Drifter Trajectories Research Articles

Asymptotic dynamics of reflecting spiral waves.

Resonantly forced spiral waves in excitable media drift in straight-line paths, their rotation centers behaving as pointlike objects moving along trajectories with a constant velocity. Interaction with medium boundaries alters this velocity and may often result in a reflection of the drift trajectory. Such reflections have diverse characteristics and are known to be highly nonspecular in general. In this context we apply the theory of response functions, which via numerically computable integrals, reduces the reaction-diffusion equations governing the whole excitable medium to the dynamics of just the rotation center and rotation phase of a spiral wave. Spiral reflection trajectories are computed by this method for both small- and large-core spiral waves in the Barkley model. Such calculations provide insight into the process of reflection as well as explanations for differences in trajectories across parameters, including the effects of incidence angle and forcing amplitude. Qualitative aspects of these results are preserved far beyond the asymptotic limit of weak boundary effects and slow resonant drift.

The Application Research of Sensors Non-autonomous Moving WSN MAC Protocol in Tailings Dams

Wireless Sensor Network (WSN) is widely used in environmental monitoring such as Tailings Dams, because of its low cost, high accuracy, and can remotely get monitoring information. We focuses on Tailings Dams monitoring application, proposed a MAC protocol with sensors non-autonomous moving. This protocol can quickly response events and fully considers about energy consumption. To develop network connectivity, this paper also developed the drift trajectory generation algorithm. At last, we make a simulation about the algorithm in MATLAB platform, and make a comparison between visual trajectory and real trajectory. The result shows that both trajectories are highly flt in speed and direct, there is an internal consistency between them.

Operational iceberg drift forecasting in Northwest Greenland

An operational iceberg drift forecast model was developed and used in 2012 to support Shell Greenland A/S, which was leading a consortium of companies to conduct a scientific coring campaign offshore northwest Greenland. The nine-week program took place in August–October 2012 in Melville Bay where there is a very high spatial density of icebergs. In order to increase operational safety and efficiency, the iceberg drift model presented here was fully integrated within the ice management strategy and its decision protocols. The model was optimized to fulfill the operational requirements in terms of (1) the format and content of the input/output, (2) the calculation of the iceberg alert zones, and (3) the derivation of the associated Closest Point of Approach (CPA) and time to CPA (T-CPA). To achieve this, the iceberg drift forecast model used as near real-time input: in-situ measured metocean parameters, observed iceberg drift and size data, tidal currents, and weather forecasts. The model forecast the 24-hour iceberg drift trajectory including the CPA and T-CPA. It also derived the T-Time (e.g., Total Time, or the time necessary to lift the coring pipe to 50m below the seabed) alert zones based on the observed mean iceberg drift speed. The iceberg trajectory forecast was optimized by running a hindcast simulation of the observed iceberg trajectory. In this simulation, the air and water iceberg form drag coefficients were tuned to minimize the difference between the hindcast and the observed iceberg drift trajectories. The forecast iceberg track, beginning at the end of the observed iceberg record, was subsequently generated using the air and water form drag coefficients derived from the hindcast simulation. The model also incorporated a method to correct for the lack of robust near real-time in-situ ocean current measurements. During this campaign, the model was used to forecast the drift of 73 icebergs and exhibited good performances in locations with strong and persistent non-tidal currents. However, further offshore where the ocean currents were dominated by tidal and inertial forcings, the model exhibited poorer performance. Nevertheless, as shown for two icebergs in this paper whose drift was dominated by tidal and inertial oscillations, model performance could be significantly improved in the hindcast mode by using the vessel's wind data and the ocean current data retrieved from a mooring deployed in the area. This illustrated the importance of using adequate near real-time ocean current and wind measured and forecast input data.

Southern Ocean velocity and geostrophic transport fields estimated by combining Jason altimetry and Argo data

AbstractZonal geostrophic velocity fields above 1975 dbar have been estimated for the Southern Ocean from 2004 into 2011 based on sea surface topography observed by Jason altimetry and temperature/salinity measured by Argo autonomous floats. The velocity at 1000 dbar estimated with the method has been compared to Argo drift trajectory at the same pressure level available from the Asia Pacific Data Research Center (APDRC). The inferred velocities agree with those from the Argo drift within the estimated sampling error of the latter, but have fewer gaps in space and time. The velocity has also been integrated from depth to surface to determine the mean and time‐variable zonal geostrophic transport in the Southern Ocean between 29.5°S and 58.5°S, primarily in the South Atlantic and South Indian Ocean basins, due to limitations in coverage of Argo. Analysis shows errors can be reduced by >70% by averaging gridded results over wide areas. Zonal transport averaged over the entire Indian Ocean basin shows a significant correlation with the Antarctic Oscillation (AAO) at low frequencies: transport is higher than normal during a positive phase of the AAO, and lower during the negative phase.

