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Studies of the Allies' grand strategy for the defeat of Japan in Southeast Asia usually focus on the discussions over Burma. This article examines the roles envisioned for the Bay of Bengal. It argues that operations within and based on the Bay of Bengal formed the basis of Allied strategy in Southeast Asia, but plans quickly diverged. The U.S. and China pushed for amphibious operations as part of the broader Burma campaign. Britain, however, wanted to use the Bay of Bengal as a springboard for operations into broader Southeast Asia. No party got what it wanted. Scrutinizing these strategic developments, however, provides a clearer understanding of the evolution of Southeast Asia's place in the Allies' grand strategy. [ABSTRACT FROM AUTHOR]

This research investigates the origins of high-salinity water in the southern Bay of Bengal (SBHSW) in summer (June to August) and its interannual variabilities associated with El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The two distinctive sources of the SBHSW, including the eastern Arabian Sea (AS) origin and the western equatorial Indian Ocean (EIO) origin mentioned in the previous studies are identified. The eastern AS origin has much higher salinity (35.5 PSU vs. 35.2 PSU), shallower isopycnal layers (1023.0–1023.5 kg m-3 vs. 1024.0–1024.5 kg m-3), and intrudes into the Bay of Bengal (BOB) approximately one month later compared to the western EIO origin, while accounting for 53% of the total salinity variability compared to 47% contribution from the western EIO origin. The interannual variabilities of SBHSW are closely linked with ENSO and IOD events, with contributions of approximately 47% and 41%, respectively. During El Niño decaying years, high-salinity water export from the western EIO origin into the southern bay (< 7°N) is enhanced due to the anomalous strong spring Equatorial Undercurrent (EUC) associated with El Niño; while in the north of 7°N, the SBHSW was freshened both by the increased rainfall and by the downwelling associate with the anomalous anticyclonic wind. Similar processes operate but in an opposite direction during La Niña decaying years. In contrast, IOD exerts its influence on the SBHSW primarily through modulating the strength of SMC. Positive (negative) IOD caused the anomalous freshening (salty) SBHSW by weakening (enhancing) SMC and consequently advecting less (more) saline water into the BOB. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are one of the major substantial pollutants in the environment and are stored in sediments worldwide, especially in marine environments. This study shed light on the abundance, distribution, sources and chemical composition of MPs present in the surface sediments collected from the shelf part of the southeast coast of India, Bay of Bengal. A total of twenty-seven surface sediment samples were collected to study MPs pollution. The abundance and morphological characteristics of MPs were determined by counting using an Olympus SXZ7 stereo microscope. Raman spectroscopy analysis was used to identify the polymer type of the MPs. The average abundance of MPs in the study area is 460±275 MPs/kg in dry sediment. Regarding colour, transparent particles were predominant (46.42%), followed by blue, green, brown, etc. With respect to particle shape and size, fibres and 500-µm sized MPs are abundant. Polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polystyrene (PS) are the polymer types characterised in the study area. The higher abundance of MPs in the study area can be attenuated to human interruptions, viz., tourism, fishing and inappropriate sewage disposal in the marine environment. In addition to this, population density also plays an important role in providing MPs to the marine environment. This study provides the most valuable data to extrapolate the research for mitigating MP pollution in oceans. It also informs mankind about their disastrous activities on the marine environment, which is expected to recuperate quickly and negatively impact human health and the functionality of the marine system. [ABSTRACT FROM AUTHOR]

An investigation was done to determine the texture, organic matter content, and geochemical characteristics of sediments collected from the continental shelf of the South Western Bay of Bengal. The present study portrays the abundance of sand followed by slightly muddy sand, muddy sand, sandy mud, sandy, and slightly sandy mud in the study area. The mean size of the sediment ranges from 0.40 to 3.57 mm (coarse sand to very fine sand). The sediments are very well to very poorly sorted, coarsely skewed to fine skewed, and platykurtic to very leptokurtic in nature. Trace metals, such as Cu, Co, Fe, Mn, Pb, Zn, Cr, and Ni were analyzed. A relatively high percentage of organic matter is attributed to the predominance of finer sediments entering through the minor and major rivers. The higher trace metal concentration in the study area is closely associated with mud content and Fe is the most abundant trace metal in the study area. Formation of Fe- and Mn-hydroxides in the near-shore regions is responsible for scavenging Pb, Zn, Cu, Ni, and Cr and effectively incorporating them into the inner shelf sediments. Among all the trace metals, the concentration of Co, Pb, Cr, and Ni is found to be higher than the average crustal abundance value marking the role of anthropogenic sources predominantly from industrial, agricultural, scrap metal recycling, sewage, and tourism activities. [ABSTRACT FROM AUTHOR]

The current study investigates the modulation of the tropical cyclone (TC) frequency (TCF) over the Bay of Bengal (BoB) by the southern annular mode (SAM). The analysis reveals that the SAM–TCF relationship during October–November–December has undergone interdecadal changes from significant during 1971–1994 to insignificant during 1995–2021. This contrasting influence of the SAM on the TCF occurrence is also echoed in the large‐scale environmental variables conducive to forming tropical cyclones (TCs). Based on the possible mechanism, we found that the SAM can imprint tripole sea surface temperature (SST) patterns in the southern Indian Ocean via altering surface wind speed from 1971 to 1994. The SAM‐related tripole SST pattern induces the surface‐level anticyclone anomaly, which enhances the south easterlies towards the western equatorial Indian Ocean. Such intensified anomalous wind crosses the equator and diverts towards the east to form the cyclone anomaly in the BoB. Meanwhile, at 200 hPa, the anomalous anticyclone over western Australia induces divergent wind flows over the study region. Consequently, the ascending motion in BoB promotes the tropical cyclone generation. During 1995–2021, however, the SAM is associated with the dipole SST pattern in the southern Indian Ocean. Correspondingly, the SAM‐related dipole SST yields anomalous atmospheric circulations confined to the Southern Hemisphere and eventually fails to impact the formation of TCs in the northern Indian Ocean, where the study region is located. The findings of this research can be useful in advancing our knowledge of the interannual variability of TCs activity in the BoB based on the remote climate signal. [ABSTRACT FROM AUTHOR]

Knowledge of spring warm pool in the Bay of Bengal (BoBWP) is key for further understanding the climate variability in this region and beyond, but little is known about the BoBWP climatological state and the related mechanisms. In this study, we investigate the spatial structure and evolution of the BoBWP using daily Optimum Interpolation SST data from 1982-2022 in combination with multi-source data. Our analysis shows that the BoBWP is located in the central bay (6°-13°N) with a thickness around 20m~ 40 m. Composite analysis indicates that the BoBWP emerges in early April, peaks in early May and dissipates in early June. During the developing period, the net heat flux dominates the formation of spring warm pool through significant air-sea coupling processes, and induces the warming rate of 0.27°C/10d in the mixed layer, which is far larger than the contribution of oceanic dynamical processes (0.01°C/10d). During the decaying period, the net heat flux also plays a dominant role, with a cooling rate of -0.21°C/10d, meanwhile ocean dynamical processes contribute to the cooling of the warm pool with a rate of -0.01°C/10d. Additionally, the SST and the area of the BoBWP are significantly correlated with ENSO (r=0.66 and 0.73, p=0.05). During El Niño decaying year, the BoBWP primarily expands in a southward direction, with a 75% increase in area. Conversely, during La Niña decaying year, the BoBWP almost disappears, with a 52% decrease. [ABSTRACT FROM AUTHOR]

