S.W.A. Naqvi

S.W.A. Naqvi

PhD

About

287
Publications
74,583
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13,000
Citations
Citations since 2017
64 Research Items
6404 Citations
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201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
Introduction
Biogeochemical cycling in low-oxygen aquatic environments both in the sea and on land, especially nitrogen cycling and production and consumption of greenhouse gases (methane and nitrous oxide)

Publications

Publications (287)
Article
Full-text available
The redox speciation of iron was determined during the iron fertilization LOHAFEX and for the first time, the chemiluminescence assay of filtered and unfiltered samples was systematically compared. We hypothesize that higher chemiluminescence in unfiltered samples was caused by Fe(II) adsorbed onto biological particles. Dissolved and particulate Fe...
Article
Full-text available
Complex interactions between microbial communities and geochemical processes drive the major element cycles and control the function of marine sediments as a dynamic reservoir of organic matter. Sulfate reduction is globally the dominant pathway of anaerobic mineralisation and is the main source of sulfide. The effective re-oxidation of this sulfid...
Article
The Arabian Sea encompasses oxygen minimum zone with denitrifying conditions. For the present study, sediments were collected across three transects off Goa transect (GT), Mangalore transect (MT) and Kochi transect (KT) in contact with water column dissolved oxygen (DO) range of 1.4–118.0 µM. Sediments were investigated for texture, clay mineralogy...
Article
Continuous measurements of hydrographic, hydrodynamic, and water quality showed marked diurnal, tidal, and seasonal variabilities in Kuwait Bay, a stressed coastal system in the northwestern Arabian/Persian Gulf. Advection of water masses and seasonality in vertical mixing regulated the Bay's hydrographic and water quality properties. Intensive str...
Conference Paper
The northwestern Arabian/Persian Gulf of Kuwait is a distinguished shallow and landlocked marine environment where hydrography and biogeochemistry changes biannually due to unique climatic conditions. In recent years, this system suffered severe anthropogenic stress due to reduction in riverine discharges, rapid urbanization, dumping of domestic se...
Article
A series of flash floods that swamped urban drainage systems in Kuwait in November-December 2018 drastically altered coastal hydrography. The phytoplankton responded quickly to the nutrient supply from land and reduced salinity despite elevated turbidity, as evident from rapid increases in chlorophyll a and net community production. Microphytoplank...
Article
Full-text available
In this paper, we outline the need for a coordinated international effort toward the building of an open-access Global Ocean Oxygen Database and ATlas (GO2DAT) complying with the FAIR principles (Findable, Accessible, Interoperable, and Reusable).
Article
Full-text available
The diverse physicochemical conditions prevailing in the Arabian Sea are expected to result in marked spatial variations in heterotrophic flagellate (HF) and ciliate communities. Here, we report the environmental association of heterotrophic micro-eukaryotes, particularly the heterotrophic flagellates and ciliates, based on 18S rRNA gene survey in...
Article
The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-spec...
Article
The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-spec...
Article
Full-text available
A correction to this paper has been published: https://doi.org/10.1007/s10661-021-08983-6
Article
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Carbon neutrality of tropical reservoirs is a big concern in recent years as some estimates project high methane emission from these reservoirs. While there are studies available on the impact of physical processes (stratification and mixing) on the biogeochemistry of tropical reservoirs, not much information is available on the inter-annual variab...
Article
Full-text available
This article describes oxygen distributions and recent deoxygenation trends in three marginal seas – Persian Gulf and Red Sea in the Northwestern Indian Ocean (NWIO) and Andaman Sea in the Northeastern Indian Ocean (NEIO). Vertically mixed water column in the shallow Persian Gulf is generally well-oxygenated, especially in winter. Biogeochemistry a...
Article
Phytoplankton are the primary producers in all the aquatic ecosystems and play an important role in key biogeochemical processes that are linked to the higher trophic levels and climate variability. The present study deals with the phytoplankton dynamics, biomass and physicochemical features in freshwater reservoir, Tillari, western India. The rese...
Article
Full-text available
The western Indian continental shelf houses the world’s largest naturally formed coastal low-oxygen zone that develops seasonally during the summer monsoon. We investigated multiple reductive nitrogen transformation pathways and quantified their rates in this system through anaerobic incubations with additions of 15N-labeled substrates during the a...
