The ocean is the largest solar energy collector on Earth. The amount of heat it can store is modulated by its complex circulation, which spans a broad range of spatial scales, from metres to thousands of kilometres. In the classical paradigm, fine oceanic scales, less than 20 km in size, are thought to drive a significant downward heat transport from the surface to the ocean interior, which increases oceanic heat uptake. Here we use a combination of satellite and in situ observations in the Antarctic Circumpolar Current to diagnose oceanic vertical heat transport. The results explicitly demonstrate how deep-reaching submesoscale fronts, with a size smaller than 20 km, are generated by mesoscale eddies of size 50–300 km. In contrast to the classical paradigm, these submesoscale fronts are shown to drive an anomalous upward heat transport from the ocean interior back to the surface that is larger than other contributions to vertical heat transport and of comparable magnitude to air–sea fluxes. This effect can remarkably alter the oceanic heat uptake and will be strongest in eddy-rich regions, such as the Antarctic Circumpolar Current, the Kuroshio Extension and the Gulf Stream, all of which are key players in the climate system.
This is a preview of subscription content, access via your institution
Subscribe to Nature+
Get immediate online access to Nature and 55 other Nature journal
Subscribe to Journal
Get full journal access for 1 year
only $9.92 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
The marine mammal data were collected and made freely available by the International MEOP Consortium and the national programs that contribute to it, and is available at www.meop.net/database/meop-databases/meop-sms-database-submesosc.html. The Ssalto/Duacs altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service with support from CNES, and is available at http://marine.copernicus.eu/services-portfolio/access-to-products/.
Munk, W. & Wunsch, C. Abyssal recipes II: energetics of tidal and wind mixing. Deep Sea Res. Part I 45, 1977–2010 (1998).
Wolfe, C., Cessi, P., McClean, J. & Maltrud, M. Vertical heat transport in eddying ocean models. Geophys. Res. Lett. 35, L23605 (2008).
Griffies, S. M. et al. Impacts on ocean heat from transient mesoscale eddies in a hierarchy of climate models. J. Clim. 28, 952–977 (2015).
Ferrari, R. & Wunsch, C. Ocean circulation kinetic energy: reservoirs, sources, and sinks. Annu. Rev. Fluid Mech. 41, 253–282 (2009).
Klein, P. & Lapeyre, G. The oceanic vertical pump induced by mesoscale and submesoscale turbulence. Annu. Rev. Mar. Sci. 1, 351–375 (2009).
Ferrari, R. A frontal challenge for climate models. Science 332, 316–317 (2011).
Mahadevan, A. The impact of submesoscale physics on primary productivity of plankton. Annu Review Mar. Sci. 8, 161–184 (2016).
McWilliams, J. C. Submesoscale currents in the ocean. Proc. R. Soc. A 472, 20160117 (2016).
Lévy, M., Frank, P. J. & Smith, S. K. The role of submesoscale currents in structuring marine ecosystems. Nat. Commun. 9, 4758 (2018).
Vallis, G. K. Atmospheric and Oceanic Fluid Dynamics (Cambridge Univ. Press, 2017).
Taylor, J. R. & Ferrari, R. Ocean fronts trigger high latitude phytoplankton blooms. Geophys. Res. Lett. 38, 23 (2011).
Thomas, L. N., Taylor, J. R., Ferrari, R. & Joyce, T. M. Symmetric instability in the Gulf Stream. Deep. Sea Res. Pt II 91, 96–110 (2013).
Bachman, S. D. & Taylor, J. R. Modelling of partially-resolved oceanic symmetric instability. Ocean Model. 82, 15–27 (2014).
Yu, X. et al. An annual cycle of submesoscale vertical flow and restratification in the upper ocean. J. Phys. Oceanogr. 49, 1439–1461 (2019).
Large, W. G. & Yeager, S. The global climatology of an interannually varying air–sea flux data set. Clim. Dynam. 33, 341–364 (2009).
Hogg, A. M. et al. Recent trends in the Southern Ocean eddy field. J. Geophys. Res. Ocean 120, 257–267 (2015).
Chelton, D. B., DeSzoeke, R. A., Schlax, M. G., El Naggar, K. & Siwertz, N. Geographical variability of the first baroclinic Rossby radius of deformation. J. Phys. Oceanogr. 28, 433–460 (1998).
Chelton, D. B., Schlax, M. G., Freilich, M. H. & Milliff, R. F. Satellite measurements reveal persistent small-scale features in ocean winds. Science 303, 978–983 (2004).
