Quantitative seismic geomorphology of a submarine channel system in SE Brazil (Espírito Santo Basin): Scale comparison with other submarine channel systems

Detailed morphological analyses of a Pleistocene-Holocene submarine channel system in terms of its hierarchical framework, were carried out using a 3D seismic volume from offshore Espírito Santo, SE Brazil. The channel morphology shows marked variations, with five segments (Segments a to e) being identified along its full length. For example, the cross-sectional area of the channel decreases by a factor of 70 from Segment a to Segment c, and is then followed by a nearly four-fold increase from Segment c to Segment d. The significant changes in channel morphology relate to temporal and spatial variations in flow volume within the channel. In the same channel system, the valley reveals three distinct segments (Segments A to C), with similar aspect ratios but marked variations in morphology along the valley distance. Valley morphological changes are chiefly affected by erosional processes. Segment B is characterised by the largest valley-base width, valley width, and cross-sectional area compared to the other two segments. Valley enlargement in Segment B results from relatively high degrees of lateral channel migration and associated cut bank erosion, leading to the widening of the valley, especially the valley base. In Segment C, the valley is characterised by inner bank erosion in the form of shallow-seated mass failures, which only enlarged the upper part of the valley wall. The spatial variations in both channel and valley morphology documented here suggest an important role of local factors (e.g. salt diapirs, tributaries, overbank collapse) in the development of channel systems. Hence, the morphological analyses developed in this work provide an effective tool for studying channels and valleys on continental slopes around the world.     

Structural styles of Albian rafts in the Espírito Santo Basin (SE Brazil): Evidence for late raft compartmentalisation on a ‘passive’ continental margin

In recent years, hydrocarbon exploration offshore SE Brazil has been focusing on Lower Cretaceous strata deformed by gravity gliding above Aptian salt. A three-dimensional (3D) seismic volume from the Espírito Santo Basin, SE Brazil is here used to: a) test the parameters considered to control raft tectonics on a margin tectonically reactivated in the Cenozoic, and b) investigate the impact of prolonged halokinesis on raft deformation. Offshore Espírito Santo, the combined effects of halokinesis and multiple (Andean) tectonic phases are expressed by local collapse, fault reactivation and late segmentation of Albian rafts. As a result of this deformation we observe four main raft geometries: a) rolled-over rafts, b) tabular rafts, c) collapsed rafts, and d) folded and tilted rafts on the flanks of salt rollers. This work shows that salt rollers formed buttresses to moving Albian-Cenomanian rafts, with withdrawal of salt from underneath some of the rafts leading to their collapse and welding onto pre-salt strata. This process occurred in the studied part of the Espírito Santo Basin with minimum control of post-raft overburden thickness on raft compartmentalisation. Salt withdrawal from underneath the rafts is an important phenomenon as it enhanced connectivity between pre-salt and post-salt units, potentially promoting the migration of hydrocarbons from syn-rift source units into post-salt reservoirs.     

Impact of rapid urbanization on the modern sedimentary environments in a semienclosed embayment: Tong’an Bay,southeast China coast

Tong’an Bay (TAB) is a semienclosed embayment in the north of Xiamen Island. The sea area of TAB was mainly used for aquaculture in enclosed areas before 2003. Since 2003, the districts surrounding TAB have been undergoing a rapid urbanization process, and the scale of land used for urban construction in these districts has been continuously increasing. Under the backdrop of rapid urbanization, the coastline of TAB has largely been transformed into an artificial coastline. Due to the large scale of land reclamation and, dredging activities and the opening of the Gaoqi-Jimei (GJ) Seawall, there have been relatively significant changes in the coastal and submarine geomorphology in central northern, western, and southern TAB and Wuyuan Bay as well as a significant increase in the area where artificial submarine geomorphologies are distributed; the number of surface sediment types in the TAB has increased, and sediments in the sea area surrounding engineering projects have been coarsening; the sediment transport pattern has not significantly changed at the mouth of TAB and in central northern TAB, but the suspended sediment transport direction near the GJ Seawall has changed to a certain extent.     

