Offshore Domains Research Articles

Volcanic weathered crust reservoir analog: Insights from fault-controlled fracture permeability in the trachytic rocks of the Pernambuco Basin, NE Brazil

Naturally fractured volcanic rocks represent a globally significant potential hydrocarbon reservoirs and can also be used for CO2 storage; however, the study of volcanic reservoirs in Brazil is limited. Although numerous volcanic reservoir types have been classified, relatively few studies are dedicated to the weathering of crust-like reservoirs, i.e., volcanic rocks undergoing subaerially alteration by weathering prior to deep burial. This study aims to characterize a volcanic weathered crust reservoir analog located in the coastal zone of the Pernambuco Basin, NE Brazil. We applied a multiscale approach motivated by the expressive potential of volcanic rocks as reservoirs in this marginal basin and considered their implications for CO2 geological storage projects. The deformational aspects observed in this analog have also been observed in other volcanic rocks that crop out in the coastal zone, thus, the data provided here can guide future characterization of both onshore and offshore reservoirs. We focused on an 80 m wide outcrop and employed geometric and topological analysis of two-dimensional fracture networks to investigate the influence of regional fault zone control on the fracture permeability tensors. The parameters of fracture systems were studied using terrestrial gravimetric data, orthophoto mosaic obtained by an unmanned aerial vehicle (UAV), petrography, and outcrop-based structural data. The investigated outcrop includes porphyritic trachytes with euhedral sanidine crystals and minor quartz phenocrysts, sourced from the Ipojuca Magmatic Suite. The residual Bouguer map indicates the influence of at least two regional rift fault zones, i.e., NW-SE (strike-slip) and NE-SW (normal) trending systems, in the studied rocks. These trachytic rocks exhibited a marked dissolution of sanidine phenocrysts and matrix, columnar disjunctions, and natural fractures, causing the porosity and permeability of the reservoir analog to increase. Geometric and topological analyses showed that the south-central sector of the outcrop exhibits heightened connectivity within the fracture network. Furthermore, the principal fracture permeability is controlled by the primary families of the fracture network and regional fault zones. Our results demonstrate that the fracture network observed in the volcanic reservoir analog was influenced by the post-rift tectonic reactivation of Cretaceous structures within the Pernambuco Basin. The secondary porosity resulting from weathering and subsequent dissolution of the primary constituents and fractures of the rocks studied demonstrates the potential for the exploration of these reservoirs as models for known occurrences of volcanic rocks in the onshore and offshore domains of the Pernambuco Basin.

Evaluating ERA5 reanalysis predictions of low wind speed events around the UK

Low wind speed events represent one of the biggest challenges in fully de-carbonising the electricity system due to the growing proportion of wind energy in the UK energy mix. While reanalysis products are a useful tool to study the spatio-temporal characteristics of these occurrences, their performance and limitations should be understood prior to usage. In this study, hourly 10 m ERA5 reanalysis wind speed data were evaluated against in-situ wind speed measurements from 205 onshore and offshore observation stations around the UK. It was found that ERA5 has biases in mean wind speed of 0.166 m/s and −0.136 m/s for onshore and offshore domains respectively, and biases in hourly wind speed standard deviation of −0.354 m/s and −0.425 m/s for onshore and offshore domains respectively. Both errors are more pronounced in autumn and winter. These errors lead to an underestimation of the percentage frequency of short-duration low wind speed events. Furthermore, the findings suggest that the largest errors are from sites which are situated in coastal and mountainous regions where short-range topographical variability and local wind effects may not be resolved by ERA5. Despite these shortcomings, ERA5 nevertheless outperforms its global reanalysis counterparts in the UK domain and therefore, can provide valuable information in the context of low wind speed events prediction.