Assimilating along-track SLA data using the EnOI in an eddy resolving model of the Agulhas system

The greater Agulhas Current is one of the most energetic current systems in the global ocean. It plays a fundamental role in determining the mean state and variability of the regional marine environment, affecting its resources and ecosystem, the regional weather and the global climate on a broad range of temporal and spatial scales. In the absence of a coherent in-situ and satellite-based observing system in the region, modelling and data assimilation techniques play a crucial role in both furthering the quantitative understanding and providing better forecasts of this complicated western boundary current system. In this study, we use a regional implementation of the Hybrid Coordinate Ocean Model and assimilate along-track satellite sea level anomaly (SLA) data using the Ensemble Optimal Interpolation (EnOI) data assimilation scheme. This study lays the foundation towards the development of a regional prediction system for the greater Agulhas Current system. Comparisons to independent in-situ drifter observations show that data assimilation reduces the error compared to a free model run over a 2-year period. Mesoscale features are placed in more consistent agreement with the drifter trajectories and surface velocity errors are reduced. While the model-based forecasts of surface velocities are not as accurate as persistence forecasts derived from satellite altimeter observations, the error calculated from the drifter measurements for eddy kinetic energy is significantly lower in the assimilation system compared to the persistence forecast. While the assimilation of along-track SLA data introduces a small bias in sea surface temperatures, the representation of water mass properties and deep current velocities in the Agulhas system is improved.

Spatial variations in mortality in pelagic early life stages of a marine fish (Gadus morhua)

Mortality of pelagic eggs and larvae of marine fish is often assumed to be constant both in space and time due to lacking information. This may, however, be a gross oversimplification, as early life stages are likely to experience large variations in mortality both in time and space. In this paper we develop a method for estimating the spatial variability in mortality of eggs and larvae. The method relies on survey data and physical–biological particle-drift models to predict the drift of ichthyoplankton. Furthermore, the method was used to estimate the spatially resolved mortality field in the egg and larval stages of Barents Sea cod (Gadus morhua). We analyzed data from the Barents Sea for the period between 1959 and 1993 when there are two surveys available: a spring and a summer survey. An individual-based physical–biological particle-drift model, tailored to the egg and larval stages of Barents Sea cod, was used to predict the drift trajectories from the observed stage-specific distributions in spring to the time of observation in the summer, a drift time of approximately 45days. We interpreted the spatial patterns in the differences between the predicted and observed abundance distributions in summer as reflecting the spatial patterns in mortality over the drift period. Using the estimated mortality fields, we show that the spatial variations in mortality might have a significant impact on survival to later life stages and we suggest that there may be trade-offs between increased early survival in off shore regions and reduced probability of ending up in the favorable nursing grounds in the Barents Sea. In addition, we show that accounting for the estimated mortality field, improves the correlation between a simulated recruitment index and observation-based indices of juvenile abundance.

Using surface drifter observations to measure tidal vortices and relative diffusion at Aransas Pass, Texas

