Regenerative Tourism

Spectral aerosol optical depths over Bay of Bengal and Chennai: I—measurements

Tropical cyclones (TCs) are the most devastating phenomena among all natural disasters, having taken more than half a million lives all over the world in the last five decades. TCs are accompanied by very strong winds, torrential rains and storm surges. The havoc caused by TCs to shipping in the high seas and coastal habitats along the Indian coasts due to above mentioned adverse weather have been known since hundreds of years. The tropical warm north Indian Ocean (NIO), like the tropical North Atlantic, the South Pacific and the NW Pacific, is a breeding ground for the disastrous TC phenomenon. Historically, in terms of loss to human life, the Bay of Bengal TCs have accounted for deaths ranging from a thousand to three hundred thousands. The Bay of Bengal has experienced more than 75 % of the total world-wide TCs causing human death of 5000 or more in last 300 years (Dube et al., 2013). For example, the death toll had exceeded 3,00,000 and 1,40,000 in earlier Bangladesh severe cyclones of 1970 and 1991 respectively in which the damages were beyond imagination. Orissa Super Cyclonic Storm (SuCS) of 29-30 October 1999 had caused over 10,000 human deaths and resulted in destruction and damage to over 1.9 million houses in 14 districts of Odisha (Kalsi, 2006; Mohapatra et al., 2002). Recently there was death toll of 1,40,000 in Myanmar due to very severe cyclonic storm, Nargis during April-May, 2008 (Tyagi et al., 2010). There are several such examples of the enormous storm-havoc along not only the Eastern Indian coast but also along the coasts of the other rim countries of Bay of Bengal and Arabian Sea. The district-wise TC hazard proneness for India has been analysed by Mohapatra et al. (2012a). It indicates that entire east and west coast of India are prone to TC activity. However, TC proneness varies from district to district, being maximum along West Bengal and north Odisha coastal districts.

The Indian subcontinent divides the north Indian Ocean (IO) into Arabian Sea (AS) and the Bay of Bengal (BoB), with different thermohaline properties. Seasonal reversal of winds and equatorial remote forcing due to proximity to equator, influences circulation of these basins. In this study, we numerically modelled the physical characteristics of AS and BoB, using MITgcm with a high spatial resolution of 1/20° (~ 5 km) and 49 vertical levels in a z-coordinate system, on a climatological scale. Temperature, salinity and flow fields were validated with satellite and gridded ARGO datasets. Statistically we established that the model setup simulates the upper ocean features and subsurface circulation in these two basins well.Then, we computed the alongshore volume, heat, and freshwater transport along the coastline of India and eastern Sri Lanka. We observed that the alongshore transport along the eastern coast is stronger with high seasonal variability due to the poleward flowing Western Boundary Current (WBC) and equatorward flowing East Indian Coastal Current (EICC). The west coast transport is influenced by intraseasonal oscillations. We computed the freshwater transport to be an order less than the volume transport. Seasonality of alongshore volume and freshwater transport contradicts each other on the western coast whereas they are in phase on the eastern coast. Then we computed the contribution of freshwater transport in total flow as a percentage of the total volume transport. In the BoB, this is maximum during JJAS season which is limited to the northeastern coast of India, followed by October-November season as it covers the entire east coast. We also observed a weak and narrow freshwater export pathway flowing across the Palk Strait into the Gulf of Mannar. The seasonality of transport and upper ocean salinity highly correlate to each other in this region.Meridional heat transport (MHT) was also computed over AS and BoB. Analysis shows that MHT over AS is stronger than BoB. Both basins act as heat source during summer monsoon and heat sink during winter monsoon. Zonal transport correlates positively with zonal wind whereas meridional transport correlates negatively with meridional wind. Various factors such as wind reversal, Ekman transport and vertical thermal wind shear play a role. Net heat flux positively correlates with total heat transport along the eastern coast of India and southeastern AS. It can be attributed to coastal currents and equatorial forcing which help in advection of heat and thermal ventilation.Understanding the effects of these exchanges on nutrient and carbon transport along the coastal waters via nearshore processes would be aided by further research into these interactions. The high-resolution climatological set-up lays the groundwork for additional research into the physical and biological processes occurring in the Indian coastal seas.

