Indian Ocean sea surface temperature (SST) variability has been represented with the two dominant variability modes: the Indian Ocean basin-wide (IOBW) and dipole (IOD) modes. Here we investigate future changes of the two modes together with mean state and El Niño and Southern Oscillation (ENSO) relationship under the anthropogenic global warming using 20 coupled models that participated in the phase five of Coupled Model Intercomparison Project by comparing the historical run from 1950 to 2005 and the RCP 4.5 run from 2050 to 2099. The five best models are selected based on the evaluation of the 20 models' performances in simulating the two modes and Indian Ocean basic state for the latest 56 years. They are capable of capturing the IOBW and IOD modes in their spatial distribution, seasonal cycle, major periodicity, and relationship with ENSO to some extent. The five best models project the significant changes in the Indian Ocean mean state and variability including the two dominant modes in the latter part of twenty-first century under the anthropogenic warming scenario. First, the annual mean climatological SST displays an IOD-like pattern change over the Indian Ocean with enhanced warming in the northwestern Indian Ocean and relatively weaker warming off the Sumatra-Java coast. It is also noted that the monthly SST variance is increased over the eastern and southwestern Indian Ocean. Second, the IOBW variability on a quasi-biennial time scale will be enhanced due to the strengthening of the ENSO-IOBW mode relationship although the total variance of the IOBW mode will be significantly reduced particularly during late summer and fall. The enhanced air-sea coupling over the Indian-western Pacific climate in response to El Nino activity in the future projection makes favorable condition for a positive IOD while it tends to derive relatively cold temperature over the eastern Indian Ocean. This positive IOD-like ENSO response weakens the relationship between the

  14. 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.

  15. 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

  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. 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.

  18. 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.

  19. Differentiating flavors of the Indian Ocean Dipole using dominant modes in tropical Indian Ocean rainfall

    NASA Astrophysics Data System (ADS)

    Weller, Evan; Cai, Wenju; Du, Yan; Min, Seung-Ki

    2014-12-01

    Phase locked to austral winter and spring, canonical positive Indian Ocean Dipoles (pIODs) generally peak in spring. In recent decades, there has been an increase in unseasonable pIODs which, different from canonical pIODs, peak and decay by September. Distinguishing unseasonable pIODs from canonical pIODs is important, as conditions leading to more frequent unseasonable events are projected to persist in a warming climate. Here using superimposition of the first two seasonally evolving dominant modes of tropical Indian Ocean rainfall variability, we differentiate these types of pIODs. The first mode reflects characteristics of canonical pIODs, in which anomalies intensify with seasonal evolution. However, the second mode, with cool and dry anomalies extending from the eastern pole, reverses from winter to spring, signifying the demise of unseasonable pIODs. Processes embedded in the second mode reflect timing of propagation in equatorial Kelvin waves and their relative importance to the first mode, in generating different pIODs.

  20. 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.

  1. Manganese and iron in Indian Ocean waters

    SciTech Connect

    Saager, P.M.; De Baar, H.J.W. ); Burkill, P.H. )

    1989-09-01

    The first vertical profiles of dissolved Mn and Fe for the (NW) Indian Ocean are reported. The area is characterized by seasonal upwelling and a broad oxygen minimum zone in intermediate waters. The dissolved Fe-profile exhibits a maximum (5.1 nM) in the oxygen minimum zone, with low values both in surface waters (0.3 nM) and deep waters (around 1 nM). Mn concentrations in the surface waters are elevated (2.0-4.3 nM), and decrease rapidly in an offshore direction. Below the first 25 m, concentrations decrease dramatically (0.5-1.3 nM), indicating removal by oxidation and particle scavenging. Further down, various Mn maxima are observed which can be related to hydrographic features. The include the facts that: intermediate water originating from the Red Sea lost its dissolved O{sub 2} while flowing northward along the Omani coast and exhibits a strong Mn maximum (4.6-6.5 nM) coincident with the deep O{sub 2} minimum; at the two inshore stations in the Gulf of Oman this is overlain by relatively modest Mn maxima ({plus minus}2.7 nM) related to Arabian Gulf overflow water; and the strong Mn maxima (4.4-5.6 nM) in the oxygen minimum zone at the two offshore stations are related to yet another watermass. Below these various maxima, concentrations decrease gradually to values as low as 90 pM at 2,000 meters depth. Towards the sea floor concentrations increase again, leading to a modest bottom water maximum (0.7-1.5 nM). The overall vertical distributions of Mn and Fe are strikingly similar, also in actual concentrations, to those previously reported for the eastern equatorial Pacific, an area also characterized by an extensive O{sub 2}-minimum zone.

  2. Intrathermocline eddies in the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nauw, J. J.; van Aken, H. M.; Lutjeharms, J. R. E.; de Ruijter, W. P. M.

    2006-03-01

    In 2001, two relatively saline intrathermocline eddies (ITEs) were observed southeast of Madagascar at 200 m depth. They are characterized by a subsurface salinity maximum of over 35.8 at potential temperatures between 18° and 22°C. The oxygen concentrations within the high salinity cores are slightly elevated compared with those of the surrounding water. Their horizontal extent is about 180 km, several times the Rossby deformation radius, while their thickness is about 150 m. The observed circulation around the ITEs is anticyclonic and maximum velocities of 20 to 30 cm/s are observed at 200 m depth. In these cores the potential density anomaly (25.0 < γ < 25.9 kg/m3) has a relatively low vertical gradient and therefore a low planetary potential vorticity. The hydrographic properties of these ITEs are distinctly different from those of the surrounding thermocline water, and especially from the much fresher water mass in the East Madagascar Current. Strong evidence has been found that the distant formation area of the water mass in the ITEs is the subtropical Southern Indian Ocean east of 90°E and south of 25°S, where Subtropical Underwater (STUW) is formed with similar characteristics. Similar high-salinity cores as the ITEs are also found in the thermocline around 200 m depth along an almost zonal section between Madagascar and 100°E. Differences between the hydrographic properties of these cores and the ITEs near Madagascar may partly be explained by interannual variations in the temperature and salinity of the surface mixed layer water in the possible formation area.

  3. 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. PMID:26723301

  4. 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.

  5. Radiocarbon in the Northern Indian Ocean two decades after GEOSECS

    NASA Astrophysics Data System (ADS)

    Dutta, Koushik; Bhushan, Ravi

    2012-06-01

    The 14C measurements in the Arabian Sea and the Bay of Bengal during the late 1990s offer a way to assess the temporal changes in the inventories of bomb-14C and its penetration into the ocean, in two decades since GEOSECS expeditions (1977-1978). The mean penetration depth of bomb radiocarbon during GEOSECS (1977-1978) was 270 m, which increased by ˜40% to 381 m in 1994-1998. The small changes in bomb-14C inventories, significant increase in the mean penetration depths and lowering of the surface Δ14C values in the northern Indian Ocean indicate the temporal variation of bomb-14C in two decades is mainly through downward transfer through mixing with deeper waters. The observed bomb-14C inventory in the northern Indian Ocean agrees with numerical model simulated values, except at the equatorial Indian Ocean. The high bomb-14C inventory at the equator can be attributed to lateral advection of 14C-enriched waters from the Pacific Ocean through the Indonesian archipelago. The air-sea CO2exchange rates in the northern Indian Ocean calculated from the bomb-14C inventories range from ˜7 mol m-2 yr-1 (in the northern Bay of Bengal) to 20 mol m-2 yr-1(in the equatorial Indian Ocean). Net sea-air flux of CO2 estimated for the northern Indian Ocean between 0° and 25°N is ˜104 ± 30 TgC yr-1. The Bay of Bengal is a net sink of atmospheric CO2 (˜-1 ± 0.4 TgC yr-1), while the Arabian Sea is a source of CO2 (˜69 ± 21 TgC yr-1).

  6. 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

  7. Rayleigh Wave Phase Velocity in the Indian Ocean Upper Mantle

    NASA Astrophysics Data System (ADS)

    Godfrey, K. E.; Dalton, C. A.

    2015-12-01

    Current understanding of the seismic properties of the oceanic upper mantle is heavily weighted toward studies of the Pacific upper mantle. However, global seismic models indicate differences in upper-mantle properties beneath the Pacific, Atlantic, and Indian oceans. Furthermore, factors such as spreading rate, absolute plate motion, and the presence of intraplate volcanism vary between these regions. It is thus important to consider the broad range in parameters when forming ideas about mantle dynamics and lithosphere evolution within ocean basins. We are developing a high-resolution basin-wide seismic model of the Indian Ocean upper mantle. The Indian Ocean contains 16,000 km of mid-ocean ridge, with spreading rates ranging from approximately 14 mm/yr along the Southwest Indian Ridge to 55-75 mm/yr along the Southeast Indian Ridge. It also contains 12 volcanic hotspots, overlies a portion of a large low-shear-velocity province in the lower mantle, and is home to the Australian-Antarctic Discordance and a negative geoid anomaly just south of India, among other features. We measure phase velocity in the period range 30-130 seconds for fundamental-mode Rayleigh waves traversing the Indian Ocean; the data set includes 831 events that occurred between 1992 and 2014 and 769 stations. In order to isolate the signal of the oceanic upper mantle, paths with >30% of their length through continental upper mantle are excluded. Variations in phase velocity in the Indian Ocean upper mantle are explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Our preliminary results indicate a strong dependence of phase velocity on seafloor age, with higher velocity associated with older seafloor, and perturbations to the age-dependent trend in the vicinity of the Australian-Antarctic Discordance and the Marion and

  8. 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

  9. 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

  10. 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

  11. Developing tsunami fragility curves based on the satellite remote sensing and the numerical modeling of the 2004 Indian Ocean tsunami in Thailand

    NASA Astrophysics Data System (ADS)

    Suppasri, A.; Koshimura, S.; Imamura, F.

    2011-01-01

    The 2004 Indian Ocean tsunami damaged and destroyed numerous buildings and houses in Thailand. Estimation of tsunami impact to buildings from this event and evaluation of the potential risks are important but still in progress. The tsunami fragility curve is a function used to estimate the structural fragility against tsunami hazards. This study was undertaken to develop fragility curves using visual inspection of high-resolution satellite images (IKONOS) taken before and after tsunami events to classify whether the buildings were destroyed or not based on the remaining roof. Then, a tsunami inundation model is created to reconstruct the tsunami features such as inundation depth, current velocity, and hydrodynamic force of the event. It is assumed that the fragility curves are expressed as normal or lognormal distribution functions and the estimation of the median and log-standard deviation is performed using least square fitting. From the results, the developed fragility curves for different types of building materials (mixed type, reinforced concrete and wood) show consistent performance in damage probability and when compared to the existing curves for other locations.

  12. Coupled ocean-atmosphere variability in the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Yamagata, Toshio; Behera, Swadhin K.; Luo, Jing-Jia; Masson, Sebastien; Jury, Mark R.; Rao, Suryachandra A.

    The Indian Ocean Dipole (IOD) is a natural ocean—atmosphere coupled mode that plays important roles in seasonal and interannual climate variations. The coupled mode locked to boreal summer and fall is distinguished as a dipole in the SST anomalies that are coupled to zonal winds. The equatorial winds reverse their direction from westerlies to easterlies during the peak phase of the positive IOD events when SST is cool in the east and warm in the west. In response to changes in the wind, the thermocline rises in the east and subsides in the west. Subsurface equatorial long Rossby waves play a major role in strengthening SST anomalies in (he central and western parts. The SINTEX-F1 coupled model results support the observational finding that these equatorial Rossby waves are coupled to the surface wind forcing associated with IOD rather than ENSO. The ENSO influence is only distinct in off-equatorial latitudes south of 10°S. Although IOD events dominate the ocean—atmosphere variability during its evolution, their less frequent occurrence compared to ENSO events leads the mode to the second seat in the interannual variability. Therefore, it is necessary to remove the most dominant uniform mode to capture the IOD statistically. The seasonally stratified correlation between the indices of IOD and ENSO peaks at 0.53 in September—November. This means that only one third of IOD events are associated with ENSO events. Since a large number of IOD events are not associated with ENSO events, the independent nature of IOD is examined using partial correlation and pure composite techniques. Through changes in atmospheric circulation and water vapor transport, a positive IOD event causes drought in Indonesia, above normal rainfall in Africa, India, Bangladesh and Vietnam, and dry as well as hot summer in Europe, Japan, Korea and East China. In the Southern Hemisphere, the positive IOD causes dry winter in Australia, and dry as well as warm conditions in Brazil. The

  13. The impact of North Indian Ocean sea surface temperatures on the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Levine, Richard; Turner, Andrew

    2010-05-01

    The relationship between sea surface temperature (SST) in the North Indian Ocean and Indian monsoon rainfall is investigated in both observational/re-analyses and climate model simulations. We focus on the partially land-enclosed Arabian Sea and Bay of Bengal, where SSTs are found to have significant correlations with All Indian Rainfall (AIR). This part of the Indian Ocean is therefore important for monsoon predictions, while this area tends to provide significant problems in coupled atmosphere-ocean model simulations. The observational variability of the SST-rainfall relationship is investigated on seasonal to decadal time-scales. This highlights a predominantly negative correlation over the monsoon trough area in North East India and a positive correlation over the rest of India, while these relationships are found to be weakened by the ENSO-monsoon teleconnection. Mechanisms are further investigated by performing a series of atmosphere-only model simulations using the Met Office Unified Model (MetUM). In these experiments we determine the response of the atmosphere to forced cold SST anomalies over isolated areas, which we also extend out into the equatorial Indian Ocean. The cold SSTs in the Arabian Sea and Bay of Bengal lead to a dramatic reduction in Indian rainfall, while cold biases in the equatorial Indian Ocean have the opposite effect, highlighting the competition between oceanic and continental Tropical Convergence Zones (TCZ). However, the impacts for the Arabian Sea and Bay of Bengal experiments are found to change between the pre-monsoon and post-monsoon onset periods.The impact on monsoon rainfall for cold SST biases in these regions is found to be the result of a balance between changes in regional low-level temperature gradients and the availability of moisture over the oceans, which determine the pathway of the monsoon jet and the moisture transport towards India. These experiments suggest that the intra-seasonal variability of the relationship

  14. 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.

  15. 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.

  16. 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.

  17. 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. PMID:26748439

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  20. 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.

  1. 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

  2. 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…

  3. Recent intensification of tropical climate variability in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Abram, Nerilie J.; Gagan, Michael K.; Cole, Julia E.; Hantoro, Wahyoe S.; Mudelsee, Manfred

    2008-12-01

    The interplay of the El Niño Southern Oscillation, Asian monsoon and Indian Ocean Dipole (IOD) drives climatic extremes in and around the Indian Ocean. Historical and proxy records reveal changes in the behaviour of the El Niño Southern Oscillation and the Asian monsoon over recent decades. However, reliable instrumental records of the IOD cover only the past 50years, and there is no consensus on long-term variability of the IOD or its possible response to greenhouse gas forcing. Here we use a suite of coral oxygen-isotope records to reconstruct a basin-wide index of IOD behaviour since AD1846. Our record reveals an increase in the frequency and strength of IOD events during the twentieth century, which is associated with enhanced seasonal upwelling in the eastern Indian Ocean. Although the El Niño Southern Oscillation has historically influenced the variability of both the IOD and the Asian monsoon, we find that the recent intensification of the IOD coincides with the development of direct, positive IOD-monsoon feedbacks. We suggest that projected greenhouse warming may lead to a redistribution of rainfall across the Indian Ocean and a growing interdependence between the IOD and Asian monsoon precipitation variability.

  4. 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.

  5. Decadal ventilation and mixing of Indian Ocean waters

    NASA Astrophysics Data System (ADS)

    Fine, Rana A.; Smethie, William M.; Bullister, John L.; Rhein, Monika; Min, Dong-Ha; Warner, Mark J.; Poisson, Alain; Weiss, Ray F.

    2008-01-01

    Chlorofluorocarbon (CFC) and hydrographic data from the World Ocean Circulation Experiment (WOCE) Indian Ocean expedition are used to evaluate contributions to decadal ventilation of water masses. At a given density, CFC-derived ages increase and concentrations decrease from the south to north, with lowest concentrations and oldest ages in Bay of Bengal. Average ages for thermocline water are 0-40 years, and for intermediate water they are less than 10 years to more than 40 years. As compared with the marginal seas or throughflow, the most significant source of CFCs for the Indian Ocean south of 12°N is the Southern Hemisphere. A simple calculation is used to show this is the case even at intermediate levels due to differences in gas solubilities and mixing of Antarctic Intermediate Water and Red Sea Water. Bottom water in the Australia-Antarctic Basin is higher in CFC concentrations than that to the west in the Enderby Basin, due to the shorter distance of this water to the Adelie Land coast and Ross Sea sources. However, by 40°S, CFC concentrations in the bottom water of the Crozet Basin originating from the Weddell Sea are similar to those in the South Australia Basin. Independent observations, which show that bottom water undergoes elevated mixing between the Australia-Antarctic Basin and before entering the subtropics, are consistent with high CFC dilutions (3-14-fold) and a substantial concentration decrease (factor of 5) south to north of the Southeast Indian Ridge. CFC-bearing bottom waters with ages 30 years or more are transported into the subtropical South Indian Ocean by three western boundary currents, and highest concentrations are observed in the westernmost current. During WOCE, CFC-bearing bottom water reaches to about 30°S in the Perth Basin, and to 20°S in the Mascarene Basin. Comparing subtropical bottom water-CFC concentrations with those of the South Pacific and Atlantic oceans, at comparable latitudes, Indian Ocean bottom water

  6. 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.

  7. 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.

  8. 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. PMID:23325220

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. Particle flux studies in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Ittekkot, Venugopalan

    There is scientific consensus that atmospheric carbon dioxide is a major controlling factor of the surface temperature of our planet. CO2 released into the atmosphere through fossil fuel burning and deforestation is believed to lead to global warming through the greenhouse effect. The CO2 content in the atmosphere is influenced not just by its release into the atmosphere, but also by its removal.Although it is generally accepted that oceans take up considerable amounts of CO2, the complex processes affecting this uptake are still poorly understood. Physicochemical exchange processes in the ocean remove large quantities of CO2, as do biological processes. During marine photosynthesis, microscopic plants in the oceans fix CO2 into their tissues in the form of organic matter. Part of this organic matter is oxidized back to CO2 in the mixed layer of the sea, which interacts with the atmosphere. The rest sinks down to the deep sea. The rate of this transfer to the deep sea determines the extent to which the formation of organic matter removes CO2 from the atmosphere.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Okamejei ornata n. sp., a new deep-water skate (Elasmobranchii, Rajidae) from the northwestern Indian Ocean off Socotra Islands

    NASA Astrophysics Data System (ADS)

    Weigmann, Simon; Stehmann, Matthias F. W.; Thiel, Ralf

    2015-05-01

    A new species of the Indo-Pacific skate genus Okamejei is described based on 10 specimens caught around the Socotra Islands (northwestern Indian Ocean). The type series of Okamejei ornata n. sp. was sampled during cruise 17 of RV 'Vityaz' along the deep western Indian Ocean in 1988/89. The new species represents the fifth species of Okamejei in the western Indian Ocean and differs from its congeners in having a unique dorsal pattern of variable dark brown spots encircled with beige pigment and arranged into rosettes. The dorsal ground color is ocher, but the anterior snout is dusky. Compared to congeners in the western Indian Ocean, the new species has a shorter preorbital snout length, a greater orbit diameter, fewer pectoral radials, an intermediate distance between first gill slits, and an intermediate number of upper jaw tooth rows.

  20. 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. PMID:23024801

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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. PMID:25996394

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

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

    PubMed Central

    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. PMID:24810172

  15. A sea surface salinity dipole mode in the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Yuhong; Du, Yan; Qu, Tangdong

    2016-10-01

    Based on the 10 years sea surface salinity (SSS) data from Argo, we identified a salinity dipole mode in the tropical Indian Ocean, termed S-IOD: a pattern of interannual SSS variability with anomalously low-salinity in the central equatorial and high-salinity in the southeastern tropical Indian Ocean. The S-IOD matures in November-December, lagging the Indian Ocean dipole (IOD) mode derived from sea surface temperature (SST) by 2 months. For the period of observations, the S-IOD persists longer than the IOD, until the following September-October. Oscillations of the two S-IOD poles are governed by different processes. Ocean advection associated with equatorial current variability dominates the SSS anomalies of the northern pole, while surface freshwater flux variability plays a key role in the SSS anomalies of the southern pole, where anomalous precipitation is sustained by preformed sea surface temperature anomalies. The S-IOD concurs with the strong IOD, reflecting an ocean-atmosphere coupling through the SST-precipitation-SSS feedback.

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

    PubMed Central

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

    2015-01-01

    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. PMID:26564801

  17. 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.

  18. 87Sr/86Sr ratios in basalts from islands in the Indian Ocean

    USGS Publications Warehouse

    Hedge, C.E.; Watkins, N.D.; Hildreth, R.A.; Doering, W.P.

    1973-01-01

    87Sr/86Sr ratios of basalts from islands in the Indian Ocean (0.7040) are higher than those of basalts dredged from the Mid-Indian Ocean Ridge (0.7034). The sources of the island basalts have apparently not been in equilibrium with the source of the ridge basalts for roughly 109 years. Both ridge and island basalts in the Indian Ocean are higher in 87Sr/86Sr than are rocks from similar settings in the eastern Pacific. ?? 1973.

  19. 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

  20. 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.

  1. Indian Ocean Research Data: Past, Present and Future

    NASA Astrophysics Data System (ADS)

    Chandler, Cynthia; Groman, Robert; Allison, Molly; Copley, Nancy; Gegg, Stephen; Kinkade, Danie; Rauch, Shannon; Glover, David; Wiebe, Peter

    2015-04-01

    Open access to well-documented data is essential to enable improved understanding of the key processes and their complex interactions in the Indian Ocean. For decades, marine ecosystem data have been collected by expeditions conducting research in this fascinating region. The data from many of the projects including the International Indian Ocean Expedition of the 1960s, the US Joint Global Ocean flux Study (JGOFS) Arabian Sea Expedition of the 1990s, and several more recent projects have been contributed by the original investigators to the Biological and Chemical Oceanography Data Management Office (BCO-DMO). BCO-DMO is funded by the US National Science Foundation to work with marine scientists to improve access to research data and ensure long term preservation of the data that comprise an important part of a research program's legacy. The data are freely available from the Web-accessible BCO-DMO system that supports data discovery, access, display, user-customizable export, and download. The authors will provide an overview of the BCO-DMO data system including examples of the range of data types and an introduction to system capabilities.

  2. Nonlinear processes reinforce extreme Indian Ocean Dipole events

    PubMed Central

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

    2015-01-01

    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. PMID:26114441

  3. 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.

  4. 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). PMID:20471674

  5. Plate tectonic models for Indian Ocean ``intraplate'' deformation

    NASA Astrophysics Data System (ADS)

    Wiens, Douglas A.; Stein, Seth; Demets, Charles; Gordon, Richard G.; Stein, Carol

    1986-12-01

    The equatorial region of the conventionally defined Indo-Australian plate has long been recognized as containing a type example of intense "intraplate" deformation. We trace the development of tectonic models for the area to illustrate techniques for the analysis of such deformation. The identification of anomalous seismicity near the Ninetyeast and Chagos-Laccadive Ridges demonstrated the existence of the deformation. Focal mechanisms from recent and historic earthquakes showed strike-slip motion occurring along the Ninetyeast Ridge; seismic moment data allowed the rate to be estimated. Similar studies showed north-south tension in the Chagos Bank region and north-south compression in the region between the Ninetyeast and Chagos ridges. Global plate motion studies indicated non-closure of the Indian Ocean triple junction, suggesting the conventional plate geometry was inadequate for a rigid plate description of the area. Gravity and marine geophysical data indicated intense north-south compressional deformation south of the Bay of Bengal. These observations are reconciled by a plate motion model in which Australia and India lie on distinct plates divided by a boundary that intersects the Central Indian Ridge near the equator. In this model Arabia, usually considered a separate plate, has negligible motion relative to India. The resulting Euler vector for Australia relative to Indo-Arabia lies just east of the Central Indian Ridge, and predicts approximately 0.5-1.5 cm/yr compression in the Central Indian Basin and 1.5-2 cm/yr strike-slip motion along the northern Ninetyeast Ridge, consistent with the seismological and geophysical data. In contrast to conventional oceanic plate boundaries, the boundary deformation is distributed over a wide zone. This diffuse nature may reflect either the boundary's recent inception or slow rate of motion. Analysis of seismicity and deformation in the boundary zone should offer insights into the mechanics of its development and its

  6. 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.

  7. 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

  8. Tropical Cyclone Kesiny northeast of Madagascar, Indian Ocean

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Tropical Cyclone Kesiny can be seen over the Indian Ocean in this true color image taken on May 6, 2002, at 6:45 UTC by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA's Terra spacecraft. When this image was taken, the cyclone was several hundred miles east of northern Madagascar and packing winds of up to 120 kilometers (75 miles) per hour. As the cyclone continues its approach southwest into Madagascar, it is forecast to increase in intensity and generate sustained winds of up to 139 kilometers (86 miles) per hour. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  9. 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

  10. 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.

  11. Salinity dominance on the Indian Ocean Eastern Gyral current

    NASA Astrophysics Data System (ADS)

    Menezes, Viviane V.; Phillips, Helen E.; Schiller, Andreas; Domingues, Catia M.; Bindoff, Nathaniel L.