Along-strike segmentation of the northeastern Brazilian margins controlled by geodynamics and lithospheric inheritance

Passive continental margins depict a wide range of crustal architectures. Such observation mainly come from wide-angle seismic that has proven to be a valuable tool to constrain margins’ onshore and offshore crustal structures. Yet, it is still unclear what are the main drivers of such diversity and whether some more general processes do also control their formation. Here, by analyzing coincident marine seismic reflection and refraction data acquired parallel to the coast of northeast Brazil we shed a unique view on the along-strike segmentation of its passive margins. Our two P-wave velocity models add up to 10 other wide-angle velocity models build in the scope of the SALSA (Sergipe ALagoas Seismic Acquisition) project to provide a coherent picture of the crustal and upper mantle architecture of the offshore domains of the Jequitinhonha, Almada, Camamu, Jacuípe, Sergipe and Alagoas margins. In the Camamu-Jacuípe segment, both crustal necking and the continent to ocean transition were shown to be sharp. Along strike, our models show extremely thin crust above a thick anomalous velocity layer and a relatively low density mantle. This architecture is interpreted as made of collapsed continental blocks above either highly intruded lower continental crust and/or serpentinized mantle that is locally exhumed. It greatly differs from the crustal structure imaged to the south, within the Jequitinhonha and Almada segments, where our models support the existence of a vast and homogeneous domain of exhumed lower continental crust. It also considerably contrasts with the offshore architecture of the Sergipe-Alagoas segment to the north. There, the necking and transition to normal oceanic crust was shown to be narrow but gradual and dominated by middle to lower continental crust. On our along-strike models, it is characterized by a thicker but also highly intruded continental crust. Crustal architecture evolves brutally at the frontiers of these segments which coincides precisely with the Camamu Triple Junction and the offshore prolongation of the Vaza Barris fault zone. The former is one of the major geodynamic features in the development of the Central Segment of the South-Atlantic Ocean while the later marks the suture between the São-Francisco Craton and the northeastern Brazilian Orogenic Belt. Therefore, we clearly evidence the first-order control of both geodynamics and lithospheric inheritance on the along-strike segmentation of the northeastern Brazilian passive margins. Our results emphasize the crucial role of plate kinematics and lithospheric strength in shaping their architectures and the exhumation of middle/lower continental crust as a more general process of their formation.

EFFICIENT ENERGY STORAGE AND HYDROGEN PRODUCTION FOR A SUSTAINABLE FUTURE INSIDE THE OIL AND GAS INDUSTRY

Hydrogen transcends its traditional perception as a standalone green energy source, assuming a pivotal role in elevating the efficiency of green energy production. Rather than serving as a primary means of energy generation, hydrogen emerges as a powerful agent for optimizing the energy production process. Its synergistic integration with fuel cell technology presents a compelling avenue for capturing and storing surplus energy, effectively tapping into otherwise unrealized potential energy resources. This paradigm shift from energy generation to energy optimization underscores the transformative impact of hydrogen in advancing the frontiers of sustainable energy research and development. The present article delves into the profound implications of harnessing hydrogen for the dual purpose of energy storage and production, elucidating its transformative potential in mitigating carbon emissions linked to both onshore and offshore operations. By embracing hydrogen as a dynamic element within the energy landscape, novel pathways emerge to revolutionize the reduction of carbon footprints, pushing the boundaries of sustainable practices and redefining the frontiers of energy efficiency in onshore and offshore domains.

Magmatic cycles in Santos Basin (S.E. Brazil): Tectonic control in the temporal-spatial distribution and geophysical signature