Detailed observations of aerosol optical and physical properties were carried out to study variability at the sea surface, along vertical profiles and total column during the Winter-Integrated Campaign on Aerosols, Gases and Radiation Budget (W-ICARB) from 27 December 2008 to 30 January 2009 in the Bay of Bengal (BoB). The results show large heterogeneity in aerosol load and characteristics; dominance of anthropogenic aerosols over the northern BoB, along the eastern Indian coast and in Far East BoB region and higher fraction of coarse-mode aerosols over the southern parts of BoB. The aerosols over the area are highly influenced by the Indian continental outflow and the biomass burning in the Southeast Asia. On the other hand, the larger fraction of coarse-mode aerosols over the southern BoB is closely associated with intense sea-surface winds producing coarse-mode sea-salt aerosols. The vertical profiles of aerosols obtained via CALIPSO data also exhibit considerable vertical heterogeneities.

Dissolved aluminium cycling in the northern, equatorial and subtropical gyre region of the Indian Ocean

The onset process of Asian summer monsoon (ASM) is investigated based on diagnostic analysis of observations of precipitation and synoptic circulation. Results show that after the ASM commences over the eastern Bay of Bengal (BOB) around early May, the onset can propagate eastwards towards the South China Sea and western Pacific but is blocked on its westward propagation along the eastern coast of India. This blocking, termed the “monsoon onset barrier (MOB)”, presents a Gill-type circulation response to the latent heating released by BOB monsoon convection. This convective condensation heating generates summertime (wintertime) vertical easterly (westerly) shear to its east (west) and facilitates air ascent (descent). The convection then propagates eastward but gets trapped on its westward path. To the east of the central BOB, the surface air temperature (SAT) cools faster than the underlying sea surface temperature (SST) due to monsoon onset. Thus more sensible heat flux supports the onset convection to propagate eastward. To the west of the central BOB, however, the land surface sensible heating over the Indian Peninsula is strengthened by the enhanced anticyclone circulation and air descent induced by the BOB monsoon heating. The strengthened upstream warm horizontal advection then produces a warm SAT center over the MOB region, which together with the in situ cooled SST reduces the surface sensible heating and atmospheric available potential energy to prevent the occurrence of free convection. Therefore, it is the change in both large-scale circulation and air–sea interaction due to BOB summer monsoon onset that contributes to the MOB formation.

The objective of the current study was to tackle the problem of incorrect identification regarding Saurida lessepsianus. In prior research conducted along the eastern coast of India, it had been mistakenly labeled as Saurida undosquamis due to their similar physical characteristics. Through a comprehensive analysis involving both morphological and genetic data, this study serves to establish that the species referred to as S. undosquamis, identifiable by its upper caudal fin with distinctive black spots, along the eastern coastline of India (Bay of Bengal), is in fact S. lessepsianus. The misidentification arose from the assumption that the presence of black dots on the upper lobes of the caudal fin was a unique feature of S. undosquamis, which was later found that this trait is shared among certain species within the same genus. This underscores the necessity for applying the accurate scientific nomenclature to species, as precision in taxonomy is fundamental for effective conservation and management efforts. Consequently, this study significantly expands the documented range of S. lessepsianus to encompass the east coast of India (Bay of Bengal), in addition to its previously recognized habitats in the Mediterranean/Red Sea region and the eastern Arabian Sea.

