Vertical Profiles Of Salinity Research Articles

Assimilation experiments in the Gdansk Basin (the southeastern Baltic): How useful are the sea level data from coastal tide gauges for modelling of hydrophysical fields?

Abstract In the Baltic modelling research, assimilation techniques were developed with advance. They were concerned to model assimilated basic parameters and observed them directly. In present paper, the most important was the assimilation of surface information and its projection deep into temperature and salinity fields. In oceanic investigations altimetry viewed from satellite was the sea level changes projected far inside and predetermined surface-to-subsurface correlations. To obtain improved modelled hydrophysical fields, sea level variations measured at coastal gauges and efficient data assimilation were taken into account. A data assimilation algorithm has been developed and used in conjunction with a three-dimensional baroclinic model of the Baltic Sea. It was based on a time and space weighted nudging technique. The sea level data were inserted continuously by updating the model solution every time step. Several sensitivity experiments with different values of time and spatial weighting scales were performed. In first series of experiments, only sea level data (SL) were assimilated. In the next simulations, seawater temperature (SWT) and seawater salinity (SWS) related directly to SL were assimilated. To evaluate the effectiveness of the assimilation scheme, modelled sea level series and vertical profiles of seawater temperature and salinity in selected coastal gauges in the Gdansk Basin were examined. Evidently low but statistically essential correlation coefficients indicated nonlinear character of vertical mixing and transfer processes. Decreasing errors obtained while comparing the model results to a control case without assimilation confirmed a real transfer of surface information deep and usefulness of such approach in modelling.

Natural and anthropogenic hydrocarbons in the water column of the Ross Sea (Antarctica)

In the framework of the Italian Research Programme in Antarctica (PNRA) an oceanographic cruise was carried out between December 2000 and February 2001 in the Western Ross Sea. n-Alkanes and PAHs concentrations were analysed in sea-water samples collected at different depths at four sites (D, B, CA2, and CA). Vertical profiles of pressure, temperature, salinity and fluorescence were also performed in order to distinguish the water masses present in the sampling areas. n-Alkanes concentrations were consistent with those found in the same area during previous expeditions and showed higher values in the particulate due to the low temperatures. n-Alkanes profiles exhibited different features in the dissolved and particulate phases. The dissolved phase was characterised by a bimodal distribution with two maxima at C16 and C24 and prevalent compounds in the range C15–C32 whereas particulate was strongly dominated by long chain n-alkanes C23–C34 with C24 (Site B, CA and CA2) or C32 (Site B) as Cmax. CPI values and Pr/Ph ratios suggested a prevalent biogenic origin for aliphatic hydrocarbons. n-Alkanes vertical distributions were affected by the dynamic of the pack-ice melting and phytoplankton activity as well by the chemical–physical properties of water masses. Higher n-alkanes values were found in the High Salinity Shelf Waters (HSSW), lower n-alkanes values were found in the Antarctic Surface Waters (AASW) and Modified Circumpolar Deep Water (MCDW). The low PAHs concentration levels confirmed the still pristine character of the Antarctic environment. Neither particular trend in total PAHs concentrations along the water column and nor correlations with the most characteristic water masses of the investigated area of the Ross Sea were observed, except that total PAH higher concentrations were generally observed in correspondence of HSSW.

Line P ocean temperature and salinity, 1956–2005

Vertical profiles of temperature and salinity have been measured for 50 years along Line P between the North American west coast and mid Gulf of Alaska. These measurements extend 1425 km into the gulf at 13 or more sampling stations. The 10–50-m deep layer of Line P increased in temperature by 0.9 °C from 1958 to 2005, but is significant only at the 90% level due to large interannual variability. Most of this increase in temperature accompanies the 1977 shift in wind patterns. Temperature changes at 100–150 m and salinity changes in both layers are not statistically significant. Much of the variance in temperature is in the upper 50 m of Line P, and temperature changes tend to be uniform along Line P except for waters on the continental margin. Salinity changes are dominated by variability in the halocline between 100 and 150 m depth and are less uniform along Line P. Largest oscillations in temperature and salinity are between 1993 and 2003. These events can be understood by considering changes in eastward wind speed and wind patterns that are revealed in the first two modes of the Pacific Decadal Oscillation. Changes in these patterns are indicators for both Ekman surface forcing (Surface ocean currents flow to the right of the wind direction) and Ekman pumping (Surface waters diverge away from regions of positive wind stress curl, leading to upwelling of colder saltier water). Changes in temperature along the nearshore part of Line P suggest Ekman surface forcing is the stronger of the two processes in the upper layer. The change in salinity anomalies in the halocline along the seaward end of Line P, following the wind shift in 1977, is in agreement with enhanced upwelling caused by stronger Ekman pumping in this region.

