ALBERT

Description: High resolution satellite turbidity and sea surface temperature observations of river plume interactions during a significant flood event Ocean Science Discussions, 12, 1669-1692, 2015 Author(s): V. E. Brando, F. Braga, L. Zaggia, C. Giardino, M. Bresciani, D. Bellafiore, C. Ferrarin, F. Maicu, A. Benetazzo, D. Bonaldo, F. M. Falcieri, A. Coluccelli, A. Russo, and S. Carniel Sea surface temperature (SST) and turbidity ( T ) derived from Landsat-8 (L8) imagery were used to characterize river plumes in the Northern Adriatic Sea (NAS) during a significant flood event in November 2014. Sea surface salinity (SSS) from an operational coupled ocean-wave model supported the interpretation of the plumes interaction with the receiving waters and among them. There was a good agreement of the SSS, T , and SST fields at the sub-mesoscale and mesoscale delineation of the major river plumes. L8 30 m resolution enabled also the description of smaller plume structures. Sharp fronts in T and SST delimited each single river plume. The isotherms and turbidity isolines coupling varied among the plumes due to differences in particle loads and surface temperatures in the discharged waters. The different plumes reflectance spectra were related to the lithological fingerprint of the sediments in the river catchments.

Description: Spatial scales of temperature and salinity variability estimated from Argo observations Ocean Science Discussions, 12, 1793-1814, 2015 Author(s): F. Ninove, P. Y. Le Traon, E. Remy, and S. Guinehut Argo observations from 2005 to 2013 are used to characterize spatial scales temperature and salinity variations from the surface down to 1500 m. Simulations are first performed to analyze the sensitivity of results to Argo sampling; they show that several years of Argo observations are required to estimate the spatial scales of ocean variability over 20° × 20° boxes. Spatial scales are then computed over several large scale areas. Zonal and meridional spatial scales ( Lx and Ly which are also zero crossing of covariance functions) vary as expected with latitudes. Scales are of about 100 km at high latitudes and more of 700 km in the Indian and Pacific equatorial/tropical regions. Zonal and meridional scales are similar: except in these tropical/equatorial regions where zonal scales are much larger (by a factor of 2 to 3) than meridional scales. Spatial scales are the largest close to the surface and have a general tendency for temperature to increase in deeper layers. There are significant differences between temperature and salinity scales, in particular, in the deep ocean. Results are consistent with previous studies based on sparse in-situ observations or satellite altimetry. They provide, however, for the first time a global description of temperature and salinity scales of variability and a characterization of their variations according to depths.

Description: A semi-analytical model for diffuse reflectance in marine and inland waters Ocean Science Discussions, 12, 1893-1912, 2015 Author(s): J. D. Pravin, P. Shanmugam, and Y.-H. Ahn A semi-analytical model for predicting diffuse reflectance of coastal and oceanic waters is developed based on the water-column optical properties and illumination conditions. Diffuse reflectance ( R ) is an apparent optical property that is related to the Gordon's parameter ( b b /(a+b b ) ) through a proportionality factor " f ". The conventional assumption of " f " as a constant (0.33) yields large errors in case of turbid and productive coastal waters and a predictive model based on this assumption is generally restricted to open-ocean waters (low chlorophyll case). In this paper, we have sorted the dependent factors that influence " f " values in the water column. Here, the parameter " f " is modeled as a function of wavelength, depth, inherent optical properties (IOPs) and illumination conditions. This work eliminates the spectral constants ( K Chl and K SS ) associated with our previous model and constrains the present model to be solely dependent on the IOPs and illumination conditions. Data used for parameterization and validation are obtained from in situ measurements in different waters within coastal environments. Validation shows good agreement between the model R and in situ R values with the overall mean relative error of less than a few percent. The model is valid for a wide range waters within coastal and open-ocean environments.

Description: Impact of variable sea-water conductivity on motional induction simulated with an OGCM Ocean Science Discussions, 12, 1869-1891, 2015 Author(s): C. Irrgang, J. Saynisch, and M. Thomas Carrying high concentrations of dissolved salt, ocean water is a good electrical conductor. As sea-water flows through the Earth's ambient geomagnetic field, electric fields are generated, which in turn induce secondary magnetic fields. In current models for oceanic induced magnetic fields, a realistic consideration of sea-water conductivity is often neglected and the effect on the variability of the oceanic induced magnetic field unknown. To model magnetic fields that are induced by non-tidal global ocean currents, an electromagnetic induction model is implemented into the Ocean Model for Circulation and Tides (OMCT). This provides the opportunity to not only model oceanic induced magnetic signals, but to assess the impact of oceanographic phenomena on the induction process. In this paper, the sensitivity of the induction process due to spatial and temporal variations in sea-water conductivity is investigated. It is shown that assuming an ocean-wide uniform conductivity is insufficient to accurately capture the temporal variability of the magnetic signal. Using instead a realistic global sea-water conductivity distribution increases the temporal variability of the magnetic field up to 45 %. Especially vertical gradients in sea-water conductivity prove to be a key factor for the variability of the oceanic induced magnetic field. However, temporal variations of sea-water conductivity only marginally affect the magnetic signal.

Description: Design and validation of MEDRYS, a Mediterranean Sea reanalysis over 1992–2013 Ocean Science Discussions, 12, 1815-1867, 2015 Author(s): M. Hamon, J. Beuvier, S. Somot, J. M. Lellouche, E. Greiner, G. Jordà, M. N. Bouin, T. Arsouze, K. Béranger, F. Sevault, C. Dubois, M. Drevillon, and Y. Drillet The French research community on the Mediterranean Sea modelling and the French operational ocean forecasting center Mercator Océan have gathered their skill and expertise in physical oceanography, ocean modelling, atmospheric forcings and data assimilation, to carry out a MEDiterranean sea ReanalYsiS (MEDRYS) at high resolution for the period 1992–2013. The ocean model used is NEMOMED12, a Mediterranean configuration of NEMO with a 1/12° (∼ 7 km) horizontal resolution and 75 vertical z levels with partial steps. At the surface, it is forced by a new atmospheric forcing dataset (ALDERA), coming from a dynamical downscaling of the ERA-Interim atmospheric reanalysis by the regional climate model ALADIN-Climate with a 12 km horizontal and 3 h temporal resolutions. This configuration is used to carry a 34 year free simulation over the period 1979–2013 (NM12-FREE) which is the initial state of the reanalysis in October 1992. The first version of MEDRYS uses the existing Mercator Océan data assimilation system SAM that is based on a reduced-order Kalman filter with a 3-D multivariate modal decomposition of the forecast error. Altimeter data, satellite SST and temperature and salinity vertical profiles are jointly assimilated. This paper describes the configuration we used to perform the MEDRYS simulation. We then first validate the skills of the data assimilation system. It is shown that the data assimilation restores a good averaged temperature and salinity in intermediate layers compared to the free simulation. No particular biases are identified in the bottom layers. However, the reanalysis show slight positive biases of 0.02 psu and 0.15 °C above 150 m depth. In the validation stage, it is also shown that the assimilation allows to better reproduce water, heat and salt transports through the Strait of Gibraltar. Finally, the ability of the reanalysis to represent the sea surface high frequency variability is pointed out.

Description: Technical Note: Could benzalkonium chloride be a suitable alternative to mercuric chloride for preservation of seawater samples? Ocean Science Discussions, 12, 1953-1969, 2015 Author(s): J. Gloël, C. Robinson, G. H. Tilstone, G. Tarran, and J. Kaiser Instrumental equipment unsuitable or unavailable for fieldwork as well as lack of ship space can necessitate the preservation of seawater samples prior to analysis in a shore-based laboratory. Mercuric chloride (HgCl 2 ) is routinely used for such preservation, but its handling and subsequent disposal incur significant risks and expense. Benzalkonium chloride (BAC) has been used previously for freshwater samples. Here, we assess BAC as a less hazardous alternative microbial inhibitor for marine samples prior to the measurement of oxygen-to-argon (O 2 /Ar) ratios, as used for the determination of plankton net community production. BAC at a concentration of 50 mg dm −3 inhibited microbial activity for at least three days in seawater with chlorophyll a (Chl a ) concentrations up to 1 mg m −3 , possibly longer when Chl a concentrations were lower. BAC concentrations of 100 and 200 mg dm −3 were no more effective than 50 mg dm −3 . With fewer risks to human health and the environment, and no requirement for expensive waste disposal, BAC could be a viable alternative to HgCl 2 for short-term preservation of seawater samples, but is not a replacement for HgCl 2 in the case of oxygen triple isotope analysis, which requires storage over weeks to months. In any event, further tests on a case-by-case basis should be undertaken if use of BAC was considered, since its inhibitory activity may depend on concentration and composition of the microbial community.

Description: Turbulence observations in the Gulf of Trieste under moderate wind forcing and different water column stratification Ocean Science Discussions, 12, 1729-1764, 2015 Author(s): F. M. Falcieri, L. Kantha, A. Benetazzo, A. Bergamasco, D. Bonaldo, F. Barbariol, V. Malačič, M. S. Sclavo, and S. Carniel During the oceanographic campaign CARPET2014, between 30 January and 4 February 2014, a total of 478 microstructure profiles (grouped into 145 ensembles) and 38 CTD casts were made in the Gulf of Trieste (Northern Adriatic Sea) under moderate wind forcing (average wind speed 10 m s -1 ) and heat fluxes (net negative heat flux in the range of 150 to 400 W m -2 ). Among the collected profiles, there were three sets of yoyo casts, each lasting for about 12 h for a total of 50 casts. Overall, these represent the first turbulence observations collected in the Gulf of Trieste. Microstructure profiles collected with a free-falling profiler must be taken in enables of repeated casts, with the objective of obtaining more statistically significant values for turbulence parameters. This approach is certainly feasible in shallow waters, but has a down side when the vertical density structure includes strong interfaces that can move up or down between subsequent casts, under the influence of tides and internal waves. In order to minimize the smearing effect of such interfacial displacements on mean quantities, we developed an algorithm to realign, according to the temperature profile, successive microstructure profiles to produce sharper and more meaningful mean profiles of measured turbulence parameters. During CARPET2014, the water column in the Gulf evolved from a well-mixed condition to a stratified one, due to Adriatic waters intruding at the bottom along the Gulf's south-eastern coast. These waters stratified the water column and changed its stability characteristics, which in turn prevented wind driven turbulence from penetrating to the bottom of the water column. In this study, we show that during a warm and relatively dry winter, such as in 2014, the Gulf of Trieste was not completely mixed because of the influence of bottom waters intruding from the open sea, even under moderate wind forcing. Inside the Gulf, two types of water intrusions from the Adriatic Sea were observed during the yoyo casts: one coming from its northern coast (i.e. warmer, saltier and more turbid) and one coming from the open sea in front of the Po Delta (i.e. cooler, fresher and less turbid). Those two intrusions behaved similarly but had a different impact on turbulence kinetic energy dissipation rate profiles. The former, with high turbidity, acted as a barrier to wind-driven turbulence, while the latter, with low sediment concentrations and a smaller density gradient when compared to the rest of the water column, was not able to suppress downward penetration of turbulence from the surface to the same degree.

Description: Monitoring Atlantic overturning circulation variability with GRACE-type ocean bottom pressure observations – a sensitivity study Ocean Science Discussions, 12, 1765-1791, 2015 Author(s): K. Bentel, F. W. Landerer, and C. Boening The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism for large-scale northward heat transport and thus plays an important role for global climate. Relatively warm water is transported northward in the upper layers of the North Atlantic Ocean, and after cooling at subpolar latitudes, sinks down and is transported back south in the deeper limb of the AMOC. The utility of in-situ ocean bottom pressure (OBP) observations to infer AMOC changes at single latitudes has been characterized in recent literature using output from ocean models. We extend the analysis and examine the utility of space-based observations of time-variable gravity and the inversion for ocean bottom pressure to monitor AMOC changes and variability between 20 and 60° N. Consistent with previous results, we find a strong correlation between the AMOC signal and OBP variations, mainly along the western slope of the Atlantic basin. We then use synthetic OBP data – smoothed and filtered to resemble the resolution of the GRACE gravity mission – and reconstruct geostrophic AMOC transport. Due to the coarse resolution of GRACE-like OBP fields, we find that leakage of signal across the step slopes of the ocean basin is a significant challenge at certain latitudes. However, overall, the inter-annual AMOC anomaly time series can be recovered from 20 years of monthly GRACE-like OBP fields with errors less than 1 Sverdrup.

