Central Bay Research Articles

Mixed Layer Temperature Budget for the Northward Propagating Summer Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal

AbstractComposite analyses of mixed layer temperature (MLT) budget terms from near‐surface meteorological and oceanic observations in the central Bay of Bengal are utilized to evaluate the modulation of air‐sea interactions and MLT processes in response to the summer monsoon intraseasonal oscillation (MISO). For this purpose, we use moored buoy data at 15°N, 12°N, and 8°N along 90°E together with TropFlux meteorological parameters and the Ocean Surface Current Analyses Real‐time (OSCAR) current product. Our analysis shows a strong cooling tendency in MLT with maximum amplitude in the central and northern BoB during the northward propagation of enhanced convective activity associated with the active phase of the MISO; conversely, warming occurs during the suppressed phase of the MISO. The surface mixed layer is generally heated during convectively inactive phases of the MISO primarily due to increased net surface heat flux into the ocean. During convectively active MISO phases, the surface mixed layer is cooled by the combined influence of net surface heat loss to the atmosphere and entrainment cooling at the base of mixed layer. The variability of net surface heat flux is primarily due to modulation of latent heat flux and shortwave radiation. Shortwave is mostly controlled by an enhancement or reduction of cloudiness during the active and inactive MISO phases and latent heat flux is mostly controlled by variations in air‐sea humidity difference.

A Twisted Bay‐Substituted Quaterrylene Phosphorescing in the NIR Spectral Region

The preparation of the first soluble quaterrylene derivative featuring peripheral tert‐butyl substituents and sterically hindering, core‐anchored triflate groups has been achieved. This involves a facile synthetic route based on an oxidative coupling of perylene precursors in the presence of H2O2 as oxidant. The steric hindrance between the TfO substituents at the central bay position of the quaterrylene board triggers a strong deformation of the central perylene planarity, which forces the quaterrylene platform to adopt a twisted geometry as shown by X‐ray analysis. Exceptionally, photophysical investigations show that the core‐twisted quaterrylene phosphoresces in the NIR spectral region at 1716 nm. Moreover, third‐order nonlinear optical measurements on solutions and thin film containing the relevant molecule showed very large second hyperpolarizability values, as predicted by theoretical calculations at the CAM‐B3LYP/6‐31G** level of theory, making this material very appealing for photonic applications.

Distribution and Genetic Structure of Fucus distichus Linnaeus 1953 (formerly F. gardneri) within Central San Francisco Bay

Fucus distichus, a rockweed common to the mid-intertidal shoreline within the San Francisco Estuary (previously known as F. gardneri), was injured during the Cosco Busan oil spill in November 2007 and subsequent clean-up actions. Restoration planning activities are underway to help recover F. distichus at sites within central San Francisco Bay where damage occurred. As a first step, we conducted shoreline surveys during the summers of 2012–2013 to map the occurrence of this rockweed. Of the 151.73 km of rocky shoreline within the central bay, F. distichus covered 32.16 km of shoreline. The alga generally occurred in narrow bands but formed expansive beds at locations with natural, flat bedrock benches. We also observed F. distichus on artificial substrata such as seawalls and riprap, but not on pilings. Samples of F. distichus from 11 sites throughout the central / east San Francisco Bay were genetically analyzed (microsatellite genotyping). The populations analyzed (1) had low genetic diversity, (2) the frequency of homozygotes was higher than expected (suggesting high inbreeding), and (3) also displayed geographic population structure, in part driven by very small differences in the midst of extremely low within-population genetic diversity. However, these genetic data do not raise concerns for restoration methods in terms of choosing donor populations and mixing F. distichus from different sites within the central bay. The choice of donor populations should be based on practical criteria for effective restoration; individuals will nonetheless be taken from locations as nearby to donor sites as possible. Various locations throughout the central San Francisco Bay are composed of cobble or small riprap that are populated with F. distichus, which could provide efficient means of translocating rockweed for future restoration activities.