Sources of moisture-feeding for the incipient tropical cyclones (TCs) over the Bay of Bengal (BoB) are least explored. Using a three-dimensional Lagrangian model running with NCEP-FNL data, the present work identified various source locations and major transport routes that contributed moisture to pre- and post-monsoon TCs genesis (TCG) over the BoB. The clustered mean trajectories identified using the k-means method demonstrated that moisture transport towards the TCG region during pre-monsoon is dominated by intense low-level westerly/south-westerly trajectories propagating across the North Indian Ocean covering the Somalia coast and the Arabian Sea. Meanwhile, during post-monsoon, north-easterly/easterly trajectories are more prevalent and bring moisture to the BoB TCG region from the South China Sea and North-West Pacific. Moreover, the study highlights the spatiotemporal variations of moisture uptake (MU) pattern and its contribution and demonstrates that robust MU with a contribution of 20–90% occurs locally before three days of TCG. Meanwhile, remote sources contribute a moisture amount of ≤ 20%. Furthermore, the composite analysis of different diagnostic parameters confirms that identified MU at the local scale is attributed to an evaporation process in association with a dynamic uplifting mechanism caused by an anomalous cyclonic circulation, which provides moisture for TCG, while the horizontal advection is the mechanism, which gradually builds moisture required for the TCG from the remote sources. [ABSTRACT FROM AUTHOR]

Sea Surface Temperature (SST) is of great importance to study several major phenomena due to ocean interactions with other earth systems. Previous studies on SST based on statistical inference methods were less accurate for longer prediction lengths. A considerable number of studies in recent years involve machine learning for SST modeling. These models were able to mitigate this problem to some length by modeling SST patterns and trends. Sequence analysis by decomposition is used for SST forecasting in several studies. Ensemble Empirical Mode Decomposition (EEMD) has been proven in previous studies as a useful method for this. The application of EEMD in spatiotemporal modeling has been introduced as Multidimensional EEMD (MEEMD). The aim of this study is to employ fast MEEMD methods to decompose the SST spatiotemporal dataset and apply a Convolutional Long Short-Term Memory (ConvLSTM)-based model to model and forecast SST. The results show that the fast MEEMD method is capable of enhancing spatiotemporal SST modeling compared to the Linear Inverse Model (LIM) and ConvLSTM model without decomposition. The model was further validated by making predictions from April to May 2023 and comparing them to original SST values. There was a high consistency between predicted and real SST values. [ABSTRACT FROM AUTHOR]

This study reports radiological deformities in the vertebral column of six fishes viz, Scomberomorus commerson, Chanos chanos, Sillago sihama, Pampus chinensis, Rastrelliger kanagurta and Netuma thalassina that were collected from the Coromandel coast, Bay of Bengal. Four main different types of vertebral column deformities were found: (i) whole body kypho-lordo-kyphosis (Sillago sihama, Rastrelliger kanagurta, Netuma thalassina); (ii) tail region kypho-lordosis (Scomberomorus commerson); (iii) tail region lordo-kyphosis (Chanos chanos); (iv) platyspondyly (Pampus chinensis). Seven types of vertebra body deformities, describing the pathology of single vertebrae, were present; reduced intervertebral space, compression, fusion, compresion & fusion, fusion center, dorsal wedgeshaped and compressed & dorsal wed-shaped. The present documentation of deformities in six different species that are also very different with regard to habitat, diet and swimming activity may suggest that fish deformities are widespread in the study area. [ABSTRACT FROM AUTHOR]

The toxic impact of microplastics (MPs) in the terrestrial and aquatic environment has recently become a global problem. The Bay of Bengal coasts is an important bio-diverse ecosystem, which help the people for their sound living and gather natural resources. However, the distribution, impact, source and transport mechanism, and policy to take initiatives for MPs pollution control at the Bay of Bengal coasts' have received less attention. Therefore, this review summarizes MPs' distribution and their source in the Bay of Bengal coasts' ecosystems. Current knowledge extends the impacts of MP on this vital ecosystem, existing policy, and further recommendations to mitigate MPs contamination are critically assessed in this study. Furthermore, mechanisms of MP on human health are also highlighted with the identification of current research gaps and future study suggestions. Given the escalating plastic usage and the prevalence of important sea products globally, there is a pressing need to prioritize research efforts on the impacts of MPs on the Bay of Bengal coasts from a long-term perspective. Knowledge obtained in this way would inform the scientists, stakeholders, and policy makers in such a way as to help them mitigate impacts of the micro- and nano-plastic legacy at this region. [ABSTRACT FROM AUTHOR]

Cyclones tracking northward across the Bay of Bengal represent a significant threat to life and safety when they make landfall. Surface moorings of the Ocean Moored Network for the Northern Indian Ocean in the Bay of Bengal have been deployed to provide real-time observations in support of improved alerts and predictions of cyclones. Engineering goals are both to develop robust surface moorings that survive and to field meteorological and oceanographic instruments that reliably provide data in real time. While the mooring design and reliability were previously reported, the focus here is on the motivations for installing the instrumentation, and on experience gained during the passage of cyclone Amphan in May 2020, examining the sensor as well as mooring performance. The paper presents reasons for fielding the chosen sensors, merits, and shortcomings during the effort to observe Amphan, and recommendations for how to better address the challenges of providing real-time observations of cyclones in the Bay of Bengal. [ABSTRACT FROM AUTHOR]

Alpheus leptocheles Banner and Banner, 1975 (Decapoda, Alpheidae) is a compressed chela snapping shrimp which was reported from Papua New Guinea earlier. The compressed nature of major chela, the shape of the orbitorostral front and the flattened dactyli of the third pereopod put this species in the Brevirostris group of the genus Alpheus (Banner). Most of the characteristic features are very close to the type specimen of A. leptocheles collected in New Guinea. This shrimp usually inhabits low depth river mouth region of marine bottoms; however, recently we have record for the first time in muddy bottom at an unusual depth of about 250-300 m in Southeast coast of India. This record may extends the distribution pattern of A. leptocheles in Bay of Bengal. Moreover, it may perhaps represent an additional alpheid species for the Indian marine faunal list.

