Search

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]

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]

Discussion about the Great War at sea tends to centre on capital ships and Jutland. Far less has been written about the crucial role played by fishermen, fishing vessels and their coastal communities. Yet armed fishing vessels and their fishermen crews were continually on the maritime front line. They formed the backbone of the Auxiliary Patrol, working principally on anti-U-boat patrols or minesweeping. Around 3000 fishing vessels were requisitioned whilst more than 39,000 fishermen joined the Trawler Section of the Royal Naval Reserve. The cultural, social and attitudinal gulf between working fishermen and many RN officers was enormous. Those vessels left fishing also played a vital role in maintaining the food supplies; many were sunk whilst working. Around 672 fishing vessels were lost through enemy action whilst either fishing or on Admiralty service. After the war, their substantial role was gradually forgotten, now hardly recognised. This paper examines their contribution. [ABSTRACT FROM PUBLISHER]

The surface transport of point and non-point source discharges into eastern Lake Ontario and upper St. Lawrence River was modeled as passive tracers using the Estuary and Lake Computer Model (ELCOM) during the ice-free period of 2006. Model hydrodynamics were validated against temperature and current observations and Lagrangian drifter tracks. Root-mean-square (RMS) errors of simulated temperature profiles were comparable to other model applications; however, current RMS errors and Fourier Norms were nominally larger than in open lake applications, and RMS errors for drifter tracks were 0.5-4.0 km (3 day duration). The errors in simulating currents and drifters, relative to temperatures, are likely the result of the difficulty in representing the complex geometry of the region, which is composed of numerous channels and islands. To determine the physical processes responsible for tracer transport, cross-correlation coefficients were calculated when model processes were switched off (e.g., wind forcing, surface thermodynamics, Earth rotation, St. Lawrence River outflow, etc.). Wind was found to be the most dominant process forcing transport of tracers both in the Kingston Basin and the St. Lawrence River, whereas the St. Lawrence River outflow, controlled by the Moses Saunders Dam, was found to influence the transport of tracers along the river. Tracers were transported -60 km eastward under moderate to strong winds (> 5 ms-1 ), remained nearshore when constrained within channels or by islands and had minimum dilutions of 20% and 39% at the Kingston Central and Kingston West drinking water intakes, respectively. The results suggest that factors such as the proximity between intakes and outfalls and presence of flow constraining topography, should be considered in future source and wastewater planning. [ABSTRACT FROM AUTHOR]

Abstract: Field measurements and numerical simulations were used to determine the effects of dominant meteorological conditions on the hydrodynamics of a wide (aspect ratio ~2), relatively deep (seasonally stratified) and open lake embayment (Vidy Bay, Lake Geneva). A three-dimensional hydrodynamic model (Delft3D-FLOW) was employed to simulate flow in the lake. High-resolution maps of wind, temperature and humidity (over the lake) were applied as input to drive the model. Because wind was the main force driving flow in the lake, currents in the embayment were investigated systematically for different wind conditions and seasonal stratification. Satisfactory model validation was achieved using drifter and moored measurements within the embayment. Markedly different circulation patterns were measured within the embayment, with the transition from one pattern to another occurring abruptly for small changes in wind direction. These distinct patterns resulted from relatively small changes in the large gyre of Lake Geneva's main basin, especially the angle between the current in front of the embayment and the embayment shoreline. The boundary between the embayment and the pelagic zone was defined by the largest gyre within the embayment. This study shows that, (i) in a large lake, complex current patterns can occur even within a minor embayment, and (ii) that these patterns can transition rapidly over a small range of wind directions. Near-shore gyre can occur for lengthy periods, which has implications for flushing of discharges within the embayment. [Copyright &y& Elsevier]

Abstract: Global set of trajectories of satellite-tracked Lagrangian drifters is used to study the dynamics of marine debris. A probabilistic model is developed to eliminate the bias in spatial distribution of drifter data due to heterogeneous deployments. Model experiments, simulating long-term evolution of initially homogeneous drifter array, reveal five main sites of drifter aggregation, located in the subtropics and maintained by converging Ekman currents. The paper characterizes the geography and structure of the collection regions and discusses factors that determine their dynamics. A new scale Rc =(4k/|D|)1/2 is introduced to characterize tracer distribution under competing effects of horizontal divergence D and diffusion k. Existence and locations of all five accumulation zones have been recently confirmed by direct measurements of microplastic at the sea surface. [Copyright &y& Elsevier]

Abstract: This article presents, for the first time, an investigation into the presence of rip currents along the southern coast of the Caspian Sea. The study site is selected at the Anzali port where 3 people were drowned in one day of summer 2007. Bathymetric surveys were obtained twice during the summers of 2008 and 2009 and rip currents were measured for two days in the summer of 2008 and the summer of 2009 with different wave conditions, using five GPS drifters. An RCM 9 current meter was installed in the rip channel for credibility of the drifter velocity. The cross-shore location of their velocity maxima and the distance they extend offshore are just two important unknowns. These questions were investigated using drifter trajectories. An oblique and a classic rip current were observed in two experiments. A field validation of the drifters shows that correspondence between the drifters and RCM 9 measurements is good. [Copyright &y& Elsevier]