    2013-11-01

    This study demonstrates the importance of salinity gradients to the formation of the Eastern Gyral Current (EGC) in the South Indian Ocean. The EGC flows eastward near 15∘S, opposite to the direction predicted by classical theories of wind-driven circulation and is a source of water for the Leeuwin Current. In the upper ocean, a strong salinity front exists between fresh water from the Indonesian Throughflow (ITF) in the South Equatorial Current (SEC) and salty subtropical waters. In that region, salinity overwhelms the temperature contribution to density gradients, generating eastward geostrophic shear and establishing the EGC. Without the salinity front the EGC cannot be maintained: If the salinity contribution is neglected in the calculation of geostrophic currents, the EGC vanishes. Our observational analysis associated with the fact that both Sverdrup and Ekman theories produce westward flows in the region strongly supports the idea that the EGC is a salinity-driven current.

  12. The Indian Ocean Dipole's influence on Atlantic tropical cyclone activity

    NASA Astrophysics Data System (ADS)

    Marinaro, Alan Joseph

    Improving early tropical cyclone forecasts would assist reinsurance decision makers as they seek information that can minimize risks. Early lead forecasts are based on model variables before December 1 (Year 0) that predict Atlantic tropical cyclone activity (Year +1). The autumn Indian Ocean Dipole (IOD) has an 8 to 14 month antecedent correlation with the El Nino - Southern Oscillation (ENSO). ENSO is traditionally the best non-lead and overall predictor of Atlantic tropical cyclone activity. Analyses were performed over a 30-year period from 1984/85-2013/14, with some time variation depending on the test. Correlation, spatial, and wavelet analyses were utilized to find associations between the IOD, west and east components of the IOD, and four other variables related to the following season's ENSO state and tropical cyclone activity. The prior western pole of the October IOD (WIOD) was demonstrated to have statistically significant r-squared values (i.e. 99% confidence interval) to upcoming tropical storm activity (i.e. explained 25% of the variance), named storm counts (28%), and ENSO (21%). The WIOD has no connection with U.S. hurricane landfalls. Wavelet analysis between October IOD variables and following August-October ENSO data was observed to have the best time-frequency relationship. Dynamic reasoning for these relationships reside within the idealized biennial IOD-ENSO cycle, Walker circulation process, and the impact of ENSO on the state of the Atlantic Basin. The WIOD's integration into early-lead forecast models could be an advantage for those in the reinsurance industry and other decision makers impacted by Atlantic tropical cyclonesn.

  13. Ionospheric perturbations associated with 26th December 2004 Indian ocean tsunami: A detailed investigation through Indian Geodetic GNSS network observations

    NASA Astrophysics Data System (ADS)

    Kannoth, S.; Vijayan, M.; Earnest, A.; Jade, S.

    2013-12-01

    perturbations over Arabian sea associated with diffracted tsunami waves around the peninsular India, which preceded tsunami arrival at tide gauges in the west coast, in addition to observations over the Indian ocean and Bay of Bengal. The earliest detection of ionospheric perturbation at sub-ionospheric pierce points (SIP) associated with tsunami is from PRN 28 at 2-3 UTC over Indian ocean - roughly an hour before tsunami reaches the east Indian coast. Similar perturbations observed from other PRNs at various SIP and its propagations are discussed in detail. The perturbations observed with respect to distance from source of the earthquake correlate well with the direction and speed of the tsunami. The results are also compared with tsunami simulation and tide gauge data which indicates the cause of perturbations are gravity waves generated by tsunami. These results further strengthen the confidence on possibilities of early warning of devastating tsunamis using ground based GPS observations.

  14. 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.

  15. Anomalous Walker circulations associated with two flavors of the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Tozuka, Tomoki; Endo, Satoru; Yamagata, Toshio

    2016-05-01

    The Walker circulation is the key component of the atmospheric zonal circulation in the tropics. In this study, it is shown that anomalous Walker circulations associated with two types of the Indian Ocean Dipole (IOD) are remarkably different. During a positive canonical IOD with negative (positive) sea surface temperature (SST) anomalies in the eastern (central to western) tropical Indian Ocean, a single-cell anomalous Walker circulation forms over the Indian Ocean. On the other hand, a double-cell anomalous Walker circulation with a rising branch in the central Indian Ocean is formed during a positive IOD Modoki, which is associated with positive (negative) SST anomalies over the central (eastern and western) tropical Indian Ocean. The above anomalous Walker circulations are found to develop as part of positive ocean-atmosphere feedback. Furthermore, the above difference in the anomalous Walker circulation may affect the biennial tendency of the IOD.

  16. A model for the natural and anthropogenic aerosols over the tropical Indian Ocean derived from Indian Ocean Experiment data

    NASA Astrophysics Data System (ADS)

    Satheesh, S. K.; Ramanathan, V.; Li-Jones, Xu; Lobert, J. M.; Podgorny, I. A.; Prospero, J. M.; Holben, B. N.; Loeb, N. G.

    1999-11-01

    The physical, chemical and radiative properties of aerosols are investigated over the tropical Indian Ocean during the first field phase (FFP) of the international Indian Ocean Experiment. The FFP was conducted during February 20 to March 31, 1998. The results shown here are from the Kaashidhoo Climate Observatory (KCO), a new surface observatory established on the tiny island of Kaashidhoo (4.965°N, 73.466°E) in the Republic of Maldives. From simultaneous measurements of aerosol physical, chemical, and radiative properties and the vertical structure from lidar, we have developed an aerosol model which, in conjunction with a Monte Carlo radiative transfer model, successfully explains (within a few percent) the observed solar radiative fluxes at the surface and at the top of the atmosphere. This agreement demonstrates the fundamental importance of measuring aerosol physical and chemical properties for modeling radiative fluxes. KCO, during the northeast monsoon period considered here, is downwind of the Indian subcontinent and undergoes variations in the aerosol visible optical depth τν from ˜0.1 to 0.4, with a monthly mean of ˜0.2. Lidar data suggest that the aerosol is confined largely to the first 3 kms. Sulfate and ammonium contribute ˜29% to τν; sea-salt and nitrate contributes ˜17%; mineral dust contributes ˜15%; and the inferred soot, organics, and fly ash contribute 11%, 20%, and 8% respectively. We estimate that anthropogenic sources may contribute as much as 65% to the observed τν. We consider both an externally and an internally mixed aerosol model with very little difference between the two in the computed radiative forcing. The observed scattering coefficients are in the upper range of those reported for other oceanic regions, the single-scattering albedos are as low as 0.9, and the Angstrom wavelength exponents of ˜1.2 indicate the abundance of submicron aerosols. In summary, the data and the model confirm the large impact of

  17. 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.

  18. 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.

  19. Thermocline Feedback Influence on Indian Ocean Dipole Skewness

    NASA Astrophysics Data System (ADS)

    Ng, B.; Cai, W.; Walsh, K. J.

    2014-12-01

    A positive Indian Ocean Dipole (IOD) tends to have stronger cold sea surface temperature anomalies (SSTAs) over the eastern Indian Ocean with greater impacts than warm SSTAs that occur during its negative phase. These impacts from positive IODs range from drought over Australia and Indonesia, to flooding over East Africa and India. Two feedbacks have been suggested as the cause of positive IOD skewness, a positive Bjerknes feedback and a negative SST-cloud-radiation (SCR) feedback, but their relative importance is debated. Using models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) and inter-model statistics, we show that the most important process for IOD skewness is an asymmetry in the thermocline feedback, whereby SSTAs respond to thermocline depth anomalies more strongly during the positive phase than negative phase. This asymmetric thermocline feedback drives IOD skewness despite positive IODs receiving greater damping from the SCR feedback. In response to global warming, although the thermocline feedback strengthens, its asymmetry between positive and negative IODs weakens. This behaviour change explains the reduction in IOD skewness that many models display under global warming.

  20. Progress in developing an Indian Ocean Tsunami Warning System (IOTWS)

    NASA Astrophysics Data System (ADS)

    Detweiler, S.; Mooney, W. D.; Kelly, A.; Atwater, B.; Sipkin, S.; Petersen, M.; Hudnut, K.

    2007-12-01

    Nearly three years following the devastating 2004 Indian Ocean tsunami, there is much progress to report on building a new Indian Ocean Tsunami Warning System (IOTWS) which will provide tsunami early warnings and framework for disaster management and response systems. To date, the IOTWS has utilized the leadership and technical expertise of many countries including Indonesia, Thailand, India, Sri Lanka, and the Maldives, together with assistance from international partners. Inter-agency cooperation has combined expertise in a broad range of disciplines to accomplish several goals including: 1) developing infrastructures for both real-time analysis of seismic data and rapid communication and warnings (including the upgrade of several Indonesian seismic and GPS stations), 2) land use planning and community preparation aimed at minimizing damage and loss of life from future disasters, and 3) international support for logistics, communications, training, management and administration. Throughout the implementation of the IOTWS, a primary focus was placed on "in-country capacity building," so that individual nations can be self-sustaining in their efforts. We believe that this has been accomplished through extensive training sessions, workshops and site visits.

  1. 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.

  2. [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.

  3. [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. PMID:27325174

  4. 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.

  5. 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.

  6. Intraseasonal variability of upwelling in the equatorial Eastern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Chen, Gengxin; Han, Weiqing; Li, Yuanlong; Wang, Dongxiao; Shinoda, Toshiaki

    2015-11-01

    By analyzing satellite observations and conducting a series of ocean general circulation model experiments, this study examines the physical processes that determine intraseasonal variability (ISV) of the equatorial eastern Indian Ocean (EIO) upwelling for the 2001-2011 period. The ISV of EIO upwelling—as indicated by sea level, thermocline depth, and sea surface temperature (SST)—is predominantly forced by atmospheric intraseasonal oscillations (ISOs), and shows larger amplitudes during winter-spring season (November-April) when atmospheric ISOs are stronger than summer-fall (May-October). The chlorophyll (Chl-a) concentration, another indicator of upwelling, however reveals its largest intraseasonal variability during May-October, when the mean thermocline is shallow and seasonal upwelling occurs. For both winter-spring and summer-fall seasons, the ISV of EIO sea level and thermocline depth is dominated by remote forcing from the equatorial Indian Ocean wind stress, which drives Kelvin waves that propagate along the equator and subsequently along the Sumatra-Java coasts. Local wind forcing within the EIO plays a secondary role. The ISV of SST, however, is dominated by upwelling induced by remote equatorial wind only during summer-fall, with less contribution from surface heat fluxes for this season. During winter-spring, the ISV of SST results primarily from shortwave radiation and turbulent heat flux induced by wind speed associated with the ISOs, and local forcing dominates the SST variability. In this season, the mean thermocline is deep in the warm pool and thus thermocline variability decouples from the ISV of SST. Only in summer-fall when the mean thermocline is shallow, upwelling has important impact on SST.

  7. 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.

  8. 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.

  9. 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

  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. 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.

  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. Evolution of Indian Ocean dipole and its forcing mechanisms in the absence of ENSO

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Murtugudde, Raghu; Kumar, Arun

    2016-10-01

    The evolution of Indian Ocean dipole (IOD) and its forcing mechanisms are examined based on the analysis of coupled model simulations that allow or suppress the El Niño-Southern Oscillation (ENSO) mode of variability. The model can reproduce the most salient observed features of IOD even without ENSO, including the relationships between the eastern and western poles at both the surface and subsurface, as well as their seasonality. This suggests that ENSO is not fundamental for the existence of IOD. It is demonstrated that cold (warm) sea surface temperature (SST) anomalies in the eastern Indian Ocean associated with IOD can be initiated by springtime Indonesian rainfall deficit (surplus) through local surface wind response. The growth of the SST anomalies depends on the initial local subsurface condition. Both the air-sea interaction and surface-subsurface interaction contribute to the development of IOD. The evolution of IOD can be represented by two leading extended empirical orthogonal function (EEOF) modes of tropical surface-subsurface Indian Ocean temperatures; one stationary and the other non-stationary. The onset, growth, and termination of IOD, as well as the transition to an opposite phase, can be interpreted as alternations between the non-propagating mode (EEOF1) and the eastward-propagating Kelvin wave (EEOF2). The evolution of IOD is also accompanied by a westward-propagating Rossby wave which is captured in the EEOF1 of the subtropical surface-subsurface Indian Ocean temperatures. Therefore, both Bjerknes feedback and a delayed oscillator operate during the evolution of IOD in the absence of ENSO also.

  14. Evolution of Indian Ocean dipole and its forcing mechanisms in the absence of ENSO

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Murtugudde, Raghu; Kumar, Arun

    2016-01-01

    The evolution of Indian Ocean dipole (IOD) and its forcing mechanisms are examined based on the analysis of coupled model simulations that allow or suppress the El Niño-Southern Oscillation (ENSO) mode of variability. The model can reproduce the most salient observed features of IOD even without ENSO, including the relationships between the eastern and western poles at both the surface and subsurface, as well as their seasonality. This suggests that ENSO is not fundamental for the existence of IOD. It is demonstrated that cold (warm) sea surface temperature (SST) anomalies in the eastern Indian Ocean associated with IOD can be initiated by springtime Indonesian rainfall deficit (surplus) through local surface wind response. The growth of the SST anomalies depends on the initial local subsurface condition. Both the air-sea interaction and surface-subsurface interaction contribute to the development of IOD. The evolution of IOD can be represented by two leading extended empirical orthogonal function (EEOF) modes of tropical surface-subsurface Indian Ocean temperatures; one stationary and the other non-stationary. The onset, growth, and termination of IOD, as well as the transition to an opposite phase, can be interpreted as alternations between the non-propagating mode (EEOF1) and the eastward-propagating Kelvin wave (EEOF2). The evolution of IOD is also accompanied by a westward-propagating Rossby wave which is captured in the EEOF1 of the subtropical surface-subsurface Indian Ocean temperatures. Therefore, both Bjerknes feedback and a delayed oscillator operate during the evolution of IOD in the absence of ENSO also.

  15. Contribution of Indian Ocean SST to Regional Rainfall Variability: Mechanisms and Implications for Forecasting

    NASA Astrophysics Data System (ADS)

    England, M. H.; Ummenhofer, C. C.; Sen Gupta, A.

    2008-12-01

    The potential impact of Indian Ocean sea surface temperature (SST) anomalies in modulating low- to mid- latitude precipitation around the Indian Ocean-rim countries is examined in a series of atmospheric general circulation model simulations. Two sets of integrations of opposite sign forced with a seasonally evolving pattern in Indian Ocean SST with characteristics of both the tropical and subtropical Indian Ocean dipoles are shown to induce precipitation changes around the adjacent land masses. In additional experiments, the relative importance of the various tropical and subtropical Indian Ocean SST poles, both individually and in combination, to regional precipitation changes is quantified. A mechanism explaining the modification in the rainfall is proposed, by which the SST anomalies induce a reorganization of the large-scale atmospheric circulation across the Indian Ocean basin. The pattern of large-scale circulation changes over the tropical Indian Ocean and adjacent land masses is consistent with an anomalous strengthening of the Walker cell. A reduction (increase) in sea level pressure over the western (eastern) half of the Indian Ocean and converging (diverging) wind anomalies over East Africa (the Indonesian Archipelago) lead to moisture convergence (divergence) and increased (reduced) convective activity over the region. In the simulations, enhancement of the East African rainy season is predominantly driven by the local warm SST anomalies in the western equatorial Indian Ocean, while the eastern cold pole of the tropical Indian Ocean dipole is of lesser importance. Over the mid-latitudes, the SST anomalies give rise to changes in the thermal properties of the atmosphere, meridional thickness gradient, subtropical jet, thermal wind, and baroclinicity. This leads to shifts in the precipitation over western and southern regions of Australia.

  16. 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.

  17. Contribution of atmospheric nitrogen deposition to new production in the nitrogen limited photic zone of the northern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Singh, Arvind; Gandhi, Naveen; Ramesh, R.

    2012-06-01

    Primary productivity in the sunlit surface layers of tropical oceans is mostly limited by the supply of reactive nitrogen (Nr) through upwelling, N2 fixation by diazotrophs, riverine flux and atmospheric deposition. The relative importance of these processes varies from region to region. Using recent data on the nitrogen content of aerosols over the ocean and marine new production in parts of the northern Indian Ocean for the period 1994-2006 CE, a quantitative assessment of the contribution of atmospheric deposition to new production in the two biogeochemically different basins of the northern Indian Ocean, viz., the Arabian Sea and the Bay of Bengal, is presented. By suitably converting the measured concentrations of aerosol nitrogen into fluxes and comparing them with 15N tracer-based direct new and primary production measurements, it is inferred that the contribution of atmospheric deposition to new production in the northern Indian Ocean could at best be ˜3%. Our estimate of ˜1.39 Tg N year-1 of Nr flux into the northern Indian Ocean through aerosols is a step toward significantly reducing the uncertainty in the global nitrogen budget.

  18. Freshening of the South Indian Ocean during the Argo period: observations, causes, and impact on regional sea level change

    NASA Astrophysics Data System (ADS)

    Llovel, William; Lee, Tong

    2015-04-01

    Steric sea level change has been identified as one of the major contributors to the regional sea level changes. This contribution varies in space and time. Temperature (thermosteric) contribution to sea level has been found to be generally more important than salinity (halosteric) effect. Based on temperature and salinity data from Argo floats during 2005-2013 and coincident sea level measurements from satellite altimetry, we found that the central-eastern part of the South Indian Ocean stood out in the entire world ocean as a region that had a more dominant halosteric contribution to sea level change. The conspicuously large halosteric contribution was associated with a freshening in the upper few hundred meters. Neither local atmospheric forcing nor halosteric signal transmitted from the Pacific can explain this freshening. An observed strengthening of the Indonesian throughflow since early 2007 and the enhanced precipitation in the Indonesian Seas inferred from various precipitation estimates compounded by strong tidal mixing are the likely causes of the freshening of the South Indian Ocean. The findings also have implications to the potential influence of regional water cycle and ocean currents in the maritime Continent region to sea level changes in the South Indian Ocean prior to the Argo era and sea level projection in the future in response to climate change. Sustained measurements of sea surface salinity from satellites will significantly enhance our capability to study the impact of regional water cycle in the Maritime Continent region to related changes in the marginal seas and the Indian Ocean.

  19. Continental crust beneath the Agulhas Plateau, Southwest Indian Ocean

    SciTech Connect

    Tucholke, B.E.; Houtz, R.E.; Barrett, D.M.

    1981-05-10

    The Agulhas Plateau lies 500 km off the Cape of Good Hope in the southwestern Indian Ocean. Acoustic basement beneath the northern one third of this large, aseismic structural high has rugged morphology, but basement in the south is anomalously smooth, excepting a 30- to 90-km-wide zone with irregular relief that trends south-southwest through the center of the plateau. Seismic refraction profiles across the southern plateau indicate that the zone of irregular acoustic basement overlies thickened oceanic crust and that continental crust, locally thinned and intruded by basalts, underlies several regions of smooth acoustic basement. Recovery of quartzo-feldspathic gneisses in dredge hauls confirms the presence of continental crust. The smoothness of acoustic basement probably results from erosion (perhaps initially subaerial) of topographic highs with depositions and cementation of debris in ponds to form high-velocity beds. Basalt flows and sills also may contribute locally to form smooth basement. The rugged basement of the northern plateau appears to be of oceanic origin. A plate reconstruction to the time of initial opening of the South Atlantic places the continental part of the southern plateau adjacent to the southern edge of the Falkland Plateau, and both abut the western Mozambique Ridge. Both the Agulhas and Falkland plateaus were displaced westward during initial rifting in the Early Cretaceous. Formation of an RRR triple junction at the northern edge of the Agulhas continental fragment during middle Cretaceous time may explain the origin of the rugged, thickened oceanic crust beneath plateau as well as the apparent extension of the continental crust and intrusion of basaltic magmas beneath the southern plateau.

  20. 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

  1. 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. PMID:23967221

  2. Bio-Argo Floats Reveal Subsurface Structure of Indian Ocean Eddies

    NASA Astrophysics Data System (ADS)

    Strutton, P. G.; Phillips, H. E.; Trull, T. W.; Duran, E.; Pump, S.

    2015-12-01

    There is increasing recognition that eddies modulate open ocean productivity, and that this influence depends on both eddy source and their evolution. Eddies in the southeast Indian Ocean have been recognised, from satellite remote sensing of sea surface height and ocean colour, as important pathways for the westward transport of elevated biomass from the eastern boundary Leeuwin Current into the oligotrophic South Indian Ocean. Further it has been hypothesized that, in some eddies, processes at the base of the mixed layer stimulate productivity and sustain phytoplankton biomass for much longer than would be expected from westward advection alone. Here we present high-frequency profiles of temperature, salinity, chlorophyll, backscatter and oxygen from autonomous floats in anti-cyclonic and cyclonic eddies in the South Indian Ocean. Satellite sea surface height data confirmed that the floats remained trapped in their respective eddies from winter to early summer, sampling the upper 300 m of the water column 6-8 times per day. The eddies were larger than average for this region, with mean amplitude and radius of 18.1 (19.3) cm and 143 (97) km for the anticyclonic (cyclonic) eddies. The total concentration of chlorophyll in the mixed layer remained relatively constant, although its vertical distribution changed over time. From September to October, it was evenly distributed throughout the mixed layer of both eddies. With the onset of spring warming, the chlorophyll became concentrated at greater depth with less chlorophyll at the surface. Satellite measurements of surface chlorophyll were 3-5 times lower than the float surface measurement throughout the record, partly because of the vertical structure in chlorophyll. There was no significant change in oxygen saturation state coincident with high phytoplankton concentrations at depth, indicating no net community production. The eddies appear to self-sustain their biomass.

  3. 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.

  4. Signals of the South China Sea summer rainfall variability in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    He, Zhuoqi; Wu, Renguang; Wang, Weiqiang

    2016-05-01

    The present study investigates signals of the South China Sea (SCS) summer rainfall variability in the Indian Ocean. It is found that the SCS summer rainfall has a negative relationship with December-January-February (DJF) western-equatorial Indian Ocean (WIO) sea surface temperature (SST), a positive relationship with an asymmetric mode of precipitation anomalies in the tropical Indian Ocean during March-April-May (MAM), and a positive relationship with June-July-August (JJA) South Indian Ocean (SIO) SST. The WIO SST anomalies induce same-sign southeast Indian Ocean SST anomalies through an anomalous zonal vertical circulation. The southeast Indian Ocean SST anomalies last from late winter to early summer and induce opposite-sign SCS summer rainfall anomalies via an anomalous meridional vertical circulation. The asymmetric mode influences the SCS summer rainfall variation via the North Indian Ocean (NIO) SST anomalies with significant cloud-radiation and wind-evaporation effect. Positive (negative) SIO SST anomalies drive an anomalous direct circulation between the SIO and the NIO, and an anomalous indirect circulation between the NIO and the SCS which facilitates the occurrence of cyclonic (anti-cyclonic) wind anomalies over the SCS-western North Pacific and results in positive (negative) SCS summer rainfall anomalies. Partial correlation analysis indicates that the influence of DJF WIO SST anomalies and JJA SIO SST anomalies on the SCS summer rainfall is partly ENSO-independent, while the MAM asymmetric mode is mostly related to the preceding DJF eastern Pacific SST anomalies.

  5. Role of Indian Ocean SST variability on the recent global warming hiatus

    NASA Astrophysics Data System (ADS)

    Arora, Anika; Rao, Suryachandra A.; Chattopadhyay, R.; Goswami, Tanmoy; George, Gibies; Sabeerali, C. T.

    2016-08-01

    Previous studies have shown a slowdown in the warming rate of the annual mean global surface temperature in the recent decade and it is referred to as the hiatus in global warming. Some recent studies have suggested that the hiatus in global warming is possibly due to strong cooling in the tropical Pacific. This study investigates the possible role of the Indian Ocean warming on the tropical Pacific cooling. Despite the continued rise in sea surface temperature (SST) over the tropical Indian Ocean, SST over the tropical Pacific has shown a cooling trend in the recent decade (2002 - 2012). It is well known fact that the Indian Ocean and the Pacific Ocean are strongly coupled to each other and the Indian Ocean basin wide warming is triggered by El Niño on interannual time scale. However, in the recent decade, this relationship is weakening. The recent Indian Ocean warming is triggering a Matsuno-Gill type response in the atmosphere by generating anomalous cyclonic circulations on either side of equator over the tropical Indian Ocean and anomalous easterlies along the tropical Pacific Ocean. These anomalous easterlies result in Ekman divergence in the equatorial Pacific and produce upwelling Kelvin waves, cools the tropical Pacific and therefore indirectly contributes to the hiatus in global warming.

  6. 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

  7. Shallow mtDNA coalescence in Atlantic pygmy angelfishes (genus Centropyge) indicates a recent invasion from the Indian Ocean.