The Santos Basin, in the offshore southeastern Brazilian margin, evolved from a continental rift system to a passive divergent margin during the Cretaceous as a onsequence of the Gondwana breakup and the formation of the proto-Atlantic Ocean. The basin exhibits several cycles of magmatism from Valanginian to Eocene times, with a regionalized distribution of igneous rocks. Using seismic, gravity, magnetic, and wellbore data, the magmatic cycles were investigated and connected with the basin's tectonic activity. Our study includes a regional analysis of the various magmatic cycles, with a focus on identifying the temporal variations and spatial differences observed in the basin's many tectonic compartments. The first magmatic cycle, named rift-onset, is observed in both coastal and offshore regions and includes magmatic rocks from ca.135 to ca. 132/130 Ma. Onshore, the rift-onset magmatic rocks are observed in the coastal dike swarm province and in the coastal alkaline province. Offshore, the riftonset is observed as a prolongation of the coastal dike swarms into the proximal basin and as flood basalts in the distal basin. The second cycle includes the synrift (ca.132-130 to 123 Ma) and postrift (ca.123 to 113-112 Ma) magmatic rocks. The separation of intrusive synrift and postrift rocks is challenging in the onshore fieldwork and in the seismic analyses offshore, which is aggravated by the basin's scarcity of geochronological dating. Therefore, these two events have been treated together when the separation is not clear. The third cycle comprises the drift (or post breakup) magmatic rocks, spanning from the Lower Cretaceous to the Tertiary (from ca. 110 to ca. 40 Ma), and is well documented in coastal and offshore domains. Drift magmatism seems to be controlled by tectonics, since magmatic bodies tend to concentrate along lines of crustal discontinuities. Magmatic cycles (rift-onset, syn/postrift, and drift) also display spatial differences, exhibiting variation in the magmatic volume and in the morphology of igneous rocks from the southern to the central/northern Santos Basin. The study of magmatism in the, Santos Basin offers an excellent opportunity to investigate the processes that occurredduring the evolution of a volcanic rifted margin.

Oncoid distribution in the shallow domains of a Kimmeridgian carbonate ramp (Late Jurassic, NE Spain)

The distribution and abundance of oncoids in the shallow domains of a latest Kimmeridgian carbonate ramp was accomplished on the basis of a detailed sedimentological and petrographic analysis of the lower part of the Higueruelas Formation (Iberian Basin, northeastern Spain). Six types of oncoids are recognized based on the internal structure of the cortex, and show a preferential distribution on the carbonate ramp, which record from intertidal, lagoon, backshoal, shoal-sand blanket, foreshoal to offshore domains. Spherical type I oncoids, composed of continuous micritic laminae, occur in all the subenvironments in low proportions. Sub-spherical type II oncoids, constituted by micritic laminae and discontinuous organism-bearing laminae of mostly Bacinella irregularis, dominate in the higher-energy shoal-sand blanket domain. Type III oncoids, with alternating micritic and organism-bearing laminae of mostly Bacinella irregularis-Lithocodium aggregatum association, include two varieties: type IIIa oncoids, with micritic and organism-bearing laminae of similar thickness, preferentially formed in the foreshoal domain; and type IIIb oncoids, with thinner micritic laminae, formed in a low-energy sheltered lagoon. Irregular type IV oncoids characterize the low-energy settings, and include two varieties: type IVa oncoids, mainly consisting of a Bacinella-Lithocodium meshwork, which occur abundantly in the lagoon; and less abundant type IVb oncoids, composed of a continuous organism-bearing laminae of Lithocodium, which are found in the offshore domain. Water energy and platform morphology played an important role in formation and distribution of the oncoids in these shallow domains, where normal-marine water and oligotrophic conditions are highlighted by the high-diversity of light-dependant micro-encrusters in type III and IV oncoids. Comparable oncoid distribution patterns of diverse Late Jurassic shallow carbonate platforms enhance their potential use as reliable palaeoenvironmental proxies.

Sedimentary evolution of a shallow carbonate ramp (Kimmeridgian, NE Spain): Unravelling controlling factors for facies heterogeneities at reservoir scale

