Coastal Shelf Areas Research Articles

Seasonal and diel patterns in Black Sea harbour porpoise acoustic activity in 2020-2022.

The Black Sea is a semi-enclosed inland sea with an unevenly distributed extensive coastal shelf area and anoxic deep waters. It is inhabited by common and bottlenose dolphins, as well as harbour porpoises, all represented by local subspecies. Between September 2020 and October 2022, 19 F-PODs deployed by research teams from Bulgaria, Georgia, Romania, Türkiye and Ukraine collected data on acoustic activity of Black Sea harbour porpoises. Strong seasonal and diel patterns were found, which varied in three regions. In the south-eastern part of the Black Sea, harbour porpoise acoustic activity was higher from January to May, with a peak in April. This pattern agrees with the seasonal anchovy migration from the winter spawning grounds in warmer waters in the south-eastern region to feeding grounds on the productive shallow north-west shelf. The diel pattern showed strong nocturnal acoustic activity, which is consistent with anchovy vertical migration. Porpoises on the western side of the Black Sea exhibited a bimodal seasonal pattern in acoustic activity, with a larger peak in April and a smaller one in October. Diel activity was primarily nocturnal. On the north-west shelf, harbour porpoise acoustic activity was mostly recorded during the warm period from April to October. The diel pattern showed activity mainly during daylight with two peaks: a smaller one approximately at dawn and a larger one at dusk. This pattern is similar to the vertical migrations of sprat. Overall, the results of the study were consistent with the prey being an important driver of seasonal and diel dynamics of harbour porpoise acoustic activity.

“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle

Current evidence suggests that macroalgal-dominated habitats are important contributors to the oceanic carbon cycle, though the role of those formed by calcifiers remains controversial. Globally distributed coralline algal beds, built by pink coloured rhodoliths and maerl, cover extensive coastal shelf areas of the planet, but scarce information on their productivity, net carbon flux dynamics and carbonate deposits hampers assessing their contribution to the overall oceanic carbon cycle. Here, our data, covering large bathymetrical (2–51 m) and geographical ranges (53°N–27°S), show that coralline algal beds are highly productive habitats that can express substantial carbon uptake rates (28–1347 g C m−2 day−1), which vary in function of light availability and species composition and exceed reported estimates for other major macroalgal habitats. This high productivity, together with their substantial carbonate deposits (0.4–38 kilotons), renders coralline algal beds as highly relevant contributors to the present and future oceanic carbon cycle.

Sedimentation Processes and the Holocene Evolution of the Indigirka Paleovalley (Coastal Shelf Area of the East Siberian Sea)

Problems of the paleogeographical evolution and changes in sedimentation environment within the Indigirka River paleovalley (the East Siberian Sea) are discussed. Based on the results of geophysical and geological research and a high-resolution study of sediment cores (grain size analysis, geochemistry, macro- and micropaleontology, pollen analysis, radiocarbon dating) the development of the Holocene marine transgression has been reconstructed, sedimentation rates have been calculated, and the basic principles of changes in sedimentation processes have been established.

АНАЭРОКОНТУР ЧЕРНОГО МОРЯ

The work is devoted to the issue of the allocation of a new contour biotope in the Black Sea. Currently, in hydrobiology, it is customary to distinguish the following contour biotopes or contact zones of the sea: aerocontour, psammocontour, lithocontour, pelocontour, potamocontour (Zaitsev, 2012, 2015), which describe the ecological structure of any reservoir except for the Black Sea. This is due to the fact that most of the deep-water area of this water basin does not have a peloconture with higher forms of life due to hydrogen sulfide in its depths. This biotope exists is only in coastal shelf areas up to depths of 150–200m, where there is still oxygen. Until the end of the last century, it was believed that the Black Sea had only oxygen and hydrogen sulfide zones, with a mixing layer (or C-layer) between them. However, at the beginning of this century, a revolutionary discovery was made in hydrochemistry (Konovalov, Murray, 2001; Konovalov et al., 2005): it turned out that the C-layer does not exist and that the oxygen and hydrogen sulfide layers of water are separated by a special water mass where there is neither oxygen nor hydrogen sulfide. It turned out that this water mass (called the Suboxic layer) has a thickness of about 30-50 m, characteristic physicochemical properties and a certain history of origin (Konovalov et al., 2005). Like any water mass in the sea, it is a biotope that in hydrobiology does not yet have a name, is poorly described and its role in the ecosystem is insufficiently studied. However, there is already evidence that it plays an extremely important role in the ecosystem of the Black Sea because clusters of specific hydrobionts form on its borders and intensive chemosynthesis occurs in it, comparable in production with the photic zone (Polikarpov et al., 1990). This biotope is an obvious contour biotope, the opposite of the aeroconture, which is in contact with the oxygen environment. It is located on the border with anoxic layer and therefore the author called it the "anaerocontour" of the Black Sea. Based on the generalization of existing data and the results of his own research, the author of this work for the first time provides a generalized description of the structural and functional characteristics of this contour biotope and describes its role in the functioning of the ecosystem of the Black Sea. The results of this work are of fundamental interest for understanding biological processes in extreme conditions and their impact on long-period changes in the ecosystem of the Black Sea.

