Southwestern Bay Research Articles

Archaeological fieldwork in Berenike in 2014 and 2015: from Hellenistic rock-cut installations to abandoned temple ruins

The report brings a comprehensive summary of archaeological fieldwork and survey carried out in Berenike on the Red Sea coast of Egypt and in the Eastern Desert hinterland over the course of two seasons in 2014 and 2015. The completed magnetic map of the site is discussed in some detail, assessing the potential for future excavations. The report covers the most important discoveries of the two seasons, which include fragments of Middle Kingdom Pharaonic stelae, possibly pushing back the foundation of the harbor, archaeological evidence of a rock-cut watercollection system forming part of the Hellenistic-age fortifications and two inscribed stone bases, one of which records a secretary of an aromatics warehouse at Berenike, discovered undisturbed in the courtyard of the Great Temple of Berenike (also called the Serapis Temple). A previously unknown religious(?) complex was discovered on the western outskirts of the site thanks to work with Corona satellite imagery. In turn, analysis of the magnetic mapping of the city revealed an administrative(?) complex in the northern part of the town; the later, 5th and 6th century layers were examined inside a chamber with niche forming part of this complex. Work also continued in the early Roman harbor, uncovering among others a complete timber ship frame, and a collection of garnets in subsidiary buildings in the late Roman temenos located in the entrance to the southwestern bay.

Two interannual dominant modes of the South Asian High in May and their linkage to the tropical SST anomalies

The variations of the intensity and position of the South Asian High (SAH) in May are critical for the interannual change in the Asian summer monsoon onset process. The present work has defined two dominant modes of the SAH in May via the principal component analysis of SAH’s strength, zonal extension and ridgeline position indices during 1979–2015. The first mode (SAH intensity mode) features a coherent enhancement of the SAH strength and zonal extension, while the second mode (SAH position mode) exhibits a meridional swing of the SAH ridgeline. Both diagnosis analysis and numerical experiments validate that the distinct evolution of ENSO in boreal spring determines its different influences on the two modes. When an El Nino decays quickly during March–May, its resultant warm anomalies of sea surface temperature (SST) in the tropical Indian Ocean can affect the SAH intensity mode by modifying the tropical convection over the southwestern Bay of Bengal, acting as a local SST forcing to the circulation. However, the SAH position mode depends on the persistence of the ENSO event during boreal spring. The remote El Nino-related SST forcing can enhance the large-scale descent over the Indo–Pacific Ocean, which suppresses the tropical convection to modify the mid–upper-level thermal structure over South Asia, inducing the interannual variation of the SAH ridgeline in May.

Complex bacterial communities in the deep-sea sediments of the Bay of Bengal and volcanic Barren Island in the Andaman Sea

Deep-sea environments are gaining global attention as potential sources of useful microorganisms, thereby warranting a better understanding of the diversity and genomic potential of the microbes present. To this end, here we provide the first insights into the composition of the bacterial communities in deep-sea sediment samples from the southwestern Bay of Bengal and the geographically distinct volcanic Barren Island in the Andaman Sea. High-throughput 16S rRNA gene sequencing of the sediments revealed the presence of >44,000 operational taxonomic units (OTUs) in each of the samples, suggesting high bacterial diversity. Actinobacteria was the most dominant phylum, representing >20% of the taxonomically assignable OTUs, followed by Firmicutes, Proteobacteria, and Chloroflexi. Numerous bacteria that are potentially involved in the sulfur cycle were observed in the Barren Island sediment sample, while bacteria with clinical and industrial potential were observed in the samples from the southwestern Bay of Bengal. Correlation analysis of the biotic and abiotic parameters showed that the differences in bacterial richness and community composition between the sampling sites were mainly dependent on sediment texture. Using a predictive functional metagenomic approach, this study also discusses the genetic variations that may provide an adaptive advantage to sediment bacterial communities for survival in these extreme deep-sea environments. The results from this study should aid future studies focused on bioprospecting and geochemical cycling in the deep sea.

