Wide Continental Shelf Research Articles

Modelling long-term fisheries data to resolve the attraction versus production dilemma of artificial reefs

The main role of artificial reefs (ARs) is to enhance the productivity and sustainability of coastal fisheries by creating new fish biomass. From a modelling point of view, the creation of new fish biomass would be realized by a shift to a state of higher carrying capacity of the environment (K) for aquatic populations and communities. However, it has not been possible to demonstrate unequivocally rising K as a result of AR deployment because of the difficulty in disentangling enhancements due to simple distributional changes (the attraction hypothesis) versus total abundance rise (the production hypothesis). Here we develop a modelling framework based on simple, inexpensive fisheries data to quantify the impact of ARs, disentangling attraction from production by assessing the rise in regional K. The rationale is that if attraction to ARs from the wider region was the main driver of increased abundance in the ARs then regional K would have remained constant before, during and after deployment of the ARs. Therefore an increase in regional K disproves the hypothesis of attraction. The study case is the fishery for the two-banded seabream Diplodus vulgaris in southern Portugal. Monthly time series of 27 years of landings, 20 years of fishing effort, were available from three small-scale fleets: one was the artisanal fleet operating on the ARs and the other two were semi-industrial fleets operating on the wider continental shelf. The model that we developed and applied incorporated the data from all fleets so it evaluated the change in regional K. We show that regional K for D. vulgaris increased by 35% after final deployment of the ARs and it did so in linear fashion during four years. From a fisheries perspective the result was more nuanced because although the deployment succeeded in raising regional K, stock biomass and thereby enhancing the artisanal fishery, it also led to a substantial rise in total fishing mortality and exploitation rate because the semi-industrial fleets operating offshore increased their harvest rate nearly 3-fold. Our modelling framework has wide applicability in other regions due to the elementary nature of the necessary fishing monitoring data.

Structure of the benthic macrofauna of an anthropogenic influenced area: Skhira Bay (Gulf of Gabès, central Mediterranean Sea).

Skhira Bay located in the Gulf of Gabès, on the southeastern coast of Tunisia, is an important area in terms of its dense vegetation coverage, wide continental shelf, and fisheries resources. However, this area with a typically micro-tidal range is subject to intensive anthropogenic pressures: soft bottom trawling, chemical pollution from phosphoric acid production, and shipping activity. The present study is the first investigation of the structure of the benthic macrofauna on this part of the Tunisian coast. In April 2010, 28 stations were sampled along four transects from the phosphogypsum outfall on an inshore-offshore gradient. A total of 239 macrobenthos taxa, belonging to nine zoological groups and 140 families, were identified with a dominance of polychaetes (33.5%), crustaceans (29.4%), and mollusks (19.6%). Results show that the stations facing the phosphogypsum discharges are the most disturbed and characterized by a poorly diversified macrofauna. The macrofauna is dominated by carnivores, suspension feeders, and selective deposit feeders, and seems to be linked more to the availability of trophic resources than to disturbance. Four benthic assemblages are identified using Cluster and MDS analyses linked to edaphic factors, such as sediment structure, organic matter content, inshore/offshore gradient, and the proximity of the phosphogypsum outfall. The biotic indices (AMBI and BO2A) calculated from macrofauna data show that the ecological status of Skhira Bay varies overall from moderate to good. This study suggests initiating a long-term monitoring program to improve our understanding of the temporal changes of this ecosystem, to recommend the necessary conservation measures in this area of high-value natural heritage.

