Spatial variability of turbulent mixing from an underwater glider in a large, deep, stratified lake
Spatial variability of turbulent mixing from an underwater glider in a large, deep, stratified lake
Recent efforts using microstructure turbulence measurements have contributed to our understanding of the overall energy budget in lakes and linkages to vertical fluxes. A paucity of lake-wide turbulence measurements hinders our ability to assess how representative such budgets are at the basin scale. Using an autonomous underwater glider equipped with a microstructure payload, we explored the spatial variability of turbulence in pelagic and near-shore regions of Lake Geneva. Dissipation rates of kinetic energy and thermal variance were estimated by fitting temperature gradient fluctuations spectra to the Batchelor spectrum. In deep waters, turbulent dissipation rates in the surface and thermocline were mild (∼10−8 W kg−1) and weakened toward the hypolimnion (∼10−11 to 10−10 W kg−1). The seasonal thermocline exhibited inhibited interior mixing, with extremely low values of mixing efficiency (Rif ≪ 0.1). In contrast, in the slope zone, a band of significantly enhanced energy dissipation (∼5 × 10−8 W kg−1) extended well above the bottom boundary layer and was associated with strong, efficient mixing (Rif > 0.17). The resulting contribution of the slope region to basin-scale mixing was large, with 90% of the basin-wide mixing—and only 30% energy dissipation—occurring within 4 km of the shoreline. This boundary mixing will modify overturning circulation and the transport pathways of dissolved compounds exchanged with the sediments. The dynamics responsible for the shift in the mixing regime, which appears crucial for the mixing budget of lakes, could not be fully unraveled with the collected observations. Additional model data analyses hint at the role of submesoscale instabilities.
Lake Geneva (Lac Léman), boundary mixing, microstructure, mixing, turbulence, underwater glider
Steiner, Oscar Sepúlveda
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Forrest, Alexander L.
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McInerney, Jasmin B.T.
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Castro, Bieito Fernández
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Lavanchy, Sébastien
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Wüest, Alfred
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Bouffard, Damien
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10 June 2023
Steiner, Oscar Sepúlveda
ce37b37a-cfdf-47bb-a1f7-91fe9e4feac7
Forrest, Alexander L.
234bd4a8-0356-4aaa-a791-7cd1e4430ca9
McInerney, Jasmin B.T.
d9c2888a-60a2-45d9-a0a9-5490bb81875a
Castro, Bieito Fernández
8017e93c-d5ee-4bba-b443-9c72ca512d61
Lavanchy, Sébastien
af48cd7d-332a-489b-aad4-eeeef90824f3
Wüest, Alfred
1d8766ff-b66d-40df-a01e-fe4062512f08
Bouffard, Damien
a3eb0e77-974e-40b5-a122-388e1c15704b
Steiner, Oscar Sepúlveda, Forrest, Alexander L., McInerney, Jasmin B.T., Castro, Bieito Fernández, Lavanchy, Sébastien, Wüest, Alfred and Bouffard, Damien
(2023)
Spatial variability of turbulent mixing from an underwater glider in a large, deep, stratified lake.
Journal of Geophysical Research: Oceans, 128 (6), [e2022JC018913].
(doi:10.1029/2022JC018913).
Abstract
Recent efforts using microstructure turbulence measurements have contributed to our understanding of the overall energy budget in lakes and linkages to vertical fluxes. A paucity of lake-wide turbulence measurements hinders our ability to assess how representative such budgets are at the basin scale. Using an autonomous underwater glider equipped with a microstructure payload, we explored the spatial variability of turbulence in pelagic and near-shore regions of Lake Geneva. Dissipation rates of kinetic energy and thermal variance were estimated by fitting temperature gradient fluctuations spectra to the Batchelor spectrum. In deep waters, turbulent dissipation rates in the surface and thermocline were mild (∼10−8 W kg−1) and weakened toward the hypolimnion (∼10−11 to 10−10 W kg−1). The seasonal thermocline exhibited inhibited interior mixing, with extremely low values of mixing efficiency (Rif ≪ 0.1). In contrast, in the slope zone, a band of significantly enhanced energy dissipation (∼5 × 10−8 W kg−1) extended well above the bottom boundary layer and was associated with strong, efficient mixing (Rif > 0.17). The resulting contribution of the slope region to basin-scale mixing was large, with 90% of the basin-wide mixing—and only 30% energy dissipation—occurring within 4 km of the shoreline. This boundary mixing will modify overturning circulation and the transport pathways of dissolved compounds exchanged with the sediments. The dynamics responsible for the shift in the mixing regime, which appears crucial for the mixing budget of lakes, could not be fully unraveled with the collected observations. Additional model data analyses hint at the role of submesoscale instabilities.