Evidence for the existence of Persian Gulf Water and Red Sea Water in the Bay of Bengal

The high-salinity water masses that originate in the North Indian Ocean are Arabian Sea High-Salinity Water (ASHSW), Persian Gulf Water (PGW), and Red Sea Water (RSW). Among them, only ASHSW has been shown to exist in the Bay of Bengal. We use CTD data from recent cruises to show that PGW and RSW also exist in the bay. The presence of RSW is marked by a deviation of the salinity vertical profile from a fitted curve at depths ranging from 500 to 1000 m; this deviation, though small (of the order of similar to 0.005 psu and therefore comparable to the CTD accuracy of 0.003 psu), is an order of magnitude larger than the similar to 0.0003 psu fluctuations associated with the background turbulence or instrument noise in this depth regime, allowing us to infer the existence of RSW throughout the bay. PGW is marked by the presence of a salinity maximum at 200-450 m; in the southwestern bay, PGW can be distinguished from the salinity maximum due to ASHSW because of the intervening Arabian Sea Salinity Minimum. This salinity minimum and the maximum associated with ASHSW disappear east and north of the south-central bay (85A degrees E, 8A degrees N) owing to mixing between the fresher surface waters that are native to the bay (Bay of Bengal Water or BBW) with the high-salinity ASHSW. Hence, ASHSW is not seen as a distinct water mass in the northern and eastern bay and the maximum salinity over most of the bay is associated with PGW. The surface water over most of the bay is therefore a mixture of ASHSW and the low-salinity BBW. As a corollary, we can also infer that the weak oxygen peak seen within the oxygen-minimum zone in the bay at a depth of 250-400 m is associated with PGW. The hydrographic data also show that these three high-salinity water masses are advected into the bay by the Summer Monsoon Current, which is seen to be a deep current extending to 1000 m. These deep currents extend into the northern bay as well, providing a mechanism for spreading ASHSW, PGW, and RSW throughout the bay.

Directional characteristics of shallow water waves along southwestern Bay of Bengal

The aim of the present research is to investigate the directional characteristics of waves along the southwestern Bay of Bengal based on the measured data during 2010 at 14m water depth. Diurnal, monthly and annual variation of reflected waves is studied for waves within a frequency range of 0.03–0.125Hz to eliminate the influence of local wave growth processes. High values of directional width during the annual cycle over the southwestern Bay of Bengal is associated with the swell reflection from the coast during southwest monsoon season (June–September) and intrusion of moderate easterly winds propagating from Gulf of Thailand over the narrow land mass of Thailand and Myanmar. The reflected wave energy is maximum (14%) during the southwest monsoon due to the presence of long period and intermediate period waves and minimum (9%) during the northeast monsoon season (October–January). During fair-weather period (February–May), 10% of the total energy is propagated towards offshore. We also analyzed the relationship between directional and non-directional wave parameters using continuous wavelet transform and wavelet coherence analysis (WCA). WCA shown that reflection coefficient and total energy is directly/inversely proportional to the swells, when signal of period approximately less/greater than one day is observed.

South-Eastern Bay of Biscay eddy-induced anomalies and their effect on chlorophyll distribution

The analysis of deep-water glider hydrographic and fluorescence data, together with satellite measurements provides a new insight into eddy-induced anomalies within the South-Eastern Bay of Biscay, during summer. Two cyclonic eddies and a SWODDY have been observed in different glider transects and by means of different sources of satellite data. Vertical profiles reveal complex structures (characteristic of the second baroclinic mode): upward/downward displacement of the seasonal/permanent thermocline in the case of X13 and the opposite thermocline displacements in the case of the cyclones. This is a typical behaviour of mode-water and “cyclonic thinny” eddies. A qualitative analysis of the vertical velocities in the anticyclone indicates that though geostrophy dominates the main water column, depressing the isopycnals, near the sea-surface the eddy-wind interaction affects the vertical currents, favouring Ekman pumping and upwelling. The analysis of the Θ-S properties corroborates that inside cyclones and between the 26 and 27 isopycnals, net downwelling occurs. These two types of intra-thermocline lenses appear to deeply impact the Chl-a fluorescence profiles, since the maximum Chl-a fluorescence is located just below the seasonal thermocline. The mean Chl-a fluorescence was higher in the anticyclone than within the cyclones and the mean for the entire study period; the highest values were observed in the centre of the anticyclone. These results are in agreement with previous findings concerning the SWODDY F90 and surrounding cyclones, located in the South-Western Bay of Biscay. Significant differences in the Θ-S properties of the two cyclonic mesoscale structures have been observed: higher temperatures and lower salinity in the easternmost cyclone. Finally, time variation of the salinity content of the shallowest water masses of the anticyclone (salinity decreasing over time), probably indicates advective mixing processes occurred during the mission.

