Aug 2026· Geophysical Research Letters· Vol 53· 0 citations· 52 references
Abstract
Submesoscale dynamics strongly influence the upper ocean, regulating mixing, air–sea exchange, and vertical heat transport. The recent Surface Water and Ocean Topography mission provides unprecedented high‐resolution observations of sea surface height (SSH), yet linking these surface measurements to subsurface ocean dynamics remains challenging. We develop a theoretical framework for diagnosing key mixed layer (ML) properties from surface‐observable states. We show that horizontal density anomalies induced by mixed layer eddies produce surface imprints that can be effectively captured by spatially filtered SSH. The filtered SSH is integrated into the ML Eddy parameterization to infer the effects of submesoscale restratification. A potential energy budget accounting for the mixing–restratification competition in the ML is diagnosed from surface buoyancy flux, wind stress, and the SSH gradient, enabling reconstruction of the mixed‐layer depth. Vertical eddy heat flux can be further reconstructed from the SSH gradient. This framework offers a promising approach for diagnosing interior submesoscale processes using surface observations.
The Surface Water and Ocean Topography satellite mission now delivers global sea surface height (SSH) observations at scales fine enough to resolve submesoscale eddies (<50 km). At these scales, the traditional geostrophic approximation, commonly used to infer surface currents from SSH, no longer holds. Here, we present a new dynamical framework that diagnoses ageostrophic currents and, in particular, divergent motions directly from SSH. The framework is trained and validated using a high‐resolution numerical simulation of a western boundary current system, where submesoscale eddies are the most energetic. This approach highlights the unique capability to reveal vertical motions in the upper ocean from SSH, allowing for diagnosing transport of heat, carbon, oxygen, and nutrients between the surface and the interior of the ocean.
H. Torres· Geophysical Research Letters· 0 citations
Current understanding of the role of ocean variability in air-sea exchange is constrained to large and mesoscale dynamics. Oceanic fronts and filaments with horizontal spatial scales of order 0.1 to 10 km-denoted submesoscale-are challenging to observe due to their fast-evolving flow and small spatiotemporal scales of variability. Observations investigating the air-sea fluxes at the submesoscale have shown substantial fluxes of heat, moisture, and momentum, affecting the structure of the overlying atmosphere. Here, modulations of the turbulent atmospheric boundary layer driven by ocean temperature anomalies are investigated using submesoscale-resolving ship and airborne measurements, providing in situ evidence of the atmospheric response to ocean submesoscale temperature variability. Observations suggest near-surface turbulent mixing driven by strong air-sea fluxes of heat and momentum, modifying the vertical structure of the planetary boundary layer. Linear regression coefficients between wind speed and sea surface temperature anomalies reveal a response similar in magnitude to that seen at larger scales, with an integrated change of 0.23 m s-1 °C-1, but occurring over smaller length-scales, implying sharper gradients. Lagged correlations and scaling analysis imply a combined influence of horizontal advection and vertical turbulent mixing of momentum in the atmosphere, previously only described by numerical simulations. Observed cross-frontal wind divergences over the lower 200 m suggest coherent circulations with vertical velocities of order 1 cm s-1. These observations confirm the rapid adjustment of the marine boundary layer to submesoscale ocean temperature variability and the importance of submesoscale-driven air-sea fluxes in changing the properties of the lower atmosphere, processes not resolved in most forecasting and prediction models.
I. Uchoa, J. Wenegrat, A. Kinsella et al.· Proceedings of the National...· 0 citations
Direct observations of coherent turbulent structures at the base of the ocean surface boundary layer are rare. Here, we present a unique dataset from a drifting thermistor chain that captured temperature structures associated with mixed layer and transition layer turbulence. Following a storm with wind speeds up to 15 m s
−1
, the mixed layer deepened from 35 to 45 m depth over 6 days. Within the transition layer we observe temperature fluctuations indicative of shear-driven turbulence, including features consistent with Kelvin-Helmholtz and Holmboe instabilities. We examine the size and frequency of these structures in the context of the surface forcing, identifying four distinct regimes based on wind, wave, and surface heat flux magnitude. Thorpe scale–based estimates of entrainment velocity align with the observed mixed layer deepening when averaged over the upper portion of the transition layer. This rare observational dataset offers new insight into the mechanisms controlling mixing at the base of the mixed layer and provides a valuable benchmark for future numerical studies of stratified turbulence that resolve turbulent overturns.
