Search

Currents and pressure records from the DeepLev mooring station and drifter data in the eastern Levantine Basin were analyzed to identify the dominant tidal constituents and their seasonal and depth variability. Harmonic and spectral analysis of seasonal segments of currents and pressure reveal key attributes of the tidal regime: (1) dominant semidiurnal sea level variability; (2) seasonal variation of semidiurnal and diurnal tides in both currents and pressure datasets; and (3) significant diurnal currents with weak semidiurnal currents across all seasons. The most dominant tidal constituent from the pressure dataset is the M2 (12.4 h). Results from pressure datasets align with previous models and observations of semidiurnal tides. In contrast, the diurnal tides are larger than previously reported by 8--9 cm in the winter and 1--2 cm in the summer. The surface current tidal regime differs from prior reports in the eastern Levantine Basin, with M2 magnitudes weaker by 1 cm s-1, while the diurnal tides (K1, O1) are 1--2 cms-1 larger. Seasonal segments showed seasonal differences in the local tidal regime's amplitudes. The most pronounced seasonal differences were with the K1 and S2 tides, with differences between winter and fall of 7 cmfor the K1 and 4 cm between summer and fall for the S2. We utilized the DeepLev datasets to compare a moored device with surface drifters near DeepLev by analyzing the M2 and S2 tides. Additionally, we examined data at different dataset lengths, considering the time constraints needed to resolve the tides adequately. Longer datasets improved the resolution of the tidal analysis and reduced amplitude leakages from nearby frequencies, resulting in a more realistic and accurate analysis of the tidal currents. Conversely, longer datasets resulted in fewer drifters remaining our study region for the allotted dataset length. From 32 available segments in 15 day dataset to 7 with a 30 day dataset, reducing the effectiveness of drifters as a local tidal research tool. [ABSTRACT FROM AUTHOR]

High-frequency radars (HFRs) provide remote information on ocean surface velocity in extended coastal areas at high resolutions in space (O (km)) and time (O (h)). They directly produce radial velocities (in the radar antenna's direction) combined to provide total vector velocities in areas covered by at least two radars. HFRs are a key element in ocean observing systems, with several important environmental applications. Here, we provide an assessment of the HFR-TirLig network in the NW Mediterranean Sea, including results from the gap-filling open-boundary modal analysis (OMA) using in situ velocity data from drifters. While the network consists of three radars, only two were active during the assessment experiment, so the test also includes an area where the radial velocities from only one radar system were available. The results, including several metrics, both Eulerian and Lagrangian, and configurations, show that the network performance is very satisfactory and compares well with the previous results in the literature in terms of both the radial and total combined vector velocities where the coverage is adequate, i.e., in the area sampled by two radars. Regarding the OMA results, not only do they perform equally well in the area sampled by the two radars but they also provide results in the area covered by one radar only. Even though obviously deteriorated with respect to the case of adequate coverage, the OMA results can still provide information regarding the velocity structure and speed as well as virtual trajectories, which can be of some use in practical applications. A general discussion on the implications of the results for the potential of remote sensing velocity estimation in terms of HFR network configurations and complementing gap-filling analysis is provided. [ABSTRACT FROM AUTHOR]

Currents and pressure records from the DeepLev mooring station and drifter data in the eastern Levantine Basin were analyzed to identify the dominant tidal constituents and their seasonal and depth variability. Harmonic and spectral analysis of seasonal segments of currents and pressure reveal key attributes of the tidal regime: (1) dominant semidiurnal sea level variability; (2) seasonal variation of semidiurnal and diurnal tides in both currents and pressure datasets; and (3) significant diurnal currents with weak semidiurnal currents across all seasons. The most dominant tidal constituent from the pressure dataset is the M2 (12.4 h). Results from pressure datasets align with previous models and observations of semidiurnal tides. In contrast, the diurnal tides are larger than previously reported by 8—9 cm in the winter and 1—2 cm in the summer. The surface current tidal regime differs from prior reports in the eastern Levantine Basin, with M2 magnitudes weaker by 1 cm s-1, while the diurnal tides (K1, O1) are 1—2 cm s-1 larger. Seasonal segments showed seasonal differences in the local tidal regime’s amplitudes. The most pronounced seasonal differences were with the K1 and S2 tides, with differences between winter and fall of 7 cm for the K1 and 4 cm between summer and fall for the S2. We utilized the DeepLev datasets to compare a moored device with surface drifters near DeepLev by analyzing the M2 and S2 tides. Additionally, we examined data at different dataset lengths, considering the time constraints needed to resolve the tides adequately. Longer datasets improved the resolution of the tidal analysis and reduced amplitude leakages from nearby frequencies, resulting in a more realistic and accurate analysis of the tidal currents. Conversely, longer datasets resulted in fewer drifters remaining our study region for the allotted dataset length. From 32 available segments in 15 day dataset to 7 with a 30 day dataset, reducing the effectiveness of drifters as a local tidal research tool.

Abstract Drift experiments are essential to understand stranding patterns and estimate the mortality of beached animals. Most studies do not use telemetry technology due to the high costs of this methodology. The objective of this paper is to describe the possibilities of tracking marine tetrapod carcasses with a low‐cost and replicable methodology. The study was carried out on the Southern Subtropical Shelf (~28°–34°S), a highly productive and key ecological region of the southwestern Atlantic Ocean (SWA). We designed and tested a low‐cost mixed methodology that includes Global Positioning System trackers, passive drifters (reused glass bottles) and Citizen Science (through an instant message platform and email) to track carcasses of marine tetrapods. We conducted four drift experiments during the four seasons of 2019. We released 787 drifters (600 nonbiological and 187 carcasses of seabirds, sea turtles, and cetaceans) at sea, at five equally separated distances (5–25 km) from the coast. Beach surveys and citizen science were implemented to recover the beached drifters. We recovered 71.83% of non‐biological drifters and 27.27% of carcasses released. We tracked the movements of 38 carcasses (25 sea turtles and 13 cetaceans) with 17 GPS devices. The drifting time, until reaching the beach, ranged from 12 h to 17 days for carcasses and 12 h to 406 days for bottles. Citizen Science was the most important source of recovery of nonbiological drifters, representing 66.67% of the total recovered bottles. For carcasses, active search was the most important recovery source, representing 64.7% of the total carcasses recovered. Our study contributes with new findings on marine tetrapod drift patterns in the SWA and describes an accessible low‐cost mixed methodology for small and medium‐budget projects that can be replicated in other coastal regions of the world for tracking a wide range of marine tetrapod species.

High-frequency radars (HFRs) provide remote information on ocean surface velocity in extended coastal areas at high resolutions in space (O(km)) and time (O(h)). They directly produce radial velocities (in the radar antenna’s direction) combined to provide total vector velocities in areas covered by at least two radars. HFRs are a key element in ocean observing systems, with several important environmental applications. Here, we provide an assessment of the HFR-TirLig network in the NW Mediterranean Sea, including results from the gap-filling open-boundary modal analysis (OMA) using in situ velocity data from drifters. While the network consists of three radars, only two were active during the assessment experiment, so the test also includes an area where the radial velocities from only one radar system were available. The results, including several metrics, both Eulerian and Lagrangian, and configurations, show that the network performance is very satisfactory and compares well with the previous results in the literature in terms of both the radial and total combined vector velocities where the coverage is adequate, i.e., in the area sampled by two radars. Regarding the OMA results, not only do they perform equally well in the area sampled by the two radars but they also provide results in the area covered by one radar only. Even though obviously deteriorated with respect to the case of adequate coverage, the OMA results can still provide information regarding the velocity structure and speed as well as virtual trajectories, which can be of some use in practical applications. A general discussion on the implications of the results for the potential of remote sensing velocity estimation in terms of HFR network configurations and complementing gap-filling analysis is provided.