The present study evaluated the performance of the Weather Research and Forecasting (WRF) model in the forecast of a very severe cyclonic storm (VSCS) Vardah that developed over the Bay of Bengal (BoB) and make landfall over the Tamil Nadu coast on 12 December 2016. The study examined the impact of microwave humidity sounder (MHS) satellite radiance data assimilation to forecast of structure, intensity and rainfall of Vardah cyclone near to the coast using two different land surface model (LSM; Noah and Noah-MP). The mean track error is about 33 and 38 km with data assimilation using Noah and Noah-MP LSM respectively and this error is about 41 km in without data assimilation using Noah and Noah-MP LSM. The predicted intensity of the storm in terms of the maximum surface wind is also slightly better predicted in data assimilation experiment with Noah LSM, this is due to the improved initial condition. Accumulated rainfall and the maximum reflectivity in terms of spatial distribution and magnitude of the VSCS Vardah is well simulated in all the experiments but slightly better in data assimilation experiments. Hovmoller diagram is also presented to see the shifting pattern of accumulated rainfall across the region during simulation period. [ABSTRACT FROM AUTHOR]

This study examines the track and intensity forecasts of two typical Bay of Bengal tropical cyclones (TC) ASANI and MOCHA. The analysis of various Numerical Weather Prediction (NWP) model forecasts [ECMWF (European Centre for Medium range Weather Forecast), NCEP (National Centers for Environmental Prediction), NCUM (National Centre for Medium Range Weather Forecast-Unified Model), IMD (India Meteorological Department), HWRF (Hurricane Weather Research and Forecasting)], MME (Multi-model Ensemble), SCIP (Statistical Cyclone Intensity Prediction) model, and OFCL (Official) forecasts shows that intensity forecasts of ASANI and track forecasts of MOCHA were reasonably good, but there were large errors and wide variation in track forecasts of ASANI and in intensity forecasts of MOCHA. Among all model forecasts, the track forecast errors of IMD model and MME were least in general for ASANI and MOCHA respectively. Also, the landfall point forecast errors of IMD were least for ASANI, and the MME and OFCL forecast errors were least for MOCHA. No model is found to be consistently better for landfall time forecast for ASANI, and the errors of ECMWF, IMD and HWRF were least and of same order for MOCHA. The intensity forecast errors of OFCL and SCIP were least for ASANI, and the forecast errors of HWRF, IMD, NCEP, SCIP and OFCL were comparable and least for MOCHA up to 48 h forecast and HWRF errors were least thereafter in general. The ECMWF model forecast errors for intensity were found to be highest for both the TCs. The results also show that although there is significant improvement of track forecasts and limited or no improvement of intensity forecast in previous decades but challenges still persists in real time forecasting of both track and intensity due to wide variation and inconsistency of model forecasts for different TC cases.

Abstract The Regional Indian Ocean model based on Modular Ocean Model (MOM4p1) was used to understand the importance of a realistic representation of bathymetry on Ocean General Circulation. The model has 1/4° uniform horizontal resolution and is forced with Coordinated Ocean-Ice Reference Experiments (CORE-II) inter-annual forcing with two simulations named BLND (realistic bathymetry) and OM3 (smoothed bathymetry), which only differ in the representation of bathymetry for the years 1992–2005. We also used recent reanalysis products from ORAS5 and SODA3 and ADCP observation to compare the subsurface currents. We show that by the inclusion of realistic bathymetry, there is a significant improvement in the upper ocean salinity, temperature, and currents, particularly near the coast. The salinity and temperature of the upper ocean are very close to the observed value near the coast. The bias in the salinity and temperature was reduced to half in BLND simulation compared to OM3, which led to a more realistic East India Coastal Current (EICC). We show the first evidence of a basin-wide cyclonic gyre over the Bay of Bengal at 1000 m depth during spring, which is just opposite to that of a basin-wide anti-cyclonic gyre at the surface. We found the presence of poleward EICC during spring at 1000 m and 2000 m depth, which is opposite to that of the surface. The presence of this deeper EICC structure is completely absent during fall. We show the presence of a boundary current along the coast of Andaman and Nicobar Island at a depth of 2000 m. The observed Wyrtki Jet (WJ) magnitude and spatial structure are most realistically reproduced in BLND simulation as compared to OM3 simulations. Both ORAS5 and SODA reanalysis products underestimate the WJ magnitude. The presence of the Maldives Islands is responsible for the westward extent of Equatorial Under Current (EUC). The presence of Maldives also creates wakes on the leeward side in the EUC zonal current. During fall, EUC is better defined in the eastern Equatorial Indian Ocean and lies at a depth of between 50 and 100 m, unlike its spring counterpart, in which its core is located slightly deeper, between 100 and 150 m depth. During peak summer months, June–July, a strong eastward zonal jet is present at 1000 m depth, similar to Wyrtki Jet (WJ). Inter-monsoon Jets, i.e., spring and fall jets, are also seen but are in the opposite direction, i.e., westward, unlike eastward in WJ.

The benthic foraminiferal community is an excellent bio-indicator of pollution in coastal and marginal marine settings. Their abundance, diversity and its relationship with environmental parameters, viz. grain size, organic carbon (Corg) and trace metals concentration, from the surface sediment layer of the southwestern shelf of the Bay of Bengal, have been used to understand the marine pollution in this study. A total of 32 surface sediment samples were collected at various water depths.The samples were analysed for grain size distribution, organic matter (OM), foraminiferal and trace metals studies. Statistical analyses such as correlation matrix, PCA (Principal Component Analysis) and cluster analysis show that the foraminiferal species composition is significantly influenced by the organic carbon (Corg), Co, Pb, Zn, Cr, and Ni concentrations. The dominance of stress-tolerant species, viz. Ammonia beccarii, Ammonia tepida, Nonion faba, Bulimina marginata, Bolivina robusta, Elphidium craticulatum and Elphidium advenum, as well as less species diversity, demonstrates the elevated Corg and trace metal pollution in the marine environment. [ABSTRACT FROM AUTHOR]

One of the crucial manifestations of climate change is Sea Level Rise (SLR). On the other hand, Tropical Cyclones (TCs) cause a huge devastation in the coastal regions. The extent of devastation caused by the TCs is further enhanced by rising sea level. A Coastal Vulnerability Index (CVI) is developed and projected till the year 2100 for different climate change scenarios, designated by Representative Concentration Pathways (RCPs), e.g., RCP2.6, RCP4.5 and RCP8.5. The head Bay region of the Bay of Bengal, comprising of the largest mangrove forest in the world (Sundarbans), is considered as study area. The region faced havoc due to land fall of cyclone Aila in May 2009. Considering Aila as the TC, current and future vulnerability maps (in terms of CVI) are developed considering SLR and other non-climatic factors. Results indicate that many parts in the study region are projected to be ‘Very High’ vulnerable that are not so currently. Future vulnerability maps that classify the coastal regions into very low, low, high and very high vulnerability classes are developed. Thus, the research outcomes are expected to be highly useful for future coastal management. The proposed procedure is general in nature, and can be used for vulnerability mapping of any coastal regions across the world. [ABSTRACT FROM AUTHOR]

