First molecular confirmation and new record of the rare deep-sea cirrate octopod Opisthoteuthis philipii Oommen 1976 from the Arabian Sea, India

ABSTRACTThis study investigates the timescale variability of key atmospheric and oceanic variables in the Arabian Sea (AS) using 45 years (1979–2023) of data. Analyzing sea surface temperature (SST), wind components, precipitation, significant wave height, and peak wave period, notable regional and seasonal variations are identified. The northern AS experiences the highest surface warming at a rate of 0.15°C per decade. The westerlies have strengthened in the southwestern AS, while the northern AS displays a weakening trend. Along the northwest coast of India, the northerlies have intensified, but along the southwest coast of India, they have weakened. Precipitation trends have significant increases only along the southwest and northwest coasts of India. The significant wave height has increased across much of the AS, with a pronounced rise observed near the Somali coast (about 0.2 cm per year), and the peak period in the eastern AS has decreased, indicating a decline in long‐period swells from the south. Even though this basin is strongly influenced by seasonal signals, the interannual variations in wave height anomalies are particularly significant in the central AS. Seasonal analysis reveals that the wave height in the central AS has a decreasing trend in June and August, despite being the peak monsoon months. This decrease corresponds with a similar decreasing trend in SST and westerlies, as well as an increase in the peak wave period. The study further explores the influence of dominant climate modes, such as the Indian Ocean Dipole (IOD) and El Niño‐Southern Oscillation (ENSO), on the AS climate. Even though the phase agreement between IOD and ENSO is relatively good (r = 0.67) during the study period, the years 1997 and 2023 have notable differences in the meridional wind patterns, which in turn influence the significant wave height. These findings emphasise the need for adaptive strategies to address the impacts of climate variability and long‐term trends on the marine environment of the AS.

While in recent years much attention has been focused on tsunamis in the Indian Ocean, generated near Indonesia, equally destructive tsunamis also could occur in the western part of the North Indian Ocean. Specifically, the last major tsunami in the Arabian Sea occurred in November 1945 due to an earthquake that originated in the Makran region. The Tunami N2 model was used to simulate numerically the tsunami propagation, run-up, and inundation on the southwest coast of India and selected locations in the Lakshadweep islands in the Arabian Sea. The simulations show that the run-up due to the 1945 Makran tsunami along the southwest coast of India and Lakshadweep islands was considerably less than that of the 2004 Sumatra tsunami.

Changes in the dynamical, thermodynamical and hydrometeor characteristics prior to extreme rainfall events along the southwest coast of India in recent decades

Radiological dose and associated risk due to 210Po in commercial inter-tidal bivalves of southwest (Arabian Sea) coast of India

Dominance of coastal upwelling over Mud Bank in shaping the mesozooplankton along the southwest coast of India during the Southwest Monsoon

The tsunami of December 26, 2004 was an eye-opener which exposed the need for establishing a tsunami warning system in the Indian Ocean. Immediately after the tsunami of 2004, Government of India subsequently established a Tsunami Warning Centre in Hyderabad. The numerical modelling of tsunami inundation and run-up also gained momentum in India. Besides inundation and run-up there are several other physical oceanographic processes which contributes in shaping tsunami characteristics along the coast. The source of tsunami generation is prominent in determining run-up values. Historical records show the generation of tsunamigenic earthquakes from Sumatra, North Andaman and Car Nicobar in the Bay of Bengal and Makran in the Arabian Sea. Though the numerical modelling studies has been reasonably carried out for the main land coast, no study has been exclusively carried out for understanding the amplification pattern occurring in gulfs and ports in the Arabian sea. Tsunami waves entering the ports and gulfs can lead to different amplification patterns. At this juncture, this paper investigates the pattern of amplification occurring along four representative sectors along the west coast namely Gulf of Kutch, Gulf of Khambhat, Mangalore port and Cochin inlet. The simulation results show trivial amplification in Gulf of Kutch and Gulf of Khambhat. The studies of numerical simulation suggest that the amplification factor depends on several other factors like orientation of the coast, coastal geometry of bays and gulfs, near shore bathymetry and depth inside gulfs and ports. How to cite this article: Praveen SS. Numerical Simulation Studies about the Resonance of Tsunami Waves in Selected Gulfs and Ports along the South West Coast of India (SWCI). J Adv Res Appl Mech Compu Fluid Dyna 2020; 4(1): 1-5. DOI: https://doi.org/10.24321/2349.7661.202001