Copyright of Methods in Ecology & Evolution is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bathymetric features such as dredged channels, constricted-inlet basins, and nearshore islands have known influences on coastal transport, which are typically studied on an individual basis. However, their interactive effects on flow when found in the same area are poorly characterized. A multi-season study was conducted to characterize surface transport in and around Wood Island Harbor, in the southwestern Gulf of Maine, where these features all exist in close proximity. Patterns of surface transport were assessed with repeated series of Uncrewed Aerial Vehicle flights and deployments of GPS drifters across tidal conditions and winds typical to the area. Transport followed a major axis through the harbor, as a result of the combined effects of the linked inlet-channel system. Despite the complex topography, the individual dynamics of transport are maintained. Tidal variations explained a majority of displacement (R2 = 0.752) along the channel axis, while across-channel wind velocity explained the majority of orthogonal displacement (R2 = 0.646). Flow in the area was friction-dominated, and both inter-island passages and the deep channel served to direct flow. The offshore transport of tidally driven flows from a constricted-inlet basin was enhanced by deep channels, with flow primarily following bathymetric contours. Our observations suggest that surrounding topography lessened the role of wave energy in governing transport. The co-occurrence of bathymetric features around a constricted-inlet basin can disrupt the typical influences of physical mechanisms on surface transport, leading to a greater importance of local conditions and the larger-scale circulation of the area. [ABSTRACT FROM AUTHOR]

Every fall, juvenile sea turtles in the Northwest Atlantic Ocean are threatened by rapidly declining water temperatures. When sea turtles become hypothermic, or cold-stunned, they lose mobility--either at the surface, subsurface, or the bottom of the water column--and eventually strand at the shoreline where rescue teams associated with the Sea Turtle Stranding and Salvage Network may search for them. Understanding the effects of ocean currents on the potential stranding locations of cold-stunned sea turtles is essential to better understand stranding hotspots and increase the probability of successful discovery and recovery of turtles before they die in the cold temperatures. Traditional oceanographic drifters--instruments used to track currents--have been used to examine relationships between current and stranding locations in Cape Cod Bay, but these drifters are not representative of sea turtle morphology and do not assess how bottom currents affect stranding locations. To address these knowledge gaps, we designed new drifters that represent the shape and dimensions of sea turtles--one that can float at the surface and one that sinks to the bottom--to track both surface and bottom currents in Cape Cod Bay. We found a marked difference between the trajectories of our new drifter models and those that were previously used for similar research. These findings bring us one step closer to identifying the transport pathways for cold-stunned sea turtles and optimizing cold-stunned sea turtle search and rescue efforts in Cape Cod. [ABSTRACT FROM AUTHOR]

Wavelet ridge analysis was applied to the data of drifters caught in the Cyprus Gyre in the eastern Mediterranean Sea to study surface currents at low (rotating circulation) and high (near-inertial motion) frequencies. Drifter observations indicate that the orbital speed is highest at about 30 km from the gyre center (reaching ~45 cm/s) and that the Rossby number in the gyre can be as high as 0.25. Drifters also show that strong near-inertial currents with speed of 35-40 cm/s can exceed the gyre rotation speed and that the background vorticity inside the gyre generally shifts the effective inertial frequency to values smaller than the local inertial frequency. As a result, the near-inertial currents are subinertial and are trapped in the mesoscale vortex. For example, the near-inertial motions in the Cyprus Gyre in June 2017 reached 40 cm/s in its inner core with a red shift of ~0.1 cpd, while on its edge they were limited to 10-20 cm/s, under similar wind forcing. This difference is due to trapping of the near-inertial energy inside the gyre. The observed inertial currents are largely driven by the local wind, especially when the effective inertial frequency becomes diurnal and resonance with wind diurnal variability occurs. A damped slab model of the inertial currents in the mixed layer is only partially successful in simulating the observations.

Every fall, juvenile sea turtles in the Northwest Atlantic Ocean are threatened by rapidly declining water temperatures. When sea turtles become hypothermic, or cold-stunned, they lose mobility—either at the surface, subsurface, or the bottom of the water column—and eventually strand at the shoreline where rescue teams associated with the Sea Turtle Stranding and Salvage Network may search for them. Understanding the effects of ocean currents on the potential stranding locations of cold-stunned sea turtles is essential to better understand stranding hotspots and increase the probability of successful discovery and recovery of turtles before they die in the cold temperatures. Traditional oceanographic drifters—instruments used to track currents—have been used to examine relationships between current and stranding locations in Cape Cod Bay, but these drifters are not representative of sea turtle morphology and do not assess how bottom currents affect stranding locations. To address these knowledge gaps, we designed new drifters that represent the shape and dimensions of sea turtles—one that can float at the surface and one that sinks to the bottom—to track both surface and bottom currents in Cape Cod Bay. We found a marked difference between the trajectories of our new drifter models and those that were previously used for similar research. These findings bring us one step closer to identifying the transport pathways for cold-stunned sea turtles and optimizing cold-stunned sea turtle search and rescue efforts in Cape Cod.

Increasing freshwater fluxes from the Greenland ice sheet and the Arctic to the Subpolar North Atlantic could cause a freshening of deep convection regions and affect the overturning circulation. However, freshwater pathways from the Greenland shelf to interior seas and deep convection regions are not fully understood. We investigate exchanges of liquid freshwater between the east Greenland shelf and neighboring seas using drifter data from five deployments carried out at different latitudes along the east Greenland shelf in 2019, 2020, and 2021, as well as satellite data and an atmospheric reanalysis. We compute Ekman transport from winds and geostrophic velocity from satellite altimetry at the shelfbreak and identify the Blosseville Basin and Cape Farewell as areas favorable to cross‐shelf exchanges. We further investigate exchange processes in these regions using drifter data. In the Blosseville Basin, drifters are brought off‐shelf toward the Iceland Sea and into the interior of the Basin. As they are advected downstream, they re‐enter the shelf and are driven toward the coast. At Cape Farewell, the wind appears to be the main driver, although on one occasion we found evidence of an eddy turning drifters away from the shelf. The drifters brought off‐shelf at Cape Farewell mostly continue around Eirik Ridge, where they re‐enter the West Greenland Current. Overall, the identified export over the east Greenland shelf is limited, small scale, and intermittent, thus unlikely to flux large amount of liquid freshwater into the interior, though exchange processes could enhance mixing in the near‐shelf region. Plain Language Summary: Climate change is expected to lead to a faster melt of the Greenland ice sheet. This may have a large effect on the ocean circulation due to its location near areas where strong winter cooling by the atmosphere turns warm ocean surface waters into cold, dense deep waters. As light fresh meltwater from Greenland enters these regions, winter cooling may not be strong enough anymore to make these waters dense enough to take part in the deep ocean circulation. In this study, we investigate tracks from drifting ocean instruments deployed near Greenland, as well as satellite data, to study where, and how much, freshwater could enter these deep water formation areas. We find two locations along the east Greenland shelf, at 60° and 68°N, where strong winds and ocean eddies can steer freshwater offshore, These processes are intermittent and only lead to small amounts of freshwater brought to areas where deep waters are formed. Key Points: We investigate cross‐shelf exchanges east of Greenland with a new data set of drifters deployed at the shelfbreak in 2019, 2020, and 2021Drifters, altimetry, and an atmospheric reanalysis, indicate enhanced cross‐shelf exchanges at the Blosseville Basin and Cape FarewellWinds, eddies, and local topography drive small scale and intermittent export east of Greenland, and can enhance mixing near the shelf [ABSTRACT FROM AUTHOR]

