Showing papers by "National Institute of Oceanography, India published in 2009"

Denitrification as the dominant nitrogen loss process in the Arabian Sea

Abstract: Primary production in over half of the world's oceans is limited by fixed nitrogen availability. The main loss term from the fixed nitrogen inventory is the production of dinitrogen gas (N(2)) by heterotrophic denitrification or the more recently discovered autotrophic process, anaerobic ammonia oxidation (anammox). Oceanic oxygen minimum zones (OMZ) are responsible for about 35% of oceanic N(2) production and up to half of that occurs in the Arabian Sea. Although denitrification was long thought to be the only loss term, it has recently been argued that anammox alone is responsible for fixed nitrogen loss in the OMZs. Here we measure denitrification and anammox rates and quantify the abundance of denitrifying and anammox bacteria in the OMZ regions of the Eastern Tropical South Pacific and the Arabian Sea. We find that denitrification rather than anammox dominates the N(2) loss term in the Arabian Sea, the largest and most intense OMZ in the world ocean. In seven of eight experiments in the Arabian Sea denitrification is responsible for 87-99% of the total N(2) production. The dominance of denitrification is reproducible using two independent isotope incubation methods. In contrast, anammox is dominant in the Eastern Tropical South Pacific OMZ, as detected using one of the isotope incubation methods, as previously reported. The abundance of denitrifying bacteria always exceeded that of anammox bacteria by up to 7- and 19-fold in the Eastern Tropical South Pacific and Arabian Sea, respectively. Geographic and temporal variability in carbon supply may be responsible for the different contributions of denitrification and anammox in these two OMZs. The large contribution of denitrification to N(2) loss in the Arabian Sea indicates the global significance of denitrification to the oceanic nitrogen budget.

Taking stock: inventory of alien species in the Mediterranean sea

Abstract: 573 alien marine metazoan species have been recorded in the Mediterranean Sea. The present checklist is the first to present the species’ native range, presumed mode of introduction, spatial extent, and the date of the first record in each country. The majority of aliens are thermophilic species originating from the Indo-Pacific or Indian Oceans, which have entered the Mediterranean through the Suez Canal. However, the means of introduction differ greatly among the phyla, and the basins of the Mediterranean. The temporal records of the alien species reflect political crises, economic development and scientific interest in studying the phenomenon—in the past two decades on average about 10 alien species new to the Mediterranean are recorded annually. Many have established durable populations and extended their range: 125 alien species have been recorded from four or more countries. The possible impacts of regulatory instruments and environmental management options are examined.

Historical records of coastal eutrophication-induced hypoxia

Abstract: . Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical indicators (proxies) derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. Those based on (1) the preserved remains of benthic organisms (mainly foraminiferans and ostracods), (2) sedimentary features (e.g. laminations) and (3) sediment chemistry and mineralogy (e.g. presence of sulphides and redox-sensitive trace elements) reflect conditions at or close to the seafloor. Those based on (4) the preserved remains of planktonic organisms (mainly diatoms and dinoflagellates), (5) pigments and lipid biomarkers derived from prokaryotes and eukaryotes and (6) organic C, N and their stable isotope ratios reflect conditions in the water column. However, the interpretation of these indicators is not straightforward. A central difficulty concerns the fact that hypoxia is strongly correlated with, and often induced by, organic enrichment caused by eutrophication, making it difficult to separate the effects of these phenomena in sediment records. The problem is compounded by the enhanced preservation in anoxic and hypoxic sediments of organic microfossils and biomarkers indicating eutrophication. The use of hypoxia-specific proxies, such as the trace metals molybdenum and rhenium and the bacterial biomarker isorenieratene, together with multi-proxy approaches, may provide a way forward. All proxies of bottom-water hypoxia are basically qualitative; their quantification presents a major challenge to which there is currently no satisfactory solution. Finally, it is important to separate the effects of natural ecosystem variability from anthropogenic effects. Despite these problems, in the absence of historical data for dissolved oxygen concentrations, the analysis of sediment cores can provide plausible reconstructions of the temporal development of human-induced hypoxia, and associated eutrophication, in vulnerable coastal environments.