Abstract The facies evolution of a Late Jurassic (latest Kimmeridgian) shallow carbonate ramp was reconstructed after the analysis and correlation of 21 logs in a 20 × 30 km outcrop area located south of Zaragoza (northeast Spain). The studied succession belongs to the Higueruelas Formation, which is of potential use as an analogue for understanding facies heterogeneities in certain hydrocarbon carbonate reservoirs (e.g. the Arab Formation, Persian Gulf). The studied succession is arranged in nine sedimentary units bounded by discontinuity surfaces that can be traced over kilometres. Facies analysis permitted the reconstruction of two sedimentary models showing the transition from inner ramp subenvironments (i.e. intertidal, lagoon, backshoal/washover, shoal-sand blanket) to the mid-ramp foreshoal and offshore domains: an oncolitic-peloidal-oolitic and an oolitic-peloidal-dominated ramp. The oncolitic-peloidal-oolitic-dominated ramp is characterized by peloidal-oolitic and oncolitic-dominated shoal-sand blankets that developed in higher-energy inner areas, protecting peloidal-oolitic backshoal and oncolitic lagoon domains including a mosaic of stromatoporoid carpets. Peloidal facies with fenestral porosity accumulated in an intertidal belt or as patches on top of the shoal-sand blankets and washover deposits. Offshore from the shoal-sand blankets, chaetetid/stromatoporoid/coral-rich buildups grew on the more proximal mid-ramp, surrounded by peloidal and peloidal-bioclastic grain- to mud-supported facies. An oolitic-peloidal-dominated ramp developed in a second stage of the evolution of the platform, characterized by the presence of a wide restricted peloidal-bioclastic-oolitic lagoon on the inner ramp grading into a backshoal area dominated by storm-related intraclastic-peloidal deposits. Stromatoporoid carpets disappeared and oncolitic-dominated deposits were constrained to the foreshoal and backshoal domains, and locally to local ponds that developed in the intertidal belt or the restricted lagoon. Internal and external factors controlling facies heterogeneity and the sedimentary evolution of the carbonate ramp include resedimentation, topographic relief, and long- to short-term sea-level fluctuations.

Distribution of Modern Dinoflagellate Cyst Assemblages in Surface Sediments of San Jorge Gulf (Patagonia, Argentina)

The presence of upwelling systems and oceanic fronts makes the Southwest Atlantic Ocean a region of high primary productivity. These same conditions are present in San Jorge Gulf (SJG) along the southern Argentinian coast, where dinoflagellates and diatoms dominate primary production. The distribution of these microorganisms, including the cysts produced by some dinoflagellates during their life cycles, is controlled in marine environments by oceanographic parameters that include salinity, surface water temperature, ice cover duration, and productivity. The objective of this study is to document the modern distribution of dinoflagellate cyst assemblages in surface sediments so that the environmental preferences of each taxon can be inferred and used to reconstruct paleoenvironmental conditions. The dinoflagellate cyst (dinocyst) assemblages of 52 surface samples collected in 2014 aboard R/V Coriolis II in the SJG were described and compared to surface oceanographic conditions and grain size data. The results indicate dinocyst concentrations vary between 64 cysts g–1 and 45,848 cysts g–1 dry sediment, with Spiniferites ramosus and Operculodinium centrocarpum the dominant species, accompanied by Spiniferites mirabilis, Dubridinium sp., cysts of Polykrikos kofoidii, and cysts of Brigantedinium simplex, Brigantedinium auranteum, and Brigantedinium spp. We have defined two spatial domains based on the distribution of dinocysts in and near the SJG: northern/southern-central gulf and offshore domains. We found an increase in dinocyst concentrations along a north-south gradient in the SJG and minimum concentrations at offshore sites. In addition, multivariate analyses reveal the relationships among the relative abundances of dinocysts, fine grain size data (<63 μm; silts and clays), and primary productivity, as well as offshore upwelling, which appear to control most of the distribution of dinocysts.

Wind-driven waterbodies: a new category of lake within an alternative sedimentologically-based lake classification

Lakes are common natural systems for which sedimentation is considered to be relatively simple, generally dominated by fluvial processes along the margin and prevailing low-energy settling in the central, deeper parts. However, for many lakes, higher-energy wind-driven processes dominate. As such, a new category of lakes is proposed, herein referred to as wind-driven waterbodies (WWB). WWB display a sedimentation largely dominated by wave related processes and wind-induced lake-scale water circulation evidenced by the construction of beach ridges, spits or cuspate spits along their shorelines, and by sediment drifts, sedimentary shelf progradation and erosional surfaces in their deeper, offshore domains. WWB are observed worldwide, they share a common physiography that favours wind-forced hydrodynamics and related sedimentation patterns. This physiography is expressed by the IWWB index, a ratio of the maximum representative fetch relative to mean basin depth. It is proposed that an index value greater than three favours the evolution of a lake as a WWB. The WWB concept represents a new end-member in an alternative, sedimentologically-based lake classification that is proposed in this paper.