Description: An improved method for the determination of dissolved nitric oxide (NO) in seawater samples Ocean Science Discussions, 12, 959-981, 2015 Author(s): H. E. Lutterbeck and H. W. Bange Nitric oxide (NO) is a short-lived intermediate of the oceanic nitrogen cycle, however, due to its high reactivity, measurements of dissolved NO in seawater are rare. Here we present an improved method to determine NO concentrations in discrete seawater samples. The set-up of our system consisted of a chemiluminescence NO analyser connected to a stripping unit. The limit of detection for our method was 5 pmol NO in aqueous solution which translates into 0.25 nmol L −1 when using a 20 mL seawater sample volume. Our method was applied to measure high resolution depth profiles of dissolved NO during a cruise to the eastern tropical South Pacific Ocean. Our method is fast and comparably easy to handle thus it opens the door for deciphering the distribution of NO in the ocean and it facilitates laboratory studies on NO pathways.

Description: Regime changes in global sea surface salinity trend Ocean Science Discussions, 12, 983-1011, 2015 Author(s): A. L. Aretxabaleta, K. W. Smith, and J. Ballabrera-Poy Recent studies have shown significant sea surface salinity (SSS) changes at scales ranging from regional to global. In this study, we estimate global salinity means and trends using historical (1950–2014) SSS data from the UK Met. Office Hadley Centre objectively analyzed monthly fields and recent data from the SMOS satellite (2010–2014). We separate the different components (regimes) of the global surface salinity by fitting a Gaussian Mixture Model to the data and using Expectation–Maximization to distinguish the means and trends of the data. The procedure uses a non-subjective method (Bayesian Information Criterion) to extract the optimal number of means and trends. The results show the presence of three separate regimes: Regime A (1950–1990) is characterized by small trend magnitudes; Regime B (1990–2009) exhibited enhanced trends; and Regime C (2009–2014) with significantly larger trend magnitudes. The salinity differences between regime means were around 0.01. The trend acceleration could be related to an enhanced global hydrological cycle or to a change in the sampling methodology.

Description: Investigation of model capability in capturing vertical hydrodynamic coastal processes: a case study in the North Adriatic Sea Ocean Science Discussions, 12, 1625-1668, 2015 Author(s): W. J. McKiver, G. Sannino, F. Braga, and D. Bellafiore In this work we consider a numerical study of hydrodynamics in the coastal zone using two different models, SHYFEM and MITgcm, to assess their capability to capture the main processes. We focus on the North Adriatic Sea during a strong dense water event that occurred at the beginning of 2012. This serves as an interesting test case to examine both the models strengths and weaknesses, while giving an opportunity to understand how these events affect coastal processes, like upwelling and downwelling, and how they interact with estuarine dynamics. Using the models we examine the impact of setup, surface and lateral boundary treatment, resolution and mixing schemes, as well as assessing the importance of nonhydrostatic dynamics in coastal processes. Both models are able to capture the dense water event, though each displays biases in different regions. The models show large differences in the reproduction of surface patterns, identifying the choice of suitable bulk formulas as a central point for the correct simulation of the thermohaline structure of the coastal zone. Moreover, the different approaches in treating lateral freshwater sources affect the vertical coastal stratification. The results indicate the importance of having high horizontal resolution in the coastal zone, specifically in close proximity to river inputs, in order to reproduce the effect of the complex coastal morphology on the hydrodynamics. A lower resolution offshore is acceptable for the reproduction of the dense water event, even if specific vortical structures are missed. Finally, it is found that nonhydrostatic processes are of little importance for the reproduction of dense water formation in the shelf of the North Adriatic Sea.

Description: Responses of atmospheric circulation to sea surface temperature anomalies in the South China Sea Ocean Science Discussions, 12, 1693-1710, 2015 Author(s): M. Zhou and G. Wang The sea surface temperature (SST) anomalies in the South China Sea (SCS) and their influences on global atmospheric circulation were studied. The results of the simple atmospheric model suggested that the SCS SST anomalies can induce several barotropic wave trains from the SCS to other regions such as North America, high latitudes of the Southern Hemisphere and the Mediterranean. The baroclinic stream function anomalies from the simple model showed an anticyclonic vortex pair in East Asia and southern tropical Indian Ocean and a cyclonic vortex pair in the North Pacific and the Southwest Pacific. It is suggested that the spatial pattern of SST anomalies in the SCS can affect the magnitude of stream function anomalies, although it cannot affect the spatial pattern of atmospheric circulation.

Description: Technical Note: Medium-term morphodynamics in an unprotected sandy beach of the Adriatic Sea Ocean Science Discussions, 12, 1711-1728, 2015 Author(s): M. Postacchini, L. Soldini, C. Lorenzoni, and A. Mancinelli In the recent years attention has been paid to the beach protection by means of soft and hard defenses. Along the Italian coasts of the Adriatic Sea, sandy beaches are the most common landscapes and around 70 % of the Marche-Region coasts (central Adriatic), is protected by defense structures. The longest free-from-obstacle nearshore area in the Region includes the beach of Senigallia, characterized by a multiple barred beach, frequently monitored during the last decades. The bathymetries surveyed in 2006, 2010, 2011, 2012 and 2013 show a good adaptation of the beach to the Dean-type equilibrium profile, though a strong short-/medium-term variability of the wave climate has been observed during the monitored periods. This suggests a slight influence of wave forcing on the long-term profiles, which seems to only depend on the sediment size. Further, the medium-term dynamics of the submerged bars and their geometric features have been related to the wave climate collected by a wave buoy located 40 km off Senigallia during the analyzed temporal windows. An overall interpretation of the complete dynamics, i.e. hydrodynamics (buoy data), sediment characteristics (equilibrium-profile A parameter) and morphodynamics (bathymetric surveys), suggests that the wave climate is fundamental for the morphodynamic changes of the beach in the medium term: waves coming from NNE/ESE are characterized by a larger/smaller steepness and induce seaward/shoreward bar migration, as well as bar smoothing/steepening. Moving southward, the bar dimension increases, while the equilibrium profile suggests a decrease of the sediment size in the submerged beach, this probably due to the presence of both harbor jetty and river mouth North of the investigated area.

Description: The near-inertial variability of meridional overturning circulation in the South China Sea as shown by an eddy-resolving ocean reanalysis Ocean Science Discussions, 12, 2123-2146, 2015 Author(s): J. Xiao, D. Wang, Q. Xie, Y. Shu, C. Liu, and J. Chen The near-inertial variability of the meridional overturning circulation in the South China Sea (SCSMOC) has been analyzed based on a global 1/12° ocean reanalysis. The wavelet analysis and power spectrum of deep SCSMOC time series shows that there is a significant signal in the near-inertial band. The maximum amplitude of the near-inertial signal in the SCSMOC is nearly 4 Sv. The spatial structure of the signal features regularly alternating counterclockwise and clockwise overturning cells. It is also found that the near-inertial signal of SCSMOC mainly originates from the Luzon Strait and propagates equatorward with the speed of 1–3 m s −1 . Further analyses suggest that the near-inertial signal in the SCSMOC is triggered by high-frequency wind variability near the Luzon Strait where geostrophic shear always exists due to Kuroshio intrusion.

Description: Recent transient tracer distributions in the Fram Strait: estimation of anthropogenic carbon content and transport Ocean Science Discussions, 12, 2189-2229, 2015 Author(s): T. Stöven, T. Tanhua, M. Hoppema, and W.-J. von Appen The storage of anthropogenic carbon in the ocean's interior is an important process which modulates the increasing carbon dioxide concentrations in the atmosphere. The polar regions are expected to be net sinks for anthropogenic carbon. Transport estimates of dissolved inorganic carbon and the anthropogenic offset can thus provide information about the magnitude of the corresponding storage processes. Here we present a transient tracer, dissolved inorganic carbon (DIC) and total alkalinity (TA) data set along 78°50′ N sampled in the Fram Strait in 2012. A theory on tracer relationships is introduced which allows for an application of the Inverse Gaussian – Transit Time Distribution (IG-TTD) at high latitudes and the estimation of anthropogenic carbon concentrations. Current velocity measurements along the same section were used to estimate the net flux of DIC and anthropogenic carbon through the Fram Strait. The new theory explains the differences between the theoretical (IG-TTD based) tracer age relationship and the specific tracer age relationship of the field data by saturation effects during water mass formation and/or the deliberate release experiment of SF 6 in the Greenland Sea in 1996 rather than by different mixing or ventilation processes. Based on this assumption, a maximum SF 6 excess of 0.5–0.8 fmol kg −1 was determined in the Fram Strait at intermediate depths (500–1600 m). The anthropogenic carbon concentrations are 50–55 μmol kg −1 in the Atlantic Water/Recirculating Atlantic Water, 40–45 μmol kg −1 in the Polar Surface Water/warm Polar Surface Water and between 10–35 μmol kg −1 in the deeper water layers, with lowest concentrations in the bottom layer. The net DIC and anthropogenic carbon fluxes through the Fram Strait indicate a balanced exchange between the Arctic Ocean and the North Atlantic, although with high uncertainties.

Description: The dynamic connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current Ocean Science Discussions, 12, 2231-2256, 2015 Author(s): E. Lambert, D. Le Bars, and W. P. M. de Ruijter East of Madagascar, wind and surface buoyancy fluxes reinforce each other, leading to frontogenesis, outcrop and an eastward along-front flow: the South Indian Ocean Countercurrent (SICC). In the east the Leeuwin Current (LC) is a unique eastern boundary current which flows poleward along Australia. It is often described as a regional coastal current forced by an off-shore meridional density gradient or a sea surface slope, yet little is known of the forcing and dynamics that control these open ocean meridional gadients. To complete this understanding, we make use of both an ocean general circulation model and a conceptual two-layer model. The SICC impinges on west Australia and adds to a sea level slope and a southward geostrophic coastal jet: the Leeuwin Current. The SICC and the LC are thus dynamically connected. An observed transport maximum of the LC around 22° S is directly related to this impingement of the SICC. The circulation of the Indonesian Throughflow (ITF) through the Indian Ocean appears to be partly trapped in the upper layer north of the outcrop line and is redirected along this outcrop line to join the eastward flow of the SICC. Shutdown of the ITF in both models strongly decreases the Leeuwin Current transport and breaks the connection between the LC and SICC. In this case, most of the SICC was found to reconnect to the internal gyre circulation in the Indian Ocean. The Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current are thus dynamically coupled.

Description: Impact of vertical and horizontal advection on nutrient distribution in the South East Pacific Ocean Science Discussions, 12, 2257-2281, 2015 Author(s): B. Barceló-Llull, E. Mason, and A. Pascual An innovative approach is used to analyse the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the distribution of a passive nutrient tracer (nitrate) in the South East Pacific. Twelve years of vertical and horizontal currents are derived from an observation-based estimate of the ocean state. Horizontal velocities are obtained through application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG Omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents are coincident, with peaks in austral summer (November–December) in accord with published observations. Two ensembles of Lagrangian particle tracking experiments that differ according to vertical forcing ( w = w QG vs. w = 0) enable a quantitative analysis of the impact of the vertical velocity. From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that the impact of vertical advection on nutrient distribution is 30 % of the contribution of horizontal advection. Despite being weaker by a factor of up to 10 −4 than the horizontal currents, vertical velocity is demonstrated to make an important contribution to nutrient distributions in the region of study.

Description: Imprint of external climate forcing on coastal upwelling in past and future climate Ocean Science Discussions, 12, 2899-2930, 2015 Author(s): N. Tim, E. Zorita, B. Hünicke, X. Yi, and K.-C. Emeis The Eastern Boundary Upwelling Systems are the major coastal upwelling regions. The trade winds are driving these upwelling regimes located in the subtropics at the eastern boundary of the Atlantic and Pacific Ocean. Here we analyse the impact of the external climate forcing, e.g. the greenhouse gas concentration, solar activity and volcano eruptions, on these upwelling systems in simulations of ensembles of two Earth System Models. The ensembles contain three simulations for each time period which cover the past millennium (900–1850), the 20th century (1850–2005) and the near future (2006–2100). Using a set of simulations, differing only in their initial conditions, enables us to detect whether the variability is driven internally or externally. Our analysis shows that the variability of the simulated upwelling is to the most driven internally and that there are no significant trends except for the scenario with the most dramatic increase of greenhouse gas concentrations.

Description: Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007–2013 Ocean Science Discussions, 12, 2863-2898, 2015 Author(s): V. Kikas and U. Lips Ferrybox measurements are carried out between Tallinn and Helsinki in the Gulf of Finland (Baltic Sea) in a regular basis since 1997. The system measures autonomously water temperature, salinity, chlorophyll a fluorescence and turbidity and takes water samples for further analyses at a pre-defined time interval. We aimed to show how the Ferrybox technology could be used to study the coastal upwelling events in the Gulf of Finland. Based on the introduced upwelling index and related criterion, 33 coastal upwelling events were identified in May–September 2007–2013. The number of events as well as frequency of their occurrence and intensity, expressed as a sum of daily average temperature deviations in the 20 km wide coastal area, were almost equal near the northern and southern coast. It is shown that the wind impulse needed to generate upwelling events of similar intensity differ between the two coastal areas whereas this difference is related to the average wind forcing in the area. Two types of upwelling events were identified – one characterized by a strong temperature front and the other revealing gradual decrease of temperature from the open to coastal area with maximum temperature deviation close to the shore.

