Wide-swath satellite altimetry unveils global submesoscale ocean dynamics

 Research suggests submesoscale eddies, small ocean currents (10-100 km), significantly impact climate and marine ecosystems, as observed by NASA's SWOT mission.  

 The SWOT satellite, launched in 2022, provides high-resolution data showing these eddies have stronger effects on heat and nutrient transport than previously thought.  

 It seems likely that these findings will improve climate models, but more data is needed for certainty.  

Overview  

Small ocean eddies, known as submesoscale eddies, are crucial for climate regulation. NASA's SWOT mission, using advanced satellite technology, has revealed their significant role in moving heat, carbon, and nutrients, affecting global climate and marine life.  

Key Findings  

The SWOT mission, launched on December 16, 2022, captures these eddies with sea surface height anomalies up to 15 cm and radii as small as 15 km. They contribute to vertical heat transport 5–10 times more than larger eddies, influencing surface warming and atmospheric moisture.  

Implications  

These observations, detailed in recent research, suggest a larger impact on ocean energetics and climate than anticipated. However, the research is still in early stages, and further data could enhance climate models and policies.  

Survey Note: Detailed Analysis of Submesoscale Eddies and SWOT Mission Findings

This section provides a comprehensive exploration of submesoscale eddies and their climate impact, as observed by NASA's Surface Water and Ocean Topography (SWOT) mission, based on recent research published in 2025. The analysis aims to synthesize findings from scientific literature, ensuring a thorough understanding for a general audience while maintaining academic rigor.

Background and Context  

Ocean circulation is a critical component of Earth's climate system, influencing weather patterns, marine ecosystems, and global temperature regulation. Traditionally, satellite altimetry, starting with the Seasat mission in 1978, has focused on large-scale ocean dynamics, including mesoscale eddies (100-300 km) that account for over 80% of ocean kinetic energy. However, submesoscale eddies, with diameters ranging from 10 to 100 km, have been less studied due to limitations in resolution and sampling, hindering a complete understanding of their role in climate dynamics.

Recent advancements in satellite technology, particularly the SWOT mission launched on December 16, 2022, have enabled the observation of these smaller-scale features. SWOT employs a Ka-band Radar Interferometer (KaRIn), achieving a 1-km spatial resolution over a 120-km swath, reducing noise by an order of magnitude compared to previous methods. This has opened a new era of global ocean observing, placing submesoscale dynamics as a critical element of Earth's climate system.

Key Observations from SWOT  

The SWOT mission has provided the first global view of submesoscale ocean dynamics, revealing several key findings:

- Characteristics and Detection: Submesoscale eddies have been detected with sea surface height anomalies (SSHA) up to 15 cm and radii as small as 15 km, which were previously missed by conventional Data Unification and Altimeter Combination System (DUACS) altimetry. For instance, an eddy off South Africa exhibited a 15 cm SSHA and a 15 km radius, with a core 2.5 °C colder than surrounding areas, indicating intense lateral buoyancy gradients.

- Velocity and Dynamics: These eddies often exhibit velocities exceeding 1 m/s when using geostrophic approximation. However, their Rossby numbers (Ro = U/fL, where U is velocity, f is the Coriolis parameter, and L is length scale) frequently exceed 0.5 in the eddy core, suggesting non-geostrophic balance. For example, in the Kuroshio Extension, eddies with diameters less than 10 km had Rossby numbers greater than 2, indicating significant dynamic complexity. Cyclogeostrophic balance, which accounts for centrifugal forces, reduces velocity estimates to around 0.5 m/s for a 15 km radius eddy (with f = 10⁻⁴ s⁻¹).

- Energy and Impact on Climate: Research suggests that the root mean square (RMS) SSHA values observed by SWOT are about three times larger than those from the highest-resolution global ocean simulations, indicating a substantial contribution to Earth's climate system. Upward vertical heat transport by submesoscale eddies is 5–10 times larger than for mesoscale eddies, warming the ocean surface and increasing atmospheric moisture supply. Vertical velocities for a Kuroshio Extension eddy ranged between -6 and -14 m/day, with expectations of higher values based on SSHA gradients, highlighting their role in mixing heat and nutrients.

- Global Variability and Distribution: Submesoscale variability is particularly notable in high-kinetic-energy regions, such as western boundary currents (e.g., Gulf Stream, Kuroshio Extension) and the Antarctic Circumpolar Current, as well as at internal gravity wave generation sites like the Amazon River mouth, Mascarene Plateau, South China Sea, Andaman Sea, and Indonesian archipelago. This global distribution underscores their widespread influence on ocean energetics and climate.

- Methods and Data: The findings are based on data from 14 SWOT cycles between July 26, 2023, and May 8, 2024, using Level-2 (L2) unsmoothed SSHA on a 250-m grid and Level-3 (L3) SSHA on a 2-km grid, version 1.0, produced by the DUACS and SWOT Science Teams.

Implications for Climate and Marine Ecosystems  

Submesoscale eddies contribute to vertical transport, acting as "ducts" for heat, carbon, oxygen, and other climatically important gases into the deep ocean, similar to alveoli in lungs facilitating gas exchange. They also support marine ecosystems by driving cold, nutrient-rich waters from depth to the surface, enhancing phytoplankton and zooplankton growth, which is vital for the marine food chain and fisheries.

The evidence leans toward these eddies having a larger-than-expected impact on ocean energetics, atmospheric weather, and Earth's climate system. For instance, internal solitary waves in the Andaman Sea, observed with 20-cm SSHA and 5-km wavelengths, had energy fluxes of 8 kW m⁻¹ (20-cm peak) and 1.8 kW m⁻¹ (10-cm peak), significantly higher than 0.8 kW m⁻¹ for coherent M₂ internal tides, indicating their potential to influence regional climate dynamics.

Challenges and Future Directions  

While SWOT has revolutionized our understanding, challenges remain, such as temporal sampling limitations and separating eddy signals from internal waves. The research is still in its early stages, and additional data collection is expected to refine climate models and inform policies related to ocean circulation and climate change. Future studies may focus on seasonal variations, as submesoscale circulation is more energetic in winter at mid-latitudes due to deeper mixed layers.

Conclusion  

The SWOT mission's findings underscore the importance of submesoscale eddies in global ocean dynamics, with significant implications for climate regulation and marine ecosystems. This research, published in 2025, marks a pivotal step in oceanography, offering new insights that could shape future climate strategies.

https://www.nature.com/articles/s41586-025-08722-8#Sec1