Nutrient Distribution in Coral Reef Degraded Areas within Sanya Bay, South China Sea

ABSTRACT Guo, J.; Yu, K.; Wang, Y.; Xu, D.; Huang, X.; Zhao, M.; Yang, H., and Zhang, R., 2017. Nutrient distribution in Coral Reef degraded areas within Sanya Bay, South China Sea. An investigation was conducted in August 2014 to explore the spatial distribution of dissolved inorganic nitrogen (DIN) and phosphate ( ) in overlying water, pore water, and surface sediment from Sanya Bay and living coral cover on Luhuitou fringing reef. Generally, nutrient contents gradually decreased from the estuary to the central bay, which confirmed that terrigenous inputs from Sanya River and Sanya Harbor were the primary nutrient sources. The results of K-means cluster analysis suggested the Luhuitou fringing reef is in danger of being affected by the pollution source. The results of nutrient diffusive fluxes at the sediment-seawater interface indicated diffusion from pore water to overlying water. Compared with other coral reef areas around the world, nutrient levels in Luhuitou fringing reef were at the medium level....

Le monastère Saint-Pierre d’Osor (île de Cres): onzième campagne d’études archéologiques.

Before the presentation of the 2016 campaign, the results of the campaign of 2015 are briefly cited. The completion of the excavation of the reduced church, the further analysis of its structures as well as the stratigraphical analysis allowed us to reformulate our hypothesis and advance our knowledge of the first church on the site which seems to have had a cruciform ground plan and have been built in the proto-Byzantine period. This year’s campaign was mostly carried out in the area of the Romanesque church vestibule (sector V) and of its north-east exterior (sector VI). Among most important contributions is the discovery of the large vessel found in the northern part of the vestibule whose space was clearly partitioned both in elevation (partition in bays) and at ground level (privileged burials in the central bay, infant burials in the southern bay). Numerous medieval tombs were found and excavated in the sector VI, as well as two graves from the iron age that were discovered under the medieval built ...

Development, implementation, and validation of a modeling system for the San Francisco Bay and Estuary

A three-dimensional numerical modeling system for the San Francisco Bay is presented. The system is based on an unstructured grid numerical model known as Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM). The lateral boundary condition is provided by a regional coastal ocean model. The surface forcing is provided by a regional atmospheric model. The SCHISM results from a decadal hindcast run are compared with available tide gauge data, as well as a collection of temperature and salinity profiles.An examination of the observed climatological annual mean salinities at the United States Geological Survey (USGS) stations shows the highest salinities to be in the open ocean and the lowest well north (upstream) of the Central Bay, a pattern that does not change substantially with season. The corresponding mean SCHISM salinities reproduced the observed variations with location quite well, though with a fresh bias. The lowest values within the Bay occur during spring and the highest values during autumn, mirroring the seasonal variations in river discharge. The corresponding observed mean temperatures within the Bay were 2 to 3° C cooler in the Central Bay than to either the north or south. This observed pattern of a cooler Central Bay was not particularly well reproduced in the SCHISM results, which also showed a cold bias. Examination of the seasonal means revealed that the cool Central Bay pattern is found only during summer in the SCHISM results. The persistent cold and fresh biases in the model control run were nearly eliminated in a sensitivity run with modifications to the surface heat flux and river discharge.The surface atmospheric forcing and the heat flux at the western boundary are found to be the two major terms in a SCHISM-based heat budget analysis of the mean seasonal temperature cycle for the Central Bay. In the Central Bay salt budget, freshwater discharged by rivers into upstream portions of the Bay to the north balanced by the influx of salt from the west are the primary drivers of the mean seasonal salinity cycle. Concerning the interannual variability in temperatures, the warm anomalies during the period 2014–16 were the strongest and most persistent departures from normal during the period analyzed and were realistically reproduced by SCHISM. The most prominent salinity anomalies in both the observations and SCHISM results were the salty anomalies that persisted for most of the four-year California drought of 2012–2015.

Patterns of bleaching and mortality following widespread warming events in 2014 and 2015 at the Hanauma Bay Nature Preserve, Hawai'i.

