A Model Study of the Circulation in the Pearl River Estuary (PRE) and Its Adjacent Coastal Waters: 1. Simulations and Comparison with Observations

The Princeton Ocean Model is used to study the circulation features in the Pearl River Estuary and their responses to tide, river discharge, wind, and heat flux in the winter dry and summer wet seasons. The model has an orthogonal curvilinear grid in the horizontal plane with variable spacing from 0.5 km in the estuary to 1 km on the shelf and 15 sigma levels in the vertical direction. The initial conditions and the subtidal open boundary forcing are obtained from an associated larger-scale model of the northern South China Sea. Buoyancy forcing uses the climatological monthly heat fluxes and river discharges, and both the climatological monthly wind and the realistic wind are used in the sensitivity experiments. The tidal forcing is represented by sinusoidal functions with the observed amplitudes and phases. In this paper, the simulated tide is first examined. The simulated seasonal distributions of the salinity, as well as the temporal variations of the salinity and velocity over a tidal cycle are described and then compared with the in situ survey data from July 1999 and January 2000. The model successfully reproduces the main hydrodynamic processes, such as the stratification, mixing, frontal dynamics, summer upwelling, two-layer gravitational circulation, etc., and the distributions of hydrodynamic parameters in the Pearl River Estuary and coastal waters for both the winter and the summer season.

A Model Study of the Circulation in the Pearl River Estuary (PRE) and Its Adjacent Coastal Waters: 2. Sensitivity Experiments

The Princeton Ocean Model is used to study the circulation in the Pear River Estuary (PRE) and the adjacent coastal waters in the winter and summer seasons. Wong et al. [2003] compares the simulation results with the in situ measurements collected during the Pearl River Estuary Pollution Project (PREPP). In this paper, sensitivity experiments are carried out to examine the plume and the associated frontal dynamics in response to seasonal discharges and monsoon winds. During the winter, convergence between the seaward spreading plume water and the saline coastal water sets up a salinity front that aligns from the northeast to the southwest inside the PRE. During the summer the plume water fills the PRE at the surface and spreads eastward in the coastal waters in response to the prevailing southwesterly monsoon. The overall alignment of the plume is from the northwest to the southeast. The subsurface front is similar to that in the winter and summer except that the summer front is closer to the mouth and the winter front closer to the head of the estuary. Inside the PRE, bottom flows are always toward the head of the estuary, attributed to the density gradient associated with the plume front. In contrast, bottom flows in the shelf change from offshore in winter to onshore in summer, reflecting respectively the wintertime downwelling and summertime upwelling. Wind also plays an essential role in controlling the plume at the surface. An easterly wind drives the plume westward regardless winter or summer. The eastward spreading of the plume during the summer can be attributed to the southerly component of the wind. On the other hand, the surface area of the plume is positively proportional to the amount of discharge.

Numerical study on the velocity structure around tidal fronts in the Yellow Sea

The velocity components across tidal fronts are examined using the Blumberg and Mellor 3-D nonlinear numerical coastal circulation model incorporated with the Mellor and Yamada level 2.5 turbulent closure model based on the reasonable model output of the M-2 tide and density residual currents. In the numerical experiments, upwelling motion appears around all the fronts with different velocity structures, accounting for surface cold water around the fronts. The experiments also suggest that the location and formation of fronts are closely related to topography and tidal mixing, as is the velocity structure around the front.

Texture, composition and provinance of innershelf sediments between Narakkal and Purakkad, Kerala with special reference to the formation of Mud Banks

The continental shelf of southwest coast of India (Kerala) is broader and . flatter compared to that of the east coast. The unique characteristic feature of the study area (innershelf between Narakkal and Purakkad) is the intermittent appearance of 'mud banks' at certain locations during southwest monsoon. The strong seasonality manifests significant changes in the wind, waves, currents, rainfall, drainage etc., along this area. Peculiar geomorphological variation with high, mid and lowlands in the narrow strip of the hinterland, the geological formations mainly consisting of rocks of metamorphic origin and the humid tropical weathering conditions play significant role in regulating the shelf sedimentation. A complementary pattern of distri bution is observed for clay that shows an abundance in the nearshore. Silt, to a major extent, depicts semblance with clay distribution . Summation of the total asymmetry of grain size distribution are inferred from the variation of skewness and kurtosis.Factor I implies a low energy regime where the transportation and deposition phases are controlled mostly by pelagic suspension process as the factor loadings are dominant on finer phi sizes. The second Factor is inferred to be the result of a high energy regime which gives higher loadings on coarser size fractions. The third Factor which might be a transition phase (medium energy regime) representing the resultant flux of coastal circulation of the re-suspension/deposition and an onshoreoffshore advection by reworking and co-deposition of relict and modern sediments. The spatial variations of the energy regime based on the three end-member factor model exhibits high energy zone in the seaward portion transcending to a low energy one towards the coast.From the combined analysis of granulometry and SEM studies, it is concluded that the sandy patches beyond 20 m depth are of relict nature. They are the resultant responses of beach activity during the lower stand of sea level in the Holocene. Re-crystallisation features on the quartz grains indicate that they were exposed to subaerial weathering process subsequent to thei r deposition