Description: Tidal elevation, current and energy flux in the area between the South China Sea and Java Sea Ocean Science Discussions, 12, 2831-2861, 2015 Author(s): Z. X. Wei, G. H. Fang, R. D. Susanto, T. R. Adi, B. Fan, A. Setiawan, S. J. Li, Y. G. Wang, and X. M. Gao The South China Sea (SCS) and the Java Sea (JS) are connected through the Karimata Strait, Gaspar Strait, and the southern Natuna Sea, where the tides are often used as open boundary condition for tidal simulation in the SCS or Indonesian seas. Tides, tidal currents and tidal energy fluxes of the principle constituents K 1 , O 1 , Q 1 , M 2 , S 2 and N 2 at five stations in this area have been analyzed using in-situ observational data. The results show that the diurnal tides are the dominant constituents in the entire study area. The constituent K 1 has the largest amplitude, exceeding 50 cm, whereas the amplitudes of M 2 are smaller than 5 cm at all stations. The amplitudes of S 2 may exceed M 2 in Karimata and Gaspar Straits. Tidal currents are mostly of rectilinear type in this area. The major semi axis lengths of the diurnal tidal current ellipses are about 10 cm s −1 , and those of the semi-diurnal tidal currents are smaller than 5 cm s −1 . The diurnal tidal energy flows from the SCS to the JS. The semi-diurnal tidal energy flows from the SCS to the JS through the Karimata Strait and the eastern part of the southern Natuna Sea but flows in the opposite direction in the Gaspar Strait and the western part of the southern Natuna Sea. Harmonic analysis of sea level and current observation also suggest that the study area is located in the loop band of the diurnal tidal waves, and in the nodal band of the semi-diurnal tidal waves. Comparisons show that the existing models are basically consistent with the observational results, but further improvements are necessary.

Description: The open boundary equation Ocean Science Discussions, 12, 925-958, 2015 Author(s): D. Diederen, H. H. G. Savenije, and M. Toffolon We present a new equation describing the hydrodynamics in infinitely long tidal channels (i.e., no reflection) under the influence of oceanic forcing. The proposed equation is a simple relationship between partial derivatives of water level and velocity. It is formally derived for a progressive wave in a frictionless, prismatic, tidal channel with a horizontal bed. Assessment of a large number of numerical simulations, where an open boundary condition is posed at a certain distance landward, suggests that it can also be considered accurate in the more natural case of converging estuaries with nonlinear friction and a bed slope. The equation follows from the open boundary condition and is therefore a part of the problem formulation for an infinite tidal channel. This finding provides a practical tool for evaluating tidal wave dynamics, by reconstructing the temporal variation of the velocity based on local observations of the water level, providing a fully local open boundary condition and allowing for local friction calibration.

Description: Shifting momentum balance and frictional adjustment observed over the inner-shelf during a storm Ocean Science Discussions, 12, 897-924, 2015 Author(s): M. Grifoll, A. Aretxabaleta, J. L. Pelegrí, and M. Espino We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a two-peak storm over the Catalan inner-shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with additional measurements at 50 m water depth. At 24 m, as the storm-related wind stress accelerated the flow, velocity increased throughout the water column, resulting in bottom stress starting to become important. The sea level also responded, with the pressure gradient force opposing the wind stress. In particular, during the second wind pulse, there were rapid oscillations in the acceleration and advective terms, apparently reflecting the incapacity of the bottom stress to dissipate the high kinetic energy of the system. The Coriolis and wave induced terms (via radiation stresses) were less important in the momentum balance. The frictional adjustment time scale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. Estimates of the frictional time and Ekman depth confirm the prevailing frictional response at 24 m. The momentum evolution in deeper parts of the shelf (50 m) showed an increase in the Coriolis force at the expense of the frictional term, typical in the transition from the inner to the mid-shelf.

Description: Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements Ocean Science Discussions, 12, 1051-1082, 2015 Author(s): Ø. Kleiv, A. Folkestad, J. Høkedal, K. Sørensen, and E. Aas During four field days in the years 2009–2011, 22 series of measurement were collected in the Inner Oslofjord. The data consist of recordings of spectral sub-surface and above-surface nadir radiances, as well as spectral downward irradiance in air. The studied wavelengths are 351, 400 nm and the 10 former MERIS channels in the range 413–754 nm. The water-leaving radiance and the reflected radiance at the sea surface can be determined from the measured nadir radiances in water and air. A simpler and much faster method, which determines the radiance reflectance at the surface as well as the water-leaving and reflected radiances solely from the measurements of upward nadir radiance and downward irradiance in air, is presented. A comparison between the quantities determined by the two methods shows that the average relative deviations between their results are less than or equal to 15% for the reflected radiance, at the studied wavelengths. The average relative deviations of the water-leaving radiance at 560 nm is 24%. We consider this to be acceptable uncertainties for a first check of satellite products in coastal waters.

Description: First year of the new Arctic AWIPEV-COSYNA cabled Underwater Observatory in Kongsfjorden, Spitsbergen Philipp Fischer, Max Schwanitz, Reiner Loth, Uwe Posner, Markus Brand, and Friedhelm Schröder Ocean Sci. Discuss., doi:10.5194/os-2016-52,2016 Manuscript under review for OS (discussion: open, 0 comments) We observed oceanographic and community data from October 2013 to November 2014 in the shallow waters of Kongsfjorden on the west coast of Svalbard (Norway) using remote controlled hydrographic and optic sensors. Daily vertical profiles of temperature, salinity and turbidity were sampled together with stereo images of the macrobiotic community, including fish. A distinct seasonal cycle in total species abundances was found with surprisingly high animal counts during the polar winter.

Description: Comparison of the simulated upper-ocean vertical structure using 1-dimensional mixed-layer models Sonaljit Mukherjee and Amit Tandon Ocean Sci. Discuss., doi:10.5194/os-2016-45,2016 Manuscript under review for OS (discussion: open, 0 comments) Atmospheric fluxes influence the momentum and scalar properties in the upper-cean. Buoyancy fluxes result in a diurnal variability in the sea-surface temperature (SST), whereas the wind stress forms near-inertial currents in the mixed layer (ML). In this study, we investigate the contrasts between the simulated SST and the vertical structure of the temperature and shear by three different mixing models: the PWP bulk mixed-layer model, the KPP non-local boundary layer model and the κ−ϵ local mixing model. We choose two upper-ocean datasets for our studies, namely the SWAPP (1990) and the MLML (1991). The SWAPP dataset shows the presence of strong near-inertial shear below the ML and negligible near-inertial shear within the ML. The MLML dataset shows a negligible rise in the SST during the first 22 day mixing phase, which is followed by a steep rise by 6 °C during the subsequent 75 day restratification phase. Comparison with the SWAPP dataset shows that the KPP and κ−ϵ models form strong shear near the surface due to weak eddy viscosities, thus producing a thin shear layer over the entire range of frequencies in the wind stress. At the ML base, the models form an inertial and a diurnal maximum. The inertial maximum extends over a substantial range of depths, and is continuous for the κ−ϵ model but discontinuous for the KPP and PWP models. Comparison with the MLML dataset reveals that the KPP yields the largest SST amplitude over a 24-hour diurnal cycle, and is followed by the κ−ϵ and PWP. However, the net warming of SST at the end of the diurnal cycle is stronger for the PWP compared to κ−ϵ and KPP. The PWP also forms stronger temperature gradients at the ML base compared to κ−ϵ and KPP. Over multiple diurnal cycles, the shallowing and deepening of the mixed layer results in multiple sharp temperature gradients in PWP, thus forming a serrated vertical profile that remains unaffected during the restratification phase of the MLML dataset.

Description: Aragonite saturation states and pH in western Norwegian fjords: seasonal cycles and controlling factors, 2005–2009 Abdirahman M. Omar, Ingunn Skjelvan, Svein Rune Erga, and Are Olsen Ocean Sci., 12, 937-951, doi:10.5194/os-12-937-2016, 2016 We have determined, for the first time, the seasonal changes and controlling processes of ocean acidification parameters across western Norwegian fjords, based on data obtained mainly with sensors on board a commercial ship, MS Trans Carrier , in 2005–2009. The study fills an important gap in our knowledge on ocean acidification in western Norwegian fjords, which are important ecosystems: important recreation areas, marine pathways, spawning grounds for different fish species, etc.

Description: Observed and simulated full-depth ocean heat-content changes for 1970–2005 Lijing Cheng, Kevin E. Trenberth, Matthew D. Palmer, Jiang Zhu, and John P. Abraham Ocean Sci., 12, 925-935, doi:10.5194/os-12-925-2016, 2016 A new method of observing ocean heat content throughout the entire ocean depth is provided. The new method is compared with simulated ocean heat content changes from climate models. The comparisons are carried out in various depth layers of the ocean waters. It is found that there is excellent agreement between the models and the observations. Furthermore, we propose that changes to ocean heat content be used as a fundamental metric to evaluate climate models.

Description: Accessing diverse data comprehensively – CODM, the COSYNA data portal Gisbert Breitbach, Hajo Krasemann, Daniel Behr, Steffen Beringer, Uwe Lange, Nhan Vo, and Friedhelm Schroeder Ocean Sci., 12, 909-923, doi:10.5194/os-12-909-2016, 2016 The coastal observation system COSYNA aims to describe the physical and biogeochemical state of a regional coastal system. The COSYNA data management (CODM) is the link between observations, model results and data usage. The challenge for CODM is the integration of diverse data sources in terms of parameters, dimensionality and observation methods to gain a comprehensive view of the observations. How this is achieved is described in the paper.

Description: Freshening of Antarctic Intermediate Water in the South Atlantic Ocean in 2005–2014 Wenjun Yao and Jiuxin Shi Ocean Sci. Discuss., doi:10.5194/os-2016-54,2016 Manuscript under review for OS (discussion: open, 0 comments) Antarctic Intermediate Water (AAIW) in the South Atlantic Ocean has experienced basin-scaled freshening from 2005 to 2014, reflected by the Argo gridded products. Two zonal sections of WOCE observation also revealed a similar quasi-decadal signal. Our analysis revealed that such freshening was induced by the contemporaneous freshwater input in the AAIW ventilation region and the reduced more saline water carried by Agulhas Leakage.

Description: Changes in extreme regional sea level under global warming S.-E. Brunnabend, H. A. Dijkstra, M. A. Kliphuis, H. E. Bal, F. Seinstra, B. van Werkhoven, J. Maassen, and M. van Meersbergen Ocean Sci. Discuss., doi:10.5194/os-2016-57,2016 Manuscript under review for OS (discussion: open, 0 comments) An important contribution to future changes in regional sea level extremes is due to the changes in intrinsic ocean variability, in particular ocean eddies. Here, we study a scenario of future dynamic sea level (DSL) extremes using a strongly eddying version of the Parallel Ocean Program. Changes in 10-year return time DSL extremes are very inhomogeneous over the globe and are related to changes in ocean currents and corresponding regional shifts in ocean eddy pathways.

Description: A stable Faroe Bank Channel overflow 1995–2015 Bogi Hansen, Karin Margretha Húsgarð Larsen, Hjálmar Hátún, and Svein Østerhus Ocean Sci. Discuss., doi:10.5194/os-2016-56,2016 Manuscript under review for OS (discussion: open, 0 comments) The Faroe Bank Channel is one of the main passages for the flow of cold dense water from the Arctic into the depths of the World Ocean where it feeds the deep branch of the AMOC transporting heat and carbon dioxide from the atmosphere into the deep ocean. Based on in situ measurements we show that the volume transport of this flow has been stable from 1995 to 2015. The water has warmed, but has not become less dense. Thus, this branch of the AMOC did not weaken during the last two decades.

Description: GEM: A Dynamic Tracking Model for Mesoscale Eddies in the Ocean Qiu-Yang Li, Liang Sun, and Sheng-Fu Lin Ocean Sci. Discuss., doi:10.5194/os-2016-49,2016 Manuscript under review for OS (discussion: open, 0 comments) Genealogical Evolution Model (GEM) is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean. It can distinguish different dynamic processes (e.g., merging and splitting) within a dynamic evolution pattern with a two-dimensional vector. All of the computational steps are linear and do not include iteration. It is very fast and is potentially useful for studying dynamic processes in other related fields, e.g., the dynamics of cyclones in meteorology.