Drastic increases in global carbon emissions in the past century have led to elevated sea surface temperatures that negatively affect coral reef organisms. Worldwide coral bleaching-related mortality is increasing and data has shown even isolated and protected reefs are vulnerable to the effects of global climate change. In 2014 and 2015, coral reefs in the main Hawaiian Islands (MHI) suffered up to 90% bleaching, with higher than 50% subsequent mortality in some areas. The location and severity of bleaching and mortality was strongly influenced by the spatial and temporal patterns of elevated seawater temperatures. The main objective of this research was to understand the spatial extent of bleaching mortality in Hanauma Bay Nature Preserve (HBNP), O‘ahu, Hawai‘i to gain a baseline understanding of the physical processes that influence localized bleaching dynamics. Surveys at HBNP in October 2015 and January 2016 revealed extensive bleaching (47%) and high levels of coral mortality (9.8%). Bleaching was highly variable among the four HBNP sectors and ranged from a low of ∼31% in the central bay at Channel (CH) to a high of 57% in the area most frequented by visitors (Keyhole; KH). The highest levels of bleaching occurred in two sectors with different circulation patterns: KH experienced comparatively low circulation velocity and a low temperature increase while Witches Brew (WB) and Backdoors (BD) experienced higher circulation velocity and higher temperature increase. Cumulative mortality was highest at WB (5.0%) and at BD (2.9%) although WB circulation velocity is significantly higher. HBNP is minimally impacted by local factors that can lead to decline such as high fishing pressure or sedimentation although human use is high. Despite the lack of these influences, high coral mortality occurred. Visitor impacts are strikingly different in the two sectors that experienced the highest mortality evidenced by the differences in coral cover associated with visitor use however, coral mortality was similar. These results suggest that elevated temperature was more influential in coral bleaching and the associated mortality than high circulation or visitor use.

Ostracod biodiversity from shelf to slope oceanic conditions, off central Bay of Bengal, India

Thirty seven surface sediment samples collected through a multi-corer in seven transects of ORV Sagar Kanya, SK 308 Leg-1 from off central Bay of Bengal (shelf to slope environment) were analysed for living and dead Ostracoda. The samples, which ranged in water depth from ~29m to 2540m, yielded a total of 46 species belonging to 32 genera. The ostracod fauna of the Bay of Bengal exhibit a depth-related distribution that is controlled by substrate and hydrographic conditions. Sandy substrates of shallow water depth (~28m) are characterized by Propontocypris sp. and Cytherelloidea malaccaensis. These species are replaced by Neonesidea cracenticlavula and Bairdoppilata paraalcyonicola in high population, which shows positive linear correlation with salinity, temperature and Total Calcium Carbonate (TCC) in the outer shelf ~55–73m. Paijenborchella sp. dominates at ~763m in the bathypelagic zone, giving way to Parakrithella sp. at greater depths of ~2540m on soft-bottom substrates. The fauna represents an interesting mixture of displaced species and others known from bathyal and abyssal depths in the Bay of Bengal, including some pandemic deep sea species. The ostracod faunal diversity is higher in shallower water than in the deeper water, which may be due to the optimum temperature, pH, salinity and substrate. The fauna are comprised of three associations (Shelf/Upper Slope; Slope; Lower Slope/Abyss). A marked faunal turnover occurs at the outer-shelf. Factor Analysis was performed to determine the correlation of water and sediment parameters with the ostracod species. This study provides a detailed account of bathymetry and ostracod biodiversity recorded in the study area.

Spatial variability of upper ocean POC export in the Bay of Bengal and the Indian Ocean determined using particle‐reactive 234Th

AbstractThe northern Indian Ocean is globally significant for its seasonally reversing winds, upwelled nutrients, high biological production, and expanding oxygen minimum zones. The region acts as sink and source for atmospheric CO2. However, the efficiency of the biological carbon pump to sequester atmospheric CO2 and export particulate organic carbon from the surface is not well known. To quantify the upper ocean carbon export flux and to estimate the efficiency of biological carbon pump in the Bay of Bengal and the Indian Ocean, seawater profiles of total 234Th were measured from surface to 300 m depth at 13 stations from 19.9°N to 25.3°S in a transect along 87°E, during spring intermonsoon period (March–April 2014). Results showed enhanced in situ primary production in the equatorial Indian Ocean and the central Bay of Bengal and varied from 13.2 to 173.8 mmol C m−2 d−1. POC export flux in this region varied from 0 to 7.7 mmol C m−2 d−1. Though high carbon export flux was found in the equatorial region, remineralization of organic carbon in the surface and subsurface waters considerably reduced organic carbon export in the Bay of Bengal. Annually recurring anticyclonic eddies enhanced organic carbon utilization and heterotrophy. Oxygen minimum zone developed due to stratification and poor ventilation was intensified by subsurface remineralization. 234Th‐based carbon export fluxes were not comparable with empirical statistical model estimates based on primary production and temperature. Region‐specific refinement of model parameters is required to accurately predict POC export fluxes.

