Geochemistry of the Cauvery Estuary,East Coast of India

Major ion chemistry of water and elemental geochemistry of suspended and surficial sediments collected from the Cauvery Estuary were studied to understand the geochemical processes in this tropical estuarine system. Specific conductance (EC), total dissolved solids (TDS), and total suspended matter (TSM) increased conservatively with increasing chlorinity. In general, SO₄ ^2?, Na, K, Ca, and Mg showed an increasing trend while H₄SiO₄ and PO₄ ^3? showed a decreasing trend toward the sea. Additional removal mechanisms operating for these ions in the Cauvery Estuary have been identified based on observed concentrations. Factor analysis pointed out the sources contributing to the observed trends in estuarine water chemistry. POC and PON decreased toward the high chlorinity zone. TSM in the Cauvery Estuary were mostly of inorganic nature. Stable carbon isotope values showed that the carbon was equally of marine and terrestrial origin and helped to delineate the contribution of river water and seawater. The ? mean size (a logarithmic grain size scale commonly used by sedimentologists) indicated that the surficial sediments were primarily comprised of coarse and silt, whereas suspended sediments were principally silt and clay. Suspended sediments were enriched in clays compared to surficial sediments. Quartz and feldspar were abundant among detritals while chlorite, kaolinite, and montmorillonite were dominant among clays. Silicon was the most abundant element in the sediments followed by Al, Ca, Na, K, Fe, Mn, and P. Heavy metals were enriched in the suspended sediments compared to the surficial bottom sediments as follows: Fe = 3.5, Mn = 7.4, Pb = 1.1, Zn = 15.2, Cu = 7.4, and Cr = 4.0. The levels of Cd, Cr, Zn, and Fe increased up the middle reaches and then decreased toward the sea due to urban effluent and fertilizer input. Size fractionation studies indicated that the metal concentration in the finer fraction was 50% higher by mass than the coarse silt and fine silt fractions. Chemical fractionation studies showed that the abundance of metals were in the order of residual > organic/sulfide > carbonate > Fe/Mn oxide > exchangeable fractions.     

Atmospheric processes responsible for generation of the 2008 Boothbay meteotsunami

We investigated the atmospheric processes and physics that were active during a tsunami-like event hitting Boothbay Harbor area (Maine, USA) on 28 October 2008. The data collected by tide gauges, ground and sounding stations and meteo–ocean buoys in the area were analyzed, together with satellite and radar images. The atmospheric processes were reproduced by the weather research and forecasting model, verified by in situ and remote sensing data. A cold front moved over the area at the time of the event, with embedded convective clouds detected by satellite and radar data and the internal gravity waves (IGWs) detected by radar and reproduced by the model at the rear of the frontal precipitation band. According to the model, the IGWs that passed over Boothbay Harbor generated strong ground air-pressure oscillations reaching 2.5 hPa/3 min. The IGWs were ducted towards the coast without significant dissipation, propagating in a stable near-surface layer capped by an instability at approximately 3.5 km height and satisfying all conditions for their maintenance over larger areas. The intensity, speed and direction of the IGWs were favourable for generation of a meteotsunami wave along the Gulf of Maine shelf. Operational observation systems were not capable of sufficiently capturing the ground disturbance due to a too coarse sampling rate, while the numerical model was found to be a useful tool in eventual future detection and warning systems.     

Characterization and cycling of atmospheric mercury along the central US Gulf Coast