Modeling wind waves from deep to shallow waters in Lake Michigan using unstructured SWAN

AbstractAccurate wind‐wave simulations are vital for evaluating the impact of waves on coastal dynamics, especially when wave observations are sparse. It has been demonstrated that structured‐grid models have the ability to capture the wave dynamics of large‐scale offshore domains, and the recent emergence of unstructured meshes provides an opportunity to better simulate shallow‐water waves by resolving the complex geometry along islands and coastlines. For this study, wind waves in Lake Michigan were simulated using the unstructured‐grid version of Simulating Waves Nearshore (un‐SWAN) model with various types of wind forcing, and the model was calibrated using in situ wave observations. Sensitivity experiments were conducted to investigate the key factors that impact wave growth and dissipation processes. In particular, we considered (1) three wind field sources, (2) three formulations for wind input and whitecapping, (3) alternative formulations and coefficients for depth‐induced breaking, and (4) various mesh types. We find that un‐SWAN driven by Global Environmental Multiscale (GEM) wind data reproduces significant wave heights reasonably well using previously proposed formulations for wind input, recalibrated whitecapping parameters, and alternative formulations for depth‐induced breaking. The results indicate that using GEM wind field data as input captures large waves in the midlake most accurately, while using the Natural Neighbor Method wind field reproduces shallow‐water waves more accurately. Wind input affects the simulated wave evolution across the whole lake, whereas whitecapping primarily affects wave dynamics in deep water. In shallow water, the process of depth‐induced breaking is dominant and highly dependent upon breaker indices and mesh types.

Persistence of hotspots and variability of seabird species richness and abundance in the southern California Current

Aggregations of seabirds at sea may provide information on centers of enhanced trophic interactions and concentrating mechanisms, however, to date most studies lack quantification of persistence, a key hotspot characteristic. Persistence statistics may reduce uncertainty about seabird habitat use, improve understanding of the spatio‐temporal scales of pelagic food web dynamics, and inform conservation planning. Using 26 years (1987–2012, 47 surveys) of shipboard surveys from a 300K km2 study area within the southern California Current Ecosystem, we conduct a spatial assessment of the inter‐annual and seasonal dynamics of the persistence of seabird hotspots and identify recurring sites of elevated seabird species richness and abundance. Previous studies document declines in abundance, but were based on broad spatial standardizations to assess where declines may have occurred. Here, we refine the hypothesis that seabird populations have declined off southern California by focusing on persistently used habitats in nearshore or offshore domains. We demonstrate that spatio‐temporal variability of seabird distribution and abundance is characterized by anomalous events embedded within trends. In addition to identifying the locations of persistence of seabird aggregations, we found significant declines in species richness and the density of sooty shearwater (Puffinus griseus) and Leach's storm petrel (Oceanodroma leucorhoa); in contrast, black‐footed albatross (Phoebastria nigripes) abundance appear to be increasing. This assessment provides a spatially‐explicit framework for future evaluations of biophysical drivers of seabird hotspots and their associations and impacts on forage fish and zooplankton populations.

