V. Venkataramana

Bio: V. Venkataramana is an academic researcher from Esso. The author has contributed to research in topics: Biomass (ecology) & Zooplankton. The author has an hindex of 3, co-authored 8 publications receiving 24 citations.

Temperature and phytoplankton size class biomass drives the zooplankton food web dynamics in the Indian Ocean sector of the Southern Ocean

Abstract: The abundance and vertical distribution of zooplankton community structure in the mesopelagic zone are important to better understand their role in the food web dynamics in the Southern Ocean ecosystem. During the austral summer of 2015, in the Indian sector of the Southern Ocean, the vertical profiles of zooplankton community structures between 0 and 1000 m were investigated using a Hydro-Bios, Multi Plankton Sampler (200-µm mesh, 0.25 m2 mouth area). A strong contrast in terms of population structure and biovolume was observed between the Subtropical Front and the Polar Front 2. High zooplankton abundance was recorded on each transect in the Polar Front. Zooplankton abundance was numerically dominated by calanoids and cyclopoids, constituting approximately 86% of the total zooplankton count. Abundance of copepods were the highest within the mixed layer depth. Under warm, stratified conditions, surface waters were dominated by picophytoplankton. These conditions result in the zooplankton being dominated by small crustaceans. This long, inefficient food web is of poor nutritional quality, supporting a smaller biomass of higher trophic levels. In contrast, under cold and well mixed conditions, surface waters were dominated by microphytoplankton. These conditions result in the zooplankton being dominated by crustaceans, such as large copepods. This short, nutritionally rich and efficient food web supports higher trophic levels.

Biophysical Control on Variability in Phytoplankton Production and Composition in the South-Western Tropical Indian Ocean During Monsoon 2014

Abstract: The existing oligotrophic conditions in the southwest tropical Indian Ocean (SWTIO) is believed to be one of the causes for low phytoplankton productivity (PP) observed in this area. Though many remote sensing based studies on PP have been carried out in SWTIO; studies on in situ estimation of PP and its cause(s) of variability are scarce. Thus, to understand the controlling environmental forcings on the variability in phytoplankton biomass (chlorophyll-a; Chl-a), community structure and productivity, time series (TS; @6h intervals for 10 days) plus point measurements (RT) were carried out in the SWTIO during southwest monsoon (June) of 2014. Strong thermohaline stratification resulted in shallow (35-40m) mixed layer (ML). Subsurface Chl-a maximum (SCM) was observed to oscillate within 40-60m with majority of peaks at ~50m, and existed just beneath the ML depth. Light availability at the time of sampling was highly conducive for algal growth; whereas nutrient ratios indicated N- and Si-limitation suggesting unfavourable conditions for diatoms and/or silicoflagellates growth within the ML. Furthermore, HPLC-based pigments analysis confirmed dominance of nano-sized plankton (53%) followed by pico-plankton (25%) and micro-plankton (22%). Column integrated production (IPP) varied from 176 - 268 (241+43 mgC m-2 d-1) and was relatively stable during the observation period, except a low value on 11-June, which was ascribed to the drastic dropdown in the daily incident PAR due to overcast sky. Vertical profiles of PP and Chl-a resembled each other and maximum PP usually corresponded with SCM depths. The Chl-a-specific PP (PB) was mostly higher within the ML and showed no surface photoinhibition, due to the dominance of smaller phytoplankton (less prone to pigment packaging effect) in the surface layer. Comparatively, higher PB within the ML is indicative of phytoplankton healthiness during the sampling time, whereas low PB below the SCM was due to light limitation. Highest integrated Chl-a (39 mg m-2) and IPP (328 mgC m-2 d-1) observed at RT-2 was clearly linked to low sea surface height anomaly (SSHA), cyclonic disturbance and associated positive Ekman pumping. Conversely, high SSHA and strong stratification conditions prevailed at TS, RT-4 and RT-6 stations leading to comparatively low IPP.

