Hydrographic Features Research Articles

Potential seamount effect on the distribution of the hydrographic features and community structure of pelagic ciliates at the Caroline seamount (tropical western Pacific) in late (2017) and early summer (2019)

Seamounts are ubiquitous features in the world ocean with potential for increasing plankton biodiversity and abundance, and providing important habitats for aquatic predators. Although ecological importance of seamount is well known, the mechanisms for supporting seamount-associated microzooplankton (e.g., pelagic ciliates) communities remains to be substantiated. In this study, pelagic ciliate community structure variations and their relationship with environmental variables were investigated in the Caroline seamount in late (2017) and early summer (2019). Above the seamount in 2019, ciliates exhibited higher abundance and biomass than off the seamount, which supported the classic hypothesis of seamount effect. Aloricate ciliate small size-fraction (10–20 μm) was dominant in bathypelagic (>1000 m) zone. Although relative abundance of small size-fraction was similar in both 2017 and 2019, the absolute abundance in 2019 seamount-effect stations were obviously higher than that in 2017. All abundant tintinnids were classified into surface- and DCM (deep Chl a maximum layer)-peak groups. Among them, four abundant tintinnids (Acanthostomella conicoides, Eutintinnus hasleae, Salpingella curta and S. minutissima) had higher abundance at DCM and might uplifted to shallower waters by upwelling at 2019 seamount-effect stations. The multivariate biota-environment analysis showed that environmental variables have significant impacts on the ciliate community structures in 2017 and 2019. Higher Chl a and nutrient concentrations, and sustained upwelling might be two potential mechanisms for microzooplankton seamount effect. Our study constitutes a rather solid foundation for quantitative and functional study of microzooplankton populations over oligotrophic tropical seamounts.

Ecological risk assessment of selected contaminants in seawater, sediment and some fish species from Alexandria beaches, South-Eastern Mediterranean Sea, Egypt

The present study aims to investigate the hydrographical characteristics, nutrient salts, and heavy metals (HM) to estimate the contamination status of selected coastal beaches along the Alexandria coastal area in the southeast Mediterranean Sea. Water and sediment samples were collected from 8 beaches along the cost of Alexandria, while 122 fish samples representing 10 species were collected from 2 beaches representing two ports at Alexandria city. All samples were subjected to specific analyses to assessment of ecological risks at study area. The study indicated that the seawater quality of the investigated beaches varied between medium to good based on the Water Quality Index (WQI = 0.233–0.713). Moreover, the highest average concentration in water was observed for Fe (33.624 μgl−1) and the lowest was detected for Cd (0.050 μgl−1). HM in sediment have the same trend of these HM in water. The most of beaches’ sediments were classified as non-contaminated (PI < 1) with all examined HM. Hazard Quotient and Hazard Index (HQ &HI < 1) this indicated that the lack of non-carcinogenic impacts for children and adults due to dermal contact with sediments of all beaches. The most abundance HM in fish were Fe and Zn. Bioaccumulation factors (BAF) in fish muscles was evaluated. MPI (Metal Pollution Index) of HM in the investigated species ranged from (0.381–2.216) in Pomatomus saltatrix and Scomberomorus commerson species respectively. HQ, HI, EDI (Estimated Daily Intake), and TR (Target Risk) values showed that the examined species are still safe for human consumption.

Enhancing U-net extraction of hydrographic features from IfSAR data in Alaska using shallow water channel depth models

Enhancing U-net extraction of hydrographic features from IfSAR data in Alaska using shallow water channel depth models

Thirty years of a bottom oxygen depletion-renewal cycle in the coastal yet deep environment of the West Saronikos Gulf (Greece): Its drivers and the impact on the benthic communities

