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N. Anilkumar

Bio: N. Anilkumar is an academic researcher from National Centre for Antarctic and Ocean Research. The author has contributed to research in topics: Subtropical front & Phytoplankton. The author has an hindex of 5, co-authored 22 publications receiving 75 citations.

Papers
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Journal ArticleDOI
TL;DR: 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, and abundance was numerically dominated by calanoids and cyclopoids.
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.

14 citations

Journal ArticleDOI
TL;DR: In this paper, upper layer diapycnal mixing in the Subtropical Front (STF) was estimated using microstructure shear profiles collected from the Indian sector of the Southern Ocean (ISSO) during the austral summer of 2012.

12 citations

Journal ArticleDOI
01 Jan 2019
TL;DR: In the Indian Ocean and the Southern Ocean marine boundary layer (MBL) during the 8th Indian Southern Ocean Expedition, observations of iodine oxide (IO) were made.
Abstract: Observations of iodine oxide (IO) were made in the Indian Ocean and the Southern Ocean marine boundary layer (MBL) during the 8th Indian Southern Ocean Expedition. IO was observed almost ubiquitously in the open ocean with larger mixing ratios south of the Polar Front (PF). Contrary to previous reports, IO was not positively correlated to sea surface temperature (SST)/salinity, or negatively to chlorophyll a. Over the whole expedition, SST showed a weak negative correlation with respect to IO while chl a was positively correlated. North of the PF, chl a showed a strong positive correlation with IO. The computed HOI and I2 fluxes do not show any significant correlation with atmospheric IO. Simulations with the global CAM-Chem model show a reasonably good agreement with observations north of the PF but the model fails to reproduce the elevated IO south of the PF indicating that the current emission parametrizations are not sufficient to explain iodine chemistry in the Southern Indian Ocean.

10 citations

Journal ArticleDOI
TL;DR: The high surface buoyancy observed during July–August is associated with weak stratification and deep mixed layer depth (MLD), which is a manifestation of ocean surface warming and presence of low saline surface waters in the SCTR region.
Abstract: Seychelles–Chagos Thermocline Ridge (SCTR, 5– 10S, 50–75E) in the southwestern tropical Indian Ocean is a unique area that experiences year-round upwelling. This is a response to the upward Ekman pumping prevalent in the region. Satellite data, model data and objectively analysed Argo temperature/ salinity data have been used to study the seasonal surface chlorophyll a (chl a) variability in SCTR. Variability of surface chl a concentration in SCTR showed a weak semiannual signature. The western part of SCTR (WSCTR, 50–62E) is characterized by higher chl a concentration than the eastern part (ESCTR, 63–75E). Average chl a concentration in WSCTR/ESCTR showed a primary peak in July– August (~0.26/~0.16 mg/m) and a secondary peak in January (~0.14/~0.12 mg/m). Minimum chl a concentration (~0.12/~0.1 mg/m) was observed during March– April and December–January. The high amplitude of chl a variability observed during July–August is associated with weak stratification and deep mixed layer depth (MLD). Deep MLD reaching to nutrient-rich thermocline entrains nutrients to the surface and thereby increases the surface chl a concentration. However, the low surface chl a concentration is a result of shallow MLD in the region. The deep MLD (30–40 m) observed during June–October is dominated by wind mixing and supported by buoyancy mixing. Shallow MLD (<30 m) observed during rest of the year is due to weak wind mixing and high surface buoyancy. The high surface buoyancy is a manifestation of ocean surface warming and presence of low saline surface waters in the SCTR region.

8 citations

Journal ArticleDOI
TL;DR: In this paper, the phytoplankton pigment indices were used to characterize the spatial succession of the community composition in the frontal regions of the subtropical front (STF), sub-Antarctic front (SAF), and polar front (PF) in the Indian Ocean sector of the Southern Ocean during austral summer 2013.
Abstract: The phytoplankton pigment indices were used to characterize the spatial succession of the community composition in the frontal regions of the subtropical front (STF), sub-Antarctic front (SAF), and polar front (PF) in the Indian Ocean sector of the Southern Ocean during austral summer 2013. Diagnostic indices revealed that the flagellates were dominant in STF (51%) and progressively declined toward SAF (39%) and PF (11%). Similarly, the prokaryotes were highest in STF (43%) and decreased to SAF (32%) and PF (28%). In contrast, the diatoms were gradually increased from STF (6%) to SAF (29%) and PF (61%). The variability of flagellates and diatoms from the STF to PF is attributed to the variability of photosynthetically available radiation, sea surface temperature, and sea surface wind speed. The in-situ pigment indices were then compared to the NASA Ocean Biogeochemical model that shows the similar patterns of frontal community distribution except their magnitude. Similarly, the satellite retrieved phytoplankton biomass (chlorophyll a) was checked for its consistency after comparing with the in-situ observations and the result shows underestimation of satellite measured values. The result suggests that the conjunctive analysis of in-situ, satellite, and model archive is suitable to study the impact of climate variability on the structure of marine ecosystems.

8 citations


Cited by
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01 Apr 2003
TL;DR: In this article, the authors applied residual mean theory to the streamwise-averaged Antarctic Circumpolar Current to obtain a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane.
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.

362 citations

Journal ArticleDOI
01 Nov 1966-Nature
TL;DR: Biology of the Antarctic Seas II as mentioned in this paper, edited by George A. Llano, was published by the American Geophysical Union of the National Academy of Sciences (AGEUS).
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.

226 citations

01 Dec 2005
TL;DR: 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, raising the possibility that the current warming trend 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.

194 citations

Journal ArticleDOI
TL;DR: In this article, a simple computer model captures key features of aggregate shape and size distribution reported recently from Cirrus clouds, and the results prompt a new way to plot the experimental size distributions leading to remarkably good dynamical scaling.
Abstract: Aggregation of ice crystals is a key process governing precipitation. Individual ice crystals exhibit considerable diversity of shape, and a wide range of physical processes could influence their aggregation; despite this we show that a simple computer model captures key features of aggregate shape and size distribution reported recently from Cirrus clouds. The results prompt a new way to plot the experimental size distributions leading to remarkably good dynamical scaling. That scaling independently confirms that there is a single dominant aggregation mechanism at play, albeit our model (based on undeflected trajectories to contact) does not capture its form exactly.

70 citations

01 Apr 2015
TL;DR: In this article, the authors describe the relationship between eddies and surface chlorophyll within the South Indian Ocean, and discuss possible mechanisms to explain the anomalous behavior of anticyclonic eddies.
Abstract: A unique feature of the subtropical South Indian Ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies. Off Western Australia, this anomalous behavior is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients. Further off-shore, two mechanisms have been suggested to explain the eddy/chlorophyll relationship: (i) eddies originating from the Australian coast maintain their chlorophyll anomaly while propagating westward; and (ii) eddy-induced Ekman upwelling (downwelling) enhances (dampens) nutrient supply in anticyclonic (cyclonic) eddies. Here we describe the relationship between eddies and surface chlorophyll within the South Indian Ocean, and discuss possible mechanisms to explain the anomalous behavior in light of new analyses performed using satellite chlorophyll data. We show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire South Indian Ocean basin (from 20 to 28°S), particularly in winter. Using Self Organizing Maps we analyze the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity. Our analysis suggests that multiple mechanisms may underlie the observed eddy/chlorophyll relationship. Based on Argo float data, we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies. Deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer, while shallower mixing in cyclonic eddies is expected to reduce it. This could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies.

58 citations