Berenike Project. Hellenistic fort, Roman harbor, late Roman temple, and other fieldwork: archaeological work in the 2012 and 2013 seasons

Brief overview of two seasons of archaeological survey and excavation carried out in 2012 and 2013 at the site of Berenike on the Red Sea coast and in two sub-projects in the Eastern Desert: the prehistoric cattle cemetery at Wadi Khashab and the Roman-era emerald mines at Sikait and Nugrus. Highpoints of the work at Berenike included discovery of the Hellenistic fort and fortifications that mark the original settlement of the site in the third quarter of the 3rd century BC, continued clearance of harbor-related structures in the southwestern bay interpreted as the early Roman harbor of Berenike and the uncovering of an earlier phase of the late Roman harbor temple (so-called Lotus Temple) of the 5th–6th century AD in the harbor.

Role of Mesoscale Eddies in the Distribution Pattern of Zooplankton Standing Stock of Western Bay of Bengal During Spring Transition

Hydrography and spatial variability of zooplankton community during spring transition associated with Anti Cyclonic Eddies (ACE) and Cyclonic Eddies (CE) in the south western Bay of Bengal is investigated. In situ data collected on board FORV Sagar Sampada and satellite derived products were used for the study. Physical parameters such as temperature, salinity, and sigma-t in the surface waters showed typical spring condition with almost uniform distribution in the region. However, MLD, ILD and BLT showed noticeable variation between ACE and CE region. The satellite derived SSHA overlaid geostrophic current pattern indicates the piling up of surface water (20cm) in the region as the result of ACE centred at 13.25°N, 83°E and negative anomaly of 24cm associated with Cyclonic eddy at 15°N, 84°E. Observed cyclonic eddies (15°N, 84°E) are characterised by depressing temperature by about 7°C at 100m depth. The forcing mechanism of ACE identified as negative wind stress curl and associated westward propagating Rossby waves and formation of CE might be due to baroclinic instability developed by equator ward flow of fresh plume water from the north during the winter monsoon period. The biological response in the primary and secondary level to these phenomena explained based on chlorophyll-a distribution and mesozooplankton standing stock. Satellite imagery showed a uniform distribution of surface chlorophyll (< 0.1 mg m˗3) in the study region, except a slight increase in the CE. Subsurface Chlorophyll Maxima (SCM) observed at the base of the mixed layer showed the preference of phytoplankton community to the optimum environmental conditions. Mesozooplankton standing stock observed was relatively higher at CE and the centre of ACE. Enhanced phytoplankton standing stock due to the nutrient enrichment at CE favoured the abundance of zooplankton community. In contrast to the general trend, core of ACE supported higher zooplankton standing with dominance of copepods, chaetognaths, ostracods etc. Relatively higher biological production in the primary as well as secondary level during the present study was associated either with the extended winter production to the early months of spring or the characteristics like intensity, age, spatial variation of prevailing physical processes.

Effect of background substrate on recruitment of benthic marine invertebrates to subtidal cobble-filled collectors

The availability of suitable substrate for settlement can alter the behaviour of larvae of benthic marine invertebrates and consequently their settlement patterns. We tested the effect of the background substrate of a site (rocky vs sediment) on recruitment of invertebrates settling into standardized cobble-filled collectors deployed at shallow subtidal sites in the south-western Bay of Fundy, Canada, in 2009 and 2010. The assemblage of invertebrates that settled into the collectors differed significantly in both abundance and species composition between “paired sites” (≈0.003–0.009 km2 in area and 345–861 m apart) with rocky vs sediment background substrate, and markedly less so between paired sites comprised of rocky bottom. Species that are known to be rock-dwelling recruited in greater abundance to cobble-filled collectors at rocky sites, while those known to be sediment-dwelling recruited more to cobble-filled collectors at sediment sites. At the smaller spatial scale of patches of sediment within one site (14–107 m apart), differences in abundance but not species composition were detected between collectors on the two types of background substrate. This study supports the idea that larvae of some species of marine invertebrates respond to substrate at a larger spatial scale than their immediate location of settlement.

Response of micro- and mesozooplankton in the southwestern Bay of Bengal to a cyclonic eddy during the winter monsoon, 2005.