    PubMed

    Bowen, B W; Muss, A; Rocha, L A; Grant, W S

    2006-01-01

    Pygmy angelfishes (genus Centropyge) are widespread and species-rich in the Indo-Pacific, but only three species are recognized in the Atlantic: Centropyge resplendens on the Mid-Atlantic Ridge, Centropyge argi in the Caribbean, and Centropyge aurantonotus in Brazil and the southern Caribbean. Atlantic species are distinguished only by color patterns and are very similar to Centropyge acanthops (Cac) in the western Indian Ocean, raising the possibility that pygmy angelfish recently invaded the Atlantic Ocean via southern Africa. To test this zoogeographic hypothesis, we compared a 454-bp segment of the mitochondrial DNA (mtDNA) control region among pygmy angelfishes of the subgenus Xiphypops, which includes the three Atlantic species, the Indian Ocean species, and an Indo-Pacific species [Centropyge fisheri (Cfi)]. The Indian Ocean species Cac is closest to the Atlantic species (d = 0.059) relative to Cfi (d = 0.077). The mtDNA genealogy indicates a colonization pathway from the Indian Ocean directly to the West Atlantic, followed by at least two waves of dispersal to the Mid-Atlantic Ridge. The gene tree for the three Atlantic species is polyphyletic, raising questions about taxonomic assignments based on color pattern. Mismatch distributions place Atlantic founder events and population expansions at about 250,000-500,000 years ago. Estimates of effective female population sizes from mismatch and coalescence analyses are consistent with founder events by tens of individuals in the western Atlantic, followed by expansions to several million individuals.

  8. 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

  9. 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.

  10. 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.

  11. 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. PMID:24919920

  12. Geochemical Evidence for Gas Hydrates in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Kastner, M.; Solomon, E.; Torres, M.; Spivack, A. J.; Borole, D. V.; Hangsterfer, A.; Das, H. C.; Robertson, G. A.

    2007-12-01

    Geochemical analyses of pore fluids collected from both non-pressurized and pressurized cores provide important constraints on the presence and distribution of gas hydrates in the Indian Ocean. Cores were recovered from two deepwater (900-1170 meter) basins offshore southeast India, the Krishna-Godavari (KG) (10 sites) and Mahanadi Basins (2 sites), and from one site in the Andaman Sea (1600 meters water depth). A bottom simulating reflector (BSR) (i.e., possible base of methane hydrate stability) was present at most of the sites cored and evidence for methane hydrate was obtained at each of the sites. The gas hydrates in most of the conventional cores decomposed prior to sampling. The former presence and distribution of methane hydrate in some of the conventional cores was inferred by indirect methods: from infra-red imaging of cold core temperatures that correlated with pore fluids having lower salinity and chloride concentrations and occasionally mousse-like textures. Chloride concentrations and salinity anomalies, assuming dilution by water released from decomposed methane hydrate, suggest pore volume occupancies on the order of, <1% to a maximum of ~61% at two of the sites in the KG Basin, and <1% to a maximum of ~76% at the site in the Andaman Sea. In the KG Basin, the highest methane hydrate concentrations were associated with fracture zones in clay/silt sediments or in some coarser grained horizons, although gas hydrate was not present in all coarse- grained sediment horizons. Overall, the % occupancies based on pressure core methane concentrations and the chloride concentrations in conventional cores were similar. The pressure core samples used for these determinations were 1 m long, and the conventional core samples were 10-30 cm whole round core samples, chosen via IR imaging. Variations in sulfate gradients were observed; the steepest gradient with the sulfate/methane interface (SMI) at 8 mbsf was observed in the KG Basin. The deepest SMI obtained, at

  13. 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

    2016-06-01

    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.

  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. 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

  16. [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.

  17. Two new dwarfgobies from the Indian and Western Pacific Oceans (Teleostei: Gobiidae: Eviota).

    PubMed

    Greenfield, David W; Jewett, Susan L

    2016-06-13

    Two new species of dwarfgobies are described, Eviota asymbasia from the Sulu Sea, Philippine Islands, south to Java and west to Damar, and E. bipunctata occurring from the Indian Ocean eastward into the western Pacific Ocean. Eviota asymbasia lacks the IT pore of the cephalic sensory-pore system and usually also the POP, has a dorsal/anal-fin formula of 8/8, has some pectoral-fin rays branched and usually 15 rays, two spots on the pectoral-fin base, no dark spot over the preural centrum, first dorsal fin may be filamentous, six ventral postanal spots, and the male genital papilla is not fimbriate. Eviota bipunctata belongs to the group with cephalic sensory-pore system pattern 2 (lacking only the IT pore), some pectoral-fin rays branched, pectoral-fin base with 1 or 2 prominent dark spots, dorsal/anal-fin formula usually 8/8, and no occipital spots.

  18. Two new dwarfgobies from the Indian and Western Pacific Oceans (Teleostei: Gobiidae: Eviota).

    PubMed

    Greenfield, David W; Jewett, Susan L

    2016-01-01

    Two new species of dwarfgobies are described, Eviota asymbasia from the Sulu Sea, Philippine Islands, south to Java and west to Damar, and E. bipunctata occurring from the Indian Ocean eastward into the western Pacific Ocean. Eviota asymbasia lacks the IT pore of the cephalic sensory-pore system and usually also the POP, has a dorsal/anal-fin formula of 8/8, has some pectoral-fin rays branched and usually 15 rays, two spots on the pectoral-fin base, no dark spot over the preural centrum, first dorsal fin may be filamentous, six ventral postanal spots, and the male genital papilla is not fimbriate. Eviota bipunctata belongs to the group with cephalic sensory-pore system pattern 2 (lacking only the IT pore), some pectoral-fin rays branched, pectoral-fin base with 1 or 2 prominent dark spots, dorsal/anal-fin formula usually 8/8, and no occipital spots. PMID:27395247

  19. 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. PMID:9545216

  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. A new atlas of temperature and salinity for the North Indian Ocean

    NASA Astrophysics Data System (ADS)

    Chatterjee, A.; Shankar, D.; Shenoi, S. S. C.; Reddy, G. V.; Michael, G. S.; Ravichandran, M.; Gopalkrishna, V. V.; Rama Rao, E. P.; Udaya Bhaskar, T. V. S.; Sanjeevan, V. N.

    2012-06-01

    The most used temperature and salinity climatology for the world ocean, including the Indian Ocean, is the World Ocean Atlas (WOA) (Antonov et al 2006, 2010; Locarnini et al 2006, 2010) because of the vast amount of data used in its preparation. The WOA climatology does not, however, include all the available hydrographic data from the Indian Exclusive Economic Zone (EEZ), leading to the potential for improvement if the data from this region are included to prepare a new climatology. We use all the data that went into the preparation of the WOA ( Antonov et al 2010; Locarnini et al 2010), but add considerable data from Indian sources, to prepare new annual, seasonal, and monthly climatologies of temperature and salinity for the Indian Ocean. The addition of data improves the climatology considerably in the Indian EEZ, the differences between the new North Indian Ocean Atlas (NIOA) and WOA being most significant in the Bay of Bengal, where the patchiness seen in WOA, an artifact of the sparsity of data, was eliminated in NIOA. The significance of the new climatology is that it presents a more stable climatological value for the temperature and salinity fields in the Indian EEZ.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  3. 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.

  4. Seasonal Characteristics of Circulation in the Southeastern Tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Qu, T.; Meyers, G.

    2004-12-01

    The circulation in the southeastern tropical Indian Ocean is studied using historical temperature and salinity data. A southward shift of the subtropical gyre at increasing depth dominates the structure of the annual mean circulation. Near the southern Indonesian coast, the westward South Equatorial Current (SEC) is at the sea surface and strongest near 10°-11°S, reflecting strong influence of the Indonesian Throughflow (ITF). In latitudes 13°-25°S the SEC is a subsurface flow and its velocity core deepens toward the south, falling below 500 m at 25°S. The Eastern Gyral Current (EGC) is a surface flow overlying the SEC, associated with the meridional gradients of near-surface temperature and salinity. The ITF supplies water to the SEC mainly in the upper 400 m, and below that depth the flow is reversed along the coast of Sumatra and Java. Monsoon-winds strongly force the annual variation in circulation. Dynamic height at the sea surface has a maximum amplitude at 10°-13°S, and the maximum at deeper levels is located further south. Annual variation is also strong in the coastal wave guides, but is mainly confined to the near-surface layer. Although the South Java Current at the sea surface is not well resolved in the present dataset, semiannual variation is markedly evident at depth and tends to extend much deeper than annual variation along the coast of Sumatra and Java.

  5. Multiple ciguatoxins present in Indian Ocean reef fish.

    PubMed

    Hamilton, Brett; Hurbungs, Mira; Jones, Alun; Lewis, Richard J

    2002-09-01

    Optimised gradient reversed-phase high-performance liquid chromatography electrospray ionisation mass spectrometry (LC/MS) methods, in combination with a [3H]-brevetoxin binding assay (RLB), revealed multiple ciguatoxins in a partially purified extract of a highly toxic Lutjanus sebae (red emperor) from the Indian Ocean. Two major ciguatoxins of 1140.6 Da (I-CTX-1 and -2) and two minor ciguatoxins of 1156.6 Da (I-CTX-3 and -4) were identified. Accurate mass analysis revealed that I-CTX-1 and -2 and Caribbean C-CTX-1 had indistinguishable masses (1140.6316 Da, at 0.44 ppm resolution). Toxicity estimated from LC/MS/RLB responses indicated that I-CTX-1 and -2 were both approximately 60% the potency of Pacific ciguatoxin-1 (P-CTX-1). In contrast to ciguatoxins of the Pacific where the more oxidised ciguatoxins are more potent, I-CTX-3 and -4 were approximately 20% of P-CTX-1 potency. Interconversion in dilute acid or on storage, typical of spiroketal and hemiketal functionality found in P-CTXs and C-CTXs, respectively, was not observed to occur between I-CTX-1 and -2. The ratio of CTX-1 and -2 varied depending on the fish extract being analysed. These results suggest that I-CTX-1 and -2 may arise from separate dinoflagellate precursors that may be oxidatively biotransformed to I-CTX-3 and -4 in fish.

  6. 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.

  7. Seroepidemiology of Dengue Virus in Mayotte, Indian Ocean, 2006

    PubMed Central

    Sissoko, Daouda; Ezzedine, Khaled; Giry, Claude; Moendandzé, Amrat; Lernout, Tinne; D'Ortenzio, Eric; Pettinelli, François; Malvy, Denis

    2010-01-01

    Background Although Dengue virus (DENV) circulation had been documented in neighbouring South-western Indian Ocean Islands, its presence in Mayotte is poorly characterised. To address this issue, we aimed to assess the seroprevalence of dengue IgG antibodies (DENV-IgG Ab) among the population and to investigate potential associations with individual and household characteristics. Methods/Principal Findings In November–December 2006 we conducted a cross-sectional serologic survey in Mayotte among 1,154 inhabitants aged ≥2 years by using a multistage cluster random sampling method. The overall prevalence of DENV-specific IgG antibodies (ELISA) was 22.73% (95% CI, 18.16–27.31). The age-specific seroprevalence increased with age (χ2 for trend = 11.86, P<0.0006), and was linked with previous known outbreaks in this region. In multivariate analysis, older age, being born in the Comoros and living in a household with a low socioeconomic index were positively associated with DENV IgG antibody positivity. Conclusions These findings document substantial prior exposure of the population of Mayotte to DENV and highlight the risk of severe illness due to the possibility of sequential DENV infections. Further investigations characterizing current DENV circulation patterns and associated serotypes are needed. PMID:21152441

  8. Teleconnections due the north Indian Ocean tropical disturbances

    NASA Astrophysics Data System (ADS)

    Jayanthi, V.; Behera, S. K.; Masumoto, Y.; Yamagata, T.

    2012-12-01

    Teleconnections due to long lasting intense tropical disturbances in the north Indian Ocean are investigated in this study. The analyses is carried out for both the pre-monsoon (April-May) and post-monsoon (Oct-Dec) periods. The OLR distribution of the pre-monsoon tropical storms in the Bay of Bengal shows a dipole like structure. The composite plot reveals strong negative OLR anomalies over the Bay region and strong positive OLR anomalies near the Indonesian region. The composite also shows negative OLR anomalies extending from the north-west Pacific region to the western Japan, which is remote from the origin of the Bay of Bengal disturbances. The associated surface temperature anomalies show positive surface temperature anomalies over the northwestern parts of India, Pakistan and Afghanistan with cold anomalies over the Arabian region which is also remote to the region of the tropical disturbances. Further analyses of the anomalies shows that, the negative OLR anomalies over western Japan are due to the Rossby waves generated by the heating over the Bay besides the enhancement of the Pacific-Japan teleconnection. However, the post-monsoon disturbances in the Bay of Bengal and the disturbances formed in the Arabian Sea in both pre- and post-monsoon seasons do not develop remote teleconnections associated with the above type of Rossby wave mechanism.

  9. Submerged reef terraces of the Maldives (Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Fürstenau, Jörn; Lindhorst, Sebastian; Betzler, Christian; Hübscher, Christian

    2010-10-01

    There is limited knowledge about the record of sea-level rise from the last glacial maximum (LGM) until the onset of Holocene reef growth in the Maldives archipelago. Multibeam data show that atoll slopes between 130 and 55 mbsl (meters below sea level) are characterized by a step-like morphology. In parts, these terraces show a raised rim and a crenate geometry. Atoll margin features can be interpreted as successive reef-growth and -drowning stages, which are attributable to changes in the rate of sea-level rise. These changes can tentatively be correlated to known records of global sea-level change since the LGM. In addition to terraces between 97 and 55 mbsl, which can be associated with the initiation of meltwater pulses MWP-1A and -1B, several reef-drowning stages between 94 and 68 mbsl are proposed. As the Maldives can be considered a tectonically stable, far-field site, the submerged reef terraces inferred from the first multibeam dataset for this region likely represent a valuable archive for global deglacial sea-level history in the Indian Ocean.

  10. 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.

  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. PMID:16580709

  13. 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.

  14. The impact of advective transport by the South Indian Ocean Countercurrent on the Madagascar plankton bloom

    NASA Astrophysics Data System (ADS)

    Huhn, F.; von Kameke, A.; Pérez-Muñuzuri, V.; Olascoaga, M. J.; Beron-Vera, F. J.

    2012-03-01

    Based on ten years (1998-2007) of satellite ocean color data we analyze the spatiotemporal patterns in the seasonal Madagascar plankton bloom with respect to the advection of the recently discovered Southern Indian Ocean Countercurrent (SICC). In maps of Finite-time Lyapunov Exponents (FTLE) and Finite-Time Zonal Drift (FTZD) computed from altimetry derived velocities we observe a narrow zonal jet that starts at ˜25°S at the southern tip of Madagascar, an important upwelling region, and extends to the east further than the largest plankton blooms (˜2500 km). In bloom years, the jet coincides with large parts of the northern boundary of the plankton bloom, acting as a barrier to meridional transport. Our findings suggest that advection is an important and so far underestimated mechanism for the eastward propagation and the extent of the plankton bloom. This supports the hypothesis of a single nutrient source south of Madagascar.

  15. 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

  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. 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.

  18. On the relationship between Indian Ocean Dipole-Indian Summer Monsoon and Summer North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Sundaram, S.; Stenchikov, G. L.

    2013-12-01

    Using 60 years of observed and re-analysis data sets a link between positive Indian Ocean dipole (PIOD), Indian Summer Monsoon (ISM) and Summer North Atlantic Oscillation (SNAO) is proposed. When positive IOD years occur independently without Elnino the presence of positive phase of SNAO is noticed. In such cases over the Atlantic region the centers of action associated with SNAO is shifted northward leading to the change in the mean position of Atlantic jet and storm tracks. Persistence of storm tracks at the new location amounts to a stationary waves, which have a barotropic structure in the vertical. Therefore, the temperature anomalies associated with the stationary wave influences the Tropospheric Temperature (TT), which is clearly seen in the average TT anomaly, showing warming over southern Eurasia and India. This affects the north-south TT gradient in the monsoon region and influences the ISM (Goswami et al., 2006). Concurrently the local Hadley cell associated with PIOD strengthens and enhances the anomalous subsidence over the Mediterranean/Sahara region which in turn strengthens the Azores high and the hence the SNAO itself. Thus the combined influence of PIOD and SNAO produces a positive feed back mechanism for ISM. On the other hand most of the PIOD years co-occurring with Elnino years are accompanied by the negative phase of SNAO. The analysis of the atmospheric circulation clearly indicates the Pacific North American (PNA) type pattern, which negatively influence the SNAO (Huang et al., 1998). This is consistent with the observation that ISM is not enhanced in all PIOD years. The analysis of 60 years historic sea surface temperature runs with the high resolution atmospheric model shows that the model is able to reproduce these teleconnections.

  19. Direct estimates of the Indonesian Throughflow entering the Indian Ocean: 2004-2006

    NASA Astrophysics Data System (ADS)

    Sprintall, Janet; Wijffels, Susan E.; Molcard, Robert; Jaya, Indra

    2009-07-01

    The mean and variable transport of the Indonesian Throughflow (ITF) are determined from full-depth velocity measurements in the three major exit passages of Lombok Strait, Ombai Strait, and Timor Passage from January 2003 through December 2006. Collectively, these passages convey the full-depth transport and stratification profile of the ITF from the Pacific Ocean to the Indian Ocean. To first order, the seasonal cycle of transport in the thermocline (˜100-150 m) in all three exit straits is dominated by regional monsoon forcing, with maximum ITF during the southeast monsoon. During the northwest monsoon, the surface transport relaxes in Timor and weakly reverses in Ombai and Lombok, so the main core of the ITF is subsurface. Below the thermocline, semiannual reversals occur in all three straits during the monsoon transitions in response to the passage of Indian Ocean wind-forced Kelvin waves. However, the reversals occur over different depth levels in each passage reflecting the influence of different sill depths along the coastal waveguide. The seasonal cycle of depth-integrated transports in Lombok and Ombai are strongly out of phase with Timor Passage, suggesting that the subthermocline flow is largely gated by these Kelvin waves. Despite the different seasonal transport phases, interannual anomalies in all three passages are remarkably similar, particularly during the strong positive Indian Ocean Dipole event in 2006 when transport in the surface layer is toward the Indian Ocean and reversed below. The deep reversals are likely in response to a series of Kelvin waves driven by anomalous zonal winds in the equatorial Indian Ocean. Total mean transport over the 3-year period is -2.6 Sv in Lombok Strait (i.e., toward the Indian Ocean), -4.9 Sv in Ombai Strait, and -7.5 Sv in Timor Passage. The transport in Timor Passage is nearly twice as large as historical estimates and represents half of the -15 Sv full-depth ITF transport that enters the Indian Ocean.

  20. 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

  1. 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

  2. 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)…

  3. 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.

  4. Hydrothermal plumes over the Carlsberg Ridge, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Ray, Durbar; Kamesh Raju, K. A.; Baker, Edward T.; Srinivas Rao, A.; Mudholkar, Abhay V.; Lupton, John E.; Surya Prakash, L.; Gawas, Rekha B.; Vijaya Kumar, T.

    2012-01-01

    Indian Ocean ridges north of the Rodriguez Triple Junction remain poorly explored for seafloor hydrothermal activity, with only two active sites confirmed north of 25°S. We conducted water column surveys and sampling in 2007 and 2009 to search for hydrothermal plumes over a segment of the Carlsberg Ridge. Here we report evidence for two separate vent fields, one near 3°42'N, 63°40'E and another near 3°41.5'N, 63°50'E, on a segment that is apparently sparsely magmatic. Both sites appear to be located on off-axis highs at the top of the southern axial valley wall, at depths of ˜3600 m or shallower (˜1000 m above the valley floor). At the 63°40'E site, plume sampling found local maxima in light scattering, temperature anomaly, oxidation-reduction potential (ORP), dissolved Mn, and3He. No water samples are available from the 63°50'E site, but it showed robust light-scattering and ORP anomalies at multiple depths, implying multiple sources. ORP anomalies are very short-lived, so the strong signals at both sites suggest that fluid sources lie within a few kilometers or less from the plume sampling locations. Although ultramafic rocks have been recovered near these sites, the light-scattering and dissolved Mn anomalies imply that the plumes do not arise from a system driven solely by exothermic serpentinization (e.g., Lost City). Instead, the source fluids may be a product of both ultramafic and basaltic/gabbroic fluid-rock interaction, similar to the Rainbow and Logatchev fields on the Mid-Atlantic Ridge.

  5. Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Ki; Park, Wonsun; Baringer, Molly O.; Gordon, Arnold L.; Huber, Bruce; Liu, Yanyun

    2015-06-01

    Global mean surface warming has stalled since the end of the twentieth century, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. This apparent contradiction has been reconciled by an anomalous heat flux into the ocean, induced by a shift towards a La Niña-like state with cold sea surface temperatures in the eastern tropical Pacific over the past decade or so. A significant portion of the heat missing from the atmosphere is therefore expected to be stored in the Pacific Ocean. However, in situ hydrographic records indicate that Pacific Ocean heat content has been decreasing. Here, we analyse observations along with simulations from a global ocean-sea ice model to track the pathway of heat. We find that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. As a result, Indian Ocean heat content has increased abruptly, which accounts for more than 70% of the global ocean heat gain in the upper 700 m during the past decade. We conclude that the Indian Ocean has become increasingly important in modulating global climate variability.

  6. 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.

  7. 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.

  8. Investigation of tropical eel spawning area in the South-Western Indian Ocean: Influence of the oceanic circulation

    NASA Astrophysics Data System (ADS)

    Pous, S.; Feunteun, E.; Ellien, C.

    2010-09-01

    In the South-Western Indian Ocean (SWIO), four eel species of the genus Anguilla (i.e. Anguilla bicolor bicolor, Anguilla nebulosa labiata, Anguilla marmorata and Anguilla mossambica) were identified, while their respective oceanic spawning area remained unknown. Based on collected larvae, glass eel captures and hydrodynamical conditions, previous studies raised the hypothesis that the eel spawning area might be common to all of those freshwater eel species, and located East of Madagascar. An original modeling approach, based on backward simulations, is developed to assess how the ocean circulation in the SWIO determines the location of the spawning areas and whether a common spawning area for each recruitment site where glass eels were found is possible. We use a hydrodynamical model, which reproduces realistically the 3D open ocean circulation in the region, associated with a Lagrangian model that calculates the possible migration pathways of larvae, represented by passive particles. Some biological parameters, provided by previous otolith microstructures analysis, are taken into account to constrain our simulations. Results suggest the existence of a common spawning area located between 13°S and 19°S and westwards of 60.5°E, although these boundaries vary on the interannual timescale. Salinity fronts were reported beside the boundaries, reinforcing this assumption. We explore the impact of hydrodynamic conditions on recruitment and migration durations from three specific regions within the common spawning area. They all allow migration to each recruitment sites consistent with duration estimated from otolith microstructure analyses. Nevertheless, there is substantial variability on intra-seasonal to interannual timescale in simulated migration durations and arrival success, with specific amplitude to each recruitment site and spawning location.

  9. 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.

  10. 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.

  11. 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.

  12. Carcharhinus humani sp. nov., a new whaler shark (Carcharhiniformes:Carcharhinidae) from the western Indian Ocean.

    PubMed

    White, William T; Weigmann, Simon

    2014-06-19

    A new species of whaler shark, Carcharhinus humani sp. nov., is described based on five type specimens from the western Indian Ocean near the Socotra Islands, off Kuwait, Mozambique, and South Africa. The new species represents the fifth species of the C. dussumieri/sealei group and the third species of the C. sealei subgroup. The new species is the only species of the C. sealei subgroup known from the western Indian Ocean. Within the C. sealei subgroup, C. humani differs from C. sealei in having a sharply demarcated black apical marking on the second dorsal fin which does not extend onto body surface (vs. black marking diffuse-edged and usually extending onto upper sides of trunk), a longer horizontal prenarial length (4.1-4.7 vs. 3.4-4.2% TL), and a longer preoral length (6.8-7.6 vs. 5.7-6.5% TL); C. humani differs from C. coatesi in having a taller second dorsal fin (its height 4.0-4.5 vs. 2.9-3.6% TL), a shorter first dorsal fin (its length 13.4-14.6 vs. 14.8-17.3% TL), and more vertebrae (total centra 152-167 vs. 134-147).

  13. 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.

  14. 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.

  15. 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. PMID:26194365

  16. Carcharhinus humani sp. nov., a new whaler shark (Carcharhiniformes:Carcharhinidae) from the western Indian Ocean.

    PubMed

    White, William T; Weigmann, Simon

    2014-01-01

    A new species of whaler shark, Carcharhinus humani sp. nov., is described based on five type specimens from the western Indian Ocean near the Socotra Islands, off Kuwait, Mozambique, and South Africa. The new species represents the fifth species of the C. dussumieri/sealei group and the third species of the C. sealei subgroup. The new species is the only species of the C. sealei subgroup known from the western Indian Ocean. Within the C. sealei subgroup, C. humani differs from C. sealei in having a sharply demarcated black apical marking on the second dorsal fin which does not extend onto body surface (vs. black marking diffuse-edged and usually extending onto upper sides of trunk), a longer horizontal prenarial length (4.1-4.7 vs. 3.4-4.2% TL), and a longer preoral length (6.8-7.6 vs. 5.7-6.5% TL); C. humani differs from C. coatesi in having a taller second dorsal fin (its height 4.0-4.5 vs. 2.9-3.6% TL), a shorter first dorsal fin (its length 13.4-14.6 vs. 14.8-17.3% TL), and more vertebrae (total centra 152-167 vs. 134-147). PMID:24989727

  17. 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.

  18. Observations and Modeling of Environmental and Human Damages by the 2004 Indian Ocean tsunami

    NASA Astrophysics Data System (ADS)

    Goto, K.; Imamura, F.; Koshimura, S.; Yanagisawa, H.