Concentrations of atmospheric Hg species, elemental Hg (Hg^°), reactive gaseous Hg (RGM), and fine particulate Hg (Hg-PM_2.5) were measured at a coastal site near Weeks Bay, Alabama from April to August, 2005 and January to May, 2006. Mean concentrations of the species were 1.6 ± 0.3 ng m⁻³, 4.0 ± 7.5 pg m⁻³ and 2.7 ± 3.4 pg m⁻³, respectively. A strong diel pattern was observed for RGM (midday maximum concentrations were up to 92.7 pg m⁻³), but not for Hg^° or Hg-PM_2.5. Elevated RGM concentrations (>25 pg m⁻³) in April and May of 2005 correlated with elevated average daytime O₃ concentrations (>55 ppbv) and high light intensity (>500 W m⁻²). These conditions generally corresponded with mixed continental-Gulf and exclusively continental air mass trajectories. Generally lower, but still elevated, RGM peaks observed in August, 2005 and January–March, 2006 correlated significantly (p < 0.05) with peaks in SO₂ concentration and corresponded to periods of high light intensity and lower average daytime O₃ concentrations. During these times air masses were dominated by trajectories that originated over the continent. Elevated RGM concentrations likely resulted from photochemical oxidation of Hg^° by atmospheric oxidants. This process may have been enhanced in and by the near-shore environment relative to inland sites. The marine boundary layer itself was not found to be a significant source of RGM.     

Radiocarbon deficiencies of US Gulf Coast lakes compromise paleo-hurricane records

Radiocarbon assays of sediments from Lake Shelby, US Gulf Coast, exhibit substantial ¹⁴C deficiencies of 9.3% and 4.7% for the limnic sapropel and associated fresh-water clams Rangia cuneata, respectively. Measured radiocarbon dates from the sapropel and clams require corrections of 785 ± 80 and 365 ± 90 ¹⁴C yr (1σ), respectively, in order to achieve consistency with the radiocarbon time scale. Lake sediments of the US Gulf Coast serve as unique repositories of pre-historic hurricane strikes. Previously unrecognized radiocarbon deficiencies likely render compromised chronologies of the paleo-hurricane records, and erroneous estimates of return period and landfall probability that are derived from the storm chronologies. The recalculated severe hurricane chronologies suggest that the annual landfall probabilities of the last millennium on the US Gulf Coast are equal to, or higher than, the preceding three millennia.     

Recruitment Ecology of Burrowing Shrimps in US Pacific Coast Estuaries

Recruitment is a strong determinant of year class strength and adult population density especially for sessile benthic invertebrates where post-settlement mortality and competition are low or relatively stable over time. A series of surveys were undertaken to characterize recruitment and post-settlement processes for two species of burrowing shrimps, Neotrypaea californiensis and Upogebia pugettensis in order to determine how they influenced broader adult populations in US west coast estuaries. On average, U. pugettensis decapodids settled earlier (April–July), recruited almost exclusively to areas with conspecific adults, and grew more rapidly during their first summer than N. californiensis. Neotrypaea californiensis decapodids settled and recruited over a longer period (June–November) and were distributed across the tidal flat. While initially more abundant in areas with conspecific adults, they also either survived better or redistributed as small juvenile shrimp to areas where adults were absent. Linear relationships were found between abundance of newly recruited (0+ age class) shrimp and that of older 1+ shrimp a year later. Positive slopes were close to one for N. californiensis but less than one for U. pugettensis, suggesting lower survival. Annual recruitment varied dramatically but was more consistent for both species in Yaquina Bay. Patterns in strong recruitment years amongst estuaries, particularly for U. pugettensis, suggest the presence of multi-estuary metapopulations linked via larval dispersal. These results have important implications for shrimp population management including control for shellfish aquaculture, but also conservation of estuarine habitats due to the strong influence of these ecosystem engineers on the benthic community.     

Modeling coastal tsunami hazard from submarine mass failures: effect of slide rheology,experimental validation,and case studies off the US East Coast

Natural Hazards - We perform numerical simulations to assess how coastal tsunami hazard from submarine mass failures (SMFs) is affected by slide kinematics and rheology. Two types of two-layer SMF...     

Comparison of electron density models with incoherent scatter radar observations at the equator

This paper points out certain discrepancies when the incoherent scatter radar observations at Jicamarca and the electron density models, (the Bent andiri) were compared. In all cases the bottomside semi-thickness of the observed profile was significantly greater than that of both Bent andiri models. The decay constants associated with the topside ionosphere for the observed profiles were generally greater than that of the two models, the difference being more pronounced in theiri model. The results call for a revision of the models so that they accurately represent the electron density distribution at the equator.     