Vertical transport pathways in the ocean are still only partially understood despite their importance for biogeochemical, pollutant, and climate applications. Detailed measurements of a submesoscale frontal jet in the Alboran Sea (Mediterranean Sea) during a period of highly variable winds were made using cross‐frontal velocity, density sections and dense arrays of surface drifters deployed across the front. The measurements show divergences as large as ±f implying vertical velocities of order 100 m/day for a ≈ 20 m thick surface layer. Over the 20 hr of measurement, the divergences made nearly one complete oscillation, suggesting an important role for near‐inertial oscillations. A wind‐forced slab model modified by the observed background frontal structure and with initial conditions matched to the data produces divergence oscillations and pattern compatible with that observed. Significant differences, though, are found in terms of mean divergence, with the data showing a prevalence of negative, convergent values. Despite the limitations in data sampling and model uncertainties, this suggests the contribution of other dynamical processes. Turbulent boundary layer processes are discussed, as a contributor to enhance the observed convergent phase. Water mass properties suggest that symmetric instabilities might also be present but do not play a crucial role, while downward stirring along displaced isopycnals is observed. Plain Language Summary: Vertical transport pathways are essential for the exchange of properties between the surface and the deeper layers of the ocean. Despite the recognized role of vertical dynamics in biogeochemical and climate applications, it is still only partially understood. This is principally due to observational challenges. Vertical transport pathways are generally very localized processes and are associated with vertical velocities comparable to instrumental uncertainty. In this work, we focus on vertical processes occurring along a front at the edge of an eddy in the Mediterranean Sea. The paper combines the analysis of multiple observations with the use of an idealized numerical model to isolate and study surface divergence patterns. These analyses allow the investigation of the role of the wind forcing and of small‐scale ocean processes in vertical transport. Key Points: Divergence and vertical velocity oscillations are observed at a submesoscale front on the edge of an anticyclone in the Alboran SeaNear‐inertial oscillations play a major role in the observed divergence oscillatory pattern as suggested by a modified slab model of a wind‐forced frontal jetTurbulent boundary layer processes and symmetric instabilities can contribute to differences between modeled and observed vertical dynamics [ABSTRACT FROM AUTHOR]

It is well established that most of the plastic pollution found in the oceans is transported via rivers. Unfortunately, the main processes contributing to plastic and debris displacement through riparian systems is still poorly understood. The Marine Litter Drifter project from the Arno River aims at using modern consumer software and hardware technologies to track the movements of real anthropogenic marine debris (AMD) from rivers. The innovative "Marine Litter Trackers" (MLT) were utilized as they are reliable, robust, self-powered and they present almost no maintenance costs. Furthermore, they can be built not only by those trained in the field but also by those with no specific expertise, including high school students, simply by following the instructions. Five dispersion experiments were successfully conducted from April 2021 to December 2021, using different types of trackers in different seasons and weather conditions. The maximum distance tracked was 2845 km for a period of 94 days. The activity at sea was integrated by use of Lagrangian numerical models that also assisted in planning the deployments and the recovery of drifters. The observed tracking data in turn were used for calibration and validation, recursively improving their quality. The dynamics of marine litter (ML) dispersion in the Tyrrhenian Sea is also discussed, along with the potential for open-source approaches including the "citizen science" perspective for both improving big data collection and educating/awareness-raising on AMD issues. [ABSTRACT FROM AUTHOR]

The accumulation of plastic debris on land and coastlines and in waterways and garbage patches is one of the greatest ecological concerns of the 21st century. In that context, the sources and pathways of plastic marine debris (PMD) have been increasingly studied in the past ten years. The purpose of this communication was to analyze, thanks to the tracks of two drifting buoys released in May–June 2019 in the North-East Pacific, two features encountered within the Great Pacific Garbage Patch (GPGP): a surface convergence, which could lead to the formation of plastic hotspots, and the persistency of the floating material in this area of the ocean. The evolution of the distance between the buoys was compared with the local circulation field divergence, a Lagrangian plastic dispersal model and sea-level anomalies (SLAs). These analyses highlighted the link between the converging behavior of the drifters and a persistent negative velocity divergence as well as a higher than average-encountered modelled plastic surface density (MPSD). The persistence of the material within the GPGP was observed thanks to the trajectory of the longest persisting drifter in comparison with the trajectory of the GPGP center and extent. [ABSTRACT FROM AUTHOR]

High-frequency (HF) radar measures sea surface currents from the radio waves transmitted and received by antenna on land. Since the data quality of HF radar measurements sensitively depend on the radio wave environment around antenna, Antenna Pattern Measurements (APM) plays an important role in evaluating the accuracy of measured surface currents. In this study, APM was performed by selecting the times when the background noise level around antenna was high and low, and radial data were generated by applying the ideal pattern and measured pattern. The measured antenna pattern for each case was verified with the current velocity data collected by drifters. The radial velocity to which the ideal pattern was applied was not affected by the background noise level around antenna. However, the radial velocity obtained with APM in the period of high background noise was significantly lower in quality than the radial velocity in a low noise environment. It is recomended that APM be carried out in consideration of the radio wave environment around antenna, and that the applied result be compared and verified with the current velocity measurements by drifters. If it is difficult to re-measure APM, we suggest using radial velocity in generating total vector with the ideal pattern through comparative verification, rather than poorly measured patterns, for better data quality. [ABSTRACT FROM AUTHOR]