Distribution of zooplankton in the Indian sector of the Southern Ocean

Abstract: The community composition of zooplankton with an emphasis on copepods was assessed in the frontal zones of the Indian sector of the Southern Ocean (SO) during summer 2013. Copepods were the dominant group in both the bongo net and multiple plankton sampler across the entire region. High zooplankton abundance was recorded along each transect in the Polar Front (PF). Community structure in this front was dominated by common taxa, including Ctenocalanus citer, Clausocalanus spp., Calanoides acutus, Calanus propinquus, Calanus australis and Rhincalanus gigas, which together accounted for > 62% of the total abundance. Calocalanus spp., Neocalanus tonsus and C. propinquus were indicator species in the Sub-Tropical Front (STF), Sub-Antarctic Front and PF, respectively. A strong contrast in population structure and biovolume was observed between then PF and the STF. The community structure of smaller copepods was associated with the high-temperature region, whereas communities of larger copepods were associated with the low-temperature region. Thus, it seems probable that physical and biological characteristics of the SO frontal regions are controlling the abundance and distribution of zooplankton community structure by restricting some species to the warmer stratified zones and some species to the well-mixed zone.

Phytoplankton biomass and community composition in the frontal zones of Southern Ocean

Abstract: Phytoplankton biomass (chlorophyll-a) and community structure in the water column was analyzed across various frontal regions in the Subtropical Front (STF), Sub-Antarctic Front (SAF), Polar Front-1 (PF1) and Polar Front-2 (PF2) in the Indian Ocean sector of the Southern Ocean (SO) during the austral summer (January–February) of 2013 and 2015 The surface chlorophyll-a (Chl-a) was maximum in PF1 (077 mg m−3) followed by the SAF (05 mg m−3), STF (026 mg m−3) and PF2 (021 mg m−3) in 2013 The Chl-a was maximum in the SAF (056 mg m−3) followed by PF1 (032 mg m−3), PF2 (028 mg m−3) and STF (020 mg m−3) during 2015, indicating that the average surface biomass was higher in 2013 The deep chlorophyll maximum (DCM) was located at 50 m in STF and SAF for 2013 and 2015 and was found at 75 m (100 m) in PF1 (PF2) during 2013 The diagnostic pigment (DP) index indicated that diatoms in the surface and water column increased from the STF to the PF In contrast, smaller cell community flagellates and prokaryotes decreased from the STF to PF Diatoms consistently increased from the surface to 120 m in SAF and PF, whereas flagellates were uniformly distributed throughout the water column Prokaryotes were consistently distributed down to the DCM level and then progressively declined towards deeper regions The nitrate (NO3−3-), phosphate (PO43−3-) and silicate (SiO4) increased considerably from the STF to PF through SAF Results indicate the biomass and community variation in the frontal regions were due to the influence of physical, chemical, and biological processes under varied environmental conditions

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.

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.

Toward a taxon-specific parameterization of bio-optical models of primary production : A case study in the North Atlantic : Subduction, water mass transformation, biochemical tracer distributions, and carbon cycle in the Northeast Atlantic Ocean at Mesoscale: The POMME Experiment

Abstract: [i] As part of the Programme Ocean Multidisciplinaire Meso Echelle (POMME) in the North Atlantic, an extensive data set of high-pressure liquid chromatography pigment concentrations, phytoplankton absorption coefficients, primary production measurements, and P versus E curves has been acquired. This data set is analyzed with the objective of testing whether photosynthetic performances of natural phytoplankton communities are related to taxonomic characteristics. This objective is addressed in two ways. The first approach concerns the bulk photosynthetic performances of the water column: the water column photosynthetic cross section, ψ*, equals 0.088 m 2 gChla -1 , i.e., ∼25% higher than the average for the world ocean. Using multiple regression, size-specific values of ψ* are subsequently derived: carbon storage by water column is more efficient with microphytoplankton (ψ* = 0.135 m 2 gChla -1 ) than with nanophytoplankton (0.089 m 2 gChla -1 ) or picophytoplankton (0.064 m 2 gChla -1 ). The second (independent) approach examines the correlations between photophysiological properties and several abiotic and biotic variables. The correlations are weak, if any, between photophysiological properties and abiotic factors (temperature, nitrate concentration, and irradiance), while significant correlations are reported with biotic factors (proportion of the different phytoplankton groups, average size of the phytoplankton assemblage). Our results suggest that when large phytoplankton populations predominate at the expense of smaller ones, the specific absorption coefficient is expectedly lower, while other photophysiological properties α B , P B max , and Φ cmax , are higher. The agreement between both independent approaches points out that large phytoplankton (essentially diatoms) are potentially more efficient in carbon storage than any other phytoplankton groups on a chlorophyll a or light absorption basis.