Article
The LOHAFEX iron fertilization experiment consisted in the fertilization of the closed core of a cyclonic eddy located south of the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. This eddy was characterized by high nitrate and low silicate concentrations. Despite a 2.5 fold increase of the chlorophyll-a (Chl-a) concentrations,...
Article
Full-text available
Repeat observations over the Kochi and Mangalore shelves of the southeastern Arabian Sea (SEAS) during April to December 2012 revealed substantial accumulation of methane (CH4) in the nearshore waters (48.6±34.4 nM) compared to the outer shelf (2.9±0.7 nM). Sediment methanogenesis and estuarine discharge appear to be the major sources of CH4 in the...
Article
We report here results of a time series study carried out to understand seasonal variability of phytoplankton in relation to changes in dissolved oxygen based on observations at the Candolim Time Series (CaTS) station located in coastal waters of Goa, Central West Coast of India. The water column remains well oxygenated during the non-southwest (SW...
Presentation
Full-text available
Benthic-pelagic coupling is an important feedback mechanism which keeps estuarine and shelf ecosystems productive, apart from nutrient input through terrestrial run-off, atmospheric deposition and coastal upwelling. Although, numerous studies on this aspect has been carried out in the temperate regions, there is still a meagre understanding of biog...
Article
Full-text available
Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-changing socioeconomic needs and require coordinated implementation. The upper oxycline (transition between high and low oxygen waters) is fundamentally important for the ecosystem structure and can be a useful proxy for multiple observing objectives con...
Article
Monthly measurements of nitrate, nitrite, ammonium and phosphate at three stations off Kuwait during 2002–2015 revealed considerable inter-annual variability, broadly corresponding to fluctuations in the Shatt-al-Arab River discharge, but a lack of secular increasing trend. Nutrient enrichment experiments during two seasons revealed nitrate uptake,...
Article
Concentrations of total dimethylsulphoniopropionate (DMSPt), Dimethylsulphide (DMS) and total dimethylsulphoxide (DMSOt) were measured at a coastal time series site, west coast of India, from September 2009 to December 2013. While, DMSPt varied between 0.35 and 252 nM (avg. 24 ± 32.3 nM), DMS varied from 0.5 to 442 nM (avg. 22.5 ± 48.3 nM). The ann...
Poster
The present study was to evaluate the ciliate community structure in different spatial sites of Arabian Sea (open ocean, continental shelf, coastal and estuarine waters) through Next-generation sequencing(NGS) approach.
Article
The Mandovi Estuary, located along the tropical west coast of India, transforms from being a freshwater-dominated body during the monsoon season to a tide-dominated system during post-monsoon season, with a salinity gradient developing from the freshwater end to the estuarine mouth (∼0–33). The sulphate reduction (SR) rates were measured by the 35S...
Article
The Mandovi Estuary, located along the tropical west coast of India, transforms from being a freshwater-dominated body during the monsoon season to a tide-dominated system during post-monsoon season, with a salinity gradient developing from the freshwater end to the estuarine mouth (∼0–33). The sulphate reduction (SR) rates were measured by the ³⁵...
Article
Eukaryotic microbes inhabiting diverse ecological niches are capable of mediating biogeochemical shifts. Here, we studied the distribution patterns of protistan community in oxygen-deficient sites in the Arabian Sea and nearby estuarine waters. Protist diversity was quantified through Illumina Miseq sequencing of the V4 region of 18S rRNA gene ampl...
Article
Most of the available information about basin-wide chemical processes in the Arabian Gulf is based on observations made during the expeditions of the Research Vessels Meteor (1965), Atlantis II (1977) and Umitaka-Maru (1993–1994) with the ongoing national programs in shallow territorial waters largely focusing on local environmental issues. Despite...
Article
The causes of organic-rich sediments in contact with the perennial oxygen minimum zone (OMZ) on the continental slope off western India have been debated extensively, largely in relation to two main controlling factors: high productivity in the water column and enhanced preservation due to oxygen deficiency in bottom waters. In order to better unde...
Article
Biological production in aquatic systems is often nitrogen limited. Nitrogen (N2) fixation is an important contributor to nitrogen requirement of phytoplankton not only in oligotrophic but also in nutrient-replete waters. However, the importance of N2 fixation in meso-polyhaline estuaries is not well known. Here we report significant N2 fixation ra...