Seismogenic sources in the Adriatic Domain

We present an overview of the seismogenic source model of the Adriatic domain included in the latest version of the DISS database (http://diss.rm.ingv.it/diss/) and in the European SHARE database (http://diss.rm.ingv.it/SHARE/). The model consists of Composite and Individual Seismogenic Sources located inside and along the margins of the Adria plate. In order to locate and parameterize the sources, we integrated a wide set of geological, geophysical, seismological and geodynamic data, either available from published literature or resulting from our own field work, seismic profile interpretations and numerical modelling studies. We grouped the sources into five regions based on geometrical and kinematic homogeneity criteria. Seismogenic sources of the Central Western Adriatic, North-Eastern Adriatic, Eastern Adriatic and Central Adriatic regions belong to the Northern Apennines, External Dinarides and offshore domains, respectively. They are characterized by NW–SE strike, reverse to oblique kinematics and shallow crustal seismogenic depth. Seismogenic sources of the Southern Western Adriatic region instead are E–W striking, dextral strike-slip faults, cutting both the upper and lower crust. The fastest moving seismogenic sources are the most southern thrusts of the Eastern Adriatic and the strike-slip sources of the Southern Western Adriatic, while the seismogenic sources of the Central Adriatic exhibit the lowest slip rates. Estimates of maximum magnitude are generally in good agreement with the historical and instrumental earthquake records, except for the North-Eastern Adriatic region, where seismogenic sources exhibit a potential for large earthquakes even though no strong events have been reported or registered. All sources included in the database are fully geometrically and kinematically parameterized and can be incorportaed in seismic hazard calculations and earthquake or tsunami scenario simulations.

Identification of the environmentally safe fairway in the South-Western Baltic Sea and Kattegat

Application of the preventive techniques for the optimisation of fairways in the south-western Baltic Sea and the Kattegat in terms of protection of the coastal regions against current-driven surface transport of adverse impacts released from vessels is considered. The techniques rely on the quantification of the offshore domains (the points of release of adverse impacts) in terms of their ability to serve as a source of remote, current-driven danger to the nearshore. An approximate solution to this inverse problem of current-driven transport is obtained using statistical analysis of a large pool of Lagrangian trajectories of water particles calculated based on velocity fields from the Denmark’s Meteorological Institute (DMI)/BSH cmod circulation model forced by the DMI-HIRHAM wind fields for 1990–1994. The optimum fairways are identified from the spatial distributions of the probability of hitting the coast and for the time (particle age) it takes for the pollution to reach the coast. In general, the northern side of the Darss Sill area and the western domains of the Kattegat are safer to travel. The largest variations in the patterns of safe areas and the properties of pollution beaching occur owing to the interplay of water inflow and outflow. The gain from the use of the optimum fairways is in the range of 10–30 % in terms of the decrease in the probability of coastal hit within 10 days after pollution release or an increase by about 1–2 days of the time it takes for the hit to occur.

A New Inversion Model to Retrieve the Particulate Backscattering in Coastal/Ocean Waters

Scientific implications and practical applications of spectral particulate backscattering (b <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bp</sub> (λ)) in oceanography are wide ranging, particularly in optical remote sensing as the light backscattered from various seawater constituents provides possibility to derive information about the particle properties of the water under investigation. Several inversion models have been previously developed for use with remote sensing reflectance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rs</sub> ) data over open ocean waters; however, when applied to coastal waters, these models return b <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bp</sub> having large differences with in situ b <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bp</sub> values primarily because of the improper definitions of parameters of the functions describing the spectra of b <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bp</sub> (λ). The present study is aimed to develop a new inversion model with appropriate definitions of parameters of the functions to provide reliable retrievals of b <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bp</sub> in a variety of waters covering both the coastal and ocean environments. The new model is tested using large independent in situ data sets (NOMAD and Carder data sets) and simulated data provided by the IOCCG working group. When applied to these data sets, the new model outperformed the currently existing inversion models (e.g., GSM, LM and QAA models). The percent mean relative error (MRE) and root mean square error (RMSE) were found to be MRE -5.16 ~ 0.35% and RMSE 0.114 ~ 0.146 (in the 412-555 nm range) for the simulated data, MRE -0.14 ~ 2.42% and RMSE 0.125 ~ 0.157 for the NOMAD data, MRE -0.77% ~ 2.23% and RMSE 0.124 ~ 0.15 for the Korean regional data, and MRE 6.88% and RMSE 0.218 for the Carder data (for 490 nm only). Slopes close to unity, high R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and low intercept values also indicated that the new model provides better performance over other models. The results further suggest that the new model is more robust and can be effectively applied to satellite ocean color data to retrieve the particulate backscattering coefficients in a variety of waters commonly found in the coastal and offshore domains.