Tidal vortices play an important role in the flushing of coastal regions. At the mouth of a tidal inlet, the input of circulation by the ebb tide may force the formation of a starting-jet dipole vortex. The continuous ebb jet current also creates a periodic sequence of secondary vortices shed from the inlet mouth. In each case, these tidal vortices have a shallow aspect ratio, with a lateral extent much greater than the water depth. These shallow vortices affect the transport of passive tracers, such as nutrients and sediment from the estuary to the ocean and vice versa. Field observation of tidal vortices primarily relies on ensemble averaging over several vortex events that are repeatable in space and can be sampled by a fixed Eulerian measurement grid. This paper presents an adaptive approach for locating and measuring within tidal vortices that propagate offshore near inlets and advect along variable trajectories set by the wind-driven currents. A field experiment was conducted at Aransas Pass, Texas to measure these large-scale vortices. Locations of the vortices produced during ebb tide were determined using near real-time updates from surface drifters deployed near or within the inlet during ebb tide, and the paths of towed acoustic Doppler current profiler (ADCP) transects were selected by analysis of the drifter observations. This method allowed ADCP transects to be collected within ebb generated tidal vortices, and the paths of the drifters indicated the presence of both the starting-jet dipole and the secondary vortices of the unstable ebb tidal jet. Drifter trajectories were also used to estimate the size of each observed vortex as well as the statistics of relative diffusion offshore of Aransas Pass. The field data confirmed the starting-jet spin-up time (time until the vortex dipole begins to propagate offshore) measured in the laboratory by Bryant et al. [6] and that the Strouhal condition of \(St=0.2\) predicts the shedding of secondary vortices from the inlet mouth. The size of the rotational core of the vortex is also shown to be approximated physically by the inlet width or by \(0.02UT\), where U is the maximum velocity through the inlet channel and T is the tidal period, and confirms results found in laboratory experiments by Nicolau del Roure et al. [23]. Additionally, the scale of diffusion was approximately 1–15 km and the apparent diffusivity was between 2–130 \(m^2/s\) following Richardsons law.

Numerical modelling of physical processes governing larval transport in the southern North Sea

Abstract. A three-dimensional hydrodynamic model (GETM) was coupled with a particle tracking routine (GITM) to study the inter-annual variability in transport paths of particles in the North Sea and English Channel. For validation, a comparison with observed drifter trajectories is also presented here. This research investigated to what extent variability in the hydrodynamic conditions alone (reflecting passive particle transport) contributed to inter-annual variability in the transport of eggs and larvae. In this idealised study, no a priori selection of specific spawning grounds or periods was made and no active behaviour (vertical migration) or mortality was included. In this study, egg and larval development towards coastal nursery areas was based solely on sea water temperature, while settlement areas were defined by a threshold water depth. Results showed strong inter-annual variability in drift direction and distance, caused by a combination of wind speed and direction. Strong inter-annual variability was observed both in absolute amount of settlement in several coastal areas, and in the relative importance of the different areas. The effects of wind and temperature variability are minor for settlement along the western shores of the North Sea and in the English Channel, but have a very significant impact on settlement along the eastern shores of the North Sea. Years with strong south-westerly winds across the Dover Straight resulted in higher settlement figures along its eastern shores of the North Sea (standard deviation 37% of the mean annual settlement value). Settlement in the western Dutch Wadden Sea did not only show inter-annual variability, but patterns were also variable within each year and revealed seasonal changes in the origin of particles: during winter, stronger currents along with colder temperatures generally result in particles originating from further away.

Compensation of heliostat drift by seasonal sampling

Heliostat image drift is a common phenomenon in central receiver solar power plants. Several geometrical errors produce drift of the heliostat solar spot at receiver surface, increasing radiation spillage. A heuristic drift compensation method is proposed, based on a polynomial approximation to the drift trajectories. Results of the practical implementation of the proposed method for the control of 10 heliostats in a solar tower facility are presented. A substantial improvement of heliostat tracking is observed on the experimental tests. Because heliostat drift experimental monitoring is a time consuming task, a numerical analysis of the yearly behavior of the compensation method, based on simulations of heliostat drift, was carried out. In these simulations, the behavior of the daily RMS deviation of the concentrated solar spot centroid is evaluated for a whole year, as the polynomial correction is applied. The simulations serve also to test the effectiveness of the proposal polynomial method in a wider range of conditions. Thus, heliostats with a variety of primary error values are simulated. Random wind induced vibrations are introduced in the simulation to evaluate the effectiveness of the calibration method under noise conditions. It is found that a very effective calibration can be achieved with a few sampling events of the heliostat behavior during the year, taking only a few minutes. The RMS deviation can be reduced to values of the order of the wind induced noise level. The proposed polynomial compensation looks like a promising alternative to be implemented in heliostat fields.

Evaluation of altimetry-derived surface current products using Lagrangian drifter trajectories in the eastern Gulf of Mexico

Lagrangian particle trajectory models based on several altimetry-derived surface current products are used to hindcast the drifter trajectories observed in the eastern Gulf of Mexico during May to August 2010 (the Deepwater Horizon oil spill incident). The performances of the trajectory models are gauged in terms of Lagrangian separation distances (d) and a nondimensional skill score (s), respectively. A series of numerical experiments show that these altimetry-based trajectory models have about the same performance, with a certain improvement by adding surface wind Ekman components, especially over the shelf region. However, their hindcast skills are slightly better than those of the data assimilative numerical model output. After 3 days' simulation the altimetry-based trajectory models have mean d values of 75–83 and 34–42 km (s values of 0.49–0.51 and 0.35–0.43) in the Gulf of Mexico deep water area and on the West Florida Continental Shelf, respectively. These satellite altimetry data products are useful for providing essential information on ocean surface currents of use in water property transports, offshore oil and gas operations, hazardous spill mitigation, search and rescue, etc.

