Salinity Fields Research Articles

The Surface-Forced Overturning of the North Atlantic: Estimates from Modern Era Atmospheric Reanalysis Datasets

Abstract Estimates of the recent mean and time varying water mass transformation rates associated with North Atlantic surface-forced overturning are presented. The estimates are derived from heat and freshwater surface fluxes and sea surface temperature fields from six atmospheric reanalyses—the Japanese 25-yr Reanalysis (JRA), the NCEP–NCAR reanalysis (NCEP1), the NCEP–U.S. Department of Energy (DOE) reanalysis (NCEP2), the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-I), the Climate Forecast System Reanalysis (CFSR), and the Modern-Era Reanalysis for Research and Applications (MERRA)—together with sea surface salinity fields from two globally gridded datasets (World Ocean Atlas and Met Office EN3 datasets). The resulting 12 estimates of the 1979–2007 mean surface-forced streamfunction all depict a subpolar cell, with maxima north of 45°N, near σ = 27.5 kg m−3, and a subtropical cell between 20° and 40°N, near σ = 26.1 kg m−3. The mean magnitude of the subpolar cell varies between 12 and 18 Sv (1 Sv ≡ 106 m3 s−1), consistent with estimates of the overturning circulation from subsurface observations. Analysis of the thermal and haline components of the surface density fluxes indicates that large differences in the inferred low-latitude circulation are largely a result of the biases in reanalysis net heat flux fields, which range in the global mean from −13 to 19 W m−2. The different estimates of temporal variability in the subpolar cell are well correlated with each other. This suggests that the uncertainty associated with the choice of reanalysis product does not critically limit the ability of the method to infer the variability in the subpolar overturning. In contrast, the different estimates of subtropical variability are poorly correlated with each other, and only a subset of them captures a significant fraction of the variability in independently estimated North Atlantic Subtropical Mode Water volume.

Seasonal variation of semidiurnal internal tides in the East/Japan Sea

The seasonal variation of semidiurnal internal tides in the East/Japan Sea was investigated using 25 month long output from a real-time ocean forecasting system. The z coordinate eddy-resolving high-resolution numerical model, called the RIAM ocean model, incorporates data assimilation that nudges temperature and salinity fields together with volume transport through the Korea Strait to produce realistic oceanic currents and stratification. In addition to atmospheric forcing, it includes tidal forcing of 16 major components along open boundaries. The model generates energetic semidiurnal internal tides around the northern entrance of the Korea Strait. Energy conversion from barotropic to baroclinic (internal) tides varies seasonally with maxima in September (ranging 0.48–0.52 GW) and minima in March (ranging 0.11–0.16 GW). This seasonal variation is induced by the seasonality in stratification near the southwestern East/Japan Sea. The propagation distance of the internal tides is associated with generation intensity and wavelength. From late summer to early winter, the semidiurnal internal tides travel relatively far from the generation region due to stratification changes; its energy dissipates less as a result of longer wavelengths. Our results suggest that spatiotemporal variation of internal-tide-induced mixing due to the seasonality in the generation, propagation, and dissipation of internal tides should be considered for a more realistic simulation of water masses and circulation in models of the East/Japan Sea.

The influence of the Maputo and Incomati rivers on the mixing and outflow of freshwater from Maputo Bay (Mozambique)

Markull, K., Lencart e Silva, J.D., Simpson, J.H., Dias, J.M., 2014. The influence of the Maputo and Incomati rivers on the mixing and outflow of freshwater from Maputo Bay (Mozambique). In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13 th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 580-585, ISSN 0749-0208. Maputo Bay is a tidally-energetic embayment, influenced by strong rainfall and associated river runoff during the wet season. Literature shows that salinity can regulate the nutrient cycle in mangrove estuarine ecosystems affecting the early life stages in these habitats which sustain the economically important shrimp stocks. The freshwater flow into Maputo Bay is for a part controlled by dam systems on its main rivers. In this work we investigate how varying flows from the Incomati and Maputo rivers interact with the tide to influence the evolution of the bay’s salinity field. A 3dimensional hydrodynamic model was applied to Maputo Bay, improving a previously published model through vertical and temporal refinement and recalibration, leading to a more accurate representation of the semidiurnal and fortnightly stratification-mixing cycles occurring during the wet season. However, the model still predicts salinities lower than those found in observations. An analysis showed that uncertainties in the salinity field increased towards the mouth of the Maputo River indicating the uncertainty of the modeled flow at the catchment as a possible cause of the underestimation of salinity in the bay. A set of experiments of varying Maputo and Incomati river flows show that for a flow as frequent as 5 times per year, the buoyancy input and the associated density driven flow contributed less than the tide in forcing the bay-shelf exchange. The inverse is observed for results where a flow with a 5-year return period leads to a more efficient bay-shelf exchange during neap tides than during spring tides. For this scenario, the results suggest that the estuarine plume was arrested inside the bay by tidal stirring during spring tide and released during neap tide when tidal stirring was subdued. The analysis of the separate and joint effects of the two rivers in setting the salinity field in Maputo Bay show a difference in extent of influence area between the rivers. These results suggest that the management of the freshwater inflow from the Maputo River can be crucial for maintaining lower salinities over parts of the bay to sustain the economically important marine resources.