Description: Sub-basin scale sea level budgets from satellite altimetry, Argo floats and satellite gravimetry in the North Atlantic Marcel Kleinherenbrink, Riccardo Riva, and Yu Sun Ocean Sci. Discuss., doi:10.5194/os-2016-50,2016 Manuscript under review for OS (discussion: open, 0 comments) Satellite altimetry measures changes in sea level, while satellite gravimetry measures mass changes and from Argo temperature and salinity profiles one can infer steric sea level. For the first time it is shown that the mass and steric components match in most cases the total sea level measured by altimetry on a sub-basin scale in terms of trend, annual amplitude and interannual variability. We also find that the choice of gravity field filter is essential to close the budget.

Description: Technical note: GODESS – a profiling mooring in the Gotland Basin Ralf D. Prien and Detlef E. Schulz-Bull Ocean Sci., 12, 899-907, doi:10.5194/os-12-899-2016, 2016 A profiling mooring with an interdisciplinary suite of sensors for water depths up to 300 m is described in this note. It can be programmed to take profiles through the water column at set times or intervals and with the standard set of batteries is able to profile about 34 km in total (e.g. 200 profiles of 170 m profiling each). The mooring was designed to observe the dynamics of the redoxcline in the Gotland Basin over periods of up to 3 months.

Description: Evaluation of Peaks-Over-Threshold Method Soheil Saeed Far and Ahmad Khairi Abd. Wahab Ocean Sci. Discuss., doi:10.5194/os-2016-47,2016 Manuscript under review for OS (discussion: open, 0 comments) In this paper, two commonly used extreme value analysis models have been developed (POT and GPD models). Both models use threshold values to censor a range of data. The results of this study show the two models are very sensitive to any changes in threshold value. Moreover, the POT model has shown some imperfections in determining true threshold value and a best fitting distribution function. Two methods were proposed by this paper to deal with the limitations in order to improve the model.

Description: Seiche excitation in a highly stratified fjord of southern Chile: the Reloncaví fjord Manuel I. Castillo, Oscar Pizarro, Nadin Ramirez, and Mario Caceres Ocean Sci. Discuss., doi:10.5194/os-2016-42,2016 Manuscript under review for OS (discussion: open, 0 comments) Here we present the results of an intensive physical oceanography study on the Reloncavi fjord (41.5º S, 72.5º W) focused on the subinertial time-scale. The along-fjord currents presented 3 days oscillations which were consistent with the natural internal period of oscillation of the fjord basin (internal seiche). This oscillation could exexplain more than 44 % of the 3 days variability and contributed levels of kinetic energy as large as the tidal currents.

Description: Marine mammal tracks from two-hydrophone acoustic recordings made with a glider Elizabeth T. Küsel, Tessa Munoz, Martin Siderius, David K. Mellinger, and Sara Heimlich Ocean Sci. Discuss., doi:10.5194/os-2016-48,2016 Manuscript under review for OS (discussion: open, 0 comments) An ocean glider was tested during the REP14-MED experiment off the western coast of the Island of Sardinia as a platform for recording sounds produced by whales and dolphins using two sensors. Sperm whale clicks as well as dolphin clicks and whistles were identified in the recordings. Automatically detected sperm whale clicks were used to estimate animal tracks. Such information is useful for marine mammal density estimation studies that use passive acoustics.

Description: The importance of external climate forcing for the variability and trends of coastal upwelling in past and future climate Nele Tim, Eduardo Zorita, Birgit Hünicke, Xing Yi, and Kay-Christian Emeis Ocean Sci., 12, 807-823, doi:10.5194/os-12-807-2016, 2016 The impact of external climate forcing on the four eastern boundary upwelling systems is investigated for the recent past and future. Under increased radiative forcing, upwelling-favourable winds should strengthen due to unequal heating of land and oceans. However, coastal upwelling simulated in ensembles of climate simulations do not show any imprint of external forcing neither for the past millennium nor for the future, with the exception of the strongest future scenario.

Description: Seasonal, Spring-Neap and Tidal Variation of Hydrodynamics and Water Constituents in the Mouth of the Elbe Estuary, Germany Jens Kappenberg, Michael Berendt, Nino Ohle, Rolf Riethmüller, Dagmar Schuster, and Thomas Strotmann Ocean Sci. Discuss., doi:10.5194/os-2016-7,2016 Manuscript under review for OS (discussion: open, 0 comments) Results of long-term measurements of CTD, current velocity, turbidity, and dissolved oxygen from three stations in the mouth of the Elbe Estuary in northern Germany are presented for the period of 2012 and 2013. The focus is on a station named HPA-Elbe 1, which is part of the COSYNA coastal observing system for northern and arctic seas, but data from two neighbouring stations are also presented for comparison and to bridge gaps in the time-series of HPA-Elbe 1. The variations of the variables exhibit distinct tidal patterns related to the longitudinal estuarine gradients of the water constituents and local sediment dynamics. On longer time-scales, spring-neap variability is observed, most prominently in the hydrodynamics. On the seasonal scale, the water temperature influences the degradation processes, which deplete the dissolved oxygen on the one hand and increase the oxygen contents by biological respiration on the other hand. Freshwater events from the catchment play an important role for sediment dynamics and mixing of riverine and coastal waters in the brackish water reach of the estuary. The periods of the deployment of the stations comprise the severest river flood observed so far in the Elbe in June 2013. The effects of the flood at the stations and along the estuary consist of a rapid flushing of the mixing zone and the turbidity maximum to the outer estuary and the transition to freshwater conditions from Hamburg to the mouth at Cuxhaven. The impact of the river flood at the stations is more pronounced in changes in salinity than in turbidity. The restoration of estuarine salinity and turbidity values comparable to those before the river flood took several months.

Description: Ocean Forecasting: From Regional to Coastal Scales Emil V. Stanev, Johannes Schulz-Stellenfleth, Joanna Staneva, Sebastian Grayek, Sebastian Grashorn, Arno Behrens, Wolfgang Koch, and Johannes Pein Ocean Sci. Discuss., doi:10.5194/os-2016-25,2016 Manuscript under review for OS (discussion: open, 0 comments) This paper describes coastal ocean forecasting practices exemplified for the North and Baltic Sea. It identifies new challenges, most of which are associated with the non-linear behavior of coastal ocean. It describes assimilation of remote sensing, in situ and HF radar data, prediction of wind waves and storm surges, as well as possible applications to search and rescue operations, and modelling support for assessing the environmental impact of wind parks. Concepts for seamless approaches to li

Description: A possibility of large scale intrusions generation in the Arctic Ocean under stable-stable stratification: an analytical consideration Natalia Kuzmina Ocean Sci. Discuss., doi:10.5194/os-2016-15,2016 Manuscript under review for OS (discussion: open, 0 comments) Some analytical solutions are found for the problem of three-dimensional instability of a weak geostrophic flow with linear velocity shear taking into account vertical diffusion of buoyancy. The analysis is based on the potential vorticity equation in a long-wave approximation when the horizontal scale of disturbances is taken to be much larger than the local baroclinic Rossby radius. It is hypothesized that the solutions found can be applied to describe stable and unstable disturbances on a planetary scale with respect, especially, to the Arctic Basin, where weak baroclinic fronts with typical temporal variability periods of the order of several years or more are observed and the beta-effect is negligible. Stable (decaying with time) solutions describe disturbances that, in contrast to the Rossby waves, can propagate to both the west and east, depending on the sign of the linear shear of geostrophic velocity. The unstable (growing with time) solutions are applied to describe large-scale intrusions at baroclinic fronts under the stable–stable thermohaline stratification observed in the upper layer of the Polar Deep Water in the Eurasian Basin. The proposed description of intrusive layering can be considered as a possible alternative to the mechanism of interleaving due to the differential mixing.

Description: Current temporal asymmetry and the role of tides: Nan-Wan Bay vs. the Gulf of Elat Yosef Ashkenazy, Erick Fredj, Hezi Gildor, Gwo-Ching Gong, and Hung-Jen Lee Ocean Sci., 12, 733-742, doi:10.5194/os-12-733-2016, 2016 Nan-Wan Bay in Taiwan and the Gulf of Elat in Israel are two different coastal environments, and as such, their currents are expected to have different statistical properties. We find that in spite of these differences, the statistical properties of the surface currents are similar in both basins. Still, surface currents are temporally asymmetric in Nan-Wan but not in Elat; we attribute this difference to the strong tides that exist in Nan-Wan but not in Elat.

Description: Developing European operational oceanography for Blue Growth, climate change adaptation and mitigation, and ecosystem-based management Jun She, Icarus Allen, Erik Buch, Alessandro Crise, Johnny A. Johannessen, Pierre-Yves Le Traon, Urmas Lips, Glenn Nolan, Nadia Pinardi, Jan H. Reißmann, John Siddorn, Emil Stanev, and Henning Wehde Ocean Sci., 12, 953-976, doi:10.5194/os-12-953-2016, 2016 This white paper addresses key scientific challenges and research priorities for the development of operational oceanography in Europe for the next 5–10 years. Knowledge gaps and deficiencies are identified in relation to common scientific challenges in four EuroGOOS knowledge areas: European ocean observations, modelling and forecasting technology, coastal operational oceanography, and operational ecology.

Description: Accelerated sea level rise and Florida Current transport Ocean Science Discussions, 12, 551-572, 2015 Author(s): J. Park and W. Sweet The Florida Current is the headwater of the Gulf Stream and is a component of the North Atlantic western boundary current from which a geostrophic balance between sea surface height and mass transport directly influence coastal sea levels along the Florida Straits. A linear regression of daily Florida Current transport estimates does not find a significant change in transport over the last decade, however, a nonlinear trend extracted from empirical mode decomposition suggests a 3 Sv decline in mean transport. This decline is consistent with observed tide gauge records in Florida Bay and the Straits, all exhibiting an acceleration of mean sea level rise over the decade. It is not known whether this recent change represents natural variability or the onset of the anticipated secular decline in Atlantic meridional overturning circulation, nonetheless, such changes have direct impacts on the sensitive ecological systems of the Everglades as well as the climate of western Europe and eastern North America.

Description: Simulation of tsunami generation, propagation and coastal inundation in the Eastern Mediterranean Ocean Science Discussions, 12, 673-699, 2015 Author(s): A. G. Samaras, T. V. Karambas, and R. Archetti In the present work, an advanced tsunami generation, propagation and coastal inundation 2-DH model (i.e. 2-D Horizontal model) based on the higher-order Boussinesq equations – developed by the authors – is applied to simulate representative earthquake-induced tsunami scenarios in the Eastern Mediterranean. Two areas of interest were selected after evaluating tsunamigenic zones and possible sources in the region: one at the Southwest of the island of Crete in Greece and one at the East of the island of Sicily in Italy. Model results are presented in the form of extreme water elevation maps, sequences of snapshots of water elevation during the propagation of the tsunamis, and inundation maps of the studied low-lying coastal areas. This work marks one of the first successful applications of a fully nonlinear model for the 2-DH simulation of tsunami-induced coastal inundation; acquired results are indicative of the model's capabilities, as well of how areas in the Eastern Mediterranean would be affected by eventual larger events.

Description: The RADMED monitoring program: towards an ecosystem approach Ocean Science Discussions, 12, 645-671, 2015 Author(s): J. L. López-Jurado, R. Balbín, B. Amengual, A. Aparicio-González, M. L. Fernández de Puelles, M. C. García-Martínez, M. Gazá, J. Jansá, A. Morillas-Kieffer, F. Moyá, R. Santiago, M. Serra, M. Vargas-Yáñez, and L. Vicente In the Western Mediterranean, the IEO-RADMED monitoring program is already conducting many of the evaluations required under the Marine Strategy Framework Directive (MFSD) along the Spanish Mediterranean coast. The different aspects of the ecosystem that are regularly sampled under this monitoring program are the physical environment and the chemical and biological variables of the water column, together with the planktonic communities, biomass and structure. Moreover, determinations of some anthropogenic stressors on the marine environment, as contaminants and microplastics, are under develop. Data are managed and stored at the IEO Data Center that works under the SeaDataNet infrastructure and are also stored under the IBAMar database. In combination with remote sensing data they are used to address open questions on the ecosystem in the Western Mediterranean sea.