A. Andriatis, Matthew H. Alford, Andrew J. Lucas et al.· Journal of Physical Oceanogr...· 0 citations
Mesoscale eddies in the Southern Ocean extend from the surface to the deep ocean and contribute to regional and global ocean heat budgets. However, sparse in situ observations have limited estimates of eddy meridional heat transport (EMHT) to the near surface, leaving deep-ocean processes poorly understood. Here we quantify deep eddy kinetic energy (EKE) and EMHT using Argo observations. We find that deep EMHT reaches at least the same order of magnitude as surface transport, despite deep EKE being only one-fifth of surface levels. Float observations and sensitivity experiments reveal that, relative to mean-flow transport alone, deep EMHT extends the meridional movement of subtropical warm waters towards Antarctica by over ten degrees of latitude. About 60% of this deep transport originates from the Indian Ocean sector. These findings provide observational evidence that mesoscale eddies can modulate deep Southern Ocean heat redistribution, with potential implications for Antarctic climate.
Tongya Liu, Xiaoming Zhai, Qingyou He et al.· Nature Communications· 0 citations
Marine heatwaves (MHWs) are increasing in frequency and intensity in global boundary current systems such as the Gulf Stream (GS), where ocean circulation regulates upper‐ocean heat and water‐mass properties. We examine temperature–salinity co‐evolution during MHWs in the Northwest (NW) Atlantic using satellite observations and ocean reanalysis for 2012–2023. Applying a consistent threshold‐based framework to sea surface temperature and sea surface salinity (SSS), we identify co‐occurring MHWs and salinity extremes and evaluate their spatial extent and vertical structure. Results reveal a statistically significant high‐salinity imprint during MHWs along the GS North wall and shelf‐break corridor, consistent with advection of warm, saline GS waters preconditioning the upper ocean for vertically extensive warming. Low‐SSS extremes tend to cover greater area on the continental shelf, where surface freshening likely favors shallow, surface‐intensified MHWs. These results underscore SSS as a critical diagnostic for advective water‐mass influence and stratification during MHWs in the NW Atlantic.
Natalie Stamper, Ganesh Gopalakrishnan, B. Subrahmanyam· Geophysical Research Letters· 0 citations
Ocean vertical velocity plays a crucial role in influencing heat exchange, water mass movement, and biogeochemical processes between the surface and deep waters. Due to the difficulty in directly measuring subsurface vertical velocity w, a promising approach is to diagnose w from high-resolution surface observations, like horizontal surface velocity and sea surface height anomaly, via remote sensing. However, both existing traditional dynamic methods and classic machine learning algorithms struggle to provide accurate estimates due to their inability to capture the multi-scale spatiotemporal structures and intense vertical fluctuations. To address these challenges, combined with theoretical ocean dynamics, we propose TriSEFormer, a novel approach that leverages frequency-embedded attention mechanism from a tri-dimensional (3D) frequency perspective. Specifically, TriSEFormer comprises cascaded TriSE blocks, each consisting of a neural dynamics cell following a refinement attention module. The 3D spectral transformation within the neural dynamics cell decomposes the attention-enhanced surface embedding into different spectral components, improving the understanding of multi-scale turbulent structures. Meanwhile, we propose depth-encoded vertical weights to selectively modulate both real and imaginary parts, enhancing the vertical representation compared to dynamic estimation. Extensive experiments on one ideal simulation and three regional ocean datasets demonstrate that TriSEFormer outperforms all baselines, achieving up to a 9.9% improvement, particularly enhancing deep-ocean w diagnosis from 300 m to 2100 m in the Indian Ocean. Code is available at https://github.com/JessiQi25/TriSEFormer.
Haonan Qi, Bin Lu, Yimian Hu et al.· Proceedings of the 32nd ACM...· 0 citations