In the period 1987–2017, a series of physical and chemical measurements related to oxygen variability at a trough area with a maximum depth of ~420 m in the West Saronikos Gulf, reveal the following: In the early 90s, deep winter mixing occurred resulting in an oxygenation down to ~420 m followed by an oxygen decline. This decline reached near-bottom hypoxic conditions (O2 < ~62 μM (μmol/L)) after 1998, while a denitrification phase occurred after 2000 and a complete bottom anoxia in 2005. In June 2012, an oxygenation down to ~350 m was detected that most likely occurred in winter 2012. The 2012 oxygenation raised the until-then anoxic bottom concentrations to hypoxic ones in the years towards 2017 via vertical diffusive oxygen transfer. Observations of the benthic communities during the hypoxia, severe hypoxia (O2 < ~15 μM) and oxygen recovery phases showed a peak of opportunists in the hypoxia and a long faunal depletion in the severe hypoxia phases. A reversal in the benthic community structure appeared after the oxygenation of 2012 with the (re)appearance of opportunists while, in 2017, the community showed signs of retreat to earlier stages. The main anthropogenic pressure that could tentatively affect the oxygen concentration in the study area is posed by the Athens treated-sewage outfall at ~40 km away from the trough, which inputs organic matter into the Saronikos Gulf through effluent water of reduced salinity that, in addition, may alter the stratification opposing the vertical mixing. We show that the treated sewage output had no influence on a) the stratification, b) the particulate and dissolved organic carbon and c) the sewage-derived organic matter. Instead, the long-term dissolved oxygen variability with the deep renewal events was mostly driven by the large-scale atmosphere-ocean conditions (heat exchange and evaporation-minus-precipitation budget) that determine the hydrographic characteristics and the winter mixing.

Pelagic ciliate (Ciliophora) communities in the Southern Ocean: Bioindicator to water mass, habitat suitability classification and potential response to global warming

Although the pelagic ciliate (microzooplankton) play important role in carbon flux of marine ecosystems, their ecological function, habitat suitability classification and response to global warming were poorly documented in the Southern Ocean (SO). During summer of 2020/2021, ciliate (including aloricate ciliates and tintinnids) communities in waters from surface to 1000 m were investigated in the SO. Rapid attenuation of ciliate abundance and biomass occurred at 100 m depth in most stations. According to distinctive hydrographic features, five water masses were identified in the SO with unique ciliate community structure. Aloricate ciliate small size-fraction (10–20 μm) was dominant in water masses deeper than 200 m. Tintinnids showed distinctive regional and vertical distribution characteristics, and their habitat suitability characterized by the Bio-index exhibiting different optimum survival zones. Variations in tintinnid habitat can be regarded as indicators for future SO climate change. Correlation between environment factors and biota revealed that depth, Chl a and dissolved oxygen were main factors determining ciliate composition. Combining tendency of phytoplankton and meso-/macro-zooplankton to rapid global warming, ciliates may become smaller and more prominent in the future SO marine pelagic ecosystem. Our study has laid a foundation for recognizing the ciliate community and reinforcing the ideas about tintinnid indication for the change of future SO marine ecosystem.

Classification of drainage crossings on high-resolution digital elevation models: A deep learning approach

ABSTRACT High-Resolution Digital Elevation Models (HRDEMs) have been used to delineate fine-scale hydrographic features in landscapes with relatively level topography. However, artificial flow barriers associated with roads are known to cause incorrect modeled flowlines, because these barriers substantially increase the terrain elevation and often terminate flowlines. A common practice is to breach the elevation of roads near drainage crossing locations, which, however, are often unavailable. Thus, developing a reliable drainage crossing dataset is essential to improve the HRDEMs for hydrographic delineation. The purpose of this research is to develop deep learning models for classifying the images that contain the locations of flow barriers. Based on HRDEMs and aerial orthophotos, different Convolutional Neural Network (CNN) models were trained and compared to assess their effectiveness in image classification in four different watersheds across the U.S. Midwest. Our results show that most deep learning models can consistently achieve over 90% accuracies. The CNN model with HRDEMs as the sole input feature was found to be the best-fit one. The addition of aerial orthophotos and their derived spectral indices is insignificant to or even worsens the model’s accuracy. The selected best-fit model exhibits excellent transferability over different geographic contexts. This work can be applied to improve elevation-derived hydrography mapping at fine spatial scales.

