R.K. Naik

Bio: R.K. Naik is an academic researcher from National Centre for Antarctic and Ocean Research. The author has contributed to research in topics: Phytoplankton & Subtropical front. The author has an hindex of 9, co-authored 29 publications receiving 328 citations. Previous affiliations of R.K. Naik include National Institute of Oceanography, India & Council of Scientific and Industrial Research.

Algal blooms: a perspective from the coasts of India

Abstract: Algal blooms have been documented along the west and east coasts of India. A review of bloom occurrences in Indian waters from 1908 to 2009 points out that a total of 101 cases have been reported. A comparison of the bloom cases reported before and after the 1950s reveals that there is an increase in the number of bloom occurrences. The reports of algal blooms indicate their predominance along the west coast of India especially the southern part. Majority of the blooms reported along the west coast of India are caused by dinoflagellates, whereas diatom blooms prevail along the east coast. There have been 39 causative species responsible for blooms, of which Noctiluca scintillans and Trichodesmium erythraeum are the most common. Reporting of massive fish mortality in Indian waters has been associated with the blooming of Cochlodinium polykrikoides, Karenia brevis, Karenia mikimotoi, N. scintillans, T. erythraeum, Trichodesmiumthiebautii and Chattonella marina. Most of the blooms occurred during withdrawal of the south-west monsoon and pre-monsoon period. In Indian waters, this process is mainly influenced by seasonal upwelling and monsoonal forcing that causes high riverine discharge resulting in nutrient-enriched waters that provides a competitive edge for blooming of phytoplankton species.

Primary description of surface water phytoplankton pigment patterns in the Bay of Bengal

Abstract: Spatial and temporal variations in surface water phytoplankton pigment distribution in the Bay of Bengal were studied during the spring intermonsoon (SpIM, February–April) and the commencement of the summer monsoon (CSM, May–June), using pigment and diagnostic indices. The Prokaryotic pigment index (ProkDP) was dominant at all the oceanic stations whereas the Flagellate pigment index (FlagDP) was dominant at the near coastal stations. However, during the commencement of summer monsoon, an oscillation in the dominance of ProkDP and FlagDP was observed in the central oceanic bay, whereas flagellates and diatoms were dominant at the near coastal stations. This change in pigment pattern is possibly related to the influence of rainfall. Comparison of pigment data with microscopic cell counts indicated a significant relationship between the diatom pigment index (DiatDP) and diatom abundance. However, the relationship between the dinoflagellate pigment index (DinoDP) and dinoflagellate abundance was not significant. Studies coupling pigment composition analysis with microscopic analysis of phytoplankton in natural conditions should thus be a prerequisite in establishing valid biogeochemical and ecosystem models.

Dinoflagellate community structure from the stratified environment of the Bay of Bengal, with special emphasis on harmful algal bloom species

Abstract: Harmful algal blooms (HABs) have been documented along the coasts of India and the ill effects felt by society at large. Most of these reports are from the Arabian Sea, west coast of India, whereas its counterpart, the Bay of Bengal (BOB), has remained unexplored in this context. The unique characteristic features of the BOB, such as large amount of riverine fresh water discharges, monsoonal clouds, rainfall, and weak surface winds make the area strongly stratified. In this study, 19 potentially harmful species which accounted for approximately 14% of the total identified species (134) of dinoflagellates were encountered in surface waters of the BOB during November 2003 to September 2006. The variations in species abundance could be attributed to the seasonal variations in the stratification observed in the BOB. The presence of frequently occurring HAB species in low abundance (≤40 cell L − 1) in stratified waters of the BOB may not be a growth issue. However, they may play a significant role in the development of pelagic seed banks, which can serve as inocula for blooms if coupled with local physical processes like eddies and cyclones. The predominance of Ceratium furca and Noctiluca scintillans, frequently occurring HAB species during cyclone-prone seasons, point out their candidature for HABs.

Phytoplankton community structure at the juncture of the Agulhas Return Front and Subtropical Front in the Indian Ocean sector of Southern Ocean: Bottom-up and top-down control

Abstract: The juncture of the Agulhas Return Front (ARF) and Subtropical Front (STF) in the Indian Ocean sector of Southern Ocean (SO) is characterized by high mesoscale turbulence, which results in sporadic, short lived phytoplankton proliferation. The biota, mainly the phytoplankton community from such a complex hydrodynamic region and its response to the mesoscale turbulence, are areas of interest for investigation. Hence, during the sixth Indian expedition to SO, a two-day time series was occupied at the ARF and STF merged region (40°S 58°30′E) from 13 to 15 January, 2012. The vertical profiles of phytoplankton (based on pigment indices) indicated variation in the percentage contribution of phytoplankton functional groups (Micro, Nano and Pico). Though the overall community structure was dominated by nanoplankton, as exhibited by pigment indices and CHEMTAX analysis, drastic shifts in the community were observed at 120 m depth at six hourly intervals. The oscillation between Flagellates (nanoplankton) to prokaryotes (picoplankton) and then to diatoms (microplankton) at this depth in three consecutive observations coincided with the significant variations in phosphate and nitrate concentrations, along with increase in abundance of the grazer community (ciliates and heterotrophic dinoflagellates). From the present study, it is evident that the flagellate group is the ideal one to survive in such a complex regime. However, the observed small interval oscillation in the phytoplankton community could be a coupled effect of bottom-up (vertical advection that alters the nutrient flux), and top-down (increased abundance of microzooplankton) factors.