Description: Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution Ocean Science Discussions, 12, 573-644, 2015 Author(s): T. S. Kostadinov, S. Milutinović, I. Marinov, and A. Cabré Owing to their important roles in biogeochemical cycles, phytoplankton functional types (PFTs) have been the aim of an increasing number of ocean color algorithms. Yet, none of the existing methods are based on phytoplankton carbon (C) biomass, which is a fundamental biogeochemical and ecological variable and the "unit of accounting" in Earth System models. We present a novel bio-optical algorithm to retrieve size-partitioned phytoplankton carbon from ocean color satellite data. The algorithm is based on existing algorithms to estimate particle volume from a power-law particle size distribution (PSD). Volume is converted to carbon concentrations using a compilation of allometric relationships. We quantify absolute and fractional biomass in three PFTs based on size – picophytoplankton (0.5–2 μm in diameter), nanophytoplankton (2–20 μm) and microphytoplankton (20–50 μm). The mean spatial distributions of total phytoplankton C biomass and individual PFTs, derived from global SeaWiFS monthly ocean color data, are consistent with current understanding of oceanic ecosystems, i.e. oligotrophic regions are characterized by low biomass and dominance of picoplankton, whereas eutrophic regions have large biomass to which nanoplankton and microplankton contribute relatively larger fractions. Global spatially integrated phytoplankton carbon biomass standing stock estimates using our PSD-based approach yield on average ~0.2–0.3 Gt of C, consistent with analogous estimates from two other ocean color algorithms, and several state-of-the-art Earth System models. However, the range of phytoplankton C biomass spatial variability globally is larger than estimated by any other models considered here, because the PSD-based algorithm is not a priori empirically constrained and introduces improvement over the assumptions of the other approaches. Satisfactory in situ closure observed between PSD and POC measurements lends support to the theoretical basis of the PSD-based algorithm. Uncertainty budget analyses indicate that absolute carbon concentration uncertainties are driven by the PSD parameter N o which determines particle number concentration to first order, while uncertainties in PFTs' fractional contributions to total C biomass are mostly due to the allometric coefficients.

Description: Sea level budget over 2005–2013: missing contributions and data errors Ocean Science Discussions, 12, 701-734, 2015 Author(s): H. B. Dieng, A. Cazenave, K. von Schuckmann, M. Ablain, and B. Meyssignac Based on the sea level budget closure approach, this study investigates the residuals between observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass) for the period January 2005 to December 2013. The objective is to identify the impact of errors in one or several components of the sea level budget on the residual time series. This is a key issue if we want to constrain missing contributions such as the contribution to sea level rise from the deep ocean (〉 2000m). For that purpose, we use several data sets as processed by different groups: six altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric sea level and three GRACE-based ocean mass products. We find that over the study time span, the observed trend differences in the residuals of the sea level budget can be as large as ~0.55mm yr −1 . These trend differences essentially result from the processing of the altimetry data (e.g., choice the geophysical corrections and method of averaging the along-track altimetry data). At short time scale (from sub-seasonal to multi-annual), residual anomalies are significantly correlated with ocean mass and steric sea level anomalies (depending on the time span), indicating that the residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric data. Efforts are needed to reduce these various sources of errors before using the sea level budget approach to estimate missing contributions such as the deep ocean heat content.

Description: Effects of surface current/wind interaction in an eddy-rich general ocean circulation simulation of the Baltic Sea H. Dietze and U. Löptien Ocean Sci. Discuss., doi:10.5194/os-2016-12,2016 Manuscript under review for OS (discussion: open, 0 comments) Winds blowing over the ocean drive ocean currents. The oceanic response to winds is, in turn, influenced by ocean currents. Theoretical considerations suggest that the latter effect is especially pronounced in the Baltic Sea where the spatial scale of current variability is much smaller than in the open ocean. The study presented here puts theses theoretical considerations in a high-resolution ocean circulation model of the Baltic Sea to the test.

Description: Turbulent heat transfer as a control of platelet ice growth in supercooled under-ice ocean boundary layers Miles G. McPhee, Craig L. Stevens, Inga J. Smith, and Natalie J. Robinson Ocean Sci., 12, 507-515, doi:10.5194/os-12-507-2016, 2016 Measurements of turbulent heat fluxes in tidally modulated flow of supercool seawater under Antarctic land-fast sea ice show that turbulent heat exchange at the ocean–ice boundary is characterized by the product of friction velocity and (negative) water temperature departure from freezing. Also, the conditions cause platelet ice growth to form on the underside of the sea ice which increases the hydraulic roughness (drag) of fast ice compared to ice without platelets.

Description: Indian Ocean Dipole modulated wave climate of eastern Arabian Sea T. R. Anoop, V. Sanil Kumar, P. R. Shanas, J. Glejin, and M. M. Amrutha Ocean Sci., 12, 369-378, doi:10.5194/os-12-369-2016, 2016 Using measured, modeled and reanalysis wave data and reanalysis wind data, we show that the Indian Ocean Dipole (IOD) plays a role in the variability of wave climate of the eastern Arabian Sea (AS). The change in wind field over the AS due to IOD influences the generation or dissipation of wave field and hence causes the decrease in northwest short period waves during positive IOD and increase during negative IOD.

Description: IEOOS: the Spanish Institute of Oceanography Observing System Elena Tel, Rosa Balbin, Jose-Manuel Cabanas, Maria-Jesus Garcia, M. Carmen Garcia-Martinez, Cesar Gonzalez-Pola, Alicia Lavin, Jose-Luis Lopez-Jurado, Carmen Rodriguez, Manuel Ruiz-Villarreal, Ricardo F. Sánchez-Leal, Manuel Vargas-Yáñez, and Pedro Vélez-Belchí Ocean Sci., 12, 345-353, doi:10.5194/os-12-345-2016, 2016 The Spanish Institute of Oceanography supports different operational programmes in order to observe and measure ocean characteristics. Their combination allows responses to ocean research activities and marine ecosystem management, as well as official agency requirements and industrial and main society demands. All these networks are linked to international initiatives, framed largely in supranational Earth observation sponsored by the United Nations and the European Union.

Description: Current temporal asymmetry and the role of tides: Nan-Wan Bay vs. the Gulf of Elat Yosef Ashkenazy, Erick Fredj, Hezi Gildor, Gwo-Ching Gong, and Hung-Jen Lee Ocean Sci. Discuss., doi:10.5194/os-2016-8,2016 Manuscript under review for OS (discussion: open, 0 comments) Nan-Wan Bay in Taiwan and the Gulf of Elat in Israel are two different coastal environments, and as such, their currents are expected to have different statistical properties. We find that in spite of these differences, the statistical properties of the surface currents are similar in both basins. Still, surface currents are temporally asymmetric in Nan-Wan but not in Elat; we attribute this difference to the strong tides that exist in Nan-Wan but not in Elat.

Description: Transition to El Niño conditions in the eastern tropical Pacific in October 2015 Lothar Stramma, Tim Fischer, Damian S. Grundle, Gerd Krahmann, Hermann W. Bange, and Christa A. Marandino Ocean Sci. Discuss., doi:10.5194/os-2016-14,2016 Manuscript under review for OS (discussion: open, 0 comments) Results from a research cruise on RV Sonne to the eastern tropical Pacific in October 2015 during the 2015–2016 El Niño show the transition of current, hydrographic and nutrient conditions to El Niño conditions in the eastern tropical Pacific in October 2015. Although in early 2015 the El Niño was strong and in October 2015 showed a clear El Niño influence on the EUC, in the eastern tropical Pacific the measurements only showed developing El Niño water mass distributions.

Description: Jason continuity of services: continuing the Jason altimeter data records as Copernicus Sentinel-6 Remko Scharroo, Hans Bonekamp, Christelle Ponsard, François Parisot, Axel von Engeln, Milen Tahtadjiev, Kristiaan de Vriendt, and François Montagner Ocean Sci., 12, 471-479, doi:10.5194/os-12-471-2016, 2016 The Sentinel-6 mission is proposed as a multi-partner programme to continue the Jason satellite altimeter data services beyond the Jason-2 and Jason-3 missions. The Sentinel-6 mission programme consists of two identical satellites flying in sequence to prolong the climate data record of sea level accumulated by the TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 missions from 2020 to beyond 2030.

Description: Wind changes above warm Agulhas Current eddies M. Rouault, P. Verley, and B. Backeberg Ocean Sci., 12, 495-506, doi:10.5194/os-12-495-2016, 2016 Our study shows that wind increases of 4 to 8 m s −1 above warm Agulhas Current eddies are not uncommon. This should be taken seriously when sailing in the “Roaring Forties”. Using microwave remote sensing from satellite is a very useful tool for monitoring such eddies. This could be displayed operationally to provide vessels with early warning and to indicate where there are likely to sustain stronger wind. The result is also relevant for the Gulf Stream and the Kuroshio Current.

Description: 〈b〉Heat, salt, and volume transports in the eastern Eurasian Basin of the Arctic Ocean from 2 years of mooring observations〈/b〉〈br〉 Andrey V. Pnyushkov, Igor V. Polyakov, Robert Rember, Vladimir V. Ivanov, Matthew B. Alkire, Igor M. Ashik, Till M. Baumann, Genrikh V. Alekseev, and Arild Sundfjord〈br〉 Ocean Sci., 14, 1349-1371, https://doi.org/10.5194/os-14-1349-2018, 2018〈br〉 This study describes along-slope volume, heat, and salt transports derived from observations collected between 2013 and 2015 in the eastern Eurasian Basin of the Arctic Ocean using a cross-slope array of six moorings. Inferred transport estimates may have wide implications and should be considered when assessing high-latitude ocean dynamics.

Description: 〈b〉Do sun spots influence the onset of ENSO and PDO events in the Pacific Ocean?〈/b〉〈br〉 Franklin Isaac Ormaza-González and María Esther Espinoza-Celi〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-125,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Sea surface temperature is affected by sun energy which in turn varies in time due to astronomical factors and sun activity. The activity can be estimated by sun spots (SS). Some oceanographic events like inter-annual El/La Niño/Niña as well as decadal processes should be affected by SS. It was found correlation between SS and various oceanographic indexes in time series from 1954 to 2017. This fact should be considered when dealing and modelling forecasts of such indexes.

Description: 〈b〉Arctic Mediterranean Exchanges: A consistent volume budget and trends in transports from two decades of observations〈/b〉〈br〉 Svein Østerhus, Rebecca Woodgate, Héðinn Valdimarsson, Bill Turrell, Laura de Steur, Detlef Quadfasel, Steffen M. Olsen, Martin Moritz, Craig M. Lee, Karin Margretha H. Larsen, Steingrímur Jónsson, Clare Johnson, Kerstin Jochumsen, Bogi Hansen, Beth Curry, Stuart Cunningham, and Barbara Berx〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-114,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 Two decades of observations of the Arctic Mediterranean (AM) exchanges shows that the exchanges have been stable in terms of volume transport during a period when many other components of the global climate system have changed. The total AM-import is found to be 9.1 Sv and has a seasonal variation of amplitude close to 17 Sv and maximum import in October. Roughly one third of the imported water leaves the AM as surface outflow with the remain two thirds leaving.

Description: 〈b〉A simple predictive model for the eddy propagation trajectory in the South China Sea〈/b〉〈br〉 Jiaxun Li, Guihua Wang, Huijie Xue, and Huizan Wang〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-116,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 A novel predictive model is built for eddy propagation trajectory using the multiple linear regression method. This simple model has related various oceanic parameters to eddy propagation position changes in the South China Sea (SCS). The performance of the proposed model is examined in the SCS based on twenty years of satellite altimeter data, and demonstrates its significant forecast skills over a 4-week forecast window comparing to the traditional persistence method.

Description: 〈b〉Predicting Ocean Waves along the U.S. East Coast During Energetic Winter Storms: sensitivity to Whitecapping parameterizations〈/b〉〈br〉 Mohammad Nabi Allahdadi, Ruoying He, and Vincent S. Neary〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-112,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 2 comments)〈br〉 Dissipation of ocean waves due to Whitecapping is one of the most important processes that affect generation of gravity waves by wind. Different behavior of traditional approaches used for quantifying Whitecapping dissipation under different wave conditions has always been a challenge to choose the most appropriate approach for a given area. The present paper examines the performance of two popular Whitecapping approaches incorporated in SWAN during the winter storms along the U.S East Coast.