Salinity modelling accuracy of a coastal lagoon: a comparative river flow analysis of basin model vs. traditional approaches

ABSTRACT Tomas, L.M., Rodrigues, M, Fortunato, A.B., Azevedo, A, Leitao, P.C., Oliveira, A., Rocha, A., Lopes, J.F., Dias, J.M., 2014. Salinity modelling accuracy of a coastal lagoon: a comparative river flow analysis of basin model vs. traditional approaches. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 586–591, ISSN 0749-0208.. The main purpose of this study is to investigate the uncertainties in the modelling of salinity fields in the Ria de Aveiro lagoon associated with the estimation of river flow discharges. The prediction of fresh water inputs is necessary to properly implement forcing conditions and consequently to provide accurate forecasts of baroclinic circulation in coastal lagoons. Located in the north-western Portuguese coast, the Ria de Aveiro is a shallow vertically homogeneous mesotidal coastal lagoon with a complex geometry. Although it is tidally dominated, it re...

A spatio-temporal process data model for characterizing marine disasters

Marine disasters are a more prevalent problem in China than in many other countries. Based on the development of a status quo of China's marine disaster the space-time process model is used. The model uses the ocean's temperature field, salinity field, water density field, surface wind field, wave field and other four-dimensional spatio-temporal quantities. This paper studies that model in detail. This study aims at using the theory to provide support during marine disasters in an effort to prevent or decrease their frequency in the future.

The water circulation near the Danube Delta and the Romanian coast modelled with finite elements

A numerical model, based on a finite element discretisation technique, was used to study water circulation in the Black Sea׳s north-western shelf, particularly near the Danube Delta and the Romanian coast. The numerical grid covers the entire Black Sea and the model resolution is gradually increased versus the Romanian coast to resolve both mesoscale and microscale hydrodynamic features. Sea level, water temperature and CTD profiles, collected in the north-western shelf, were used to validate the model. The seasonal and daily coastal hydrodynamics, in 2009, were studied using 3-D water current and salinity fields. Moreover, different numerical tracers were released on the Danube׳s arms to characterise the Danube׳s plume extension. Results show that near the Danube Delta the strong salinity stratification confines most of the wind momentum input to the surface water layer, while the subsurface current is mostly influenced by the open sea circulation. In the southern Romanian coast, the vertical salinity gradient is weaker and the action of the wind can reach deeper layers. The numerical tracers show a net predominance of the Kilia branch and how coastal anticyclonic eddies can trap the river freshwater, carrying it away from the coast. This happens especially in spring, when the Danube׳s discharge is high and a large eddy is active in front of the Kilia branch.

Impact of improved assimilation of temperature and salinity for coupled model seasonal forecasts