Air—sea CO2 fluxes in a coastal embayment affected by upwelling: physical versus biological control

Water column pCO₂ and air-sea CO₂ fluxes were studied during an 18-month period (May 1994–September 1995) in a coastal embayment affected by upwelling, located in the northwestern Iberian Peninsula (Ria de Vigo and adjacent shelf). Overall, the region acted as a net annual atmospheric CO₂ sink, with magnitude ranging from 0.54 mgC m⁻²d⁻¹ in the Ria estuary to 22 mgC m⁻²d⁻¹ offshore. During moderate upwelling and upwelling relaxation conditions the sampling area was a sink for atmospheric CO₂. By contrast, during winter conditions and during intense upwelling the flux reversed towards the atmosphere. The relative influence of physical and biological processes on pCO₂ was evaluated using two different approaches: firstly, statistical analysis of physico-chemical correlations, and secondly, a thermodynamic analysis in the oceanic CO₂ system. Both methods yielded consistent results, showing that the main processes controlling seasonal and spatial pCO₂ variability were the production and remineralization of organic matter, explaining ca. 70 % of the total variability. In the inner part of the embayment, air-sea CO₂ exchange was mainly modulated by CO₂ partial pressure gradient, whereas in the adjacent shelf, wind speed largely contributed to CO₂ fluxes between the ocean and the atmosphere.     

Importance of microzooplanktonic crustaceans in the coastal food chain: Bay of Marennes-Oléron,France

Modelling biological processes in marine ecosystems requires a good knowledge of the relationships between the different compartments of the ecosystems. Microzooplanktonic crustaceans are often neglected in field feeding studies, due to the difficulties in identification and to their small size. In coastal areas, difficulties are enhanced by the great quantities of particulate organic matter in the water column.Euterpina acutifrons is the major component of the zooplankton community in the Bay of Marennes-Oléron (south-west France) during the algal spring bloom (nauplii strongly dominate the copepod community). The grazing impact of the copepod Euterpina acutifrons (microzooplanktonic and mesozooplanktonic fractions) on the algal standing stock was estimated in the Marennes-Oléron Bay during this period by means of both laboratory experiments and field data. The results suggest that grazing pressure of the microzooplanktonic stages was similar to the pressure exerted by the mesozooplanktonic ones, underlining the significant role of small copepod stages in marine systems in terms of grazing impact. Our results indicate that the daily grazing pressure exerted by the whole population is quite low in the Marennes-Oléron Bay (about 15 % of the algal standing stock).     

Co-evolving geomorphical and socio-economic dynamics in a coastal fishing village of the Bragança region (Pará, North Brazil)

In the area of a coastal fishing village on the mangrove peninsula of Bragança, State of Pará, North Brazil, coastal changes were observed by a beach profile monitoring programme between 1997 and 2001. The assessment allowed a subdivision of the region into four small coastal cells (1–3 km), partly exhibiting heavy erosion. A number of related socio-economic problems, such as loss of alternative income sources caused by the locally unpredictable erosion patterns were identified in three separate village sections. This results in a year-round dependence on seasonally low fishery incomes and increases the risk of poverty. Since limited options for action are available to the local population, different social groups have evolved different land use patterns, which in turn influence local coastal morphodynamics. Not only the hydrodynamic signature, but also the socio-economic organisation of a coastal community and the co-evolutionary path between these two variables thus indicate the state of a coastal system and the most promising policy actions towards sustainable coastal management.     

Sediment quality assessment in a tropical estuary: The case of Ceará River,Northeastern Brazil

The present study aimed to assess the sediment quality in a tropical estuary located in the northeast of Brazil under semi-arid conditions and multiple sources of contamination, using both toxicity bioassays and metal distribution. The metal distribution followed a concentration gradient decreasing one order of magnitude from the inner station toward the outer estuary, with amounts in the following order: Fe > Al > Zn > Cr > Pb > Cu. The index of geoaccumulation indicated a metal enrichment in the Ceará river sediment, mainly at inner sites, considered from moderately to strongly contaminated by Al, Cu, Cr and Zn. Sediment samples were considered toxic by means of whole sediment tests with copepods (reproduction) and amphipods (survival), and also elutriate fraction and sediment–water interface with sea urchin embryos (development). Acute and chronic toxicity did not exhibit a significant correlation with metals, emphasizing the influence of other contaminants mainly related to the pollution sources installed in the mid-estuary.     