A cyclonic eddy (CE) in the southwestern Bay of Bengal (SWBoB; 10-15° N; 81-87° E) during winter monsoon 2005 and associated changes in the open ocean hydrography and productivity patterns were studied using satellite observations and in situ measurements. Analysis of the satellite-derived sea surface height anomaly (SSHA) indicated the existence of a large eddy (10-15° N; 81-87° E) from November to January, with its core centered at 13° N and 82° E. The large positive wind stress curl (~1.8 × 10(-7) N m(-2)) and resultant Ekman pumping (~3 × 10(-2) cm s(-1)) were identified as the prominent forcing mechanisms. In addition, the cyclonic storms and depressions experienced in the region during the study period seem to have served to maintain the strength of the CE through associated Ekman pumping. The cold (~26.6 °C), nutrient-enriched (NO3 > 2 μM, PO4 > 0.73 μM and SiO4 > 3 μM) upwelled waters in the upper layers of the CE enhanced the biological production (chl. a > 0.56 mg m(-3)). Dissolved oxygen in the surface waters was > 200 μM. The phytoplankton and zooplankton biomass recorded during the season was comparable or perhaps higher than the peak values reported from the northeastern Arabian Sea (chlorophyll a concentrations of 0.2 to 0.4 mg m(-3) and zooplankton biovolume 0.6 ml m(-3)) during winter. Occurrence of a higher mesozooplankton biovolume (0.8 ml m(-3)) and relatively low abundance of microzooplankton indicates the prevalence of a short food chain. In conclusion, high biological production, both at primary as well as secondary level, suggests the prevalence of an efficient food web as a result of physical forcing and subsequent ecological interactions evident up to tertiary level in an oligotrophic basin like BoB.

Observed Variability of Near-Surface Salinity Field on Seasonal and Interannual Time Scales and Its Impact on the Evolution of Sea Surface Temperature of the Tropical Indian Ocean

A subset of the newly published salinity and temperature climatologies of the global ocean is assembled to examine the observed seasonal variability of the near-surface salinity field of the tropical Indian Ocean. The role of vertical haline stratification in the near-surface layers on the manifestation of the barrier layer thickness in the new climatology is addressed. The warm pool of the tropical Indian Ocean is characterized to identify the geographic regions where the near-surface haline stratification and the warm pool core co-exist. Among the three regions within the warm pool of the tropical Indian Ocean, viz., southeastern Arabian Sea, southwestern Bay of Bengal and eastern equatorial Indian Ocean, a strong coupling between the near-surface haline stratification and the subsequent evolution of the warm pool core is most prominently seen only in the southeastern Arabian Sea. The observed year to year co-variability of the near-surface low salinity pool and the warm pool core in the southeastern Arabian Sea is examined.

Diurnal Variability of Ambient Noise in Shallow Tropical Waters, South Western Bay of Bengal

Ambient noise recorded at shallow southwestern Bay of Bengal during September 2010 has been analyzed for spectral characteristics in the band 0.1–5.0 kHz. The noise level (NL) exhibits diurnal periodicity in the band 0.5–2.0 kHz, during most of the day. The in situ wind data at the site correlates well with the NL, which also shows a diurnal cycle. Wavelet analysis further carried out establishes of the diurnal periodicity in wind/NL pattern during fair weather conditions under the influence of local wind effects. Wavelet coherence shows wind and noise to be in phase or wind leading noise. Diurnal variation in wind is more frequently observed along the coast in tropical regions due to differential heating of land and sea, and this has attributed to the NL pattern at the site. The period of measurement is also favorable for the formation of such localized circulation since it is the sunny unclouded period prior to the Bay of Bengal cyclone season and the northeast monsoon.

Foraminiferal record of Holocene paleo-earthquakes on the subsiding south-western Poverty Bay coastline, New Zealand

Foraminiferal faunas in 29 short cores (maximum depth 7 m) of estuarine and coastal wetland sediment were used to reconstruct the middle–late Holocene (last 7 ka) elevational history on the southern shores of Poverty Bay, North Island, New Zealand. This coast is on the southwest side of a rapidly subsiding area beneath western Poverty Bay. Modern Analogue Technique paleo-elevation estimates based on fossil foraminiferal faunas indicate that the four study areas have gradual late Holocene (<3.5 ka) subsidence rates that increase from the southwest (mean c. 0.5 m ka–1) to northeast (mean c. 1.0 m ka–1). Only two rapid, possibly co-seismic, vertical displacement events are recognised: (1) c. 1.2 m of subsidence at 5.7 ± 0.4 ka (cal yr BP), which may have been generated by a subduction interface earthquake centred offshore and recorded in other published studies in northern Hawkes Bay, c. 35 km to the south; and (2) c. 1 m of uplift (relative sea-level fall) at c. 4.5 ± 0.3 ka, which might have been generated by rupture on an offshore upper plate fault that also uplifted coastal terraces at Pakarae and Mahia, 40 km to the north and south of the study area, or by rupture on the subduction interface penetrating beneath Poverty Bay. No sudden displacement events are recognised during the last 4 ka although subsidence, possibly aseismic, has continued.