In the Earth's atmosphere, greenhouse gases (GHGs) and reactive trace gases are essential components of chemistry–climate interactions. These trace gases are emitted from both natural and anthropogenic sources over terrestrial and marine regions. Air–sea exchange is the dominant process controlling the distribution of several important trace gases over remote marine regions. Although the ocean–atmosphere interface covers ~70% of the Earth's surface, the quantitative air–sea exchange of reactive trace gases is estimated over the limited oceanic regions. The production and air–sea exchange of trace gases are controlled by physical conditions at both sides of the interface and ocean biogeochemistry. The northern Indian Ocean (NIO) experiences strong seasonal monsoon winds and intense tropical cyclones. Consisting of the Arabian Sea and the Bay of Bengal, it is one of the most biologically productive regimes of the world ocean and home to the intense oxygen minimum zone (OMZ) of the Arabian Sea with dissolved oxygen concentrations. Thus, the NIO offers a unique system to investigate the air–sea exchange processes of reactive trace gases. So far, most of the studies of air–sea exchange of trace gases is focused on the Atlantic and Pacific Oceans, while studies over the northern Indian Ocean are very limited and reported mainly for CH4, CO2 and N2O. Although progress has been made in recent years, studies of air–sea exchange of reactive trace gases such as non-methane hydrocarbon (NMHCs), oxygen-, sulfur- and halogen-containing hydrocarbons remain scarce. This paper addresses the current understanding of air–sea exchange processes and fluxes of reactive trace gases, including NMHCs, dimethyl sulfide (DMS), oxygenated volatile organic compounds (OVOCs), halocarbons, carbon monoxide (CO) and ozone (O3) in the northern Indian Ocean. This review summarizes the studies on the air–sea exchange of trace gases over the northern Indian Ocean and common parametrization approaches used to estimate the air–sea flux of gases. Flux range for ethene (3–10.35 µmol m–2 d–1), isoprene (0.215–0.172 µmol m–2 d–1), acetaldehyde (–6.75–11.35 µmol m–2 d–1), acetone (–9–9 µmol m–2 d–1), DMS (0.03–41.4 µmol m–2 d–1) and CO (1.4–5.4 µmol m–2 d–1) over the NIO were summarized from various in-situ and modelling studies. The paper addresses the importance of the northern Indian Ocean apropos the production and exchange of reactive trace gases, the knowledge gaps and the future scientific scope. Additionally, it emphasizes the need for a multidisciplinary study of oceanic reactive trace gas cycling and its impact on regional atmospheric chemistry over the northern Indian Ocean. [ABSTRACT FROM AUTHOR]

This study examines the track and intensity forecasts of two typical Bay of Bengal tropical cyclones (TC) ASANI and MOCHA. The analysis of various Numerical Weather Prediction (NWP) model forecasts [ECMWF (European Centre for Medium range Weather Forecast), NCEP (National Centers for Environmental Prediction), NCUM (National Centre for Medium Range Weather Forecast-Unified Model), IMD (India Meteorological Department), HWRF (Hurricane Weather Research and Forecasting)], MME (Multi-model Ensemble), SCIP (Statistical Cyclone Intensity Prediction) model, and OFCL (Official) forecasts shows that intensity forecasts of ASANI and track forecasts of MOCHA were reasonably good, but there were large errors and wide variation in track forecasts of ASANI and in intensity forecasts of MOCHA. Among all model forecasts, the track forecast errors of IMD model and MME were least in general for ASANI and MOCHA respectively. Also, the landfall point forecast errors of IMD were least for ASANI, and the MME and OFCL forecast errors were least for MOCHA. No model is found to be consistently better for landfall time forecast for ASANI, and the errors of ECMWF, IMD and HWRF were least and of same order for MOCHA. The intensity forecast errors of OFCL and SCIP were least for ASANI, and the forecast errors of HWRF, IMD, NCEP, SCIP and OFCL were comparable and least for MOCHA up to 48 h forecast and HWRF errors were least thereafter in general. The ECMWF model forecast errors for intensity were found to be highest for both the TCs. The results also show that although there is significant improvement of track forecasts and limited or no improvement of intensity forecast in previous decades but challenges still persists in real time forecasting of both track and intensity due to wide variation and inconsistency of model forecasts for different TC cases. [ABSTRACT FROM AUTHOR]

Tropical cyclones have resulted in casualties and economic losses in the areas surrounding the Bay of Bengal (BoB). Thus, a comprehensive investigation of these tropical cyclones holds vital implications for disaster preparedness and mitigation. This paper compares the occurrence of storms in the last two decades, i.e., 2002–2011 and 2012–2021, and results reveal that such storms exhibited predominantly a northwesterly track towards the northwestern BoB, with a severer intensity but equal total storm frequencies. Over the past decade, a southeast-northwest pathway (SNP) was identified, demonstrating a higher incidence of severe tropical cyclones (STC, with lifetime maximum intensity ≥ 64 knots) over the BoB. Further analysis of the changes in the environmental conditions between these two decades indicates that a southeasterly anomaly in the steering flow contributed to the formation of the SNP. During the same period, the more favorable oceanic conditions during the last decade, including higher sea surface temperatures, a greater upper ocean heat content, a thicker warm water layer, and a thicker barrier layer beneath the SNP, favored the development of these storms by providing more heat energy to the storms. The atmospheric conditions, including increased air-sea heat fluxes, moisture, and instability within the lower troposphere, as well as reduced vertical wind shear, facilitated the development of convection within these storm systems. These favorable conditions improved the potential for storm development into STCs and elevated the risk of the northwestern BoB being impacted by more destructive storms. [ABSTRACT FROM AUTHOR]

Interannual variability of summer monsoon depressions (MDs) over the Bay of Bengal (BoB) is investigated with special emphasis on developing and decaying El Niño phases during the period 1979–2020. Previous studies have overlooked the relationship between MDs frequency and El Niño phenomena, despite of their stronger association with Indian Summer Monsoon (ISM) rainfall. Our analysis revealed that the number of MDs has reduced remarkably by a factor of 2 during El Niño decay summers (more than half) as compared to climatology and in fact, no such decline is depicted in developing El Niño years. The strong easterlies extending from the southern flank of the Western North Pacific (WNP) anticyclone to the southern BoB cause negative low-level vorticity anomalies and reduce the Barotropic instability during El Niño decay summers. These conditions are unfavourable for the formation of MDs in the BoB. It is also noted that the Genesis Potential Parameter (GPP) for the MDs over the BoB and WNP region is weaker in the El Niño decay summers compared to developing El Niño and normal years. Moreover, during the El Niño decay summers less number of Tropical Cyclones (TCs) over WNP due to weak GPP, reduced the chances of westward propagating remnants of TCs from the Philippine Sea to the BoB, which is not favourable for the formation of MDs. Essentially, the reduction in the frequency of MDs would influence the seasonal rainfall distribution over the Indian subcontinent and largely impacts the regional agriculture activities and water management sector. Further, the Indo-western Pacific capacitor (IPOC) effect, which is strongly tied to decaying El Niño phase plays a critical role in altering the number of MDs by maintaining WNP anticyclone. Thus, predicting IPOC pattern during the decay phase of El Niño would provide useful insights on a number of MDs and ISM rainfall prediction. [ABSTRACT FROM AUTHOR]