Flood–ebb and spring–neap variations of mixing, stratification and circulation in Chesapeake Bay

A three-dimensional hydrodynamic model is used to investigate intra-tidal and spring–neap variations of turbulent mixing, stratification and residual circulation in the Chesapeake Bay estuary. Vertical profiles of salinity, velocity and eddy diffusivity show a marked asymmetry between the flood and ebb tides. Tidal mixing in the bottom boundary layer is stronger and penetrates higher on flood than on ebb. This flood–ebb asymmetry results in a north–south asymmetry in turbulent mixing because tidal currents vary out of phase between the lower and upper regions of Chesapeake Bay. The asymmetric tidal mixing causes significant variation of salinity distribution over the flood–ebb tidal cycle but insignificant changes in the residual circulation. Due to the modulation of tidal currents over the spring–neap cycle, turbulent mixing and vertical stratification show large fortnightly and monthly fluctuations. The stratification is not a linear function of the tidal-current amplitude. Strong stratification is only established during those neap tides when low turbulence intensity persists for several days. Residual circulation also shows large variations over the spring–neap cycle. The tidally averaged residual currents are about 50% stronger during the neap tides than during the spring tides.

Simulations of ARGO profilers and of surface floating objects: applications in MFSTEP

Abstract. In this work we describe part of the activities performed in the MFSTEP project by means of numerical simulations of ARGO profilers and surface floating objects. Simulations of ARGO floats were used to define the optimal time cycling in order to maximize independent observations of vertical profiles of temperature and salinity and to minimize the error on the estimate of the velocity at the parking depth of the profilers. Instead, the Mediterranean Forecasting System archive of Eulerian velocity field from 2000 to 2004 was used to build a related surface Lagrangian archive, systematically integrating numerical particles released and constrained to drift at surface. Here we use such Lagrangian archive to study the interannual variability of the surface Lagrangian transport in two key areas of the Western Mediterranean, also introducing an exponential decay in the particles concentration.

Derivation of Salinity Profiles in the Indian Ocean from Satellite Surface Observations

Subsurface salinity profiles in the Indian Ocean have been constructed using a combined empirical orthogonal function analysis technique and a nonlinear data-fitting algorithm, which is known as a genetic algorithm. The purpose is to establish a methodology to generate a 3-D structure of salinity using satellite-derived surface observations, which will be useful for assimilating in numerical models. This acquires greater significance in view of the upcoming satellite salinity missions. In this letter, we have been able to generate vertical profiles of salinity using a combination of sea surface temperature derived by the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager onboard TRMM and sea surface salinity from Argo floats. The root mean square error of the retrieved salinity varies from less than 0.05 psu-78 at the surface to about 0.15 psu-78 at greater depths. A sensitivity study of the retrieval algorithm with the anticipated uncertainties in surface salinity from the European Soil Moisture and Ocean Salinity satellite has also been carried out

ON THE RESIDUAL CURRENT DISTRIBUTION IN THE INNERMOST PARTOF THE ARIAKE SEA

Tidal currents in the bay are basic quantities and those of the Ariake Sea have been observed by many administrative agencies and researchers. However, a residual current distribution has been hardly obtained. This is one of the most effective parts for material transport and environment of the bay. In this study, the residual currents in the innermost part of the Ariake Sea were obtained from 13 hours velocity measurements with ADCPs. At the same time, temperature and salinity vertical profiles in wide area of this field were also measured. The observations were conducted in July15, 2005, November 1, 2005 and March 10, 2006. A distinct density-stratification was found in July and March, whereas vertically well mixed condition was seen in November. In every seasons, residual current along the longitudinal section of the bay basically showed a two-layered structure; upper layer flowed offshore and lower layer did inward. These results indicate that estuarine circulation was dominated in every seasons.