The planktonic food web in the Gulf of Naples based on the analysis of carbon and nitrogen stable isotope ratios

AbstractPlankton play a key role in marine food webs by producing and transferring organic matter and energy to higher trophic levels. To define the trophic structure and interactions within the planktonic communities in the Gulf of Naples, we determined carbon and nitrogen stable isotope ratios in particulate organic matter (POM, &lt;20 μm), phytoplankton (20–200 μm), and bulk (unsorted) and sorted mesozooplankton (200–2000 μm) on a weekly basis in 2019. The stable isotope values of POM and, to a lesser extent, phytoplankton reflected the short‐term (weekly) alternation between offshore and coastal waters within seasonal variability. Although the isotopic signatures of coastal and offshore sources were still detectable in bulk mesozooplankton, δ13C and δ15N of single groups remained almost unchanged throughout the year. The trophic niches of mesozooplankton groups defined using the Stable Isotope Bayesian Ellipses in R software showed a high degree of overlap among them, which was corroborated by the tendency of most groups toward omnivory, beyond their known feeding habits, as indicated by MixSIAR models. Collectively, our results highlight that the complex network of interactions within the planktonic community in the Gulf of Naples can buffer natural variability due to the specific hydrographic features of the system. This characteristic makes the trophic structure of this community an ideal model for monitoring the response of planktonic food webs to climate‐ and anthropic‐driven changes.

Surface network and drainage network: towards a common data structure

The surface network is an application of the Morse-Smale complex to digital terrain models connecting ridges and thalwegs of the terrain in a planar, undirected graph. Although it provides a topological structure embedding critical elements of the terrain, its application to morphological analysis and hydrology remains limited mainly because the drainage network is the most relevant structure for analysis and it cannot be derived from the surface network. The drainage network is a directed, hierarchical graph formed by streams. Ridges of the surface network are not equivalent to drainage divides, which are not contained in the drainage network, and there is no direct association between thalwegs and streams. Therefore, this paper proposes to extend the surface network into a new structure that also embeds the drainage network. This is done by (1) revising the definition of ridges so that they include drainage divides and (2) assigning a flow direction to each thalweg, taking into account spurious depressions to avoid flow interruption. We show that this extended surface network can be used to compute the flow accumulation and different hydrographic features such as drainage basins and the Strahler order. The drainage network extracted from the extended surface network is compared to drainage networks computed with the traditional D8 approach in three case studies. Differences remain minor and are mainly due to the elevation inaccuracy in flat or slightly convex areas. Hence, the extended surface network provides a richer data structure allowing the use of a common topological data structure in both terrain analysis and hydrology.

A fully coupled superficial runoff and soil erosion basin scale model with efficient time stepping

We present a numerical model of soil erosion at the basin scale that allows one to describe surface run-off without a priori identifying drainage zones, river beds and other water bodies. The model is based on robust semi-implicit numerical techniques and guarantees exact mass conservation and positivity of the surface and subsurface water layers. Furthermore, the method is equipped with a geostatistical preprocessor that can perform downscaling of data retrieved from digital databases at coarser resolutions. Numerical experiments on both idealized and realistic configurations demonstrate the effectiveness of the proposed method in reproducing transient high resolution features at a reduced computational cost and to reproduce correctly the main hydrographic features of the considered catchment. Furthermore, probabilistic forecasts can be carried out based on soil data maps automatically generated by the geostatistical preprocessor that are distributed among the available MPI ranks to carry out simulations independently thus reducing the total cost of the simulation. The numerical experiments show the ability of the model to provide robust estimates of water levels, discharge and of the order of magnitude of the total sediment yield.