Ocean productivity is the foundation of marine food web, which continuously removes atmospheric carbon dioxide and supports life at sea and on land. Spatio-temporal variability of net primary productivity (NPP), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), and euphotic zone depth (EZD) in the northern Bay of Bengal (BoB) during three monsoon seasons were examined in this study based on remote sensing data for the period 2005 to 2020. To compare the NPP distribution between the coastal zones and open BoB, the study area was divided into five zones (Z1–Z5). Results suggest that most productive zones Z2 and Z1 are located at the head bay area and are directly influenced by freshwater discharge together with riverine sediment and nutrient loads. Across Z1–Z5, the NPP ranges from 5 315.38 mg/(m2·d) to 346.7 mg/(m2·d) (carbon, since then the same). The highest monthly average NPP of 5 315.38 mg/(m2·d) in February and 5 039.36 mg/(m2·d) in June were observed from Z2, while the lowest monthly average of 346.72 mg/(m2·d) was observed in March from Z4, which is an oceanic zone. EZD values vary from 6–154 m for the study area, and it has an inverse correlation with NPP concentration. EZD is deeper during the summer season and shallower during the wintertime, with a corresponding increase in productivity. Throughout the year, monthly SST shows slight fluctuation for the entire study area, and statistical analysis shows a significant correlation among NPP, and EZD, overall positive between NPP and MLD, whereas no significant correlation among SSS, and SST for the northern BoB. Long-term trends in SST and productivity were significantly positive in head bay zones but negatively productive in the open ocean. The findings in this study on the distribution of NPP, SST, SSS, MLD, and EZD and their seasonal variability in five different zones of BoB can be used to further improve the management of marine resources and overall environmental condition in response to climate changes in BoB as they are of utmost relevance to the fisheries for the three bordering countries. [ABSTRACT FROM AUTHOR]

This study reports the gametogenic cycle and condition index (CI) of blood cockle, Tegillarca granosa (L., 1758), by applying biometry and histology of monthly samples obtained from the west coast of Moheshkhali Island, Cox’s Bazar, Bangladesh, over a year. Histology revealed gametogenic activity of T. granosa around the year in the habitat. Pattern of gametogenesis, maturation, spawning, and resorption were similar in males and females with the sexes displaying similar temporal pattern of spawning activity. The initiation of gametogenesis of T. granosa started in September, December, and May in the habitat. Over a 12-month study period, T. granosa exhibited a protracted spawning period from August to April with two major pulses timing September to December and March. CIs as the ratio of tissue wet weight to shell length varied from 1.24 to 3.36 with two distinct peak periods timing August 2018 (1.62 ± 0.42) and June 2019 (2.58 ± 0.48). CIs closely followed the gametogenic cycle of the species. Monthly changes in CIs and spawning season determined from histology suggest that harvesting of T. granosa from the west coast of Moheshkhali, Cox’s Bazar could be economically feasible during June without interrupting the spawning of the species. Pearson correlation analysis indicated a weak correlation between maturity index and environmental variables, as well as CI and environmental variables. Further study is needed on the timing of spatfall of T. granosa in the habitat based on spawning season confirmed in the current study for the collection of spats to supply seeds for commercial farming. [ABSTRACT FROM AUTHOR]

The breakup of India from Antarctica in the Early Cretaceous and subsequent seafloor spreading in the NW‐SE direction initiated the formation of the Bay of Bengal and its conjugate Enderby Basin. Two hypotheses are proposed to explain the evolutionary tectonics between India and Antarctica. One involves a single breakup, while the second invokes another breakup episode. Further, a major reorganization of the plate boundaries in the mid‐Cretaceous caused the spreading center to align E‐W by Late Cretaceous. The tectonics involved in this spreading direction change is unknown and difficult to understand as it occurred in the mid‐Cretaceous, coincident with the Cretaceous Normal Superchron. In the present study, we have generated a revised magnetic isochron map of the Bay of Bengal and used the modulus of its analytic signal to understand the evolutionary tectonics between the two plates, India and Antarctica. Mesozoic magnetic anomalies M12n to M0, and mid‐Cretaceous incursion Q2 (108 Ma) are identified in the western basin of the Bay of Bengal, while Q2, Q1 (92 Ma) and Late Cretaceous isochron A34 are inferred in its eastern basin. Gravity grid reconstructions demonstrate asymmetrical crustal accretion in the conjugate corridors. Fan‐shaped spreading and a southward ridge jump between 108 and 92 Ma in the eastern basin, aided the ∼40° clockwise rotation of the spreading center. The presence of volcanic basement beneath the additional crust suggests on‐axis mode of formation for the Ninetyeast Ridge by 100 Ma. The present study favors the two‐phase breakup model for the evolution of these plates. Key Points: Clockwise rotation (∼40°) of the spreading center between India and Antarctica during the mid‐CretaceousFan‐shaped spreading and a southward ridge jump facilitated the clockwise rotation of the spreading centerNinetyeast Ridge formed as on‐axis volcanism during the mid‐Cretaceous [ABSTRACT FROM AUTHOR]

This study investigates the activity of tropical cyclones (TCs) in the Bay of Bengal (BOB) from 1979 to 2018 to discover the mechanism affecting the contribution rate to the meridional moisture budget anomaly (MMBA) over the southern boundary of the Tibetan Plateau (SBTP). May and October–December are the bimodal phases of BOB TC frequency, which decreases month by month from October to December and is relatively low in May. However, the contribution rate to the MMBA is the highest in May. The seasonal variation in the meridional position of the westerlies is the key factor affecting the contribution rate. The relatively southern (northern) position of the westerlies in November and December (May) results in a lower (higher) contribution rate to the MMBA. This mechanism is confirmed by the momentum equation. When water vapor enters the westerlies near the trough line, the resultant meridional acceleration is directed north. It follows that the farther north the trough is, and the farther north the water vapor can be transported. When water vapor enters the westerlies from the area near the ridge line, for Type-T (Type-R) TCs, water vapor enters the westerlies downstream of the trough (ridge). Consequently, the direction of the resultant meridional acceleration is directed south and the resultant zonal acceleration is directed east (west), which is not conducive to the northward transport of water vapor. This is especially the case if the trough or ridge is relatively south, as the water vapor may not cross the SBTP. [ABSTRACT FROM AUTHOR]

In the process of wave modeling in the Bay of Bengal, it is particularly important to study the initial parameter adjustment of the SWAN model. Given the complexity and variability of wave characteristics in the region, an in-depth evaluation of the simulation results of the SWAN model under various initial parameter configurations was conducted by using wave buoy data. The research results show that under certain specific conditions, merely increasing the computational resolution cannot significantly enhance the accuracy of the model's simulation; therefore, choosing the appropriate resolution is crucial to ensure the balance between computational efficiency and simulation accuracy. Especially when analyzing the data from theBD08, BD11, and BD14 buoys, it was found that when the model is set to a 10-minute time step and a maximum iteration number of 1, the wave height simulation showed a high degree of stability and accuracy. Therefore, it is recommended to use shorter time steps and reduce the number of iterations during the simulation process, especially in areas with dramatic changes in water depth and nearshore areas, to improve the accuracy and efficiency of the model's simulation. Meticulous adjustment of the SWAN model's initial parameters is crucial for improving the simulation accuracy and efficiency of the model in different regions. [ABSTRACT FROM AUTHOR]

The present study investigates the mixed layer variations near mesoscale eddies in the Bay of Bengal (BoB) using satellite altimeter and Argo data. Furthermore, the factors responsible for sea surface variations near mesoscale eddies are analyzed using the mixed layer heat and salinity budgets estimated from Argo profiles. In the diagnostic mixed layer heat budget analysis, the entrainment term is parametrized based on the presence and absence of the barrier layer. The role of inversion and barrier layers on eddy-induced temperature variations is also examined near eddy locations. Results showed that anti-cyclonic eddies deepen mixed layer depth (MLD) and barrier layer thickness (BLT). Whereas, near cyclonic eddies shallower MLD and BLT is evident. However, MLD and BLT variations near mesoscale eddies are prominent during monsoon and winter seasons, respectively. Heat budget analysis near eddy locations depicts that surface heat fluxes and vertical entrainment are the primary factors responsible for temperature variations near mesoscale eddies. Similarly, the salinity budget analysis near eddy locations reveals that horizontal advection (stirring effect) is the predominant processes responsible for the salinity variations. The outcome of the present study is believed to be useful in validating and improving the eddy-resolving ocean models. [ABSTRACT FROM AUTHOR]

