Impact of seasonal anoxic events on phytoplankton dynamics over the Western Indian shelf: An intra- and inter-annual study.

Coastal deoxygenation impacts phytoplankton communities crucial for marine productivity. The inter- and intra-annual variability in phytoplankton communities at a shallow (27 m) station over the Western Indian Shelf (CaTS site, off Goa) during deoxygenation events of the late southwest monsoon (LSWM September-October) were studied from 2020 to 2023. The water column (0-27 m depth) experienced seasonal hypoxia/anoxia at subsurface depths (0-1.

Suboxic waters of the eastern Arabian Sea shelter secondary chlorophyll maximum dominated by heterotrophic dinoflagellate Pronoctiluca spp. (order Noctilucales).

In the present study, we investigated the dinoflagellate assemblages in the upper water column (< 150-m depth), focusing on the suboxic waters of the eastern Arabian Sea (EAS) along 68°E from 8°N to 21°N during the southwest monsoon 2020 (SWM-2020). Dinoflagellate abundance was higher in the upper water column (0-80-m depth, mean ± SD = 411 ± 903 cells L) compared to deeper waters (80-150-m depth, mean ± SD = 128 ± 216 cells L). Among 11 identified taxonomic dinoflagellate orders, Peridinales were predominant in the upper waters column (71%, mean ± SD = 285 ± 858 cells L).

Dynamics of subsurface chlorophyll maxima in the northern Indian Ocean.

Subsurface chlorophyll maxima (SCM) significantly contributes to oceanic primary productivity, emphasizing the need to study its dynamics and governing mechanisms. We used datasets from various platforms to investigate relationships between the SCM characteristics (SCM depth (Z), SCM magnitude (Chl), SCM thickness (T)) and environmental variables modulated by various physical processes in the Northern Indian Ocean (NIO). In the Arabian Sea (western NIO), seasonal processes like convective mixing and upwelling, primarily regulated the SCM characteristics.

Daylight driven vertical migration of mesozooplankton in the Arabian sea and the Bay of Bengal.

Diurnal vertical migration (DVM) of mesozooplankton in the Deep Scattering Layer (DSL) of the Indian seas is poorly studied. This cyclical vertical migration substantially controls the carbon sequestration in the ocean. The present research is a comprehensive examination to analyse the factors affecting the DVM pattern of the zooplankton community in the Arabian Sea (AS) and the Bay of Bengal (BoB).

Seasonally varying biogeochemical regime around the coral habitats off central west coast of India.

The Western Indian Continental Shelf (WICS) experiences upwelling during the Southwest Monsoon (SWM), leading to deoxygenation and acidification of subsurface waters. The region has patchy growth of corals, e.g.

Contrasting patterns in pH variability in the Arabian Sea and Bay of Bengal.

Continuous understanding of the ongoing ocean acidification (OA) is essential for predicting the future impact of OA on marine ecosystems. Here we report the results of open ocean time-series measurements (19 cruises) of seawater pH in total hydrogen ion scale (pH) and associated parameters in the Arabian Sea (AS) and the Bay of Bengal (BoB). During southwest monsoon (SWM), the pH within the 30 to 100 m water column shows the maximum difference between the two basins with BoB pH being lower (up to ~0.

Response of oceanic subsurface chlorophyll maxima to environmental drivers in the Northern Indian Ocean.

Subsurface Chlorophyll Maxima (SCM) contributes a significant proportion to depth-integrated ocean primary production, making it important to understand its spatiotemporal variability in changing environmental conditions. Based on field observations and in situ data, we studied SCM characteristics in four distinct environmental settings across Northern Indian Ocean: SEAS-south eastern Arabian Sea (coastal upwelling zone), SAS-Southern Arabian Sea (Arabian Sea mini warm pool-ASMWP), SBOB-Southern Bay of Bengal (presence of mesoscale eddies) and ANS-Andaman Sea (region of active volcanoes). SCM displayed significant spatial variability: Z (SCM depth) ranged between 25 and 88 m (mean = 59.

A study on microzooplankton community from the coastal waters of eastern Arabian Sea: emphasis on the dominance of heterotrophic dinoflagellates.

We studied the community composition of microzooplankton (MZP) from the surface waters off Candolim, Goa. The MZP communities were examined for the year 2013, covering different seasons and four stations (Near-shore: G3 & G4, offshore: G5 & G6). A total of 30 species belonging to 24 genera were recorded, which include loricate ciliates (LC: 14 species of 13 genera), aloricate ciliates (ALC: 5 species of 3 genera), heterotrophic dinoflagellates (HDS: 11 species of 8 genera), and copepod nauplii.

Applications of Machine Learning in Chemical and Biological Oceanography.

Machine learning (ML) refers to computer algorithms that predict a meaningful output or categorize complex systems based on a large amount of data. ML is applied in various areas including natural science, engineering, space exploration, and even gaming development. This review focuses on the use of machine learning in the field of chemical and biological oceanography.

Recurrence of Gonyaulax polygramma bloom in the southeastern Arabian Sea.

Gonyaulax polygramma, a bloom-forming dinoflagellate, has been repeatedly observed along the southeastern Arabian Sea in recent years. During our study in October 2021, a patch of reddish-brown water was observed in the nearshore waters off Kannur (southwest coast of India) and later identified as Gonyaulax polygramma using scanning electron microscopy (SEM) and HPLC-based phytoplankton marker pigments. Gonyaulax polygramma accounted for 99.

Rice husk as a potential source of silicate to oceanic phytoplankton.