Assessing meteotsunami potential of high-frequency air pressure oscillations observed in the middle Adriatic

High-resolution air pressure series collected from a triangle of middle Adriatic microbarograph stations between April 2009 and March 2011 have been analysed to extract the rapid pressure changes normally found during meteotsunamis. Five-minute air pressure tendencies were used to detect an event. Wavelet and cross-wavelet analysis showed that the energies of high-frequency pressure changes that occurred during the warm part of the year were an order of magnitude higher than those that occurred during the cold part of the year. Coherence between stations was normally found at periods longer than 1 h, while air pressure disturbances were dispersive and not coherent at shorter periods. This implies that the disturbances had little to no potential to generate meteotsunamis in the middle Adriatic area, as the eigenoscillations in bays and harbours of the region are over timescales of minutes up to a few tens of minutes.     

Observations of meteotsunami on the Louisiana shelf: a lone soliton with a soliton pack

The paper reports unique high-resolution observations of meteotsunami by a large array of oceanographic instruments deployed on the Atchafalaya Shelf (Louisiana, USA) in 2008 with the primary aim to study wave dissipation in muddy environments. The meteotsunami event on March 7, 2008, was caused by the passage of a cold front which was monitored by the NOAA NEXRAD radar. The observations of water surface elevations on the shelf show a highly detailed textbook picture of an undular bore (solibore) in the process of its disintegration into a train of solitons. The picture has a striking feature never reported before not only for the meteotsunamis but in other contexts of disintegration of a long-wave perturbation into a sequence of solitons as well—the persistent presence of a single soliton, well ahead of the solibore. Data analysis and simulations based on the celebrated variable-coefficient KdV (vKdV) equation first proposed by Ostrovsky and Pelinovsky (Izv Atmos Ocean Phys 11:37–41, 1975) explain the physics of this phenomenon and suggest that the formation of the lone soliton ahead of the solibore is very likely to be the result of the specific interplay of natural meteotsunami forcing and nearshore bathymetry. The analysis strongly suggests that the patterns of coexisting lone solitons and packets of cnoidal waves should be quite common for meteotsunamis. They were not observed before only because of the scarcity of high-resolution observations. The results highlight the effectiveness of the vKdV equation in providing understanding of the fundamental mechanisms of the complex natural phenomenon that would otherwise require computationally very expensive numerical models.     

Late Cretaceous stratigraphy,sediments and structure: Gems of the Dorset and East Devon Coast World Heritage Site (Jurassic Coast), England

Extraordinary, long-distance litho-marker beds such as the Lewes and Shoreham Tubular Flints and associated marl seams and fossils, recognised in cliff exposures and cliff-fall boulders, are keys to unlocking the stratigraphy and tectonic structures in the Late Cretaceous of the Dorset and East Devon Coast World Heritage Site (Jurassic Coast). Durdle Cove is a special gem exposing the Lewes and Seaford Chalk stratigraphy where new marker beds are identified and sediments and tectonic structures provide clues to timing of movements that produced a Late Cretaceous pericline which grew into a Miocene monocline along the line of the underlying Purbeck Reverse Fault. During ‘inversion’ along this fault some Late Cretaceous Chalk formations were in part or completely ‘lost’ (e.g. Middle Turonian New Pit Chalk Formation) and others were condensed (e.g. Late Santonian and Early Campanian Newhaven Chalk Formation). Excavation of the A354 road cutting at the Lower Bincombe Farm, has greatly added to the stratigraphical records of Late Cretaceous fossils in South Dorset, especially Coniacian and Early Campanian inoceramid bivalves and the various stratigraphically specific forms of the Late Santonian to Early Campanian echinoid fossil Echinocorys scutata spp. not recorded before in this coastline. The very large bivalve fossil Platyceramus sp. provides clues to chalk sea-floor environments.     