Chlorophyll bloom in response to tropical cyclone Hudhud in the Bay of Bengal: Bio-Argo subsurface observations

Though previous studies have documented substantial increases in chlorophyll concentrations as a result of cyclones, most of them were based on satellite observations dealing with surface chlorophyll blooms. This study documents the subsurface biological response and the subsequent chlorophyll bloom observed in response to the tropical cyclone Hudhud as evident from a Bio-Argo float located at the central Bay of Bengal. Results show high chlorophyll concentrations of up to 4.5mgm−3 which is anomalous in the normally warm, stratified, and oligotrophic Bay of Bengal. The chlorophyll bloom is attributed to the combined effect of subsurface chlorophyll entrainment and nutrient injection. The presence of a pre-existing cyclonic eddy and the decreased translation speed of the cyclone over this region could have played a role in inducing the biological response. This is the first ever report to document the evolution of a subsurface chlorophyll bloom in response to cyclone forcing using Bio-Argo observations.

Effect of Ferro-cement retrofit in the stiffened infill RC frame

This paper presents an experimental investigation on the contribution of RCC strip in the in-filled RC frames. In this research, two frames were tested to study the behavior of retrofitted RC frame under cyclic loading. In the two frame, one was three bay four storey R.C frame with central bay brick infill with RCC strip in-between brick layers and the other was retrofitted frame with same stiffened brick work. Effective rehabilitation is required some times to strengthened the RC frames. Ferrocement concrete strengthening was used to retrofit the frame after the frame was partially collapsed. The main effects of the frames were investigated in terms of displacement, stiffness, ductility and energy dissipation capacity. Diagonal cracks in the infill bays were entirely eliminated by introducing two monolithic RCC strips. Thus more stability of the frame was obtained by providing RCC strips in the infill bays. Load carrying capacity of the frame was increased by enlarging the section in the retrofitted area.

INRRI-EDM/2016: the first laser retroreflector on the surface of Mars

During Summer 2015 the SCF_Lab (Satellite/lunar/GNSS laser ranging/altimetry and cube/microsat Characterization Facilities Laboratory, www.lnf.infn.it/esperimenti/etrusco) Team of INFN-LNF, with support by ASI, carried out an intense activity of final design, manufacturing and testing in order to construct, space qualify and finally integrate INRRI-EDM/2016 on ESA’s ExoMars EDM spacecraft (also dubbed ‘Schiaparelli’), which was successfully launched on March 14, 2016. INRRI (INstrument for landing-Roving laser Retroreflector Investigation) for the EDM (Entry descent and landing Demonstration Module) 2016 mission is a compact, lightweight, passive, maintenance-free array of eight cube corner laser retroreflectors fixed to an aluminum alloy frame through the use of silicon rubber suitable for space applications. INRRI was installed on the top panel of the EDM Central Bay on October 14, 2015. It will enable the EDM to be laser-located from Mars orbiters, through laser ranging and altimetry, lidar atmospheric observations from orbit, laser flashes emitted by orbiters, and lasercom. One or all of the above means of observation can be supported by INRRI when there is an active, laser-equipped orbiter, especially after EDM end-of-life and for a long time. INRRI goals will cover science (Mars geodesy/geophysics, future Mars test of General Relativity, GR), technology and exploration. Concerning the latter two, INRRI will support mars-georeferencing of the EDM landing site, support potential precision lidar-based landing next to the EDM, support test & diagnostics of lasercom for data exchange among Mars orbit, Mars surface and Earth, and it will be a precursor for additional Mars surface retroreflectors, for example on exploration rovers. This paper describes in detail our innovative payload, hopefully the very first to be deployed safely with the lander Schiaparelli on the Mars surface, and its space qualification for the ExoMars EDM 2016 mission. Despite the fate of the Schiaparelli landing, which is still under the investigation of ESA and the industry, this paper remains a valuable reference for next INRRI-like laser retroreflectors arrays.