This study addresses the underrepresentation of the Bay of Bengal (BoB) in CMIP6 models, despite its significance in climate change research. Our objective is to propose a methodology to bridge this gap. Through skill score analysis, we identify CIESM as the optimal CMIP6 model for accurately estimating sea surface salinity in the northern BoB. Furthermore, we introduce the novel application of machine learning, specifically artificial neural networks, to enhance predictions from CIESM. This study pioneers the use of ML techniques to improve CMIP6 data for the BoB. Moreover, we examine the relationship between salinity and pH in the BoB, considering the influence of freshwater discharge from multiple rivers. Our findings demonstrate a positive correlation between salinity and pH, highlighting the role of freshwater influx in suppressing acidification. As the intensity of freshwater spread increases, the rate of acidification diminishes. This analysis method presents an efficient approach to curate oceanic parameter data like salinity, contributing to a better understanding of the BoB's dynamics. [ABSTRACT FROM AUTHOR]

The terrestrial magnetic minerals of marine sediments are utilized to track the climatic changes in the source area and the dynamic characteristics of sedimentation processes. However, due to the varied source‐to‐sink environments, the magnetic response to ambient climate cannot be generalized. Here, we conducted systematic environmental magnetic analyses on core CJ04‐50 from the Ninetyeast Ridge and investigated its magnetic response to source‐to‐sink environmental changes. Core CJ04‐50 covers the last 60 Kyr based on accelerator mass spectrometry (AMS) 14C dating and the relative paleointensity (RPI) record. Rare earth element (REE) results suggest that the terrestrial materials are fed by the Ganges‐Brahmaputra (G‐B) and Irrawaddy/Indo‐Burma Ranges. High/low magnetic mineral content corresponds to strong/weak terristrial input during the cold/warm period. This pattern differs from that in the East Asian marginal seas, which have a high magnetic mineral content in warm periods. It might be attributed to the heavier Indian summer monsoon (ISM) precipitation than that of East Asian summer monsoon. Excessive moisture (>1,500 mm/year) would not favor the formation and preservation of magnetic minerals in the source area during interglacials. By contrast, the enhanced physical weathering during glacials results in more magnetic contributions. A significant local magnetite dissolution occurred at the layer of Middle MIS 3, which may be caused by the non‐steady state diagenesis following deposition. Plain Language Summary: Magnetic minerals in marine sediments can record climate and environmental change information, which vary with the source‐to‐sink environmental changes. Here, we extracted magnetic mineral signals from sediments in the Ninetyeast Ridge since the last 60 Kyr. We found that the Ganges‐Brahmaputra (G‐B) and Irrawaddy Rivers are the major detrital sources. The magnetic mineral concentration of the Bay of Bengal is high in glacial period but low in interglacial period, unlike that of East Asian marginal marine sediments. It may be caused by the different monsoon precipitations in South Asia and East Asia. The heavier Indian summer monsoon (ISM) precipitation may result in poor magnetic preservation. In addition, a magnetite dissolution is detected at the layer of Middle MIS 3, which may be caused by a local deep‐sea environmental shift. Key Points: Millennial environmental magnetic records in Ninetyeast Ridge from the past 60 Kyr are reportedDifferent summer monsoon precipitations lead to divergent magnetic responses to chemical weathering in East and South AsiaA local magnetite dissolution was detected at the layer of middle MIS 3 caused by the non‐steady state diagenesis following deposition [ABSTRACT FROM AUTHOR]

Tropical cyclones (TCs) over the Bay of Bengal (BOB) can interact with the South Branch Trough (SBT) as they move northward and potentially amplify Rossby waves. This study evaluates the features of Rossby waves and their downstream impact on rainfall in South China. Results indicate that TC‐SBT interactions primarily occur in May and October‐November (Oct‐Nov), with probabilities of 59% and 53% respectively. Notably, the Rossby wave train associated with BOB TCs is more pronounced during Oct‐Nov due to the stronger subtropical westerly jet, in contrast to May. The downstream atmospheric response results in positive (negative) rainfall anomalies over South China in May (Oct‐Nov), particularly on the day following the maximum interaction day. Previous researches concerning TC‐extratropical flow interaction mainly focus on other basins where TCs move to higher latitudes, this study provides fresh insights into Rossby waves related to TC‐SBT interactions over the southern Tibetan Plateau. Plain Language Summary: During bimodal periods of tropical cyclone (TC) activity over the Bay of Bengal (BOB) in May and October‐November (Oct‐Nov), the Asian subtropical westerly jet is usually located at lower latitudes over the southern Tibetan Plateau, where South Branch Trough (SBT) is active. We quantified the extent of BOB TC‐SBT interaction based on the negative potential vorticity advection by TC‐associated irrotational wind. The mean location of the TC center and maximum interaction point are around (20°N, 88°E) and (33°N, 89°E), respectively. Rossby wave trains (RWT) associated with BOB TCs may extend eastward to 150°W, dispersing at a faster zonal group speed in May compared to Oct‐Nov. In May, the downstream response in South China featured by amplified upper‐level divergent outflow, intensified mid‐level warm and cold air convergence, and enhanced low‐level southwesterly water vapor transport, which was conducive to precipitation. In Oct‐Nov, the RWT shifted northward and the anticyclone anomaly related to the subtropical high dominated South China, leading to a northward shift in water vapor transport, unfavorable for precipitation in South China. The results are significant for the short‐ to medium‐range weather forecasts in downstream regions of BOB TCs. Key Points: Tropical cyclones (TC) over the Bay of Bengal (BOB) interacting with the South Branch Trough (SBT) can amplify mid‐latitude Rossby wavesThe Rossby wave associated with interactions between BOB TCs and SBTs is stronger in October‐November than in MayThe atmospheric response results in positive (negative) precipitation anomalies over South China in May (October‐November) [ABSTRACT FROM AUTHOR]

The Queenfish, Scomberoides commersonnianus, is a large commercial fish in Bangladesh. This is the first study on the Queenfish that aims to elucidate life history parameters and stock status to suggest authority for sustainable management and to support future research on this economically significant species in the region. We used three length‐based approaches to establish a standard for sustainable management of the fishery: (1) TropFishR to give the growth parameters and current exploitation status, (2) the length‐based Bayesian biomass estimation (LBB) to quantify stock biomass, (3) and Froese's sustainability indicators (LBI). The length–weight relationship of Queenfish was a negative allometric pattern (b = 2.84; R2 = 0.98). Growth parameters for Queenfish were L∞ = 124.22 cm, K = 0.31 year−1. Instantaneous total mortality Z = 0.71 year−1, instantaneous natural mortality M = 0.36 year−1, and instantaneous fishing mortality F = 0.35 year−1. Based on the LBB approach, the current estimated stock biomass was overexploited (B/BMSY = 0.65). We recommend strictly maintaining mesh size of nets to reduce harvest of immature fish shorter than 62 cm, while focusing harvest on fish 62–74 cm, to minimise recruitment and growth overfishing. [ABSTRACT FROM AUTHOR]