Description: 〈b〉Contribution of future wide-swath altimetry missions to ocean analysis and forecasting〈/b〉〈br〉 Antonio Bonaduce, Mounir Benkiran, Elisabeth Remy, Pierre Yves Le Traon, and Gilles Garric〈br〉 Ocean Sci., 14, 1405-1421, https://doi.org/10.5194/os-14-1405-2018, 2018〈br〉 〈p〉The impact of forthcoming wide-swath altimetry missions on the ocean analysis and forecasting system was investigated by means of OSSEs (observing system simulation experiments). These experiments were performed with a regional data assimilation system, implemented in the Iberian–Biscay–Ireland (IBI) region, at 〈span〉1∕12〈/span〉〈span〉〈sup〉∘〈/sup〉〈/span〉 resolution using simulated observations derived from a fully eddy-resolving free simulation at 〈span〉1∕36〈/span〉〈span〉〈sup〉∘〈/sup〉〈/span〉 resolution over the same region. The objective of the experiments was to assess the ability of different satellite constellations to constrain the ocean analyses and forecasts, considering both along-track altimeters and future wide-swath missions; consequently, the capability of the data assimilation techniques used in the Mercator Ocean operational system to effectively combine the different kinds of measurements was also investigated. These assessments were carried out as part of a European Space Agency (ESA) study on the potential role of wide-swath altimetry in future versions of the European Union Copernicus programme. The impact of future wide-swath altimetry data is evident for investigating the reliability of sea level values in OSSEs. The most significant results were obtained when looking at the sensitivity of the system to wide-swath instrumental error: considering a constellation of three nadir and two “accurate” (small instrumental error) wide-swath altimeters, the error in ocean analysis was reduced by up to 50 % compared to conventional altimeters. Investigating the impact of the repetitivity of the future measurements, the results showed that two wide-swath missions had a major impact on sea-level forecasting – increasing the accuracy over the entire time window of the 5-day forecasts – compared with a single wide-swath instrument. A spectral analysis underlined that the contributions of wide-swath altimetry data observed in ocean analyses and forecast statistics were mainly due to the more accurate resolution, compared with along-track data, of ocean variability at spatial scales smaller than 100 km. Considering the ocean currents, the results confirmed that the information provided by wide-swath measurements at the surface is propagated down the water column and has a considerable impact (30 %) on ocean currents (up to a depth of 300 m), compared with the present constellation of altimeters. The ocean analysis and forecasting systems used here are those currently used by the Copernicus Marine Environment and Monitoring Service (CMEMS) to provide operational services and ocean reanalysis. The results obtained in the OSSEs considering along-track altimeters were consistent with those derived from real data (observing system experiments, OSEs). OSSEs can also be used to assess the potential of new observing systems, and in this study the results showed that future constellations of altimeters will have a major impact on constraining the CMEMS ocean analysis and forecasting systems and their applications.〈/p〉

Description: 〈b〉Cold vs. warm water route – sources for the upper limb of the AMOC revisited in a high-resolution ocean model〈/b〉〈br〉 Siren Rühs, Franziska U. Schwarzkopf, Sabrina Speich, and Arne Biastoch〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-134,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 We revisit the sources for the upper limb of the overturning circulation in the South Atlantic by tracking fluid particles in a high-resolution ocean model. Our results suggest that the upper limb’s transport is dominantly supplied by waters with Indian Ocean origin, but the contribution of waters with Pacific origin is substantially larger than previously estimated with coarse-resolution models. Yet, a large part of upper limb waters get their thermohaline properties within the South Atlantic.

Description: 〈b〉A multiscale ocean data assimilation approach combining spatial and spectral localisation〈/b〉〈br〉 Ann-Sophie Tissier, Jean-Michel Brankart, Charles-Emmanuel Testut, Giovanni Ruggiero, Emmanuel Cosme, and Pierre Brasseur〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-132,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 2 comments)〈br〉 To better exploit the observational information available for all scales in data assimilation systems, we investigate a new method to introduce scale separation in the algorithm. It consists in carrying out the analysis with spectral localisation for the large scales and spatial localisation for the residual scales. The performance is then checked explicitly and separately for all scales. Results show that accuracy can be improved for the large scales while preserving reliability at all scales.

Description: 〈b〉What can seabirds tell us about the tide?〈/b〉〈br〉 Matthew Cooper, Charles Bishop, Matthew Lewis, David Bowers, Mark Bolton, Ellie Owen, and Stephen Dodd〈br〉 Ocean Sci., 14, 1483-1490, https://doi.org/10.5194/os-14-1483-2018, 2018〈br〉 This paper describes a feasibility study carried out to determine if information gathered for one discipline could be 〈q〉repurposed〈/q〉 to provide insight in another. Data gathered during a study of bird distribution were used to investigate whether these same data could be used to measure tidal current velocities and direction. The paper concludes that there is potential to use GPS-tagged birds as 〈q〉drifters of opportunity〈/q〉 and that interdisciplinary sharing of data can provide additional insight.

Description: 〈b〉Hybrid improved EMD-BPNN model for the prediction of sea surface temperature〈/b〉〈br〉 Zhiyuan Wu, Changbo Jiang, Mack Conde, Bin Deng, and Jie Chen〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-101,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 Sea surface temperature (SST) is related to ocean heat content, an important topic in the debate over global warming. In this manuscript, we propose a novel SST predicting method based on the hybrid improved EMD algorithms and BP neural network method. SST prediction results based on the hybrid EEMD-BPNN and CEEMD-BPNN models are compared and discussed. Cases study of SST in the North Pacific shows that the proposed hybrid CEEMD-BPNN model can effectively predict the time-series SST.

Description: 〈b〉Modelling study of transformations of the exchange flows along the Strait of Gibraltar〈/b〉〈br〉 Antonio Sanchez-Roman, Gabriel Jorda, Gianmaria Sannino, and Damia Gomis〈br〉 Ocean Sci., 14, 1547-1566, https://doi.org/10.5194/os-14-1547-2018, 2018〈br〉 We explore the vertical transfers of heat, salt and mass between the inflowing and outflowing layers at the Strait of Gibraltar by using a 3-D model with very high spatial resolution that allows for a realistic representation of the exchange. Results show a significant transformation of the water mass properties along their path through the strait, mainly induced by the recirculation of water between layers, while mixing seems to have little influence on the heat and salt exchanged.

Description: 〈b〉The CMEMS GlobColour 〈i〉Chlorophyll-a〈/i〉 Product Based on Satellite Observation〈/b〉〈br〉 Philippe Garnesson, Antoine Mangin, Odile Fanton d'Andon, Julien Demaria, and Marine Bretagnon〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-155,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉This work concerns the chlorophyll products based on Satellite Observation and disseminated in the frame of the Copernicus Marine Environmental Monitoring Service (CMEMS).〈/p〉 〈p〉 This work highlights the main advantages provided by the Copernicus Globcolour processor which is used to serve the CMEMS with a long time series from 1997 to present with level 3 & 4 products at Global level (4 km of spatial resolution) and for the Atlantic level 4 product (1 km).〈/p〉 〈p〉 It discusses the different ways to merge data coming from different sensors and it is shown that the GlobColour processor approach provide a better flexibility. At present, it is the only one CMEMS processor able to ingest the OLCI-S3A in the merged product (OLCI-S3A data are ingested in the operational CMEMS products since the April 2018 release).〈/p〉 〈p〉 Behind the merging, the flagging strategy to go from level 2 provided by spatial agencies to the level 3 CMEMS products is also discussed. A better spatial coverage is demonstrated, including the coastal area which is of particular interest for many users involved in the EU Water Framework and Marine Strategy Framework Directive.〈/p〉

Description: 〈b〉The effect of vertical mixing on the horizontal drift of oil spills〈/b〉〈br〉 Johannes Röhrs, Knut-Frode Dagestad, Helene Asbjørnsen, Tor Nordam, Jørgen Skancke, Cathleen E. Jones, and Camilla Brekke〈br〉 Ocean Sci., 14, 1581-1601, https://doi.org/10.5194/os-14-1581-2018, 2018〈br〉 Simulations of hypothetical oil spills are presented to investigate how the vertical mixing of oil affects transport towards various directions. It is shown that the horizontal transport of oil greatly varies for different oil types and weather conditions. These differences are a consequence of the entrainment of oil from the surface into the ocean. While oil spills often get entrained into the water by waves, we show that submerged oil typically resurfaces after a few hours or days.

Description: 〈b〉Hydrography, transport and mixing of the West Spitsbergen Current: the Svalbard Branch in summer 2015〈/b〉〈br〉 Eivind Kolås and Ilker Fer〈br〉 Ocean Sci., 14, 1603-1618, https://doi.org/10.5194/os-14-1603-2018, 2018〈br〉 Measurements of ocean currents, stratification and microstructure collected northwest of Svalbard are used to characterize the evolution of the warm Atlantic current. The measured turbulent heat flux is too small to account for the observed cooling rate of the current. The estimated contribution of diffusion by eddies could be limited to one half of the observed heat loss. Mixing in the bottom boundary layer, driven by cross-slope flow of buoyant water, can be important.

Description: 〈b〉Can wave coupling improve operational regional ocean forecasts for the North-West European Shelf?〈/b〉〈br〉 Huw W. Lewis, Juan Manuel Castillo Sanchez, John Siddorn, Robert R. King, Marina Tonani, Andrew Saulter, Peter Sykes, Anne-Christine Pequignet, Graham P. Weedon, Tamzin Palmer, Joanna Staneva, and Lucy Bricheno〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-148,2018〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Forecasts of ocean temperature, salinity, currents and sea height can be improved by linking state-of-the-art ocean and wave models, so that they can interact to better represent the real world. We test this approach in an ocean model of north-west Europe which can simulate small-scale details of the ocean state. The intention is to implement the system described in this study for operational use so that improved information can be provided to users of ocean forecast data.

Description: On the observability of turbulent transport rates by Argo: supporting evidence from an inversion experiment Ocean Science Discussions, 12, 1107-1143, 2015 Author(s): G. Forget, D. Ferreira, and X. Liang Although estimation of turbulent transport parameters using inverse methods is not new, there is little evaluation of the method in the literature. Here, it is shown that extended observation of the broad scale hydrography by Argo provides a path to improved estimates of regional turbulent transport rates. Results from a 20 year ocean state estimate produced with the ECCO v4 non-linear inverse modeling framework provide supporting evidence. Turbulent transport parameter maps are estimated under the constraints of fitting the extensive collection of Argo profiles collected through 2011. The adjusted parameters dramatically reduce misfits to in situ profiles as compared with earlier ECCO solutions. They also yield a clear reduction in the model drift away from observations over multi-century long simulations, both for assimilated variables (temperature and salinity) and independent variables (bio-geochemical tracers). Despite the minimal constraints imposed specifically on the estimated parameters, their geography is physically plausible and exhibits close connections with the upper ocean ocean stratification as observed by Argo. The estimated parameter adjustments furthermore have first order impacts on upper-ocean stratification and mixed layer depths over 20 years. These results identify the constraint of fitting Argo profiles as an effective observational basis for regional turbulent transport rates. Uncertainties and further improvements of the method are discussed.

Description: How essential are Argo observations to constrain a global ocean data assimilation system? Ocean Science Discussions, 12, 1145-1186, 2015 Author(s): V. Turpin, E. Remy, and P. Y. Le Traon Observing System Experiments (OSEs) are carried out over a one-year period to quantify the impact of Argo observations on the Mercator-Ocean 1/4° global ocean analysis and forecasting system. The reference simulation assimilates sea surface temperature (SST), SSALTO/DUACS altimeter data and Argo and other in situ observations from the Coriolis data center. Two other simulations are carried out where all Argo and half of Argo data sets are withheld. Assimilating Argo observations has a significant impact on analyzed and forecast temperature and salinity fields at different depths. Without Argo data assimilation, large errors occur in analyzed fields as estimated from the differences when compared with in situ observations. For example, in the 0–300 m layer RMS differences between analyzed fields and observations reach 0.25 psu and 1.25 °C in the western boundary currents and 0.1 psu and 0.75 °C in the open ocean. The impact of the Argo data in reducing observation-model forecast error is also significant from the surface down to a depth of 2000 m. Differences between independent observations and forecast fields are thus reduced by 20 % in the upper layers and by up to 40 % at a depth of 2000 m when Argo data are assimilated. At depth, the most impacted regions in the global ocean are the Mediterranean outflow and the Labrador Sea. A significant degradation can be observed when only half of the data are assimilated. All Argo observations thus matter, even with a 1/4° model resolution. The main conclusion is that the performance of global data assimilation systems is heavily dependent on the availability of Argo data.

Description: Accuracy of the mean sea level continuous record with future altimetric missions: Jason-3 vs. Sentinel-3a Ocean Science Discussions, 12, 1511-1536, 2015 Author(s): L. Zawadzki and M. Ablain The current mean sea level (MSL) continuous record, essential for the understanding of climate evolution, is computed with the altimetric measurements of the TOPEX/Poseidon mission, succeeded by Jason-1 and later Jason-2. The accurate continuity of the record is ensured by the conservation of the "historical" TOPEX orbit, but also by calibration phases between the successive missions which enable a rigorous computation of their relative biases. In order to extend the current MSL record, Jason-3 will be the natural successor of Jason-2: on the same orbit with a calibration phase. Shortly after Jason-3, another altimetric climate-oriented mission, Sentinel-3a, will be launched on a different orbit. In this paper, simulated altimetric sea level data is used to study the sensitivity of the MSL continuous record to the change of the "historical" orbit for the new Sentinel-3a orbit. By estimating the impact of the absence of calibration phase on the MSL continuous record trend accuracy at global and regional scale and the impact of the orbit change on the long-term continuity of this MSL record, this study shows that linking Sentinel-3a data instead of Jason-3 to the MSL continuous record would prevent from meeting climate users requirements regarding the MSL trend accuracy.