The geographical variability, frequency content, and vertical structure of near‐surface oceanic kinetic energy (KE) are important for air‐sea interaction, marine ecosystems, operational oceanography, pollutant tracking, and interpreting remotely sensed velocity measurements. Here, KE in high‐resolution global simulations (HYbrid Coordinate Ocean Model; HYCOM, and Massachusetts Institute of Technology general circulation model; MITgcm), at the sea surface (0 m) and at 15 m, are compared with KE from undrogued and drogued surface drifters, respectively. Global maps and zonal averages are computed for low‐frequency (<0.5 cpd), near‐inertial, diurnal, and semidiurnal bands. Both models exhibit low‐frequency equatorial KE that is low relative to drifter values. HYCOM near‐inertial KE is higher than in MITgcm, and closer to drifter values, probably due to more frequently updated atmospheric forcing. HYCOM semidiurnal KE is lower than in MITgcm, and closer to drifter values, likely due to inclusion of a parameterized topographic internal wave drag. A concurrent tidal harmonic analysis in the diurnal band demonstrates that much of the diurnal flow is nontidal. We compute simple proxies of near‐surface vertical structure—the ratio 0 m KE/(0 m KE + 15 m KE) in model outputs, and the ratio undrogued KE/(undrogued KE + drogued KE) in drifter observations. Over most latitudes and frequency bands, model ratios track the drifter ratios to within error bars. Values of this ratio demonstrate significant vertical structure in all frequency bands except the semidiurnal band. Latitudinal dependence in the ratio is greatest in diurnal and low‐frequency bands. Plain Language Summary: It is important to map and understand ocean surface currents because they affect climate and marine ecosystems. Recent advances in global ocean models include the addition of astronomical tidal forcing alongside atmospheric forcing and the usage of more powerful computers that can resolve finer features. Here, we evaluate ocean surface currents in high‐resolution simulations of two different ocean models through comparison with observations from surface drifting buoys. We examine near‐inertial motions, forced by fast‐changing winds; semidiurnal tides, forced by the astronomical tidal potential; diurnal motions, arising from tidal and other sources; and low‐frequency currents and eddies, forced by atmospheric fields. Global patterns in the models and drifters are broadly consistent. The two models differ in their degree of proximity to drifter measurements in the near‐inertial band, most likely due to different update intervals for atmospheric forcing and in the semidiurnal band, most likely due to different damping schemes. A simple proxy for vertical structure of the currents, measured by differences in drifter flows at the surface versus 15 m depth, is tracked reasonably well by the models. Discrepancies between models and observations motivate future improvements in the models. Key Points: We examine frequency content of ocean kinetic energy (KE) at the sea surface (0 m) and 15 m depth with global drifter data and two modelsNear‐surface near‐inertial and tidal KE in numerical models are sensitive to atmospheric forcing frequency and dampingThe ratio 0 m KE/(0 m KE + 15 m KE) in models lies within error bars of the observational ratios over some latitudes and frequency bands [ABSTRACT FROM AUTHOR]

Measuring vertical motions represent a challenge as they are typically 3–4 orders of magnitude smaller than the horizontal velocities. Here, we show that surface vertical velocities are intensified at submesoscales and are dominated by high frequency variability. We use drifter observations to calculate divergence and vertical velocities in the upper 15 m of the water column at two different horizontal scales. The drifters, deployed at the edge of a mesoscale eddy in the Alboran Sea, show an area of strong convergence (O $\mathcal{O}$(f)) associated with vertical velocities of −100 m day−1. This study shows that a multilayered‐drifter array can be an effective tool for estimating vertical velocity near the ocean surface. Plain Language Summary: The study of vertical motions in the ocean is a key challenge as they are difficult to measure and predict although their impact is crucial on the exchange of water properties in the water column. Here, we use high resolution drifter observations to calculate vertical velocities in the upper layers of a surface density front. This study shows high values of downward speed combined with a high temporal variability at the surface layer. Key Points: Horizontal divergence and vertical vorticity computed from drifter observationsMaximum downward speeds of 100 m day−1 in the upper 15 m on a subducting regionThe vertical velocity time series shows a high temporal variability, varying from 50 to −100 m day−1 over 4 hr [ABSTRACT FROM AUTHOR]

We identify loops and eddies from the trajectories of the drifters in the North Indian Ocean (NIO) from October 1985 to March 2019. We use the geometric identification method to identify loops and eddies and compare them with the loops identified from loopers provided by Lumpkin (2016). In NIO, the number of loops estimated from loopers is less than the number of loops and eddies identified by the geometric identification method. A total of 761 loops are identified, of which 346 are eddies, whereas the loops identified from loopers are only 149. Larger radii loops and eddies are observed in the western and central Bay of Bengal (BoB) and the southwestern part of the Arabian Sea (AS). Temporal variation of loops and eddies shows a peak during April–May in the AS and September–October in the BoB. In the BoB, the temporal variation of cyclonic eddies matches with the variation in chlorophyll.

The Patos Lagoon coastal plume is a small-scale outflow that is strongly controlled by meteorological tides. However, the riverine discharge of the lagoon is subject to high decadal variability. Hence, the discharge amount alters the scale of this coastal plume and its effects over the inner shelf environment. This study uses hydrodynamic simulations and a Lagrangian model to estimate the spreading of the plume under two different discharge conditions.Through scale parameters, we characterized the contrasts of the plume structure between high discharge and low discharge conditions. During a strong discharge regime, the width and thickness of the plume are enhanced, and the inertial processes increase against the frictional effect of the wind. The consequences of these differences include higher values of alongshore and cross-shore spreading of the drifters for the strong discharge regime. These findings indicate that under similar wind conditions, different amounts of riverine discharges alter the extent to which the material delivered by the plume can spread over the inner continental shelf. [ABSTRACT FROM AUTHOR]

It is well established that most of the plastic pollution found in the oceans is transported via rivers. Unfortunately, the main processes contributing to plastic and debris displacement through riparian systems is still poorly understood. The Marine Litter Drifter project from the Arno River aims at using modern consumer software and hardware technologies to track the movements of real anthropogenic marine debris (AMD) from rivers. The innovative “Marine Litter Trackers” (MLT) were utilized as they are reliable, robust, self-powered and they present almost no maintenance costs. Furthermore, they can be built not only by those trained in the field but also by those with no specific expertise, including high school students, simply by following the instructions. Five dispersion experiments were successfully conducted from April 2021 to December 2021, using different types of trackers in different seasons and weather conditions. The maximum distance tracked was 2845 km for a period of 94 days. The activity at sea was integrated by use of Lagrangian numerical models that also assisted in planning the deployments and the recovery of drifters. The observed tracking data in turn were used for calibration and validation, recursively improving their quality. The dynamics of marine litter (ML) dispersion in the Tyrrhenian Sea is also discussed, along with the potential for open-source approaches including the “citizen science” perspective for both improving big data collection and educating/awareness-raising on AMD issues.

The accumulation of plastic debris on land and coastlines and in waterways and garbage patches is one of the greatest ecological concerns of the 21st century. In that context, the sources and pathways of plastic marine debris (PMD) have been increasingly studied in the past ten years. The purpose of this communication was to analyze, thanks to the tracks of two drifting buoys released in May–June 2019 in the North-East Pacific, two features encountered within the Great Pacific Garbage Patch (GPGP): a surface convergence, which could lead to the formation of plastic hotspots, and the persistency of the floating material in this area of the ocean. The evolution of the distance between the buoys was compared with the local circulation field divergence, a Lagrangian plastic dispersal model and sea-level anomalies (SLAs). These analyses highlighted the link between the converging behavior of the drifters and a persistent negative velocity divergence as well as a higher than average-encountered modelled plastic surface density (MPSD). The persistence of the material within the GPGP was observed thanks to the trajectory of the longest persisting drifter in comparison with the trajectory of the GPGP center and extent.