We assess the impact of improved ocean initial conditions for predicting El Nino-Southern Oscillation (ENSO) and Indian Ocean dipole (IOD) using the Bureau of Meteorology’s Predictive Ocean Atmosphere Model for Australia (POAMA) coupled seasonal prediction model for the period 1982–2006. The new ocean initial conditions are provided by an ensemble-based analysis system that assimilates subsurface temperatures and salinity and which is a clear improvement over the previous optimal interpolation system which used static error covariances and was univariate (temperature only). Hindcasts using the new ocean initial conditions have better skill at predicting sea surface temperature (SST) variations associated with ENSO than do the hindcasts initialized with the old ocean analyses. The improvement derives from better prediction of subsurface temperatures and the largest improvements come during ENSO–IOD neutral years. We show that improved prediction of the Nino3.4 SST index derives from improved initial depiction of the thermocline and halocline in the equatorial Pacific but as lead time increases the improved depiction of the initial salinity field in the western Pacific become more important. Improved ocean initial conditions do not translate into improved skill for predicting the IOD but we do see an improvement in the prediction of subsurface temperatures in the Indian Ocean (IO). This result reflects that the coupling between subsurface and surface temperature variations is weaker in the IO than in the Pacific, but coupled model errors may also be limiting predictive skill in the IO.

Modelling metal speciation in the Scheldt Estuary: Combining a flexible-resolution transport model with empirical functions

Predicting metal concentrations in surface waters is an important step in the understanding and ultimately the assessment of the ecological risk associated with metal contamination. In terms of risk an essential piece of information is the accurate knowledge of the partitioning of the metals between the dissolved and particulate phases, as the former species are generally regarded as the most bioavailable and thus harmful form. As a first step towards the understanding and prediction of metal speciation in the Scheldt Estuary (Belgium, the Netherlands), we carried out a detailed analysis of a historical dataset covering the period 1982–2011. This study reports on the results for two selected metals: Cu and Cd. Data analysis revealed that both the total metal concentration and the metal partitioning coefficient (Kd) could be predicted using relatively simple empirical functions of environmental variables such as salinity and suspended particulate matter concentration (SPM). The validity of these functions has been assessed by their application to salinity and SPM fields simulated by the hydro-environmental model SLIM. The high-resolution total and dissolved metal concentrations reconstructed using this approach, compared surprisingly well with an independent set of validation measurements. These first results from the combined mechanistic-empirical model approach suggest that it may be an interesting tool for risk assessment studies, e.g. to help identify conditions associated with elevated (dissolved) metal concentrations.

Coupling Basin and Reservoir Simulators for an Improved CO2 Injection Flow Model

Abstract The goal of this work is to model the present basin-scale groundwater flow of the Paris basin with a basin modelling approach and to use it to initialise a reservoir model for CO 2 injection. It is part of the ULTimateCO2 FP7 European funded project which aims to significantly enhance our knowledge of specific processes that may affect the long-term fate of geologically stored CO 2 . Basin models simulate the history of sedimentary basins through time by coupling geological events such as deposition, erosion, compaction, structural deformation and subsurface flow simulation. In order to construct the basin model of the Paris Basin in IFPEN basin software TemisFlow®, several types of data were gathered. The current surface topography and 11 horizons representing the top of selected main geological layers (from basement to surface) were constructed from outcrop boundaries, wells and isobath maps. Seven erosion maps for the main unconformities recorded in the Paris Basin were also constructed to complete the burial history of the sedimentary basin. TemisFlow® computes pressure, temperature and salinity fields over the basin history up to the present-day. The final state of the basin simulation is then used as initial state of the reservoir numerical model (Coores TM ). The latter is used to simulate the injection of CO 2 and its effects on the pressure field for instance.

Development and Analysis of the Systematically Merged Atlantic Regional Temperature and Salinity Climatology for Oceanic Heat Content Estimates

Abstract An oceanic climatology to calculate upper-ocean thermal structure was developed for application year-round in the North Atlantic Ocean basin. The Systematically Merged Atlantic Regional Temperature and Salinity (SMARTS) Climatology is used in a two-layer model to project sea surface height anomalies (SSHA) into the water column at ¼° resolution. SMARTS blended monthly temperature and salinity fields from the World Ocean Atlas 2001 (WOA01) and Generalized Digital Environmental Model (GDEM) version 3.0 based on their performance compared to in situ measurements. Daily mean isotherm depths of 20°C (D20) and 26°C (D26) (and their mean ratio), reduced gravity, and mixed layer depth (MLD) were estimated from the climatology. This higher-resolution climatology resolves features in the Gulf of Mexico (GOM), including the Loop Current (LC) and eddy shedding region. Using SMARTS with satellite-derived SSHA and SST fields, daily values of isotherm depths, mixed layer depths, and ocean heat content (OHC) were calculated from 1998 to 2012. OHC is an important scalar when determining the ocean’s impact on tropical cyclone intensification, because it is a better predictor of SST cooling during hurricane passage. Airborne- and ship-deployed expendable bathythermographs (XBT), long-term moorings, and Argo profiling floats provided over 50 000 thermal profiles to assess satellite retrievals of isotherm depths and OHC using the SMARTS Climatology. The OHC calculation presented in this document reduces errors basinwide by 20%, with a 35% error reduction in the GOM.