Marine Mammals on the Egyptian Mediterranean Coast "Records and Vulnerability"

This work documents strandings and sightings of vulnerable marine mammals on the Egyptian Coast of the Mediterranean Sea, with an emphasis on 2013 to 2018 as well as previous non documented strandings observed by other persons. Marine mammal cases were described and identified to six species: the fin whale (<i>Balaenoptera physalus</i> Linnaeus, 1758), the sperm whale (<i>Physeter microcephalus</i>), Gervais’ beaked whale <i>Mesoplodon europaeus</i> (Gervais, 1855), the common bottlenose dolphin (<i>Tursiops truncates</i>), the rough-toothed dolphin (<i>Steno bredanensis</i>) that which was stranded on the Gamasa coast and was not completely confirmed. The sixth species was California sea lion (<i>Zalophus californianus</i> Lesson, 1828) which was reported for the first time. Moreover, the monk seal (<i>Monachus monachus</i>) was also reported here but has not been observed by the authors; this observation increases the reported species on the Mediterranean coast of Egypt into seven species. The first five species are cetaceans including a baleen whale (Mysticeti) for first whale and toothed species (Odontoceti) for the remaining four species, while the last two ones belong to Pinnipeds (sea lion and monk seal). Most of the observed cases were strandings, while the sea lion was sighted alive. The sea lion is not endemic for Mediterranean sea and its presence may be an accidental or may escape from aquarium. There were also few other records of dead delphinid carcasses that were in a highly decomposed state and could not be identified. In conclusion, this work is important issue in term of documenting marine mammals in the Egyptian Mediterranean water and indicates that the coast has increasingly become a visiting area for many marine mammals, with a concomitant increase in stranding's. These observations reflect their vulnerability due to anthropogenic activities such as fishing operations, shipping, and seismic activities. Moreover, the Egyptian coast has shallower and wider continental shelf in the Nile Delta region which may increase the probability of marine mammals' visitors stranding's, particularly a mong species that inhabit deep water. The repeated sightings of these species may be due to climatic changes that affect their migration and mobility from one place to another. Stakeholders should pay more attention to marine mammals in Egypt through increased awareness and the continuous monitoring, documentation and mapping of recorded strandings to further suggest measures on how to protect these important and vulnerable species.

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact

ESTIMATING METEO-TSUNAMI OCCURRENCES FOR THE US EAST COAST

Meteorological tsunamis, also called meteo-tsunamis, are significant ocean surface waves generated by atmospheric forcing. The waves typically result from energy transfer from atmosphere to ocean through the Proudman resonance phenomena, where translation speed of the storm system in the atmosphere coincides with the free wave speed of long surface waves. These tsunami-like waves can be hazardous, either through direct inundation of shorelines or through generation of harbor oscillations and other disruptions to maritime activities. The wide continental shelf bathymetry of the United States (US) East Coast provides a long potential fetch length for the resonant generation process, making the region particularly susceptible to meteo-tsunamis. In this study, we carry out a probabilistic analysis of potential meteo-tsunami hazard on the US East Coast, extending the earlier work of Geist et al. (2014) to include a wider range of storm conditions and additional response types including coastally-trapped edge waves. The work, carried out under the auspices of the National Tsunami Hazard Mitigation Program (NTHMP), extends the previous efforts of Geist et al. to include a representation of inundation and maritime hazards in at-risk areas. The work is conducted using the fully nonlinear Boussinesq wave model FUNWAVE-TVD (Shi et al., 2012), extended to include atmospheric pressure and wind forcing.