Observations collected from a fast-flowing buoyant river plume entering the head of Doubtful Sound, New Zealand, were analysed to examine the drivers of plume lateral spreading. The near-field plume is characterised by flow speeds of over 2 ms−1, and strong stratification (N2 > 0.1 s−2), resulting in enhanced shear which supports the elevated turbulence dissipation rates (ϵ > 10−3 W kg−1). Estimates of plume lateral spreading rates were derived from the trajectories of Lagrangian GPS surface drifters and from cross-plume hydrographic transects. Lateral spreading rates derived from the latter compared favourably with estimates derived from a control volume technique in a previous study. The lateral spreading of the plume was driven by a baroclinic pressure gradient toward the base of the plume. However, spreading rates were underestimated by the surface drifters. A convergence of near-surface flow from the barotropic pressure gradient concentrated the drifters within the plume core. The combination of enhanced internal turbulence stress and mixing at the base of the surface layer, and the presence of steep fjord sidewalls likely reduced the rate of lateral spreading relative to the theoretical spreading rate. The estimates of plume width from the observations provided evidence of scale-dependent dispersion which followed a 4/3 power law. Two theoretical models of dispersion, turbulence and shear flow dispersion, were examined to assess which was capable of representing the observed spreading. An analytical horizontal shear-flow dispersion model generated estimates of lateral dispersion that were consistent with the observed 4/3 law of dispersion. Therefore, horizontal shear dispersion appeared to be the dominant mechanism of dispersion, thus spreading, in the surface plume layer.

• The altimetric product DT18 reproduces the sea level variability in the Norwegian Sea with an average error 3–4 cm. • Statistical tests conducted for the DT18 reveal some problems. • Errors of the DT18 have a shape of "diamonds" in the open sea. • Ageostrophic factors influence strongly the real current velocities in the Norwegian Sea. The objective of this paper is to assess the quality of the gridded altimetric sea level product DT18 as well as altimetry data from the Sea Level Climate Change Initiative in the Norwegian Sea. We compare the satellite altimetry data with two types of instrumental data. We use tide gauge records to assess the quality in the coastal zone and data from surface drifting buoys to assess the quality in the open ocean. Thus, we aim to complement previous studies by providing the objective assessment of the quality and performance of satellite altimetry in this important region. We demonstrate that the product DT18 reproduces the sea level variability in the coastal zone at an acceptable level (an average error is 3–4 cm), and it reproduces the structure of the time series quite well (almost with a 96% correlation). We found out that altimetry substantially smoothes the pattern of the sea level. This pattern is revealed in the coastal zone as well as in the open sea, where, in addition, it also manifests errors in a shape of "diamonds", which can be due to data interpolation from satellite tracks. We detected the influence of ageostrophic factors on the current velocities using altimetry in the open sea, and this is also true for the coastal zone. Statistical tests also showed some discrepancies between altimetry data and field (buoys and drifters) data in the open sea. This is manifested in the statistical inequality of variances and in differences of empirical distribution functions. Summing up, we assert that some errors or discrepancies in altimetric data are still observed in high latitudes, both in the coastal zone and in the open part of the Norwegian Sea. [ABSTRACT FROM AUTHOR]

• Satellite observations constrain scales with a ¼ power point of 220 km. • A decorrelation scale of 36 km provides lowest trajectory errors. • Filtering unconstrained features reduces trajectory errors by 20%. Observation space-time resolution limits the scales at which ocean forecast systems provide skillful information. The ocean processes of concern are mesoscale instabilities for which an ocean forecast system requires regular corrections of initial conditions to maintain skillful forecasts, and the observations considered are the regular satellite and in situ. Predominantly, the satellite altimeter constellation is the main observing system for this problem. We define constrained scales as those in which the forecast system has skill. The constrained scales are determined by successively filtering small-scale variability from 1 km resolution assimilative model experiments to reach a minimum error relative to ground truth data. Independent observations are from the LAgrangian Submesoscale ExpeRiment (LASER) consisting of over 1000 surface drifters persisting for three months in the Gulf of Mexico. We also vary the decorrelation scale of the assimilation system to determine the decorrelation scale that produces the smallest forecast trajectory errors. In present ocean forecast systems using regular observations, the constrained scales are larger than defined by a Gaussian filter with e-folding scale of 58 km or ¼ power point of 220 km. The decorrelation scale of 36 km used in the assimilation second order auto-regressive correlation function provides lowest trajectory errors. Filtering unconstrained variability from the model solutions reduces trajectory errors by 20%. [ABSTRACT FROM AUTHOR]

Rip currents are known as one of the most dangerous hazards on sandy beaches worldwide. Indian beaches are least explored to study the variability of rip currents in space and time. The present study is the first attempt made to understand its dynamics by utilizing indigenously developed GNSS (Global Navigation Satellite System) drifters and Rhodamine-B dye experiments. The Rama Krishna (RK) and Rushikonda Beaches of Visakhapatnam are chosen for this study, due to a recorded number of rip current-related drowning cases observed during the past decade. Few experiments were conducted during pre- and post-monsoon seasons of 2018. Drifters work on the Lagrangian principle, where they measure the current velocities along their paths driven by the surface currents. Error analysis of drifter measurements showed that they are capable of resolving surf zone motions very accurately. Strong rip currents were observed in few locations in the study area, where at times current velocities reached ~1 ms−1. Also, Rhodamine-B dye was released into the rip current prone zones along with the drifters and observed that the dye patches also followed the drifters. From these experiments, it has been observed that the rip currents are relatively strong during the post-monsoon season, which could be due to the change in the beach morphology. Similar experiments with more number of drifters would help in understanding rip current dynamics and would help in reducing rip current drowning in the beaches. Research highlights: GNSS based drifters have been designed, developed and field-tested to measure rip currents in the surf zone. Post-Processing Kinematic (PPK) resulted in position estimates with centimeter level accuracy. The drifters are capable to resolve the surf zone motions more accurately in the order of greater than 0.02 ms−1. Several drifter deployments and Rhodamine-B dye experiments were carried out at RK and Rushikonda Beaches to measure the dangerous rip currents and coastal currents. [ABSTRACT FROM AUTHOR]

Search and rescue (SAR) modeling applications, mostly based on Lagrangian tracking particle algorithms, rely on the accuracy of met-ocean forecast models. Skill assessment methods are therefore required to evaluate the performance of ocean models in predicting particle trajectories. The Skill Score (SS), based on the Normalized Cumulative Lagrangian Separation (NCLS) distance between simulated and satellite-tracked drifter trajectories, is a commonly used metric. However, its applicability in coastal areas, where most of the SAR incidents occur, is difficult and sometimes unfeasible, because of the high variability that characterizes the coastal dynamics and the lack of drifter observations. In this study, we assess the performance of four models available in the Ibiza Channel (Western Mediterranean Sea) and evaluate the applicability of the SS in such coastal risk-prone regions seeking for a functional implementation in the context of SAR operations. We analyze the SS sensitivity to different forecast horizons and examine the best way to quantify the average model performance, to avoid biased conclusions. Our results show that the SS increases with forecast time in most cases. At short forecast times (i.e., 6 h), the SS exhibits a much higher variability due to the short trajectory lengths observed compared to the separation distance obtained at timescales not properly resolved by the models. However, longer forecast times lead to the overestimation of the SS due to the high variability of the surface currents. Findings also show that the averaged SS, as originally defined, can be misleading because of the imposition of a lower limit value of zero. To properly evaluate the averaged skill of the models, a revision of its definition, the so-called SS∗, is recommended. Furthermore, whereas drifters only provide assessment along their drifting paths, we show that trajectories derived from high-frequency radar (HFR) effectively provide information about the spatial distribution of the model performance inside the HFR coverage. HFR-derived trajectories could therefore be used for complementing drifter observations. The SS is, on average, more favorable to coarser-resolution models because of the double-penalty error, whereas higher-resolution models show both very low and very high performance during the experiments.