A new species of Metaprosekia Leistikow, 2000 (Oniscidea, Philosciidae) from caves of the State of Mato Grosso, Brazil

ABSTRACT The present work aims to describe a new species of Metaprosekia from siliciclastic caves from Caverna Nova and Caverna Ponte de Pedra, Utiariti Formation, Municipality of Diamantino, State of Mato Grosso. Metaprosekia utiariti n. sp. easily differs from the congeneric species in the shape of male pleopods 1 and 2. Moreover, a map illustrating the lithology and hydrographic characteristics where the specimens were collected and conservation remarks are given. http://www.zoobank.org/urn:lsid:zoobank.org:pub:F0B93B6A-0FBF-4B66-B6F0-3E5B67DD9C53.

Temporal changes in plankton diversity in relation to hydrographical characteristics at Perumal Lake, Cuddalore District, Tamil Nadu, India

BackgroundThe fresh water environment supports the productivity of phyto- and zooplankters and fin and shell fishes. The rate of fish productivity of an aquatic ecosystem solely depends on the rate of plankton productivity, and which in turn critically depend on the concentration and variation of hydrographical features. The current investigation was focused on the distributional pattern of phyto- and zooplankton vis-à-vis physicochemical characteristics in Perumal Lake, Cuddalore District, Tamil Nadu State (India).ResultsThe hydrographical factors and phytoplankton as well as zooplankton diversity were studied at the monthly interval of 12 months by following the standard methods in freshwater of Perumal Lake from September 2018 to August 2019. Presently a total of 15 species of phytoplankton and 15 species of zooplankton were recorded in Perumal Lake. The present study reveals good variation in the hydrographical characteristics, such as temperature (24.2–30.1 °C), turbidity (10.4–43.2 NTU), total suspended solids (300.2–1800.8 mg/L), conductivity (3.25–10.54 mhos/cm), pH (6.92–8.2), total hardness (8.58–23.8 mg/L), dissolved oxygen (2.8–7.26 mg/L), dissolved carbon dioxide (0.96–13.2 mg/L), chloride (1.92–23.8 mg/L), nitrate (0.28–3.18 mg/L), sulphate (1.1–8.2 mg/L) and phosphate (0.19–3.34 mg/L).ConclusionsThe findings of the present study indicate that the temperature has influence on phytoplankton as well as zooplankton diversity of species. Regular monitoring of hydro-biological parameters is necessary to assess the health of the lake ecosystem.

Coastal connectivity of an abundant inshore fish species: model-data comparison along the southern coast of South Africa

Biophysical models are often used to estimate larval dispersal patterns for the assessment of marine metapopulation spatial structure. However, comparisons of these models with field observations are relatively rare, and the extent to which models reproduce true marine connectivity patterns is unclear. We developed a biophysical model for larvae of the blacktail seabream Diplodus capensis (Sparidae), an abundant recreational and subsistence fishery species along the south-east coast of South Africa, and compared outputs from various configurations of that model to results from a field study conducted in a large regional embayment (Algoa Bay). Seasonal patterns of dispersal and recruitment produced by the model agreed best with field observations when thermal constraints on spawners and larvae were included. Spatial gradients in settling larvae also matched well, with the model capturing observed high settler densities within the lee of a major headland. Nevertheless, stronger spatial gradients were observed in larval densities from the field study when compared with model results, which may be explained by behavioural post-settlement processes. Model-based dispersal patterns revealed up to 5 subpopulations along the southern coast, with barriers to connectivity between subpopulations generally linked to hydrographic features. Overall, our results suggest that thermally mediated spawning behaviour, physical transport and post-settlement processes all play important roles in determining marine connectivity for the blacktail seabream. Refining physiological larval constraints may be an important component that needs to be considered going forward.