Carbon pools and fluxes in the China Seas and adjacent oceans

The China Seas include the South China Sea, East China Sea, Yellow Sea, and Bohai Sea. Located off the Northwestern Pacific margin, covering 4700000 km2 from tropical to northern temperate zones, and including a variety of continental margins/basins and depths, the China Seas provide typical cases for carbon budget studies. The South China Sea being a deep basin and part of the Western Pacific Warm Pool is characterized by oceanic features; the East China Sea with a wide continental shelf, enormous terrestrial discharges and open margins to the West Pacific, is featured by strong cross-shelf materials transport; the Yellow Sea is featured by the confluence of cold and warm waters; and the Bohai Sea is a shallow semi-closed gulf with strong impacts of human activities. Three large rivers, the Yangtze River, Yellow River, and Pearl River, flow into the East China Sea, the Bohai Sea, and the South China Sea, respectively. The Kuroshio Current at the outer margin of the Chinese continental shelf is one of the two major western boundary currents of the world oceans and its strength and position directly affect the regional climate of China. These characteristics make the China Seas a typical case of marginal seas to study carbon storage and fluxes. This paper systematically analyzes the literature data on the carbon pools and fluxes of the Bohai Sea, Yellow Sea, East China Sea, and South China Sea, including different interfaces (land-sea, sea-air, sediment-water, and marginal sea-open ocean) and different ecosystems (mangroves, wetland, seagrass beds, macroalgae mariculture, coral reefs, euphotic zones, and water column). Among the four seas, the Bohai Sea and South China Sea are acting as CO2 sources, releasing about 0.22 and 13.86– 33.60 Tg C yr−1 into the atmosphere, respectively, whereas the Yellow Sea and East China Sea are acting as carbon sinks, absorbing about 1.15 and 6.92 –23.30 Tg C yr−1 of atmospheric CO2, respectively. Overall, if only the CO2 exchange at the sea-air interface is considered, the Chinese marginal seas appear to be a source of atmospheric CO2, with a net release of 6.01 –9.33 Tg C yr−1 , mainly from the inputs of rivers and adjacent oceans. The riverine dissolved inorganic carbon(DIC) input into the Bohai Sea and Yellow Sea, East China Sea, and South China Sea are 5.04, 14.60, and 40.14 Tg C yr−1 , respectively. The DIC input from adjacent oceans is as high as 144.81 Tg C yr−1 , significantly exceeding the carbon released from the seas to the atmosphere. In terms of output, the depositional fluxes of organic carbon in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea are 2.00, 3.60, 7.40, and 5.92 Tg C yr−1 , respectively. The fluxes of organic carbon from the East China Sea and South China Sea to the adjacent oceans are 15.25–36.70 and 43.93 Tg C yr−1 , respectively. The annual carbon storage of mangroves, wetlands, and seagrass in Chinese coastal waters is 0.36 –1.75 Tg C yr−1 , with a dissolved organic carbon (DOC) output from seagrass beds of up to 0.59 Tg C yr−1 . Removable organic carbon flux by Chinese macroalgae mariculture account for 0.68 Tg C yr−1 and the associated POC depositional and DOC releasing fluxes are 0.14 and 0.82 Tg C yr−1 , respectively. Thus, in total, the annual output of organic carbon, which is mainly DOC, in the China Seas is 81.72 –104.56 Tg C yr−1 . The DOC efflux from the East China Sea to the adjacent oceans is 15.00 –35.00 Tg C yr−1 . The DOC efflux from the South China Sea is 31.39 Tg C yr−1 . Although the marginal China Seas seem to be a source of atmospheric CO2 based on the CO2 flux at the sea-air interface, the combined effects of the riverine input in the area, oceanic input, depositional export, and microbial carbon pump (DOC conversion and output) indicate that the China Seas represent an important carbon storage area.

Structuring of larval fish assemblages along a coastal-oceanic gradient in the macro-tidal, tropical Eastern Indian Ocean

In the eastern Indian Ocean, the Kimberley region off north-western Australia is characterised by a wide continental shelf, complex coastal topography and very large tides (>10 m). Diversity of fishes is high although little is known about the distribution of their larvae in this dynamic region. This study investigated spatial variation in ichthyoplankton assemblages along four coastal-oceanic transects and related the results to tidal cycles and other environmental variables. Larvae representing 92 neritic and 21 mesopelagic teleost families were collected; this far exceeds the diversity described for other comparable tropical continental shelf and oceanic systems. Distinct ichthyoplankton assemblages characterised inner shelf (Engraulidae and Gobiidae were dominant families), outer shelf / slope (mixed neritic and mesopelagic taxa) and oceanic waters (mesopelagic taxa, particularly Myctophidae, Gonostomatidae and Phosichthyidae), and were correlated with changes in environmental variables (water depth, seawater density, mixed layer depth and zooplankton). The spring-neap tidal cycle and subsequent tides (same stations sampled 12 h apart) had no significant influence on larval fish assemblages. Coastal waters were delineated by a density front and larval fish assemblages were significantly different from offshore assemblages. This study provides new insights into the pelagic ecosystem in the tropical eastern Indian Ocean and contributes to the understanding of the role of environmental variables and physical forcing in the structuring of larval fish assemblages.