The study of a marine environment is a challenging task because of the spatio–temporal variations of ocean phenomena and the disturbances caused by ocean currents. As such, we must collect data over long time periods to better assess and understand marine environments. To achieve this, we investigate the long-term trajectories of inexpensive and underactuated drifting vehicles called drifters. These vehicles drift passively with ambient ocean currents. Vertical actuation (buoyancy) enables them to alter their depth and achieve controllability by the use of different current layers in the ocean. We aim to utilize these persistent assets to explore oceanic regions exhaustively; patrolling the surface, covering a 3-D phenomenon (e.g., algal bloom), or examining the seafloor with downward-facing cameras. In this article, we present a data-driven deployment and planning approach for the drifters. We extract the generalized flow pattern within a given region from ocean model predictions, develop a Markov chain-based motion model, and analyze the water flow behavior. Given an initial deployment location of the drifter on the water surface and the flow patterns within the region, our approach finds attractors and their transient groups at different depths as the persistent behavior of the environment. We then determine a minimum number of deployment locations for the drifters using these attractors and their transient groups. All possible reachable locations from the initial deployment location of the drifter are determined as its planned, long-term drifter trajectory based on the computed attractors and transient groups. An optimal navigation policy is developed to demonstrate the best possible action from any location to a goal location in the environment. Our simulation results based on data from ocean model predictions validate the variability in the persistent behavior of the environment and the long-term trajectory of the drifter over space and time. Preliminary results from field trials also validate the practical application of our approach for persistent, large-scale ocean monitoring. [ABSTRACT FROM AUTHOR]

Freshwater input into deep convection regions could affect the overturning circulation. With a set of 15 Consortium for Advanced Research for the Transport of Hydrocarbon in the Environment (CARTHE) drifters and 15 Surface Velocity Program (SVP) drifters, we investigate the circulation over the south‐east Greenland shelf and the potential for off‐shelf freshwater export. Part of the East Greenland Current flow is steered into the East Greenland Coastal Current immediately upstream of Sermilik Trough. Between the trough and Cape Farewell, two separate cores are visible. Just past Cape Farewell drifters are redistributed into a shelfbreak core and a slow eddying shelf flow. A coastal core is reestablished downstream. Exchanges between the shelfbreak and coastal flows take place both on the east and west Greenland shelf, allowing fresher water to be diverted away from the coast. Five of 15 shallower CARTHE drifters were exported, mainly at Cape Farewell. CARTHE motion shows a higher correlation with local winds, which are more favorable for off‐shelf transport in this area. Plain Language Summary: The Atlantic Meridional Overturning Circulation is a key element of the climate system. Global warming causes an influx of freshwater over the east Greenland shelf, that could affect the Atlantic circulation if it is exported into areas where deep water is formed. We deployed 30 surface drifters in August 2019, which we combine here with existing drifter and satellite data to describe the circulation over the south‐east Greenland shelf. The export of five shallow water drifters into the Irminger Sea suggests that wind could be a driver for freshwater export away from the shelf. Key Points: Drifter tracks show steering from shelfbreak toward the East Greenland Coastal Current (EGCC) at Sermilik Trough and exchanges between the East Greenland Current (EGC) and EGCC downstreamWest of Cape Farewell, drifters in the EGC and EGCC are redistributed into a shelfbreak core and a slow, eddying inner‐shelf flowFive of 15 shallow drifters were exported, mainly near Cape Farewell. Cold water leakage is observed from sea surface temperature (SST) data in the same area [ABSTRACT FROM AUTHOR]

Shallow marine environments are characterized by complex and variable physical processes that have significance for biological and human communities. However, the global disparity in scientific resources limits examination of the coastal ocean in some regions, so the development of universal and accessible technologies is needed. We combined a compact, GPS-equipped drifter design with long-range (LoRa) radio telemetry and a receiver system housed on a research vessel to develop a low-cost, easily assembled system of drifters. LoRa transmission of real-time location data while deployed was used to increase recoverability, minimizing the initial and long-term costs of constructing and maintaining the operation of this drifter system. Bench and field testing confirmed the performance of the system, which was optimized for LoRa transmission, which is compromised when occurring near the sea surface. The swift currents, complex coastline, and varied sea states present in our study area provided a rigorous testing environment for the drifter system. We established the working limits of battery life and LoRa data transmission within our configuration of transmitters and receiver, evaluated the accuracy of the GPS receivers, and determined the most robust variant of the drifter body design. This study offers proof of concept for a radio-tracked drifter system that is ready for deployment to track nearshore surface currents. Both the drifter system and the data telemetry protocol can be adapted to other investigations of the marine environment by integrating new sensors, modifying the configuration or deployment procedure, or applying LoRa radios to transfer data from fixed sensing platforms. [ABSTRACT FROM AUTHOR]

A tidal energy development site has been designated in Minas Passage (Bay of Fundy, Nova Scotia, Canada) for testing in-stream turbines and producing renewable energy. Concern remains that turbines might harm local populations of marine animals as they sweep by within a fastflowing water mass. Drifters approximately track a water mass and can support instrumentation for detecting fish that carry an acoustic tag. A tagged Atlantic salmon tracked sufficiently similarly to the drifter for it to be continuously within detection range for three intervals of up to 56 minutes over a 21-hour period. The same fish was briefly detected near the drifter five days later. Two types of quasi-stable drifter trajectory were found to make many transits through the fast-flowing waters of Minas Passage, with tidal excursion extending far beyond the passage. Drifter trajectories characterize water areas that are likely to be influenced by fish-turbine interaction over the tidal timescale. One quasi-stable trajectory is associated with accumulations of floating debris that may interfere with tidal energy devices. Most drifter tracks passed south of the tidal energy development site. Less commonly, drifters passed through the development site during flood tide and these tracks are associated with northerly extremes of quasi-stable trajectories. Few drifter tracks passed through the development site on the ebb tide and those that did quickly transitioned to quasi-stable trajectories that mostly pass south of the development site. Regardless of drifters mostly bypassing the development site, the monthly probability of drifter collision with a 500 kW near-surface tidal energy device was estimated to be 0.18. Collision probability for fish is argued to be lower. [ABSTRACT FROM AUTHOR]