Increasing Efficiency of Nautical Chart Production and Accessibility to Marine Environment Data through an Open-Science Compilation Workflow

Electronic Navigational Chart (ENC) data are essential for safe maritime navigation and have multiple other uses in a wide range of enterprises. Charts are relied upon to be as accurate and as up-to-date as possible by the vessels moving vast amounts of products to global ports each year. However, cartographic generalization processes for updating and creating ENCs are complex and time-consuming. Increasing the efficiency of the chart production workflow has been long sought by the nautical charting community. Toward this effort, approaches must consider intended scale, data quality, various chart features, and perform consistently in different scenarios. Additionally, supporting open-science initiatives through standardized open-source workflows will increase marine data accessibility for other disciplines. Therefore, this paper reviews, improves, and integrates available open-source software, and develops new custom generalization tools, for the semi-automated processing of land and hydrographic features per nautical charting specifications. The robustness of this approach is demonstrated in two areas of very different geographic configurations and the effectiveness for use in nautical charting was confirmed by winning the first prize in an international competition. The presented rapid data processing combined with the ENC portrayal of results as a web-service provides new opportunities for applications such as the development of base-maps for marine spatial data infrastructures.

Habitat and abundance of cetaceans in Atlantic Ocean continental slope waters off the eastern USA

This study quantifies the abundance and spatial distribution of the cetacean community occupying continental shelf edge and inner continental slope waters along the US southeast Atlantic coast. A shipboard visual line-transect survey was conducted between June and August of 2004 that included effort in waters &gt;50m deep encompassing the shelf break and inner continental slope off the US east coast between 28°N and 38°N latitude. The abundance of nine cetacean taxa was estimated using line-transect distance analysis and an independent observer approach to correct for visibility bias. Canonical correspondence analysis was used to examine the spatial distribution of the cetaceans encountered during the survey as a function of surface temperature, surface salinity, surface fluorescence, bottom depth, and bottom slope. The abundance estimates for most species were much higher than those from a study of the area conducted in 1998. This is primarily due to increased coverage of the shelf-break region and correction for visibility bias. The multivariate analysis indicated four distinct groups of cetaceans that partitioned habitat as a function of salinity, depth, and a latitudinal gradient. These groups were associated with specific water masses and hydrographic features including mid-Atlantic shelf waters (Group I), the shelf break (Group II), mid-Atlantic slope waters (Group III), and south Atlantic slope water (Group IV). Areas where water masses converge such as the continental shelf break along the mid-Atlantic and near Cape Hatteras, North Carolina are therefore areas of both high diversity and density of cetaceans.

ГЕОДЕЗІЯ, КАРТОГРАФІЯ І АЕРОФОТОЗНІМАННЯ

Nowadays, GIS Technologies are used in many areas of human life, both in everyday life and scientific research. The purpose of the presented study is to identify the relationship between the scale of topographic maps and the main hydrographic characteristics of the river based on the data of observations in the Siverskyi Donets basin. The study is based on the results of the identification of the hydrographic network, which was performed based on the Open Street Map in the GIS environment of the QGIS program using the method of A. N. Straller and I. N. Hartzman. The process of identifying, describing, and analyzing subcontracted connections consists in assigning its identification order to each element of the river network, which makes it possible to compare and standardize streams. Operating with a hierarchical "tree" of the channel network, the main characteristic of which is the number of elementary, unbranched streams, it is possible to identify and analytically describe the dependencies between the detailing of the map and the main characteristics of the river network structures, such as water discharges, network density, drainage basin area, and river length. The basis for describing these relationships was the method of B.V. Kindiuk, who introduced the concept of the coefficient of the river network structure or the fractional order of the stream as a basis for approximating the above-mentioned dependencies, which allows mathematically describing the obtained functions and obtaining numerical values of empirical parameters. Using QGIS made it possible to create maps of the Siverskyi Donets hydrographic network within Ukraine based on maps of scales 1:50 000 and 1:200, 000. With their help, as well as data from a 1:100,000 map, the number of elementary unbranched watercourses was calculated, and each element of the system was identified, where the order of the main river changes depending on the map scale. The change in these indicators shows a tendency to increase the density and complexity of the river network with increasing map detail, and, as a result, potential changes in indicators of the catchment area, water runoff, and river length. The identified dependencies were expressed mathematically in the form of functions, and are also characterized by high values of the approximation reliability coefficient, which made it possible to construct a general transitional graph from the order of the water flow to the scale of the map with the corresponding values of the calculation parameters. The novelty and practical significance lie in the fact that the use of modern GIS technologies in hydrological science significantly increases the quality of cartographic data and concerning the studied object - the Siverskyi Donets River creates a database in the form of digital maps for further use in hydrographic studies. This sub‑basin has not been previously studied using the methodology proposed by B. V. Kindiuk about the influence of map scales on the characteristics of the river network structure. Such study from a practical point of view, can significantly help the work of engineers, researchers, and designers with cartographic data. This study is designed to explain the peculiarities in the scaling of river networks and propose a mechanism for a scientifically based transition from the existing map scale to the desired one within the Siverskyi Donets sub-basin.