Pelagic marine refugia and climatically sensitive areas in an eastern boundary current upwelling system.

Refugia are areas relatively buffered from contemporary climate change that enable the persistence of valued physical, ecological, or sociocultural resources. Spatially identifying refugia is important for conservation and applied management. Yet the concept of refugia has not been broadly extended to marine ecosystems. Here, we analyze data from a unique and long-term (1999-2015) standardized survey of pelagic marine and anadromous species off Oregon and Washington in the northern California Current to identify such refugia. We use quantitative approaches to assess locations with high species richness and community persistence relative to local and basin-scale environmental fluctuations. We have identified a potential climate change refugial zone along the continental shelf of Washington State in the Northeastern Pacific Ocean, characterized by a species-rich community with low interannual temporal community change. This region contrasts with adjacent areas to the south and offshore that have lower species richness, and higher temporal species community change. Also, using spatially variant generalized additive mixed models, we identify areas with species compositions that are more influenced by basin-scale climatic fluctuations than others. We propose that upwelling regions with retentive topographic features, such as wide continental shelves, can function as marine refugia for pelagic fauna, whereas offshore locations are potentially more climatically sensitive and experience high temporal change in species composition. Further identification of these marine refugia using insitu data for pelagic biodiversity and climatically sensitive areas can help guide management in the face of inevitable climatically driven change.

Scattering of a Semidiurnal Barotropic Kelvin Wave into Internal Waves over Wide Continental Shelves

AbstractIn boundary areas of the World Ocean, a semidiurnal tide propagates in the form of a Kelvin wave mode trapped by the coastline. Over wide continental shelves, the semidiurnal tide is no longer a pure Kelvin wave but attains features of a zero-mode edge wave. As a result, the wave structure and the alongshore energy flux concentrate over the continental shelf and slope topography and become very sensitive to the variations of shelf geometry. When a semidiurnal Kelvin wave encounters alongshore changes of the shelf width, its energy scatters into other wave modes, including internal waves. A particularly strong scattering occurs on wide shelves, where Kelvin wave structure undergoes significant modifications over short alongshore distances. These dynamics are studied using the Regional Ocean Modeling System (ROMS). This study found that when the alongshore energy flux in the Kelvin wave mode converges on the shelf, the offshore wave radiation occurs through barotropic waves, while for the divergent alongshore energy flux, internal waves are generated. Under favorable conditions, more than 10% of the incident barotropic Kelvin wave energy flux can be scattered into internal waves. For the surface-intensified stratification mostly the first internal mode is generated, while for the uniform with depth stratification, multiple internal modes are present in the form of an internal wave beam. A nondimensional internal wave scattering parameter is derived based on the theoretical properties of a Kelvin wave mode, bottom topography, and stratification.

Interannual evolution of (sub)mesoscale dynamics in the Bay of Biscay

Abstract. In the north-east Atlantic Ocean, the Bay of Biscay is an intersection between a coastal constrained dynamics (wide continental shelf and shelf break regions) and an eastern boundary circulation system. In this framework, the eddy kinetic energy is 1 order of magnitude lower than in western boundary systems. To explore this coastal complex system, a high-resolution (1 km, 100 vertical sigma layers) model experiment including tidal dynamics over a period of 10 years (2001–2010) has been implemented. The ability of the numerical environment to reproduce main patterns over interannual scales is demonstrated. Based on this experiment, the features of the (sub)mesoscale processes are described in the deep part of the region (i.e. abyssal plain and continental slope). A system with the development of mixed layer instabilities at the end of winter is highlighted. Beyond confirming an observed behaviour of seasonal (sub)mesoscale activity in other regions, the simulated period allows exploring the interannual variability of these structures. A relationship between the winter maximum of mixed layer depth and the intensity of (sub)mesoscale related activity (vertical velocity, relative vorticity) is revealed and can be explained by large-scale atmospheric forcings (e.g. the cold winter in 2005). The first submesoscale-permitting exploration of this 3-D coastal system shows the importance of (sub)mesoscale activity in this region with its evolution implying a potentially significant impact on vertical and horizontal mixing.