    2008-05-01

    On 26 December 2004, one of the largest tsunamis in human history (the 2004 Indian Ocean tsunami) struck coastal areas of countries surrounding the Indian Ocean, causing severe property damage and loss of life and causing us to think anew about the fearful consequences of a tsunami disaster. The tsunami devastated more than 10 countries around the ocean including Indonesia, Sri Lanka, India, and Thailand. Since its energy remains almost constant, the tsunami wave height grows tremendously in shallow water. It ranged in runups of ~48m on the western shore of Sumatra, ~18m in Thailand, and ~15m in Sri Lanka. The tsunami killed nearly 230,000 people, including visitors from foreign countries, resulting in great economic losses. The tsunami was also affected coastal environment at these countries and induced severe topographic change, and damages to the marine ecosystems as well as vegetations on land. Immediately following the tsunami, number of research teams has investigated damages of environment and human communities by tsunamis. Numerical analyses of tsunami propagation have also been carried out to understand the behavior and wave properties of tsunamis. However, there are few studies that focused on the integration of the field observations and numerical results, nevertheless that such analysis is critically important to evaluate the environmental and human damages by the tsunami. In this contribution, we first review damages to the environment and humans due to the 2004 Indian Ocean tsunami at Thailand, Indonesia, and Sri Lanka based on our field observations, and then we evaluate these damages based on high resolution numerical results. For example, we conducted field observation as well as high-resolution (17 m grid cells) numerical calculation for damages of corals (reef rocks) and mangroves at Pakarang Cape, Thailand. We found that hundreds of reef rocks were emplaced on the tidal bench, and 70 % of mangroves were destroyed at the cape. Our numerical

  19. 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.

  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. 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.

  2. Experimental observations of air-sea parameters and fluxes associated with anomalous event in the Indian Ocean during 1997-1998 El Niño period

    NASA Astrophysics Data System (ADS)

    Ramana, M. V.; Krishnan, Praveena; Muraleedharan Nair, S.; Kunhikrishnan, P. K.

    2004-04-01

    This paper describes the variation of air-sea parameters and fluxes during winter months of 1997 (pre-INDOEX) and 1998 (INDOEX-FFP) using ship-based in situ measurements in the latitude range 15°N to 20°S over the Indian Ocean and Arabian Sea. The 1998 cruise period coincided with one of the strongest El Niño events in the decade over the Pacific Ocean. The tropical Indian Ocean underwent a highly anomalous series of events during 1998 with warm sea surface temperature (SST) anomaly over 2 °C during February 1998 and easterly winds associated with the reversed Walker circulation. In situ observations during 1998 cruise period show that the winds in the Indian Ocean region had basically resumed their climatological state as of March 15, 1998 with lesser wind speeds as El Niño waned. However, the sea surface temperatures in Indian Ocean were found to be high even though climatological state had resumed. The present results are the observational evidence to show that the reduced latent heat flux due to low wind speeds could have contributed to the surface warming in the Indian Ocean. The sensible heat and latent heat fluxes are found to be high during anomalous period due to higher sea surface temperature and wind speeds in comparison to the normal period.

  3. 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.

  4. 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. PMID:27196065

  5. 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.

  6. 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

  7. 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

  8. A qualitative study on sea surface temperature over the tropical Indian Ocean and performance of Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Singh, Umesh Kumar; Singh, Gyan Prakash

    2012-08-01

    A careful analysis of the sea surface temperature (SST) over the tropical Indian Ocean using the available SST data sets (namely, Hadley Center Ice SST, tropical rainfall measuring mission microwave imager SST, and optimum interpolation SST) at different time scales has been presented in the present study. By simple visual inspection of the SST plots, it has been shown that the qualitative prediction of Indian summer monsoon condition (weak/normal) and northern limit of monsoon (NLM) can be possible a month in advance using SST. The present qualitative study may be useful for common man to know the behavior of summer monsoon well a month in advance. Therefore, the qualitative study may enable the common man to show the application of satellite data to bring out the information regarding the onset of summer monsoon and related performance of Indian summer monsoon well in advance.

  9. 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.

  10. 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.

  11. 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.

  12. Meridional variability of atmospheric convection associated with the Indian Ocean Dipole Mode.

    PubMed

    Weller, Evan; Cai, Wenju

    2014-01-07

    The Indian Ocean Dipole Mode (IODM) impacts many surrounding and remote regions of the Indian Ocean, with devastating floods over East Africa but severe droughts in countries surrounding Indonesia during a positive IODM event. Understanding the dynamics is important for seasonal prediction and climate projections, but the role of meridional temperature and circulation anomalies remains unclear. Here, we show that in combination with the zonal structure of temperature and rainfall anomalies, northward contraction of the warm water pool over the eastern equatorial Indian Ocean region (EEIO) also generates an anomalous meridional cross-equatorial temperature gradient in the east. This meridional temperature gradient controls northward retreat of the atmospheric convection in association with northward cross-equatorial winds, and hence declining rainfall over the EEIO. Our results have important implications for the mean state change under greenhouse warming.

  13. The Indian Ocean Experiment: Widespread Air Pollution from South and Southeast Asia

    NASA Astrophysics Data System (ADS)

    Lelieveld, J.; Crutzen, P. J.; Ramanathan, V.; Andreae, M. O.; Brenninkmeijer, C. A. 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. J.; 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.

    2001-02-01

    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°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.

  14. Meridional variability of atmospheric convection associated with the Indian Ocean Dipole Mode.

    PubMed

    Weller, Evan; Cai, Wenju

    2014-01-01

    The Indian Ocean Dipole Mode (IODM) impacts many surrounding and remote regions of the Indian Ocean, with devastating floods over East Africa but severe droughts in countries surrounding Indonesia during a positive IODM event. Understanding the dynamics is important for seasonal prediction and climate projections, but the role of meridional temperature and circulation anomalies remains unclear. Here, we show that in combination with the zonal structure of temperature and rainfall anomalies, northward contraction of the warm water pool over the eastern equatorial Indian Ocean region (EEIO) also generates an anomalous meridional cross-equatorial temperature gradient in the east. This meridional temperature gradient controls northward retreat of the atmospheric convection in association with northward cross-equatorial winds, and hence declining rainfall over the EEIO. Our results have important implications for the mean state change under greenhouse warming. PMID:24395079

  15. 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

    2016-01-01

    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. PMID:27615853

  16. 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

  17. 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

  18. 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.

  19. The Neogene monsoon and oceanic currents in the Indian Ocean: The Maldives archipelago.

    NASA Astrophysics Data System (ADS)

    Betzler, C.; Hübscher, C.; Lüdmann, T.; Reijmer, J.; Eberli, G.; Kroon, D.; Droxler, A.; Tiwari, M.; Gischler, E.

    2012-04-01

    New seismic data from the Maldives show that the Neogene of the Maldives carbonate edifice image large drift deposits. The stacking pattern of depositional sequences through the Lower to Middle Miocene traces variations of accommodation space, which are proposed to be primarily governed by fluctuations of relative sea level. During the late Middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank drowning and associated deposition of giant sediment-drifts. Drowned banks show shapes attesting the occurrence of strong surface currents. Therefore, this turnover is attributed to the onset and/or intensification of oceanic currents and related upwelling. Drift sediments, characterized by offlapping geometries, formed as large-scale prograding complexes. Findings are not only expected to be applicable to other examples of Tertiary platforms in the Indo-Pacific region but also to other carbonate platforms in the geological record. Onset, type and variations of drift deposits in the platform edifice further provide not only a new and valuable proxy for the reconstruction of the oceanic currents around the Maldives but also for the development of the associated large-scale oceanographic current system with a world-wide impact. Additionally, the sedimentary record of the drift deposits may represent an excellent archive of the Indian monsoon history. The overall aim of an IODP drilling campaign thus would be to place the Maldives current system into the larger scale development of the global oceanographic current system by integrating results from other ODP and IODP expeditions like the south Atlantic or the Mediterranean outflow expedition.

  20. 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.

  1. Carbonaceous aerosols over the Indian Ocean during the Indian Ocean Experiment (INDOEX): Chemical characterization, optical properties, and probable sources

    NASA Astrophysics Data System (ADS)

    Mayol-Bracero, O. L.; Gabriel, R.; Andreae, M. O.; Kirchstetter, T. W.; Novakov, T.; Ogren, J.; Sheridan, P.; Streets, D. G.

    2002-10-01

    We measured carbonaceous material and water-soluble ionic species in the fine fraction (Dp < 1.3 μm) of aerosol samples collected on NCAR's C-130 aircraft during the intensive field phase (February-March 1999) of the Indian Ocean Experiment (INDOEX). Polluted layers were present over most of the study region north of the equator at altitudes up to 3.2 km. The estimated aerosol mass (sum of carbonaceous and soluble ionic aerosol components) of fine-mode particles in these layers was 15.3 ± 7.9 μg m-3. The major components were particulate organic matter (POM, 35%), SO42- (34%), black carbon (BC, 14%), and NH4+ (11%). The main difference between the composition of the marine boundary layer (MBL, 0 to ˜1.2 km), and the overlying residual continental boundary layer (1.2 to ˜3.2 km) was a higher abundance of SO42- relative to POM in the MBL, probably due to a faster conversion of SO2 into SO42- in the MBL. Our results show that carbon is a major, and sometimes dominant, contributor to the aerosol mass and that its contribution increases with altitude. Low variability was observed in the optical properties of the aerosol in the two layers. Regression analysis of the absorption coefficient at 565 nm on BC mass (BC < 4.0 μg C m-3) yielded a specific absorption cross section of 8.1 ± 0.7 m2 g-1 for the whole period. The unusually high fraction of BC and the good correlation between the absorption coefficient and BC suggest that BC was responsible for the strong light absorption observed for the polluted layers during INDOEX. High correlation between BC and total carbon (TC) (r2 = 0.86) suggest that TC is predominantly of primary origin. Good correlations were also found between the scattering coefficient at 550 nm and the estimated aerosol mass for the fine fraction. These yielded a specific scattering cross section of 4.9 ± 0.4 m2 g-1. The observed BC/TC, BC/OC, SO42-/BC, and K+/BC ratios were fairly constant throughout the period. These ratios suggest that between

  2. 2004 Indian Ocean tsunami flow velocity measurements from survivor videos

    NASA Astrophysics Data System (ADS)

    Fritz, Hermann M.; Borrero, Jose C.; Synolakis, Costas E.; Yoo, Jeseon

    2006-12-01

    The tsunami of 26th December 2004 severely affected Banda Aceh along the North tip of Sumatra (Indonesia) at a distance of 250 km from the epicenter of the magnitude 9.0 earthquake. This tsunami flow velocity analysis focused on two survivor videos recorded within Banda Aceh more than 3 km from the open ocean. The exact locations of the tsunami eyewitness video recordings were revisited by the survey team between February 22 and 25, 2005 to record camera calibration ground control points. The motion of the camera during the recordings was determined. The individual video images were rectified with a direct linear transformation (DLT) assuming a planar water surface at the level. Finally a cross-correlation based particle image velocimetry (PIV) analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields. The measured tsunami flow velocities were within the range of 2 to 5 m/s.

  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. Réunion (Indian Ocean) Oceanic Island Volcanism: Seismic Structure and Heterogeneity of the Upper Lithosphere

    NASA Astrophysics Data System (ADS)

    Hirn, A.

    2002-12-01

    Réunion island in the Indian Ocean is commonly considered as the recent and active expression of the hotspot that formed the Deccan traps, although both the hypothesis of recent small hotspots for both Reunion and Mauritius, or of relation with the plate heterogeneity have been proposed. Structural studies by seismic methods, from the scale of the upper cone of the active Fournaise volcano to that of the crust 100 km around, have been carried out. At this scale significant departures appear from the Hawaiian case to which it is traditionally compared, with the seismic signature of active volcanism showing differences too. Refraction-reflection seismics do not see a geometry of the top of the underlying plate towards the island, expected in plate flexure modelling by analogy with other hotspot island. Where it is sampled, doming is suggested instead. There appears to be less magmatic products than if there was a large amount buried in a flexural depression. The velocity structure resolved for the volcanic island, apart from high velocity cores under the volcanoes leads to smaller overall density than usually considered in flexure modelling. The same appears to hold for the material of the cone of about 120 km radius rising above the regional sea-bottom level to the 30 km radius island, from coincident reflection and refraction seismics on several lines radial to the southeastern half of the island. At the crust-mantle level, there is evidence from reflection-refraction line extending 150 km either side of the island for a layer of velocity intermediate between normal crust and mantle values. Two radial reflection line to the SSW, close to each other detect a differences in depth of the oceanic basement. This may coincide with a fracture zone suggested from the reconstruction of the sea-floor spreading history from the magnetic anomaly pattern. The latter has been interpreted previously to indicate that the western part of Réunion developed atop a Paleogene fossil

  5. Coupled atmosphere-ocean model simulations of El Nino/Southern Oscillation with and without an active Indian Ocean

    SciTech Connect

    Nagai, T.; Kitamura, Y.; Endoh, M.; Tokioka, T.

    1995-01-01

    An atmospheric general circulation model (GCM) was coupled with an ocean GCM covering the Pacific. This coupled model (PAC) was integrated over a 30-year period. The PAC model stimulates well the mean seasonally varying atmospheric and ocean fields and reproduces interannual variations corresponding to ENSO (El Nino/Southern Oscillation). The same atmospheric GCM was coupled with an ocean GCM covering the Indian Ocean and the tropical Pacific. This coupled model (IPC) was integrated over a 35-year period. The model climate in IPC is fairly reasonable, and its Pacific part is very similar to the Pacific climate of the PAC model. ENSO is the major interannual variability in the IPC model. The dynamics of ENSO in IPC are essentially the same as that in PAC. In the Pacific, the subsurface ocean heat content anomalies are formed by wind anomalies and show westward propagation centered off the equator. After they reach the western Pacific, they show eastward propagation along the equator. They produce changes in the thermocline structure in the eastern equatorial Pacific resulting in anomalies in SSTs. The SST anomalies provide wind anomalies, the sign of which is opposite to that of the wind anomalies in the first stage, so that this chain will continue. ENSO in the PAC and IPC models can be regarded as the {open_quotes}delayed oscillator{close_quotes} operating in the Pacific. Although the major interannual variability in the Indian Ocean is linked to ENSO in the Pacific, the Indian Ocean does not play any active role in the ENSO cycle in the IPC model. Interannual variability of monsoon activity in the IPC model is more reasonable than that in the PAC model. However, any definite mechanism for the relationship between monsoon activity and ENSO does not emerge in the present study. 31 refs., 14 figs.

  6. Biogeochemical variability in the central equatorial Indian Ocean during the monsoon transition

    NASA Astrophysics Data System (ADS)

    Strutton, P. G.; Coles, V. J.; Hood, R. R.; Matear, R. J.; McPhaden, M. J.; Phillips, H. E.

    2015-04-01

    In this paper we examine time-series measurements of near-surface chlorophyll concentration from a mooring that was deployed at 80.5°E on the equator in the Indian Ocean in 2010. These data reveal at least six striking spikes in chlorophyll from October through December, at approximately 2-week intervals, that coincide with the development of the fall Wyrtki jets during the transition between the summer and winter monsoons. Concurrent meteorological and in situ physical measurements from the mooring reveal that the chlorophyll pulses are associated with the intensification of eastward winds at the surface and eastward currents in the mixed layer. These observations are inconsistent with upwelling dynamics as they occur in the Atlantic and Pacific oceans, since eastward winds that force Wyrtki jet intensification should drive downwelling. The chlorophyll spikes could be explained by two alternative mechanisms: (1) turbulent entrainment of nutrients and/or chlorophyll from across the base of the mixed layer by wind stirring or Wyrtki jet-induced shear instability or (2) enhanced southward advection of high chlorophyll concentrations into the equatorial zone. The first mechanism is supported by the phasing and amplitude of the relationship between wind stress and chlorophyll, which suggests that the chlorophyll spikes are the result of turbulent entrainment driven by synoptic zonal wind events. The second mechanism is supported by the observation of eastward flows over the Chagos-Laccadive Ridge, generating high chlorophyll to the north of the equator. Occasional southward advection can then produce the chlorophyll spikes that are observed in the mooring record. Wind-forced biweekly mixed Rossby gravity waves are a ubiquitous feature of the ocean circulation in this region, and we examine the possibility that they may play a role in chlorophyll variability. Statistical analyses and results from the OFAM3 (Ocean Forecasting Australia Model, version 3) eddy

  7. Boreal spring Southern Hemisphere Annular Mode, Indian Ocean sea surface temperature, and East Asian summer monsoon

    NASA Astrophysics Data System (ADS)

    Nan, Sulan; Li, Jianping; Yuan, Xiaojun; Zhao, Ping

    2009-01-01

    The relationships among the boreal spring Southern Hemisphere Annular Mode (SAM), the Indian Ocean (IO) sea surface temperature (SST), and East Asian summer monsoon (EASM) are examined statistically in this paper. The variability of boreal spring SAM is closely related to the IO SST. When the SAM is in its strong positive phase in boreal spring, with low-pressure anomalies over the south pole and high-pressure anomalies over middle latitudes, SST over the subtropics and middle latitudes of the South Indian Ocean (SIO) increases, which persists into the summer. Following the positive SST anomalies over the subtropics and midlatitudes of the SIO, SST in the equatorial Indian Ocean and Bay of Bengal increases in summer. Moreover, the variability of SST in the equatorial Indian Ocean and Bay of Bengal is closely related to EASM. When SST in the equatorial Indian Ocean and Bay of Bengal increases, EASM tends to be weak. Therefore the IO SST may play an important role bridging boreal spring SAM and EASM. The atmospheric circulations and surface heat exchanges contribute to the SST anomalies in the SIO. When the spring SAM is in its strong positive phases, the regional Ferrel Cell weakens, and the anomalous upward motions at 20°S-30°S cause an increase of low cloud cover and downward longwave radiation flux. The surface atmospheric circulations also transport more (less) warmer (cooler) air from middle latitudes north of 50°S (high latitudes south of 60°S) into 50°S-60°S and warm the air, which reduces the temperature difference between the ocean and atmosphere and consequently reduces sensible heat flux from the ocean to atmosphere. The increased downward longwave radiation and decreased sensible heat are responsible for the SST increase in the SIO. The atmospheric circulation and surface heat flux anomalies are of opposite signs following the strong negative phases of SAM.

  8. Decadal Ocean Heat Content Westward Shift in the Indian Ocean during the Global Surface Warming and Hiatus

    NASA Astrophysics Data System (ADS)

    Wu, X.; Yan, X. H.; Li, Y.

    2015-12-01

    Understanding the ocean's role in Earth's energy budget is fundamental to evaluate climate variability and change, including the rate of global warming and the recent 18-years' so-called Global Surface Warming Hiatus (GSWH). Previous studies have shown that basin-wide warming in the Atlantic Ocean triggers the intensification of trade wind and wind-driven circulation since late 1990s, resulting in Global Surface Warming Hiatus (GSWH). A recent work revealed that missing heat in the Pacific during the GSWH was transported to the Indian Ocean by the Indonesia throughflow. It brings the Indian Ocean to the platform of the GSWH study and suggests that the global ocean is at play in the GSWH and in the ocean heat content (OHC) westwards shifting. The westwards shifting of the OHC was detected from in-situ data and model/in-situ reanalysis data. The shifting has a period of about 30 years, and takes about 60 years to travel from the eastern Pacific to the western Atlantic. Heat was distributed to deeper layers after the warm OHC passed the southern tip of the Africa continent. This may shed light on the understanding of the physical mechanisms for the multi-decadal climate variability.

  9. Serpentinization of Ocean Core Complex in the Central Indian Ridge: Reactions and Hydrogen Production

    NASA Astrophysics Data System (ADS)

    Omori, S.; Yoshizaki, M.; Shibuya, T.; Suzuki, K.; Yamamoto, S.; Morishita, T.; Kumagai, H.; Maruyama, S.

    2012-12-01

    The submarine hydrothermal system has been considered as a birthplace of life, and it is suggested that hydrothermal alteration of the ocean-floor rocks could influence metabolic system of the early life. The present submarine hydrothermal systems are possible analogs for the early ecosystem, and the serpentinite-hosted system is a candidate for the earliest one. In this study, we report a petrogenetic analysis of a serpentinite sampled from 25 ° S Ocean Core Complex (OCC) near the Rodriguez triple junction, based on textures and compositions of serpentine and other minerals. Phase diagrams for the serpentinite including redox and hydrogen-forming reactions are constructed to interpret the observations. Rodriguez triple junction 25 ° S OCC is located along the Indian Central Ridge (25.5 ° S, 70 ° E), near the Rodriguez triple junction that is formed by three ridges (the Southeast Indian Ridge, Central Indian Ridge, and Southwest Indian Ridge) and located where three plate boundaries (Africa Plate, Indo-Australian Plate, Antarctic Plate) meet. The studied samples are strongly serpentinized, however some relict minerals are preserved (~2%). The alteration minerals are mainly serpentine and magnetite. Most of the serpentine minerals were identified as chrysotile by laser Raman analyses. The relict minerals are orthopyroxene (opx), olivine, clinopyroxene, and spinel. Serpentine shows two types of texture; the one is bustite and the other is mesh texture. Magnetite is found in the mesh texture, and is not present in the bustite. The relict olivine and orthopyroxene were rarely preserved in the center of mesh texture and/or bustite. Size of spinel is 1-2mm, and color of the spinel is brownish-red. Brucite, which is a common product of the abyssal serpentinization, is not observed by optical, SEM, and FE-EPMA analyses. Serpentine minerals were classified into two groups by their chemical compositions; the one is the low-Mg#(90-94) type, which has comparable Mg# with

  10. 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

  11. Discovery of hantavirus circulating among Rattus rattus in French Mayotte island, Indian Ocean.

    PubMed

    Filippone, Claudia; Castel, Guillaume; Murri, Séverine; Beaulieux, Frédérik; Ermonval, Myriam; Jallet, Corinne; Wise, Emma L; Ellis, Richard J; Marston, Denise A; McElhinney, Lorraine M; Fooks, Anthony R; Desvars, Amélie; Halos, Lénaı G; Vourc'h, Gwenaël; Marianneau, Philippe; Tordo, Noël

    2016-05-01

    Hantaviruses are emerging zoonotic viruses that cause human diseases. In this study, sera from 642 mammals from La Réunion and Mayotte islands (Indian Ocean) were screened for the presence of hantaviruses by molecular analysis. None of the mammals from La Réunion island was positive, but hantavirus genomic RNA was discovered in 29/160 (18 %) Rattus rattus from Mayotte island. The nucleoprotein coding region was sequenced from the liver and spleen of all positive individuals allowing epidemiological and intra-strain variability analyses. Phylogenetic analysis based on complete coding genomic sequences showed that this Murinae-associated hantavirus is a new variant of Thailand virus. Further studies are needed to investigate hantaviruses in rodent hosts and in Haemorrhagic Fever with Renal Syndrome (HFRS) human cases. PMID:26932442

  12. Semiannual NO2 plumes during the monsoon transition periods over the central Indian Ocean

    NASA Astrophysics Data System (ADS)

    Kunhikrishnan, T.; Lawrence, Mark G.; von Kuhlmann, Rolf; Richter, Andreas; Ladstätter-Weißenmayer, Annette; Burrows, John P.

    2004-04-01

    In this study we identify recurring plumes of tropospheric NO2 originating from Africa and Indonesia during the monsoon transition periods over the central Indian Ocean (CIO, 5°N-30°S, 55°E-95°E), based on GOME satellite observations and global model (MATCH-MPIC) simulations. Despite the relatively short lifetime of NOx, these strong plumes can develop due to the pronounced anti-cyclonic circulation over the CIO, and the weak maritime convection, which limits vertical mixing. Model results indicate that the plumes are mainly transported in the middle troposphere (MT). Thus, the CIO in the Southern Hemisphere (SH) is not always as pristine as found in INDOEX during the winter monsoon.

  13. 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.

  14. Cretaceous evolution of the Indian Plate and consequences for the formation, deformation and obduction of adjacent oceanic crust

    NASA Astrophysics Data System (ADS)

    Gaina, C.; Van Hinsbergen, D. J.; Spakman, W.

    2012-12-01

    As part of the gradual Gondwana dispersion that started in the Jurassic, the Indian tectonic block was rifted away from the Antarctica-Australian margins, probably in the Early-Mid Cretaceous and started its long journey to the north until it collided with Eurasia in the Tertiary. In this contribution first we will revise geophysical and geological evidences for the formation of oceanic crust between India and Antarctica, India and Madagascar, and India and Somali/Arabian margins. This information and possible oceanic basin age interpretation are placed into regional kinematic models. Three important compressional events NW and W of the Indian plate are the result of the opening of the Enderby Basin from 132 to 124 Ma, the first phase of seafloor spreading in the Mascarene basin approximately from 84 to 80 Ma, and the incipient opening of the Arabian Sea and the Seychelles microplate formation around 65 to 60 Ma. Based on retrodeformation of the Afghan-Pakistan part of the India-Asia collision zone and the eastern Oman margin, the ages of regional ophiolite emplacement and crystallization of its oceanic crust, as well as the plate tectonic setting of these ophiolites inferred from its geochemistry, we evaluate possible scenarios for the formation of intra-oceanic subduction zones and their evolution until ophiolite emplacement time. Our kinematic scenarios are constructed for several regional models and are discussed in the light of global tomographic models that may image some of the subducted Cretaceous oceanic lithosphere.