Being the only tropical ocean bounded by a continent to the north, the Indian Ocean is home to the most powerful monsoon system on Earth. Monsoonal rains and winds induce huge river discharges and strong coastal currents in the northern Bay of Bengal. To date, the paucity of salinity data has prevented a thorough description of the spreading of this freshwater into the bay. The potential impact of the salinity on cyclones and regional climate in the Bay of Bengal is, however, a strong incentive for a better description of the water cycle in this region. Since May 2005, the National Institute of Oceanography conducts a program in which fishermen collect seawater samples in knee-deep water at eight stations along the Indian coastline every 5 days. Comparison with open-ocean samples shows that this cost-effective sampling strategy is representative of offshore salinity evolution. This new dataset reveals a salinity drop exceeding 10 g kg−1 in the northern part of the bay at the end of the summer monsoon. This freshening signal propagates southward in a narrow (~100 km wide) strip along the eastern coast of India, and reaches its southern tip after 2.5 months. Satellite-derived alongshore-current data shows that the southward propagation of this “river in the sea” is consistent with transport by seasonal coastal currents, while other processes are responsible for the ensuing erosion of this coastal freshening. This simple procedure of coastal seawater samples collection could further be used to monitor phytoplankton concentration, bacterial content, and isotopic composition of seawater along the Indian coastline.

Compound hazards, such as the sequential occurrence of Tropical Cyclones (TC) and humid heatwaves in close succession, are more destructive than individual and isolated occurrences of each hazard. While landfalling TCs cause catastrophic consequences from storm surges, strong winds, heavy rain, and pluvial flooding, they are often compounded by anomalous heat. The TC-heat joint occurrence raises significant concerns for public health and critical infrastructure, particularly since powerful TCs may lead to major power outages. For example, TC Remal in May 2024 damaged the coastlines of India and Bangladesh, bordering the Bay of Bengal (BoB), impacting > 10 million people without access to electricity and shelter, with an estimated damage totaling $600 million. For the eastern coast of India, with many small to large port cities, including two major urban agglomerates, Kolkata and Chennai, with populations > 10 million, the likelihood of TC-heat joint occurrence has not been assessed so far. We analyze 251 landfalling TCs on the eastern coast of India between 1982 and 2023. We show that ~16% of terrestrial humid heatwave peaks are compounded by the landfalling TCs, and ~8% of moist heat follows TCs. Further, we show the relative increase in peak wet-bulb temperature in TC-compounded heatwaves is as high as around 7−10% in pre-monsoon (April−May) and post-monsoon (October−December) seasons compared to heatwaves not compounded by the TCs. An anomalous rise in TC-compounded heatwave peaks is more pronounced and often exceeds terrestrial heatwave peaks during the post-monsoon season. Although the annual counts of landfalling TCs over BoB show a decreasing trend, our observational analysis of precursor coincidence rate confirms the increased likelihood of TC-compounded humid heat stress, preconditioned by strong to severe marine heat waves. The derived insights highlight a need to prepare adaptation planning for unprecedented compound tropical cyclones and extreme heat hazards when such sequential hazards are expected to occur more frequently in a warming climate.

The Indian Ocean maskray, Neotrygon indica, is a recently described species from the Bay of Bengal in the eastern coast of India. The conspicuous morphology and less genetic information of this group are often confusing for their identity and phylogeography. In this study, we have collected the specimens from Odisha coast in eastern India and generated the DNA barcode data for comparative analysis with publicly available barcodes of N. indica and other congeners. The morphological characters are similar to the previous record of N. indica. However, the generated barcode data of N. indica showed 2.2–8.0% inter-species genetic distances with the other six species. The studied population of N. indica showed 0.2–1.5% genetic distances with a different known population (Tamil Nadu, Andhra Pradesh, and Bangladesh) in the Bay of Bengal. The BA phylogeny revealed monophyletic clustering of all the studied species. Henceforth, the shallow genetic divergences within the different population of N. indica depicted possible female precise natal philopatric affinity within their range distribution. To corroborate this unique phylogeographic structure, this study evoked more rigorous sampling and detailing with other molecular markers. This study also exhibits the expand range distribution of N. indica beyond its type locality and furnishes a new state record for Odisha. Our data would be a valuable resource for further studies on genetic diversity of N. indica and related species, which will provide new insights for better conservation plans.