In this study, we investigate the connection between planetary equatorial waves, modulated by the Indian Ocean dipole (IOD) and El Niño Southern Oscillation (ENSO), and the interannual variabilities of the salinity distribution in the Bay of Bengal (BoB) in October–December (OND), along with its associated dynamics, using satellite and reanalysis datasets. In OND 2010 and 2016 (1994, 1997, 2006, and 2019), positive (negative) sea surface salinity anomalies (SSSAs) were distributed in the eastern equatorial Indian Ocean (EIO) and Andaman Sea. Moreover, the southward movement of negative (positive) SSSAs along the eastern Indian coast was observed. This phenomenon was caused by large-scale anomalous currents associated with zonal wind over the EIO. During OND 2010 and 2016 (1994, 1997, 2006, and 2019), due to anomalous westerlies (easterlies) over the EIO and anomalous downwelling (upwelling) Kelvin waves, the strengthened (weakened) Wyrtki jet and the basin-scale anomalous cyclonic (anticyclonic) circulation in the BoB gave rise to positive (negative) SSSAs within the eastern EIO and Andaman Sea. In addition, the intensified (weakened) eastern Indian coastal currents led to the southward movement of negative (positive) SSSAs. It is worth noting that downwelling Kelvin waves reached the western coast of India during OND 2010 and 2016, while upwelling Kelvin waves were only confined to the eastern coast of India during OND 1994, 1997, 2006, and 2019. Furthermore, westward salinity signals associated with reflected westward Rossby waves could modulate the spatial pattern of salinity. The distribution of salinity anomalies could potentially influence the formation of the barrier layer, thereby impacting the sea surface temperature variability and local convection. [ABSTRACT FROM AUTHOR]

The unicellular calcareous planktic foraminifera sequester a significant portion of the carbon dioxide dissolved in the ocean, thus burying the carbon in sediments for millions of years. The global warming and associated processes are likely to affect the planktic foraminiferal abundance and diversity. Therefore, their baseline distribution has to be documented and correlated with ambient parameters to assess its fate under different climate change scenarios. Here, we report an exceptionally high abundance of planktic foraminifera and thus large carbon burial in the southwestern Bay of Bengal. The very high absolute abundance of planktic foraminifera in the Cauvery River basin is attributed to biannual productivity, warmer and saline waters. Globigerinita glutinata is the highest abundant species followed by Globigerinoides ruber and Globigerina bulloides. Globigerina bulloides is abundant on the shelf, where the upwelling is more frequent. The relative abundance of Globorotalia menardii is positively correlated with thermocline salinity and negatively correlated with thermocline temperature. Similarly, Neogloboquadrina dutertrei and Globoquadrina conglomerata are negatively correlated with mixed layer as well as thermocline temperature and mixed layer salinity. Both these species are positively correlated with thermocline salinity. Globigerina falconensis is more abundant in the southernmost transect influenced by intense winter monsoon precipitation. We report that G. ruber prefers high saline and warmer waters with the highest abundance in the southernmost transect. From the foraminiferal distribution, it is evident that the temperature and salinity of the mixed layer as well as thermocline, food availability, and monsoon-associated processes affect the planktic foraminiferal abundance and thus carbon burial in the southwestern Bay of Bengal. The changes in influx of southeastern Arabian Sea water will affect the planktic foraminiferal population and subsequent carbon burial in the southwestern Bay of Bengal. [ABSTRACT FROM AUTHOR]

Bangladesh is one of the most vulnerable countries in the world to climate change. However, data relevant to ocean warming (OW) and ocean acidification (OA) are not readily available. This is the first study to review the available data relating to OW and OA covering the three parts (eastern, central and western parts) of the coastal marine waters (CMWs) of the Bay of Bengal (BoB), Bangladesh. The review compared the data collected from the three parts of the BoB, Bangladesh with the data and information of previous research carried out within the Indian subcontinent of the BoB (2000-2023). The present research provides an overview of water quality data relevant to OW and OA and the correlation among different water quality parameters. Our research found that the sea surface temperature is increasing and pH levels are decreasing in the BoB, Bangladesh. The current pH in BoB, Bangladesh is still alkaline, with an overall mean pH of 7.58 compared with the global ocean pH of 8.1. DO (overall mean: 6.09 mg/L), Ωarg (overall mean: 2.27) and Ωcal (overall mean: 3.59) levels were found to be within the safe thresholds for marine biota (fish, crustaceans, mussels, oysters, corals and echinoderms). Conversely, nitrate levels (mean: 2.29 mg/L) were found to be high, the concentration of which may enhance nitrogen pollution, algal blooms and hypoxia in the BoB, Bangladesh. The implications of OW and OA on Bangladesh's fisheries and seafood have been briefly discussed. [ABSTRACT FROM AUTHOR]

Present study reports black-edged fin sandlance, Bleekeria nigrilinea Psomadakis, Yoshinaga, Wah et Ida, 2021, for the first time from the Bay of Bengal, Indian waters, on the basis of three specimens. Specimens were collected from the Shankarpur fishing harbour and identified as Bleekeria nigrilinea through molecular analysis and were subjected to full morphological analysis. This species has previously been reported from the Andaman Sea (Myanmar and Thailand). [ABSTRACT FROM AUTHOR]

Tropical cyclones over the Bay of Bengal (BoBTC) affect the precipitation over China, with distinct seasonal and daily variabilities. This study quantitatively examines the daily standardized precipitation anomalies (SPAs) over China on the days with BoBTC activities (storm-days) and related circulations, based on rainfall measurements at surface meteorological stations and ECMWF reanalysis data on a 0.25° × 0.25° resolution during 1979–2019. Significant positive SPA is found over the stations in the two adjacent regions around BoB (Southwest China in May/November and southern Tibetan Plateau in October) and three distant regions (Southeast China and the northeastern boundary of the Qinghai–Tibet Plateau in May, and central North China in October). The SPA distributions are remarkably consistent with the integrated water vapor transport (IVT) anomalies. Enhanced IVT is found associated with the interaction between southwesterly (southerly) of the BoBTC circulation and low-level monsoonal flow in May (midlevel westerly in winter months). The probabilities of extreme precipitation (EP) occurrences over the above regions all increase on storm-days. For adjacent regions, EP is significantly correlated with the northward IVT anomalies to the east of BoBTC circulation, which strengthen the water vapor input through the southern border. Such IVT anomalies are stronger in May, benefited by the deep monsoonal southwesterlies than those in November. For distant regions, EP is more closely related to the IVT anomaly extending back from BoB. Enhanced moisture from BoB concentrates along a local low-level convergence line over Southeast China, being further facilitated by coexistence of the BoBTC depression and midlevel westerly trough in midlatitudes. Our results highlight the interactions between BoBTCs and local weather systems that influence the general precipitation anomalies and occurrence of EP over China, especially over distant regions. [ABSTRACT FROM AUTHOR]