Analysis of the impact and causes of Enteromorpha prolifera disaster in the Yellow Sea

The Southwest Yellow Sea is close to Chinese mainland and belongs to the coastal temperate shelf area. In the summer of 2008, the world’s largest green tide (mainly Enteromorpha prolifera) event occurred in Qingdao, and every year thereafter, Enteromorpha prolifera disaster events have occurred along the southwest coast of the Yellow Sea. Based on the observation data of Enteromorpha prolifera and the results of previous studies, the influence and causes of Enteromorpha prolifera disaster in the Yellow Sea are analyzed in this paper. It is found that the duration of Enteromorpha prolifera disaster is about 3 months, with significant inter-annual variation characteristics. This helps to provide direct and effective new cognition for the prevention and control of Enteromorpha prolifera from multiple perspectives, and better serve the environmental protection and sustainable development planning of the Yellow Sea.

Revisit the Sedimentary Stratigraphic Evolution and Environmental Changes on the Outer Shelf of the East China Sea Since MIS 5

The East China Sea (ECS) is featured by the broad continental shelf, huge terrigenous sediment input and striking river-sea interaction during the Quaternary. Despite the numerous studies, mostly on the delta, coastal and inner shelf areas, the late Quaternary stratigraphy and sedimentary environment on the mid-outer ECS shelf were poorly documented. In particular, it is still controversial in issues such as the recognition of marine transgression deposits in the interglacial period and the occurrence and ages of deposits in the glacial period. This study presents new data of high-resolution seismic reflection profiles and collective evidences from lithology, microfossil assemblages and geochronology of borehole SFK-1 on the ECS outer shelf, aiming to revisit the sedimentary stratigraphic evolution and environmental changes since the Marine Isotopic Stage 5 (MIS 5). Sixty-one ages were obtained by radiocarbon and Optical Stimulation Luminescence (OSL), providing robust constraints on the chronostratigraphy. Three marine regression/transgression cycles were identified, which primarily constrained the sedimentary environmental evolution over the past 100 kyrs. Although the strong river-sea interaction accompanied with sea level fluctuations characterized the late Quaternary depositional environment on the shelf, this study clearly identified the stratigraphic boundaries between MIS 1 and MIS 5, and confirmed the tide-influenced fluvial deposition formed during the Last Glacial Maximum on the outer shelf. We infer that tidal forcing significantly superimposed its influence on sea level change and thus formed the most striking feature on the late Quaternary stratigraphy of the open ECS shelf. With the combination of a large number of absolute depositional ages with high-resolution core records, the major findings of this study may allow better understanding of the Quaternary sedimentary evolution and river-sea interaction on open shelves dominated by siliciclastic sedimentation.

Source analysis of dissolved methane in Chukchi Sea and Bering Strait during summer–autumn of 2012 and 2013