Time-dependence of salinity in monsoonal estuaries

Abstract: The theories and classification schemes commonly used for understanding estuarine dynamics often refer to a steady state of the estuary in which the salinity field is time-independent. In this state salinity-ingress into the estuary due to different process (diffusion, gravity current formation, impact of tidal asymmetries, etc.) is balanced by salinity-egress induced by runoff. Here we point out that the salinity field of the estuaries that are located on the coasts of the Indian subcontinent and come under the influence of the Indian Summer Monsoon (ISM) is never in a steady state. We refer to such estuaries as “monsoonal estuaries”, an example of which is the Mandovi estuary located on the west coast of India. We describe the annual cycle of the salinity field in this estuary and conclude that the essential unsteadiness of the salinity field arises from two features of the runoff into it. First, most of the runoff occurs as a series of episodes of highs and lulls spread over about 4 months of the wet summer monsoon. Second, the total runoff is large, well over an order of magnitude larger than the estuarine volume. We define two parameters to represent these two features, and show that they can be used to distinguish the monsoonal estuaries from others.

Ocean- Atmosphere Interactions During Cyclone Nargis

Abstract: Cyclone Nargis (Figure 1a) made landfall in Myanmar (formerly Burma) on 2 May 2008 with sustained winds of approximately 210 kilometers per hour, equivalent to a category 3–4 hurricane. In addition, Nargis brought approximately 600 millimeters of rain and a storm surge of 3–4 meters to the low-lying and densely populated Irrawaddy River delta. In its wake, the storm left an estimated 130,000 dead or missing and more than $10 billion in economic losses. It was the worst natural disaster to strike the Indian Ocean region since the 26 December 2004 tsunami and the worst recorded natural disaster ever to affect Myanmar.

CO2 Supersaturation and Net Heterotrophy in a Tropical Estuary (Cochin, India): Influence of Anthropogenic Effect : Carbon Dynamics in Tropical Estuary ()

Abstract: Carbon biogeochemistry of a tropical ecosystem (The Cochin Estuary, India) undergoing increased human intervention was studied during February (premonsoon), April (early monsoon) and September (monsoon) 2005. The Cochin estuary sustains high levels of pCO2 (up to 6000 μatm) and CO2 effluxes (up to 274 mmolC m−2 d−1) especially during monsoon. A first-order estimate of the carbon mass balance shows that net production of dissolved inorganic carbon is an order of magnitude higher than the net loss of dissolved and particulate organic carbon from the estuary. This imbalance is attributed to the organic inputs to the estuary through anthropogenic supplies. The bacteria-mediated mineralization of organic matter is mainly responsible for the build-up of pCO2 and increased CO2 emission to the atmosphere indicating heterotrophy. The linear correlation between excess CO2 and apparent oxygen utilization indicates respiration as the chief mechanism for CO2 supersaturation. An increase in the net negative ecosystem production (–ve NEP) between premonsoon (−136 mmolC m−2 d−1 or −376 MgC d−1) and monsoon (−541 mmolC m−2 d−1 or −1500 MgC d−1) is supported by a corresponding increase in O2 influxes from 17 mmol O2 m−2 d−1 (126 MgC d−1) to −128 mmol O2 m−2 d−1 (−946 MgC d−1) and CO2 emissions from 65 mmolC m−2 d−1 (180 MgC d−1) to 267 mmolC m−2 d−1 (740 MgC d−1). There is a significant north-south gradient in metabolic rates and CO2 fluxes attributable to the varying flow patterns and anthropogenic inputs into the estuary. The study reveals that the Cochin estuary, a previously autotrophic (CO2 sink) system, has been transformed to a heterotrophic (CO2 source) system following rapid urbanization and industrialization. Moreover, the export fluxes from the Cochin estuary appear to be quite important in sustaining net heterotrophy in the southeastern Arabian Sea.

Denitrifying Bacterial Community Composition Changes Associated with Stages of Denitrification in Oxygen Minimum Zones

Abstract: Denitrification in the ocean is a major sink for fixed nitrogen in the global N budget, but the process is geographically restricted to a few oceanic regions, including three oceanic oxygen minimum zones (OMZ) and hemipelagic sediments worldwide. Here, we describe the diversity and community composition of microbes responsible for denitrification in the OMZ using polymerase chain reaction, sequence and fragment analysis of clone libraries of the signature genes (nirK and nirS) that encode the enzyme nitrite reductase, responsible for key denitrification transformation steps. We show that denitrifying assemblages vary in space and time and exhibit striking changes in diversity associated with the progression of denitrification from initial anoxia through nitrate depletion. The initial denitrifying assemblage is highly diverse, but succession on the scale of 3-12 days leads to a much less diverse assemblage and dominance by one or a few phylotypes. This progression occurs in the natural environment as well as in enclosed incubations. The emergence of dominants from a vast reservoir of rare types has implications for the maintenance of diversity of the microbial population and suggests that a small number of microbial dominants may be responsible for the greatest rates of transformations involving nitrous oxide and global fixed nitrogen loss. Denitrifying blooms, driven by a few types responding to episodic environmental changes and distributed unevenly in time and space, are consistent with the sampling effect model of diversity-function relationships. Canonical denitrification thus appears to have important parallels with both primary production and nitrogen fixation, which are typically dominated by regionally and temporally restricted blooms that account for a disproportionate share of these processes worldwide.