Article
Full-text available
Mudbanks, a unique coastal oceanographic phenomenon occurring along the southwest (SW) coast of India during the SW monsoon season, are synonymous with the fishery of this region. Here we examine the validity of the popular notion that mudbanks directly support rich fisheries, using a high temporal resolution water column data collected from the Al...
Article
Full-text available
The genesis of phytoplankton blooms and the fate of their biomass in iron-limited, high-nutrient−low-chlorophyll regions can be studied under natural conditions with ocean iron fertilization (OIF) experiments. The Indo-German OIF experiment LOHAFEX was carried out over 40 d in late summer 2009 within the cold core of a mesoscale eddy in the product...
Cover Page
Full-text available
A flock of egrets/cranes during their flight in the mud bank (chakara) region off Alappuzha, Kerala, India. Mud bank forms in several stretches of Kerala coast mostly during the Southwest Monsoon (June - September). Mud bank, being calm with smooth sea surface, acts mainly as launching/landing place and safe anchorage for fishing vessels to exploit...
Article
Full-text available
Mud banks (Chakara) of Kerala are calm coastal waters that form in several isolated stretches along the coast usually during the southwest monsoon (SWM) period (June–September). They are characterized by the damping of incident waves, generating localized calm sea environment conducive for fishing activities, while the high monsoon waves create hos...
Article
The continental slope of India is exposed to an intense perennial oxygen minimum zone (OMZ) supporting pelagic denitrification. Sediments that are presently in contact with the lower boundary of the denitrification zone indicate marked changes in the intermediate and bottom waters ventilation of OMZ during the past 9,500 years. The δ¹⁵N of sediment...
Article
The Western Continental Shelf of India experiences water-column anoxia during late summer/early autumn, thereby providing conducive conditions for methane (CH4) accumulation. Measurements of CH4 along with other ancillary physico-chemical variables were made during the period of anoxia (September–October) in 2003, 2005 and 2009. The shelf waters ex...
Article
Measurements of total organic carbon (TOC) for two years in Kuwaiti waters showed high TOC levels (101.0–318.4, mean 161.2 μM) with maximal concentrations occurring within the polluted Kuwait Bay and decreasing offshore, indicating substantial anthropogenic component. Analysis of winter-time data revealed a large increase in density over the past f...
Article
Full-text available
The fate of the enormous amount of reactive nitrogen released to the environment by human activities in India is unknown. Here we show occurrence of seasonal stratification and generally low concentrations of dissolved inorganic combined nitrogen, and high molecular nitrogen (N2) to argon ratio, thus suggesting seasonal loss to N2in anoxic hypolimn...
Article
Full-text available
Considering Alappuzha Mud Bank in the southern Kerala coast as a typical case of biologically productive Mud Banks that form along the southwest coast of India during the Southwest Monsoon (June - September), the present study addresses several pertinent missing links between the physical environment in Mud Banks and their influence on plankton sto...
Article
Phytoplankton abundance and composition in two contrasting physical regimes - convective mixing in the northeastern Arabian Sea (NEAS) and Arabian Sea mini warm pool (ASMWP) in the southeastern Arabian Sea (SEAS) - were investigated during the northeast monsoon (NEM) of 2015 and 2017. Observations in 2015 were carried out late during the season, an...
Article
Full-text available
Beneath the waves, oxygen disappears As plastic waste pollutes the oceans and fish stocks decline, unseen below the surface another problem grows: deoxygenation. Breitburg et al. review the evidence for the downward trajectory of oxygen levels in increasing areas of the open ocean and coastal waters. Rising nutrient loads coupled with climate chang...
Article
Seasonal variation in POC export flux, from the upper ocean, was studied during post southwest monsoon (October–November 2013) and spring intermonsoon (May 2014) at selected locations in the central and southern Arabian Sea and during northeast monsoon (January 2014) and spring intermonsoon (March 2014) in the northern Bay of Bengal. POC fluxes est...
Article
The LOHAFEX iron fertilization experiment was conducted for 39. days in the closed core of a cyclonic mesoscale eddy located along the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. Mixed layer (ML) waters were characterized by high nitrate (~. 20. μM), low dissolved iron (DFe ~. 0.2. nM) and low silicate concentrations (below...
Article
An analytic gap exists between the lower limit of detection of oxygen (O2) by conventional sensors (LOD, ~1 − 3 µM O2) and the appearance of NO2– from NO3– reduction (~0.05 µM O2), which signifies the secondary nitrite maximum. The near-anoxic milieu where precise O2 measurements could not be made until very recently even by current optodes, favors...
