Coupling of the Surface and Near‐Bottom Currents in the Gulf of Mexico

Abstract

Coupling between the surface and near-bottom currents in the Gulf of Mexico (GoM) has been reported in many case studies. However, geographical variations of this coupling need more examination. In this study, surface geostrophic currents derived from satellite-observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the GoM. The short-period (30-90 days) fluctuations generated by the Loop Current (LC) and the LC eddies (LCEs) have a more vertically coherent structure and stronger deep ocean expressions than the long-period fluctuations (>90 days). In addition, the strength of the coupling is modulated by the long-period variations of the LC and LCE sheddings. Moreover, the surface and bottom coupling varies geographically. In the LC region, the surface fluctuations along the eastern side of the LC are important in causing the bottom current fluctuations through baroclinic instability under the LC and through traveling topographic Rossby waves (TRWs) north of the LC. In the central deep GoM, the bottom currents are affected by the upper fluctuations of the northern LC through both local baroclinic instability and remote TRW propagation. In the northwestern GoM, the bottom current fluctuations are largely related to the remote surface variability from the west side of the LC by TRWs propagating northwestward. This study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties. Plain Language Summary Bottom currents in the Gulf of Mexico (GoM) are important in many ways, such as transporting fish larvae and spilled oil. However, in contrast to surface currents that are easily derived from the abundant satellite observations, our understanding of the bottom currents is very limited. In this study, the relationships between surface and near-bottom current fluctuations in different parts of the GoM are investigated by combining a collection of historical near-bottom current measurements and satellite data. The results show that the bottom current variability is linked to local processes such as current instability or remote processes through planetary wave propagation. The surface and bottom coupling is mainly related to the short-period variability generated along the Loop Current and the Loop Current eddies and has a significant influence on the bottom currents. Although the long-period fluctuations have weak bottom expressions, they can modulate the strength of the short-period coupling. Studying the coupling between the surface and bottom current fluctuations in the GoM can advance our understanding of mechanisms of the bottom currents that are important for the deep ocean ecosystem and industrial operations.

Influence of the Kuroshio Intrusion on Deep Flow Intraseasonal Variability in the Northern South China Sea

“…We further conduct a lead‐lag correlation analysis of the intraseasonal KE (i.e., K 1 ) between the upper and deep layers to highlight the dynamic differences between different regions. In the region to the east of the Dongsha Islands, the deep‐layer K 1 shows more significant correlations (higher than 0.4, at the 95% confidence level) with the upper‐layer processes that lead by several days, whereas this correlation is not clear in the west (Figures 7c and 7d), which is consistent with the pressure work pattern in Figure 5a and a recent observational study on the coupling of the surface and near‐bottom currents in the Gulf of Mexico (Zhu & Liang, 2020).…”

Physical Characteristics and Evolution of a Long-Lasting Mesoscale Cyclonic Eddy in the Straits of Florida

“…The algorithm can also identify eddy splitting and merging, thus helping to explore eddy-eddy interactions and to accurately identify the formation areas of long-lived eddies. These are the main advantages of the AMEDA algorithm, and this algorithm has been used widely in many studies on ocean eddies (e.g., Ioannou et al, 2017;de Marez et al, 2019de Marez et al, , 2020Morvan et al, 2020;Zhu and Liang, 2020;Pegliasco et al, 2021;Stegner et al, 2021).…”

Observed Variability of Bottom‐Trapped Topographic Rossby Waves Along the Slope of the Northern South China Sea

“…TRW propagation can result in intensified bottom EKE (Hamilton, 2009;Zhu & Liang, 2020). A ray-tracing model (see Appendix A) was used to identify TRW energy propagation.…”

“…In addition to mesoscale perturbations in upper ocean, the instability (e.g., barotropic or baroclinic instabilities) of the background flow is believed to stimulate a great release of energy that initialize the TRWs (e.g., Ma et al, 2019). For example, the coupling between upper-layer fluctuations and bottom TRWs through baroclinic instability has been revealed by simulations and observations in the Gulf of Mexico (Oey & Lee, 2002;Zhu & Liang, 2020). Although the relationship between bottom TRWs and upper-ocean fluctuations was identified under the limitations of single observations in the deep ocean, more full-depth observations are needed to further reveal the local coupling processes between upper-layer currents and deep currents and validate the spatial distribution of bottom TRWs on the continental slope of NSCS.…”