Fracturing and calcite cementation controlling fluid flow in the shallow-water carbonates of the Jandaíra Formation,Brazil

The shallow-marine carbonate rocks of the Jandaíra Formation have been subject to significant permeability variations through time due to various events of fracturing and calcite cementation. As a consequence, the Jandaíra Formation accommodated fluid flow only during specific moments in time. We reconstructed these episodes of fluid flow based on isotope characterizations and microscope characteristics of calcite veins and host rock cements. The Jandaíra Formation, which belongs to the post-rift sequence of the Potiguar Basin in northeast Brazil, was deposited from the Turonian onward until a marine regression exposed it in the Campanian. Due to the subaerial exposure, meteoric waters flushed out marine connate waters, leading to an event of early diagenesis and full cementation of the Jandaíra Formation. Fluid flow through the resulting impermeable carbonate formation appears to be closely related to fracturing. Fracturing in the Late Cretaceous induced a drastic increase in permeability, giving rise to extensive fluid circulation. Host rock dissolution associated to the circulating fluids led to calcite vein cementation within the fracture network, causing it to regain an impermeable and sealing character. In the research area, fluid flow occurred during early burial of the Jandaíra Formation at estimated depths of 400–900 m. This study documents the first application of fluid inclusion isotope analysis on vein precipitates, which allowed full isotopic characterization of the paleo-fluids responsible for calcite vein cementation. The fluid inclusion isotope data indicate that upwelling of groundwater from the underlying Açu sandstones provided the fluids to the fracture network. In Miocene times, renewed tectonic compression of a lower intensity created a secondary fracture network in the Jandaíra Formation. The density of this fracture network, however, was too low to induce a new episode of fluid circulation. As a result, this tectonic event is associated with the development of barren extensional fractures.     

Export production in the Bay of Biscay as estimated from barium – barite in settling material: a comparison with new production

We present barium data for sediment traps deployed in a northeast Atlantic margin environment (Bay of Biscay). Fluxes of excess barium were measured with the objective of calculating carbon export production rates from the surface mixed layer and thus contribute to the understanding of organic carbon transport in a margin environment. Therefore, it was necessary to properly understand the different processes that affected the barium fluxes in this margin environment. Seasonal variability of POC/Ba flux ratios and decrease of barium solubilisation in the trap cups with increasing depth in the water column probably indicate that the efficiency of barite formation in the organic micro-environment varies with season and that the process is relatively slow and not yet completed in the upper 600 m of water column. Thus barite presence in biogenic aggregates will significantly depend on water column transit time of these aggregates. Furthermore, it was observed that significant lateral input of excess-Ba can occur, probably associated with residual currents leaving the margin. This advected excess-Ba affected especially the recorded fluxes in the deeper traps (>1000 m) of the outer slope region. We have attempted to correct for this advected excess-Ba component, using Th (reported by others for the same samples) as an indicator of enhanced lateral flux and assigning a characteristic Ba/Th ratio to advected material. Using transfer functions relating excess-Ba flux with export production characteristic of margin areas, observed Ba fluxes indicate an export production between 7 and 18 g C m⁻² yr⁻¹. Such values are 3–7 times lower than estimates based on N-nutrient uptake and nutrient mass balances, but larger and more realistic than is obtained when a transfer function characteristic of open ocean systems is applied. The discrepancy between export production estimates based on excess-Ba fluxes and nutrient uptake could be resolved if part of the carbon is exported as dissolved organic matter. Results suggest that margin systems function differently from open ocean systems, and therefore Ba-proxy rationales developed for open ocean sites might not be applicable in margin areas.     