Thompson, A. F. et al. Open-ocean submesoscale motions: a full seasonal cycle of mixed layer instabilities from gliders. J. Phys. Oceanogr. 46, 1285–1307 (2016).
duPlessis, M., Swart, S., Ansorge, I. J. & Mahadevan, A. Submesoscale processes promote seasonal restratification in the Subantarctic Ocean. J. Geophys. Res. Ocean 122, 2960–2975 (2017).
Viglione, G. A., Thompson, A. F., Flexas, M. M., Sprintall, J. & Swart, S. Abrupt transitions in submesoscale structure in southern Drake Passage: glider observations and model results. J. Phys. Oceanogr. 48, 2011–2027 (2018).
d’Ovidio, F. & Fernández, V. & Hernández-García, E. & López. Mixing structures in the Mediterranean Sea from finite-size Lyapunov exponents. Geophys. Res. Lett. 31, L17203 (2004).
Hoskins, B. J., Draghici, I. & Davies, H. C. A new look at the ω-equation. Q. J. R. Meteorol. Soc. 104, 31–38 (1978).
McGillicuddy Jr, D. J. Mechanisms of physical–biological–biogeochemical interaction at the oceanic mesoscale. Annu. Review Mar. Sci. 8, 125–159 (2016).
Salmon, R. Baroclinic instability and geostrophic turbulence. Geophys. Astrophys. Fluid Dyn. 15, 167–211 (1980).
Su, Z., Wang, J., Klein, P., Thompson, A. F. & Menemenlis, D. Ocean submesoscales as a key component of the global heat budget. Nat. Commun. 9, 775 (2018).
Rio, M. H. et al. Improving the altimeter-derived surface currents using high-resolution sea surface temperature data: a feasibility study based on model outputs. J. Atmos. Ocean. Technol. 33, 2769–2784 (2016).
Ubelmann, C., Klein, P. & Fu, L. L. Dynamic interpolation of sea surface height and potential applications for future high-resolution altimetry mapping. J. Atmos. Ocean. Technol. 32, 177–184 (2015).
Ballarotta, M. et al. On the resolutions of ocean altimetry maps. Ocean Sci. 15, 1091–1109 (2019).
Waugh, D. W., Abraham, E. R. & Bowen, M. M. Spatial variations of stirring in the surface ocean: a case study of the Tasman Sea. J. Phys. Oceanogr. 36, 526–542 (2006).
d’Ovidio, F., Isern-Fontanet, J., López, C., Hernández-García, E. & García-Ladona, E. Comparison between Eulerian diagnostics and finite-size Lyapunov exponents computed from altimetry in the Algerian Basin. Deep. Sea Res. Pt I 56, 15–31 (2009).
Siegelman, L. et al. Correction and accuracy of high-and low-resolution CTD data from animal-borne instruments. J. Atmospheric Ocean. Technol. 36, 745–760 (2019).
Intergovernmental Oceanographic Commission The International Thermodynamic Equation of Seawater—2010: Calculation and Use of Thermodynamic Properties (Includes Corrections up to 31st October 2015) (UNESCO, 2015);https://www.oceanbestpractices.net/bitstream/handle/11329/286/TEOS-10_Manual.pdf?sequence=1
Molemaker, J., McWilliams, J. & Yavneh, I. Baroclinic instability and loss of balance. J. Phys. Oceanogr. 35, 1505–1517 (2005).
Thomas, L. N., Tandon, A. & Mahadevan, A. in Ocean Modeling an Eddying Regime (eds Hecht, M. W. & Hasumi, H.) 17–38 (Geophysical Monograph Series Vol. 177, American Geophysical Union, 2008).
Giordani, H., Prieur, L. & Caniaux, G. Advanced insights into sources of vertical velocity in the ocean. Ocean. Dyn. 56, 513–524 (2006).
Burns, K. J., Vasil, G. M., Oishi, J. S., Lecoanet, D. & Brown, B. Dedalus: Flexible Framework for Spectrally Solving Differential Equations (Astrophysics Source Code Library, 2016).
Vallis, G. K. Climate and the Oceans (Princeton Univ. Press, 2012).
Foussard, A., Lapeyre, G. & Plougonven, R. Response of surface wind divergence to mesoscale SST anomalies under different wind conditions. J. Atmos. Sci. 76, 2065–2082 (2019).