A century of landscape disturbance and urbanization of the San Francisco Bay region affects the present-day genetic diversity of the California Ridgway’s rail (Rallus obsoletus obsoletus)

Fragmentation and loss of natural habitat have important consequences for wild populations and can negatively affect long-term viability and resilience to environmental change. Salt marsh obligate species, such as those that occupy the San Francisco Bay Estuary in western North America, occupy already impaired habitats as result of human development and modifications and are highly susceptible to increased habitat loss and fragmentation due to global climate change. We examined the genetic variation of the California Ridgway’s rail (Rallus obsoletus obsoletus), a state and federally endangered species that occurs within the fragmented salt marsh of the San Francisco Bay Estuary. We genotyped 107 rails across 11 microsatellite loci and a single mitochondrial gene to estimate genetic diversity and population structure among seven salt marsh fragments and assessed demographic connectivity by inferring patterns of gene flow and migration rates. We found pronounced genetic structuring among four geographically separate genetic clusters across the San Francisco Bay. Gene flow analyses supported a stepping stone model of gene flow from south-to-north. However, contemporary gene flow among the regional embayments was low. Genetic diversity among occupied salt marshes and genetic clusters were not significantly different. We detected low effective population sizes and significantly high relatedness among individuals within salt marshes. Preserving genetic diversity and connectivity throughout the San Francisco Bay may require attention to salt marsh restoration in the Central Bay where habitat is both most limited and most fragmented. Incorporating periodic genetic sampling into the management regime may help evaluate population trends and guide long-term management priorities.

Kościół Surb Sargis w Tekor w Armenii. Między Persją a Bizancjum

The Surb Sargis (St. Sergei’s) church in Tekor, in the Shirak region of the present-day Turkey, is nowadays in total ruin. Fortunately, before its destruction by the 1911 earthquake, it had been extensively studied (e.g. by T. Toramanian and J. Strzygowski) and the documentation preserved allows us to treat it as one of the most important early-Christian buildings in both Armenia and the whole Orbis Christianus (Fig. 1-3). It is highly probable that the church was built at the site of an earlier pa­gan temple, utilising the former building’s tall 9-step crepidoma. Between the beginning of the 4th and the ending of the 5th century a three-nave basilica with­out a dome was built on the earlier base, only to be thoroughly rebuilt in the years 478-504 (dating based on the inscription at the lintel of the western portal; Fig. 4). After the rebuilding, the church acquired its 9-square structure designed by 3 naves and 3 bays. The central bay was covered with a small cupola, or rather, a cupola-structure (Fig. 5 and 7). Taking into account the contemporary state of research one may suppose that this innovative construction is the earliest known link in the process of emerging of the cross-cupola plan of churches, dominating till today in the church architecture of Eastern Christianity. The reduction of the corners of the central bay – in order to adjust its square shape to the circular base of the dome – was achieved by the construction of four small squinches (Fig. 8). This solution was most probably taken over from the 2nd – 3rd-century architecture of Persia, with which the pre-Christian Armenia had long maintained strong and varied contacts. Apart from the Tekor basilica, squinches were also used in two other buildings on the Ararat Upland near Erevan: in the small grave chapel at the Voghjaberd cemetery (5th – 6th century; Fig. 9-12) and in the one-nave church Surb Poghos- Petros (St. Paul and Peter’s) in Zovuni (between the ending of the 5th and the turning of the 6th and 7th centuries). These examples allow one to treat Armenia as a bridge between the architecture of Persia and Byzantium, where similar con­structions appeared and spread widely in later periods.