The impact of non–local birds on yellow–legged gulls (Larus michahellis) in the Bay of Biscay: a dump–based assessment

Understanding how animals exploit non–natural feeding sources such as garbage dumps is necessary from many perspectives, including conservation, and population dynamics and management. Several large predatory gulls (Larus spp.) are among the species which most clearly benefit from using dumps. The yellow–legged gull (L. michahellis) is the most abundant gull in the southwestern Palaearctic, and its fast population increase until at least the 2000s was partly due large waste dumps becoming more numerous. The Bay of Biscay is an area that hosts resident local and also wintering non–local yellow–legged gulls. Using data collected over a period of eight years (bird counts, identification of colour–ringed individuals) at four dumps situated within a 60–km radius from the colonies of Gipuzkoa (southwestern Bay of Biscay), we aimed to answer: (1) the origin of gulls using dumps at the Bay of Biscay; (2) the impact of local and non–local gulls at these dumps; (3) the possible age–dependent use of these sites; and (4) the possible seasonal fluctuations in the use of dumps by gulls. Gulls in our area (study dumps) came from nearby colonies in Gipuzkoa, Atlantic Iberia, the Mediterranean region, and other areas such as Atlantic France and inland colonies (Navarra, Germany). Our study dumps seemed to be used mostly by local gulls.

Size-at-age and body condition of juvenile American lobsters (Homarus americanus) living on cobble and mud in a mixed-bottom embayment in the Bay of Fundy

American lobsters, Homarus americanus, prefer structurally complex cobble bottom for settlement and early development, but this habitat is sparse and some juveniles are likely forced to exploit other habitats, such as mud bottom. Size-at-age and body condition of juvenile lobsters may vary between cobble and mud habitats, due to differences in food and shelter the habitats provide. In this study, we used cobble-filled collectors deployed on mud and cobble bottom to capture juvenile lobsters occupying cobble and mud seafloor in a mixed-bottom embayment in the southwestern Bay of Fundy, Canada. We compared their size-at-age using a recently developed age-determination technique, and their body condition using mass–length relationship, RNA/DNA ratio and protein content. Individuals 3 and 4 years of age inhabiting mud bottom had greater carapace length than same-age conspecifics on cobble, which could be due to greater growth of juveniles in the less preferred mud habitat. We also found that for a similar carapace length lobsters on mud had slightly lower body mass than those on cobble. RNA/DNA ratio and protein content did not differ between juveniles sampled from the two habitats. Our results suggest that mud bottom represents a more important habitat for young lobsters than is currently appreciated. We hypothesize that mud bottom has become a more important juvenile habitat in recent years due to high lobster abundance, which may be forcing some juveniles to move from preferred but saturated cobble patches to other habitats, such as mud.

The diurnal salinity cycle in the tropics

AbstractObservations from 35 tropical moorings are used to characterize the diurnal cycle in salinity at 1 m depth. The amplitude of diurnal salinity anomalies is up to 0.01 psu and more typically ∼0.005 psu. Diurnal variations in precipitation and vertical entrainment appear to be the dominant drivers of diurnal salinity variability, with evaporation also contributing. Areas where these processes are strong are expected to have relatively strong salinity cycles: the eastern Atlantic and Pacific equatorial regions, the southwestern Bay of Bengal, the Amazon outflow region, and the Indo‐Pacific warm pool. We hypothesize that salinity anomalies resulting from precipitation and evaporation are initially trapped very near the surface and may not be observed at the 1 m instrument depths until they are mixed downward. As a result, the pattern of diurnal salinity variations is not only dependent on the strength of the forcing terms, but also on the phasing of winds and convective overturning. A comparison of mixed‐layer depth computed with hourly and with daily averaged salinity reveals that diurnal salinity variability can have a significant effect on upper ocean stratification, suggesting that representing diurnal salinity variability could potentially improve air‐sea interaction in climate models. Comparisons between salinity observations from moorings and from the Aquarius satellite (level 2 version 3.0 data) reveal that the typical difference between ascending‐node and descending‐node Aquarius salinity is an order of magnitude greater than the observed diurnal salinity anomalies at 1 m depth.