  15. 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.

  16. 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.

  17. Redescription of the percoid fish Symphysanodon andersoni Kotthaus (Symphysanodontidae) from the northwestern Indian Ocean, based on the holotype and the second known specimen.

    PubMed

    Anderson, William D; Chesalin, Mikhail V; Jawad, Laith A; Al Shajibi, Said R

    2015-01-01

    Symphysanodon andersoni was described in 1974 from a single specimen collected southwest of Socotra Island, near the entrance to the Gulf of Aden. A more recent report (2003) of its capture in the Gulf of Kutch, Arabian Sea, was based on a misidentification. The second known specimen of the Bucktoothed Slopefish, S. andersoni, (at 204 mm SL the largest known specimen of the genus Symphysanodon) was collected off the south coast of Oman, Arabian Sea, in April 2014. Symphysanodon andersoni is distinguishable from its congeners by number of tubed scales in the lateral line, 60 to 65 versus 42 to 59 in the other species of the genus. In view of the fact that S. andersoni is poorly known, we redescribe it based on the holotype and the new specimen collected off Oman and provide the first color photograph of the species. PMID:26624144

  18. Redescription of the percoid fish Symphysanodon andersoni Kotthaus (Symphysanodontidae) from the northwestern Indian Ocean, based on the holotype and the second known specimen.

    PubMed

    Anderson, William D; Chesalin, Mikhail V; Jawad, Laith A; Al Shajibi, Said R

    2015-01-01

    Symphysanodon andersoni was described in 1974 from a single specimen collected southwest of Socotra Island, near the entrance to the Gulf of Aden. A more recent report (2003) of its capture in the Gulf of Kutch, Arabian Sea, was based on a misidentification. The second known specimen of the Bucktoothed Slopefish, S. andersoni, (at 204 mm SL the largest known specimen of the genus Symphysanodon) was collected off the south coast of Oman, Arabian Sea, in April 2014. Symphysanodon andersoni is distinguishable from its congeners by number of tubed scales in the lateral line, 60 to 65 versus 42 to 59 in the other species of the genus. In view of the fact that S. andersoni is poorly known, we redescribe it based on the holotype and the new specimen collected off Oman and provide the first color photograph of the species.

  19. Evaluation of three harvest control rules for Bigeye Tuna ( Thunnus obesus) fisheries in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Tong, Yuhe; Chen, Xinjun; Kolody, Dale

    2014-10-01

    The stock of Bigeye tuna ( Thunnus obesus) in the Indian Ocean supports an important international fishery and is considered to be fully exploited. The responsible management agency, the Indian Ocean Tuna Commission (IOTC), does not have an explicit management decision-making framework in place to prevent over-fishing. In this study, we evaluated three harvest control rules, i) constant fishing mortality (CF), from 0.2 to 0.6, ii) constant catch (CC), from 60000 to 140000 t, and iii) constant escapement (CE), from 0.3 to 0.7. The population dynamics simulated by the operating model was based on the most recent stock assessment using Stock Synthesis version III (SS3). Three simulation scenarios (low, medium and high productivity) were designed to cover possible uncertainty in the stock assessment and biological parameters. Performances of three harvest control rules were compared on the basis of three management objectives (over 3, 10 and 25 years): i) the probability of maintaining spawning stock biomass above a level that can sustain maximum sustainable yield (MSY) on average, ii) the probability of achieving average catches between 0.8 MSY and 1.0 MSY, and iii) inter-annual variability in catches. The constant escapement strategy ( CE=0.5), constant fishing mortality strategy ( F=0.4) and constant catch ( CC=80000) were the most rational among the respective management scenarios. It is concluded that the short-term annual catch is suggested at 80000 t, and the potential total allowable catch for a stable yield could be set at 120000 t once the stock had recovered successfully. All the strategies considered in this study to achieve a `tolerable' balance between resource conservation and utilization have been based around the management objectives of the IOTC.

  20. Mean Sea Level Derived from Altimetry and Wind-Driven Numerical Models in the Indian Ocean

    NASA Technical Reports Server (NTRS)

    Perigaud, C.; Delecluse, P.; Greiner, E.; Rogel, P.

    1995-01-01

    Wind-driven model skill in simulating sea level variations in the Indian Ocean depends on our knowledge of the mean ocean dynamic topography. This is demonstrated by running the nonlinear or linear version of a shallow-water model driven by observed winds over Geosat and TOPEX periods. Geosat variations are assimilated in the nonlinear shallow-water model with the objective of obtaining topography data.

  1. Challenges for present and future estimates of anthropogenic carbon in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Goyet, C.; Touratier, F.

    One of the main challenges we face today is to determine the evolution of the penetration of anthropogenic CO2 into the Indian Ocean and its impacts on marine and human life. Anthropogenic CO2 reaches the ocean via air-sea interactions as well as riverine inputs. It is then stored in the ocean and follows the oceanic circulation. As the carbon dioxide from the atmosphere penetrates into the sea, it reacts with water and acidifies the ocean. Consequently, the whole marine ecosystem is perturbed, thus potentially affecting the food web, which has, in turn, a direct impact on seafood supply for humans. Naturally, this will mainly affect the growing number of people living in coastal areas. Although anthropogenic CO2 in the ocean is identical with natural CO2 and therefore cannot be detected alone, many approaches are available today to estimate it. Since most of the results of these methods are globally in agreement, here we chose one of these methods, the tracer using oxygen, total inorganic carbon, and total alkalinity (TrOCA) approach, to compute the 3-D distribution of the anthropogenic CO2 concentrations throughout the Indian Ocean. The results of this distribution clearly illustrate the contrast between the Arabian Sea and the Bay of Bengal. They further show the importance of the southern part of this ocean that carries some anthropogenic CO2 at great depths. In order to determine the future anthropogenic impacts on the Indian Ocean, it is urgent and necessary to understand the present state. As the seawater temperature increases, how and how fast will the ocean circulation change? What will the impacts on seawater properties be? Many people are living on the bordering coasts, how will they be affected?

  2. 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).

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Mohapatra, M.; Vijay Kumar, V.

    2016-05-01

    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.

  5. 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. PMID:26555626

  6. 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…

  7. 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.

  8. Underdiagnosis of chikungunya virus infections in symptomatic dutch travelers returning from the Indian ocean area.

    PubMed

    Reusken, Chantal B E M; Bakker, Jacinta; Reimerink, Johan H J; Zelena, Hana; Koopmans, Marion G P

    2013-01-01

    A putative underdiagnosis of clinical chikungunya virus infection in Dutch travelers to the Indian Ocean area was addressed by retrospective screening of all sera for which requested dengue virus serology was negative in the period 2007 to 2010. Evidence for a recent infection was observed in 6.5% of 107 patients, indicating a substantial underdiagnosis and the need for increased awareness among physicians.

  9. 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.

  10. 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.

  11. 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. PMID:27068838

  12. 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.

  13. 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.

  14. Investigation of Microbial Communities in Deep-sea Polymetallic Nodules from the Pacific Ocean and Indian Ocean

    NASA Astrophysics Data System (ADS)

    Luo, X.; Zhou, P.; Wu, Y. H.; Yang, J. Y.; Wang, C. S.; Xu, X. W.

    2015-12-01

    Deep-sea polymetallic nodules are valuable for their high abundance of metals, such as manganese, nickel, cobalt and copper. Microorganisms were known involved in the formation of nodules. Yet it is poorly understood what kinds of microorganisms are involved in the geochemical formation of nodules. To better understand the relationships between metals and microbial communities in deep-sea polymetallic nodules and surrounding sediments, we investigated samples of 20 deep-sea polymetallic nodules and 9 surrounding sediments from the Pacific Ocean and Indian Ocean. The results of metal composition showed that manganese, cobalt, copper, and nickel are much more abundant in the nodules than those in the surrounding sediments. Some metals have significant high correlation, such as 0.96 (p-value<0.001) between copper and nickel. Relative abundance of taxa in the microbial communities was investigated by using culture-independent high-throughput sequencing, followed by classification and statistic analysis. Principal component analysis showed the microbial communities in the nodules are significantly different from those in surrounding sediments. Correlation-based network analysis was performed, which helped us obtain a comprehensive understanding of relationships between metals and microorganisms. The order Rhizobiales, to which some Mn(II)-oxidizing microorganisms belong, shows high correlation (r>0.6, p-value<0.001) with manganese, nickel and copper. The order Solirubrobacterales shows high correlation (r>0.6, p-value<0.001) with manganese and cobalt. The results suggest that the microorganisms belonging to these two orders may play important roles in the geochemical formation of nodules. This study shed light on further studies concerning the formation of the deep-sea polymetallic nodules and isolation of the uncultured microorganisms involved in this geochemical process.

  15. Sensitivity of NOx over the Indian Ocean to emissions from the surrounding continents and nonlinearities in atmospheric chemistry responses

    NASA Astrophysics Data System (ADS)

    Kunhikrishnan, T.; Lawrence, M. G.

    2004-08-01

    The sensitivity of the Indian Ocean atmospheric chemistry to continental NOx emissions is examined using a global chemistry-transport model (MATCH-MPIC). NOx responds nonlinearly to changes in emissions, since O3 and OH, which depend on NOx, influence its lifetime. Due to this feedback and the contribution from other NOx sources (e.g., lightning), much of the Indian Ocean lower troposphere (LT) is only weakly sensitive to continental NOx emissions. In contrast to INDOEX (Indian Ocean Experiment) results for aerosols, CO, etc., during the winter monsoon the central Indian Ocean (CIO) is weakly sensitivity to Indian NOx emissions. However, the Bay of Bengal LT is very sensitive to NOx emissions from India (summer) and SE Asia and China (winter). Higher up, NOx over the CIO is most sensitive to African and SE Asian emissions, while the northern regions are influenced by the summer monsoon plume from India, SE Asia and China.

  16. The role of Equatorial Undercurrent in sustaining the Eastern Indian Ocean upwelling

    NASA Astrophysics Data System (ADS)

    Chen, Gengxin; Han, Weiqing; Shu, Yeqiang; Li, Yuanlong; Wang, Dongxiao; Xie, Qiang

    2016-06-01

    By combining volume transport and salinity analysis from 1958 to 2014, this paper investigates how the transient Equatorial Undercurrent (EUC) sustains the summer-fall equatorial eastern Indian Ocean (EIO) upwelling. On seasonal time scales, the EIO upwelling is mainly supplied by the salty water from the western basin through a buffering process: The winter-spring EUC carries the salty water from the western basin eastward, induces downwelling in the EIO, and pushes portion of the salty water below the central thermocline, which subsequently upwells to the central thermocline during summer-fall and sustains the EIO upwelling. On interannual time scales, enhanced upwelling occurs during positive Indian Ocean Dipole (+IOD) years. The strong summer-fall EUC associated with the +IOD supplies water for the intensified upwelling. This research provides new knowledge for basin-scale mass and property exchanges associated with the EIO upwelling, contributing to our understanding of three-dimensional ocean circulation and climate variability.

  17. 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.

  18. The shallow meridional overturning circulation in the northern Indian Ocean and its interannual variability

    NASA Astrophysics Data System (ADS)

    Hu, Ruijin; Liu, Qinyu; Wang, Qi; Godfrey, J. Stuart; Meng, Xiangfeng

    2005-03-01

    The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years (1987 1996). It is shown that the shallow meridional overturning circulation has a prominent seasonal reversal characteristic. In winter, the flow is northward in the upper layer and returns southward at great depth. In summer, the deep northward inflow upwells north of the equator and returns southward in the Ekman layer. In the annual mean, the northward inflow returns through two branches: one is a southward flow in the Ekman layer, the other is a flow that sinks near 10°N and returns southward between 500 m and 1000 m. There is significant interannual variability in the shallow meridional overturning circulation, with a stronger (weaker) one in 1989 (1991) and with a period of about four years. The interannual variability of the shallow meridional overturning circulation is intimately related to that of the surface wind stress. Several indices are proposed to describe the anomaly of this circulation associated with the cross-equatorial part.

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

    PubMed Central

    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. PMID:25977785

  20. 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. PMID:25977785

  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. PMID:27407295

  2. 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.

  3. 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.

  4. Biogeochemical variability in the equatorial Indian Ocean during the monsoon transition

    NASA Astrophysics Data System (ADS)

    Strutton, P. G.; Coles, V. J.; Hood, R. R.; Matear, R. J.; McPhaden, M. J.; Phillips, H. E.

    2014-04-01

    In this paper we examine time-series measurements of near-surface chlorophyll concentration from a mooring that was deployed at 80.5° E on the equator in the Indian Ocean in 2010. These data reveal at least six striking spikes in chlorophyll in October through December, with approximately 2 week periodicity, that coincide with the development of the fall Wyrtki jets during the transition between the summer and winter monsoons. Concurrent meteorological and in situ physical measurements from the mooring reveal that the chlorophyll pulses are associated with intensification of eastward winds at the surface and eastward currents in the mixed layer. These observations are inconsistent with upwelling dynamics as occurs in the Atlantic and Pacific Oceans, since eastward winds that force Wyrtki jet intensification should drive downwelling. The chlorophyll spikes could be explained by two alternative mechanisms: (1) turbulent entrainment of nutrients and/or chlorophyll from across the base of the mixed layer by wind stirring or Wyrtki jet-induced shear instability; or (2) enhanced horizontal advection of high chlorophyll concentrations into the convergent equatorial zone. The first mechanism is supported by the phasing and amplitude of the relationship between wind stress and chlorophyll, which suggests that the chlorophyll spikes are the result of turbulent entrainment driven by synoptic zonal wind events. The second mechanism is supported by satellite chlorophyll observations that reveal a clear connection between the increased chlorophyll concentrations at the mooring location and larger-scale topographic wake effects from the Chagos-Lacadive Ridge upstream. The biweekly periodicity of the chlorophyll spikes appears to be related to the presence of mixed Rossby-gravity waves, also known as Yanai waves, which can be seen throughout the time-series as a biweekly periodicity in the meridional velocities with upward phase propagation. Consistent with hypothesis 2, eastward

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

    DOE PAGES

    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)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

  6. 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

  7. Miocene Indian Ocean Circulation: A High-Resolution Multivariate Analysis of Interbasinal Records

    NASA Astrophysics Data System (ADS)

    Irving, D. H.; Smart, C.; Ramsay, A. T.; Thomas, E.

    2006-12-01

    Ocean circulation in the Indian Ocean during the Miocene progresses through three configurations in response to changes in plate movement and global climate. Principal Component Analysis (PCA) was carried out on benthic foraminifera, stable isotope and sedimentological data sampled at 100 kyr intervals from cores recovered from ODP sites 237, 707, 709 and 710 in the Somali Basin (SOB) and sites 214, 216 and 238 in the Mid-Indian Basin (MIB). These analyses provide insight into the structure and dynamics of the Indian Ocean through most of the Miocene (25--6 Ma) and suggest forcing mechanisms of the circulation system in this and adjacent ocean basins. Bulk responses of infaunal and epifaunal species mask local and regional oceanic signals that this study extracts by analysis at the species level. Isotopic ratios are used to describe the depth structure of the two basins. Coupled with sedimentological data, the dynamics of the basins is described in terms of the major events of the Miocene, namely Tethyan closure, the growth of the West Antarctic Ice Sheet (WAIS) and the initiation of the monsoon. PCA of the time series data show three separate components which correlate with these three phases in the history of the Indian Ocean. These are: i) 25-18 Ma, a stratified SOB with warm dense Tethyan outflow waters (TOW) underlying cooler, less dense water that is weakly coupled across the Chagos- Laccadive Ridge (CLR) with an unstratified MIB; ii) 18-12 Ma, mixing in the SOB as TOW diminishes due to seaway closure, and increasing cool bottom waters which penetrate further north with time, accompanied by stratification of the MIB and stronger coupling of surface waters promoting nutrient transfer eastwards; iii) 12-6 Ma, overturn and upwelling in the SOB with occasional strong fluxes of cooler WAIS bottom water and strong stratification in the MIB, with a westerly flux of warm water overtopping a more greatly subsided CLR.

  8. 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.

  9. 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.

    2015-02-01

    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 in February and 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. 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. 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. Compared to the Indian Ocean Experiment (INDOEX) conducted in winter 1999, elevated aerosol layers with increased aerosol number concentration were observed more frequently in 2012. However, lower particle absorption at the surface (σabs(520 nm)=8.5±4.2 Wm-1) was found during CARDEX compared to INDOEX 1999. By combining vertical in-situ measured particle absorption with scattering calculated with Mie-theory, layers with single-scattering albedo (SSA) values of specific source regions were derived and utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for dry conditions were found to be 0.94±0.02 and 0.91±0.02 for air masses from the Arabian Sea (and

  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. Climate model biases in the Indian Ocean meant state, variability and change

    NASA Astrophysics Data System (ADS)

    Xie, S. P.; Li, G.

    2015-12-01

    Long-standing biases of climate models limit the skills of climate prediction and projection. The monsoonal tropical Indian Ocean (IO) has been overlooked in bias studies because model errors compensate among seasons and do not manifest prominently in the annual means. In the phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel ensemble, we have identified a common error pattern in climate models that resembles the IO dipole (IOD) mode of interannual variability in nature, with an excessive equatorial easterly wind bias during boreal autumn accompanied by physically consistent biases in precipitation, sea surface temperature (SST), and subsurface ocean temperature. The analyses show that such IOD-like biases can be traced back to errors in the South Asian summer monsoon. A southwest summer monsoon that is too weak over the Arabian Sea generates a warm SST bias over the western equatorial IO. In boreal autumn, Bjerknes feedback helps amplify the error into an IOD-like bias pattern in wind, precipitation, SST, and subsurface ocean temperature. Such mean state biases result in an interannual IOD variability that is too strong. Most models project an IOD-like future change for the boreal autumn mean state in the global warming scenario, which would result in more frequent occurrences of extreme positive IOD events in the future with important consequences to Indonesia and East Africa. The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) characterizes this future IOD-like projection in the mean state as robust based on consistency among models, but the authors' results cast doubts on this conclusion since models with larger IOD amplitude biases tend to produce stronger IOD-like projected changes in the future.

  12. 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

  13. 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

  14. 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

  15. 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.

  16. Future projections of Indian Ocean SSTs and its impact on monsoon

    NASA Astrophysics Data System (ADS)

    Thelliyil Sabeerali, Cherumadanakadan; Ravindran, Ajayamohan

    2016-04-01

    Assessing the future projections of the Indian Ocean (IO) Sea Surface Temperatures (SSTs) under the global warming scenario has a paramount societal impact considering its potential to alter the seasonal mean rainfall over the Indian subcontinent. Observations show a pronounced warming in the western tropical IO compared to other ocean basins. Here, we explore the projections of boreal summer SSTs over the IO using the Representative Concentration Pathways 8.5 (RCP8.5) scenarios of Coupled Model Intercomparison Project Phase5 (CMIP5) simulations. Consistent with observations, most of the CMIP5 models show a faster warming rate over the western tropical IO compared to other ocean basins. Model simulations indicate a shift in the mean Walker circulation with an anomalous ascending motion over the central equatorial Pacific and an anomalous descending motion over the eastern tropical IO. As a consequence of this, a negative SST skewness is evident in the eastern tropical IO which leads to the increased frequency of positive Indian Ocean Dipole (IOD) events. Mechanisms responsible for this pronounced western IO warming is studied by analyzing the changes in the mean thermocline depth and circulation features. The impact of these changes in IO SST on seasonal mean monsoon precipitation and circulation in a warming scenario and its associated mechanisms are also investigated.

  17. Equatorial variability and resonance in a wind-driven Indian Ocean model

    SciTech Connect

    Jensen, T.G.

    1993-12-15

    A numerical isopycnal ocean model has been designed and applied to model the Indian Ocean north of 25{degrees}S. Vertical normal modes are used in the open boundary conditions and for selections of initial layer depths. A 21-year integration with a reduced Hellerman-Rosenstein monthly averaged wind stress has been made with 3.5-layer and 1.5-layer versions of the model. Both solutions reproduce the main features of the observed wind-driven seasonal circulation in the Indian Ocean above the main thermocline. The transient semiannual equatorial surface jets are more intense, more coherent, and in better phase agreement with observations when three layers are active. The associated undercurrents below the main thermocline are also included in the 3.5-layer model solution. Second baroclinic-mode, reflecting, equatorial Kelvin and Rossby waves combine to give a semiannual, resonant basin mode. Experiments with an equatorial band of semiannual zonal winds suggest a very strong response of the Indian Ocean to wind forcing with this period. Further, the amplitudes of the 28-30 day oscillations in the western equatorial model region are found to be strongly damped with depth; they have upward phase propagation and downward energy propagation. 43 refs., 22 figs., 2 tabs.

  18. Chemical characterization of aerosols in the equatorial atmosphere over the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Balasubramanian, Rajasekhar; Karthikeyan, Sathrugnan; Potter, John; Wurl, Oliver; Durville, Caroline

    2013-10-01

    The region of the Indian Ocean and adjacent countries has received increased attention in recent years in the context of particulate air pollution. Aerosol samples were collected over the equatorial Indian Ocean during a one-year-long sailing cruise that covered the northeast and southwest monsoons, and an inter-monsoon period. The concentrations of airborne particulate matter (PM), selected metals and water-soluble ions were measured. In general, the PM concentrations were influenced by the proximity of sampling locations to land and air mass origins. The enrichment of metals in PM relative to those in the crustal material was very high (up to 40,000). The metal concentrations were significantly higher in PM samples which were influenced by volcanic emissions from the land masses of Indonesia. Volcanic plumes were traced using backward air mass trajectory and chemical tracers, and identified as a major particulate pollution source to the otherwise pristine air of the southern hemisphere of the Indian Ocean. NO3-, NH4+ and SO42- were low in aerosols collected over the open ocean, but a linear relationship between NH4+ and SO42- indicates their importance in the formation of cloud condensation nuclei.

  19. 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

  20. 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.

  1. 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.

  2. Oceanic factors controlling the Indian summer monsoon onset in a coupled model

    NASA Astrophysics Data System (ADS)

    Prodhomme, Chloé; Terray, Pascal; Masson, Sébastien; Boschat, Ghyslaine; Izumo, Takeshi

    2015-02-01

    Despite huge socio-economical impacts, the predictability of the Indian summer monsoon (ISM) onset remains drastically limited by the inability of both current forced and coupled models to reproduce a realistic monsoon seasonal cycle. In the SINTEX-F2 coupled model, the mean ISM onset estimated with rainfall or thermo-dynamical indices is delayed by approximately 13 days, but it occurs 6 days early in the atmosphere-only component of the coupled model. This 19 days lag between atmospheric-only and coupled runs, which is well above the observed standard-deviation of the ISM onset (10 days in the observations), suggests a crucial role of the coupling, including Sea Surface Temperatures (SST) biases, on the delayed mean onset in the coupled model. On the other hand, the key-factors governing the interannual variability of the ISM onset date are also fundamentally different in the atmospheric and coupled experiments and highlight the importance of El Niño-Southern Oscillation (ENSO) and ocean-atmosphere coupling for a realistic simulation of the variability of the ISM onset date. At both interannual and seasonal timescales, we demonstrate the importance of the meridional gradients of tropospheric temperature, moisture and vertical shear of zonal wind in the Indian Ocean for a realistic ISM onset simulation. Taking into account that the tropical tropospheric temperature and the vertical shear are not only controlled by local processes, but also by large-scale processes, we need to examine not only the Indian Ocean SST biases, but also those in others tropical basins in order to understand the delay of the mean onset date in the coupled model. During April and May, the main tropical SST biases in the coupled model are a strong warm bias in the Indian, Pacific and Atlantic Oceans, associated with an important excess of equatorial precipitations, and thus a warmer equatorial free troposphere. In order to identify the keys tropical SST regions influencing the mean ISM

  3. 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.

  4. 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

  5. The ocean-atmosphere response to wind-induced thermocline changes in the tropical South Western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Manola, Iris; Selten, F. M.; de Ruijter, W. P. M.; Hazeleger, W.

    2015-08-01

    In the Indian Ocean basin the sea surface temperatures (SSTs) are most sensitive to changes in the oceanic depth of the thermocline in the region of the Seychelles Dome. Observational studies have suggested that the strong SST variations in this region influence the atmospheric evolution around the basin, while its impact could extend far into the Pacific and the extra-tropics. Here we study the adjustments of the coupled atmosphere-ocean system to a winter shallow doming event using dedicated ensemble simulations with the state-of-the-art EC-Earth climate model. The doming creates an equatorial Kelvin wave and a pair of westward moving Rossby waves, leading to higher SST 1-2 months later in the Western equatorial Indian Ocean. Atmospheric convection is strengthened and the Walker circulation responds with reduced convection over Indonesia and cooling of the SST in that region. The Pacific warm pool convection shifts eastward and an oceanic Kelvin wave is triggered at thermocline depth. The wave leads to an SST warming in the East Equatorial Pacific 5-6 months after the initiation of the Seychelles Dome event. The atmosphere responds to this warming with weak anomalous atmospheric convection. The changes in the upper tropospheric divergence in this sequence of events create large-scale Rossby waves that propagate away from the tropics along the atmospheric waveguides. We suggest to repeat these types of experiments with other models to test the robustness of the results. We also suggest to create the doming event in June so that the East-Pacific warming occurs in November when the atmosphere is most sensitive to SST anomalies and El Niño could possibly be triggered by the doming event under suitable conditions.