Marine Oil Spill Simulation: A Scenario-Based Classroom Application of Meteorology and Oceanography to Environmental Protection

Predicting oil spill impacts and designing an effective response requires knowledge from several disciplines, including environmental chemistry, meteorology, oceanography, and marine ecology. In this poster, we describe an interactive computer modeling exercise that expands student understanding of principles in the natural sciences by applying them to an oil spill response scenario. The exercise is based on the software package, GNOME v.1.3.7, available from the National Oceanic and Atmospheric Administration (NOAA). Students begin by selecting one of numerous coastal locations in the United States and an oil product to be spilled (e.g., medium crude, diesel fuel, No. 6 fuel oil). They predict oil drift trajectories by accessing surface weather analysis charts, upper air charts, and marine forecasts produced by the National Weather Service as well as real-time oceanographic data available from NOAA's Data Buoy Center and the Tides and Currents database. Students consult the Atlas of Pilot Charts from the National Geospatial Intelligence Agency to evaluate any influence of large-scale currents. Drawing from knowledge of the chemical properties of oil, weathering processes, leeway, Ekman dynamics, tides, and geostrophic flow, students forecast the amount and location of oil remaining after 48 hours. Predictions are tested in GNOME, which simulates an oil spill with the chosen characteristics, at the chosen location, under the same environmental conditions. Based on the model results, students evaluate environmental impacts by referring to Environmental Sensitivity Index (ESI) maps for affected coastlines. These maps are available from NOAA's Office of Prevention and Response and contain site-specific information on shoreline habitat sensitivity, conservation status of biological populations, and location of vulnerable coastal infrastructure. Students prioritize areas for protection and design a response plan with appropriate clean-up countermeasures. Response plans are communicated to the instructor in the form of a recommendation addressed to the Captain of the Port. This exercise has been successfully incorporated into several courses at the Coast Guard Academy, with modifications to accommodate various audiences and learning objectives. All versions include multidisciplinary and collaborative learning techniques, higher-level cognitive thinking, and communication requirements. Data and software packages for this exercise are freely available from federal government websites, making possible its widespread use at other colleges and agencies seeking to provide students with hands-on opportunities to explore scientific concepts in the context of environmental protection.

Roles of biological and physical processes in driving seasonal air–sea CO2 flux in the Southern Ocean: New insights from CARIOCA pCO2

On a mean annual basis, the Southern Ocean is a sink for atmospheric CO2. However the seasonality of the air–sea CO2 flux in this region is poorly documented. We investigate processes regulating air–sea CO2 flux in a large area of the Southern Ocean (38°S–55°S, 60°W–60°E) that represents nearly one third of the subantarctic zone. A seasonal budget of CO2 partial pressure, pCO2 and of dissolved inorganic carbon, DIC in the mixed layer is assessed by quantifying the impacts of biology, physics and thermodynamical effect on seawater pCO2. A focus is made on the quantification at a monthly scale of the biological consumption as it is the dominant process removing carbon from surface waters. In situ biological carbon production rates are estimated from high frequency estimates of DIC along the trajectories of CARIOCA drifters in the Atlantic and Indian sector of the Southern Ocean during four spring–summer seasons over the 2006–2009 period. Net community production (NCP) integrated over the mixed layer is derived from the daily change of DIC, and mixed layer depth estimated from Argo profiles. Eleven values of NCP are estimated and range from 30 to 130mmolCm−2d−1. They are used as a constraint for validating satellite net primary production (NPP). A satellite data-based global model is used to compute depth integrated net primary production, NPP, for the same periods along the trajectories of the buoys. Realistic NCP/NPP ratios are obtained under the condition that the SeaWiFS chlorophyll are corrected by a factor of ≈2–3, which is an underestimation previously reported for the Southern Ocean. Monthly satellite based NPP are computed over the 38°S–55°S, 60°W–60°E area. pCO2 derived from these NPP combined with an export ratio, and taking into account the impact of physics and thermodynamics is in good agreement with the pCO2 seasonal climatology of Takahashi (2009). On an annual timescale, mean NCP values, 4.4 to 4.9molCm−2yr−1 are ≈4–5 times greater than air–sea CO2 invasion, 1.0molCm−2yr−1. Our study based on in situ and satellite observations provides a quantitative estimate of both seasonal and mean annual uptake of CO2 in the subantarctic zone of the Southern Ocean. These results bring important constraints for ocean circulation and biogeochemical models investigating future changes in the Southern Ocean CO2 fluxes.