Mudbanks (MBs) are a natural phenomenon, forming along the southwest coast of India during southwest monsoon (SWM), almost every year. High waves initiate these formations. The temporal variability (both intra-annual and multi-decadal) of wave climate of the southeastern Arabian Sea (AS) is related to main climate indices which determine climate fluctuations in this region, and based on that, occurrence of MBs is illustrated. Voluntary Observing Ships data and climate indices such as El Niño phenomenon index for the site 5N-5S and 170W-120W (NINO3.4), El Niño/Southern Oscillation (ENSO), Southern Oscillation Index (SOI), Pacific Decadal Oscillation (PDO), AAO, Atlantic Multi-decadal Oscillation (AMO), and IO Dipole (IOD) have been analyzed. Using wavelet correlation method, high correlations with positive and negative phase of climatic indices (IOD, SOI, NINO3.4, ENSO, AMO, PDO, and AAO) fluctuations in heights of wind waves and swell and time lags between them on monthly, yearly, decadal, and multi-decadal time scales are identified. For the first time, high correlation between the annual fluctuations of AMO and monthly average wave heights is shown. It has been found that the El Niño phenomenon plays a major role in the variability of wave climate of the southeastern AS for all time scales. A strong variability in wave climate at short time scales, such as 0.5, 1, 3.0–3.5, 4–5, and 7–8 years, is evident from the analyses. Decadal changes correspond to 10, 12–13, and 16 years. The influence of El Niño is manifested with a delay of several months (3–6) on annual time scales and about 1–2 years on a decadal and multi-decadal time scales. Possible connection between the occurrence of MBs and variability in wave climate in the southeastern AS is shown for the periods 7, 10–12, 18–20, and about 40 years correlating with fluctuation in the climate indices—IOD, ENSO, NINO3.4, and SOI. It is shown that intra-annual fluctuations in occurrence and duration of existence of MBs depend on the distribution of highest monthly averaged significant wave heights (SWHs) in the summer monsoon cycle.

The life cycle and the large‐scale factors driving extreme heavy rainfall events over the south west coast of India are studied. The extreme rainfall events are linked to the development of monsoon depressions and the associated large‐scale dynamics. Strengthening of these parameters intensifies the monsoon low‐level circulation over the Arabian Sea and the west coast via steepened meridional pressure gradient. The intensification of the low‐level jet stream speed and its extension in the vertical causes an increase in the humidity flux in the lower and midtroposphere. The consequent ascending motion is from the midtroposphere to the upper troposphere, resulting in the formation of deep convective cloud clusters over the west coast and eastern parts of the Arabian Sea. This results in the incidence of extreme heavy rainfall over the south west coast of India. It is observed that during days of extreme rainfall, the direction of wind in the lower troposphere tends to be almost perpendicular to the Western Ghats favouring a strong orographic lift. The extreme rainfall events over the south west coast do not necessarily occur during the active cycle of monsoon intraseasonal oscillation, but are linked to the north westwards propagating monsoon depressions. We show that the signatures of extreme rainfall can be observed in several meteorological variables developing over different parts of the monsoon region. A synergistic analysis of these variables may help in the accurate and timely prediction of these events.

Discriminating the biophysical impacts of coastal upwelling and mud banks along the southwest coast of India

Mudbank is a unique phenomenon observed along the south-west coast of India among all the Indian coastal regions during the Southwest Monsoon Season. The scientific reasons behind the formation and its persistence are vague. Mudbank is considered as a boon to the fishermen of Kerala, as they are getting reasonable catches during the occurrence of mudbanks using indigenous boats from the calm sea, which otherwise is in a fury during the rough Southwest Monsoon Season. Since the region, the Arabian Sea, is significant as a carbon sink due to its very high productivity because of different coastal ocean features, variations in the smaller and highly restricted coastal processes due to climate change can have a significant impact on the rates of global warming. Here, we consolidate the previous publications on various aspects of mudbanks with the reports of the occurrence of mudbanks on the south-west coast of India. A model for the prediction of the formation and location of mudbanks, inclusive of all the intrinsic and extrinsic parameters involved, through an extensive study is much relevant as far as the socio-economic and food security significance is concerned. Here, we discuss the most conducive factors for the formation of mudbank and its characteristics with special reference to Alappuzha, where the frequency of occurrence of mudbanks is maximum among the Indian coastal regions.