  6. Endangered medicinal species of the Indian Ocean: radical need for conservation.

    PubMed

    Pandey, Pt Kartikay

    2009-07-01

    Life originated in the Oceans, which are also the most fertile source of chemically distinctive natural products that are mainly accumulated in living organisms. Several of these compounds show pharmacological activities, and are helpful for the invention and discovery of bioactive compounds, primarily for several fatal diseases. The Indian Ocean is home to several exotic species of flora and fauna. Several environmental and man-made factors are responsible for deterioration of several precious biodiversity areas of the Ocean. The author, while highlighting the medicinal importance of these organisms, underlines the need for comprehensive conservatory measures on the part of the international community to be taken in order to maintain the rich Oceanic biodiversity.

  7. 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

  8. 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

  9. 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

  10. 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

  11. A new species of Munidopsis from a seamount of the Southwest Indian Ocean Ridge (Decapoda: Munidopsidae).

    PubMed

    Macpherson, Enrique; Amon, Diva; Clark, Paul F

    2014-01-07

    Wood and whale bone colonisation experiments were undertaken on the Southwest Indian Ocean Ridge, 18 November 2009. Later, 14 December 2011, squat lobsters were recovered from the submerged wood and assigned to Munidopsis sp. Further study indicated that the specimens belonged to the group of species having a rostrum without lateral spines, presence of two strong epigastric spines, unarmed abdominal segments, one dorsal eye-spine, and with the second pereiopod not reaching the end of the first. They were similar to M. hemingi Alcock & Anderson, 1899 but differed in that the epigastric spines are well developed (vs. tubercles in M. hemingi), the lateral margins of the carapace are straight (vs. more convex in M. hemingi), the eye has a tubercular process mediodorsally (vs. a papilliform spinule at mesial angle) and the epipods on the fourth pereiopod were absent (vs. present in M. hemingi). Consequently the Munidopsis specimens from the Southwest Indian Ocean Ridge were considered to be an undescribed species.

  12. 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.

  13. The influence of Indian Ocean atmospheric circulation on Warm Pool hydroclimate during the Holocene epoch

    NASA Astrophysics Data System (ADS)

    Tierney, J. E.; Oppo, D. W.; Legrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.

    2012-10-01

    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 preëminence 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.

  14. 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.

  15. 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.

  16. 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.

  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. Chikungunya Fever in Travelers Returning to Europe from the Indian Ocean Region, 2006

    PubMed Central

    Panning, Marcus; Grywna, Klaus; van Esbroeck, Marjan; Emmerich, Petra

    2008-01-01

    Chikungunya fever has spread through several Indian Ocean islands and India, including popular travel destinations. To compare usefulness of diagnostic tests and to understand reasons for the magnitude and severity of an outbreak, we used 3 diagnostic methods to test 720 samples from 680 patients returning to Europe from the Indian Ocean region in 2006. Chikungunya infection was confirmed for 24.4% patients in the first half of the year and for 9.9% in the second half. Reverse transcription–PCR was positive for all samples taken up to day 4 after symptom onset. Immunofluorescence detected immunoglobulin (Ig) M on day 1 and IgG on day 2 for some patients, and in all patients from day 5 onward. Soon after onset of symptoms, patients had IgG and IgM and high viral loads (some >109 copies/mL plasma). These data will help healthcare providers select diagnostic tests for returning travelers. PMID:18325256

  19. 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.

  20. 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

  1. 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.

  2. Hydrological and chlorofluoromethane measurements of the Indonesian throughflow entering the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Fieux, M.; Andrié, C.; Charriaud, E.; Ilahude, A. G.; Metzl, N.; Molcard, R.; Swallow, J. C.

    1996-05-01

    The Java Australia Dynamic Experiment high-resolution February-March 1992 conductivity-temperature-depth and chlorofluoromethane section obtained between Australia and Bali and on the sills between Flores, Sumba, Sawu, Roti, and the Australian continental shelf allows detailed examination of the water masses distribution and their inferred circulation. A sharp hydrological front between the Indonesian waters and the southern Indian Ocean waters is found between 13°S and 14°S in both seasons (February-March 1992 and August 1989). It separates the high-salinity surface waters to the south from the lower-salinity surface waters derived from the Indonesian Seas to the north. It reaches the surface in February 1992, whereas it was capped by a particularly low salinity surface layer in August 1989. Near Bali, the NW monsoon of February-March produces large intrusions of low-salinity water from the Java Sea, through Lombok Strait in the upper 100 m. At depth, the North Indian Intermediate Water, flowing along the Indonesian coast, brings salty, low-oxygen and low-chlorofluorocarbon water. It enters the Sawu Sea through Sumba Strait toward the east, while it undergoes strong mixing with the Indonesian Seas water. The primary pathway of the Indonesian waters is found north of the front and south of the North Indian Intermediate Water, between 13°S and 9°30'S, and the associated salinity minimum can be followed all across the Indian Ocean.

  3. 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

  4. Remote sensing of precipitation over Indian land and oceanic regions by synergistic use of multisatellite sensors

    NASA Astrophysics Data System (ADS)

    Mishra, Anoop; Gairola, R. M.; Varma, A. K.; Agarwal, Vijay K.

    2010-04-01

    In the present study, an attempt was made to estimate rainfall by synergistically analyzing collocated thermal infrared (TIR) brightness temperatures from Meteosat along with rainfall estimates from active microwave precipitation radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) over Indian land and oceanic regions. In this study, we used broad and frequent TIR measurements from a geostationary satellite for rainfall estimation, calibrating them with sparse but more accurate PR rain rates. To make the algorithm robust, we used a two-step procedure. First, a cloud classification scheme was applied to TIR measurements using the 6.7 μm water vapor channel and TIR radiances to delineate the rain-bearing clouds. Next, the concurrent TIR and PR observations were used to establish a regression relation between them. The relationship thus established was used to estimate rainfall from TIR measurements by applying it to rain-producing systems during southwest and northeast monsoons and tropical cyclones. Comparisons were made with TRMM-merged (3B42 V6) data, Global Precipitation Climatology Project (GPCP) monthly rain rate data, ground-based rain gauge observations from automatic weather stations, and Doppler weather radar over India. The results from combined infrared and microwave sensors were in very good agreement with the ground-based measurements, TRMM-3B42 V6, as well as GPCP.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Maculabatis ambigua sp. nov., a new whipray (Myliobatiformes: Dasyatidae) from the Western Indian Ocean.

    PubMed

    Last, Peter R; Bogorodsky, Sergey V; Alpermann, Tilman J

    2016-01-01

    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. PMID:27615825

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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. PMID:20547419

  17. Modulation of East African Precipitation by the Indian Ocean Dipole (IOD) and ENSO

    NASA Astrophysics Data System (ADS)

    Shaaban, Ahmed A.

    Tropical East Africa is influenced by two main rainy seasons, during autumn and spring. During autumn, tropical East African precipitation is clearly influenced by Indian Ocean Dipole (IOD) and/or ENSO. During spring, there is no clear SST pattern in the Indian Ocean. The association between El Nino and positive IOD phases is much stronger than the association between La Nina and negative IOD during October and November. During October, the association between El Nino and wet condition over tropical eastern Africa is stronger than association between La Nina and dry conditions. During November, the association between positive IOD and eastern African precipitation is stronger than the association between La Nina and dry conditions. During short wet phases (such as autumn) over eastern Africa, two anticyclones form in the lower troposphere with upper baroclinic structure. These anticyclones decay rapidly by December. These anticyclones are responsible for supplying East Africa with increased moisture. Most strong positive IOD events are associated with wet outcomes over eastern Africa. Not all strong El Nino events lead to wet outcomes. It is well known that during northern spring, precipitation over eastern Africa is not connected to any inter-annual SST modes of variability. During northern spring, SST in Indian Ocean is nearly always sufficiently high to sustain convection, however, convection is not always active. We found that precipitation over eastern Africa during spring is associated with a dipole pattern of outgoing longwave radiation anomaly (OLRA) not associated with SST variability.

  18. Assessment Of Sea Surface Salinity Obtain From SMOS And Aquarius Satellites Over Indian Ocean

    NASA Astrophysics Data System (ADS)

    Calla, O. P. N.; Dadhich, Harendra Kumar; Singhal, Shruti

    2013-12-01

    In this paper, assessment is done of Sea Surface Salinity (SSS) obtained from both SMOS and Aquarius satellites for couple of months over Indian Ocean (IO). The SSS values of the Southern Indian Ocean (SIO) are being investigated as the North Indian Ocean (NIO) is found much corrupted with the Radio Frequency Interference and even due to large variability of SSS in IO; the study area has been divided into different sub regions. The data of both the satellites at same location and of same processing level that is Level-2 have been procured and evaluated. The resolution factor is also being taken care for both onboard sensors. The resolution of SMOS L2 data products [1] is 15 X 15 Km and for Aquarius there are three different resolutions according to the BEAM's. BEAM 1 has a resolution of 76 X 94 Km, BEAM 2 has 84X120Km and BEAM3 has 96X156Km. The data have been averaged of SMOS [2] in the same way so as to match up with Aquarius resolution. By this paper we want to convince the readers that measuring SSS from space is a practical idea. SSS remote sensing now bears no more scientific perils than other remote sensing techniques did in their formative years. Advancing technology with proper resources has significantly reduced the errors.

  19. 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. PMID:26800249

  20. Descriptions of four new species of Thysanophrys (Scorpaeniformes: Platycephalidae) from the Western Indian Ocean.

    PubMed

    Knapp, Leslie W

    2013-01-01

    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. PMID:24614455

  1. Southeast Indian Ocean-Ridge Earthquake Sequences from Cross-correlation Analysis of Hydro-acoustic Data

    NASA Astrophysics Data System (ADS)

    Yun, S.; Ni, S.; Park, M.

    2006-12-01

    Earthquake sequences (location and timing of foreshocks and aftershocks) are critical for understanding dynamics of mid-ocean ridge and transform faults. Unfortunately whole sequences (including very small earthquakes) in the ocean can not be well recorded by land-based seismometers mostly because of large epicentral distances. Recent hydro-acoustic studies have demonstrated that T waves are very effective in detecting small submarine earthquakes because of little energy loss of T waves propagating in SOFAR channel. For example, a Mw6.2 (03/06/2006, Latitude -40.11, Longitude 78.49) transform earthquake occurred at the Southeastern Indian Ocean Ridge (an intermediate spreading rate ridge, 58-76 mm/year), but NEIC only reports 3 aftershocks in the first following week. We applied progressive multi-channel cross-correlation methods to hydro-acoustic data from the IMS arrays in Indian Ocean to detect the whole earthquake sequence. We also correlate waveform envelopes to accurately locate aftershocks and found consistent pattern of earthquake migration along the transform fault. In contrast to transform fault earthquake sequences at fast spreading ridge (East Pacific Rise, 142 mm/year) where foreshocks are observed, we failed to detect any foreshocks for the Mw6.2 earthquake though we found many aftershocks. The lack of foreshocks may be caused by lower spreading rate (hence lower temperature) or too small scale ridge segmentation. Still the number of aftershocks is much less than that of typical tectonic earthquake such as subduction or continental earthquakes, arguing different fault dynamics for mid ocean ridge systems, perhaps due to higher water content or presence of melt.

  2. 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

  3. Far-field tsunami hazard from mega-thrust earthquakes in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Okal, Emile A.; Synolakis, Costas E.

    2008-03-01

    We evaluate far-field tsunami hazard in the Indian Ocean Basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin. They represent worst-case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record. In a series of numerical experiments in which the source parameters of the 2004 Sumatra tsunami are allowed to vary one by one, while keeping the seismic moment and the fault orientation unchanged, we document that the main patterns of far-field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth, exact centroid location, and slip distribution on the fault plane. These results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise. We consider seismic sources located at the extremities of the 2004 Sumatra-Andaman rupture, namely along the southern coast of Sumatra and in the Andaman-Myanmar province; along the Makran coast of Pakistan and Iran; and also along the southern coast of Java, where the possibility of a large interplate thrust earthquake cannot be entirely dismissed. The results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the Indian Ocean Basin is primarily controlled by the classical effect of source directivity, and additionally by refraction and focusing along bathymetric features. As a result, many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004. This pattern is particularly important along the coast of East Africa, from Somalia to and including South Africa, in Madagascar and the Mascarene Islands, especially under a South Sumatra scenario involving an earthquake comparable to, or even possibly larger than, the 1833 event, whose epicentral area is widely believed to be under enhanced seismic

  4. 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.

  5. 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

  6. Adaptations of phytoplankton in the Indian Ocean sector of the Southern Ocean during austral summer of 1998—2014

    NASA Astrophysics Data System (ADS)

    Mishra, R. K.; Naik, R. K.; Anil Kumar, N.

    2015-12-01

    This study investigates the effects of light and temperature on the surface water diatoms and chlorophytes, phytoplankton in the Indian Ocean sector of the Southern Ocean (SO) during the austral summer of 1998‒2014. Significant longitudinal variations in hydrographic and biological parameters were observed at the Sub tropical front (STF), Sub Antarctic front (SAF) and Polar front (PF) along 56°E‒58°E. The concentrations of total surface chlorophyll a ( Chl a), diatoms, and chlorophytes measured by the National Aeronautics Space Agency (NASA) estimated by the Sea-Viewing Wide Field-of-View Sensors (SeaWiFS), the Moderate Resolution Imaging Spectro Radiometer (MODIS), and the NASA Ocean Biological Model (NOBM) were used in the study. Variations in the concentration of total Chl a was remarkable amongst the fronts during the study period. The contribution of diatoms to the total concentration of surface Chl a increased towards south from the STF to the PF while it decreased in the case of chlorophytes. The maximum photosynthetically active radiation (PAR) was observed at the STF and it progressively decreased to the PF through the SAF. At the PF region the contribution of diatoms to the total Chl a biomass was ≥80%. On the other hand, the chlorophytes showed a contrary distribution pattern with ≥70% of the total Chl a biomass recorded at the STF which gradually decreased towards the PF, mainly attributed to the temperate adaptation. This clearly reveals that the trend of diatoms increased at the STF and decreased at the SAF and the PF. Further, the trend of chlorophytes was increased at the STF, SAF and PF with a shift in the community in the frontal system of the Indian Ocean sector of the SO.

  7. Seasonality and Predictability of the Indian Ocean Dipole Mode: ENSO Forcing and Internal Variability

    NASA Astrophysics Data System (ADS)

    Yang, Y.

    2015-12-01

    This study evaluates the relative contributions to the Indian Ocean Dipole (IOD) mode of interannual variability from the El Niño-Southern Oscillation (ENSO) forcing and ocean-atmosphere feedbacks internal to the Indian Ocean. The ENSO forcing and internal variability is extracted by conducting a 10-member coupled simulation for 1950-2012 where sea surface temperature (SST) is restored to the observed anomalies over the tropical Pacific but interactive with the atmosphere over the rest of the world ocean. In these experiments, the ensemble mean is due to ENSO forcing and the inter-member difference arises from internal variability of the climate system independent of ENSO. These elements contribute one third and two thirds of the total IOD variance, respectively. Both types of IOD variability develop into an east-west dipole pattern due to Bjerknes feedback and peak in September-November. The ENSO forced and internal IOD modes differ in several important ways. The forced IOD mode develops in August with a broad meridional pattern, and eventually evolves into the Indian Ocean Basin mode; while the internal IOD mode grows earlier in June, is more confined to the equator and decays rapidly after October. The internal IOD mode is more skewed than the ENSO forced response. The destructive interference of ENSO forcing and internal variability can explain early-terminating IOD events, referred to IOD-like perturbations that fail to grow during boreal summer. Our results have implications for predictability. Internal variability, as represented by pre-season sea surface height anomalies off Sumatra, contributes to predictability considerably. Including this indicator of internal variability, together with ENSO, improves the predictability of IOD.

  8. 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.

  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. Mechanistic analysis of the suppressed convective anomaly precursor associated with the initiation of primary MJO events over the tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Yong, Yangyang; Mao, Jiangyu

    2016-02-01

    A primary Madden-Julian oscillation (MJO) event is one with no immediately preceding MJO event. Most primary MJO events initiating over the tropical Indian Ocean are preceded by a local suppressed convective anomaly (SCA). Based on daily outgoing longwave radiation and atmospheric circulation reanalysis data, composite analyses are performed to reveal the dynamical and thermodynamical mechanisms responsible for the generation of the precursor SCA associated with anomalous descending motion. During the developing stage, before the maximum SCA, the anomalous descending motion in the upper troposphere is dynamically forced by anomalous convergence over the eastern equatorial Indian Ocean. The anomalous convergent winds result from changes in subtropical circulation structures forced by extratropical disturbances in association with equatorward advection of positive potential vorticity. In the lower troposphere, the anomalous stable boundary layer with a strong thermal inversion is the dominant factor leading to descending motion. The sea surface temperature (SST) perturbations in the tropical Indian Ocean are an external forcing that generates the SCA through surface energy exchange. The negative SST anomalies in the northwestern portion of the tropical Indian Ocean act as a heat sink to cool the lower-tropospheric atmosphere, forcing strong descending motion and forming an anomalous anticyclone north of the equator. Meanwhile, the positive SST anomalies in the southeastern portion act as a heat source that forces anomalous divergent westerlies and northwesterlies toward the warmer SST area. Thus, anomalous descending motion is induced around the equator.

  11. 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.

  12. The role of ocean salinity in the water cycle associated with Indian monsoon

    NASA Astrophysics Data System (ADS)

    Tang, W.; Yueh, S. H.; Liu, W. T.

    2014-12-01

    Indian monsoon is one of the most important of all tropical climate systems. Its onset and spatial/temporal variability have strong economic impact and may cause severe human suffering. Using sea surface salinity (SSS) data from Aquarius/SAC-D satellite mission, we study the seasonal and interannual variability of SSS, to identify the potential sources for the monsoon moisture supply. Preliminary analysis shows the rainfall integrated over India subcontinent, which often used as an indicator for the monsoon onset and intensity, is correlated higher with Aquarius SSS in Indian Ocean than the state-of-art estimate of evaporation (OAflux) minus precipitation (GPCP), indicating the important role of the oceanic processes. We also examine the relative importance of salinity tendency (dSSS/dt) and salinity advection at various stages of the monsoon. Ocean current data from OSCAR project is used to estimate the salinity advection. The role of ocean processes relative to other components of the water cycle is investigated in conjunction with data from multiple satellite missions. The atmospheric integrated moisture transport (IMT) is derived from ocean vector wind (OceanSAT2) and atmospheric precipitable water (SSMIS F17). Moisture in and out of the continent can be estimated by integrating IMT along the coasts, providing a quantitative description of moisture supply in the water budget. We analyze how IMT is influenced by oceanic processes and further related with large-scale circulation. This study underscores the importance of continuous good-quality and high-resolution spacebased observations towards the characterization, understanding, and prediction of the global water cycle.

  13. 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

  14. The Proto-Indian Ocean and a probable paleozoic/mesozoic triradial rift system in East Africa

    NASA Astrophysics Data System (ADS)

    Cannon, R. T.; Simiyu Siambi, W. M. N.; Karanja, F. M.

    1981-02-01

    A revised Paleozoic/Mesozoic stratigraphy of coastal Kenya (including, in particular, the Karroo) based on current geological mapping near Mombasa is briefly described. This stratigraphy provides the geological framework for proposals concerning the Proto-Indian Ocean and the tectonic setting of the Karroo depositional basins. Recent geophysical evidence suggests that, within Gondwanaland, Madagascar was situated off East Africa near Kenya/Tanzania. The southern limits of the marine Lower Jurassic and southern limits of the marine Middle and Upper Jurassic are in similar positions in mainland Africa and Madagascar using the latter reconstruction. These paleogeographic limits also define the position, during the Jurassic, of an embayment from an ocean to the north. Regional geological similarities also support this reconstruction and are reinforced by paleocurrent data from the Karroo of Kenya indicating drainage north-northeast during the Permian and Triassic and possibly the Lower Jurassic. Marine connections during Karroo times appear to be of different ages in Kenya, Tanzania, Somalia, and Madagascar, probably reflecting physical limitations to marine access in fault-separated basins. The above embayment encroached across the Karroo depositional basins from northeast Kenya to southern Tanzania during the Lower and Middle Jurassic, i.e. from the direction towards which the Karroo drainage had been previously directed. Marine conditions remain to the present day so this embayment can be considered the Proto-Indian Ocean for East Africa. The marine incursion took place before the breakup of Gondwanaland suggesting that during the Jurassic the Proto-Indian Ocean in East Africa was an epicontinental sea and not a true ocean (i.e. floored by simatic crust). The epicontinental nature of this sea is confirmed by the lithologies of the associated sediments. Paleontological data indicate that this sea was an arm of Tethys. True oceanic conditions could not have been

  15. Seasonal Cycles of Meridional Overturning and Heat Transport of the Indian Ocean

    NASA Technical Reports Server (NTRS)

    Lee, Tong; Marotzke, Jochem

    1998-01-01

    A general circulation model of the Indian Ocean is fitted to monthly averaged climatological temperatures, salinities, and surface fluxes using the adjoint method. Interannual variability is minimized by penalizing the temporal drift from one seasonal cycle to another during a two-year integration. The resultant meridional overturning and heat transport display large seasonal variations, with maximum amplitudes of 18 and 22 (x 10(exp 6) cubic m/s) for the overturning and 1.8 and 1.4 (x 10(exp 15) W) for heat transport near 10 S and 10 N, respectively. A dynamical decomposition of the overturning and heat transport shows that the time-varying Ekman How plus its barotropic compensation can explain a large part of the seasonal variations in overturning and heat transport. The maximum variations at 10 deg N and 10 deg S are associated with monsoon reversal over the northern Indian Ocean and changes of the easterlies over the southern Indian Ocean. An external mode with variable topography has a moderate contribution where the Somali Current and the corresponding gyre reverse direction seasonally. Contribution front vertical shear (thermal wind and ageostrophic shear) is dominant near the southern boundary and large near the Somali Current latitudes. The dominant balance in the zonally integrated heat budget is between heat storage change and heat transport convergence except south of 15 S. Optimization with seasonal forcings improves estimates of sea surface temperatures, but the annual average overturning and heat transport are very similar to previous results with annual mean forcings. The annual average heat transport consists of roughly equal contributions from time-mean and time-varying fields of meridional velocities and temperatures in the northern Indian Ocean. indicating a significant rectification to the heat transport due to the time-varying fields. The time-mean and time-varying contributions are primarily due to the overturning and horizontal gyre

  16. 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

  17. 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.

  18. 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.

  19. Abrupt shifts in Horn of Africa hydroclimate and the influence of the Indian Ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Tierney, J. E.; deMenocal, P. B.

    2013-12-01

    The timing and abruptness with which Northeast Africa transitioned into and out of the Early Holocene African Humid Period is a subject of ongoing debate, with direct consequences for our understanding of climate stability and paleoenvironments. Here we present a new proxy record of regional hydroclimate, based on the hydrogen isotopic composition of leaf waxes, from a marine core in the Gulf of Aden that documents rapid, century-scale transitions into and out of the African Humid Period across the Horn of Africa. The Gulf of Aden record also documents large drying events during the last deglacial, synchronous with Heinrich Event 1 and the Younger Dryas. Similar and generally synchronous abrupt transitions at other East African sites suggest that rapid shifts in hydroclimate are regionally coherent. In addition, the termination of the African Humid Period in East Africa is synchronous with the termination along the western Saharan margin. A probabilistic analysis of the abruptness of the transitions in East Africa suggests that they likely occurred within centuries, underscoring the sensitivity of northeast African hydroclimate to external forcings. We speculate that the non-linear behavior of hydroclimate in the Horn of Africa is related to convection thresholds in the western Indian Ocean, and test this hypothesis with preliminary SST proxy data.

  20. Isolation and Characterization of New Leptospira Genotypes from Patients in Mayotte (Indian Ocean)

    PubMed Central

    Bourhy, Pascale; Collet, Louis; Clément, Sabine; Huerre, Michel; Ave, Patrick; Giry, Claude; Pettinelli, François; Picardeau, Mathieu

    2010-01-01

    Background Leptospirosis has been implicated as a severe and fatal form of disease in Mayotte, a French-administrated territory located in the Comoros archipelago (southwestern Indian Ocean). To date, Leptospira isolates have never been isolated in this endemic region. Methods and Findings Leptospires were isolated from blood samples from 22 patients with febrile illness during a 17-month period after a PCR-based screening test was positive. Strains were typed using hyper-immune antisera raised against the major Leptospira serogroups: 20 of 22 clinical isolates were assigned to serogroup Mini; the other two strains belonged to serogroups Grippotyphosa and Pyrogenes, respectively. These isolates were further characterized using partial sequencing of 16S rRNA and ligB gene, Multi Locus VNTR Analysis (MLVA), and pulsed field gel electrophoresis (PFGE). Of the 22 isolates, 14 were L. borgpetersenii strains, 7 L. kirschneri strains, and 1, belonging to serogoup Pyrogenes, was L. interrogans. Results of the genotyping methods were consistent. MLVA defined five genotypes, whereas PFGE allowed the recognition of additional subgroups within the genotypes. PFGE fingerprint patterns of clinical strains did not match any of the patterns in the reference strains belonging to the same serogroup, suggesting that the strains were novel serovars. Conclusions Preliminary PCR screening of blood specimen allowed a high isolation frequency of leptospires among patients with febrile illness. Typing of leptospiral isolates showed that causative agents of leptospirosis in Mayotte have unique molecular features. PMID:20582311

  1. 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.