Shaping of deep scattering layers by the seascape dynamics in the Canary islands

Vertical distribution of deep scattering layers (DSL) has been related to dissolved oxygen and illuminance levels as well as to horizontal water mass boundaries. Regional differences have precluded from establishing generic relationships between DSLs vertical distribution and the local hydrographical characteristics. This study used data collected at 18 and 38 kHz (that allow to discriminate between migrant and non-migrant layers) during two surveys carried out in the Canary islands in autumn 2016 and 2017. We evaluated the influence of water masses and their nutrient content, eddies and upwelling areas. While the permanent coastal upwelling increased the scattering of migrant mesopelagic fishes (that are driven through a secondary-order effect by primary production), the non-migrant layers were not affected by it. As in other areas, the main non-migrant acoustic layer (400–600 m depth) was located at horizontal water masses interfaces. The secondary non-migrant DSL, deeper than the main one, was located at depths rich in remineralized nutrients. Eddies modulated the shape of scattering layers into domes (cyclonic) and M-shapes (anticyclonic). This study contributes to a better understanding of how seascape dynamics influence the distribution and shapes of deep scattering layers in the Canary islands.

Performance of automated geoprocessing methods for culvert detection in remote Forest environments

Greater availability of digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) has made it possible to map precisely hydrographic features such as streams over large watersheds. Road embankments are precisely detected, given that DEMs are especially accurate over open areas, while culverts are not. Consequently, mapped stream positions are often erroneous along and through these anthropogenic structures. The position of actual culverts is often imprecise, incomplete or unavailable for large territories; thus, there is a need to develop and evaluate automated methods to locate culvert positions by remote sensing. Six geoprocessing methods were tested and compared to field-based culvert positioning data gathered in forested areas. These methods rely on preprocessing of depressions, manipulation of road embankment elevation, or both. When exact locations of culverts were unknown, the ‘Breach Depressions’ algorithm (WhiteBox GAT) was most accurate in reducing omission and commission errors. Depending upon the expected stream flow regime, it was possible to reduce cumulative error from 10% to 30% by using this method compared to less effective methods. When exact locations of culverts were known, it was possible to reduce cumulative error from 20% to 45% by burning them into the DEM. Comparisons of two different methods revealed that no automated geoprocessing allowed accurate detection of poorly located culverts, i.e. where small streams deviated into road-side ditches. Despite automated geoprocessing methods that are available, a database geolocating all culverts within a territory is the best way to create exact hydrographic networks without road embankment influence.

Simulating the Interconnected Eastern Mediterranean–Black Sea System on Climatic Timescales: A 30-Year Realistic Hindcast

Inter-basin water exchanges can be quite important in climatic-scale numerical studies simulating the circulation and hydrographic characteristics of neighboring oceanic basins connected through narrow straits. The crucial role of the interaction between the Mediterranean and the Black Seas is often overseen in simulations, which rely mostly on parameterizations to describe the exchange, essentially decoupling the two basins. In this study, the fully interconnected Eastern Mediterranean–Black Sea system is simulated for the historical period (1985–2015) using realistic boundary conditions (lateral, atmospheric and hydrological), with a hydrodynamic fully three-dimensional ocean modeling system. The setup of such a configuration is thoroughly described and the performance of the 30-year hindcast product is validated exhaustively against observations and model results, by evaluating the representation of surface fields, circulation, three-dimensional hydrographic characteristics, volumetric water exchanges, and the spatio-temporal variability of the above. The comparison shows exceptional performance, minimal drift, and substantial improvement compared to modeling studies that do not include the interaction. Moreover, due to the free-run configuration of the simulation (i.e., absence of assimilation schemes) no additional input is required other than the respective boundary conditions, making it possible to reliably extend the same setup for scenarios where observational data are not available, such as in future projections.