Eulerian and Lagrangian Correspondence of High-Frequency Radar and Surface Drifter Data: Effects of Radar Resolution and Flow Components

AbstractThis study investigated the correspondence between the near-surface drifters from a mass drifter deployment near Martha’s Vineyard, Massachusetts, and the surface current observations from a network of three high-resolution, high-frequency radars to understand the effects of the radar temporal and spatial resolution on the resulting Eulerian current velocities and Lagrangian trajectories and their predictability. The radar-based surface currents were found to be unbiased in direction but biased in magnitude with respect to drifter velocities. The radar systematically underestimated velocities by approximately 2 cm s−1 due to the smoothing effects of spatial and temporal averaging. The radar accuracy, quantified by the domain-averaged rms difference between instantaneous radar and drifter velocities, was found to be about 3.8 cm s−1. A Lagrangian comparison between the real and simulated drifters resulted in the separation distances of roughly 1 km over the course of 10 h, or an equivalent separation speed of approximately 2.8 cm s−1. The effects of the temporal and spatial radar resolution were examined by degrading the radar fields to coarser resolutions, revealing the existence of critical scales (1.5–2 km and 3 h) beyond which the ability of the radar to reproduce drifter trajectories decreased more rapidly. Finally, the importance of the different flow components present during the experiment—mean, tidal, locally wind-driven currents, and the residual velocities—was analyzed, finding that, during the study period, a combination of tidal, locally wind-driven, and mean currents were insufficient to reliably reproduce, with minimal degradation, the trajectories of real drifters. Instead, a minimum combination of the tidal and residual currents was required.

Topology of drift trajectories of charged particles in a tokamak

The topology of drift orbits in a tokamak is analyzed in the entire cross section of the device both near the magnetic axis and at the periphery of the plasma column. The use of invariants of the drift equations (the generalized momentum, magnetic moment, and total energy) as variables for the entire cross section of the plasma column and self-similar variables near the magnetic axis makes it possible to comprehensively classify closed drift orbits in a tokamak. When describing orbits of different types and domains of their existence, discriminant and locus curves obtained by the methods of differential geometry are used to determine the ranges in which the invariants vary. The influence of the nonuniformity of the longitudinal current on the drift trajectories of fast particles is studied. The works in which, together with known types of orbits, trajectories along which particles leave the plasma column and can fall on the chamber wall are analyzed.

Assimilating the along-track sea level anomaly into the regional ocean modeling system using the ensemble optimal interpolation

The ensemble optimal interpolation (EnOI) is applied to the regional ocean modeling system (ROMS) with the ability to assimilate the along-track sea level anomaly (TSLA). This system is tested with an eddy-resolving system of the South China Sea (SCS). Background errors are derived from a running seasonal ensemble to account for the seasonal variability within the SCS. A fifth-order localization function with a 250 km localization radius is chosen to reduce the negative effects of sampling errors. The data assimilation system is tested from January 2004 to December 2006. The results show that the root mean square deviation (RMSD) of the sea level anomaly decreased from 10.57 to 6.70 cm, which represents a 36.6% reduction of error. The data assimilation reduces error for temperature within the upper 800 m and for salinity within the upper 200 m, although error degrades slightly at deeper depths. Surface currents are in better agreement with trajectories of surface drifters after data assimilation. The variance of sea level improves significantly in terms of both the amplitude and position of the strong and weak variance regions after assimilating TSLA. Results with AGE error (AGE) perform better than no AGE error (NoAGE) when considering the improvements of the temperature and the salinity. Furthermore, reasons for the extremely strong variability in the northern SCS in high resolution models are investigated. The results demonstrate that the strong variability of sea level in the high resolution model is caused by an extremely strong Kuroshio intrusion. Therefore, it is demonstrated that it is necessary to assimilate the TSLA in order to better simulate the SCS with high resolution models.