Behavioural observations of the common octopus Octopus vulgaris in Baía dos Tigres,southern Angola

Observations on the behaviour of the common octopus Octopus vulgaris were made during daytime and night-time sampling on an unexploited rocky reef habitat in Baía dos Tigres, southern Angola. The relative numerical abundance sampled was 0.47 octopus person^–1 h^–1 during the day and 5.33 octopus person^–1 h^–1 during the night, suggesting that the population under study was nocturnal. The activity patterns differed between sizes of octopus. Small octopus (<20 cm total length [TL]) were observed roaming during the night, whereas the large individuals (>20 cm TL) generally fed in their dens. This ontogenetic behavioural shift may be due to tidal constraints or could be a strategy to avoid cannibalism. Octopus inhabiting a shallow, small-boulder substratum made extensive modifications to their habitat, excavating dens of up to 1 m deep in the sand below the boulders. These dens were not visible during the day as the octopus appeared to retract the small boulders over their den entrances. This unique behavioural strategy is thought to be a means to reduce predation and reduce light intensity during the day. Octopus were not observed in the small-boulder habitat during the five hours of daytime sampling. With nocturnal activity and extensive habitat modification, it is likely that avoidance of predation may be an important driver influencing the behaviour of the octopus population under study.     

Characterization of iron diagenesis in marine sediments using refined iron speciation and quantized iron(Ⅲ)-oxide reactivity:a case study in the Jiaozhou Bay,China

As a case study, refined iron(Fe) speciation and quantitative characterization of the reductive reactivity of Fe(Ⅲ)oxides are combined to investigate Fe diagenetic processes in a core sediment from the eutrophic Jiaozhou Bay.The results show that a combination of the two methods can trace Fe transformation in more detail and offer nuanced information on Fe diagenesis from multiple perspectives. This methodology may be used to enhance our understanding of the complex biogeochemical cycling of Fe and sulfur in other studies. Microbial iron reduction(MIR) plays an important role in Fe(Ⅲ) reduction over the upper sediments, while a chemical reduction by reaction with dissolved sulfide is the main process at a deeper( 12 cm) layer. The most bioavailable amorphous Fe(Ⅲ) oxides [Fe(Ⅲ)am] are the main source of the MIR, followed by poorly crystalline Fe(Ⅲ) oxides [Fe(Ⅲ)pc)]and magnetite. Well crystalline Fe(Ⅲ) oxides [Fe(Ⅲ)wc] have barely participated in Fe diagenesis. The importance of the MIR over the upper layer may be a combined result of the high availability of highly reactive Fe oxides and low availability of labile organic matter, and the latter is also the ultimate factor limiting sulfate reduction and sulfide accumulation in the sediments. Microbially reducible Fe(Ⅲ) [MR-Fe(Ⅲ)], which is quantified by kinetics of Fe(II)-oxide reduction, mainly consists of the most reactive Fe(Ⅲ)am and less reactive Fe(Ⅲ)pc. The bulk reactivity of the MR-Fe(Ⅲ) pool is equivalent to aged ferrihydrite, and shows down-core decrease due to preferential reduction of highly reactive phases of Fe oxides.     

Seasonal dynamics of the density of the crab larvae (Decapoda: Brachyura et Anomura) in Minonosok Bay of Pos’eta Bay (Peter the Great Bay, Sea of Japan)

As the materials for this project, we used data on the distribution of the larvae of the Asian paddle crab Charybdis japonicus (A. Milne-Edwards, 1861); the spider crabs Hyas coarctatus ursinus (=Hyas ursinus) (Rathbun, 1924), Pugettia quadridens (de Haan, 1839), and Pisoides bidentatus (H. Milne-Edwards, 1873); the samurai crab Paradorippe granulata (=Dorippe granulata) (de Haan, 1841); the pea crab Pinnixa rathbuni (Sakai, 1934); and the porcelain crab Pachycheles stevensii (Stimpson, 1858) in Minonosok Bay of Pos’eta Bay obtained during 2000–2002 and in 2004. The planktonic samples were collected from the last third of May to September. The greatest density of the larvae was observed in May, mid-June, late June-early July, and late July-early August. The greatest densities of the crab larvae and the decapod larvae ranged from 20.4 to 48.2 and from 88.4 to 245.3 specimens/m³. The schedule of the crab larvae’s occurrence in the plankton is provided for the first time. The distribution of the density showed pronounced patchiness.     