Circulação recente de sedimentos costeiros nas praias de santos durante eventos de tempestades: Dados para a gestão de impactos físicos costeiros

The beachs of Santos are situated in Santos Bay, central portion of paulista coast, in São Paulo state. This beachs are frequently affected by cold fronts with winds and currents from the South. These fronts are responsible for the removal and transport of sediments (sand) in Santos beaches. In order to quantify this sedimentation the channels of Santos were analysed, due to their function as box colectors of sediments during storm events. The channels are filled by sands, which volume in channels 1 to 6 was estimated, by using the length, width and height of sand sedimented in the channels, in the event of 22-27 april 2005. The chanels 2, 3 and 1 presented the larger volumes of sands, confirming that the central and SW portion of the beaches of Santos present higher levels of sedimentation or re-sedimentation. That is due to the transport by ocean waves and currents and currents from the Channel of the Port of Santos. This central portion suffer invasion of marine water over street and buildings, caracterizated of geological rise area.

Early Life History and a Modeling Framework for Lobster (Homarus Americanus) Populations in the Gulf of Maine

Beginning in the late 1980s, lobster (Homarus americanus) landings for the state of Maine and the Bay of Fundy increased to levels more than three times their previous 20-year means. Reduced predation may have permitted the expansion of lobsters into previously inhospitable territory, but we argue that in this region the spatial patterns of recruitment and the abundance of lobsters are substantially driven by events governing the earliest life history stages, including the abundance and distribution of planktonic stages and their initial settlement as Young-of-Year (YOY) lobsters. Settlement densities appear to be strongly driven by abundance of the pelagic postlarvae. Postlarvae and YOY show large-scale spatial patterns commensurate with coastal circulation, but also multi-year trends in abundance and abrupt shifts in abundance and spatial patterns that signal strong environmental forcing. The extent of the coastal shelf that defines the initial settlement grounds for lobsters is important to future population modeling. We address one part of this definition by examining patterns of settlement with depth, and discuss a modeling framework for the full life history of lobsters in the Gulf of Maine.

(Table B2) Relative abundances of diatom species used in the Canoco analysis at sediment surface samples from the Chinese inshore waters

Canonical correspondence analysis has been used to analyze and to visualize the relationships between the main species and selected environmental variables in a study of diatoms from surface sediment samples in Chinese inshore waters. The result shows that the diatom distribution in Chinese inshore waters is closely correlated with the environmental variables and that the measured environmental variables account for the major changes of the diatom composition. Winter sea-surface temperature (WST), winter sea-surface salinity (WSS), water depth and summer sea-surface salinity (SSS) play an important role for the diatom distribution. Among the environmental factors, winter sea-surface temperature is the most important, controlling the distribution of diatoms in the surface sediments in Chinese inshore waters, and therefore, it may be potentially reconstructed in palaeoceanographic studies. Three diatom assemblages are distinguished, representing environments with different hydrological characteristics. The temperate-water diatom assemblage may be used as an indicator of the coastal circulation system of Bohai Sea and Yellow Sea. While the warm-temperate water diatom assemblage is closely related to Shanghai-Zhejiang-Fujian coastal currents and Northern Bay coastal currents of South China Sea. The deep water diatom assemblage is a response to that the waters are less controlled by coastal currents, but are more influenced by open sea currents, such as Kuroshio.