Rhizocorallium in estuarine Ingersoll shale (Upper Cretaceous Eutaw Formation, Eastern Alabama coastal plain)

The ichnofossil Rhizocorallium—an oblique to horizontal U-shaped spreiten burrow—has been recognized in a broad range of Phanerozoic continental, marginal marine, and shallow to deep marine facies. Nonetheless, occurrences of this ichnotaxon in Cretaceous estuarine deposits are rarely described. Herein we document Rhizocorallium in the Ingersoll shale, a carbonaceous clay lens within an estuarine succession contained in the Upper Cretaceous (Santonian) Eutaw Formation exposed in the eastern U.S. Gulf coastal plain. The Ingersoll Rhizocorallium specimens, assigned to R. commune var. irregulare based on their basic morphology, horizontal disposition, dimensions, and actively filled spreiten, record a change in depositional conditions and substrate consistency linked to transgression. The Ingersoll shale accumulated rapidly in a restricted tidal channel in a bayhead delta setting and hosts an impoverished resident ichnofauna reflecting soupground conditions. In contrast, attributes of Rhizocorallium (e.g., burrow wall bioglyphs) and associated Thalassinoides in the upper part of the Ingersoll shale reflect firm substrates (i.e., Glossifungites ichnofacies). Firmground development and colonization reflect burial dewatering and subsequent exhumation by bay-shoreline ravinement of clays and the concomitant shift to estuarine central bay deposition. The biological affinity of the Rhizocorallium trace makers cannot be confidently established. However, based on relatively straight and seemingly current-aligned axes, passive burrow fills, lack of associated fecal pellets, and emplacement in firm clay, these structures were likely produced by suspension-feeding organisms—either crustaceans or worms—that took advantage of wave- or tide-induced currents in shallow areas near the estuary head.

Monsoon Mixing Cycles in the Bay of Bengal: A Year-Long Subsurface Mixing Record

Based on the first year-long record of mixing collected in the eastern central Bay of Bengal, we quantify the role that subsurface turbulent heat fluxes play in upper-ocean cooling brought on by southwest (SW) and northeast (NE) monsoons. During the NE (dry, or winter) monsoon, atmospheric and subsurface turbulent heat fluxes each contribute about 50% of the net sea surface cooling. During the SW (wet, or summer) monsoon, the atmospheric heat flux varied widely due to “active” and “break” cycles of the monsoon intraseasonal oscillations, but had a net positive seasonal average. The subsurface turbulent heat flux during the SW monsoon led to surface cooling at rates more than three times greater than those measured during the NE monsoon. Since the seasonally averaged atmospheric heat flux was positive, subsurface mixing accounted for nearly all of the cooling during the SW monsoon. During the transition between the NE and SW monsoons, subsurface heat flux was near zero, and atmospheric heating rapidly warmed the sea surface. Following the SW monsoon, passage of Tropical Storm Hudhud led to O(1) m2 s–1 rates of turbulence diffusivity and strong subsurface heat flux, accounting for roughly half of the 1.4°C surface cooling that occurred over a 60-hour period.

Influence of Ferro Cement Retrofit in the Stiffened In-fill RC Frame

The design of RCC frame usefully ignored the beneficial or adverse effect of infill walls. By strengthening the interface of frame and infill RC frame system can be kept together and forcing them to work as a whole until the end of the earthquake. The present study deals with the load carrying capacity of three bay four storey retrofitted RC frame with central bay stiffened brick infill under cyclic loading. The effectiveness of the retrofitted frame under cyclic load is to be investigated in terms of displacement, stiffness, and ductility and energy dissipation.

A 10-year climatology of vertical properties of most active convective clouds over the Indian regions using TRMM PR

Vertical distribution of hydrometeors in the most intense convective clouds over the Indian region during the summer monsoon season (JJAS) is described for ten climatologically important areas. Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) 3D radar reflectivity data is used in the present study for 10 years (2001-2010). The study constructs a convective cloud cell based on reflectivity thresholds, known as most intense convective cloud. The cloud cells are formed by taking the maximum reflectivity (Ze) at each altitude in the convective area with at least one radar pixel containing reflectivity of 40 dBZ or more. TRMM 2A23 data was used to eliminate the stratiform clouds from our analyses. The Vertical structure of convective clouds were studied over the east and west coast of India, and observation shows that the east coast consists of a higher frequency of convective clouds with high reflectivity values in average vertical profiles. It is observed that over the northeastern parts of the Indian subcontinent, similar to 30 % of convective cells extend beyond 15-km height whereas it is only similar to 4 % over the central Bay of Bengal. Over the Western Ghats, similar to 13 % of the cells have their tops below the freezing level, i.e. warm clouds do give heavy rain here. The regional differences in the vertical profile are high between the 5- and 12-km altitude. Most intense convective cells (MICCs) with a cloud top height more than 10 and 15 km show different characteristics, and the Western Ghats shows the most intense average vertical profile. Above 12 km, the western coast shows increased reflectivity value. Convective intensity is higher over the land-dominated areas for the cloud cells and decreases when we restrict the cloud cells to a certain altitude.

