Extreme Sub-surface Currents Observed in the Northern Brazil - Suriname Region

Abstract

Offshore waters from Northern Brazil to Suriname are subject to extreme curents driven by the North Brazil Current (NBC) and NBC Rings which represent a significant metocean hazard for the O&G Industry. Although extreme surface currents are well known, there is still a gap in the understanding of extreme sub-surface currents in that region. The objective of this paper is to further elucidate the characteristics of significant sub-surface currents and provide metocean guidance to the O&G Industry based on three separate long-term mooring campaigns in the region. Our investigation demonstrates that extreme sub-surface current events exist offshore Northern Brazil, French Guyana and Suriname. The events were mainly characterized by northwestward peak currents from 0.82m/s to 1.22m/s within 150m-300m below the surface. They were more frequent offshore Northern Brazil and French Guyana where events were observed within 2-3 months of each other. Offshore Suriname, only one event was reported in 14 months. Sub-surface current events took place during times when the surface circulation was relatively weak and during times when surface currents were strong and affected by the NBC / NBC Ring circulation. Offshore Northern Brazil and French Guyana, it is suggested that significant sub-surface currents could take place around the time when a NBC Ring is sheeding and the surface circulation is unstable. Extreme sub-surface currents could be decoupled from the surface circulation and that poses an additional challenge in terms of predicting when extreme sub-surface currents could take place. The findings of our study provide a new regional picture of extreme sub-surface currents from Northern Brazil to Suriname and highlight that those events must be accounted for by offshore O&G developments in that region.