  2. A new species of Neenchelys (Anguilliformes: Ophichthidae: Myrophinae) from the eastern Indian Ocean.

    PubMed

    Hibino, Yusuke; Satapoomin, Ukkrit; Kimura, Seishi

    2015-01-01

    A new worm eel, Neenchelys andamanensis, is described based on a single specimen collected from a depth of 520-531 m, Andaman Sea, eastern Indian Ocean. The new species is similar to N. daedalus, N. nudiceps, and N. similis in its total vertebral count and slender body, however, it differs from the latter three in having a shorter tail (60% TL vs. 70-76%), more numerous preanal vertebrae (77 vs. 59-71), and shorter pectoral fins (2.4% HL vs. 21-27%). Although the new species resembles N. mccoskeri in some proportional characters, the former species is distinguishable from the latter by its higher total vertebral count (221 vs. 172-184), position of the dorsal-fin origin (horizontal distance from the origin to a vertical through mid-anus 65% of trunk length vs. 46-59%) and width of the interorbital region (4.5% of head length vs. 8.2-16%). A revised key to the species of Neenchelys is provided. PMID:26701591

  3. Chelidoperca stella, a new species of perchlet (Perciformes: Serranidae) from the Andaman Sea, eastern Indian Ocean.

    PubMed

    Matsunuma, Mizuki; Motomura, Hiroyuki

    2016-01-01

    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]. PMID:27394461

  4. 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.

  5. 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

  6. 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.

  7. Processes of interannual mixed layer temperature variability in the thermocline ridge of the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Praveen Kumar, B.; Vialard, J.; Lengaigne, M.; Murty, V. S. N.; Foltz, G. R.; McPhaden, M. J.; Pous, S.; de Boyer Montégut, C.

    2014-11-01

    Sea-surface temperature interannual anomalies (SSTAs) in the thermocline ridge of the southwestern tropical Indian Ocean (TRIO) have several well-documented climate impacts. In this paper, we explore the physical processes responsible for SSTA evolution in the TRIO region using a combination of observational estimates and model-derived surface layer heat budget analyses. Vertical oceanic processes contribute most to SSTA variance from December to June, while lateral advection dominates from July to November. Atmospheric fluxes generally damp SSTA generation in the TRIO region. As a result of the phase opposition between the seasonal cycle of vertical processes and lateral advection, there is no obvious peak in SSTA amplitude in boreal winter, as previously noted for heat content anomalies. Positive Indian Ocean Dipole (IOD) events and the remote influence of El Niño induce comparable warming over the TRIO region, though IOD signals peak earlier (November-December) than those associated with El Niño (around March-May). Mechanisms controlling the SSTA growth in the TRIO region induced by these two climate modes differ strongly. While SSTA growth for the IOD mostly results from southward advection of warmer water, increased surface shortwave flux dominates the El Niño SSTA growth. In both cases, vertical oceanic processes do not contribute strongly to the initial SSTA growth, but rather maintain the SSTA by opposing the effect of atmospheric negative feedbacks during the decaying phase.

  8. 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.

  9. Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Rai, Ajai K.; Srinivasan, M. S.

    1994-12-01

    An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance of U. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance of U. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence of Bulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas. B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance of Stilostomella lepidula occurs close to the Early/Late Pleistocene boundary.

  10. Wave hindcast experiments in the Indian Ocean using MIKE 21 SW model

    NASA Astrophysics Data System (ADS)

    Remya, P. G.; Kumar, Raj; Basu, Sujit; Sarkar, Abhijit

    2012-04-01

    Wave prediction and hindcast studies are important in ocean engineering, coastal infrastructure development and management. In view of sparse and infrequent in-situ observations, model derived hindcast wave data can be used for the assessment of wave climate in offshore and coastal areas. In the present study, MIKE 21 SW Model has been used to carry out wave hindcast experiments in the Indian Ocean. Model runs have been made for the year 2005 using QuickSCAT scatterometer winds blended with ECMWF model winds. In order to study the impact of southern ocean swells, the model has been run in two different domains, with the southern boundary being shifted far south for the Domain 60S model. The model simulated wave parameters have been validated by comparing with buoy and altimeter data and various statistical yardsticks have been employed to quantify the validation. Possible reason for the poorer performance of the model in the Arabian Sea has also been pointed out.

  11. Distribution of runup heights of the December 26, 2004 tsunami in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Choi, Byung Ho; Hong, Sung Jin; Pelinovsky, Efim

    2006-07-01

    A massive earthquake with magnitude 9.3 occurred on December 26, 2004 off the northern Sumatra generated huge tsunami waves affected many coastal countries in the Indian Ocean. A number of field surveys have been performed after this tsunami event; in particular, several surveys in the south/east coast of India, Andaman and Nicobar Islands, Sri Lanka, Sumatra, Malaysia, and Thailand have been organized by the Korean Society of Coastal and Ocean Engineers from January to August 2005. Spatial distribution of the tsunami runup is used to analyze the distribution function of the wave heights on different coasts. Theoretical interpretation of this distribution is associated with random coastal bathymetry and coastline led to the log-normal functions. Observed data also are in a very good agreement with log-normal distribution confirming the important role of the variable ocean bathymetry in the formation of the irregular wave height distribution along the coasts.

  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

    2004-09-01

    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. 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.

  16. Early Paleogene variations in the calcite compensation depth: new constraints using old borehole sediments from across Ninetyeast Ridge, central Indian Ocean

    NASA Astrophysics Data System (ADS)

    Slotnick, B. S.; Lauretano, V.; Backman, J.; Dickens, G. R.; Sluijs, A.; Lourens, L.

    2015-03-01

    Major variations in global carbon cycling occurred between 62 and 48 Ma, and these very likely related to changes in the total carbon inventory of the ocean-atmosphere system. Based on carbon cycle theory, variations in the mass of the ocean carbon should be reflected in contemporaneous global ocean carbonate accumulation on the seafloor and, thereby, the depth of the calcite compensation depth (CCD). To better constrain the cause and magnitude of these changes, the community needs early Paleogene carbon isotope and carbonate accumulation records from widely separated deep-sea sediment sections, especially including the Indian Ocean. Several CCD reconstructions for this time interval have been generated using scientific drill sites in the Atlantic and Pacific oceans; however, corresponding information from the Indian Ocean has been extremely limited. To assess the depth of the CCD and the potential for renewed scientific drilling of Paleogene sequences in the Indian Ocean, we examine lithologic, nannofossil, carbon isotope, and carbonate content records for late Paleocene - early Eocene sediments recovered at three sites spanning Ninetyeast Ridge: Deep Sea Drilling Project (DSDP) Sites 213 (deep, east), 214 (shallow, central), and 215 (deep, west). The disturbed, discontinuous sediment sections are not ideal, because they were recovered in single holes using rotary coring methods, but remain the best Paleogene sediments available from the central Indian Ocean. The δ13C records at Sites 213 and 215 are similar to those generated at several locations in the Atlantic and Pacific, including the prominent high in δ13C across the Paleocene carbon isotope maximum (PCIM) at Site 215, and the prominent low in δ13C across the early Eocene Climatic Optimum (EECO) at both Site 213 and Site 215. The Paleocene-Eocene thermal maximum (PETM) and the K/X event are found at Site 213 but not at Site 215, presumably because of coring gaps. Carbonate content at both Sites 213 and

  17. 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.

  18. 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

  19. Century scale climatic rhythms in the equatorial Indian Ocean during the late Quaternary: Faunal and geochemical proxies from the Maldivian Archipelago

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Gupta, A. K.

    2012-04-01

    The equatorial Indian Ocean is swept by the Indian Ocean equatorial westerlies (IEW) which are strong during monsoon transitions in April-May and October-November, driving Eastward Equatorial Current (EEC) in the upper ocean. This study is based on the biogenic sediments from Ocean Drilling Program (ODP) Hole 716A, recovered beneath the narrow equatorial track (7 Degree North to 7 Degree South) along which the IEW prevail. We analyzed 300 Kyr record of benthic and planktic foraminifera, pteropods combined with stable isotope values measured on planktic foraminifer Globigerinoides ruber from 451 core samples to understand paleoceanographic and paleoclimatic changes in the equatorial Indian Ocean during the late Quaternary (~450 - 150 Kyrs). Factor and cluster analyses of the 53 highest-ranked benthic foraminiferal species enabled to identify five biofacies, indicating varied nature of deep-sea environments during the late Quaternary, with a major shift across the middle Brunhes epoch (across Marine Isotope Stage 9 and 8). Biofacies Robulus nicobarensis - Trifarina reussi (Rn-Tr), Uvigerina porrecta - Reussella simplex (Upo-Rs) and Cymbaloporetta squammosa - Bolivinita sp. (Cs-Bsp) document high organic flux with low oxygen paleoenvironment dominating before the mid-Brunhes event, similar to Globigerina bulloides population, while benthic foraminiferal biofacies Hoeglundina elegans - Miliolinella subrotunda (He-Ms) and Uvigerina peregrina - Quinqueloculina seminulum (Upe-Qs) record high seasonality in food supply with well-oxygenated deep water after ~300 Kyr. These changes are also visible in planktic foraminifera and pteropod record. In the present day, the strength of the IEW is inversely related to the Indian Ocean Dipole (IOD). The IEW weakened across MIS 9/8 during which time the IOD strengthened, causing heavy rains and floods over the equatorial East Africa and deficient rainfall over Australasia. The proxy response changed from low to high frequency cycles

  20. 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.

  1. 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

  2. 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

    2014-01-01

    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. K, Rb, Sr and 87Sr 86Sr in rocks from the Mid-Indian Oceanic Ridge

    USGS Publications Warehouse

    Subbarao, K.V.; Hedge, C.E.

    1973-01-01

    The 87Sr 86Sr ratios of Mid-Indian Oceanic Ridge (MIOR) basalts are nearly identical (0.7032 to 0.7035), with the exception of one more highly radiogenic sample (0.7043). These values are consistently higher than the strontium isotopic ratios of the ridge basalts from Atlantic and Pacific Oceans, suggesting that the source of the MIOR basalts was depleted in alkalies more recently and/or to a lesser degree than the basalts from other oceans. ?? 1973.

  4. Patterns of variations in large pelagic fish: A comparative approach between the Indian and the Atlantic Oceans

    NASA Astrophysics Data System (ADS)

    Corbineau, A.; Rouyer, T.; Fromentin, J.-M.; Cazelles, B.; Fonteneau, A.; Ménard, F.

    2010-07-01

    Catch data of large pelagic fish such as tuna, swordfish and billfish are highly variable ranging from short to long term. Based on fisheries data, these time series are noisy and reflect mixed information on exploitation (targeting, strategy, fishing power), population dynamics (recruitment, growth, mortality, migration, etc.), and environmental forcing (local conditions or dominant climate patterns). In this work, we investigated patterns of variation of large pelagic fish (i.e. yellowfin tuna, bigeye tuna, swordfish and blue marlin) in Japanese longliners catch data from 1960 to 2004. We performed wavelet analyses on the yearly time series of each fish species in each biogeographic province of the tropical Indian and Atlantic Oceans. In addition, we carried out cross-wavelet analyses between these biological time series and a large-scale climatic index, i.e. the Southern Oscillation Index (SOI). Results showed that the biogeographic province was the most important factor structuring the patterns of variability of Japanese catch time series. Relationships between the SOI and the fish catches in the Indian and Atlantic Oceans also pointed out the role of climatic variability for structuring patterns of variation of catch time series. This work finally confirmed that Japanese longline CPUE data poorly reflect the underlying population dynamics of tunas.

  5. Indian Ocean zonal mode activity in 20th century observations and simulations

    NASA Astrophysics Data System (ADS)

    Sendelbeck, Anja; Mölg, Thomas

    2016-04-01

    The Indian Ocean zonal mode (IOZM) is a coupled ocean-atmosphere system with anomalous cooling in the east, warming in the west and easterly wind anomalies, resulting in a complete reversal of the climatological zonal sea surface temperature (SST) gradient. The IOZM has a strong influence on East African climate by causing anomalously strong October - December (OND) precipitation. Using observational data and historical CMIP5 (Coupled Model Intercomparison Project phase 5) model output, the September - November (SON) dipole mode index (DMI), OND East African precipitation and SON zonal wind index (ZWI) are calculated. We pay particular attention to detrending SSTs for calculating the DMI, which seems to have been neglected in some published research. The ZWI is defined as the area-averaged zonal wind component at 850 hPa over the central Indian Ocean. Regression analysis is used to evaluate the models' capability to represent the IOZM and its impact on east African climate between 1948 and 2005. Simple correlations are calculated between SST, zonal wind and precipitation to show their interdependence. High correlation in models implies a good representation of the influence of IOZM on East African climate variability and our goal is to detect the models with the highest correlation coefficients. In future research, these model data might be used to investigate the impact of IOZM on the East African climate variability in the late 20's century with regard to anthropogenic causes and internal variability.

  6. Aerial transport of pesticides over the Northern Indian ocean and adjacent seas

    NASA Astrophysics Data System (ADS)

    Bidleman, Terry F.; Leonard, Ross

    Between 1976 and 1978 airborne organochlorines were measured over the northern Indian Ocean and the North Atlantic. Shipboard measurements in the Indian Ocean were made in the equatorial and northern Arabian Sea, the Persian Gulf and the Red Sea. In the North Atlantic samples were collected at Barbados, the southern tip of Newfoundland, and from shipboard on a cruise across the trades region. Collections were made by pulling air through a glass fiber filter followed by a column of polyurethane foam. Analyses were done by packed and glass capillary gas chromatography using electron capture detection. The most striking difference in organochlorine patterns between the two oceans is the much higher DDT concentrations over the eastern seas. Average DDT levels in the Arabian Sea-Persian Gulf-Red Sea area were 25-40 times the 3.0 pg m -3 North Atlantic background value. These higher levels most likely result from the continued use of DDT in countries bordering these areas. By contrast, DDT use in the United States, Canada and most northern European countries has ceased. The most prevalent chlorinated pesticides over the North Atlantic were chlordane and polychloroterpenes, both of which are still used in the United States.

  7. 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.

  8. Assessing the impact of the Indian Ocean tsunami on households: a modified domestic assets index approach.

    PubMed

    Arlikatti, Sudha; Peacock, Walter Gillis; Prater, Carla S; Grover, Himanshu; Sekar, Arul S Gnana

    2010-07-01

    This paper offers a potential measurement solution for assessing disaster impacts and subsequent recovery at the household level by using a modified domestic assets index (MDAI) approach. Assessment of the utility of the domestic assets index first proposed by Bates, Killian and Peacock (1984) has been confined to earthquake areas in the Americas and southern Europe. This paper modifies and extends the approach to the Indian sub-continent and to coastal surge hazards utilizing data collected from 1,000 households impacted by the Indian Ocean tsunami (2004) in the Nagapattinam district of south-eastern India. The analyses suggest that the MDAI scale is a reliable and valid measure of household living conditions and is useful in assessing disaster impacts and tracking recovery efforts over time. It can facilitate longitudinal studies, encourage cross-cultural, cross-national comparisons of disaster impacts and inform national and international donors of the itemized monetary losses from disasters at the household level. PMID:20298262

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. Pacific-to-Indian Ocean connectivity: Tasman leakage, Indonesian Throughflow, and the role of ENSO

    NASA Astrophysics Data System (ADS)

    Sebille, Erik; Sprintall, Janet; Schwarzkopf, Franziska U.; Sen Gupta, Alex; Santoso, Agus; England, Matthew H.; Biastoch, Arne; Böning, Claus W.

    2014-02-01

    The upper ocean circulation of the Pacific and Indian Oceans is connected through both the Indonesian Throughflow north of Australia and the Tasman leakage around its south. The relative importance of these two pathways is examined using virtual Lagrangian particles in a high-resolution nested ocean model. The unprecedented combination of a long integration time within an eddy-permitting ocean model simulation allows the first assessment of the interannual variability of these pathways in a realistic setting. The mean Indonesian Throughflow, as diagnosed by the particles, is 14.3 Sv, considerably higher than the diagnosed average Tasman leakage of 4.2 Sv. The time series of Indonesian Throughflow agrees well with the Eulerian transport through the major Indonesian Passages, validating the Lagrangian approach using transport-tagged particles. While the Indonesian Throughflow is mainly associated with upper ocean pathways, the Tasman leakage is concentrated in the 400-900 m depth range at subtropical latitudes. Over the effective period considered (1968-1994), no apparent relationship is found between the Tasman leakage and Indonesian Throughflow. However, the Indonesian Throughflow transport correlates with ENSO. During strong La Niñas, more water of Southern Hemisphere origin flows through Makassar, Moluccas, Ombai, and Timor Straits, but less through Moluccas Strait. In general, each strait responds differently to ENSO, highlighting the complex nature of the ENSO-ITF interaction.

  14. 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.

  15. 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.

  16. 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.

  17. Different Impacts of Various El Niño Events on the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Wang, X.; Wang, C.

    2013-12-01

    Our early work (Wang and Wang 2013) separates El Niño Modoki events into El Niño Modoki I and II because they show different impacts on rainfall in southern China and typhoon landfall activity. The warm SST anomalies originate in the equatorial central Pacific and subtropical northeastern Pacific for El Niño Modoki I and II, respectively. El Niño Modoki I features a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific, whereas El Niño Modoki II shows an asymmetric distribution with the warm SST anomalies extending from the northeastern Pacific to the equatorial central Pacific. The present paper investigates the influence of the various groups of El Niño events on the Indian Ocean Dipole (IOD). Similar to canonical El Niño, El Niño Modoki I is associated with a weakening of the Walker circulation in the Indo-Pacific region which decreases precipitation in the eastern tropical Indian Ocean and maritime continent and thus results in the surface easterly wind anomalies off Java-Sumatra. Under the Bjerknes feedback, the easterly wind anomalies induce cold SST anomalies off Java- Sumatra, and thus a positive IOD tends to occur in the Indian Ocean during canonical El Niño and El Niño Modoki I. However, El Niño Modoki II has an opposite impact on the Walker circulation, resulting in more precipitation and surface westerly wind anomalies off Java-Sumatra. Thus, El Niño Modoki II is favorable for the onset and development of a negative IOD on the frame of the Bjerknes feedback.

  18. Different impacts of various El Niño events on the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Wang, Chunzai

    2013-03-01

    Our early work (Wang and Wang in J Clim 26:1322-1338, 2013) separates El Niño Modoki events into El Niño Modoki I and II because they show different impacts on rainfall in southern China and typhoon landfall activity. The warm SST anomalies originate in the equatorial central Pacific and subtropical northeastern Pacific for El Niño Modoki I and II, respectively. El Niño Modoki I features a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific, whereas El Niño Modoki II shows an asymmetric distribution with the warm SST anomalies extending from the northeastern Pacific to the equatorial central Pacific. The present paper investigates the influence of the various groups of El Niño events on the Indian Ocean Dipole (IOD). Similar to canonical El Niño, El Niño Modoki I is associated with a weakening of the Walker circulation in the Indo-Pacific region which decreases precipitation in the eastern tropical Indian Ocean and maritime continent and thus results in the surface easterly wind anomalies off Java-Sumatra. Under the Bjerknes feedback, the easterly wind anomalies induce cold SST anomalies off Java- Sumatra, and thus a positive IOD tends to occur in the Indian Ocean during canonical El Niño and El Niño Modoki I. However, El Niño Modoki II has an opposite impact on the Walker circulation, resulting in more precipitation and surface westerly wind anomalies off Java-Sumatra. Thus, El Niño Modoki II is favorable for the onset and development of a negative IOD on the frame of the Bjerknes feedback.

  19. Different Impacts of Various El Niño Events on the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Wang, Chunzai

    2014-05-01

    Our early work (Wang and Wang 2013) separates El Niño Modoki events into El Niño Modoki I and II because they show different impacts on rainfall in southern China and typhoon landfall activity. The warm SST anomalies originate in the equatorial central Pacific and subtropical northeastern Pacific for El Niño Modoki I and II, respectively. El Niño Modoki I features a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific, whereas El Niño Modoki II shows an asymmetric distribution with the warm SST anomalies extending from the northeastern Pacific to the equatorial central Pacific. The present paper investigates the influence of the various groups of El Niño events on the Indian Ocean Dipole (IOD). Similar to canonical El Niño, El Niño Modoki I is associated with a weakening of the Walker circulation in the Indo-Pacific region which decreases precipitation in the eastern tropical Indian Ocean and maritime continent and thus results in the surface easterly wind anomalies off Java-Sumatra. Under the Bjerknes feedback, the easterly wind anomalies induce cold SST anomalies off Java- Sumatra, and thus a positive IOD tends to occur in the Indian Ocean during canonical El Niño and El Niño Modoki I. However, El Niño Modoki II has an opposite impact on the Walker circulation, resulting in more precipitation and surface westerly wind anomalies off Java-Sumatra. Thus, El Niño Modoki II is favorable for the onset and development of a negative IOD on the frame of the Bjerknes feedback.

  20. Different impacts of various El Niño events on the Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Wang, Chunzai

    2014-02-01

    Our early work (Wang and Wang in J Clim 26:1322-1338, 2013) separates El Niño Modoki events into El Niño Modoki I and II because they show different impacts on rainfall in southern China and typhoon landfall activity. The warm SST anomalies originate in the equatorial central Pacific and subtropical northeastern Pacific for El Niño Modoki I and II, respectively. El Niño Modoki I features a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific, whereas El Niño Modoki II shows an asymmetric distribution with the warm SST anomalies extending from the northeastern Pacific to the equatorial central Pacific. The present paper investigates the influence of the various groups of El Niño events on the Indian Ocean Dipole (IOD). Similar to canonical El Niño, El Niño Modoki I is associated with a weakening of the Walker circulation in the Indo-Pacific region which decreases precipitation in the eastern tropical Indian Ocean and maritime continent and thus results in the surface easterly wind anomalies off Java-Sumatra. Under the Bjerknes feedback, the easterly wind anomalies induce cold SST anomalies off Java- Sumatra, and thus a positive IOD tends to occur in the Indian Ocean during canonical El Niño and El Niño Modoki I. However, El Niño Modoki II has an opposite impact on the Walker circulation, resulting in more precipitation and surface westerly wind anomalies off Java-Sumatra. Thus, El Niño Modoki II is favorable for the onset and development of a negative IOD on the frame of the Bjerknes feedback.

  1. Phase locking of convectively coupled equatorial atmospheric Kelvin waves over Indian Ocean basin

    NASA Astrophysics Data System (ADS)

    Baranowski, Dariusz; Flatau, Maria; Flatau, Piotr; Matthews, Adrian

    2015-04-01

    The properties of convectively coupled Kelvin waves in the Indian Ocean and their propagation over the Maritime Continent are studied. It is shown that Kelvin waves are longitude - diurnal cycle phase locked over the Maritime Continent, Africa and the Indian Ocean. Thus, it is shown that they tend to propagate over definite areas during specific times of the day. Over the Maritime Continent, longitude-diurnal cycle phase locking is such that it agrees with mean, local diurnal cycle of convection. The strength of the longitude-diurnal cycle phase locking differs between 'non-blocked' Kelvin waves, which make successful transition over the Maritime Continent, and 'blocked' waves that terminated within it. It is shown that a specific combination of Kelvin wave phase speed and time of the day at which a wave approaches the Maritime Continent influence the chance of successful transition into the Western Pacific. Kelvin waves that maintain phase speed of 10 to 11 degrees per day over the central-eastern Indian Ocean and arrive at 90E between 9UTC and 18UTC have the highest chance of being 'non-blocked' by the Maritime Continent. The distance between the islands of Sumatra and Borneo agrees with the distance travelled by an average convectively coupled Kelvin wave in one day. This suggests that the Maritime Continent may act as a 'filter' for Kelvin waves favoring successful propagation of those waves for which propagation is in phase with the local diurnal cycle of precipitation. The AmPm index, a simple measure of local diurnal cycle for propagating disturbances, is introduced and shown to be useful metric depicting key characteristics of the convection associated with propagating Kelvin waves.

  2. Late Quaternary sea-level highstands in the central and eastern Indian Ocean: A review

    NASA Astrophysics Data System (ADS)

    Woodroffe, Colin D.