Skin diseases in Guiana dolphins (Sotalia guianensis) from the Paranaguá estuary,Brazil: A possible indicator of a compromised marine environment

We report on the presence of lobomycosis-like disease (LLD) and nodular skin disease (NSD) in a community of Guiana dolphins (Sotalia guianensis) inhabiting the biologically and chemically contaminated Paranaguá estuary (Brazil) and on their absence in the community living in the cleaner Cananéia estuary. Prevalence rates of LLD and NSD were 3.9% and 12.6%, respectively, in 103 photo-identified (PI) dolphins from the Paranaguá estuary in the period 2006–2007. Adults and calves were affected. Lobomycosis-like lesions may be extensive and form large plaques. Skin nodules were sometimes ulcerated and associated with cutaneous traumas suggesting that traumatic injuries may play a role in the pathogenesis of this condition. In two adult dolphins, NSD evoked the beginning of LLD. In 1996–2007 none of the 200 PI Cananéia S. guianensis had LLD or NSD, a highly significant difference. Interestingly, these dolphins were reported to harbour relatively low concentrations of organochlorines. LLD and NSD are possibly indicators of environmental changes.     

Geomorphological and ecological features of blowouts in a western Mediterranean coastal dune complex: a case study of the Es Comú de Muro beach-dune system on the island of Mallorca, Spain

Many of the coastal dune systems along western Mediterranean shores are in an advanced state of fragmentation and show distinct signs of erosion, largely because of blowout development along the dune front. The Es Comú de Muro beach-dune system on the island of Mallorca (Spain) is a good example of this. In order to better understand and quantify the current situation, 58 blowouts along a ca. 1.5-km-long dune front were investigated. In each case, a number of morphometric and ecological variables were analyzed as a basis for comparison and classification, in particular blowout dimensions and orientation, inner morphometry and topography, morphological types, the role of vegetation in defining the state of the foremost dune line, and the link between vegetation and blowout typology. In comparison with a recent preliminary investigation, the results of the present study provide a more comprehensive picture of the advanced state of fragmentation along the dune front. The blowouts are not evenly distributed, highest densities occurring along the southernmost part of the beach, lowest densities along the northern part. The blowouts were subdivided into two categories on the basis of their shape and general structure, trough blowouts being the most prevalent, followed by mixed trough-saucer shapes. Distinctly saucer-shaped blowouts could not be distinguished. In addition, the blowouts were subdivided into two morphological categories, i.e. simple and branched. It was also possible to link the morphological state of the dune front to certain ecological parameters, in particular vegetation which, in the present case, comprised herbaceous and woody plants. Cluster analyses of species associations (Bray-Curtis similarity indices) were carried out on the basis of the presence/absence of each species. It is shown that, on account of presence counts and the degree of similarity of species associations, some species play a more important role in stabilizing the mobile dune sands than others, a foremost candidate being Ammophila arenaria. It is concluded that active support for such plants should form part of any management strategy aiming to reduce and reverse coastal dune fragmentation processes.     

Interannual variability of Kelvin wave propagation in the wave guides of the equatorial Indian Ocean,the coastal Bay of Bengal and the southeastern Arabian Sea during 1993–2006

