Observations of New North Brazil Current Rings Profiles Offshore Guyana

Abstract

Abstract The North Brazil Current Rings (NBCRs) are a dominant phenomenon in the Atlantic Ocean offshore Guyana, which introduces substantial challenges and risks to offshore activities. Gaining a comprehensive grasp of the vertical current structure and variations linked to NBCRs is important for design and safe operations in the region. This study addresses the intricate attributes of NBCRs, utilizing data acquired from two deepwater moorings offshore Guyana. These moorings, equipped with current measuring instruments, were stationed along the pathway of NBCRs with the goal to capture their dynamic behavior and inherent variability. One mooring was deployed in the water depth of about 1600 meters for 18 months. During this time, a total of seven NBCRs were observed, which were sorted into distinct categories based on their temporal and vertical characteristics. Four of these rings displayed surface current intensification, with peak near surface currents reaching 1.62 m/s. These rings were confined to the uppermost 200 meters of the water column. Diverging from this pattern, two rings exhibited a distinctive attribute—both surface and subsurface intensifications—with peak subsurface currents reaching ~1 m/s at a depth between 200 and 300 meters. Finally, one ring lacked the typical surface intensification and only exhibited subsurface intensification (currents reaching ~ 1 m/s at 300m below the surface). Throughout the measurement period, a prevailing southwesterly-directed reversal current persisted within the lower part of the water column. The second mooring was positioned in the water depth of around 1850 meters. Its 12-month deployment period overlapped with the final year of the first mooring’s deployment, therefore this secondary mooring witnessed the occurrence of four rings observed by the other mooring. The observations confirmed the occurrence of the distinctive current profiles: two rings with surface plus subsurface intensification and one ring with subsurface intensification only. The second mooring also demonstrated the spatial and temporal variability of those rings. This study’s significance extends beyond mere rings’ identification and description, unveiling the presence of novel current profiles with simultaneous near-surface and subsurface intensifications of comparable magnitudes. Additionally, it brought to light increased subsurface current speeds and distinct temporal behavior of these currents. These findings demonstrate the need for continuing measurements and modeling of circulation in the area to better understand and predict the events.