We thank K. Richards for his insightful comments, F. d’Ovidio for providing the code to compute FSLE. The elephant seal work was supported as part of the SNO-MEMO and by the CNES-TOSCA project Elephant seals as Oceanographic Samplers of submesoscale features led by C. Guinet with support of the French Polar Institute (programmes 109 and 1201). This research was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). High-end computing resources for the numerical simulation were provided by the NASA Advanced Supercomputing Division at the Ames Research Center. This work was partly funded by the CNES (OSTST-OSIW) and the Laboratoire d’Excellence LabexMER (ANR-10-LABX-19). L.S. is a NASA-JVSRP affiliate and is supported by a joint CNES-Région Bretagne doctoral grant. P.K. is supported by the NASA-CNES SWOT mission and a NASA Senior NPP Fellowship. A.F.T. is supported by the David and Lucille Packard Foundation and NASA grant NNX16AG42G. M.F. is supported by NASA grant NNX15AG42G.
The authors declare no competing interests.
Peer review information Primary Handling Editor(s): Heike Langenberg.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Same as Fig. 2 but for i) 2014/11/24 to 2014/12/20 with the SSH snapshot in a) taken on 2014/12/07. The seal crosses a large anti-cyclonic region (grey trajectory in Fig. 1) characterized by weaker currents (smaller SSH anomalies) and referred to as the weakly turbulent area. ii) 2014/12/22-29 with the SSH snapshot in a) taken on 2014/12/26. The seal follows the edges of mesoscale eddies over a distance of ~600 km. This region is referred to as the southern eddy (in orange in Fig. 1). Bold black arrows indicate the direction of the seal.
Extended Data Fig. 2 Lateral gradient of buoyancy and Richardson number in the strongly turbulent area.
a) RMS of lateral gradients of buoyancy, |bx|, as a function of depth in the strongly turbulent area. b) Scatter plot between lateral gradients of buoyancy, |bx|, and Richardson number, Ri, in the strongly turbulent area. Ri<2 coincide with strong buoyancy gradients (|bx|>2.5 x 10-7s-2), highlighting the ageostrophic character of the dynamical regime encountered by the seal and the expected strong frontogenesis processes at play.
Map of FSLE over the entire domain on 13 November 2014. FSLE are greatly enhanced in the strongly turbulent region (black rectangle and in red in Fig. 1) compared to the rest of the domain.
Extended Data Fig. 4 Finite size Lyapunov exponents and horizontal gradient of buoyancy, vertical velocities and vertical heat transport at 300 m.
Times series of a) Horizontal gradients of buoyancy at 300 m sampled by the seal (in black) and FSLE derived from satellite altimetry along the seal’s track (in blue). b) Vertical velocities at 300 m derived from the seal and satellite data by solving the omega equation (see main text and Methods). c) Vertical heat transport (see Methods). The areas described in the main text and in Fig. 1 are highlighted by the colored rectangles.
Extended Data Fig. 5 Daily averaged vertical velocities and vertical heat transport from the high-resolution numerical simulation.
Daily averaged vertical section from the high-resolution numerical simulation for November 22, 2011 at 52°S of a) Vertical velocities b) Vertical heat transport. Isopycnals are shown by the black lines. Enhanced vertical velocities and heat transport with a width of 5-10 km are found in the ocean interior and, in particular, below the mixed layer, similar to the observation presented in the main text.
Extended Data Fig. 6 Averaged vertical heat transport from the high-resolution numerical simulation.
2-D (x,y) view of 10-day averaged vertical heat transport (VHT) at a) 50 m and b) 200 m. Isotherms are shown in black. Domain averaged values are respectively 92 and 197 W/m2. VHT is enhanced at depth and follows the isotherms on the eddy edges, and its averaged value is directed upward (positive value), all of which is consistent with the observational results presented in the main text.
Extended Data Fig. 7 Domain averaged vertical heat transport from the high-resolution numerical simulation.
Monthly averaged vertical heat transport (<VHT>) as a function of depth over the entire domain from the high-resolution numerical simulation. VHT is directed upwards (positive values) and its magnitude is similar - although even higher - than what is derived from the observational data presented in the main text.
Extended Data Fig. 8 Distance between two dives and angle between the seal’s trajectory and the fronts.
a) Histogram of the distance between two dives. Median distance between two dives is 700 m (dotted line) and the shortest distance is 100 m. b) Histogram of the angle between the seal’s trajectory and the stretching FSLE it encounters for FSLE>0.15 day-1. Oblique crossings are most frequent and a normalization is implemented to correct for it (see Methods).
About this article
Cite this article
Siegelman, L., Klein, P., Rivière, P. et al. Enhanced upward heat transport at deep submesoscale ocean fronts. Nat. Geosci. 13, 50–55 (2020). https://doi.org/10.1038/s41561-019-0489-1