Dinámica de flujo, del campo salino y de los sedimentos finos en el Río de la Plata

This article summarizes the main advances made by our group in the study of flow and substance transport dynamics in the Río de la Plata, based on the implementation of various models (RMA, MOHID, MARS) and incorporating existing high-quality field information. In the Río de la Plata, the main forcings that influence water circulation are flow discharge from its tributaries, tide waves (astronomic and meteorologic), and winds. There is a clear difference between the inner-middle region and the outer region of the Río de la Plata. The division between these two regions is known as the frontal region, where there is considerable widening of the section and an increase in depth. Because of these characteristics, the salinity field coming from the Atlantic Ocean reaches this region, with greater intensity in the deep regions where the saline stratification is more pronounced. This in turn gives the residual velocities in the middle region the typical two-dimensional characteristics of a flow discharge (net transport toward the outer region), while the residual flow in the outer region shows more complex, three-dimensional characteristics, with mainly incoming flow toward the continent in the deep areas and flow discharge mainly through the shallow coastal areas. There is an area of almost nil residual current in the frontal region. In addition to this clear spacial difference in the behavior of the body of the water, the meteorological conditions have a determining influence. The present study discusses diverse behaviors of the currents, salinity and fine sediment dynamics under calm and storm conditions.

Using Depth-Normalized Coordinates to Examine Mass Transport Residual Circulation in Estuaries with Large Tidal Amplitude Relative to the Mean Depth

Abstract Residual (subtidal) circulation profiles in estuaries with a large tidal amplitude-to-depth ratio often are quite complex and do not resemble the traditional estuarine gravitational circulation profile. This paper describes how a depth-normalized σ-coordinate system allows for a more physical interpretation of residual circulation profiles than does a fixed vertical coordinate system in an estuary with a tidal amplitude comparable to the mean depth. Depth-normalized coordinates permit the approximation of Lagrangian residuals, performance of empirical orthogonal function (EOF) analysis, estimation of terms in the along-stream momentum equations throughout depth, and computation of a tidally averaged momentum balance. The residual mass transport velocity has an enhanced two-layer exchange flow relative to an Eulerian mean because of the Stokes wave transport velocity directed upstream at all depths. While the observed σ-coordinate profiles resemble gravitational circulation, and pressure and friction are the dominant terms in the tidally varying and tidally averaged momentum equations, the two-layer shear velocity from an EOF analysis does not correlate with the along-stream density gradient. To directly compare to theoretical profiles, an extension of a pressure–friction balance in σ coordinates is solved. While the barotropic riverine residual matches theory, the mean longitudinal density gradient and mean vertical mixing cannot explain the magnitude of the observed two-layer shear residual. In addition, residual shear circulation in this system is strongly driven by asymmetries during the tidal cycle, particularly straining and advection of the salinity field, creating intratidal variation in stratification, vertical mixing, and shear.

Effects of waves on coastal water dispersion in a small estuarine bay

A three‐dimensional wave‐current model is used to investigate wave‐induced circulations in a small estuarine bay and its impact on freshwater exchanges with the inner shelf, related to stratified river plume dispersion. Modeled salinity fields exhibit a lower salinity surface layer due to river outflows, with typical depth of 1 m inside the bay. The asymmetric wave forcing on the bay circulation, related to the local bathymetry, significantly impacts the river plumes. It is found that the transport initiated in the surf zone by the longshore current can oppose and thus reduce the primary outflow of freshwater through the bay inlets. Using the model to examine a high river runoff event occurring during a high‐energy wave episode, waves are found to induce a 24 h delay in freshwater evacuation. At the end of the runoff event, waves have reduced the freshwater flux to the ocean by a factor 5, and the total freshwater volume inside the bay is increased by 40%. According to the model, and for this event, the effect of the surf zone current on the bay flushing is larger than that of the wind. The freshwater balance is sensitive to incident wave conditions. Maximum freshwater retention is found for intermediate offshore wave heights 1 m < Hs < 2 m. For higher‐energy waves, the increase in the longshore current reduces the retention, which is two times lower for Hs = 4 m than for Hs = 2 m.