Physical water column observations during summer breeze winds

During summer seasons (from 2012 to 2015) high resolution observation were performed in the Civitavecchia coastal area (Northern Tyrrhenian sea, west coast). All sampling was carried out from a small boat (5m rigid inflatable) starting in the early morning typically around 06:00 a.m. , and lasting from 2 to 8 h, depending on the weather conditions. The purposes of the experiment was to observe the variations of both the coastal circulation and the water column in response to rotation of 180 ° in the wind direction. During surveys both current measurements and yo-yo time series were performed. Current data were acquired using an ADCP SonTeck (500 Khz, sampling interval from 20sec to 60 sec, average interval 50% sampling, cell thickness 1 meter) and the yo-yo time series employing a small instrument package (CTD). The CTD contained an Idronaut 316 Plus and a SeaPoint fluorometer. The sampling rate for the CTD was 10Hz, profiling with the CTD was done by allowing the instrument package to free-fall, at an average descent rate of 1 m/s. During the summer 2012, the sampling plan consisted in four stations spaced a quarter of a mile (St. 1 - 10 m; St. 2 - 20 m; St. 3 - 30 m; and St. 4 - 40 m), in which yo-yo time series were performed with an interval of 20 min. In order to study fluorescence of Chlorophyll a pathes distribution in coastal zone. Breeze induced circulation was the goal of the following summers surveys, in these current measurements and yo-yo time series were performed moored at a depth of 40 m. Offshore station (St. 1 -40m) has been chosen to perform measurement, basis of previously observations (2012 sampling surveys). It was decided as wind driven circulation and mixing phenomena are less influenced by seabed than the other stations. Acquired data have been processed by NEMO SeaDataNet software.

Circulation and salinity distribution in coastal inlets

The mathematical model developed by Hansen and Rattray based on Pritchard's equations for a coastal-plain estuary has been analysed to study the circulation and salinity distributions in coastal inlets with constant width and depth. Numerical solutions of the basic equations have been obtained without placing any restriction on Rayleigh numbers. A noteworthy contribution of the present analysis is that solutions of equations have been obtained for higher Rayleigh numbers, which was not possible in the earlier model. It is found that the effect of higher Rayleigh numbers is to increase the vertical advection, making the salinities in the upper and lower layers more uniform with a distinct halocline near the mid-depths. Solutions are discussed for some special cases of practical interest.

Coastal upwelling and downwelling forcing of circulation in a semi-enclosed bay: Ria de Vigo

Semi-enclosed bays in upwelling regions are exposed to forcing related to winds, currents and buoyancy over the shelf. The influence of this external forcing is moderated by factors such as connectivity to the open ocean, shelter by surrounding topography, dimensions of the bay, and freshwater outflows. Such bays, preferred locations for ports, mariculture, marine industry, recreational activities and coastal settlement, present a range of characteristics, understanding of which is necessary to their rational management. Observations in such a semi-enclosed bay, the Ria de Vigo in Spain, are used to characterize the influence of upwelling and downwelling pulses on its circulation. In this location, near the northern limit of the Iberian upwelling system, upwelling events dominate during a short summer season and downwelling events the rest of the year. The ria response to the external forcing is central to nutrient supply and resultant plankton productivity that supports its high level of cultured mussel production. Intensive field studies in September 2006 and June 2007 captured a downwelling event and an upwelling event, respectively. Data from eight current profiler moorings and boat-based MiniBat/ADCP surveys provided an unprecedented quasi-synoptic view of the distribution of water masses and circulation patterns in any ria. In the outer ria, circulation was dominated by the introduction of wind-driven alongshore flow from the external continental shelf through the ria entrances and its interaction with the topography. In the middle ria, circulation was primarily related to the upwelling/downwelling cycle, with a cool, salty and dense lower layer penetrating to the inner ria during upwelling over the shelf. A warmer, lower salinity and less dense surface layer of coastal waters flowed inward during downwelling. Without external forcing, the inner ria responded primarily to tides and buoyancy changes related to land runoff. Under both upwelling and downwelling conditions, the flushing of the ria involved shelf responses to wind pulses. Their persistence for a few days was sufficient to allow waters from the continental shelf to penetrate the innermost ria. Longer term observations supported by numerical modeling are required to confirm the generality of such flushing events in the ria and determine their typical frequency, while comparative studies should explore how these scenarios fit into the range of conditions experienced in other semi-enclosed bays.