Geoindicator-based assessment of Santa Catarina (Brazil) sandy beaches susceptibility to erosion

In the actual scenario of progressive coastal occupation man-made infrastructure is increasingly threatened by natural hazards. As a consequence, in the last two decades different methodologies have been proposed to assess coastal vulnerability to the potential impacts of storm surges on developed areas. In this study, the susceptibility of sandy beaches to erosion was assessed by using an analytical approach based on geoindicators survey. This framework considers that a selected set of variables can express short-term environmental dynamics and be used, therefore, as proxies for the multiplicity of factors acting over coasts. Geoindicators are site-specific and rely on the description of coastal geomorphic features, both natural or man-induced. Santa Catarina State, located in southern Brazil, was selected as case study. Its shoreline contains beaches of different extents that alternate with headlands and a wide continental shelf on the adjoining Atlantic Ocean. It is regularly under influence of extra-tropical cyclones and other storm systems that frequently reach southern Brazil. Due to the occurrence of high energy episodes, damages resulting from short-term coastal erosion and inundation have been increasingly reported over the years. In this research, 302 points were surveyed during 40 days of field work and 32 geoindicators were considered representative of susceptibility. They were identified in the field, ranked in risk levels, weighted using AHP (Analytic Hierarchy Process) and tabulated, resulting in an index expressing local susceptibility in five progressive classes. In average, most of Santa Catarina sampled points were classified around intermediate degrees of susceptibility (High + Medium + Low = 82%), with a slight tendency to higher levels. Very Low levels of susceptibility were identified in 10% of the points, while Very High in 8%. Spatial distribution of data indicates that lower susceptibility values dominate in the south of the area while in the north prevails an alternating distribution of susceptibility classes, with a tendency to higher values. The different levels of coastal indentation along the state, a result of the regional geological setting, and the induced susceptibility resulting from sectors of dense human concentration close to the shore explain the observed pattern. The selected geoindicators were effective to evaluate the erosional propensity of Santa Catarina's sandy beaches, and allowed a relatively fast and low-cost approach for susceptibility assessment and monitoring analysis, with a potential practical use in coastal zone planning and management.

Use of Particle Tracking to Determine Optimal Release Dates and Locations for Rehabilitated Neonate Sea Turtles

Sea turtles found stranded on beaches are often rehabilitated before being released back into the wild. The location and date of release is largely selected on an informal basis, which may not maximise the chance of survival. As oceanic conditions have a large influence on the movements of neonate sea turtles, this study aimed to identify the best locations and months to release rehabilitated sea turtles that would assist in their transport by ocean currents to the habitat and thermal conditions required for their survival. A particle tracking model, forced by ocean surface velocity fields were used to simulate the dispersal pathways of millions of passively drifting particles released from different locations in Western Australia. The particles represented rehabilitated, neonate turtles requiring oceanic habitats (green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and loggerheads (Caretta caretta)) and flatback turtles (Natator depressus) which require neritic habitats. The results clearly identified regions and months where ocean currents were more favourable for transport to suitable habitats. Tantabiddi, near Exmouth on the north-west coast, was consistently the best location for release for the oceanic species, with dominant offshore-directed currents and a very narrow continental shelf reducing the time taken for particles to be transported into deep water. In contrast, release locations with more enclosed geography, wide continental shelves, and/or proximity to cooler ocean temperatures were less successful. Our results produced a decision support system for the release of neonate marine turtles in Western Australia and our particle tracking approach has global transferability.