Variation of the southern Subtropical Countercurrent related to sea surface height and eddies in the northwest tropical pacific

The ADCP records obtained at about 18°N, 135°E show the southern branch of the Subtropical Countercurrent (STCC). The sea surface heights (SSH) show that there is a tendency to increase and decrease in the south/north of STCC, respectively. So the variability of SSH ultimately contributes to the strengthening of STCC through geostrophic balance. The southern STCC branch distinctly persists from winter to spring. Since 2005, the southern STCC exists almost throughout the year, and the STCC is clearly stronger to the east of 145°E. Anticyclonic and cyclonic eddies exist seemingly as bands around 17.5°N and 20.5°N, respectively. The STCC flowing eastward, which is formed by the geostrophic balance, is maintained with the interaction between geostrophic currents and anticyclonic-cyclonic eddies. The rotating eddies exert an additional driving force to maintain the eastward flow of STCC, and then the STCC reveals a meandering movement due to the interaction with the eddies. The trajectories of surface drifters together with the altimeter data analysis in June 2009 dictate the variability of the STCC induced by the interaction between eddies and the eastward flow. These results suggest that the southern STCC slowly changes from an intra-seasonal event an annual one with time duration of over 21 months.

The controversial path of Atlantic Water in the Eastern Mediterranean

The Atlantic Water (AW) path suggested by two decades of thermal satellite data observations in the Eastern Mediterranean is similar to the path followed by the AW in the Western Mediterranean but is in contrast with the scheme proposed after the Physical Oceanography of the Eastern Mediterranean (POEM) experiment during the 1990s. Evidence of the AW path along the Libyo-Egyptian coast (Libyo-Egyptian Current; LEC) and around anti-cyclonic eddies of variable size and position (Libyo-Egyptian Eddies; LEEs) is reported in XBT transects, high resolution models and drifter trajectories. In the POEM scheme, the AW was carried eastwards by the Mid-Mediterranean Jet (MMJ) flowing in the middle of the Levantine basin. The MMJ is still noted in recent drifter trajectory analyses, and seasonal surveys and glider missions report that the AW is transferred towards the Levantine basin by the MMJ in subsurface layers.The issue is investigated in this study by considering whether the determination of the AW path and the resolution of the surface circulation are, unlike in the Western Mediterranean, two distinct problems. Historical hydrographic datasets and numerical experiments illustrated in this study demonstrate that satellite observations in the Eastern Mediterranean reveal the path of the surface water of Atlantic origin, which is modified by heating and evaporation into the saltier and warmer Levantine Surface Water (LSW), but do not reveal the path of the submerged AW that maintains the distinctive character of fresh AW in the Levantine basin. Differences between the surface and the submerged circulation in the Mersa-Matruh area explain the reason for the discrepancy.In summer the AW departs from the Sicily Channel at the sea surface and crosses the Ionian Sea in a surface layer 30m deep. At the entrance to the Levantine basin, part of the AW re-circulates westwards in two separate branches, one directed to the Southern Ionian and the other towards the Central Ionian, causing meanders in the incoming AW. In the Levantine basin, before the Cretan Passage, the AW is close to the Libyan coast with surface layers already modified into LSW and a subsurface fresh AW core centered at 50m depth. Surface and subsurface flows diverge within the Cretan Passage as they approach the Mersa-Matruh area. According to satellite observations, the LSW flows along the Libyo-Egyptian coast (LEC) and around anti-cyclonic LEEs of variable size and position. In the subsurface layers, the blend and fragmented anti-cyclonic circulation found at the surface is augmented by the AW itself, which becomes saltier and negatively buoyant, and veers offshore joining the MMJ. In summer, the jet assumes the aspect of a submerged injection of fresh AW into the Levantine basin below a depth of 60–70m. From the Ionian eastwards, the depth of the fresh core of AW sinks by tens of meters from the beginning to the end of summer. In the Sicily Channel, the AW in winter is saltier than in other periods of the year due to evaporation and mixing occurring between the fresh AW and the saltier Ionian Surface Water intruding into the southern side of the Channel in summer.