Rapid sea-ice retreat in the Arctic Ocean can promote the release of methane (CH4) from microbe and from sediment on the continental shelf. The released methane can be the cause or effect of strong climate feedback. Nevertheless, few observations have been reported of temporal changes of dissolved CH4 in the Arctic Ocean, especially in western coastal shelf areas (Chukchi Sea and Bering Strait). This study therefore describes the spatial and temporal distributions of the concentrations and stable carbon isotope ratios (δ13C value) of CH4 in the western Arctic Ocean during August–October in 2012 and 2013. In both years, surface water was supersaturated with CH4 with respect to the atmosphere, but concentrations in 2013 were 2–3 times higher than in 2012. In 2012, the concentrations in the bottom layer were higher (up to 55.9 nmol kg−1), whereas δ13C values were lower (down to −63.8‰) than in the surface layer, indicating that CH4 was produced mainly by organic matter degradation in seafloor sediment via methanogens. In 2013, however, because of stronger vertical mixing than in 2012, vertical gradients of CH4 concentration and δ13C value were not prominent. Short-term (19 days) time series observations were also conducted at a fixed station in 2013. An episodic high CH4 concentration in the surface layer (17.2 nmol kg−1 with δ13C = −52.9‰) observed after a strong wind event suggests that CH4 production is accelerated because nutrients are supplied from the bottom of the mixed layer increase plankton activity. These findings suggest that the dynamic variation of dissolved CH4 in the Chukchi Sea in autumn 2012 and 2013 depended mainly on the strength of stratification by sea-ice melt water. Strong winds increase biological activity in the surface layer, consequently accelerating CH4 production.

Capitellidae (Annelida) from the Brazilian Continental Margin (SW Atlantic): new occurrences of three genera and description of new species

The Brazilian Continental Margin hosts several deep seafloor landscapes. However, this deep margin is still poorly studied and monitored, compared to coastal and continental shelf areas, historically limited to areas of particular economic interest. Some studies financed by the Brazilian oil and gas company have been conducted off Southeast (SE) Brazil (Esprito Santo and Campos Basins) as part of the environmental licensing process for resource exploration. Similar results showed that annelid polychaetes dominated on the continental shelf and upper slope. Within a wide bathymetric range, Capitellidae species belonging to three different genera represented new records for Brazil: Mastobranchus Eisig, 1887, Peresiella Harmelin, 1968, and Polymastigos Green, 2002. Mastobranchus braziliensis sp. nov. was found in shallow waters (20147m) of both Esprito Santo and Campos Basins; Peresiella megapapilata sp. nov. occurred from 21 to 446m of both Esprito Santo and Campos Basins; and Polymastigos profundus sp. nov. inhabited greater depths (9901361m) of the Esprito Santo Basin only. Three new species are described and compared to other species of the respective genus, the diagnosis of some genera amended and the type material of Mastobranchus loii Gallardo, 1968 redescribed. Although the three genera have the same number of thoracic chaetigers, they present several morphological differences, and the current effort being made is to translate those differences into characters to be included on the generic diagnosis of each genus. Additionally, two new morphological characters were proposed for the family, the shape of thoracic chaetigers and depth of intersegmental groove.

Changing River Discharge and Suspended Sediment Transport to the Georgia Bight: Implications to Saltmarsh Sustainability

Windom, H.L. and Palmer, J.D., 2022. Changing river discharge and suspended sediment transport to the Georgia Bight: Implications to saltmarsh sustainability. Journal of Coastal Research, 38(3), 512–522. Coconut Creek (Florida), ISSN 0749-0208. Suspended sediment delivered in river discharge to the Georgia Bight (the coastal-shelf area of the SE U.S. Atlantic coasts of Georgia and South Carolina) provides a continuous supply of fine grain sediments to support coastal saltmarshes. Archived data on discharge and suspended sediment loads for Piedmont and Coastal Plain rivers collected over eight to nine decades were used to estimate the present rate of sediment discharge to the Bight to be about 1 × 106 metric tons annually. The data used in this assessment are for the period after major reservoir/dam construction and other streamflow diversions occurring during the 1950s–1970s, which had a major effect on sediment yields of SE Atlantic watersheds. The estimated annual sediment delivery is about two-thirds of that needed to maintain vertical saltmarsh stability as sea level rises at the present regional rate of 3.3 mm/y. The observed 2% per decade decreasing trend in river discharge to the Bight, related to rapid population and temperature rise since ca. 1960, and the continual depletion of sediment stored in river floodplains below dams, suggests that the fine sediment supply to the coast will continue to decline.