The observed variability of the Kelvin waves and their propagation in the equatorial wave guide of the Indian Ocean and in the coastal wave guides of the Bay of Bengal (BoB) and the southeastern Arabian Sea (AS) on seasonal to interannual time scales during years 1993–2006 is examined utilizing all the available satellite and in-situ measurements. The Kelvin wave regime inferred from the satellite-derived sea surface height anomalies (SSHA) shows a distinct annual cycle composed of two pairs of alternate upwelling (first one occurring during January–March and the second one occurring during August–September) and downwelling (first one occurring during April–June and the second one occurring during October–December) Kelvin waves that propagate eastward along the equator and hit the Sumatra coast and bifurcate. The northern branches propagate counterclockwise over varied distances along the coastal wave guide of the BoB. The potential mechanisms that contribute to the mid-way termination of the first upwelling and the first downwelling Kelvin waves in the wave guide of the BoB are hypothesized. The second downwelling Kelvin wave alone reaches the southeastern AS, and it shows large interannual variability caused primarily by similar variability in the equatorial westerly winds during boreal fall. The westward propagating downwelling Rossby waves triggered by the second downwelling Kelvin wave off the eastern rim of the BoB also shows large interannual variability in the near surface thermal structure derived from SODA analysis. The strength of the equatorial westerlies driven by the east–west gradient of the heat sources in the troposphere appears to be a critical factor in determining the observed interannual variability of the second downwelling Kelvin wave in the wave guides of the equatorial Indian Ocean, the coastal BoB, and the southeastern AS.     

Seabed morphology and gas venting features in the continental slope region of Krishna–Godavari basin,Bay of Bengal: Implications in gas-hydrate exploration

Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, Krishna–Godavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor.     

Spatial distribution of sedimentary P pools in a Mediterranean coastal lagoon ‘Albufera d’es Grau’ (Minorca Island,Spain)

The method for the sequential extraction of P proposed by Jensen et al. [Mcglathery, K.J., Marino, R., Howarth, R.W. (1998) Limnol. Oceanogr. 43, 799–810] was used to study the spatial distribution of sedimentary P in superficial sediments of a mesohaline coastal lagoon located in a watershed formed by carboniferous sandstone in the Western Mediterranean (Minorca Island, Spain). Dissolved inorganic phosphate (IP), dissolved organic phosphate (OP), Fe, Ca, Al, and F were analyzed in the extractions to assess adequacy of this method to clay sediments. The elemental composition of the solid phase (Al, Fe, K, Ti, Si, Mg and Ca) was also analyzed to relate concentrations of P pools to the mineral composition. Samples from marine carbonated sediments, rock and some materials of biological origin (tubes of polychaete Ficopomatus enigmaticus, bivalve shell debris) were analyzed for comparative purposes. The sequential procedure allowed to extract almost all sedimentary P from carbonate sediments and biogenic debris, but only 70% of total phosphorus (TP) from clay sediments and rock. Main IP pools in the lagoon were Fe-bound P (16.6% of TP), CaCO₃-bound P mainly from Ficopomatus tubes (12.0% of TP), and detrital carbonate fluorapatite (7.8% of TP). The most abundant P pool was refractory P (20.3% of TP), which appeared associated to the (Fe,K)Al-silicate fraction and to humic P. This indicated that clay–humic–organic P complexes were the main P reservoir in the lagoon. Spatial distribution of P pools reflected differential sedimentation of allochthonous materials, authigenic precipitation of Fe-oxides, and Fe-bound P as well as the differential distribution of organisms such as Ficopomatus.     

Effects of a tanker accident and an oil blowout in Bristol Bay,Alaska, on returning adult sockeye salmon (Oncorhynchus nerka)—A simulation study

The effects of a tanker accident releasing 34000 tons of diesel fuel and a blowout releasing 3000 t/day of crude oil on adult sockeye salmon returning through Bristol Bay, Alaska, were simulated. Parameters in the simulation were chosen to maximize possible effects of the oil. Mortalities from the tanker accident were predicted to range from 2% to 18% of the adults passing through the spill area or 1% to 5% of the total returning population. From 3% to 7% of the adults surviving migration through the spill area, or 1% to 2% of the total population, could be tainted at or above 0·6 ppm of hydrocarbons in the flesh. As many as 30% of the adults returning to fishing grounds closest to the spill area could be tainted. Effects of the blowout on returning salmon were less severe than those of the tanker accident, with mortalities reaching a maximum of 0·2% of the adults passing through the area of the blowout, and no tainting predicted above 0·6 ppm.