A study of transport and impact strength of Fukushima nuclear pollutants in the north pacific surface

Based on the statistics of surface drifter data of 1979–2011 and the simulation of nuclear pollutant particulate movements simulated using high quality ocean reanalysis surface current dataset, the transport pathways and impact strength of Fukushima nuclear pollutants in the North Pacific have been estimated. The particulates are used to increase the sampling size and enhance the representativeness of statistical results. The trajectories of the drifters and particulates are first examined to identify typical drifting pathways. The results show that there are three types of transport paths for nuclear pollutants at the surface: 1) most pollutant particles move eastward and are carried by the Kuroshio and Kuroshio-extension currents and reach the east side of the North Pacific after about 3.2–3.9 years; 2) some particles travel with the subtropical circulation branch and reach the east coast of China after about 1.6 years according to one drifter trajectory and about 3.6 years according to particulate trajectories; 3) a little of them travel with local, small scale circulations and reach the east coast of China after about 1.3–1.8 years. Based on the particulates, the impact strength of nuclear pollutants at these time scales can be estimated according to the temporal variations of relative concentration combined with the radioactive decay rate. For example, Cesium-137, carried by the strong North Pacific current, mainly accumulates in the eastern North Pacific and its impact strength is 4% of the initial level at the originating Fukushima area after 4 years. Due to local eddies, Cesium-137 in the western North Pacific is 1% of the initial pollutant level after 1.5 years and continuously increases to 3% after 4 years. The vertical movement of radioactive pollutants is not taken into account in the present study, and the estimation accuracy would be improved by considering three-dimensional flows.

Influence of Dardanelles outflow induced thermal fronts and winds on drifter trajectories in the Aegean Sea

The data provided by 12 drifters deployed in the Northern Aegean Sea in the vicinity of the Dardanelles Strait in August 2008 and February 2009 are used to explore the surface circulation of the basin and the connectivity to the Black Sea. The drifters were deployed within the Dardanelles outflow of waters of Black Sea origin in the Northeastern Aegean. Thanks to the particular choice of the drifter deployment positions, the data set provides a unique opportunity to observe the branching behaviour of the surface currents around Lemnos Island. Such pathways were notpossible to study with previous drifter deployments that were far from the Dardanelles Strait. In addition, the drifter tracks covered the Aegean basin quite thoroughly, mapping major circulation features and supporting the overall general circulation patterns described by previous observational and modelling studies. The collected data display cases in which drifters are driven by winds and thermal fronts. Wind products were used to estimate the influence of the atmospheric forcing on the drifter trajectories. Satellite sea surface temperature images were connected to the drifter tracks, demonstrating a high correlation between the remote and in situ observations. The waters of Black Sea origin were traced all the way to the Southern Aegean, establishing a strong connectivity link between the Aegean and Black Sea basins.

Floating along buoyancy levels: Dispersal and survival of western Baltic fish eggs

Vertical distribution is an important feature of pelagic fish eggs and yolk sac larvae impacting their survival and dispersal, especially in heterogeneous and highly variable estuarine environments like the Baltic Sea. Egg densities determining the vertical distribution pattern were experimentally ascertained for cod (Gadus morhua), plaice (Pleuronectes platessa) and flounder (Platichthys flesus) from the western Baltic Sea. Plaice eggs floated at lower mean (±standard deviation) density range (1.0136±0.0007gcm−3) compared to cod (1.0146±0.0009gcm−3) and flounder eggs (1.0160±0.0015gcm−3), which floated on the highest density level. In flounder egg diameter was significantly related to egg density and in cod a weak correlation could be found between egg dry weight and density. All other relationships between female size, egg size, egg dry weight and egg density were not significant for any of the species. Available egg density data for Baltic Sea cod, plaice and flounder are summarized considering ICES subdivisions and stock management units. A hydrodynamic drift modeling approach was applied releasing drifters in the Belt Sea continuously from December to May, covering the species’ spawning seasons. The model implemented experimentally derived egg density ranges and included ontogenetic egg density modifications for cod eggs, increasing egg density from a late egg development stage to first hatch. A drifter was removed from the model, i.e. considered dead, when its initially prescribed density value exceeded the density range available at the temporally resolved geographical positions along the drift trajectories. Highest survival occurred during releases in April and May but no cohorts survived if they were drifted east into the central Arkona Basin or the central Baltic Sea, irrespective of whether a major Baltic Inflow (1992/1993) or a stagnation-year (1987/1988) was simulated. The dispersal characteristics of the surviving yolk sac larvae of all three species reflected retention within the Belt Sea or northwards transport through the Great Belt into the Kattegat and partly into the Skagerrak. There was no successful transport to more eastern Baltic areas past a hypothetical line from the island of Moen (Denmark) to Kap Arkona on Rügen Island (Germany).