Sea level surges of June 2011 in the NE Atlantic Ocean: observations and possible interpretation

We present a synthesis of tide gauge data recorded on June 26–28, 2011, along the NE Atlantic and the English Channel coastlines, which show a significant sea level disturbance observed from Portugal to England during several hours. Though the amplitude was low (a few centimeters at most), the main disturbance was observed in about 30 harbors. The phenomenon started in south Spain and Portugal in the last hours of 26 June and reached the French west coastline on 27 June, at about noon. Finally, it was observed in the English Channel (UK and France) from 27 June to 28 June and also noticed by witnesses as tidal bores in Cornwall. For some of the places investigated, it was followed by a second signal about 12 h later, especially in the SE of the Bay of Biscay. Spectral analyses show a dominant periods of 25 min present on almost all data and that the phenomenon highlighted the resonant periods of the harbors. Using travel time modeling, we observe that the disturbance traveled much more slowly than long-wave propagation and that the timing does not compel with a single source for all the recordings. A comparison with available atmospheric data reveals that a pressure anomaly traveled the same day across the area, from south Portugal to the English Channel and was probably the origin of several sources for the phenomenon, with a second one completing the later signals. Finally, historic facts present that these kinds of event can be potentially lethal or damaging.     

Studies on the variations of heavy metals in the marine sediments off Kalpakkam,East Coast of India

During the last two decades, the coastal environment of southeast India has experienced intense developments in industry, urbanization and aquaculture. Moreover, the 2004 mega tsunami has devastated this coast, thus affecting the coastal sediment characteristics. These two phenomena prompted a study to characterize the sediment, to understand the mechanisms influencing the distribution of heavy metals and to create baseline data for future impact assessment. Results showed that the coastal sediment was carpeted with a mosaic of sand and silty sand with a minor amount of clay. Heavy metal values showed maximum variation for Fe and minimum for Cd. Their average values showed the following decreasing trend: Fe > Cu > Zn > Pb > Cr > Ni > Cd. This study shows that the major source of metals at Kalpakkam coast are land-based anthropogenic ones, such as, discharge from industrial waste, agricultural waste, urban, municipal and slum sewage into the Buckingham canal, which in turn discharges into the sea through backwaters, particularly during northeast monsoon period. A clear signature of the role of backwater discharge increasing the concentration of a few metals in the coastal sediments during monsoon period was observed. Assessments of the degree of pollution, concentration factor (CF), geoaccumulation index (I _geo) and pollution load index (PLI) have been calculated. CF values and I _geo indicated that the coastal sediment is moderately polluted by Cu and Cd. Increase in Cu, Pb and Zn concentration during the monsoon period (October–January) compared to the rest of the year was noticed. Factor analysis and correlation among the heavy metals concluded that Cr, Ni, Cd and Fe are of crustal origin, whereas, Cu, Pb and Zn are from anthropogenic sources. Organic carbon content in the sediment increased during monsoon period, pointing to the role of land runoff and backwater discharge in enhancing its content. The study also elucidates the impact of the recent tsunami in depleting metal content in the coastal sediment as compared to the pre-tsunami period.     

Authigenic Gypsum in Gas-Hydrate Associated Sediments from the East Coast of India (Bay of Bengal)

Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcites were noticed in distinct intervals in a 32 m long piston core, collected in the gas hydrate- bearing sediments in the northern portion of the Krishna-Godavari basin, eastern continental margin of India at a water depth of 1691 m. X-ray diffraction and energy dispersive spectrum studies confirm presence of pyrite, gypsum, calcite, and other mineral aggregates. The occurrence of gypsum in such deep sea environment is intriguing, because gypsum is a classical evaporite mineral and is under saturated with respect to sea water. Sedimentological, geochemical evidences point to diagenetic formation of the gypsum due to oxidation of sulphide minerals (i.e. pyrite). Euhedral, transparent gypsum crystals, with pyrite inclusions are cemented with authigenic carbonates, possibly indicating that they were formed authigenically in situ in the gas hydrate-influenced environment due to late burial diagenesis involving sulphate reduction and anaerobic oxidation of methane (AOM). Therefore, the authigenic gypsums found in sediments of the Krishna-Godavari and Mahanadi offshore regions could be seen as one of the parameters to imply the presence of high methane flux possibly from gas hydrate at depth.