Resource partitioning within major bottom fish species in a highly productive upwelling ecosystem

Abstract The Saharan Bank (21–26°N) is a wide subtropical continental shelf and a highly productive upwelling ecosystem. The bottom communities are dominated by octopus and sparid fish, which are the main targets of bottom-trawl fishing fleets. To investigate resource partitioning within the bottom fish community, adult fish from 14 of the most abundant species were investigated for stomach content analysis. Samples were collected during two periods: October 2003 and May 2007. The diet of the analysed species showed more variation between periods than between size classes, suggesting that temporal or spatial variability in prey availability appears to play a significant role in their diet. Multivariate analysis and subsequent clustering led to a grouping of the species within five trophic guilds. Two species were fish feeders, and the others mainly fed on benthic invertebrates, where epibenthic crustaceans, lamellibranchs and fish were the most important groups in defining trophic guilds. We found that the studied species had a high rate of overlapping spatial distributions and overlapping trophic niches. In this highly productive upwelling ecosystem, where food resources may not be a limiting factor, inter-specific competition did not appear to be an important factor in structuring bottom fish communities. For the species that showed differences in the proportions of prey categories in comparison with other ecosystems, the rise of the proportion of epibenthic crustaceans in their diet was a common feature; a possible consequence of the benthic productivity of this highly productive upwelling ecosystem.

On the effect of topography and wind on warm water inflow—An idealized study of the southern Weddell Sea continental shelf system

AbstractAn idealized eddy‐resolving numerical model, with topographic features common to the southern Weddell Sea, is constructed to study mechanisms through which warm deep water enters a wide continental shelf with a trough. The open ocean, represented by a 1700 m deep channel, is connected to a 400 m deep shelf with a continental slope. The shelf is narrow (50 km) in the east but widens to 300 km at the center of the model domain. Over the narrow shelf, the slope front is balanced by wind‐driven Ekman downwelling and counteracting eddy overturning, favoring on‐shelf transport of warm water in summer scenarios when fresher surface water is present. Over the wide shelf, the Ekman downwelling ceases, and the mesoscale eddies relax the front. Inflow of warm water is sensitive to along‐shelf salinity gradients and is most efficient when denser water over the wide shelf favors up‐slope eddy transport along isopycnals of the V‐shaped slope front. Inflow along the eastern side of the trough cannot penetrate the sill region due to potential vorticity constraints, while along the western trough flank, eddy‐induced inflow crosses the sill and reaches the ice front. The warm inflow into the trough is sensitive to the density of the outflowing dense shelf water. For weaker winds, absence of the dense water outflow leads to a reversal of the trough circulation and a strong inflow of warm water, while for stronger winds, baroclinic effects become less important and the inflow is similar to experiments including dense water outflow.

Swell Propagation Caused by Typhoon Passage to the Yellow and East China Seas

ABSTRACT Kim, K.O.; Yuk, J.-H.; Jung, K.T., and Choi, B.H., 2017. Swell propagation caused by typhoon passage to the Yellow and East China Seas. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 144–148. Coconut Creek (Florida), ISSN 0749-0208. Typhoons generate big swells frequently propagating over the East China Sea, the wide continental shelf sea with depth shallower than 200 m. The characteristic features of swell propagation into the Yellow and East China Seas caused by typhoon Herb in 1996 has been investigated applying a ray-tracing technique and a spectral wave model (SWAN) with an unstructured-mesh grid system. This study discusses the generation and propagation of the swells into the Yellow and East China Seas using the integration of ray trajectories and model-based simulated wave. Calculated and observed wave heights and periods at Gadeokdo, Korea are found to be in reas...

Oceanography promotes self-recruitment in a planktonic larval disperser.

