Submesoscale variability enhances shoreline oiling: deepwater blowout simulations in the Agulhas current.

This study critically examines oil spill simulations for a hypothetical 15 day deepwater blowout spill scenario off the east coast of South Africa, coincident with the upper reaches of the Agulhas Current. Our aim is to quantify the impact of submesoscale circulations on the fate of the oil by comparing a submesoscale permitting (2.5 km) versus a mesoscale resolving (7.5 km) ocean model. The bimodal nature of the Agulhas Current plays a crucial role in the fate of the oil. Off the east coast, the relative stability of the current limits shoreline impacts, while downstream the increased variability of the current and its meandering is associated with the generation of submesoscale circulations that drive entrainment of oil onto the continental shelf. Oil entrainment is therefore enhanced in the submesoscale permitting model, and the predicted oiling of South Africa's south coast is found to vary in concert with seasonally varying winds.

Oceanographic anomalies coinciding with humpback whale super-group occurrences in the Southern Benguela.

Seasonal feeding behaviour of humpback whales (Megaptera novaeangliae) has been observed in the coastal waters of the Southern Benguela where the species has been observed forming super-groups during the austral spring in recent years since 2011. Super-groups are unprecedented densely-packed aggregations of between 20 and 200 individuals in low-latitude waters and their occurrences indicate possible changes in feeding behaviour of the species. We accessed published data on super-groups occurrence in the study area in 2011, 2014 and 2015, and investigated oceanographic drivers that support prey availability in this region. We found that enhanced primary production is a necessary but not sufficient condition for super-groups to occur. Positive chlorophyll anomalies occurring one month prior to the super-group occurrences were identified, but only a concurrent significantly reduced water volume export from the region throughout October were conducive to the aggregations in the specific years. Hydrodynamic model results attributed the anomalous decreased volume export to the strength and orientation of the Goodhope Jet and associated eddy activity. The combination of random enhanced primary production typical of the region and emerging anomalous conditions of reduced water export in October since 2011 resulted in favourable food availability leading to the unique humpback whale aggregations. The novelty of this grouping behaviour is indicative of the lack of such oceanographic conditions in the past. Given the recency of the events, it is difficult to attribute this reduction in ocean transport to climatic regime shifts, and the origin should be likely investigated in the distant water mass interaction with the greater Agulhas system rather than in local intensifications of the upwelling conditions. A positive trend in the humpback whale population abundance points to the need to monitor the exposure of the species to the changing climate conditions.