Mantle geodynamics and source domain of the East Vietnam Sea opening- induced volcanism in Vietnam and neighboring regions

The spreading of the East Vietnam Sea (EVS, also known as Bien Dong, or the South China Sea), leading to the occurrence of syn-spreading (33-16 Ma) and post-spreading (< 16 to present) volcanism. Syn-spreading magma making up thick layers of tholeiitic basalt with a geochemical composition close to the refractory and depleted mid-ocean ridge basalt (MORB) is mainly distributed inside the EVS basin. The post-spreading magma is widely distributed inside the basin and extended to South and SE China, Hainan island, Southern Laos (Bolaven), Khorat Plateau (Thailand), and Vietnam, showing the typical intraplate geochemistry. Basaltic samples were collected at many places in Indochina countries, Vietnam’s coastal and continental shelf areas, to analyze for eruption age, petrographical, geochemical, and isotopic composition to understand the similarities and differences in the mantle sources between regions. The results reveal that basalts from some areas show geochemical features suggesting they were derived subsequently by spinel peridotite and garnet peridotite melting, forming high-Si, low-Mg, and low-Ti tholeiitic basalt to low-Si, high-Mg, and high-Ti alkaline basalt with the trace element enrichment increasing over time. Other basalts have geochemical and isotopic characteristics unchanged over a long period. The post-spreading basalt’s radiogenic Sr-Nd-Hf-Pb isotopic compositions show different regional basalts distribute in the various fields regardless of eruption age, suggesting that their mantle source feature is space-dependent. The post-EVS spreading basalts expose the regional heterogeneity, reflecting the mixture of at least three components, including a depleted mantle (DM) represented by the syn-EVS spreading source, similar to the DUPAL-bearing Indian MORB source; an enriched mantle type 1 (EM1), and type 2 (EM2). The DM may interact and acquire either EM1 or EM2 in the sub-continental lithospheric mantle; as a result, different eruption at different area acquires distinct isotopic signature, reflecting the heterogeneous nature of the subcontinental lithospheric mantle. The study proposes a suitable mantle dynamic model that explains the EVS spreading kinematics and induced volcanism following the India - Eurasian collision from the Eocene based on the research outcomes.

Conserving threatened marine species and biodiversity requires 40% ocean protection

Global prioritisation of where to locate Marine Protected Areas (MPA) has not considered both a comprehensive range of measures of biodiversity as well as threatened species distributions. Using maps of 974 threatened species ranges, we found that areas of high threatened species richness are distributed throughout the world's coastal and continental shelf areas as well as in offshore regions and well-known biodiversity hotpots. We then assessed whether Representative Biodiversity Areas (RBAs), the top 30% of the global ocean prioritised based on holistic measures of biodiversity from genes to ecosystems, adequately cover the ranges of threatened species. Implementing RBAs could protect a minimum of 30% of most threatened species ranges, but 26 threatened species have distributions in areas with poor overlap with biodiversity priorities.Using decision support software we found that a minimum of 40% of the ocean is required to adequately protect over 68% of all aspects of biodiversity and 30% of IUCN Red List threatened species ranges. Priority areas outside Exclusive Economic Zones (39%) demonstrate the importance of the High Seas (59% of the global oceans) to biodiversity conservation. Recognising the uncertainties inherent in our approach due to the limited proportion of taxa assessed by the IUCN Red List, we used an uncertainty analysis to support our findings. We found that currently, only 2.5% of priority areas are within marine reserves, highlighting the urgent need for increased protection of important areas for biodiversity and threatened species across EEZs and the High Seas.

Long-Term Trends of Sea Surface Wind in the Northern South China Sea under the Background of Climate Change

The long-term trends of sea surface wind are of great importance to our understanding of the effects of climate change on the marine environment. In the northern South China Sea (SCS), the long-term changes in coastal sea surface wind are not well-understood. Based on the latest reanalysis (ERA5) data from 1979 to 2019, our analysis showed a decreasing trend in the annual mean wind speed in the coastal area and an increasing trend in the open sea. There was a significant weakening trend in the easterly wind component in the coastal and continental shelf areas, whereas there was an increasing trend in the northerly wind component in the open sea. The Mann–Kendall mutation analysis suggested that there were significant changes in the wind speed and frequency of strong wind. Significant correlations were found between the variation of the wind field and El Niño–Southern Oscillation by wave coherence analysis. The strengthening of the wind stress curl was an important factor for the enhancement of coastal upwelling along the coast of the northern SCS. The wind field plays an important role in modulating the climatic change of significant wave height.