Biophysical Processes in the Indian Ocean

Abstract: Basic physical processes that impact biological activity in the Indian Ocean (IO), namely, near-surface processes (upwelling, entrainment, detrainment, and advection) and subsurface circulations (shallow overturning cells and subthermocline currents), are reviewed. In the Arabian Sea, there are upwelling blooms during the southwest monsoon (SWM) along Somalia, Oman, and the west coast of India. In the central Arabian Sea, the overall SWM (northeast monsoon; NEM) blooms appear to be a series of entrainment (detrainment) blooms forced by intraseasonal winds. In the western Bay of Bengal, a prominent NEM bloom results from the entrainment of a preexisting deep chlorophyll maximum (DCM). South of Sri Lanka, the SWM bloom is caused by coastal upwelling and Ekman suction, and is swept into the Bay of Bengal by the Southwest Monsoon Current. In the tropical, South IO (5―20°S), there is a weak, surface bloom during boreal summer when new production is enhanced by nutrient entrainment; the surface bloom is even weaker (or absent) during boreal winter because the mixed layer is thinner, the thermocline is deeper, and hence, nutrient entrainment weaker. At intraseasonal timescales, blooms are associated with wind events and Rossby waves/eddies, and they can be generated by both new production and entrainment of a preexisting DCM. During the 1997/1998 El Nino―Southern Oscillation/IO zonal dipole event, there was an upwelling bloom near Sumatra/Java in fall 1997, a much deeper DCM and weaker surface bloom along 5―10°S in spring 1998, and a weaker bloom in the Arabian Sea during the SWM of 1998.

Photosynthetic performance of outdoor Nannochloropsis mass cultures under a wide range of environmental conditions

Abstract: The unicellular alga Nannochloropsis sp. (Eustigmatophyta) is a rich source of lipids, polyunsaturated fatty acids (such as eicosapentaenoic acid) and carotenoids (violaxanthin), which makes it valuable for human consumption, aquaculture and biofuel production. Mass production of Nannochloropsis sp. can be easily achieved in high-rate algal ponds (HRAP), in flat panel photobio- reactors (FPP) or in tubular photobioreactors. While easy to operate, these systems are prone to un- favorable growth conditions, which affect productivity. In the present study, we cultivated Nan- nochloropsis sp. in 2 outdoor production systems and monitored photosynthetic activity. Unfavorable conditions (stressors), such as high temperature and high pH in combination with high irradiance, were induced in FPP, causing a substantial reduction in the photosynthetic rate. The measurements of Nannochloropsis sp. photosynthetic activity using several chlorophyll fluorescence techniques as well as oxygen production measurements showed that this species is able to withstand high irradi- ance levels. Although some photodamage due to high irradiance was found, the cultures rapidly recovered. Nannochloropsis sp. coped well with high pH conditions under physiological tempera- tures. However, a temperature rise above 32°C was detrimental, with repair processes being unable to keep up with the rate of damage. The cultures in the FPP were more prone to damage by extreme temperatures than those in the HRAP due to the high surface:volume ratio, which complicated tem- perature regulation within the physiological range.

Estimating mass-wasting processes in active earth slides – earth flows with time-series of High-Resolution DEMs from photogrammetry and airborne LiDAR

Abstract: . This paper deals with the use of time-series of High-Resolution Digital Elevation Models (HR DEMs) obtained from photogrammetry and airborne LiDAR coupled with aerial photos, to analyse the magnitude of recently reactivated large scale earth slides – earth flows located in the northern Apennines of Italy. The landslides underwent complete reactivation between 2001 and 2006, causing civil protection emergencies. With the final aim to support hazard assessment and the planning of mitigation measures, high-resolution DEMs are used to identify, quantify and visualize depletion and accumulation in the slope resulting from the reactivation of the mass movements. This information allows to quantify mass wasting, i.e. the amount of landslide material that is wasted during reactivation events due to stream erosion along the slope and at its bottom, resulting in sediment discharge into the local fluvial system, and to assess the total volumetric magnitude of the events. By quantifying and visualising elevation changes at the slope scale, results are also a valuable support for the comprehension of geomorphological processes acting behind the evolution of the analysed landslides.