Global oceans are witnessing changes in the phytoplankton community composition due to various environmental stressors such as rising temperature, stratification, nutrient limitation, and ocean acidification. The Arabian Sea is undergoing changes in its phytoplankton community composition, especially during winter, with the diatoms being replaced by harmful algal blooms (HABs) of dinoflagellates. Recent studies have already highlighted dissolved silicate (DSi) limitation and change in Silicon (Si)/Nitrogen (N) ratios as the factors responsible for the observed changes in the phytoplankton community in the Arabian Sea.

Light stress induced DMS(P) production in Skeletonema costatum: An experimental approach and field observation.

Dimethylsulphide is a dominant biogenic sulphur anti-greenhouse gas produced by marine phytoplankton. A non-axenic culture of Skeletonema costatum was studied to comprehend the effects of different growth stages and light stress on DMSP/DMS production. The intracellular DMSP concentration increased during late exponential to mid-stationary phase and attained a maximum (0.

Malformation in coccolithophores in low pH waters: evidences from the eastern Arabian Sea.

Oceanic calcifying plankton such as coccolithophores is expected to exhibit sensitivity to climate change stressors such as warming and acidification. Observational studies on coccolithophore communities along with carbonate chemistry provide important perceptions of possible adaptations of these organisms to ocean acidification. However, this phytoplankton group remains one of the least studied in the northern Indian Ocean.

Organic carbon dynamics in the continental shelf waters of the eastern Arabian Sea.

The seasonal and spatial distribution of total organic carbon (TOC) is presented for the coastal waters of the eastern Arabian Sea, which experiences seasonal suboxia during the late southwest monsoon (SWM). This study reveals that high TOC was observed off Kochi as compared to Goa and Mangalore transects, and may be attributed to stronger upwelling along the Kerala coast. This is also supported by the excess carbon due to upwelling during the late SWM that varied from 37 μM (Goa), 39 μM (Mangalore), to 51 μM (Kochi).

Impact of physical processes on oxygen loss and production of hydrogen sulphide and methane in a tropical freshwater reservoir.

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 variability in the low-oxygen conditions and production/accumulation of hydrogen sulphide (HS) and methane (CH) during summer. This paper presents time series data based on monthly in situ observations from a tropical reservoir (Tillari, Maharashtra) situated in the Western Ghats in India.

Meta-analysis cum machine learning approaches address the structure and biogeochemical potential of marine copepod associated bacteriobiomes.

Copepods are the dominant members of the zooplankton community and the most abundant form of life. It is imperative to obtain insights into the copepod-associated bacteriobiomes (CAB) in order to identify specific bacterial taxa associated within a copepod, and to understand how they vary between different copepods. Analysing the potential genes within the CAB may reveal their intrinsic role in biogeochemical cycles.

Total organic carbon and its role in oxygen utilization in the eastern Arabian Sea.

We report seasonal and temporal variation of total organic carbon (TOC) in the eastern Arabian Sea (AS). In comparison to the deep, TOC in the top 100 m showed spatial variation with higher concentrations towards northern AS during North east monsoon (NEM) and South west monsoon (SWM). A comparison with the US-JGOFS data (1995) shows warmer temperatures, enhanced TOC and low chlorophyll in the recent years.

Role of oceanic fronts in enhancing phytoplankton biomass in the eastern Arabian Sea during an oligotrophic period.

In the present study, using in-situ and satellite observations, we investigate the influence of physical processes on the enhancement of phytoplankton biomass in the eastern Arabian Sea (EAS). Water column measurements were carried out from 9⁰N to 21⁰N (stations II-2 to II-14) along 68⁰E transect in the EAS during the beginning of fall intermonsoon (FIM) of 2014. Both in-situ and satellite-derived chlorophyll a (Chl a) showed higher biomass at 15⁰N (station II-8) compared to northern and southern stations.

Variation in phytoplankton community and its implication to dimethylsulphide production at a coastal station off Goa, India.

Seasonal hypoxia/suboxia (at times anoxia) towards the end of Southwest monsoon (SWM; June to September) at the coastal time series site off Goa, West coast of India was found to influence the dynamics of phytoplankton biomass, community structure and production of climatically active gas, dimethylsulphide (DMS). In this diatom dominated study region, high DMS production in the subsurface waters during late SWM might possible be attributed to the stress experienced by micro- and macro-algae from the prevailing low oxygen subsurface waters through different pathways specifically believed to be via methylation pathway (see Schafer et al., 2010).

Variability of organic nitrogen and its role in regulating phytoplankton in the eastern Arabian Sea.

The relative importance of organic nitrogen (ON) and inorganic nitrogen (IN) as nitrogen sources for the phytoplankton communities were studied through a seasonal time series of nitrogen species in the eastern Arabian Sea. Seasonal data on nitrogen species showed that ON dominates the system throughout the year and account for >90% of the total nitrogen (TN) during north east monsoon (NEM). The average ON concentration in the study region was 11.

A checklist of tintinnids (loricate ciliates) from the coastal zone of India.

We report here a checklist of tintinnids (loricate ciliates) for the coastal zone of India. Based on available literature (1978 to 2017), a total of 25 stations were studied from 5 distinct areas of Indian coastal waters. A total of 151 species of 33 genera belonging to 14 families of tintinnids were documented.

Seasonal variations and relationships between environmental parameters and heavy metal concentrations in tissues of Crassostrea species and in its ambience from the tropical estuaries.

This study aimed to evaluate the relationship between physicochemical parameters and heavy metal (Cu, Ni, Pb, and Cd) concentrations from sediment, seawater, and its accumulation in tissues of oyster species (Crassostrea madrasensis and C. gryphoides) from the three sites (Chicalim Bay (CB), Nerul Creek (NC), Chapora Bay (ChB)) along the Goa coast (India). Results showed enrichment of Cu and Ni in sediment exceeding the effect range low (ERL) level.