Article
Estuaries are known to be important sources of methane (CH4) to the atmosphere. However, a lack of adequate field studies in understanding the sources/sinks of CH4 in estuaries hampers the global atmospheric budgeting. Therefore, more studies are needed to bridge the gap and improve our understanding of fluxes of CH4 to the atmosphere. We report he...
Article
The Arabian Sea experiences bloom of the diazotroph Trichodesmium during certain times of the year when optimal sea surface temperature and oligotrophic condition favour their growth. We measured nitrogen fixation rates in the euphotic zone during one such event in the Eastern Arabian Sea using 15 N 2 tracer gas dissolution method. The measured rat...
Article
Full-text available
The seasonal upwelling along the west coast of In-dia (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, favoring very low oxygen concentrations in the surface waters during late boreal summer and fall. This yearly-recurring coastal hypoxia is more severe during some years, leading to coastal anoxia that has strong...
Article
Coastal upwelling and mud banks are two oceanographic processes concurrently operating along certain stretches of the southwest (Kerala) coast of India during the Southwest Monsoon period (June–September), facilitating significant enhancement in plankton biomass. Mud banks have scientific and societal attention from time immemorial, predominantly d...
Article
Full-text available
Isotopic composition of nitrate (δ¹⁵N and δ¹⁸O) and particulate organic matter (POM; δ¹⁵N and δ¹³C) were measured in the Tillari Reservoir, located at the foothills of the Western Ghats, Maharashtra, western India. The reservoir, which is stratified during spring-summer and autumn seasons but gets vertically mixed during the southwest monsoon (SWM)...
Article
Full-text available
Repeat measurements of dissolved nitrous oxide (N2O) along two transects of the western continental shelf of India in 2012 revealed high concentrations of 45±32 nM (off Kochi) and 73±63 nM (off Mangalore) during the summer monsoon (SM). N2O concentrations increased non-linearly during the peak of the SM upwelling, when low O2 (<25 µM) conditions pr...
Article
Full-text available
A third or more of the fixed nitrogen lost from the oceans as N2 is removed by anaerobic microbial processes in open ocean oxygen minimum zones. These zones have expanded over the past decades, and further anthropogenically induced expansion could accelerate nitrogen loss. However, in the Bay of Bengal there has been no indication of nitrogen loss,...
Article
Time series measurements on suspended particulate matter (SPM) were made at one non-mud bank (M1) and two mud bank stations (M2 and M3) off Alleppey, south west coast of India. The mean SPM was low in surface (6.2 mg/l) and mid-depth (3.7 mg/l) waters and higher in bottom-depth waters (24.6 mg/l) of these stations, during both pre-monsoon and monso...
Article
Full-text available
The mudbank formation along south-western Indian coast has been a scintillating phenomenon during monsoon season, and the source of mud is a debatable issue till now. In the midst of many hypotheses, the subterranean passage is considered a possible one but needs to have supportive scientific evidence. This present study endeavours to demonstrate t...
Article
Full-text available
Effects of the cyclonic storm Phyan, which hit the states of Goa and Maharashtra in western India during 9-12 November 2009, on coastal waters were studied. Mixing induced by the cyclone appreciably affected the vertical thermohaline structure, composition and growth of plankton. The phytoplankton biomass increased by a factor exceeding 4, and a sh...
Article
Full-text available
Isotopic composition of nitrate (δ15N and δ18O) and particulate organic matter (POM) (δ15N and δ13C) were measured in Tillari Reservoir, located at the foothills of the Western Ghats, Maharashtra, western India. The reservoir that is stratified during spring-summer and autumn seasons but gets vertically mixed during the Southwest Monsoon (SWM) and...
Article
Monsoon-induced coastal upwelling, land run-off, benthic and atmospheric inputs make the western Indian shelf waters biologically productive that is expected to lead to high rates of mineralisation of organic matter (OM) in the sediments. Dissimilatory sulphate reduction (SR) is a major pathway of OM mineralisation in near-shore marine sediments ow...
Article
The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters 10 to the continental shelf, leading to very low oxygen concentrations at shallow depths during late boreal summer and fall. This yearly-recurring coastal hypoxia is sometimes more severe, leading to coastal anoxia that has strong impacts...