Description: Seasonal renewal time variability in the Curonian Lagoon caused by atmospheric and hydrographical forcing Ocean Science Discussions, 12, 2043-2072, 2015 Author(s): G. Umgiesser, P. Zemlys, A. Erturk, A. Razinkova-Baziukas, J. Mėžinė, and C. Ferrarin The aim of this study was to investigate the variability of the water exchanges in the Curonian Lagoon based on the hydraulic regime and the atmospheric forcings. A finite element hydrodynamic model has been applied to the Curonian Lagoon to simulate the circulation patterns for ten years. With the help of a transport-diffusion model the salinity distribution and the renewal times of the Curonian Lagoon have been investigated when forced by river runoff, wind and Baltic Sea level fluctuations. The hydrodynamic model has been validated using in situ salinity measurements. Model results show that the variability depends mainly on seasonal changes in hydrographic forcing and on the dominant wind regimes that prevail over the Curonian Lagoon. Exchanges between the southern and the northern part of the lagoon are mostly depended on the wind forcing and are much less influenced by the river discharge. However, when looking at the water renewal time, the most important factor is the river discharge into the lagoon. Other physical forcings are only marginally determining the renewal time, and not even ice cover is able to influence it. Even if ice cover is strongly inhibiting the exchanges between southern and northern lagoon, it is basically not able to change the absolute value of the renewal times.

Description: River bulge evolution and dynamics in a non-tidal sea – Daugava River plume in the Gulf of Riga, Baltic Sea Ocean Science Discussions, 12, 2423-2454, 2015 Author(s): E. Soosaar, I. Maljutenko, R. Uiboupin, M. Skudra, and U. Raudsepp Satellite remote sensing imagery and numerical modelling were used for the study of river bulge evolution and dynamics in a non-tidal sea, the Gulf of Riga (GoR) in the Baltic Sea. Total suspended matter (TSM) images showed a clearly formed anti-cyclonically rotating river bulge from Daugava River discharge during the studied low wind period. In about 7–8 days the bulge grew up to 20 km in diameter, before being diluted. Bulge growth rate was estimated as r b ~ t 0.31± 0.23 ( R 2 = 0.87). A high resolution (horizontal grid step of 125 m) General Estuarine Transport Model (GETM) was used for detailed description of the development of the river plume in the southern GoR over the period when satellite images were acquired. In the model simulation, the r b ~ t 0.5± 0.04 ( R 2 = 0.90). Both the model simulation and the satellite images showed that river water was mainly contained in the bulge and there were numerous intrusions at the outer perimeter of the bulge. We made numerical sensitivity tests with actual bathymetry and measured river runoff without wind forcing: (1) having initial 3-dimensional density distribution, (2) using initially a homogeneous ambient density field. In the first case, the anti-cyclonic bulge did not develop within the course of the model simulation and coastal current was kept offshore due to ambient density-driven circulation. In the second case, the river plume developed steadily into an anti-cyclonically recirculating bulge and a coastal current. This showed a significant effect of the wind in the evolution of the river bulge, even if the wind speed was moderate (3–4 m s −1 ). In the second case, r b ~ t 0.28± 0.01 ( R 2 = 0.98). While previous studies conclude that mid-field bulge region is governed by balance between centrifugal, Coriolis and pressure gradient terms, our study showed that geostrophic balance is valid for the entire mid-field of the bulge. In addition, while there is discharge into the homogenous GoR in case of high inflow Rossby number, the river inflow might split into two jets, with strong mixing zone in-between, in the plume near field region.

Description: Major improvement of altimetry sea level estimations using pressure-derived corrections based on ERA-Interim atmospheric reanalysis Loren Carrere, Yannice Faugère, and Michaël Ablain Ocean Sci., 12, 825-842, doi:10.5194/os-12-825-2016, 2016 New dynamic atmospheric (DAC_ERA) and dry tropospheric (DT_ERA) correction have been computed for the altimeter period using the ERA-Interim meteorological reanalysis. The corrections improve sea level estimations in Southern Ocean and in shallow waters; the impact is the most important for the first decade of altimetry, when operational meteorological models had a weaker quality. DT_ERA remains better in the recent period. New corrections significantly impact long-term regional trends.

Description: Quality assessment of the TOPAZ4 reanalysis in the Arctic over the period 1991–2013 Jiping Xie, Laurent Bertino, Francois Counillon, Knut A. Lisæter, and Pavel Sakov Ocean Sci. Discuss., doi:10.5194/os-2016-38,2016 Manuscript under review for OS (discussion: open, 0 comments) The Arctic Ocean plays an important role in the global climate system, but the concerned interpretation about its changes is severely hampered by the sparseness of the observations of sea ice and ocean. The focus of this study is to provide a quantitative assessment of the performance of the TOPAZ4 reanalysis for ocean and sea ice variables in the pan-Arctic region (north of 63 °N) in order to guide the user about its skills and limitations.

Description: Seabirds as samplers of the marine environment – a case study in Northern Gannets Stefan Garthe, Verena Peschko, Ulrike Kubetzki, and Anna-Marie Corman Ocean Sci. Discuss., doi:10.5194/os-2016-22,2016 Manuscript under review for OS (discussion: open, 0 comments) Understanding distribution patterns, activities, and foraging behaviours of seabirds requires interdisciplinary approaches. In this paper, we provide examples of the data and analytical procedures from a new study in the German Bight, North Sea, tracking Northern Gannets (Morus bassanus) at their breeding colony on the island of Helgoland. Individual adult Northern Gannets were equipped with different types of data loggers for several weeks, measuring geographic positions and other parameters mostly at 3–5 min intervals. Birds flew in all directions from the island to search for food, but most flights targeted areas to the (N)NW of Helgoland. Foraging trips were remarkably variable in duration and distance; most trips lasted 1–15 h and extended from 3–80 km from the breeding colony on Helgoland. Dives of gannets were generally shallow, with more than half of the dives only reaching depths of 1–3 m. The maximum dive depth was 11.4 m. Gannets showed a clear diurnal rhythm in their diving activity, with dives being almost completely restricted to the daylight period. Most flight activity at sea occurred at an altitude between the sea surface and 40 m. Gannets mostly stayed away from the wind farms and passed around them much more frequently than flying through them. Detailed information on individual animals may provide important insights into various processes, based on multi-layer information.

Description: Operational Assimilation of glider temperature and salinity in a mesoscale flow field: Eastern Mediterranean test case Daniel R. Hayes, Srdjan Dobricic, and Hezi Gildor Ocean Sci. Discuss., doi:10.5194/os-2016-43,2016 Manuscript under review for OS (discussion: open, 0 comments) This research has shown that it is possible to estimate ocean currents more accurately when using autonomous underwater glider observations of ocean temperature and salinity in conjunction with numerical ocean current models. This allows offshore activities to be more safely carried out, since currents can transport pollutants or disrupt operations in unpredictable ways. Using only models is not as reliable as using a merged result of observations and models, which can be done in near real time.

Description: An atmosphere-wave regional coupled model: improving predictions of wave heights and surface winds in the Southern North Sea Kathrin Wahle, Joanna Staneva, Wolfgang Koch, Luciana Fenoglio-Marc, Ha T. M. Ho-Hagemann, and Emil V. Stanev Ocean Sci. Discuss., doi:10.5194/os-2016-51,2016 Manuscript under review for OS (discussion: open, 0 comments) Reduction of wave forecasting errors is a challenge especially in dynamically complicated coastal ocean areas as the southern part of the North Sea area. We study the effects of coupling between an atmospheric and a wind wave model. This leads to a reduction of both the surface wind speeds and wave heights and improves the agreement between observations and simulations. The improved skills resulting from the proposed method justifies its implementations for operational and climate studies.

Description: Observed El Niño conditions in the eastern tropical Pacific in October 2015 Lothar Stramma, Tim Fischer, Damian S. Grundle, Gerd Krahmann, Hermann W. Bange, and Christa A. Marandino Ocean Sci., 12, 861-873, doi:10.5194/os-12-861-2016, 2016 Results from a research cruise on R/V Sonne to the eastern tropical Pacific in October 2015 during the 2015–2016 El Niño show the transition of current, hydrographic, and nutrient conditions to El Niño conditions in the eastern tropical Pacific in October 2015. Although in early 2015 the El Niño was strong and in October 2015 showed a clear El Niño influence on the EUC, in the eastern tropical Pacific the measurements only showed developing El Niño water mass distributions.

Description: Effects of surface current–wind interaction in an eddy-rich general ocean circulation simulation of the Baltic Sea Heiner Dietze and Ulrike Löptien Ocean Sci., 12, 977-986, doi:10.5194/os-12-977-2016, 2016 Winds blowing over the ocean drive ocean currents. The oceanic response to winds is, in turn, influenced by ocean currents. Theoretical considerations suggest that the latter effect is especially pronounced in the Baltic Sea. The study presented here puts theses theoretical considerations in a high-resolution ocean circulation model of the Baltic Sea to the test.

Description: Impact of vertical and horizontal advection on nutrient distribution in the southeast Pacific Bàrbara Barceló-Llull, Evan Mason, Arthur Capet, and Ananda Pascual Ocean Sci., 12, 1003-1011, doi:10.5194/os-12-1003-2016, 2016 Vertical velocity in the ocean makes an important contribution to the modulation of marine ecosystems through its impact on fluxes of nutrients and phytoplankton. Here, we estimate full 3-D current velocity fields from an observation-based data product. The 3-D currents are used to force a set of particle-tracking (Lagrangian) experiments. The Lagrangian results show that vertical motions induce local increases in nitrate uptake reaching up to 30 %.

Description: Parameterization of the light absorption properties of chromophoric dissolved organic matter in the Baltic Sea and Pomeranian lakes Justyna Meler, Piotr Kowalczuk, Mirosława Ostrowska, Dariusz Ficek, Monika Zabłocka, and Agnieszka Zdun Ocean Sci., 12, 1013-1032, doi:10.5194/os-12-1013-2016, 2016 Three alternative models for estimation of absorption of chromophoric dissolved organic matter (CDOM) have been formulated. The models were based on empirical database containing measurements from different regions of the Baltic Sea and three Pomeranian lakes in Poland. An assumption regarding continuum of inherent optical properties in marine and estuarine waters and freshwater has been proved and enabled the accurate estimation of CDOM absorption in various environments.

Description: El Niño, La Niña, and the global sea level budge Christopher G. Piecuch and Katherine J. Quinn Ocean Sci. Discuss., doi:10.5194/os-2016-66,2016 Manuscript under review for OS (discussion: open, 0 comments) We use satellite and in situ data to elucidate global-mean sea level (GMSL) changes related to El Niño-Southern Oscillation (ENSO) over 2005–2015. Steric and mass effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize mass contributions. Results exemplify the usefulness of the Global Ocean Observing System for understanding the Earth's radiation imbalance and hydrological cycle.

Description: Characteristics of Global Oceanic Rossby Wave and Mesoscale Eddies Propagation from Multiple Datasets Analysis Yunfan Zhang, Fenglin Tian, and Ge Chen Ocean Sci. Discuss., doi:10.5194/os-2016-64,2016 Manuscript under review for OS (discussion: open, 0 comments) The oceanic rossby wave and mesoscale eddies are widely existed in oceans worldwide. They are closely related to our life as they would more or less affect local or global climate. We present this study to investigate the relationship between the waves and the eddies by using multiple datasets and low-pass filtering method. We have found that the Rossby wave may play an accelerative or moderative role in the eddy propagation, and the results will help us to further understand them.

Description: Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007–2013 Villu Kikas and Urmas Lips Ocean Sci., 12, 843-859, doi:10.5194/os-12-843-2016, 2016 Ferrybox measurements have been carried out between Tallinn and Helsinki in the Gulf of Finland (Baltic Sea) on a regular basis since 1997. The system measures autonomously water temperature, salinity, chlorophyll  a fluorescence and turbidity and takes water samples for further analyses at a predefined time interval. We aimed to show how the Ferrybox technology could be used to study the coastal upwelling events in the Gulf of Finland. Based on the introduced upwelling index and related criteria, 33 coastal upwelling events were identified in May–September 2007–2013. The number of events, as well as the frequency of their occurrence and intensity expressed as a sum of daily average temperature deviations in the 20 km wide coastal area, were almost equal near the northern and southern coasts. Nevertheless, the wind impulse, which was needed to generate upwelling events of similar intensity, differed between the northern and southern coastal areas. It is suggested that the general thermohaline structure adapted to the prevailing forcing and the estuarine character of the basin weaken the upwelling created by the westerly to southwesterly (up-estuary) winds and strengthen the upwelling created by the easterly to northeasterly (down-estuary) winds. Two types of upwelling events were identified – one characterized by a strong temperature front and the other revealing gradual decrease in temperature from the open sea to the coastal area, with maximum temperature deviation close to the shore.