Denitrification often occurs in the water column, underlying zones of intense productiv- ity and decomposition in upwelling regions. In the denitrifying zone off the southwest coast of India, high concentrations of nitrite (>15 µM) and nitrous oxide (>500 nM) have been reported near the sediment-water interface (<80 m). We investigated the chemical and molecular indicators of denitri- fication along the southwest coast of India during the southwest monsoon season of October 2001. Nitrite reduction to nitric oxide is the key step in the denitrification pathway, and is catalyzed by the enzyme nitrite reductase, which is encoded by the genes nirS and nirK. Here we report the diversity and distribution of nirS genes in relation to nitrite and nitrate distribution in the Arabian Sea coastal denitrifying region. nirS gene fragments were PCR-amplified, cloned, and sequenced from DNA extracted from the water column. Clone libraries were also subjected to restriction fragment length polymorphism (RFLP) and rarefaction analyses. These are the first nitrite reductase sequences reported from a water column denitrifying regime. nirS was amplified from DNA extracted from all water samples in which nitrite was present at high concentrations within the low oxygen waters, but was only rarely amplified from waters containing hydrogen sulfide or from well-oxygenated waters. Phylogenetic analysis grouped 132 nirS Arabian Sea sequences into 12 major clusters. Most of the nirS sequences from the coastal water column did not show a high level of identity with other nirS sequences previously reported from marine and estuarine sediments. Identities of the Arabian Sea sequences to those in the public database ranged from 44 to 99% at the amino acid level. The domi- nant sequence type from 1 surface sample showed 99% identity to the nirS sequence of the cultivated denitrifier Pseudomonas aeruginosa. Rarefaction analysis, based on both sequence and RFLP data, indicated the highest diversity in a sample in which relatively high nitrite concentrations implied the presence of active denitrification, and the lowest diversity in a surface sample where nitrite was undetectable, suggesting a link between functional diversity and ecosystem chemistry.

Submarine groundwater discharge and associated nutrient flux from southwest coast of India

Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea) and its impact on trace metal concentrations in seawater

Though microbial processes in the oxygen minimum zones (OMZs) of the Arabian Sea (AS) are well documented, prokaryote-virus interactions are less known. The present study was carried out to determine the potential physico-chemical factors influencing viral abundances and their life strategies (lytic and lysogenic) along the vertical gradient in the OMZ of the AS (southwest coast of India). Water samples were collected during the southwest monsoon (SWM) season in two consecutive years (2015 and 2016) from different depths, namely, the surface layer, secondary chlorophyll a maxima (~30–40 m), oxycline (~70–80 m), and hypoxic/suboxic layers (~200–350 m). The high viral abundances observed in oxygenated surface waters (mean ± SD = 6.1 ± 3.4 × 106 viral-like particles (VLPs) mL−1), drastically decreased with depth in the oxycline region (1.2 ± 0.5 × 106 VLPs mL−1) and hypoxic/suboxic waters (0.3 ± 0.3 × 106 VLPs mL−1). Virus to prokaryote ratio fluctuated in the mixed layer (~10) and declined significantly (p < 0.001) to 1 in the hypoxic layer. Viral production (VP) and frequency of virus infected cells (FIC) were maximum in the surface and minimum in the oxycline layer, whereas the viral lysis was undetectable in the suboxic/hypoxic layer. The detection of a high percentage of lysogeny in suboxic (48%) and oxycline zones (9–24%), accompanied by undetectable rates of lytic viral infection support the hypothesis that lysogeny may represent the major survival strategy for viruses in unproductive or harsh nutrient/host conditions in deoxygenated waters.

Valliyar is one of the main river systems in Kanyakumari District, originates from Velimalai Hills in Western Ghats and enters into Arabian Sea through Kadiyapattanam estuary. The concentration of heavy metals was analysed from water samples collected at different location in coastal waters adjacent to Kadiyapattanam estuary in Kanyakumari District, Tamil Nadu, south west coast of India. Samples were collected continuously throughout the year during monsoon, post monsoon and pre-monsoon seasons in the year 2015–2016. To carry out present study 5 sampling stations were selected and 7 heavy metals such as lead, zinc, copper, cadmium, iron manganese and Mercury were estimated following standard methods and procedures. Study area is situated near Indian rare earth limited corporation in Manavalakurichi. Mercury was found absent in the samples throughout the year in the present study. Concentration of iron was found higher compared to other metals. The metal concentration in samples was determined using Perkin Elmer A Analyst 200 Atomic absorption spectroscopy. The order of heavy metal content in the study area was Fe > Cd > Pb > Cu > Mn > Zn > Hg. In the present study the concentration of Zinc, copper, and manganese are within the permissible limit in all seasons. Lead and cadmium shows higher values in some season. The result of the study indicates that the river Valliyar and coastal waters of kadiyapattanam estuary are polluted due to the discharge of toxic heavy metals, agro chemical waste runoff and anthropogenic activities.