    2005-11-01

    The relative sea-level history of several atolls in the central and eastern Indian Ocean, including the Cocos (Keeling) Islands, Chagos Archipelago, and the Maldives-Laccadive Archipelagoes, has been debated for over a century but takes on a particular significance in the face of anticipated climate change. For each of these central and eastern Indian Ocean atolls Pleistocene limestone is encountered at depths of 6-20 m below sea level. On the Cocos (Keeling) Islands this has been dated to Last Interglacial age. Conglomerate platform underlies the reef islands on Cocos within which a sequence of fossil microatolls of massive and branching Porites records a gradual fall of sea level relative to the atoll. In the Maldives, the significance of outcrops of 'reef rock' has been vigorously debated without resolving sea-level history. Although in situ Heliopora occurs on the reef flat of Addu Atoll, dated at around 2700 radiocarbon yrs BP, other evidence for higher sea level remains poorly constrained. Conglomerates of a similar age have been described from the Chagos Archipelago, but it has not been unequivocally demonstrated that they formed under conditions of relatively higher sea level. In contrast to reefs further west in the Indian Ocean, each of these atolls has living microatolls of massive Porites that have been constrained in their upward growth by sea level. Interpretation of the upper surface of two such specimens from the Cocos (Keeling) Islands indicates broad fluctuations in the sea surface over the past century; similar microatolls are described from the Maldives implying little change in sea level over recent years. Regardless of minor past fluctuations, most reef islands in the Maldives are particularly low-lying and appear vulnerable to inundation, and extracting a more detailed sea-level history remains an important challenge.

  3. 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

  4. 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.

  5. 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

  6. In situ measurement of the biogeochemical properties of Southern Ocean mesoscale eddies in the Southwest Indian Ocean, April 2014

    NASA Astrophysics Data System (ADS)

    de Villiers, S.; Siswana, K.; Vena, K.

    2015-10-01

    Several open-ocean mesoscale features, a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S, as well as an adjacent cold-core (cyclonic) eddy at 56° S, were surveyed during a M/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, that will be suitable for comparison and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards into the Southern Ocean. Results show that the older warm-core eddy at 57.5° S is, at its core, 2.7 °C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chl a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chl a and dissolved nutrient data (for NO3-, NO2-, PO43- and SiO2) have been processed, quality-controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013.

    PubMed

    Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain

    2016-07-20

    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.

  12. 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

  13. 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.

  14. 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.

  15. Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013

    NASA Astrophysics Data System (ADS)

    Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain

    2016-07-01

    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.

  16. Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013.

    PubMed

    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

  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. 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)).

  20. 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).

  1. 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). PMID:26193772

  2. Modeling Reef Fish Biomass, Recovery Potential, and Management Priorities in the Western Indian Ocean.

    PubMed

    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

  3. 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)). PMID:26362332

  4. 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

  5. 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.

  6. Contemporary sedimentation in the Cocos (Keeling) Islands, Indian Ocean: interpretation using settling velocity analysis

    NASA Astrophysics Data System (ADS)

    Kench, Paul S.

    1997-12-01

    Textural parameters of grain-size distributions derived from sieve analysis and component analysis have been used to the exclusion of other methods to examine sedimentary processes in modern reef environments. However, because these methods do not reflect the hydraulic behaviour of bioclastic sediment this study uses settling velocity analysis (accounting for grain size, density, and shape variability), and component analysis of separated settling velocity fractions, to describe and differentiate bioclastic deposits and infer transport pathways in the Cocos (Keeling) Islands, an Indian Ocean atoll. Principal Component and Cluster analysis of settling (251 samples), and component (90 samples) characteristics, discriminated eight settling velocity and five component classes. A derived settling velocity classification, reflecting the hydraulic properties of the sediments, describes a lagoonward gradient from those with fast settling characteristics on the outer reef flat to those with moderate settling character on sand aprons. The active sediment transport system is constrained between these zones. Component analysis of bulk samples identifies two broad sediment types: (1) those with reef-derived components, found throughout the active transport zone (reef flat to sand aprons); and (2) those characterised by greater proportions of gastropod and Halimeda fragments which are produced and deposited in situ in the lagoon. Component analysis of settling fractions further resolves details of sediment movement in the active transport zone. Sediment is transported from the productive reef flat to passage entrances which form initial depositional environments. Slower settling material is selectively transported from the entrances, through the passage conduits, to passage exit environments. These form the main depositional areas under mean energy conditions. During moderate- to high-energy events sediment is flushed from the passage to sand apron zones, with slower settling

  7. 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.

  8. 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

  9. A review of Chiromantes obtusifrons (Dana, 1851) (Decapoda: Brachyura: Sesarmidae), with descriptions of four new sibling-species from Christmas Island (Indian Ocean), Guam and Taiwan.

    PubMed

    Davie, Peter J F; Ng, Peter K L

    2013-01-01

    The identity of Chiromantes obtusifrons (Dana, 1851), previously considered widespread in the tropical West Pacific region to the eastern Indian Ocean, is revised and found to be a species-complex. Chiromantes obtusifrons is now considered endemic to the Hawaiian Is., and four new species are described from Guam, Taiwan and Christmas Island. Two species live sympatrically in Taiwan. Species separation is based on carapace and frontal shape and granulation, leg proportions, abdominal somite proportions, and distinctive live colouration.

  10. Atmospheric deposition of N, P and Fe to the Northern Indian Ocean: implications to C- and N-fixation.

    PubMed

    Srinivas, Bikkina; Sarin, M M

    2013-07-01

    This study presents the first data set on atmospheric input of N, P and Fe to the Northern Indian Ocean. Based on the chemical analysis of ambient aerosols, collected from the marine atmospheric boundary layer (MABL) during the continental outflow (January-April), we document that dry-deposition fluxes (μmolm(-2) d(-1)) of N (2-167), P (0.5-4.8) and Fe (0.02-1.2) to the Bay of Bengal are significantly higher compared to those over the Arabian Sea [N: 0.2-18.6; P: 0.3-0.9; Fe: 0.001-0.015]. Using atmospherically derived P and Fe, C-fixation (1.1 Pg yr(-1)) in the Bay of Bengal is dominated by anthropogenic sources. In contrast, C-fixation (0.03 Pg yr(-1)) in the Arabian Sea is limited by P and Fe. This is attributed to the poor fractional solubility of atmospheric mineral dust transported to the Arabian Sea. However, N-fixation by diazotrophs in the two oceanic regions is somewhat similar (0.5 Tg yr(-1)). Our estimate of N-deposition (0.2 Tg yr(-1)) to the Northern Indian Ocean is significantly lower compared to model results (~800-1200 mg-Nm(-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); ~0.8 Tg yr(-1) by Kanakidou et al. (2012)). An overestimate of N-deposition by models could arise due to inappropriate parameterization of temporal variability associated with the continental outflow spread over only four months. PMID:23584188

  11. Atmospheric deposition of N, P and Fe to the Northern Indian Ocean: implications to C- and N-fixation.

    PubMed

    Srinivas, Bikkina; Sarin, M M

    2013-07-01

    This study presents the first data set on atmospheric input of N, P and Fe to the Northern Indian Ocean. Based on the chemical analysis of ambient aerosols, collected from the marine atmospheric boundary layer (MABL) during the continental outflow (January-April), we document that dry-deposition fluxes (μmolm(-2) d(-1)) of N (2-167), P (0.5-4.8) and Fe (0.02-1.2) to the Bay of Bengal are significantly higher compared to those over the Arabian Sea [N: 0.2-18.6; P: 0.3-0.9; Fe: 0.001-0.015]. Using atmospherically derived P and Fe, C-fixation (1.1 Pg yr(-1)) in the Bay of Bengal is dominated by anthropogenic sources. In contrast, C-fixation (0.03 Pg yr(-1)) in the Arabian Sea is limited by P and Fe. This is attributed to the poor fractional solubility of atmospheric mineral dust transported to the Arabian Sea. However, N-fixation by diazotrophs in the two oceanic regions is somewhat similar (0.5 Tg yr(-1)). Our estimate of N-deposition (0.2 Tg yr(-1)) to the Northern Indian Ocean is significantly lower compared to model results (~800-1200 mg-Nm(-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); ~0.8 Tg yr(-1) by Kanakidou et al. (2012)). An overestimate of N-deposition by models could arise due to inappropriate parameterization of temporal variability associated with the continental outflow spread over only four months.

  12. 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

  13. Multi-elemental concentrations in the tissues of the oceanic squid Todarodes filippovae from Tasmania and the southern Indian Ocean.

    PubMed

    Kojadinovic, Jessica; Jackson, Christine H; Cherel, Yves; Jackson, George D; Bustamante, Paco

    2011-07-01

    This study investigates 14 elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn) in the tissues of the oceanic ommastrephid squid Todarodes filippovae from waters surrounding Île Amsterdam (southern Indian Ocean) and Tasmania (Australia). As for other cephalopod species, the digestive gland and branchial hearts showed the highest concentrations of many elements (Ag, Cd, Se, V and Zn, and Cr and Ni, respectively) highlighting their role in bioaccumulation and detoxification processes. With the exception of As and Hg, the muscles showed relatively low trace element concentrations. Squid size was positively correlated to Ag, As, Cd, Hg and Zn concentrations in Tasmanian squid and negatively correlated to all but Hg and Zn concentrations in Île Amsterdam squid. Furthermore, no differences in elemental concentrations were noted between sexes. There were, however, some differences between mated and non-mated females from Tasmania. Comparing elemental concentrations in squid from both islands, higher concentrations of Cd, Co, Cr, Ni, Pb and V in squid sampled in Île Amsterdam reflect different exposure conditions. When considering T. filippovae as a dietary resource for humans it should be noted that, given their Hg content, squids from Île Amsterdam are not recommended for consumption on a regular basis. Moreover, regardless of the squid's origin, digestive glands should be avoided as Cd and Hg concentrations were above the European Union authorized limits in these organs.

  14. The tidal regimes of three indian ocean atolls and some ecological implications

    NASA Astrophysics Data System (ADS)

    Pugh, D. T.; Rayner, R. F.

    1981-10-01

    Coral atolls are areas of high biological productivity, supporting diverse and largely closed ecosystems. Cycling of nutrients within such systems and the input of additional nutrients from ocean waters are strongly influenced by wave and tidally induced water exchange. Tidal water exchange exerts a stabilizing effect on the physical and chemical characteristics of a lagoon. Tides affect the residence time of lagoon water, and the amount by which lagoon temperatures exceed ocean surface water temperatures, typically 2°C in cloud-free windless weather. Lagoon excess temperatures are independent of depth but vary inversely with the tidal range, with significant spring-neap modulations, but harmonic variations of lagoon temperatures at diurnal and semidiurnal periods are small except in very shallow lagoons. The effects on lagoon winds are also small, implying that measured winds are representative of open ocean conditions. The growth and zonation of corals and other organisms inhabiting shallow reef flats may be affected by the phase of the solar semidiurnal tide (S 2), which determines the time of day at which extremely low tidal levels occur. Measurements at three Indian Ocean atolls are used to illustrate these effects.

  15. The Indigo V Indian Ocean Expedition: a prototype for citizen microbial oceanography

    NASA Astrophysics Data System (ADS)

    Lauro, Federico; Senstius, Jacob; Cullen, Jay; Lauro, Rachelle; Neches, Russell; Grzymski, Joseph

    2014-05-01

    Microbial Oceanography has long been an extremely expensive discipline, requiring ship time for sample collection and thereby economically constraining the number of samples collected. This is especially true for under-sampled water bodies such as the Indian Ocean. Specialised scientific equipment only adds to the costs. Moreover, long term monitoring of microbial communities and large scale modelling of global biogeochemical cycles requires the collection of high-density data both temporally and spatially in a cost-effective way. Thousands of private ocean-going vessels are cruising around the world's oceans every day. We believe that a combination of new technologies, appropriate laboratory protocols and strategic operational partnerships will allow researchers to broaden the scope of participation in basic oceanographic research. This will be achieved by equipping sailing vessels with small, satcom-equipped sampling devices, user-friendly collection techniques and a 'pre-addressed-stamped-envelope' to send in the samples for analysis. We aim to prove that 'bigger' is not necessarily 'better' and the key to greater understanding of the world's oceans is to forge the way to easier and cheaper sample acquisition. The ultimate goal of the Indigo V Expedition is to create a working blue-print for 'citizen microbial oceanography'. We will present the preliminary outcomes of the first Indigo V expedition, from Capetown to Singapore, highlighting the challenges and opportunities of such endeavours.

  16. State of knowledge of coastal and marine biodiversity of Indian Ocean countries.

    PubMed

    Wafar, Mohideen; Venkataraman, Krishnamurthy; Ingole, Baban; Ajmal Khan, Syed; Lokabharathi, Ponnapakkam

    2011-01-01

    The Indian Ocean (IO) extends over 30% of the global ocean area and is rimmed by 36 littoral and 11 hinterland nations sustaining about 30% of the world's population. The landlocked character of the ocean along its northern boundary and the resultant seasonally reversing wind and sea surface circulation patterns are features unique to the IO. The IO also accounts for 30% of the global coral reef cover, 40,000 km² of mangroves,some of the world's largest estuaries, and 9 large marine ecosystems. Numerous expeditions and institutional efforts in the last two centuries have contributed greatly to our knowledge of coastal and marine biodiversity within the IO. The current inventory, as seen from the Ocean Biogeographic Information System, stands at 34,989 species, but the status of knowledge is not uniform among countries. Lack of human, institutional, and technical capabilities in some IO countries is the main cause for the heterogeneous level of growth in our understanding of the biodiversity of the IO. The gaps in knowledge extend to several smaller taxa and to large parts of the shelf and deep-sea ecosystems, including seamounts. Habitat loss, uncontrolled developmental activities in the coastal zone, over extraction of resources, and coastal pollution are serious constraints on maintenance of highly diverse biota, especially in countries like those of the IO, where environmental regulations are weak. PMID:21297949

  17. State of knowledge of coastal and marine biodiversity of Indian Ocean countries.

    PubMed

    Wafar, Mohideen; Venkataraman, Krishnamurthy; Ingole, Baban; Ajmal Khan, Syed; Lokabharathi, Ponnapakkam

    2011-01-31

    The Indian Ocean (IO) extends over 30% of the global ocean area and is rimmed by 36 littoral and 11 hinterland nations sustaining about 30% of the world's population. The landlocked character of the ocean along its northern boundary and the resultant seasonally reversing wind and sea surface circulation patterns are features unique to the IO. The IO also accounts for 30% of the global coral reef cover, 40,000 km² of mangroves,some of the world's largest estuaries, and 9 large marine ecosystems. Numerous expeditions and institutional efforts in the last two centuries have contributed greatly to our knowledge of coastal and marine biodiversity within the IO. The current inventory, as seen from the Ocean Biogeographic Information System, stands at 34,989 species, but the status of knowledge is not uniform among countries. Lack of human, institutional, and technical capabilities in some IO countries is the main cause for the heterogeneous level of growth in our understanding of the biodiversity of the IO. The gaps in knowledge extend to several smaller taxa and to large parts of the shelf and deep-sea ecosystems, including seamounts. Habitat loss, uncontrolled developmental activities in the coastal zone, over extraction of resources, and coastal pollution are serious constraints on maintenance of highly diverse biota, especially in countries like those of the IO, where environmental regulations are weak.

  18. 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 the reliability in the Indian Ocean of the biohorizons recently identified at Site 711 (Fioroni et al., in press), by means of high resolution sampling, new taxonomic updates, quantitative analyses on calcareous nannofossils allowed to increase the number of useful bioevents and to compare their reliability and synchroneity. The new magnetostratigraphic analyses and integrated stratigraphy allow also to achieve an accurate biochronology of the time interval spanning Chrons C20 (middle Eocene) and C12 (early Oligocene). In addition, this equatorial site represents an opportunity to study the carbonate accumulation history and the large fluctuations of the carbonate compensation depth (CCD) during the Eocene (e.g. Pälike et al., 2012). The investigated interval encompasses the Middle Eocene Climatic Optimum (MECO), and the long cooling trend that leads to the Oligocene glacial state. By means of our new bio-magnetostratigraphic data and paleoecological results we provide further insights on

  19. Hotspot-ridge interaction in the Indian Ocean: constraints from Geosat/ERM altimetry

    NASA Astrophysics Data System (ADS)

    Grevemeyer, Ingo

    1996-09-01

    Upper-mantle structure of Indian Ocean spreading ridges was investigated by track segments of Geosat/ERM altimeter measurements. To determine the upper-mantle structure of the Earth's gravity field, a low-degree and -order spherical harmonic representation of the geoid was removed. A test of several reference fields suggested that a degree 2-25 field with gradually rolled off coefficients (Sandwell & Renkin 1988) offers an adequate representation of the long-wavelength geoidal undulations. Filtered profiles of three individual ridge segments display a strong asymmetry in geoid versus age trends of conjugated rift flanks. The unusually low geoid slopes on one flank can perhaps best be explained as a dynamic or thermal phenomenon reflecting a flow connection between a neighbouring off-axis hotspot plume and the ridge axis, while the other flank simply cools as it spreads away from the axial zone. It seems reasonable to hypothesize that the Southwest Indian Ridge and the Southeast Indian Ridge act as sinks for plumes beneath Agulhas Plateau and Kerguelen Islands, respectively. The Carlsberg Ridge data suggest that the Réunion hotspot contaminated northwestern African lithosphere until 15 Ma. Moreover, symmetric flattening of geoid versus age trends of conjugated ridge flanks offers evidence that plume events affect geoid versus age trends

  20. First overview of the Culicoides Latreille (Diptera: Ceratopogonidae) livestock associated species of Reunion Island, Indian Ocean.

    PubMed

    Desvars, A; Grimaud, Y; Guis, H; Esnault, O; Allène, X; Gardès, L; Balenghien, T; Baldet, T; Delécolle, J C; Garros, C

    2015-02-01

    This study establishes the first faunistic inventory of livestock associated Culicoides (Diptera: Ceratopogonidae) species of Reunion Island (Indian Ocean), where bluetongue and epizootic hemorrhagic disease are regularly recorded. Single night-catches were performed at 41 sites using light suction traps at altitudes ranging from 0 to 1525 m, from March to April 2005. Five species were recorded: Culicoides imicola, Culicoides bolitinos, Culicoides enderleini, Culicoides grahamii, and Culicoides kibatiensis, among which at least the first three species are known to be involved in virus transmission to ruminants and equids. This is the first record of C. bolitinos, C. kibatiensis, and C. enderleini on the island. C. imicola was the most abundant species along the sea coast. C. bolitinos was more abundant inland and on two sites on the east coast. C. kibatiensis and C. grahamii were less abundant than the other three species and limited to two foci. Spatial distribution analysis of the different species showed that C. bolitinos, C. enderleini and C. imicola were collected at low altitudes, while the other two species were found at higher altitude. A morphological identification key for adult females and males is given, as well as cytochrome oxydase subunit I sequences. Phylogenetic reconstructions showed a clear divergence between C. bolitinos from Reunion Island and mainland Africa. This monograph will help to identify the Culicoides species in the poorly known entomological fauna of the south-western Indian Ocean region.

  1. Back to Gondwanaland: can ancient vicariance explain (some) Indian Ocean disjunct plant distributions?

    PubMed

    Pirie, Michael D; Litsios, Glenn; Bellstedt, Dirk U; Salamin, Nicolas; Kissling, Jonathan

    2015-06-01

    Oceans, or other wide expanses of inhospitable environment, interrupt present day distributions of many plant groups. Using molecular dating techniques, generally incorporating fossil evidence, we can estimate when such distributions originated. Numerous dating analyses have recently precipitated a paradigm shift in the general explanations for the phenomenon, away from older geological causes, such as continental drift, in favour of more recent, long-distance dispersal (LDD). For example, the 'Gondwanan vicariance' scenario has been dismissed in various studies of Indian Ocean disjunct distributions. We used the gentian tribe Exaceae to reassess this scenario using molecular dating with minimum (fossil), maximum (geological), secondary (from wider analyses) and hypothesis-driven age constraints. Our results indicate that ancient vicariance cannot be ruled out as an explanation for the early origins of Exaceae across Africa, Madagascar and the Indian subcontinent unless a strong assumption is made about the maximum age of Gentianales. However, both the Gondwanan scenario and the available evidence suggest that there were also several, more recent, intercontinental dispersals during the diversification of the group.

  2. John Murray / MABAHISS expedition versus the International Indian Ocean Expedition (IIOE) in retrospect

    NASA Astrophysics Data System (ADS)

    Aleem, A. A.; Morcos, S. A.

    In addition to its scientific achievements, the John Murray/Mabahiss Expedition was a unique experiment in technology transfer and it pioneered bilateral relations in the field of oceanography, at a time when the Law of the Sea was not even an embryonic concept. The Expedition will be remembered for its profound influence on the development of oceanography in Egypt, and subsequently in several Arab and African countries, as well as for its socio-economic impact in Egypt. The International Indian Ocean Expedition (IIOE) was an elaborate exercise involving both the most sophisticated developments in oceanography of the day and the full complexity of international relations which necessitated the scientific, coordinating and supporting mechanisms of SCOR, IOC and Unesco combined. Each exercise separated by 25 years represented a significant event in the development of oceanography. Each was a natural product of the prevailing state of the art and the international climate. Oceanography had made a quantum jump in technology in the intervening quarter of a century, which had put the cost of deep sea oceanography quite beyond the financial capabilities of many developing countries, an important factor to bear in mind when comparing the impact of the John Murray/Mabahiss Expedition on Egypt with that of the IIOE, on the Indian Ocean countries.

  3. Crustal Magnetization Model of Maud Rise in the Southwest Indian Ocean

    NASA Technical Reports Server (NTRS)

    Kim, Hyung Rae; vanFrese, Ralph R. B.; Golynsky, Alexander V.; Taylor, Patrick T.; Kim, Jeong Woo

    2004-01-01

    We modeled the crustal magnetization for the Maud Rise in the south-west Indian Ocean off the coast of East Antarctica using magnetic observations from the Oersted satellite and near-surface surveys complied by the Antarctic Digital Magnetic Anomaly Project (ADMAP). A new inversion modeling scheme of the multi-altitude anomaly fields suggests that the magnetic effects due to crustal thickness variations and remanence involving the normal polarity Cretaceous Quiet Zone (KQZ) become increasingly dominant with altitude. The magnetic crustal thickness effects were modeled in the Oersted data using crustal thickness variations derived from satellite altitude gravity data. Remanent magnetization modeling of the residual Oersted and near-surface magnetic anomalies supports extending the KQZ eastwards to the Astrid Ridge. The remaining near-surface anomalies involve crustal features with relatively high frequency effects that are strongly attenuated at satellite altitudes. The crustal modeling can be extended by the satellite magnetic anomalies across the Indian Ocean Ridge for insight on the crustal properties of the conjugate Agulhas Plateau. The modeling supports the Jurassic reconstruction of Gondwana when the African Limpopo-Zambezi and East Antarctic Princess Astrid coasts were connected as part of a relatively demagnetized crustal block.

  4. Modulation of interannual variability of tropical cyclone activity over Southeast Indian Ocean by negative IOD phase

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Yu, Weidong; Li, Kuiping; Liu, Baochao; Wang, Guanlin

    2015-12-01

    Tropical cyclones (TCs) over Southeast Indian Ocean (SEIO) have the notable interannual variability caused by ENSO and Indian Ocean Dipole (IOD). In the September-November of El Niño and October-November of positive IOD (PIOD), SEIO TCs is far less than its climatology. However, it is hard to separately understand El Niño and PIOD's impact on SEIO TCs due to their similar occurrence time and time scale. Unlike El Niño and PIOD, SEIO TCs is remarkably more than its climatology only in September-November of negative IOD (NIOD) instead of La Niña. Consequently, it is concluded NIOD mainly affects SEIO TCs' increase. Diagnose results suggest the relative humidity (RH) contributes mostly to the TCs' increase, vertical wind shear provides the secondary positive contribution, vorticity term also makes a weak positive contribution and PI term's contribution even may be negligible. The study still uncovers the process of RH change: NIOD reaches its peak period and changes atmosphere circulation to make a positive low-level vorticity anomaly over SEIO. Vorticity anomaly strengthens upward motion. The vertical velocity anomaly and climatogical specific humidity (SH) work together to make vertical advection play a dominant role in SH variation. SH's change mainly reflects in RH variation. Eventually, all of these associates with NIOD lead to more SEIO TCs in September-November and the significance of difference is above 99%.

  5. Source level estimation of two blue whale subspecies in southwestern Indian Ocean.

    PubMed

    Samaran, Flore; Guinet, Christophe; Adam, Olivier; Motsch, Jean-François; Cansi, Yves

    2010-06-01

    Blue whales produce intense, stereotypic low frequency calls that are particularly well suited for transmission over long distances. Because these calls vary geographically, they can be used to gain insight into subspecies distribution. In the Southwestern Indian Ocean, acoustic data from a triad of calibrated hydrophones maintained by the International Monitoring System provided data on blue whale calls from two subspecies: Antarctic and pygmy blue whales. Using time difference of arrival and least-squares hyperbolic methods, the range and location of calling whales were determined. By using received level of calls and propagation modeling, call source levels of both subspecies were estimated. The average call source level was estimated to 179+/-5 dB re 1 microPa(rms) at 1 m over the 17-30 Hz band for Antarctic blue whale and 174+/-1 dB re 1 microPa(rms) at 1 m over the 17-50 Hz band for pygmy blue whale. According to previous estimates, slight variations in the source level could be due to inter-individual differences, inter-subspecies variations and the calculation method. These are the first reported source level estimations for blue whales in the Indian Ocean. Such data are critical to estimate detection ranges of calling blue whales. PMID:20550278

  6. Identification and prevalence of coral diseases on three Western Indian Ocean coral reefs.

    PubMed

    Séré, Mathieu G; Chabanet, Pascale; Turquet, Jean; Quod, Jean-Pascal; Schleyer, Michael H

    2015-06-01

    Coral diseases have caused a substantial decline in the biodiversity and abundanc