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How the ocean circulation changes in a warming climate is an important but poorly understood problem. Using a global ocean model, we decompose the problem into distinct responses to changes in sea surface temperature, salinity, and wind. Our results show that the surface warming effect, a robust feature of anthropogenic climate change, dominates and accelerates the upper ocean currents in 77% of the global ocean. Specifically, the increased vertical stratification intensifies the upper subtropical gyres and equatorial currents by shoaling these systems, while the differential warming between the Southern Ocean upwelling zone and the region to the north accelerates surface zonal currents in the Southern Ocean. In comparison, the wind stress and surface salinity changes affect regional current systems. Our study points a way forward for investigating ocean circulation change and evaluating the uncertainty.

Marginal seas are usually fulfilled with strongly varying mesoscale eddies (MEs), which evolutions plays vital roles in regulating global oceanic energy equilibrium, triggering subemesoscale processes with strong vertical velocity, and inducing high biogeochemistry transport. But the temporal evolutions of MEs and submesoscale processes with several kilometers' resolutions are difficult to be measured by traditional observations with passive working mode. The automatic underwater gliders (AUGs) and vehicles (AUVs) positively observe oceanic motion, and could provide us spatiotemporal synchronization information for strongly varying MEs. Here, we present a 9-year high dense dataset of AUVs/AUGs observations in 2014–2022 in the South China Sea (SCS) can be downloaded from https://doi.org/10.57760/sciencedb.11996 (Qiu et al., 2024b). Totally, 9 AUG and 2 AUV cruise experiments were conducted, and 83 AUGs (2 AUVs) equipment were deployed with zonal and temporal resolutions of < 7 km and <6 hour. It covers the area of eddy's birth, propagation, and dissipation, presenting us the most complete data to investigate the evolution of MEs at different life stages. 40 % of them reach resolutions < 1 km and < 1 hour, which provides us the dynamic characteristics of submesoscale instabilities across and along front at the eddy edge. This dataset has potential in improving the forecast accuracy in physical and biogeochemistry numerical model. Much more aggressive field investigation programs will be promoted by the NSFC in future. [ABSTRACT FROM AUTHOR]

In the eastern off-equatorial Indian Ocean, deep current intraseasonal variability within a typical period of 10–20 days was revealed by a mooring at 5°N, 90.5°E, accounting for over 50% of the total bottom subtidal velocity variability. The 10–20-day oscillations were more energetic in the cross-isobathic direction (STD = 3.02 cm s−1) than those in the along-isobathic direction (STD = 1.50 cm s−1). The oscillations were interpreted as topographic Rossby waves (TRWs) because they satisfied the TRWs dispersion relation that considered the smaller Coriolis parameter and stronger β effect at low latitude. Further analysis indicated significant vertical coupling between the deep cross-slope oscillations and cross-isobathic 10–20-day perturbations at the depth of 300–950 m. The 10–20-day TRWs were generated by cross-isobathic motions under the potential vorticity conservation adjustment. The Mercator Ocean output reproduced the generation of kinetic energy (KE) of deep current variability. The associated diagnostic analysis of multiscale energetics showed that the KE of TRWs was mainly supplied by vertical pressure work. In the seamount region (2°–10°N, 89°–92°E), vertical and horizontal pressure works were identified to be the dominant energy source (contributing to 94% of the total KE source) and sink (contributing to 98% of the total KE sink) of the deep current variability, transporting energy downward and redistributing energy horizontally, respectively. [ABSTRACT FROM AUTHOR]

Observations of currents and temperatures from four moorings deployed around the deep slope (∼2500 m) of Caiwei Guyot in the Pacific Prime Crust Zone were utilized to investigate topographically trapped waves at low-latitude seamounts. Contrasting with commonly reported persistent diurnal seamount-trapped wave cases at middle and high latitudes, the subinertial variability in deep currents and temperatures at the slope of Caiwei Guyot was primarily characterized by two distinct lower-frequency bands (i.e., 13–24 and 3.3–4.7 days). These subinertial variabilities are interpreted as intermittent seamount-trapped waves and topographic Rossby waves (TRWs). During certain time periods, the observations include key signatures of seamount-trapped waves, such as near-opposite phases of azimuthal velocity (and temperature) on opposite flanks of the seamount, and patterns of temporal current rotation consistent with counterrotating cells of horizontal current propagating counterclockwise around the seamount. After comparing these observations to idealized seamount-trapped wave solutions, we conclude that the 13–24-day (3.3–4.7-day) energy is mainly due to radial–vertical mode 5 (3) for azimuthal wavenumber 1 (3). Sometimes the subinertial energy remained pronounced at only one flank of the seamount, primarily explained as TRWs with 192–379-m vertical trapping scale and 14–28-km wavelength. Upper-layer mesoscale perturbations might provide energy for deep seamount-trapped waves and TRWs. This study highlights the role of topographically trapped waves in modulating the deep circulation at low-latitude seamounts. [ABSTRACT FROM AUTHOR]