The Challenge to Observe Antarctic Toothfish (Dissostichus mawsoni) under Fast Ice

In situ observation of Antarctic toothfish (Dissostichus mawsoni) is challenging as they typically live at depths greater than 500 m, in dark and ice-covered Antarctic waters. Searching for adequate methodologies to survey Antarctic toothfish in their habitat, we tested a miniaturized Baited Remote Underwater Video camera (BRUV), deployed through holes drilled in the sea ice in the Ross Sea region, over three field seasons. In 2015 three BRUVs were deployed at McMurdo Sound, and paired with a vertical longline sampling. In 2017, three opportunistic deployments were performed at Terra Nova Bay. In 2018 seven deployments at Terra Nova Bay provided preliminary data on the habitat preferences of the species. The design and configuration of the mini-BRUV allowed to collect high-quality video imagery of 60 Antarctic toothfish in 13 deployments from the fast sea ice. The behaviour of fish at the bait, intra-species interactions, and potential biases in individual counting were investigated, setting baselines for future studies on the abundance and distribution of Antarctic toothfish in sea-ice covered areas. This work represents the first step towards the development of protocols for non-extractive monitoring of the Antarctic toothfish in the high-Antarctica coastal shelf areas, of great value in the Ross Sea region where the largest MPA of the world has recently been established.

Chemically unidentified dissolved organic carbon: A pivotal piece for microbial activity in a productive area of the Northern Patagonian shelf

The biochemical composition and fluorescence properties of DOM were assessed in relation to phytoplankton and major aquatic bacterial clades in a regenerative area of the Argentine Shelf. DOM was mainly of autochthonous biological origin, containing humic- and protein-like substances of medium degree of unsaturation and diagenesis. Biochemical-DOM accounted for 25% of total DOC, being dissolved combined amino acids (DCAA) the dominant fraction followed by free carbohydrates. Phytoplankton was the main source of serine, alanine, and valine, and particulate carbohydrates. Gammaproteobacteria abundance correlated negatively with ammonium and positively with DCAA, suggesting a coupling between ammonium consumption and refractory amino acid production. A preferential utilization of alanine, leucine and threonine as nitrogen source was inferred from the distribution of Cytophaga-Flavobacteria-Bacteroidete in relation with dissolved free amino acids (DFAA). Notably, Alpha- and Betaproteobacteria correlated with the large pool (75%) of chemically unidentified DOC and not with DCAA or dissolved combined carbohydrates. Particularly, Alphaproteobacteria (∼40% of EUB total heterotrophic bacteria) either significantly contribute to the production of the “humic”, refractory fraction of marine DOM, or the latter impairs resource control on their abundance. Spatial heterogeneity inherent to coastal-shelf areas drives important regional variability in the biochemical properties of DOM.

Struktura bimodal'nosti napravleniya pribrezhnogo techeniya u Yuzhnogo berega Kryma v 2002–2008 godakh

This paper aims at improvement of knowledge about the structure of bimodal distribution of coastal current direction repeatability at Cape Kikineiz of the Southern coast of Crimea as per monitoring data obtained at the stationary oceanographic platform of the Black Sea hydrophysical sub-satellite testing area of the MHI RAS. Used for monitoring, a vertical measuring antenna with a fixed aperture of Euler testers of the current horizontal component provided verifiable and synchronic isolation of the current's structural characteristics with a vertical velocity shift and multiscale coherent oscillations of the current. New results of analysis of in situ data are presented regarding characteristics of the coastal current and its variability. The data were obtained within the period from November 2001 to 2008. Change patterns of the long-term coastal current regime are noted. The current's characteristics are matched to the results obtained at Cape Kikineiz of the Southern coast of Crimea for the period from September 2008 to 2019. Regular intense oscillations of the coastal current at the local inertial (17 hrs) and daily component as well as current oscillations with a period of 11.6 day are defined. Evolution is analyzed of probability density distribution of the velocity module and current vector direction after calculations, during which a corresponding vector distribution of intensive inertial-gravitational, mesoscale and synoptic oscillations was excluded in the original vector series of dynamics using a digital filtration method. When excluding the contribution of daily and inertial oscillations, the backward and primary mode ratio in the histograms of the coastal current direction repeatability decreases by more than three times. When excluding the contribution of mesoscale and synoptical oscillations, the backward mode of current is almost absent and there exists only a large-scale coastal current coinciding with a cyclonic direction of the coastal edge of the Black Sea Rim Current. Bimodal distribution of the coastal current direction repeatability is a result of superposition of velocity vectors of a large-scale current and variable contribution of existing orbital velocities of multiscale wave and vortex formations present in the coastal-shelf area.

