Vertical Structure and the Circulation Impact of the North Brazil Current Rings Off Guyana

Current measurements from a subsurface mooring offshore Guyana have been conducted by ExxonMobil in support for the oil and gas development in the area from March 2016 to March 2017. Understanding the current structure and inertial and sub-inertial period variations associated with the North Brazil Current (NBC) rings in the area are important to the development of the design and operational criteria off Guyana given the increase in activities by the oil and gas industry in the study region. The mooring was deployed near 57°W, 8°N in the water depth of 1678 m. Four NBC rings, which were measured during the one-year measurement campaign, can be categorized into three types based on their temporal and spatial (vertical) structures. The first two rings measured in the boreal spring of 2016 are shallow, fast-moving rings with the maximum penetration depth around 200m. The third ring is a slow-moving, deep feature with the penetration depth up to 1000 m. The fourth one is a fast-moving, deep ring with the penetration depth up to 800 m. A reversal current is observed flowing southwesterly along the coastline beneath all of the rings for the most part of the measurement period. Noteworthy inertial period variations are measured in the upper 200 m only with the arrival of the NBC rings and persistently in summer. Enhancement of the sub-inertial (5-10 days) variations is also detected in association with all four rings, suggesting that sub-inertial oscillations can be excited by the NBC rings.