Variation of Fish Habitat and Extent of the Low-Salinity Zone with Freshwater Flow in the San Francisco Estuary

We used the UnTRIM San Francisco Bay–Delta hydrodynamic model to examine the spatial distribution of salinity as a function of freshwater flow in the San Francisco Estuary. Our particular focus was the covariation of flow with the spatial extent of the low-salinity zone (LSZ: salinity = 0.5 to 6), and with the extent of habitat for common species of -nekton as defined by their salinity ranges. The UnTRIM model has an unstructured grid which allowed us to refine earlier estimates of the availability of suitable salinity ranges, particularly for species resident in low salinity. The response of the salinity field to flow was influenced by the bathymetry of the estuary. Area and volume of the LSZ were bimodal with X2, the distance up the axis of the estuary to a near-bottom salinity of 2, roughly the middle of the LSZ. The smallest area and volume occurred when the LSZ was in the Delta or Carquinez Strait, moderate values when it was in Suisun Bay, and the highest values when it was in broad, shallow San Pablo Bay. Resource selection functions for the distributions of common nekton species in salinity space were up-dated from previous values and used to calculate salinity-based habitat indices using the UnTRIM results. These indices generally increased with decreasing X2 (increasing flow), but the slopes of these relationships were mostly inconsistent with corresponding relationships of abundance to flow. Thus, although the salinity range used by most nekton expands as flow increases, other mechanisms relating population size to flow are likely more important than the physical extent of suitable salinity.

Variability in a fjord-like coastal estuary I: Quantifying the circulation using a formal multi-tracer inverse approach

During 2002–2005, a comprehensive set of observations covering physical, biological, radiative and atmospheric parameters was obtained from the southern Strait of Georgia (SoG), Western Canada by the STRATOGEM program. Monthly time series of estuarine layer transports over 2002–2005 were estimated using a time-dependent 2-box model in a formal inverse approach. The formal inverse approach builds up upon a so-called “pseudo-inverse” and the Singular Value Decomposition methodology. The transports are then consistent with the temperature and salinity fields, as well as riverine freshwater inflow (R) and detailed atmospheric heat fluxes. Uncertainty was analyzed by resampling observations using bootstrap methods.Analysis of these time series suggests that the SoG estuarine circulation is not very sensitive to the seasonal changes of R. Comparison of the surface layer transport (U1) and R yields the first observational relationship between the SoG estuarine circulation and R. The analysis of this relationship shows that U1 has a fractional form as R to the power of 1/n with n < 1. Such fractional relationship shows that the flows change only slightly with the freshet. A 5-fold change in R results only in a 40% change in U1. However, freshwater range and uncertainty in the data prevented us from clearly determining the fraction n.Analysis of the transports in light of the residuals in the mass, heat and salt budgets suggests that our inversion procedure works properly and improves on the SVD inverse procedure. Analysis of the transports sensitivity to inversion parameters shows that the transports are close to both the a priori and true transports and that they are dependent on both a priori information and data.

Po River plume pattern variability investigated from model data

The Adriatic Sea is a semi-enclosed basin located in the NE part of the Mediterranean Sea and it is strongly influenced by riverine inputs. In its northern sub-basin the freshwater plume of the Po River, together with those of numerous smaller rivers, plays a fundamental role in driving the physical and biogeochemical processes of the whole basin. In this paper we characterize the surface plume structure and identify its patterns and temporal variability on seasonal and inter-annual scales relating it to its major forcings (i.e., river discharges and winds). To perform this analysis, a 3D hydrodynamic numerical model was implemented over the whole Adriatic for the period 2003–2010 and the resulting outputs were analyzed through a series of statistical tools. The inter-annual and seasonal averages of Sea Surface Salinity (SSS) fields show that the average patterns are composed of a coastal plume, wider or narrower depending on the season, that flows southward of the Po River mouths. The first two modes of the Empirical Orthogonal Functions (EOF) analysis show a similar distribution with a cumulative explained variance up to 60%; the third mode, instead, presents a plume shape that extends well into the basin. To obtain a more detailed representation of the plume, a 2×3 Self-Organizing Map (SOM) analysis was performed over the surface salinity fields. Two antithetic patterns were depicted: (i) a small plume confined to coastal areas, typical of low discharges and/or Bora wind events and (ii) a wider plume that extends into the basin, typical of high river discharges and/or Sirocco winds. The comparison between wind regimes, riverine inputs and the time series of the SOM's Best Matching Units (BMU) suggested that, on long time scales, river discharges represent the dominant forcing in defining the plume size and surface pattern, while on time scales of few days the plume dynamics are modulated mostly by the wind structure.