Description: Glider Technology for Ocean Observations: A Review David Meyer Ocean Sci. Discuss., doi:10.5194/os-2016-40,2016 Manuscript under review for OS (discussion: open, 0 comments) This review covers a wide range of topics – from the history and the development of glider technology to its application in a variety of field studies regarding ocean sciences. It offers a comprehensive overview of both, the technical and the scientific dimension, facilitating a fast access to the world of glider. It was shown that glider can be used for very specific research tasks, as well as for common environmental monitoring purposes.

Description: Technical Note: Algal Pigment Index 2 in the Atlantic off the Southwest Iberian Peninsula: standard and regional algorithms Priscila Costa Goela, Sónia Cristina, Tamito Kajiyama, John Icely, Gerald Moore, Bruno Fragoso, and Alice Newton Ocean Sci. Discuss., doi:10.5194/os-2016-41,2016 Manuscript under review for OS (discussion: open, 0 comments) In this study, the MERIS (ocean colour sensor from European Space Agency) algorithm for the quantification of Chlorophylla in coastal waters – API2 – is investigated in an area located in the Atlantic off the southwestern Iberian Peninsula. The study demonstrates the importance of regional algorithms for the study area that could complement upcoming standard results of the present Sentinel-3/OLCI space mission.

Description: Modelling wave–current interactions off the east coast of Scotland Alessandro D. Sabatino, Chris McCaig, Rory B. O'Hara Murray, and Michael R. Heath Ocean Sci., 12, 875-897, doi:10.5194/os-12-875-2016, 2016 The present research describes the effect of wave–current interactions and wave–wave interactions during severe storms on the east coast of Scotland. In this area, results show that the currents contribute substantially to the modification of wave properties in the shallow coastal areas, while the wave–wave interactions are more important offshore.

Description: Effects of lateral processes on the seasonal water stratification of the Gulf of Finland: 3-D NEMO-based model study Roman E. Vankevich, Ekaterina V. Sofina, Tatiana E. Eremina, Vladimir A. Ryabchenko, Mikhail S. Molchanov, and Alexey V. Isaev Ocean Sci., 12, 987-1001, doi:10.5194/os-12-987-2016, 2016 This paper aims to fill the gaps in knowledge of processes affecting the seasonal water stratification in the Gulf of Finland (GOF). We used a state-of-the-art modelling framework NEMO (Nucleus for European Modelling of the Ocean) designed for oceanographic research, operational oceanography, seasonal forecasting, and climate studies to build an eddy-resolving model of the GOF. To evaluate the model skill and performance, two different solutions were obtained on 0.5 km eddy-resolving and commonly used 2 km grids for a 1-year simulation. We also explore the efficacy of non-hydrostatic effect (convection) parameterizations available in NEMO for coastal application. It is found that the solutions resolving submesoscales have a more complex mixed layer structure in the regions of the GOF directly affected by the upwelling/downwelling and intrusions from the open Baltic Sea. Presented model estimations of the upper mixed layer depth are in good agreement with in situ CTD (BED) data. A number of model sensitivity tests to the vertical mixing parameterization confirm the model's robustness. Further progress in the submesoscale process simulation and understanding is apparently not connected mainly with the finer resolution of the grids, but with the use of non-hydrostatic models because of the failure of the hydrostatic approach at submesoscale.

Description: Effects of lateral processes on the seasonal water stratification of the Gulf of Finland: 3-D NEMO-based model study Ocean Science Discussions, 12, 2395-2421, 2015 Author(s): R. E. Vankevich, E. V. Sofina, T. E. Eremina, A. V. Ryabchenko, M. S. Molchanov, and A. V. Isaev This paper tries to fill the gaps in knowledge of processes affecting the seasonal water stratification in the Gulf of Finland (GOF). We used state-of-the-art modeling framework NEMO aimed for oceanographic research, operational oceanography, seasonal forecasting and climate studies to build an eddy resolving model of the GOF. To evaluate the model skill and performance two different solutions where obtained on 0.5 km eddy resolving and commonly used 2 km grids for one year simulation. We also explore the efficacy of nonhydrostatic effect (convection) parameterizations available in NEMO for coastal application. It is found that the solutions resolving sub-mesoscales have a more complex mixed layer structure in the regions of GOF directly affected by the upwelling/downwelling and intrusions from the open Baltic Sea. Presented model estimations of the upper mixed layer depth are in a good agreement with in situ CTD data. A number of model sensitivity tests to the vertical mixing parameterization confirm the model robustness.

Description: Occurrence and characteristics of mesoscale eddies in the tropical northeast Atlantic Ocean Ocean Science Discussions, 12, 3043-3097, 2015 Author(s): F. Schütte, P. Brandt, and J. Karstensen Coherent mesoscale features (referred to here as eddies) in the tropical northeast Atlantic (between 12–22° N and 15–26° W) are examined and characterised. The eddies' surface signatures are investigated using 19 years of satellite derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo–Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and salinity (SSS) are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are associated with elevation/depression of SLA and enhanced/reduced SST and SSS patterns. However, about 20 % of all detected anticyclones show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year are identified (52 % cyclones, 39 % anticylones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in-situ temperature and salinity profile data (from Argo float, shipboard and mooring data) inside of the three eddy types, their distinct differences in vertical structure is determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland region and carry South Atlantic Central Water that originates from the northward transport within the Mauretania coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d −1 ) is confined to distinct corridors with a small meridional deflection dependent on the eddy type (anticyclones – equatorward, cyclones – poleward, ACMEs – no deflection). Heat and salt flux out of the coastal region and across the Cap Verde Frontal Zone, which separates the shadow zone from the ventilated gyre, are calculated.

Description: Coupling of wave and circulation models in coastal-ocean predicting systems: a case study for the German Bight Ocean Science Discussions, 12, 3169-3197, 2015 Author(s): J. Staneva, K. Wahle, H. Günther, and E. Stanev This study addresses the impact of coupling between wind wave and circulation models on the quality of coastal ocean predicting systems. This is exemplified for the German Bight and its coastal area known as the Wadden Sea. The latter is the area between the barrier islands and the coast. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales, which in many cases are due to unresolved nonlinear feedback between strong tidal currents and wind-waves. In this study we present analysis of wave and hydrographic observations, as well as results of numerical simulations. A nested-grid modelling system is used to producing reliable nowcasts and short-term forecasts of ocean state variables, including wind waves and hydrodynamics. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecast system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and sea level are investigated by considering the wave-dependent stress and wave breaking parameterization. Also the effects which the circulation exerts on the wind waves are tested for the coastal areas using different parameterizations. The improved skill of the coupled forecasts compared to the non-coupled ones, in particular during extreme events, justifies the further enhancements of coastal operational systems by including wind wave models.

Description: Modelling wave–current interactions off the east coast of Scotland Ocean Science Discussions, 12, 3099-3142, 2015 Author(s): A. D. Sabatino, C. McCaig, R. B. O'Hara Murray, and M. R. Heath Densely populated coastal areas of the North Sea are particularly vulnerable to severe wave conditions, which overtop or damage sea-defences leading to dangerous flooding. Around the shallow southern North Sea, where the coastal margin is low-lying and population density is high, oceanographic modelling has helped to develop forecasting systems to predict flood risk. However coastal areas of the deeper northern North Sea are also subject to regular storm damage but there has been little or no effort to develop coastal wave models for these waters. Here we present a high spatial resolution model of northeast Scottish coastal waters, simulating waves and the effect of tidal currents on wave propagation, driven by global ocean tides, far-field wave conditions, and local air pressure and wind stress. We show that the wave–current interactions and wave–wave interactions are particularly important for simulating the wave conditions close to the coast at various locations. The model can simulate the extreme conditions experienced when high (spring) tides are combined with sea-level surges and large Atlantic swell. Such a combination of extremes represents a high risk for damaging conditions along the Scottish coast.

Description: Ocean colour products from geostationary platforms, opportunities with Meteosat Second and Third Generation Ocean Science Discussions, 12, 3143-3167, 2015 Author(s): E. J. Kwiatkowska, K. Ruddick, D. Ramon, Q. Vanhellemont, C. Brockmann, C. Lebreton, and H. G. Bonekamp Ocean colour applications from medium-resolution polar-orbiting satellite sensors have now matured and evolved into operational services. The examples include the Sentinel-3 OLCI missions of the European Earth Observation Copernicus programme and the VIIRS missions of the US Joint Polar Satellite System programme. Key drivers for Copernicus ocean colour services are the national obligations of the EU member states to report on the quality of marine, coastal and inland waters for the EU Water Framework Directive and Marine Strategy Framework Directive. Further applications include CO 2 sequestration, carbon cycle and climate, fisheries and aquaculture management, near-real-time alerting to harmful algae blooms, environmental monitoring and forecasting, and assessment of sediment transport in coastal waters. Ocean colour data from polar-orbiting satellite platforms, however, suffer from fractional coverage, primarily due to clouds, and inadequate resolution of quickly varying processes. Ocean colour remote sensing from geostationary platforms can provide significant improvements in coverage and sampling frequency and support new applications and services. EUMETSAT's SEVIRI instrument on the geostationary Meteosat Second Generation platforms (MSG) is not designed to meet ocean colour mission requirements, however, it has been demonstrated to provide valuable contribution, particularly in combination with dedicated ocean colour polar observations. This paper describes the ongoing effort to develop operational ocean colour water turbidity and related products and user services from SEVIRI. A survey of user requirements and a study of technical capabilities and limitations of the SEVIRI instruments are the basis for this development and are described in this paper. The products will support monitoring of sediment transport, water clarity, and tidal dynamics. Further products and services are anticipated from EUMETSAT's FCI instruments on Meteosat Third Generation satellites (MTG), including potential chlorophyll a products.

Description: Typhoon effect on Kuroshio and Green Island wake: a modelling study Ocean Science Discussions, 12, 3199-3233, 2015 Author(s): T.-W. Hsu, M.-H. Chou, T.-H. Hou, and S.-J. Liang Green Island located in the typhoon active eastern Taiwan coastal water is the potential Kuroshio power plant site. In this study, a high resolution (250–2250 m) shallow-water equations (SWEs) model is used to investigate the effect of typhoon on the hydrodynamics of Kuroshio and Green Island wake. Two wind induced flows, typhoon Soulik and Holland's wind field model, are studied. Simulation results of the typhoon Soulik indicate that salient characteristics of Kuroshio and downstream island wake seems less affected by the typhoon Soulik because typhoon Soulik is 250 km away Green Island and the wind speed near Green Island is small. Moreover, Kuroshio currents increase when flow is in the same direction as the counterclockwise rotation of typhoon, and vice versa. This finding is in favorable agreements with the TOROS observed data. The SWEs model, forced by the Kuroshio and Holland's wind field model, successfully reproduces the downstream recirculation and meandering vortex street. Numerical results unveil that the slow moving typhoon has a more significant impact on the Kuroshio and downstream Green Island wake than the fast moving typhoon does. Due to the counterclockwise rotation of typhoon, Kuroshio currents increase (decrease) in the right (left) of the moving typhoon's track. This rightward bias phenomenon is evident, especially when typhoon moves in the same direction as the Kuroshio mainstream.

Description: Technical note: Common characteristics of directional spreading–steepness joint distribution in freak wave events Shouhua Liu, Yizhen Li, and Xinyang Yue Ocean Sci., 12, 781-786, doi:10.5194/os-12-781-2016, 2016 Common visual features were found in the joint distribution of directional spreading--steepness when freak waves occurred among seven “freakish” sea states. It's interesting that the visual features look similar. The common visual features supply an important cue for the theoretical and experimental research of freak waves.

Description: Core operational Sentinel-3 marine data product services as part of the Copernicus Space Component Hans Bonekamp, Francois Montagner, Vincenzo Santacesaria, Carolina Nogueira Loddo, Sally Wannop, Igor Tomazic, Anne O'Carroll, Ewa Kwiatkowska, Remko Scharroo, and Hilary Wilson Ocean Sci., 12, 787-795, doi:10.5194/os-12-787-2016, 2016 This paper describes the marine data available from the Marine Centre, part of the Sentinel-3 Payload Data Ground Segment, located at the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Descriptions include the scientific and operational feedback mechanisms on the performance of the services as well as practical information and user support mechanisms.