Distribution and abundance of humpback whales, Megaptera novaeangliae, off the coast of Mozambique, 2003

Humpback whales within the southwestern Indian Ocean undertake annual migrations from summer Antarctic/Southern Ocean feeding grounds towinter breeding grounds in the tropical and sub-tropical coastal waters of Mozambique, Madagascar and the central Mozambique Channel Islands.Little is known of the inter-relationship of humpback whales on each of these wintering grounds, or the inter-relationship of these wintering groundswith the summer Antarctic feeding grounds.A line-transect survey of cetacean species was carried out in Mozambique coastal waters between Cabo Inhaca (26°00’S, 33°05’E) and just northof Mozambique Island (14°26’S, 40°53’E) and between the 20 and 200m isobaths, over the period 26 August to 7 September 2003. The majority(98.1%) of 951.8 n.miles of search effort carried out on this survey was in passing mode due to the high densities of whales encountered. Humpbackwhales were the only large whales to be identified and the distribution of 691 sightings of an estimated 1,130 individual humpback whales and 132sightings of an estimated 154 large unidentified whales show distribution throughout the survey region. Two sightings of individual small whaleswere made in the region of Inhambane.In general, higher than expected sighting densities (based on survey effort) were recorded in the region between Cabo Inhaca and Xai-Xai, andin the region of the Pantaloon and David Shoals to the north east of Quelimane. Lower than expected sighting densities were recorded over theSofala Banks. No distribution trends could be ascribed to environmental parameters, apart from whales being distributed in waters of higher salinitiesthan expected, possibly due to turbidity associated with low salinity water arising from river input. Groups containing a cow and calf pair weredistributed across the entire region surveyed.Analyses of unstratified data result in a total abundance estimate of 6,808 (CV = 0.14) humpback and unidentified whales in the 14,029.5 n.mile2area surveyed. As a result of the differences in width of the coastal shelf area along the coast of Mozambique, the line transect survey data werefurther analysed in four strata. Pooling of estimates over these four strata results in a total abundance of 6,664 whales (CV = 0.16), with highestdensities in the southernmost stratum and the lowest densities in the narrow shelf region across the Sofala Banks. Similar analyses of humpbackwhales only resulted in abundance estimates of 5,930 (CV = 0.15) (unstratified data) and 5,965 whales (CV = 0.17) (data analysed by four strata).Although not directly comparable due to differing survey platforms, these estimates indicate the population to have increased since previous surveysin the early 1990s.

First Detection of Paralytic Shellfish Toxins from Alexandrium pacificum above the Regulatory Limit in Blue Mussels (Mytilus galloprovincialis) in New South Wales, Australia.

In 2016, 2017 and 2018, elevated levels of the species Alexandrium pacificum were detected within a blue mussel (Mytilus galloprovincialis) aquaculture area at Twofold Bay on the south coast of New South Wales, Australia. In 2016, the bloom persisted for at least eight weeks and maximum cell concentrations of 89,000 cells L−1 of A. pacificum were reported. The identity of A. pacificum was confirmed using molecular genetic tools (qPCR and amplicon sequencing) and complemented by light and scanning electron microscopy of cultured strains. Maximum reported concentrations of paralytic shellfish toxins (PSTs) in mussel tissue was 7.2 mg/kg PST STX equivalent. Elevated cell concentrations of A. pacificum were reported along the adjacent coastal shelf areas, and positive PST results were reported from nearby oyster producing estuaries during 2016. This is the first record of PSTs above the regulatory limit (0.8 mg/kg) in commercial aquaculture in New South Wales since the establishment of routine biotoxin monitoring in 2005. The intensity and duration of the 2016 A. pacificum bloom were unusual given the relatively low abundances of A. pacificum in estuarine and coastal waters of the region found in the prior 10 years.