Numerical model of the hydrodynamics of the Black Sea and the Sea of Azov with variational initialization of temperature and salinity

A numerical primitive-equation model of the hydrodynamics of the Black Sea and the Sea of Azov in σ-coordinates is proposed. The model has a resolution of ∼4 × 4 km in horizontal coordinates with 40-σ levels in the vertical and includes the four-dimensional variational initialization of temperature and salinity fields. A numerical initialization algorithm combines splitting methods and adjoint equations. Flow, temperature, sea level, and salinity fields driven by atmospheric forcing are calculated for the year 2008. The calculations are made in a variational initialization — prediction regime. Temperature and salinity fields are initialized at the end of each month. The optimality system includes forward and adjoint transport-diffusion equations for heat and salt that are linearized on the assimilation interval. Results of three numerical experiments with different sets of assimilated data in comparison with the prediction obtained from the forward model are discussed.

Impact of Innovations on Future Energy Supply – Chemical Enhanced Oil Recovery (CEOR)

The International Energy Agency (IEA) expects an increase of global energy demand by one-third during next 20 years together with a change in the global energy mix. A key-influencing factor is a strong expected increase in oil and gas production in the United States driven by 'new' technologies such as hydraulic fracturing. Chemical enhanced oil recovery (CEOR) is another strong growing technology with the potential of a step change innovation, which will help to secure future oil supply by turning resources into reserves. While conventional production methods give access to on average only one-third of original oil in place, the use of surfactants and polymers allows for recovery of up to another third of this oil. In the case of polymer flooding with poly acrylamide, the number of full field implementations has increased in recent years. In the meantime new polymers have been developed to cover previously unmet needs - such polymers can be applied in fields of high salinity and high temperature. Use of surfactants is in an earlier stage, but pilot tests show promising results.

The circulation of Icelandic waters – a modelling study

Abstract. The three-dimensional flow, temperature and salinity fields of the North Atlantic, including the Arctic Ocean, covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The simulation reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC) and the path of the Atlantic Water south-east of Iceland. The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts, which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a hitherto unnamed current over the southern and south-eastern shelf, which is simulated to be an upstream precursor of the Faroe Current (FC). Both currents are driven by barotropic pressure gradients induced by a sea level slope across the Greenland–Scotland Ridge. The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85% during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27%. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.

Small-scale features of temperature and salinity surface fields in the Coral Sea

The small-scale features in sea surface temperature and salinity fields (SST and SSS) of the Coral Sea are examined using high horizontal spatial and short-term temporal in situ measurements. These features are extracted from thermosalinographs (TSGs) gathered onboard commercial and research vessels and at one long-term fixed station. The analyses are performed along the vessel tracks and the structures of small-scale features are extracted by high-pass spatial filtering the original TSG data. For SSS, it is shown that the features at the scale of mesoscale eddies (approximate to 100 km) vary from about -1.1 to +0.6 psu in the Coral Sea region. Processes sustaining such range include rainfall events, stirring by mesoscale eddies, and the latitudinal displacement of the sharp front associated with the edge of the Western Pacific Warm Pool at the seasonal time scales. The TSG data have revealed the presence of a sharp front (0.4-0.6 psu) between the subtropical and equatorial waters instead of a smooth gradient in the standard SSS climatologies. Within the context of recent remotely sensed observations of salinity, this could represent an important limitation for the validation and calibration of satellite products. In addition to these spatial considerations, temporal variations at one long-term station near Vanuatu show that the coupled air-sea responses to intraseasonal tropical variability, such as the Madden-Julian Oscillation, may have a signature in both SST and SSS fields. However, this response is found to be complex and not necessarily in phase. In the Coral Sea region, our results suggest that MJO-induced variability on SST and SSS exhibit little coherency at the seasonal time scales.