Observed oceanic response to tropical cyclone Jal from a moored buoy in the south-western Bay of Bengal

Upper oceanographic and surface meteorological time-series observations from a moored buoy located at 9.98°N, 88°E in the south-western Bay of Bengal (BoB) were used to quantify variability in upper ocean, forced by a tropical cyclone (TC) Jal during November 2010. Before the passage of TC Jal, salinity and temperature profiles showed a typical BoB post-monsoon structure with relatively warm (30 °C) and low-saline (32.8 psu) waters in the upper 30- to 40-m layer, and relatively cooler and higher salinity (35 psu) waters below. After the passage of cyclone, an abrupt increase of 1 psu (decrease of 1 °C) in salinity (temperature) in the near-surface layers (up to 40-m depth) was observed from buoy measurements, which persisted up to 10–12 days during the relaxation stage of cyclone. Mixed layer heat budget analysis showed that vertical processes are the dominant contributors towards the observed cooling. The net surface heat flux and horizontal advection together contributed approximately 33 % of observed cooling, during TC Jal forced stage. Analysis showed the existence of strong inertial oscillation in the thermocline region and currents with periodicity of ∼2.8 days. During the relaxation stage of the cyclone, upward movement of thermocline in near-inertial frequencies played significant role in mixed layer temperature and salinity variability, by much freer turbulent exchange between the mixed layer and thermocline.

Fluorescent dissolved organic matter in the continental shelf waters of western Bay of Bengal

Fluorescent dissolved organic matter (FDOM) of southwestern Bay of Bengal surface water during southwest monsoon consisted five fluorophores, three humic-like and two protein-like. The humification index (HIX) and humic fluorophores, viz., visible (C), marine (M) and UV (A) humic-likes indicated, better than biogeochemical constituents analyzed, that the northern-half region of the study area which is closer to the head bay (less salinity) is distinctly more terrestrially influenced. Similarly, the southern-half region (less dissolved oxygen) is indicated as more in situ influenced. This region is enriched with tyrosine protein-like fluorophore (B), an indicator of bacterial metabolism in some of its samples due to upwelled water. Although chlorophyll a is less in this (southern) region, the fluorescence based biological index (BIX) which is an index of recent phytoplankton production is about the same in the two regions, and the lower chlorophyll a of southern region is attributed to greater grazing pressure. Fluorescence properties, e.g., BIX are more informative about phytoplankton production than chlorophyll a.

Monsoon and cyclone induced wave climate over the near shore waters off Puduchery, south western Bay of Bengal

Seasonal and annual variations in wave characteristics are studied based on measurements during 2009–2011 using wave rider buoy. Presence of swells generated by the south Indian Ocean cyclones are found over the south western Bay of Bengal during pre-monsoon season. Maximum significant wave height is measured 6m during Thane cyclone in December, 2011. Long period waves are observed mostly during the summer (SW) monsoon and are negligible in the winter (NE) monsoon period. Short period waves dominate (63%) the wave climate during the NE monsoon. Wave spectra during the SW monsoon are multi peaked whereas during the post monsoon season single peaked spectra are found. Single peaked spectra observed during SW monsoon of 2011 coincides with the presence of positive Indian Ocean Dipole. Waves during the pre monsoon and SW monsoon season are influenced by sea breeze. Analysis indicates that directional width is minimum for waves from the NE since they are wind waves and maximum for waves from SE since they are swells. Study indicates that wave climate of the south western Bay of Bengal is in contrast to that in eastern Arabian Sea during the SW monsoon.

Temporal Distribution of Dissolved Trace Metal in the Coastal Waters of Southwestern Bay Of Bengal, India

The objective of the present study was to characterize the concentrations of selected dissolved trace metals in the coastal waters (500 m from shore) of Kalpakkam, Tamil Nadu, India. The order of dissolved concentration of these metals was found to be as follows: Co (cobalt) < Cd (cadmium) < Cr (chromium) < Mn (manganese) < Cu (copper) < Ni (nickel) < Pb (lead) < Zn (zinc). The levels of these trace metals were found to be relatively low as compared to the reported values for other Indian coastal waters, which indicates negligible pollution at this location. Cadmium was the only metal found to increase its concentration during the monsoon period, suggesting its allochthonous input. Factor analysis indicated that chromium, nickel, zinc, cobalt, copper, manganese, and lead were of common origin, and external inputs through land runoff had nominal or little impact, typifying in-situ regeneration and remineralization linkage with their temporal variation. However, levels of zinc, cobalt, and copper remained relatively high during the summer period, and abrupt increases in their concentration during December (monsoon season) may be due to their dual (autochthonous as well as allochthonous) input.