The application of high-resolution genetic data has revealed that oceanographic connectivity in marine species with planktonic larvae can be surprisingly limited, even in the absence of major barriers to dispersal. Australia’s southern coast represents a particularly interesting system for studying planktonic larval dispersal, as the hydrodynamic regime of the wide continental shelf has potential to facilitate onshore retention of larvae. We used a seascape genetics approach (the joint analysis of genetic data and oceanographic connectivity simulations) to assess population genetic structure and self-recruitment in a broadcast-spawning marine gastropod that exists as a single meta-population throughout its temperate Australian range. Levels of self-recruitment were surprisingly high, and oceanographic connectivity simulations indicated that this was a result of low-velocity nearshore currents promoting the retention of planktonic larvae in the vicinity of natal sites. Even though the model applied here is comparatively simple and assumes that the dispersal of planktonic larvae is passive, we find that oceanography alone is sufficient to explain the high levels of genetic structure and self-recruitment. Our study contributes to growing evidence that sophisticated larval behaviour is not a prerequisite for larval retention in the nearshore region in planktonic-developing species.

Wind-driven intensification of the Tsushima Warm Current along the Japanese coast detected by sea level difference in the summer monsoon of 2013

This study found an unusually large variation in the coastal sea level difference (SLD) in the southwestern Japan Sea from July to October 2013. The time and horizontal scales were about 4 months and 1000km along the coast, respectively. During the exceptionally hot summer of 2013, strong monsoon winds blew through the Tsushima Straits into the southwestern Japan Sea, because the North Pacific High was located farther west than average. The southwesterly winds averaged 7ms−1 parallel to the coast in July 2013, resulting in Ekman transport toward the coast. The most noticeable SLD was measured between Omijima and Mishima, normal to the 250km rectilinear coastal line. The velocity of the first branch of the Tsushima Warm Current increased to about 50cms−1 between Omijima and Mishima from late July to early August. Although the SLD seemed to simultaneously increase and decrease along the Japanese coast with large time scale, the variation in coastal SLD propagated along the Japanese coast, reaching Niigata-nishi in the eastern Japan Sea. The propagation speed in the wide continental shelf of the southern Japan Sea was much higher than that in the narrow eastern shelf, which was consistent with the behavior of continental shelf waves.

Offshore Southern California lithospheric velocity structure from noise cross‐correlation functions

AbstractA new shear wave velocity model offshore Southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, is used to measure ambient noise correlation functions and Rayleigh wave dispersion curves which are inverted for 3‐D shear wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present‐day strike‐slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now &gt;200 km wide continental shelf. Our velocity model suggests the persistence of the uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low‐velocity anomaly underlying the San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground‐shaking simulations for risk estimates.

Improving Modeling of Tides on the Continental Shelf off the West Coast of India

ABSTRACT Testut, L. and Unnikrishnan, A.S., 2016. Improving modeling of tides on the continental shelf off the west coast of India. Global tidal solutions are sometimes inaccurate in coastal regions. This is particularly true in some regions of the northern Indian Ocean, which are characterized by wide continental shelves and large tidal ranges. We show that these global solutions are inaccurate on the shelf region off Mumbai, off the west coast of India. In this region, the shelf is very wide, and it opens into the Gulf of Khambhat, where large tides are observed. Moreover, in regions of large semidiurnal tides in the Bay of Bengal, such as the head Bay, Gulf of Martaban, etc., global tidal solutions are not accurate. In the present work, we focus on the shelf region off the west coast of India. We used a new approach in developing a high-resolution hydrodynamic tidal model for the inner shelf region (8°N to 22°N). The open boundary of the model is aligned to the altimetry tracks, which allowed us to pre...

About this title ‐ River-Dominated Shelf Sediments of East Asian Seas

The rivers of East Asia are some of the largest and most important to human society and the global economy. They drain a variety of terrains from the Tibetan plateau, the hill country of southern China and the steep mountains of Taiwan. The sediment they carry potentially records the long-term evolution of continental environments within the marine stratigraphic record. Sediments reaching the ocean have to traverse the wide continental shelves where they may be reworked and transported by longshore currents, typhoon storm waves, as well as large ocean currents such as the Kuroshio. Deciphering any marine record requires us to understand the dynamics of sediment transport on the continental shelves, and this region acts as a global type example of such processes. Studies in this volume span a wide range of subdisciplines in the marine sciences and provide new insights into how sediment is distributed offshore after leaving the river mouths.