Satellite remote sensing of a low-salinity water plume in the East China Sea

Abstract. With the aim to map and monitor a low-salinity water (LSW) plume in the East China Sea (ECS), we developed more robust and proper regional algorithms from large in-situ measurements of apparent and inherent optical properties (i.e. remote sensing reflectance, Rrs, and absorption coefficient of coloured dissolved organic matter, aCDOM) determined in ECS and neighboring waters. Using the above data sets, we derived the following relationships between visible Rrs and absorption by CDOM, i.e. Rrs (412)/Rrs (555) vs. aCDOM (400) (m−1) and aCDOM (412) (m−1) with a correlation coefficient R2 0.67 greater than those noted for Rrs (443)/Rrs (555) and Rrs (490)/Rrs (555) vs. aCDOM (400) (m−1) and aCDOM (412) (m−1). Determination of aCDOM (m−1) at 400 nm and 412 nm is particularly necessary to describe its absorption as a function of wavelength λ using a single exponential model in which the spectral slope S as a proxy for CDOM composition is estimated by the ratio of aCDOM at 412 nm and 400 nm and the reference is explained simply by aCDOM at 412 nm. In order to derive salinity from the absorption coefficient of CDOM, in-situ measurements of salinity made in a wide range of water types from dense oceanic to light estuarine/coastal systems were used along with in-situ measurements of aCDOM at 400 nm, 412 nm, 443 nm and 490 nm. The CDOM absorption at 400 nm was better inversely correlated (R2=0.86) with salinity than at 412 nm, 443 nm and 490 nm (R2=0.85–0.66), and this correlation corresponded best with an exponential (R2=0.98) rather than a linear function of salinity measured in a variety of water types from this and other regions. Validation against a discrete in-situ data set showed that empirical algorithms derived from the above relationships could be successfully applied to satellite data over the range of water types for which they have been developed. Thus, we applied these algorithms to a series of SeaWiFS images for the derivation of CDOM and salinity in the context of operational mapping and monitoring of the springtime evolution of LSW plume in the ECS. The results were very encouraging and showed interesting features in surface CDOM and salinity fields in the vicinity of the Yangtze River estuary and its offshore domains, when a regional atmospheric correction (SSMM) was employed instead of the standard (global) SeaWiFS algorithm (SAC) which revealed large errors around the edges of clouds/aerosols while masking out the nearshore areas. Nevertheless, there was good consistency between these two atmospheric correction algorithms over the relatively clear regions with a mean difference of 0.009 in aCDOM (400) (m−1) and 0.096 in salinity (psu). This study suggests the possible utilization of satellite remote sensing to assess CDOM and salinity and thus provides great potential in advancing our knowledge of the shelf-slope evolution and migration of the LSW plume properties in the ECS.

Taconic events in Pennsylvania: Datable phases of a 20 m.y. orogeny

A suite of well-dated graptolite and conodont locations allows division of about 54 m.y. of Late Cambrian through Late Ordovician events into three time segments in Pennsylvania: 1) Pre-Taconic, offshore deepwater sediments including olistostromes were deposited and deformed in several offshore domains in Iapetus (*sensu lato*) from ∼ 497 to ∼ 459 Ma; 2) Taconic Phase I began as these rocks were translated onto the foreland as allochthons, some with piggyback basins from ∼ 459 to ∼ 450 Ma. This was accomplished first by thrusting onto the shelf edge, creating a foreland peripheral bulge and local depositional basins, then by depressing the larger foreland region to allow emplacement of allochthons of the Dauphin Formation (the erroneous "Hamburg klippe" of past literature), and finally with deposition of the thick, widespread fill of the traditional Martinsburg Formation; 3) Taconic Phase II advanced diachronously across the foreland with regional overturning and nappe formation (the classic "Taconic" orogeny in Pennsylvania), driven as the ongoing collision overrode and incorporated the platform and its foreland basin into alpine-scale nappes. This phase started at ∼ 459 Ma at the shelf edge and lasted from ∼450 to ∼ 443 Ma in the present location of the Great Valley foreland and eastward. This series of well-dated events may be a model for timing of a "simple" orogenic cycle in a convergent margin with application to other parts of the Appalachians and beyond.