Coastal and shelf circulation in the vicinity of Camamu Bay (14 degrees S), Eastern Brazilian Shelf

The Camamu Bay (CMB) is located on the narrowest shelf along the South American coastline and close to the formation of two major Western Boundary Currents (WBC), the Brazil/North Brazil Current (BC/NBC). These WBC flow close to the shelf break/slope region and are expected to interact with the shelf currents due to the narrowness of the shelf. The shelf circulation is investigated in terms of current variability based on an original data set covering the 2002-2003 austral summer and the 2003 austral autumn. The Results show that the currents at the shelf are mainly wind driven, experiencing a complete reversal between seasons due to a similar change in the wind field. Currents at the inner-shelf have a polarized nature, with the alongshore velocity mostly driven by forcings at the sub-inertial frequency band and the cross-shore velocity mainly supra-inertially forced, with the tidal currents playing an important role at this direction. The contribution of the forcing mechanisms at the mid-shelf changes between seasons. During the summer, forcings in the two frequency bands are important to drive the currents with a similar contribution of the tidal currents. On the other hand, during the autumn season, the alongshore velocity is mostly driven by sub-inertial forcings and tidally driven currents still remain important in both directions. Moreover, during the autumn when the stratification is weaker, the response of the shelf currents to the wind forcing presents a barotropic signature. The meso-scale processes related to the WBC flowing at the shelf/slope region also affect the circulation within the shelf, which contribute to cause significant current reversals during the autumn season. Currents at the shelf-estuary connection are clearly supra-inertially forced with the tidal currents playing a key role in the generation of the along-channel velocities. The sub-inertial forcings at this location act mainly to drive the weak ebb currents which were highly correlated with both local and remote wind forcing during the summer season. (C) 2010 Elsevier Ltd. All rights reserved.

Study of the circulation processes in the northern Adriatic sea - coastal area and Venice lagoon inlets

This work is a detailed study of hydrodynamic processes in a defined area, the littoral in front of the Venice Lagoon and its inlets, which are complex morphological areas of interconnection. A finite element hydrodynamic model of the Venice Lagoon and the Adriatic Sea has been developed in order to study the coastal current patterns and the exchanges at the inlets of the Venice Lagoon. This is the first work in this area that tries to model the interaction dynamics, running together a model for the lagoon and the Adriatic Sea. First the barotropic processes near the inlets of the Venice Lagoon have been studied. Data from more than ten tide gauges displaced in the Adriatic Sea have been used in the calibration of the simulated water levels. To validate the model results, empirical flux data measured by ADCP probes installed inside the inlets of Lido and Malamocco have been used and the exchanges through the three inlets of the Venice Lagoon have been analyzed. The comparison between modelled and measured fluxes at the inlets outlined the efficiency of the model to reproduce both tide and wind induced water exchanges between the sea and the lagoon. As a second step, also small scale processes around the inlets that connect the Venice lagoon with the Northern Adriatic Sea have been investigated by means of 3D simulations. Maps of vorticity have been produced, considering the influence of tidal flows and wind stress in the area. A sensitivity analysis has been carried out to define the importance of the advection and of the baroclinic pressure gradients in the development of vortical processes seen along the littoral close to the inlets. Finally a comparison with real data measurements, surface velocity data from HF Radar near the Venice inlets, has been performed, which allows for a better understanding of the processes and their seasonal dynamics. The results outline the predominance of wind and tidal forcing in the coastal area. Wind forcing acts mainly on the mean coastal current inducing its detachment offshore during Sirocco events and an increase of littoral currents during Bora events. The Bora action is more homogeneous on the whole coastal area whereas the Sirocco strengthens its impact in the South, near Chioggia inlet. Tidal forcing at the inlets is mainly barotropic. The sensitivity analysis shows how advection is the main physical process responsible for the persistent vortical structures present along the littoral between the Venice Lagoon inlets. The comparison with measurements from HF Radar not only permitted a validation the model results, but also a description of different patterns in specific periods of the year. The success of the 2D and the 3D simulations on the reproduction both of the SSE, inside and outside the Venice Lagoon, of the tidal flow, through the lagoon inlets, and of the small scale phenomena, occurring along the littoral, indicates that the finite element approach is the most suitable tool for the investigation of coastal processes. For the first time, as shown by the flux modeling, the physical processes that drive the interaction between the two basins were reproduced.