New results on the resistivity structure of Merapi Volcano (Indonesia), derived from three-dimensional restricted inversion of long-offset transient electromagnetic data

Author(s): Commer, Michael; Helwig, Stefan, L.; Hordt, Andreas; Scholl, Carsten; Tezkan, Bulent | Abstract: Three long-offset transient electromagnetic (LOTEM) surveys werecarried out at the active volcano Merapi in Central Java (Indonesia) during the years 1998, 2000, and 2001. The measurements focused on the general resistivity structure of the volcanic edifice at depths of 0.5-2 km and the further investigation of a southside anomaly. The measurements were insufficient for a full 3D inversion scheme, which could enable the imaging of finely discretized resistivity distributions. Therefore, a stable, damped least-squares joint-inversion approach is used to optimize 3D models with a limited number of parameters. The mode ls feature the realistic simulation of topography, a layered background structure, and additional coarse 3D blocks representing conductivity anomalies. Twenty-eight LOTEM transients, comprising both horizontal and vertical components of the magnetic induction time derivative, were analyzed. In view of the few unknowns, we were able to achieve reasonable data fits. The inversion results indicate an upwelling conductor below the summit, suggesting hydrothermal activity in the central volcanic complex. A shallow conductor due to a magma-filled chamber, at depths down to 1 km below the summit, suggested by earlier seismic studies, is not indicated by the inversion results. In conjunction with an anomalous-density model, derived from arecent gravity study, our inversion results provide information about the southern geological structure resulting from a major sector collapse during the Middle Merapi period. The density model allows to assess a porosity range andthus an estimated vertical salinity profile to explain the high conductivities on a larger scale, extending beyond the foothills of Merapi.

Inter-comparing five forecast operational systems in the North Atlantic and Mediterranean basins: The MERSEA-strand1 methodology

The methodology to achieve a real time inter-comparison of five state-of-the-art operational forecast systems for the North Atlantic and Mediterranean basins is presented. All systems provide analysis and near real-time prediction of the three-dimensional ocean through Opendap servers. A standard set of diagnostics called metrics, is described. Definition and examples of metrics are given. An inter-comparison of the five systems is conducted over a 1 year period using those metrics. It is shown that the methodology developed allows a successful inter-comparison. It has been adopted by the GODAE community. It is also shown that the systems are consistent with the current knowledge of the ocean circulation and climatologies. Systems are deficient in the representation of specific water masses characteristics as Mode waters. Data assimilation of vertical profiles of temperature and salinity solve such deficiencies. Metrics also allow a monitoring of the system's North Atlantic overturning stream function and will allow detecting any changes in the coming year system's thermohaline circulation.

Modeling the salinity profile of undeformed Arctic sea ice

The salinity of sea ice affects its physical and ecological properties. Here, a multilayer one‐dimensional halo‐thermodynamic sea ice model is used to simulate the vertical salinity profile of undeformed Arctic sea ice. The model successfully reproduces the desalination pattern observed in first‐year (FY) and multi‐year (MY) ice. The model can also be integrated with a prescribed, time‐independent salinity profile. Substantial differences in the simulated mass balance and ice‐ocean salt flux arise depending on the salinity. After 10 years into the simulation, the annual mean ice thickness is 2.85 m with the interactive halodynamic component, compared to 2.53 m (2.29 m) with a prescribed, time‐independent, vertically varying (constant) salinity profile. Modelling sea ice salinity is especially important when sea ice is transitioning from a MY to FY ice regime. Thus including a halodynamic component in sea ice models would significantly improve simulations of future climate.

Climate impacts of systematic errors in the simulation of the path of the North Atlantic Current

[1] Experiments employing an adjustment of the pressure field in the ocean component of a coupled climate system model are undertaken in both ocean-only and coupled experiments to assess the climatic impacts of reducing the systematic errors in the North Atlantic Current. This conservative and adiabatic adjustment process substantially decreases North Atlantic Ocean SST biases and locally reverses the associated surface heat flux balance in both model configurations. Ice concentrations in the Labrador Sea increase as the oceanic surface heat fluxes are displaced by the adjustment. Downstream, in the Nordic Seas, the subsurface ocean responds favorably to this adjustment, as the vertical profiles of potential temperature and salinity converge towards the observations. Atmospheric stationary wave patterns show a modest improvement, with a slight weakening of the excessively deep Icelandic low. Further unresolved errors in the coupled model framework potentially contribute to the continued presence of biases in the North Atlantic.