Phytoplankton biomass and primary production in Delagoa Bight Mozambique: Application of remote sensing

Abstract: A non-linear model that uses satellite-derived chlorophyll to estimate water-column primary production was developed and tested using data from the Delagoa Bight, where the model results compared well with local estimates. The data were also used to assess variations in phytoplankton biomass and daily water-column primary production (PZT ;m g Cm � 2 day � 1 ), in relation to physico-chemical variables. The distribution of phytoplankton biomass and primary production was partly influenced by gyre circulation and other water flow in the Bight, such as eddies, eastern Madagascar current and the Agulhas current. The locally-developed model could be applied throughout the region to estimate primary production. For low biomass (<0.3 mg m � 3 ), the model tends to underestimate PZT in a systematic way. However, such bias could be corrected using a 5th-order polynomial function. After this correction, the PZT estimated using remotely-sensed chlorophyll a compared well with that calculated using in situ measurements. This outcome suggests that the model could be implemented for the estimation of mesoscale (regional) or large-scale (global) primary production. 2007 Elsevier Ltd. All rights reserved.

Residual-mean solutions for the Antarctic Circumpolar Current and its associated overturning circulation

Abstract: Residual-mean theory is applied to the streamwise-averaged Antarctic Circumpolar Current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane. Simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated (residual) meridional overturning circulation.

Parameters of photosynthesis: definitions, theroy and interpretation of results

Abstract: A global assessment of carbon flux in the world ocean is one of the major undertakings of the Joint Global Ocean Flux Study (JGOFS). This has to be undertaken using historical in situ data of primary productivity. As required by the temporal and spatial scales involved in a global study, it can be conveniently done by combining, through appropriate models, remotely sensed information (chlorophyll a, temperature) with basic information about the parameters related to the carbon uptake by phytoplanktonic algae. This requires a better understanding as well as a more extended knowledge of these parameters which govern the radiative energy absorption and utilization by algae in photosynthesis. The measurement of the photosynthetic response of algae [the photosynthesis (P) versus in-adiance (£) curves], besides being less shiptime consuming than in situ primary production experiments, allows the needed parameters to be derived and systematically studied as a function of the physical, chemical and ecological conditions. The aim of the present paper is to review the significance of these parameters, especially in view of their introduction into models, to analyze the causes of their variations in the light of physiological considerations, and finally to provide methodological recommendations for meaningful determinations, and interpretation, of the data resulting from /"versus £ determinations. Of main concern are the available and usable irradiance, the chlorophyll a-specific absorption capabilities of the algae, the maximum light utilization coefficient (a), the maximum quantum yield (4>m), the maximum photosynthetic rate (Pm) and the light saturation index (£k). The potential of other, non-intrusive, approaches, such as the stimulated variable fluorescence, or the sun-induced natural fluorescence techniques is also examined.