The high-frequency radar coastal network in Toulon operates in multistatic mode for the monitoring of the ocean circulation in the Northwestern Mediterranean Sea. With 2 transmitters and 2 receivers on 3 distant sites, it measures 4 different elliptical components of the surface velocity. We provide a methodology for improved current mapping using this augmented number of available projections and we show some typical results obtained during the year 2019. The validity and the quality of the reconstruction are assessed through comparisons with two types of in situ measurements, namely drifters' velocities from a dedicated campaign and acoustic Doppler current profiler data from an opportunity oceanographic campaign. The results of these assessments confirm the accuracy of these high-frequency radar measurements and their ability to capture the meso- to submeso-scale variability of the near shelf circulation. [ABSTRACT FROM AUTHOR]

Mesoscale eddies are common oceanic phenomena. Although many related studies have been conducted, the ability for mesoscale eddies to carry real particles remains poorly addressed. We considered the drifters as real particles to characterize the capability of mesoscale eddies to carry particles. Firstly, mesoscale eddies in the northwest Pacific (99°E–180°E, 0°–66°N) were identified using sea level anomaly (SLA) data from 1993 to 2015. Secondly, three important parameters (the carrying days, the number of circles the drifter revolving around the eddy center, and the carrying distances) were calculated by colocalizing eddy data with drifters. Finally, statistical analysis and composite analysis were conducted, reflecting the capability of mesoscale eddies to carry particles. The mechanisms on the carrying capability of eddies were also discussed. Results show that (1) the motion of carried drifters reflects the upper limit of rotational speed of eddies that the drifters revolve around the eddy center by ≤ 90° for one day in most cases; (2) the drifters tend to be carried for a longer time when their minimal distances to the eddy center measured with normalized distance are small; (3) there are two types of eddies (cyclonic and anticyclonic eddies) in different subregions of northwest Pacific, and each has a different carrying capability (on average, similar in the tropical ocean and Subtropical Countercurrent, cyclonic eddies tend to have stronger carrying capability in Southern Kuroshio Extension, and anticyclonic eddies tend to have stronger carrying capability in Northern Kuroshio Extension and Subarctic Gyre); (4) on average, the carried drifters tend to travel for a longer time around the normalized eddy radii ranging from 0.41 to 0.76; (5) the carrying days are related to the Rossby number of the eddy (in general when the Rossby number is smaller, the carrying days are longer). [ABSTRACT FROM AUTHOR]

Surface dispersion properties give an immediate characterization of the spreading of passive and active tracers in the ocean, like pollutant and marine species. The Mediterranean sub-basins (Tyrrhenian, Adriatic, Ionian, Levantine and Aegean) are known as complex dynamic regions due to the presence of coherent structures on different motion scales. This paper focus on dispersion of the surface Mediterranean flow using the surface current data derived from two different drifter designs: the Coastal Ocean Dynamics Experiment (CODE) and the Surface Velocity Program (SVP) drifters. The absolute dispersion for small time scales (15 days) and spatial scale larger than DI, our results emphasize a similarity in all the sub-basins with the presence of a quasi Random-walk regime and a quasi diffusive regime for the absolute and relative dispersion, respectively.

Instruments drifting at the ocean surface are quasi-Lagrangian, that is, they do not follow exactly the near-surface ocean currents. The currents measured by three commonly-used drifters (CARTHE, CODE and SVP) are compared in a wide range of sea state conditions (winds up to 17 m/s and significant wave height up to 3 m). Nearly collocated and simultaneous drifter measurements in the southwestern Mediterranean reveal that the CARTHE and CODE drifters measure the currents in the first meter below the surface in approximately the same way. When compared to SVP drogued at 15 m nominal depth, the CODE and CARTHE currents are essentially downwind (and down-wave), with a typical speed of 0.5–1% of the wind speed. However, there is a large scatter in velocity differences between CODE/CARTHE and SVP for all wind and sea state conditions encountered, principally due to vertical and horizontal shears not related to the wind. For the CODE drifter with wind speed larger than 10 m/s and significant wave height larger than 1 m, about 30–40% of this difference can be explained by Stokes drift.

Atlantic Water takes various pathways through the Nordic Seas, and its transformation to denser waters forms a crucial connection to the lower limb of the Atlantic Meridional Overturning Circulation. Circulation maps often schematize two distinct pathways of Atlantic Water: one following the Norwegian Atlantic Slope Current along the continental slope of Norway and one following the Norwegian Atlantic Front Current along the Mohn and Knipovich Ridges. In this paper, the connectivity between the northward flow along these ridges is investigated. Analyzing trajectories of surface drifters and ARGO floats, we find that only 8% of the floats that travel near the mid‐ocean ridges take the frontal pathway to the north. Indeed, by tracing numerical particles in a realistic numerical simulation, part of the water mass traveling along the Mohn Ridge follows the 2,500 m isobath eastward and joins the slope current, instead of flowing north along the Knipovich Ridge. Furthermore, north of 74°N, frequent exchange between the slope current and the front current is observed. Therefore, the slope current and front current are less isolated than often schematized. Additionally, the observational data set reveals substantial cross‐ridge exchange; 31% of the floats that travel within 60 km from the mid‐ocean ridges cross it. Results from numerical simulations indicate that the cross‐ridge exchange leads to cooling and freshening of the Atlantic Water along the front. Deployments of floats near the mid‐ocean ridges are needed to investigate the pathway of Atlantic Water and its exchange across the ridge in more detail. Plain Language Summary: The Atlantic Ocean plays a crucial role for global climate by redistributing heat and salt via the Atlantic Meridional Overturning Circulation (AMOC). A key region for maintaining this circulation is the Nordic Seas, where Atlantic Water is modified due to large ocean heat losses to the atmosphere. The transformation of Atlantic Water is not uniform, as the water mass can take various pathways. Two main routes are often described: one along the continental slope of Norway and one along the topographic ridges that separate the warm eastern basin from the cold western basin. In this paper, we investigate the latter pathway using a Lagrangian approach. That is, we follow the flow, instead of investigating properties at fixed positions. We find that the flow along the mid‐ocean ridges is not continuous as often schematized; substantial exchange between the flow along the ridge and the flow along the continental slope occurs. Furthermore, we observe various trajectories that cross the mid‐ocean ridge. Results from numerical simulations indicate that this cross‐ridge exchange can lead to enhanced transformation of the Atlantic Water. Therefore, this process is important for setting the properties of water masses that enter the Arctic Ocean and of water masses that contribute to the AMOC. Key Points: The northward flow along the Mohn Ridge does not form a one‐to‐one connection to the northward flow along the Knipovich RidgeSignificant exchange takes place between the inner and outer branch of the Norwegian Atlantic Current north of 72° NExchange across the mid‐ocean ridge cools and freshens Atlantic Water as it travels north along the ridge [ABSTRACT FROM AUTHOR]