Coastal barrier morphogenic categories in Mississippi Delta plain development

Coastal barriers are defined as shore-parallel, aggraded-prograded supratidal beach ridge sets and individual single ridge-landforms, composed of sand and/or gravel. Island, spit, and mainland barriers represent the three major topographic subdivisions. In terms of bathymetric and hydrographic characteristics, bottom sediment types and associated habitats, barriers separate the marine offshore from inshore facies. This definition is not uniformly accepted and applied in the literature. Barriers impose reduced salinities inshore, diminish storm impact and moderate inland inundation, protect critical habitats and may mark ancient longshore transport directions, shore and sea-level positions. A wide range of dimensions, topography, and other factors characterize mainland strandplains. Shoal aggradation appears to be the prime island-forming mechanism, followed by accretion around semi-consolidated, elevated cores. Smaller islands may also form by barrier spit fragmentation. Detachment of dune ridges from the mainland shore is an often cited but at best unlikely mode of island genesis. Review of the literature and remote-sensed images created new insights, utilized barrier definitions and genetic theories, as applied in the Mississippi Delta Complex. A three-stage concept, involving dune ridge or barrier spit-detachment by marine encroachment and landward shift of fragmented transgressive islands forms the basis of a recent invited Marine Geology research article. That model assumes spit-growth from delta headlands, followed by splintering into landward-migrating islands. Submerged, they become permanent shoals. For several reasons, this “island-cycle” hypothesis is questionable and a reassessment of the geomorphic and stratigraphic context of this delta coast is required.Contradicting the geomorphic setting of assumed Stage 1, key component of the cycle-model, evidence is lacking for subrecent delta lobes and erosional headland in spawning barrier islands. In addition, the delta headland-flanking islands reveal only progradational (regressive) development and in situ disintegration,. Transgressive landward migrations is known only from the Chandeleur chain's prehistory. Sand from decaying Terrebonne-Lafourche 6 Subdelta headland was the dominant source for the Caminada Strandplain and for the shoal /or island predecessor of Grand Isle. Wave refraction around an inferred Lafourche delta lobe (dated provisionally between ∼2900 - ∼ 2300 yrs. BP) and its decayed erosional headland remnant resulted in diametric reversal of littoral sand transport. An earlier proferred ∼750–300 yrs. BP Caminada Strandplain age range is now replaced by a loosely defined ∼2200- to- ∼800 yrs. BP value, based on ages of Grand Isle and reworked delta hinterland sediments incorporated into the Strandplain.

Double duct propagation in the Arctic

Recent experiments in the Beaufort Sea encountered the “Beaufort Lens,” a hydrographic feature named by Russian acousticians, where warmer Pacific water enters the Bering Straits and rests above Atlantic water. This creates a “double duct” subsurface duct with this “lens” being near ubiquitous in space and time throughout the Beaufort. As part of the ONR Task Force Ocean program we found subsurface ducts in the Irminger Sea over the Reykjanes Ridge not reliably predicted by HYCOM. Propagation in these “double ducts” has some remarkable features and is well understood using normal modes and analogies to potential wells in quantum mechanics. These include the (i) filling of individual wells preferentially according to the modal phase speeds; (ii) tunneling phenomena when the phase speeds approaches the height of the potential barrier or maximum speed separating the ducts; (iii) issues of degeneracy when the modal phase speeds appear to cross; (iv) appearance of “mini convergence zones” for the transmission losses in each duct; (v) differences in modal group speeds with very small differences in phase speeds; and (vi) very low transmission loss when both source and receiver are in the subsurface duct separated from the water and/or ice surfaces.