The Bay of Bengal (BoB) is home to a range of commercially important species with different food habits and feeding features. Microplastic (MP) contamination in the fish of BoB, like in many other marine environments, is a significant environmental concern. The study aimed to investigate the presence of microplastics (MPs) in the gastrointestinal tracts (GITs) of selected commercial marine fishes from the Bangladesh coast of the BoB. Six fish species (Escualosa thoracata, Tenualosa ilisha, Johnius belangerii, Trichiurus lepturus, Planiliza parsia, and Mystus gulio) were investigated (n = 120) following hydrogen peroxide digestion, and floatation (saline solution) protocols. After analyses, a total number of 696 MPs (dimension 0.3 to 5 mm) were identified. Moreover, the highest occurrence of MPs in fish GITs was found in planktivorous fish (average of 7.7 items/individual), followed by omnivorous (average of 5.2 items/individual), and carnivorous fish (average of 4.6 items/individual) (p < 0.001). However, planktivorous E. thoracata showed the highest number of MPs per g of GIT (average of 30.99 items/g GIT), whereas T. ilisha showed the lowest count (average of 0.77 items/g GIT). Different types of MPs (fibers (19 to 76%), fragments (6 to 61%), films (8 to 35%), microbeads (0 to 5%), and foams (0 to 2%)) were also observed. In terms of the color of MPs, the transparent, black, green, and blue types were the most common. Polymers were found as polyethylene (35 to 43%), polyethylene terephthalate (28 to 35%), polyamide (20 to 31%), and polystyrene (0 to 7%). The study provides a significant incidence of MPs in fish from the Bangladesh part of the BoB, which is very concerning. Therefore, long-term research is indispensable to ascertain the variables affecting the presence of MPs in fish, their origins, and their potential effects on the BoB fisheries. Stringent policies on plastic use and disposal should be strongly urged in this coastal region. [ABSTRACT FROM AUTHOR]

The elasmobranch population is declining in the Bay of Bengal of Bangladesh due to large-mesh gill net fishing, locally known as the Lakkha net, which primarily targets Indian threadfin (Leptomelanosoma indicum). This study was the first attempt to identify megafaunal bycatch in Lakkha fishing and assess its vulnerability using Productivity Susceptibility Analysis. A total of 40 elasmobranch bycatch species were identified, with sharks comprising 13 species from three families, while 27 rays belonged to six families, with the majority belonging to the Myliobatiformes order (60 %). Productivity and susceptibility scores were assigned to all identified species, with values ranging from 1.27 to 2.73 and 1.50 to 2.63, respectively. The target Lakkha fish exhibited the highest susceptibility score, followed by several pelagic sharks and eagle rays. Vulnerability assessment revealed that 31.7 % (n = 13) of species were highly vulnerable, while 43.9 % (n = 18) were classified as moderate, and 24.4 % (n = 10) were considered to have low vulnerability. All the high-risk megafauna species (n = 13) are classified as threatened by the global IUCN Red List. Sensitivity analysis highlighted susceptibility as a major contributor to species’ vulnerability. Alterations in susceptibility scores led to significant changes in the vulnerability status of many species. The overall data quality assessment indicated moderate data quality across species, with variability observed between productivity (76 % of species received a poor data quality score) and susceptibility attributes. However, vulnerability of these species can be reduced through adequate gear modification, shorter net deployment periods, adoption of safe discharge techniques, identification of critical habitats, and establishment of marine protected areas within this region. This study provides valuable insights into the species composition and vulnerability of elasmobranchs in the Lakkha gill net fishery, emphasizing the need for conservation measures to mitigate bycatch impacts on threatened species.

Nitrate uptake is an essential nutrient for primary production. A study focused on the surface waters of the Bay of Bengal (BoB), new, regenerated, and total production were estimated from nitrate, ammonia, and urea (nitrogen uptakes). Understanding nitrogen uptake rates in coastal waters, where nutrient limitations can disturb environmental biological productivity, is essential. A detailed study of these uptake rates and metabolic processes is required to develop effective mitigation strategies to prevent further degradation of these ecosystems. Total production ranged between 1.39 and 7.43 mmol N m2 d−1, new production ranged between 0.58 and 2.83 mmol N m2 d−1 and regenerated production ranged between 0.83 and 4.59 mmol N m2 d−1. The study observed a significant negative correlation nitrogen uptake along with pH, sea surface salinity (SSS), and sea surface temperature (SST) was observed in the study. The R2 values for SST were 0.605, 0.619, 0.503, 0.601, and 0.627; for SSS they were 0.688, 0.511, 0.498, 0.579, and 0.644 with nitrogen (Na15NO3), ammonium (15NH4Cl), urea (CO(15NH2)2), regenerated, and total production uptake, respectively. pH was highly correlated with nitrate uptake (R2 = 0.525), had a low correlation with ammonium uptake (R2 = 0.439) and a moderate correlated with urea uptake (R2 = 0.526). A positive relationship of nitrogen uptakes with chlorophyll-a, dissolved oxygen, and dissolved inorganic nitrogen (DIN) were observed. Chlorophyll-a had R2 value of 0.608, 0.126, 0.524, 0.526, 0.578, with Na15NO3, 15NH4Cl, CO(15NH2)2, regenerated and total production uptake respectively. Dissolved oxygen (DO) related to ammonium uptake showed a very poor correlation (R2 = 0.079) but a better correlation with urea (R2 = 0.534). New production uptake rate showed a high positive correlation with DO (R2 = 0.645), whereas regenerative production uptake rates showed a relatively low correlation (R2 = 0.519). The positive relationship between DIN and nitrogen uptake had corresponding R2 value of 0.642, 0.591, 0.558, 0.652 and 0.675 for nitrite, ammonium, urea, regenerated and total production uptakes respectively. Total nitrogen: Total phosphate (TN:TP) showed a positive correlation with ammonium. The TN:TP relationship fit nicely with R2 = 0.576 (nitrate uptake), 0.524 (ammonium uptake), and 0.503 (urea uptake) in the coastal BoB. Hence, by applying statistical analysis, principal component analysis and pearson correlation, the interdependency of the environmental parameters enhancing the new production has been confirmed.

Anodontostoma chacunda is a commercial fish species in the market and is usually consumed in fresh, smoked, and dried forms. This study investigated the population structure, length-weight relationships (LWR), condition factor (KF), size at sexual maturity (Lm), and breeding season of A. chacunda in the Bay of Bengal, Bangladesh, using the data collected from January to December 2020. A total of 1061 individuals were collected in the sampling period with the help of fishers. Total length (TL) and body weight (BW) were measured using a measuring board and an electronic balance. The TL ranged from 12.50 to 26.70 cm. The allometric coefficient (b) value was 3.34, indicating positive allometric growth in this species. The fish is in good condition, evidenced by its condition factor (KF) ranging between 0.88 and 1.73. Maturity size ranged from 15.40 to 16.80 cm (TL) based on three distinguished models. Spawning time lasts from January to May and from September to December. The peak spawning time was December of A. chacunda in the Bay of Bengal. This information could prove valuable for fisheries researchers and biologists, facilitating efforts toward the conservation and sustainable management of this species.