A comparative study of macrobenthic community from harbours along the central west coast of India.

Abstract: Harbours are heavily stressed coastal habitats characterised by high concentration of contaminant and low diversity of benthic community. The west coast of India harbours most of the major harbours compared to the east coast. Very few studies have compared the macrobenthic community between different Indian harbours. The present study was therefore conducted in three important harbour (Ratnagiri, Goa, Karwar) along the central west coast of India. The paper discusses the health status of the three harbours diagnosed using various biotic indices. Sediment samples were collected using van Veen grab (0.11 m2) on board CRV Sagar Sukti. A total of 55 macrobenthic taxa were identified and were numerically dominated by polychaete. Biomass was high (0.14–145.7 g m–2) and was made largely by echiurans (>80%). Overall, polychaete dominated the macrobenthic diversity. Opportunistic P.pinnata, Notomastus sp. and Mediomastus sp., dominated the macrobenthic community responding to the increased in the harbour. Biotic indices (Polychaete:Amphipod ratio, ABC curve and geometric class abundance) and the dominance of opportunistic species indicate that, the three harbours are under stress from anthropogenic activities.

Seasonally varying nitrogen isotope biogeochemistry of particulate organic matter in Lake Kinneret, Israel.

Abstract: Large temporal variations in the nitrogen isotopic composition (d15N) of particulate organic matter (POM) and dissolved inorganic nitrogen (DIN) species in Lake Kinneret occurred in response to seasonal phasing of dominant nitrogen cycle processes. The lowest d15N POM values (25.5%) were observed in early winter, a consequence of isotopic fractionation by chemoautotrophic microbial NH z assimilation, and during the first phase of the nitrification period, by seasonally dominant NH z oxidizers. Nitrification itself was strongly fractionating, producing 15N-depleted NO { and strongly enriching water-column NH z in 15N. Toward the end of nitrification and into the phytoplankton bloom period in later winter and early spring, there was a corresponding 15–30% jump in POM d15N because of assimilation of high-d15 NN H z . Maximal d15N POM values were thus measured during the algal blooms of Peridinium gatunense in 2004 and Debarya sp. and Microcystis sp. in 2005. Toward the end of the blooms in mid- to late spring, POM d 15 N values decreased to values similar to d 15 N for NO { (8–12%), indicating a switch to this DIN source. NO { assimilation into POM appeared to occur without isotopic fractionation. Late spring was also the denitrification period with NO { removal in the newly suboxic hypolimnion. Though d 15 NO { increased in the residual NO { , complete consumption by denitrification suggests no net effect, as supported by a lack of increase in d 15 N POM at this time. Oligotrophic conditions are found in the epilimnion in late summer and early autumn and low (3.3%) d15N POM was found during the bloom of the filamentous N2-fixing cyanobacteria Aphanizomenon ovalisporum and Cylindrospermopsis cuspis. The d15N-dissolved organic nitrogen isotopic signature at this time was significantly higher, 8–12%, suggesting a phytoplankton source from earlier in the seasonal cycle. Overall, the largest known seasonal variations in N isotope composition have been observed in Lake Kinneret, providing a uniquely useful biogeochemical tool for studying N cycling in lakes as well as detecting long-term changes in N source and cycling in response to watershed land use changes and climate change. The nitrogen and carbon isotopic composition of particulate organic matter (POM) in aquatic environments reflects and integrates the influence of biogeochemical processes in the water column and sediments, including primary production, redox-sensitive nitrogen transformations, and carbonate chemistry. Both source (allochthonous, autochthonous) and transformation processes encode information in the natural distribution of stable isotopes, making these measurements valuable in situ indicators of N

Intraseasonal response of the northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation