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JGR Oceans - 2023 - Sep lveda Steiner - Spatial Variability of Turbulent Mixing From an Underwater Glider in a Large Deep
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Accepted/In Press date: 22 May 2023
e-pub ahead of print date: 10 June 2023
Published date: 10 June 2023
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Funding Information:
We want to thank Hannah Chmiel, Theo Baracchini, Rafael Reiss, and Claudio Thomas Halaby for their assistance during fieldwork and Cordielyn Goodrich for remote surveillance of the glider during overnight missions. Anton Schleiss (LCH, EPFL) kindly allowed us to use his pool for ballasting purposes. The staff of Rockland Scientific provided timely feedback and troubleshooting during the field campaign. We are grateful to Lucas Merckelbach for guidance and technical support with the flight model and Ilker Fer and Andreas Lorke for their comments on an early version of the manuscript. Valuable feedback from Kenneth Larrieu on analyzing glider navigational data, Alberto Naveira Garabato on centrifugal instabilities, Cintia Ramón Casañas on numerical modeling, Jay Austin on rotary spectra and Louis Vuilleumier on statistics strengthened the manuscript's presentation and discussion. We acknowledge Theo Baracchini for leading the development of meteolakes.ch and James Runnalls for currently maintaining it. The authors would like to thank one anonymous reviewer, Jeff Carpenter and the Editor Lars Umlauf, for their very constructive feedback as the manuscript improved remarkably through the review process. This work was funded by the Swiss National Science Foundation Sinergia grant CRSII2_160726 (). The ENAC Visiting Professor Program funded A.L.F's visit to EPFL during 2018. O.S.S. was partially supported in 2022 by an Eawag Academic Transition Grant (ATG). Open access funding provided by ETH‐Bereich Forschungsanstalten. A Flexible Underwater Distributed Robotic System for High‐Resolution Sensing of Aquatic Ecosystems
Funding Information:
We want to thank Hannah Chmiel, Theo Baracchini, Rafael Reiss, and Claudio Thomas Halaby for their assistance during fieldwork and Cordielyn Goodrich for remote surveillance of the glider during overnight missions. Anton Schleiss (LCH, EPFL) kindly allowed us to use his pool for ballasting purposes. The staff of Rockland Scientific provided timely feedback and troubleshooting during the field campaign. We are grateful to Lucas Merckelbach for guidance and technical support with the flight model and Ilker Fer and Andreas Lorke for their comments on an early version of the manuscript. Valuable feedback from Kenneth Larrieu on analyzing glider navigational data, Alberto Naveira Garabato on centrifugal instabilities, Cintia Ramón Casañas on numerical modeling, Jay Austin on rotary spectra and Louis Vuilleumier on statistics strengthened the manuscript's presentation and discussion. We acknowledge Theo Baracchini for leading the development of meteolakes.ch and James Runnalls for currently maintaining it. The authors would like to thank one anonymous reviewer, Jeff Carpenter and the Editor Lars Umlauf, for their very constructive feedback as the manuscript improved remarkably through the review process. This work was funded by the Swiss National Science Foundation Sinergia grant CRSII2_160726 (A Flexible Underwater Distributed Robotic System for High-Resolution Sensing of Aquatic Ecosystems). The ENAC Visiting Professor Program funded A.L.F's visit to EPFL during 2018. O.S.S. was partially supported in 2022 by an Eawag Academic Transition Grant (ATG). Open access funding provided by ETH-Bereich Forschungsanstalten.
Publisher Copyright:
© 2023 The Authors.
Keywords:
Lake Geneva (Lac Léman), boundary mixing, microstructure, mixing, turbulence, underwater glider
Identifiers
Local EPrints ID: 477858
URI: http://eprints.soton.ac.uk/id/eprint/477858
ISSN: 2169-9275
PURE UUID: b9b97d48-8397-4cc9-a50e-7dee3c5f86d4
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Date deposited: 15 Jun 2023 16:56
Last modified: 17 Mar 2024 04:04
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Contributors
Author:
Oscar Sepúlveda Steiner
Author:
Alexander L. Forrest
Author:
Jasmin B.T. McInerney
Author:
Sébastien Lavanchy
Author:
Alfred Wüest
Author:
Damien Bouffard
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