Variations of wave parameter statistics as influenced by water depth in coastal and inner shelf areas

Wave height, pressure and orbital velocity statistics, as influenced by the factor of water depth, are analyzed on the basis of five data sets collected in situ from two intertidal sites with a mean water depth of 0.8–2.7 m and three inner shelf sites (water depths 14.6–27.6 m). Acoustic Doppler Velocimeters (ADVs) were used to measure instantaneous wave pressure and current velocity at 0.20–0.35 m above sea bed. The zero-crossing wave analysis method was applied to analyze the wave data to determine the wave pressure amplitude P and orbital velocity amplitude U of individual waves, together with the frequency of occurrence distributions of P and U, which are compared with the three commonly-used, classic Rayleigh, modified Rayleigh and Weibull distributions. It is found that the distribution of P is almost identical to that of U for each of the five study sites. The distributions of P and U for the intertidal flat sites fit the Weibull distribution better than the classic or modified Rayleigh ones, indicating a shallowness effect which is associated with finite-banded wind-wave spectra and possible wave breaking or near-bed turbulence. On the other hand, the distributions of P and U measured at the three inner shelf sites agree almost equally with the three distributions. With increasing water depth, the distributions of P and U are shown to reduce from the two-parameter Weibull distribution at the shallow intertidal sites to the classic Rayleigh at the deep-water sites. For coastal engineering applications, an empirical formula is proposed to estimate more accurately the significant wave height in intermediate coastal waters based on the surface water elevation data.

A VORTEX DROP STRUCTURE AS DEAERATION SYSTEM FOR A SUBMARINE OUTFALL PIPELINE

Use of submarine outfall pipelines became more common since World Bank Group issued a new guideline for maximum emissions levels for thermal power plants in 1998 (van Dijk, 2005). The more restrictive levels for temperature increase at the receiving water, requires outfall systems to conduct the water down to greater depths to achieve the required dilution standard. However, air entrainment control into outfall pipes could be challenging, especially for discharges with high flowrates for which conventional deaeration chambers become too large. The problem could turn more difficult in coastal shelf areas at seismic zones, where the hydraulic height of the incoming flow must be effectively controlled and the design not only has to pursue hydraulic objectives but also stability requirements for these massive structures subjected to relevant seismic thrusts. A vortex drop structure was designed for the cooling water discharge system of a thermal power plant in Mejillones Bay, Chile. The structure addresses the elevation difference between the return flow pipe and the ocean outfall pipelines while adhering to the spatial restrictions at the project site. Energy dissipation as well as limitation of air entrainment into the outfall pipelines were critical design considerations. Tests where done on a 1:12.5 scale (Froude) physical model. Prototype structure is under construction. Operation is planned to start on mid-2018.

Ecosystem damage from anthropogenic seabed disturbance: A life cycle impact assessment characterisation model

Despite the high amount of pressure placed on benthic habitats by anthropogenic activities, particularly in coastal shelf areas, as yet, the impact of seabed damaging activities on ecosystem quality has not been included in Life Cycle Assessment (LCA). We present a globally applicable impact characterisation approach, parameterized within 17 marine ecoregions in Europe. Our modelling approach includes two perspectives: the single-impact perspective and the repeated-impact perspective. The approach for the single-impact perspective is a function of the spatio-temporal scale and intensity of the anthropogenic disturbance, the initial benthic response, and an estimated ecological recovery period. The approach for the repeated-impact perspective additionally accounts for the industry-specific interval between disturbance events, allowing for consideration of potentially incomplete ecological recovery between disturbance events and therefore the potential for both recoverable and non-recoverable potential impacts. We exemplify the repeated-impact perspective for the benthic trawl fishing industry in Europe.Analogous to current approaches for characterizing land use impacts in LCA, we quantify characterisation factors (CFs) for both occupation and transformation impacts. CFs for occupation impacts are ecoregion-specific. CFs for transformation impacts are spatially differentiated at the resolution of seabed substrate type, categories of hydrodynamic energy, i.e. water movement due to the influence of waves and currents, fisheries management zone (repeated-impact perspective only) and marine ecoregion. We estimate ecological recovery times with consideration of the influence of seabed substrate type, hydrodynamic energy at the seabed and the stock of potential recolonizers.The characterisation factors allow for quantifying indicators of ecosystem damage from seabed disturbance in terms of a time-integrated relative species loss. With a single-impact perspective, the largest impact intensities are found in areas with the longest estimated ecological recovery time. In the repeated-impact perspective, the largest intensity of time-integrated non-recoverable impact occurs when the disturbance interval is equal to half the ecological recovery time.