To evaluate the genetic diversity of a mangrove species and clarify the genetic structure of its populations, we studied nucleotide polymorphism in two DNA regions of Bruguiera gymnorhiza collected from the southern islands of Japan, Thailand, Malaysia, Indonesia, Micronesia, and India. The two DNA sequences were the chloroplast (cp) intergenic spacer between trnL and trnF genes (ca. 300 bp), and a part (ca. 550 bp) of the nuclear gene coding for glyceraldehyde-3-phosphate dehydrogenase (GapCp). Little polymorphism was found within each of the three geographical regions, Pacific Ocean, Bay of Bengal and Arabian Sea. Throughout the vast regions east of the Malay peninsula including Indonesia, Thailand, Micronesia and the southern islands of Japan (Pacific Ocean), essentially only one haplotype (apart from variation in number of a T repeat) was present. A second haplotype was present on the western coast of Malay Peninsula and the eastern coast of India (Bay of Bengal). On the southwest of Malay Peninsula both of these haplotypes were present. Finally a third haplotype was found only on the western coast of India (Arabian Sea). When taken over all geographic populations, total nucleotide variation within the species was large (μ = 0.006, average of the two genes). Our results are consistent with the hypothesis that this low genetic diversity within any local population and differentiation between the different oceans or regions are caused by very low gene flow between each of the different oceans coupled with frequent fluctuation of population sizes due to the change in sea level. The significance of these results is discussed from evolutionary point of the mangrove forests.

Summary Based on light and scanning electron microscopical studies, a new gonad-infecting species of Philometra Costa, 1845, P. dissimilis n. sp. (Nematoda: Philometridae), is described from the marine fish (Belanger’s croaker) Johnius belangerii (Cuvier) (Sciaenidae, Perciformes) in the Bay of Bengal, off the eastern coast of India. The species is mainly characterized by the body length of male 2.73 – 3.37 mm and that of gravid female 145 – 171 mm, needle-like, equal spicules 96 – 120 μm long, length of the gubernaculum 75 – 90 μm, distal end of the gubernaculum with lamellar structures forming a simple dorsal protuberance and by the V-shaped male caudal mound. Philometra dissimilis is the seventh known gonad-infecting species of this genus parasitizing sciaenid fishes. Moreover, an additional two species of Philometra (only females) were recorded from fishes in the Bay of Bengal: P. lobotidisMoravec, Walter et Yuniar, 2012 from the abdominal cavity of Lobotis surinamensis (Bloch) (Lobotidae, Perciformes), which is a new geographical record, and Philometra sp. from the ovary of Platycephalus indicus (Linnaeus) (Platycephalidae, Scorpaeniformes), representing probably an undescribed species.

Lateral variation in crustal and mantle structure in Bay of Bengal based on surface wave data

Amid the COVID-19 pandemic and countrywide lockdown, the super-cyclone Amphan collided with the eastern coast of India, majorly affecting the Indian state of West Bengal. The lockdown restricted the industrial emissions of greenhouse gases known for increasing the average global temperature, however the sea-surface temperature (SST) profile over the Bay of Bengal indicated higher than average SST values in preceding 5 years. The unexpected increase in sea-surface temperature might have played a major role in formation cyclonic disturbances over the Bay of Bengal, which might have triggered the formation of super cyclone Amphan. The anomalous increase in average SST could be attributed to the sudden lowering of particulate matter concentration due to the lockdown, which resulted in the increase in levels of solar insolation on the sea-surface due to the absence of particulate matter load, which reflects/absorbs the incoming solar radiation to the surface keeping the sea-surface temperature at lower levels.

Using MST Radar located at the Indian tropical station of Gadanki (13.5°N, 79.2°E; near the eastern coast of India), studies have been made on the characteristics of inertia‐gravity waves generated in the lower troposphere during deep depression developed over the Bay of Bengal on 20–24 June 2007. Filtering and the hodograph analyses of horizontal winds indicate that the low‐pressure system has generated inertia gravity waves, propagating outward from the core of the depression. Strong enhancement of radar reflectivity (SNR) in the heights of ∼4–7 km for a few days around 22 June 2007 and the upward propagation of gravity wave energy above this height range indicate that the source of the waves is located at ∼4–7 km. This is in agreement with earlier theoretical expectations. The vertical and horizontal wavelengths of gravity waves are found to be ∼2.2 km and ∼240 km respectively in the troposphere.