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Ocean Science An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/os-2020-20
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2020-20
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 31 Mar 2020

Submitted as: research article | 31 Mar 2020

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This preprint is currently under review for the journal OS.

A new method to assess mesoscale contributions to meridional heat transport in the North Atlantic Ocean

Andrew Delman and Tong Lee Andrew Delman and Tong Lee
  • Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Abstract. The meridional heat transport (MHT) in the North Atlantic is critically important to climate variability and the global overturning circulation. A wide range of ocean processes contribute to North Atlantic MHT, ranging from basin-scale overturning and gyre motions to mesoscale instabilities (such as eddies). However, previous analyses of eddy MHT in the region have mostly focused on the contributions of time-variable velocity and temperature, rather than considering the spatial scales that are more fundamental to the physics of ocean eddies. In this study, a zonal spatial-scale decomposition separates large-scale from mesoscale velocity and temperature contributions to MHT, in order to characterize the physical processes driving MHT. Using this approach, we found that the mesoscale contributions to the time mean and interannual/decadal (ID) variability of MHT in the North Atlantic Ocean are larger than large-scale horizontal contributions, though smaller than the overturning contributions. Considering the 40° N transect as a case study, large-scale ID variability is mostly generated in the deeper part of the thermocline, while mesoscale ID variability has shallower origins. At this latitude, most ID MHT variability associated with mesoscales originates in two regions: a western boundary region (70°–60° W) associated with 1–4 year interannual variations, and an interior region (50°–35° W) associated with decadal variations. Surface eddy kinetic energy is not a reliable indicator of high MHT episodes, but the large-scale meridional temperature gradient is an important factor, by influencing the local temperature variance as well as the local correlation of velocity and temperature. Most of the mesoscale contribution to MHT at 40° N is associated with transient and propagating processes, but stationary mesoscale dynamics contribute substantially to MHT south of the Gulf Stream separation, highlighting the differences between the temporal and spatial decomposition of meridional temperature fluxes.

Andrew Delman and Tong Lee

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Andrew Delman and Tong Lee

Andrew Delman and Tong Lee

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Latest update: 29 May 2020
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Short summary
The oceans play an important role in moving heat between the equatorial and polar regions, with both large current systems and smaller eddies contributing to this heat transport. This analysis separates the contribution of the larger scale and eddy-scale flows in the North Atlantic, finding that eddy-scale flows account for 25–40 % of the heat transport in middle latitudes near 40° N. The study also shows how the year-to-year variability of eddies contributes to heat transport changes at 40° N.
The oceans play an important role in moving heat between the equatorial and polar regions, with...
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