Nitrogen in the sea : forms, abundances, and rate processes

Abstract: INTRODUCTION. A HISTORICAL OVERVIEW OF NITROGEN STUDY IN THE SEA. Determination of Nitrogenous Compounds in the Sea. Biological Transformation of Nitrogen. Stoichiometric Model of Organic-Matter Mineralization. Natural 15N Abundance. THE NITROGEN CYCLE. PHYSICO-CHEMICAL PROPERTIES OF NITROGEN. PROPERTIES OF THE NITROGEN ATOM AND BONDING. THERMODYNAMIC FUNCTIONS OF NITROGEN. BIOGEOCHEMICAL SKETCH OF NITROGEN. NITROGEN ISOTOPES. GENESIS OF ISOTOPES OF LIGHT ELEMENTS. ISOTOPE ABUNDANCE AND FRACTIONATION. ISOTOPIC EXCHANGE REACTIONS. KINETIC ISOTOPE EFFECTS. OVERALL ISOTOPIC FRACTIONATION. One-Step Reaction. Unidirectional Two-Step Reaction at Steady State. Two-Step Reaction with a Reversible First Step at a Steady State. Three-Step Reactions. Multistep Reactions. ISOTOPIC EXCHANGE EQUILIBRIA OF NITROGEN. NITROGEN KINETIC ISOTOPE EFFECTS DURING NITRATE REDUCTION. Chemical Systems. Biological Systems. ISOTOPE FRACTIONATION IN BRANCHED REACTIONS AND ITS ECOLOGICAL SIGNIFICANCE. ISOTOPE MASS BALANCE IN MARINE ECOSYSTEMS. Two-Source Model. Three-Source Model. COMPONENTS, SYSTEMS, AND PROCESSES. NITROGENOUS COMPOUNDS IN THE SEA: ABUNDANCE, SOURCES, AND SINK. PHYSICAL FACTORS. Water Movement and Mixing of Water. Solar Radiation. Effects of Temperature and Pressure on Chemical and Biochemical Reactions. Nitrogen Supply by River Runoff and Precipitation. CHEMICAL FACTORS. Chemical Behavior of Nitrogenous Compounds in the Sea. Hydrogen Ion Concentration. Oxidation-Reduction Potential. BIOCHEMICAL PROCESSES. Nitrogen Uptake and Assimilation. Mineralization. Nitrification. Nitrate Respiration and Denitrification. N2 Fixation. ABUNDANCE AND DISTRIBUTION OF NITROGEN IN THE SEA AND THEIR PHYSICAL, CHEMICAL, AND BIOCHEMICAL REGULATION. ROLES OF THE OCEAN IN THE GLOBAL NITROGEN CYCLE. The Buildup of the Biogeochemical Cycle. Nitrogen Inventories. Nitrogen Budgets. DISSOLVED NITROGEN GAS. Atmospheric Pressure. Occlusion of Air Bubbles. Effect of Mixing of Different Water Masses. Biological Effects. AMMONIUM, NITRITE, AND NITRATE. Distribution of Ammonium. Distribution of Nitrite. Distribution of Nitrate. NITROUS OXIDE. UREA. OTHER NITROGENOUS COMPOUNDS IN A WATER COLUMN. NITROGEN UPTAKE BY PHYTOPLANKTON. MECHANISM OF FORMATION OF THE PRIMARY NITRITE MAXIMUM. Nitrification in the Sea. Nitrite Production from Nitrate by Microalgae. Nitrite Assimilation. Formation of Primary Nitrite Maximum. NITROGEN DYNAMICS IN VARIOUS OCEANIC SYSTEMS. HIGH LATITUDINAL AREAS RICH IN NITRATE. OLIGOTROPHIC AREAS. Kuroshio Area. Anticyclonic Gyre Off Shikoku. SUBTROPICAL AND TROPICAL AREAS WITH SUPPLY OF NITRATE. Upwelling Region. Regional Upwelling. SEA AREAS WHERE NITROGEN FIXATION OCCURS. Trichodesmium Ecosystems. Local Ecosystems Characterized by N2 Fixation. SUBSURFACE ECOSYSTEMS. Decomposition of Organic Matter in the Subsurface Water. Nitrogen Diagenesis in Sediments. SEA AREAS WHERE DENITRIFICATION OCCURS. Denitrification in the Subsurface Water. Marine Sediments. NEAR SHORE AND ESTUARINE SYSTEMS. Flooded Soil Ecosystems. Tokyo Bay. VARIATION OF 15N/14N IN NITROGEN CYCLING AND ITS SIGNIFICANCE IN MARINE ENVIRONMENTS. ISOTOPE FRACTIONATION IN THE NITROGEN CYCLE. Isotope Exchange Reactions. Fractionation in Biological Metabolic Processes. DISTRIBUTION OF 15N IN NATURE. General Patterns of 15N Distribution. 15N in Antarctica. 15N Abundance and the Biogeochemical Cycle. INTEGRATED NITROGEN ISOTOPE FRACTIONATION IN ECOSYSTEMS. Enrichment of 15N in a Feeding Process. d15N-d13C Relationship. MARINE ECOSYSTEMS. Phytoplankton and Particulate Organic Matter. The Area Characterized by N2 Fixation. Isotope Biogeochemistry of the Antarctic Ecosystem. Dentrification in the Marine Aquatic System as Investigated Based on 15N Abundance Data. 15N and 13C Abundance in River, Estuarine, and Coastal Areas. Seabird Rookeries. The Deep-Sea World. Animal Behavior. FUTURE STUDIES ON NITROGEN DYNAMICS. HUMAN IMPINGEMENT ON THE NITROGEN CYCLE IN MARINE SYSTEMS. Long-Term Effects. Short-Term Effects. A NEW PARADIGM. Isotope Biogeochemistry. From Components to Systems. REFERENCES. INDEX.

Biology of the Southern Ocean

Abstract: Biology of the Antarctic Seas II Edited by George A. Llano. (Antarctic Research Series, Vol. 5. Publication No. 1297.) Pp. xi + 280. (Washington, D.C.: American Geophysical Union of the National Academy of Sciences—National Research Council, 1965.) $12.

Warming of the Eurasian Landmass is Making the Arabian Sea More Productive

Abstract: The recent trend of declining winter and spring snow cover over Eurasia is causing a land-ocean thermal gradient that is particularly favorable to stronger southwest (summer) monsoon winds. Since 1997, sea surface winds have been strengthening over the western Arabian Sea. This escalation in the intensity of summer monsoon winds, accompanied by enhanced upwelling and an increase of more than 350% in average summertime phytoplankton biomass along the coast and over 300% offshore, raises the possibility that the current warming trend of the Eurasian landmass is making the Arabian Sea more productive.