Anisotropic dispersive Henry problem

The Henry problem has played a key role in our understanding of seawater intrusion into coastal aquifers and in benchmarking density dependent flow codes. This paper seeks to modify Henry’s problem to ensure sensitivity to density variations and vertical salinity profiles that resemble field observations. In the proposed problem, the “dispersive Henry problem”, mixing is represented by means of the traditional Scheidegger dispersion tensor (dispersivity times water flux). Anisotropy in the hydraulic conductivity is acknowledged and Henry’s seaside boundary condition of prescribed salt concentration is replaced by a flux dependent boundary condition, which represents more realistically salt transport across the seaside boundary. This problem turns out to be very sensitive to density variations and its solution gets closer to reality. However, an improvement in the traditional Henry problem (gain in sensitivity and realism) can be also achieved if the value of the Peclet number is significantly reduced. Although the dispersive problem lacks an analytical solution, it can shed light on flow in coastal aquifers. It provides significant information about the factors controlling seawater penetration, width of the mixing zone and influx of seawater. The width of the mixing zone depends basically on dispersion with longitudinal and transverse dispersion controlling different parts of the mixing zone but displaying similar overall effects. Toe penetration is mainly controlled by the horizontal permeability and by the geometric mean of the dispersivities. Finally, transverse dispersivity and the geometric mean of the hydraulic conductivity are the leading parameters controlling the amount of saltwater that enters the aquifer.

Simulating tropical river plumes, a set of parametrizations based on macroscale data: A test case in the Mekong Delta region

A year‐long simulation of the Mekong river plume is conducted. The purpose is to identify the main processes impacting the fate of tropical freshwater runoff onto the shelf for later inclusion into a global ocean circulation model. Factors influencing the river plume in a general case are listed and are included in a coastal ocean configuration of the Princeton Ocean Model. This is achieved either explicitly, as for wind forcing, or using parametrizations corresponding to the length and timescales of river plumes physics, as for tides or estuaries. Results exhibit a strong seasonal variability related to the monsoon wind and river flow regimes of the region. A comparison with in situ measurements made during a campaign carried out in 1997 shows a good agreement. Vertical salinity profiles extracted from the model configuration correspond to conductivity‐temperature‐depth salinity profiles behavior established during the campaign. This model configuration also provides a good estimate of sea surface salinity in the vicinity of the coast of the Mekong Delta.

An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada

Electrical conductivity (EC) and geochemical data were interpreted to determine the nature, origin and distribution of salinity in pore waters of sediments in a deltaic environment. The role of diffusion as a mechanism for transporting saline water within lower permeability prodelta and delta slope sediments is specifically investigated. Characteristic vertical salinity profiles at several different regions of the Fraser River Delta, British Columbia (Canada) are identified, including relatively shallow salinity zones in areas currently and historically near main river channels, and deeper salinity zones reaching up to 300 m depth in delta-front and inland areas. Comparison of salinity profiles with the results of a simple salt transport model suggests that diffusion may be a significant mechanism controlling the observed distribution of salinity in current or former estuarine areas of the delta.Density-effects were found not to be significant given the low permeability of the silt through which the salt is diffusing; however, in similar environments with higher permeability sediments, density effects may be significant. In inland and delta front areas, salinity extends to a considerable depth in the silts, beyond what would appear to be possible by diffusion alone, and points to a connate origin.

A calibration method of Argo floats based on multiple regression analysis

Argo floats are free-moving floats that report vertical profiles of salinity, temperature and pressure at regular time intervals. These floats give good measurements of temperature and pressure, but salinity measurements may show significant sensor drifting with time. It is found that sensor drifting with time is not purely linear as presupposed by Wong (2003). A new method is developed to calibrate conductivity data measured by Argo floats. In this method, Wong’s objective analysis method was adopted to estimate the background climatological salinity field on potential temperature surfaces from nearby historical data in WOD01. Furthermore, temperature and time factors are taken into account, and stepwise regression was used for a time-varying or temperature-varying slope in potential conductivity space to correct the drifting in these profiling float salinity data. The result shows salinity errors using this method are smaller than that of Wong’s method, the quantitative and qualitative analysis of the conductivity sensor can be carried out with our method.

Stratification and fine sediment transport mechanisms in a semi‐enclosed tidal lagoon (Pagham Harbour, West Sussex)

AbstractPreliminary analysis of data collected at a macrotidal semi‐enclosed lagoon (Pagham Harbour, UK) has revealed useful information about long‐term patterns of siltation and some of the related mechanisms. Sediment surface‐level measurements made over 2 years at different sites within Pagham Harbour have shown a steady siltation, in common with earlier measurements, which is moderated by seasonal effects due to erosion by locally generated waves. Furthermore, inspection of vertical profiles of salinity and turbidity over individual tidal cycles has revealed that the degree of sediment transport on the flood tide is related to the vertical salinity gradient. Thus, at the Ferry Pool site, which is characterised by episodic pumped discharges from a nearby sewage treatment plant, landward sediment transport is enhanced by the high degree of salinity stratification observed during the flood tide. The mobility of the sediment, and the greater distribution of softer, less well‐consolidated sediment deposits, is greater here than at the other significant freshwater inflow at the Salthouse site, where the fresh water flow is instead moderated by a tidal flap gate. Preliminary analyses suggest that the higher the salinity stratification, the greater the landward sediment transport during the flood tide. Such analyses could help inform future policy on the methods of land drainage to macrotidal lagoons, and on the potential for managed realignment at such sites.