Abstract: A new observational record of upper-ocean currents at 15°N on the western coast of India is dominated by intraseasonal (55-110 day) variations of alongshore currents, whereas sea level at the same location has a clear seasonal signal. These observations can be interpreted within the framework of linear wave theory. At 15°N, the minimum period for planetary waves is ~90 day, meaning that intraseasonal energy is largely trapped at the coast in the form of poleward-propagating Kelvin waves, while lower-frequency signals associated with the annual cycle can radiate offshore as planetary waves. This dynamical difference results in a steeper offshore slope of sea level at intraseasonal timescale, and thus stronger geostrophic alongshore currents. A consequence is that the alongshore currents are in-phase with intraseasonally-filtered sea level near the coast, and a gridded satellite product is shown to reproduce the current variations reasonably well. The intraseasonal current variations along the west coast of India are part of basin-scale sea-level fluctuations of the Northern Indian Ocean equatorial and coastal waveguides. The wind forcing associated with this basin scale circulation closely matches surface wind signals associated with the Madden-Julian Oscillation Copyright 2009 by the American Geophysical Union.

An expeditious I2-catalyzed entry into 6H-indolo[2,3-b]quinoline system of cryptotackieine.

Abstract: A synthesis of a series of novel 6H-indolo[2,3-b]quinolines with different substituents on the quinoline ring is described. The method involves reaction of indole-3-carboxyaldehyde with aryl amines in the presence of a catalytic amount of iodine in refluxing diphenyl ether to yield indolo[2,3-b]quinolines in one-pot. The present approach provides a new route for the synthesis of polycyclic structures related to an alkaloid cryptotackieine (neocryptolepine).

Evidence of paleo–cold seep activity from the Bay of Bengal, offshore India

Abstract: [1] We report evidence of paleo–cold seep associated activities, preserved in methane-derived carbonates in association with chemosynthetic clams (Calyptogena sp) from a sediment core in the Krishna-Godavari basin, Bay of Bengal Visual observations and calculations based on high-resolution wet bulk density profile of a core collected on board R/V Marion Dufresne (May 2007) show zones of sharp increase in carbonate content (10–55 vol %) within 16–20 meters below seafloor (mbsf) The presence of Calyptogena clam shells, chimneys, shell breccias with high Mg calcite cement, and pyrite within this zone suggest seepage of methane and sulfide-bearing fluid to the seafloor in the past Highly depleted carbon isotopic values (δ13C ranges from −41 to −52‰ VPDB) from these carbonates indicate carbon derived via anaerobic oxidation of methane Extrapolated mean calendar age (∼587 ka BP) of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the U-Th based depositional age (462 ± 37 and 530 ± 16 ka) of authigenic carbonates sampled from this level, thereby constraining the younger age limit of the carbonate deposition/methane expulsion events The observed carbonate deposition might have resulted from the flow of methane-enriched fluids through the fracture network formed because of shale diapirism

Multidisciplinary investigations exploring indicators of gas hydrate occurrence in the Krishna–Godavari Basin offshore, east coast of India

Abstract: We report some main results of multidisciplinary investigations carried out within the framework of the Indian National Gas Hydrate Program in 2002–2003 in the Krishna–Godavari Basin offshore sector, east coast of India, to explore indicators of likely gas hydrate occurrence suggested by preliminary multi-channel seismic reflection data and estimates of gas hydrate stability zone thickness. Swath bathymetry data reveal new evidence of three distinct geomorphic units representing (1) a delta front incised by several narrow valleys and mass flows, (2) a deep fan in the east and (3) a WNW–ESE-trending sedimentary ridge in the south. Deep-tow digital side-scan sonar, multi-frequency chirp sonar, and sub-bottom profiler records indicate several surface and subsurface gas-escape features with a highly resolved stratification within the upper 50 m sedimentary strata. Multi-channel seismic reflection data show the presence of bottom simulating reflections of continuous to discrete character. Textural analyses of 76 gravity cores indicate that the sediments are mostly silty clay. Geochemical analyses reveal decreasing downcore pore water sulphate (SO42−) concentrations (28.7 to <4 mM), increasing downcore methane (CH4) concentrations (0–20 nM) and relatively high total organic carbon contents (1–2.5%), and microbial analyses a high abundance of microbes in top core sediments and a low abundance of sulphate-reducing bacteria in bottom core sediments. Methane-derived authigenic carbonates were identified in some cores. Combined with evidence of gas-escape features in association with bottom simulating reflections, the findings strongly suggest that the physicochemical conditions prevailing in the study area are highly conducive to methane generation and gas hydrate occurrence. Deep drilling from aboard the JOIDES Resolution during 2006 has indeed confirmed the presence of gas hydrate in the Krishna–Godavari Basin offshore.