Water Constituents in the North-western Black Sea from Optical Remote Sensing and In situ Data

Satellite-based optical observations of surface waters have been used to assess the main environmental interactions in the north-western Black Sea, as a contribution to the EROS 21 project. Such observations allow evaluations of the presence and abundance of water constituents (primarily phytoplankton pigments), providing essential information on the processes which are taking place in the area and on their spatial and temporal scales. An analysis of ocean colour imagery was performed, using historical data collected by the CZCS (1978–1986), and by the MOS before, during and after the EROS 21 oceanographic cruise which took place in April/May 1997. The time series of CZCS-derived parameters (i.e. chlorophyll-like pigment concentration) originates from the archive generated by the OCEAN project. The MOS data were processed to apply sensor calibration, to correct for atmospheric contamination so as to assess water-leaving radiances for each visible channel, and to estimate geophysical parameters such as pigment concentration and in-water optical depth, which is correlated to suspended matter concentration. The atmospheric correction was performed with a novel algorithm developed especially for MOS application. The bio-optical algorithms used to derive in-water parameters were obtained by comparison with the concurrent in situ measurements of optically active parameters collected in the north-western Black Sea in the framework of the EROS 21 project. The multi-satellite data set highlights the differences between western and eastern sub-basins, inshore and offshore domains, northern and southern near-coastal areas. In the Danube delta area, the water constituents trace complex interactions of near-coastal and basin-wide features of the Black Sea.

Simulation of a coastal jet retention process using a barotropic model

In the southern Benguela, sardine and anchovy spawn on the Western Agulhas Bank. Eggs and larvae are transported to the West coast nursery ground by a coastal current. Once the larvae reach the West coast, retention within the favorable coastal domain is key to larvae survival and recruitment. The Cape Columbine-St Helena Bay area is the main nursery ground along the West Coast. In this area, the interaction between upwelling and topography results in the formation of an upwelling plume. The plume, and the associated circulation patterns, is thought to be the mechanism providing retention within the coastal domain. The dynamics of the plume are studied using a set of numerical experiments. It is shown that an equatorward wind forcing produces a cyclonic eddy in the lee of Cape Columbine. A balance between advection and bottom friction regulates the evolution of this eddy. The eddy contributes to create a dynamic boundary between the coastal and the offshore domains. Retention induced by the eddy is quantified using a tracer. The magnitude of retention is positively related to the wind for weak to moderate wind intensities. For strong wind intensity, retention reaches a maximum or slightly decreases. This is in agreement with previous results relating recruitment success with wind speed.

Distribution and sea‐air fluxes of biogenic trace gases in the eastern Atlantic Ocean

A number of atmospherically important trace gases (dimethyl sulphide (DMS), methyl iodide (CH3I), and nonmethane hydrocarbons (NMHCs)) were measured simultaneously in the eastern Atlantic Ocean during May 1997. This investigation was part of the U.K. Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) Community Research Program and covered a 200 by 200 nautical mile (1 nautical mile is 1.852 km) area to the west of the Mace Head Atmospheric Research Station on the coast of Ireland. Different spatial and temporal patterns were observed for each of the gases, showing that distinct sources dominate their production in this region: specific species of phytoplankton (DMS), macroalgae (CH3I), total phytoplankton biomass (isoprene), and photochemistry (ethene). Sea‐to‐air fluxes of the gases are calculated for near and offshore domains, and their temporal variations are discussed. A simple photochemical box model has been used to assess the contributions of the gas fluxes to the levels of the gases observed at Mace Head. Results show that the area studied may constitute a substantial source of DMS, a weak source of CH3I, a small source of ethene at night, and an insignificant source of isoprene to atmospheric levels of these gases measured at Mace Head in western Ireland.