Spatial and temporal variations of near-inertial currents in the deep Gulf of Mexico

Near-inertial oscillations in the deep ocean are important in many ways, such as transporting biogeochemical particles and providing energy for deep-ocean mixing. Spatial and temporal variations of near-inertial oscillations in the deep Gulf of Mexico (GoM) are rarely reported. In this study, a collection of moored current observations is used to describe the characteristics of near-inertial currents in the GoM. The observed velocity shows an energy peak around the local inertial frequency (about 1 cycle per day, which is close to the diurnal tidal frequency) in most current records. The energy density at the near-inertial frequency generally decreases from the surface to about 1200 m and then remains a relatively small value below. In the Loop Current region and the northeastern GOM, however, high near-inertial energy appears in both the upper (above 800 m depth) and the bottom ocean (below 1000 m depth and within 200 m above the bottom). Although downward energy propagation from the upper layer to the deep ocean is common, upward propagation in the deep ocean is also observed, consistent with bottom generation of near-inertial oscillations. To explore possible relationships between the low-frequency variations of near-inertial currents and the subinertial bottom currents, we also calculate and compare the low-frequency modulation of near-inertial currents with the bottom subinertial currents. Moreover, since surface and bottom current coupling exists in some regions of the GoM, we also compare the modulation of bottom near-inertial currents with local and remote surface currents, which provide potential ways to predict modulation of deep-ocean near-inertial currents by examining surface observed features.