Characterisation of extreme winter precipitation in Mediterranean coastal sites and associated anomalous atmospheric circulation patterns

We present an analysis of daily extreme precipitation events for the extended winter season (October–March) at 20 Mediterranean coastal sites covering the period 1950–2006. The heavy tailed behaviour of precipitation extremes and estimated return levels, including associated uncertainties, are derived applying a procedure based on the Generalized Pareto Distribution, in combination with recently developed methods. Precipitation extremes have an important contribution to make seasonal totals (approximately 60% for all series). Three stations (one in the western Mediterranean and the others in the eastern basin) have a 5-year return level above 100 mm, while the lowest value (estimated for two Italian series) is equal to 58 mm. As for the 50-year return level, an Italian station (Genoa) has the highest value of 264 mm, while the other values range from 82 to 200 mm. Furthermore, six series (from stations located in France, Italy, Greece, and Cyprus) show a significant negative tendency in the probability of observing an extreme event. The relationship between extreme precipitation events and the large scale atmospheric circulation at the upper, mid and low troposphere is investigated by using NCEP/NCAR reanalysis data. A 2-step classification procedure identifies three significant anomaly patterns both for the western-central and eastern part of the Mediterranean basin. In the western Mediterranean, the anomalous southwesterly surface to mid-tropospheric flow is connected with enhanced moisture transport from the Atlantic. During ≥5-year return level events, the subtropical jet stream axis is aligned with the African coastline and interacts with the eddy-driven jet stream. This is connected with enhanced large scale ascending motions, instability and leads to the development of severe precipitation events. For the eastern Mediterranean extreme precipitation events, the identified anomaly patterns suggest warm air advection connected with anomalous ascent motions and an increase of the low- to mid-tropospheric moisture. Furthermore, the jet stream position (during ≥5-year return level events) supports the eastern basin being in a divergence area, where ascent motions are favoured. Our results contribute to an improved understanding of daily precipitation extremes in the cold season and associated large scale atmospheric features.

Long-term fluid circulation in extensional faults in the central Catalan Coastal Ranges: P-T constraints from neoformed chlorite and K-white mica

The neoformation of chlorite and K-white mica in fault rocks from two main faults of the central Catalan Coastal Ranges, the Vallès and the Hospital faults, has allowed us to constrain the P–T conditions during fault evolution using thermodynamic modeling. Crystallization of M1 and M2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton (290 °C > T > 370 °C) in the Permian. After that, three tectonic events have been distinguished. The first tectonic event, attributed to the Mesozoic rifting, is characterized by precipitation of M3 and M4 phengite together with chlorite and calcite C1 at temperatures between 190 and 310 °C. The second tectonic event attributed to the Paleogene compression has only been identified in the Hospital fault with precipitation of low-temperature calcite C2. The shortcut produced during inversion of the Vallès fault was probably the responsible for the lack of neoformed minerals within this fault. Finally, the third tectonic event, which is related to the Neogene extension, is characterized in the Vallès fault by a new generation of chlorite, associated with calcite C4 and laumontite, formed at temperatures between 125 and 190 °C in the absence of K-white mica. Differently, the Hospital fault is characterized by the precipitation of calcite C3 during the syn-rift stage at temperatures around 150 °C and by low-temperature fluids precipitating calcites C5, C6 and PC1 during the post-rift stage. During the two extensional events (Mesozoic and Neogene), faults acted as conduits for hot fluids producing anomalous high geothermal gradients (50 °C/km minimum).

Numerical study of circulation in the Caspian Sea and its effects on the southern coastal currents

In this study, numerical simulation of the Caspian Sea circulation was performed using COHERENS three-dimensional numerical model and field data. The COHERENS three-dimensional model and FVCOM were performed under the effect of the wind driven force, and then the simulation results obtained were compared. Simulation modeling was performed at the Caspian Sea. Its horizontal grid size is approximately equal to 5 Km and 30 sigma levels were considered. The numerical simulation results indicate that the winds' driven-forces and temperature gradient are the most important driving force factors of the Caspian circulation pattern. One of the effects of wind-driven currents was the upwelling phenomenon that was formed in the eastern shores of the Caspian Sea in the summer. The simulation results also indicate that this phenomenon occurred at a depth less than 40 meters, and the vertical velocity in July and August was 10 meters and 7 meters respectively. During the upwelling phenomenon period the temperatures on the east coast compared to the west coast were about 5°C lower. In autumn and winter, the warm waters moved from the south east coast to the north and the cold waters moved from the west coast of the central Caspian toward the south. In the subsurface and deep layers, these movements were much more structured and caused strengthening of the anti-clockwise circulation in the area, especially in the central area of Caspian. The obtained results of the two models COHERENS and FVCOM performed under wind driven-force show a high coordination of the two models, and so the wind current circulation pattern for both models is almost identical.