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

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

Sources, pathways, and abatement strategies of macroplastic pollution: an interdisciplinary approach for the southern North Sea

The issue of marine plastic pollution has been extensively studied by various scientific disciplines in recent decades due to its global threat. However, owing to its complexity, it requires an interdisciplinary approach to develop effective management strategies. The multidisciplinary scientific approach presented here focuses on understanding the sources and pathways of macroplastic litter and developing abatement strategies in the southern North Sea region. Over 2.5 years, more than 63,400 biodegradable wooden drifters were deployed with the help of citizen science to study the sources, pathways, and accumulation areas of floating marine litter. Rivers act as sinks of most of the floating marine litter released within their waterways. Short-term field experiments were also conducted to analyse the hydrodynamic and atmospheric processes that govern the transport of floating litter particles at the sea surface. Numerical models were used to examine the transport of virtual litter particles in the entire North Sea and in coastal regions. It was found that there are no permanent accumulation areas in the North Sea, and the Skagerrak and fronts can increase the residence times of floating marine litter and favour sinking. Field surveys revealed that the majority of litter objects originate from fisheries and consumer waste. To develop effective abatement strategies, the key stakeholder landscape was analysed on a regional level. The interdisciplinary approach developed in this study highlights the importance of synergizing scientific resources from multiple disciplines for a better understanding of marine plastic pollution and the development of effective management strategies

Transport variability of the ACC and teleconnection with the Southern Annular Mode (SAM) south of Africa.

To study the Antarctic Circumpolar Current (ACC) volume transport several cruises have taken place. The results of these cruises show snapshots without information about the time variability. To investigate the time variability of the ACC the Alfred Wegener Institute operates an array of Pressure Inverted Echo Sounders (PIES) along a satellite altimeter ground track south of Africa. PIES monitor ocean bottom pressure and acoustic travel time across the water column. A Gravest Empirical Mode (GEM, Meinen and Watts 1998) was applied to determine the geostrophic transport between the PIES. These time series were used to compute a transfer function between satellite Sderived transport and geostrophic transport. Satellite altimetry offers the possibility to calculate ACC transport between 1992 and 2010. A mean transport of 115 Sv and a variability of 7 Sv were derived for the Topex/Poseidon, Jason 1 and Jason 2 time period. A wavelet analysis shows that the ACC transport highly correlates with the winter and spring SAM index, whereas a direct correlation on a monthly scale could not be shown

Frontal eddies along a western boundary current

Cyclonic frontal eddies are distinguishable from the surrounding water due to their unique biological and physical characteristics and have been observed in all western boundary current regions. These eddies spawn from cut-off meanders and are found on the landward side of the current. Here, we report for the first time observed frontal eddies for the intensification zone (north of 28 oS) of the East Australian Current (EAC) off Southeast Queensland, Australia, by analysing remotely sensed sea surface temperature (SST) and chlorophyll-a (Chl-a) data. The frontal eddies were detected initially in the analysis of satellite tracked surface drifters. The shelf-crossing cyclonic drifter pathways indicated the presence of drifter-trapping cyclonic frontal eddies. The subsequent analysis of satellite images allows to quantify key eddy characteristics, cross-shelf volume transports associated with eddy filaments, eddy-driven shelf water renewal time scales, and export of total Chl-a and carbon per day. The observed frontal eddies have core radii of approximately 13 km and 15 km. The cold core surface SST anomaly and elevated chl-a indicates eddy entrainment of shelf water. The translational or core displacement velocity is estimated with 0.17 m.s-1 or 15 km per day and the tangential velocity quantified from tracking surface drifters is 0.28 m.s-1 to - 0.5 m.s-1. This results in a rotational period of 1.9 days to 3.9 days. We use maximum Chl-a and SST gradients to approximate the width of importing and exporting filaments associated with the frontal eddy to derive volume transports of 1.5 Sv and 1.9 Sv (import) and 0.3 Sv and 1.8 Sv (export), respectively. Chl-a concentrations of the exporting filaments are about 0.4 mg.m-3 to 0.6 mg.m-3 yielding a total export of 13 t to 78 t of Chl-a per day. The frontal eddy induced on-shelf transport of 130 km3 - 160 km3 per day represents between 18 % and 22 % of the shelf volume. Therefore, it would take approximately five days to renew all shelf water. We conclude that the observed frontal eddies of the northern intensification zone of the EAC potentially play an important role in determining cross-shelf exchanges, contribute to on-shelf marine conditions, enhancing coastal primary productivity and are possibly important to the export of shelf water properties such as the fish larvae of subtropical species via entrainment