The paper presents results of experimental investigations of currents in the nearshore region of the south Baltic Sea. The analysis is based on the field data collected near Lubiatowo (Poland) using the measuring equipment which was simultaneously operated both by the Polish and Russian research teams. The venture was aimed at detection of rip currents that are rare and insufficiently explored phenomena in the south Baltic coastal zone. The data include wind velocity and direction, deep-water wave buoy records and currents surveyed by means of drifters. The measurements were carried out in the area whose hydrodynamics, lithodynamics and morphodynamics are typical of the south Baltic sandy coast. It appears that the nearshore water flows are mostly represented by longshore wavedriven currents with mean velocities of 0.22-0.53 m/s, and the maximum velocity of 1.32 m/s. Water circulation patterns resembling rip currents with velocities of up to 0.34 m/s were identified only on one day, when specific wave conditions occurred at the study site. Contrary to strong longshore currents generated by storm waves, rip currents occur under mild or moderate wave conditions, when many beach users are willing to swim in nearshore waters. The present findings can therefore be useful for the improvement of swimmers' safety in the south Baltic Sea regions. [ABSTRACT FROM AUTHOR]

A new estimate of Agulhas leakage transport is calculated using profiling floats and drifters. Since Richardson's seminal estimate of 15 Sv in 2007, the number of floats and drifters passing through the Agulhas Current has quadrupled. Within uncertainties we find the same leakage percentages as Richardson, with 34% of drifters leaking at the surface and 21% of floats leaking at 1,000 m depth. We find that the drifters tend to follow a northward leakage pathway via the Benguela Current compared to the northwestward leakage pathway of the floats along the Agulhas Ring corridor. We simulate the isobaric and profiling behavior of the floats and drifters using two high resolution models and two offline Lagrangian tracking tools, quantifying for the first time the sampling biases associated with the observations. We find that the isobaric bias cannot be robustly simulated but likely causes an underestimate of observed leakage by one or two Sverdrups. The profiling behavior of the floats causes no significant bias in the leakage. Fitting a simulated vertical leakage profile to the observed leakage percentages from the floats and drifters and using the mean Agulhas transport observed by a moored array at 34°S we find an improved Agulhas leakage transport of 21.3 Sv, with an estimated error of 4.7 Sv. Our new leakage transport is higher primarily because we account for leakage at depths down to 2,000 m, while Richardson considered only the top 1,000 m of the water column. Plain Language Summary: We calculate a new estimation of Agulhas leakage using floats and drifters. Since most recent estimate of 15 Sv was calculated in 2007, we have had four times as many observations pass through the Agulhas Current. We find more drifters leak at the surface than floats at intermediate depth. The drifters follow a northward leakage passage compared to the northwestward passage of the floats. Using two models and two particle tracking tools, we mimic the behavior of these floats and drifters to better understand and quantify the sampling biases associated with these observations. Combining the results from the observations and these simulations, we calculate a new improved leakage transport of 21.3 Sv with an error of 4.7 Sv. Key Points: Using observations of drifters and floats we estimate Agulhas leakage to be 21 Sv, significantly larger than the previous understandingTwelve percent more drifters leak than floats with drifters following a northward leakage pathway and floats a northwestward pathwayOur simulations show that the profiling behavior of the floats does not introduce a significant bias to the Lagrangian estimate of leakage [ABSTRACT FROM AUTHOR]

The deployment of 206 surface drifters over 3 years in a fjord system in northern British Columbia allows examination of drift and dispersion in complex coastal regions on time scales up to 10 days. The surface drift is found to be seasonally variable, with stronger dispersion and outflows in the spring and fall, and negligible outflow in the summer. Dispersion at time scales less than 10 hr is well described by fractional Brownian motion, where the drifter tracks exhibit fractal characteristics with a dimension of 1.34 over scales of 2 to 13 km. Drifters are found to reach less energetic nearshore regions within 12–15 hr, which slows along‐channel dispersion. The comparison of the drifter statistics (from 2014–2016) with observations of the spatial distribution of oil sheen following an oil spill in 2006 shows that the drifter results provide a reasonable proxy for oil drift in this area. A statistical model for the extent of along‐channel transport of spilled oil is proposed for use in planning emergency response activities in the area. Plain Language Summary: This paper is an analysis of the movement of 206 surface drifting buoys (drifters), which were released in the Kitimat fjord system in northwestern British Columbia between 2014 and 2016. This fills a knowledge gap concerning drift of objects at the ocean surface in narrow fjord systems over times longer than 1 day. Drift is toward the ocean on average and stronger in the spring and fall than in the summer. Drifters move approximately twice as fast near midchannel than they do near the shorelines and are found to come in close proximity of the shoreline within 12–15 hr of being released. Consequently, this cross‐channel movement slows drift along the channel. Comparison with observations of sheening from a previous oil spill in the study region suggests that the drifters are an adequate proxy for spilled oil. A statistical model for the maximum likely extents of oil spills in the fjord system after times up to 10 days is proposed. Key Points: Analysis of ocean surface dynamics in a multiply connected fjord system from 3 years of drifter dataOver time scales longer than 15 hr interaction between the drifters and channel walls restrict along‐channel dispersionThe drifters are an adequate proxy for oil and results can be used for spill response planning [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geophysical Research. Oceans is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The coastal area of Chalastra (NW Thessaloniki's Gulf, Northern Greece) features prominent mussel farming activity as well as fishing activity. These activities are closely related to the hydrodynamics of the basin's seawaters. The prevailing hydrodynamic force for the circulation of coastal waters of Chalastra is wind stresses. The hydrodynamics of this coastal region may be further influenced by three rivers outflowing to the southwestern part of the basin; however, this runoff has dramatically decreased during the last few decades. Concerning the wind forcing regime, this is distinguished by two characteristic regimes. The first one is realized in winter and the other mainly in summer. Systematic field studies were conducted during one year for current and density measurements. Seawater samples were collected and chemically analyzed for dissolved oxygen, chlorophyll α and nutrients. Data revealed some cases of flow currents of opposite direction between the upper and the lower water layer, and a characteristic captured downwelling which seemed to evolve periodically on a diurnal time scale, especially in summer. Furthermore, a two layer mathematical model was developed and applied for the study of the water circulation and the investigation of downwelling processes under specific conditions; the tracing as well as the temporal and spatial evolution of these hydrodynamic processes in the mussels' culture study area constituted the main aim of the present work. The formation of such events, which were observed mainly during summer periods, may affect the mussels' development and has to be considered when designing farming practices in the area. [ABSTRACT FROM AUTHOR]

The moment when Grierson's Drifters film was first screened to audiences at the end of 1929 coincided with the technological transition in British cinema from accompaniment by musicians playing live in the auditorium to the introduction of fully synchronized sound on film. Arthur Dulay's 'Musical Suggestions for Drifters' furnish plain evidence of not only how complex the work of projectionists and their assistants could be, but also how, until the transition to recorded sound was complete, a variety of methods were deployed in different cinemas to add music and sound effects to pictures. [ABSTRACT FROM AUTHOR]

The Lagrangian dispersion statistics of the Black Sea are estimated using satellite-tracked drifters, satellite altimeter data and a high-resolution ocean model. Comparison between the in-situ measurements and the model reveals good agreement in terms of the surface dispersion. The mean sub-basin coherent structures and currents of the Black Sea are well reproduced by the model. Seasonal variability of the dispersion in the upper (15 m), intermediate (150 m) and deep (750 m) layers are discussed with a special focus of the role of sub-basin scale structures and currents on the turbulent dispersion regimes. In terms of the surface relative dispersion, the results show the presence of the three known turbulent exponential, Richardson and diffusive-like regimes. The non-local exponential regime is only detected by the model for scales