Modelling seabed shear stress, sediment mobility, and sediment transport in the Bay of Fundy

Information about seabed stability and sediment dynamics is part of the fundamental geoscience knowledge required for the extraction of tidal energy in the Bay of Fundy and for the integrated management of the Bay. Waves, tidal currents, and wind-driven and circulation currents were obtained from oceanographic models to assess the wave and current processes for the broader Bay of Fundy. The wave and current outputs were coupled with observed grain size in a sediment transport model to predict, for the first time, the seabed shear stresses, sediment mobility, and sediment transport patterns for the entire Bay. The root mean square tidal current, highest in the upper Bay (>1.4 m·s−1), is reduced to moderate in the central Bay (0.5–0.8 m·s−1) and decreases further in the outer Bay (0.2–0.5 m·s−1). The maximum tidal current occurs in the Minas Passage and is >5 m·s−1. The mean significant wave height, in contrast, is the greatest in the outer Bay (∼1.3 m) and gradually decreases to the northeast in the central and upper Bay (<0.5 m). Seabed shear in the Bay of Fundy is mostly due to tides, and wave effects are only important in coastal areas. The strongest mean shear velocity of 10 cm·s−1occurs in the Minas Passage area. Strong shear velocity of 4–5 cm·s−1also occurs in Minas Basin, in the central Bay, and in the narrows around Grand Manan Island. Sediment mobilization in the Bay of Fundy is predominantly by tidal current. Mobilization frequency is >30% of the time over most of the Bay and reaches 100% of the time in some areas. The maximum total-load sediment transport rate under spring tide can reach ∼5 kg·m−1·s−1and is to the northeast during flood and to the southwest during ebb. Net sediment transport flux, however, is dominantly to the northeast and reaches 2 kg·m−1·s−1. Eddies of net transport are found to occur around headlands and at the narrows of Grand Manan Island, largely due to the occurrence of eddies of residual tidal flows. The regional distribution of substrate types and bedform fields and patterns of seabed erosion and deposition are well correlated with tidal current strength and sediment transport patterns.

Hydrology, sediment circulation and long-term morphological changes in highly urbanized Shenzhen River estuary, China: A combined field experimental and modeling approach

Summary The Shenzhen River estuary is a small estuary in highly urbanized regions between Shenzhen and Hong Kong, China. An increasing amount of sediment has been observed to accumulate in the estuary, imposing a severe impact on the ecological environment. In this study we utilized a series of hydrographic and bathymetry surveys to study the hydrology, sediment transport and morphological processes in the estuary. Flow and sediment circulation patterns in different seasons were inferred using current velocity, salinity and suspended sediment concentration (SSC) time series collected in the hydrographic surveys in conjunction with fathometer profiles in bathymetry surveys. Historical time series at two stations were also analyzed by Mann–Kendall test for possible trends of the driving forces for estuarine morphological processes. The two-dimensional depth-averaged DELFT numerical model was employed to simulate the flow, salinity and SSC fields during the synchronous surveys and to predict the long-term morphological processes in the estuary. A bimodal SSC distribution was observed with two high-SSC zones separated by a low-SSC zone near the central bay, which cannot be explained by the conventional nongravitational transport theory of Postma (1967). It is hypothesized that sediment circulation in the estuary can be separated into two different systems: the “tidal zone” is under the influence of marine sediment from the Pearl River estuary, whereas the “fluvial zone” is mainly affected by terrestrial sediment from the river. Sediment mass exchange between the two systems is limited due to the presence of the low-SSC zone, the location of which could vary with the relative strengths of river flow and tides. The trend analysis of historical time series shows that the river discharge and the mean sea level are increasing and the flood tide range and the ebb tide range are decreasing. These trends are closely related to the intense human activities in the urbanization of Shenzhen. The long-term simulations show depositional trends for the inner bay and the coastline of the outer bay, which could be further aggravated by the detected trends of the driving forces.