Shelf circulation patterns off Nigeria

Abstract

Little has been published about the shelf circulation off the coast of Nigeria. Due to increased activity and associated incidents in the shallow waters offshore Nigeria, there is a need to more clearly define the near-shore circulation patterns. An oil spill occurred in January of 1998, the slick drifted in the opposite direction at twice the speed as was anticipated. It was believed that the heavy discharge from the Niger River Delta would have a strong influence on the near-shore circulation patterns and was the reason for this unexpected drift. This thesis investigates the river discharge by examining hydrographic data taken along the coastline. Using Acoustic Doppler Current Profilers, this thesis also investigates other possible forcing factors to gain an overall understanding of Nigeria??s shallow water circulation. Indeed river discharge plays an important role in the near-shore circulation as the coastal waters are highly stratified; however, the coastal waters are also strongly influenced by a cross-shelf semidiurnal tide, weather events and seasonal events, such as eddies and coastal upwelling. The resulting currents are a combination of a strong bi-directional cross-shelf tidal current with a strong bi-directional alongshelf current. The waters off Nigeria are highly stratified; they have spatial coherence and a uniform vertical structure along the coastline. These coastal waters may also be influenced by a remotely forced upwelling event and by northerly drift from the Congo River. The shelf circulation is clearly a complicated system and will require further investigation to be fully defined.