A State-of-the-Art Compact Surface Drifter Reveals Pathways of Floating Marine Litter in the German Bight

Abstract

Lagrangian observations are important for the understanding of complex transport patterns of floating macroscopic litter items at the ocean surface. Satellite-tracked drifters and numerical models are an important source of information relevant to transport processes as well as distribution patterns of floating marine litter (FML) on a regional to global scale. Sub-mesoscale processes in coastal and estuarine systems have an enormous impact on pathways and accumulation zones of FML and are yet to be fully understood. Here we present a state-of-the-art, low-cost and robust design of a satellite-tracked drifter applicable in studying complex pathways and sub-mesoscale dynamics of floating litter in tidally influenced coastal and estuarine systems. It is compact, lightweight <5 kg, capable of refloating, easily recovered and modified. The drifter motion resolves currents of the ocean surface layer (top 0.5 m layer) taking into account wind induced motions. We further showcase findings from seven of our custom-made drifters deployed from RV Heincke and RV Senckenberg in the German Bight during spring and autumn 2017. Drifter velocities were computed from high resolved drifter position data and compared to local wind field observations. It was noted that the net transport of the drifters in areas far away from the coast was dominated by wind-driven surface currents, 1% of the wind speed, whereas the transport pattern in coastal areas was mainly overshadowed by local small-scale processes like tidal jet currents, interactions with a complex shoreline and fronts generated by riverine freshwater plumes.

Submesoscale dispersion of surface drifters in a coastal sea near offshore wind farms

“…The value 0.006 is assigned to weighting factor β. This value, estimated by Callies et al (2017) for the same drifter type, seems largely consistent with findings of a more recent experimental study by Meyerjürgens et al (2019). From seven drifters tracked in the German Bight they estimated a wind slip of 0.27 % and a total wind-induced drifter motion of 1 % of 10 m winds.…”

“…As a possible problem these authors mention the presence of tidal movements which according to Beron-Vera and LaCasce (2016) can cause conflicting results between different types of analyses. Middleton (1985) addresses the general question of how Eulerian spectra translate into their Lagrangian counterparts. Elaborating on an original idea of Corrsin (1959), Middleton (1985) found that spectra observed in an Eulerian and Lagrangian framework should agree when velocity changes depend more on local variations than on advective processes (see also LaCasce, 2008, for a summary of the concept).…”

Environmental and Biological Factors Influencing Dispersal of Neonate Leatherback Turtles (Dermochelys coriacea) From an Endangered Costa Rican Nesting Population

“…It is worth noting that in computing the true headings of the neonates, wave, wind, and inertial influences could differentially impact the neonates and the drifters. However, inertial influences are unlikely to be important, as the mean size of the neonates gives them an effective radius that minimizes inertial effects to less than 5 • of the deflection angle (Beron-Vera et al, 2015;Brooks et al, 2019) and at the modest wind speeds measured (1-5 m s −1 ), assuming a 0.27% windage effect calculated from a similar drifter (Meyerjürgens et al, 2019), the error associated with the windage would be (0.0027-0.0135 m s −1 ), which is orders of magnitude smaller than the neonate swimming speeds. Wave influences, or Stokes drift, would be aligned onshore in these nearshore waters and perpendicular to the isobaths and would potentially hinder the neonate's offshore trajectory and slow their swimming speed.…”

The Fate of Marine Litter in Semi-Enclosed Seas: A Case Study of the Black Sea

“…Therefore, the experiments described in the previous section aim at obtaining an overall geophysical consistency based primarily on the oceanographic conditions, atmospheric and river forcing. Regarding the validation of the Lagrangian model, in the present study, we use the same model used by Stanev et al (2019a), who validated its performance against GPS-surface drifters (Meyerjurgens et al, 2019) and wooden drifters in the North Sea. The performance of the model as demonstrated by Stanev et al (2019a) was very encouraging, in particular when simulating the stranding positions (see Figure 7 in the cited work).…”