On the sensitivity of undeformed Arctic sea ice to its vertical salinity profile

The temporal evolution of sea ice salinity affects the temperature profile and vertical growth and decay of the ice cover, as well as many other important properties. Here, we use a one‐dimensional thermodynamic sea ice model to explore the sensitivity to the vertical profile of ice salinity of (1) Arctic first‐year and equilibrium multiyear sea ice thickness, and (2) the salt/freshwater flux at the ice/ocean interface. Results indicate that increasing the mean salinity induces a higher thermal inertia reducing summer melt and finally increasing ice thickness. The shape of the profile is also important, since low salinity at the surface must be captured to produce enough surface melt. This study gives accurate hints on what the minimum complexity of a parameterization of the temporal evolution of sea ice salinity should be.

Upper ocean heat and freshwater budgets in the eastern Pacific warm pool

This study focuses on upper ocean budgets of heat and freshwater, which yield estimates of net surface heat flux and rainfall minus evaporation. The budgets are based on a 19 day ship survey conducted as part of the Eastern Pacific Investigation of Climate Processes in the Coupled Ocean‐Atmosphere System 2001 in September 2001. Underway measurements included temperature and salinity sections from an undulating platform, SeaSoar, and horizontal currents from an acoustic Doppler current profiler along a 146 × 146 km survey pattern centered near 10°N, 95°W in the eastern Pacific warm pool. Additional measurements from a second ship at the center of the survey pattern included radar backscatter from rainfall, air‐sea fluxes, and vertical profiles of temperature, salinity, microstructure, and horizontal velocity. Satellite measurements of surface height, temperature, and rainfall were also analyzed. The heat budget of 20 and 25 m surface layers indicated that storage, advection, turbulent transport, and penetrative solar radiation were all significant components of the heat budget with a net surface cooling of 41 W m−2 estimated as a residual, which agreed with atmospheric measurements (30 W m−2). The precipitation rate from the freshwater budget was 29 mm d−1, which was in excellent agreement with in situ measurements on both ships and in good agreement with satellite estimates for the same period. Lateral transports of heat and salt were influenced by an anticyclonic eddy in the survey area, and it is suggested that anticyclonic eddies, which form near the Central American coast, may carry anomalously warm sea surface temperature toward the west and become preferential sites for heavy rainfall.

Residual Flow Structure at a Scour-hole in Bahia Blanca Estuary, Argentina

Abstract Two-dimensional data of mean and sediment flow collected at a natural confluence of channels in the inner Bahia Blanca Estuary are presented. We describe the two-dimensional flow field to assess the role of changes in bed morphology occurring during transport-effective events on the structure of flow at a confluence; and to examine how the flow structure varies with changes in the ratio of momentum flux. At each station, vertical profiles of velocity, salinity, temperature and suspended sediment were obtained during the whole tidal cycle and residual fluxes were obtained. Lagrangean flux is higher than possible fresh water input, denoting an extra output of water which is the flux over the tidal flats along the southern and northern coasts of the channel. The effect of the junction produces a distortion of the vertical profile flow and in the suspended sediment transport. The effect of the particular conformation of the system makes necessary for consider the lateral effect of the tidal flats in ...

Objective analyses of hydrographic data for referencing profiling float salinities in highly variable environments

The development of a broad-scale array of about 3000 autonomous profiling floats, known as Argo, has been underway since 2000. This array will deliver up to 100,000 vertical profiles of temperature, salinity and other parameters from the surface to depths up to 2000 m. While floats are expected to give good measurements of temperature and pressure, salinity measurements sometimes show significant sensor drift with time or offsets. Unless a float is recovered before the battery fails, recalibrations cannot be performed and a remote calibration method is required. Such a quality control system has been set up for the North Atlantic to identify and correct salinity sensor drifts by using historical hydrographic data. An objective mapping method is used that takes the spatial and temporal variations in water mass properties into account. These scales aim to represent the hydrographic structure of the North Atlantic, which follow the large-scale contours of the potential vorticity. The float measurements of each profile are compared to the mapped salinities in potential conductivity space by weighted least-squares, giving one correction for each profile. It is assumed that any conductivity offset changes slowly over time, so that a linear fit of the profile based corrections over the float time series is done. The result is a set of calibrated salinity data with corresponding uncertainties.