The Mona Passage is a major shipping lane to the Panama Canal and a key route for illegal traffic into the United States. We have emplaced two high-frequency radar (HFR) stations on the west coast of Puerto Rico intended to allow mapping of the ocean surface vetocity field of the eastern Mona Passage and to explore its performance in vessel detection and tracking. The array provides coverage of the southeastern quadrant of the Passage extending west to Mona Island and north to Rincon. Hourly results are posted online in near-real time. To optimize our results, we twice measured the antenna beam patterns and applied these corrections to the resulting radial returns. To assess the basic capability of the Mona Passage HFR array to measure surface currents in this tropical environment, we undertook validation measurements, including repeated deployment of Lagrangian drifters, deployment of an acoustic Doppler current profiler, and comparison with modeled tidal currents. Our experimental measurements showed good agreement to both modeled and in situ data lending confidence to the area-wide surface current maps generated by this system. Repeated measurements showed limited temporal variability of antenna distortion patterns, demonstrating that these are in large part the product of the surrounding environment. Comparison between a numerical particle tracking algorithm and experimental Lagrangian trajectories showed mixed results, with better agreement during periods of low intrahour variability in current direction than during periods of rapid tidal reversal. [ABSTRACT FROM AUTHOR]

Abstract: Field observations of flows in coastal zone are scarce, but important for understanding the spatial variability of currents. The design of small, low-cost GPS drifters for collecting accurate Lagrangian data in the coastal zone is described. The drifters are intended for using in nearshore environments, lakes and estuaries over timescales of a few minutes up to several hours and are a low-cost alternative for applications which do not require drifter’s sea-going capability. Two field tests of GPS drifters in the south coast of Caspian Sea in Anzali port, Iran, in November 2008 and July 2009 were successful. [ABSTRACT FROM AUTHOR]

A main conclusion following the oil spill from the Prestige tanker was that improvements in ocean circulation models were necessary; this was in order to predict, more accurately, the trajectories followed by the oil slicks and hence assist in fight against oil pollution operations. In this contribution, the results of the validation of a semi-empirical ocean circulation model, parameterised for the Bay of Biscay and forced with operational oceano-meteorological remote sensing observations, are shown. The model results have been validated with observations from drifting buoys, deployed in the Bay of Biscay during the crisis. The results show that the model explains a relatively large percentage of the current variability. The comparisons between the real and the estimated drifter trajectories indicate that for 3, 5 and 7 day-long trajectories, the drifter position is estimated with errors of approximately 23, 35 and 46km, respectively. The model reproduces relatively well the trajectory followed by the drifter with the shortest period (23 days). [Copyright &y& Elsevier]

The word "backpacker" produces a particular image in our minds, and is often thought of as a countercultural wanderer dressed in "ethnic" styles. Over time, backpacking has progressively widened its sociocultural base and "drifters" are being consigned to the margins. The transition has only been acknowledged recently, though the seeds of the change were planted decades ago. Previously unpublished research on the dress and styles of 112 backpackers, collected during the 1990s, provided insights into the changes that have occurred in South Asia. On the "beaten track" of international travel, it can be difficult to separate backpackers from conventional tourists if one relies on their appearance. While alternative developments are also occurring, "mainstream" b ackpacking appears to be increasingly conformist with its new styles and interests. [ABSTRACT FROM AUTHOR]

The dynamics of crude oil and different surface ocean drifters were compared to study the physical processes that govern the transport and landfall of marine oil spills. In a wave-tank experiment, drifters with drogue did not follow oil slicks. However, patches of undrogued drifters and thin bamboo plates did spread at the same rate and in the same direction as the crude oil slicks. Then, the trajectories of the Deepwater Horizon oil spill and 1300 drifters released near the spill source were investigated. Undrogued drifters were transported twice as fast as drogued drifters across the isobaths. 25% of the undrogued drifters landed, versus about 5% of the drogued ones, for the most part, on the same coastline locations where oil was found after Deepwater Horizon. Results highlight the importance of near surface gradients in controlling the cross-shelf transport and landing of surface material on the Gulf of Mexico's northern shores. • Undrogued drifters and crude oil slicks advect and disperse similarly in waves. • Undrogued drifters make landfall 5 times more than near-surface drogued drifters. • Near-surface vertical shear sets the cross-shelf transport of surface material. [ABSTRACT FROM AUTHOR]

As oil production worldwide continues to increase, particularly in the Gulf of Mexico, marine oil spill preparedness relies on deeper understanding of surface oil spill transport science. This paper describes experiments carried out on a chronic release of crude oil and aims to understand the residence time of oil slicks using a combination of remote sensing platforms and GPS tracked drifters. From April 2017 to August 2018, we performed multiple synchronized deployments of drogued and un-drogued drifters to monitor the life time (residence time) of the surface oil slicks originated from the MC20 spill site, located close to the Mississippi Delta. The hydrodynamic design of the two types of drifters allowed us to compare their performance differences. We found the un-drogued drifter to be more appropriate to measure the speed of oil transport. Drifter deployments under various wind conditions show that stronger winds lead to reduce the length of the slick, presumably because of an increase in the evaporation rate and entrainment of oil in the water produced by wave action. We have calculated the residence time of oil slicks at MC20 site to be between 4 and 28 h, with average wind amplitude between 3.8 and 8.8 m/s. These results demonstrate an inverse linear relationship between wind strength and residence time of the oil, and the average residence time of the oil from MC20 is 14.9 h. • Satellite remote sensing can be used to track oil displacement. • GPS tracked drifters and UAS can be used to estimate the oil residence time. • Wind strength is inversely correlated to oil time residence. • River plumes will influence the oil transport despite wind and currents. [ABSTRACT FROM AUTHOR]