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Ventilation of the upper oxygen minimum zone in the coastal region off Mexico: Implications of El Niño 2015–2016

Ventilation of the upper oxygen minimum zone in the coastal region off Mexico: Implications of El Niño 2015–2016
Ventilation of the upper oxygen minimum zone in the coastal region off Mexico: Implications of El Niño 2015–2016
As a result of anthropogenic activities, it has been predicted that the ocean will be challenged with rising temperature, increased stratification, ocean acidification, stronger more frequent tropical storms, and oxygen depletion. In the tropical Pacific off central Mexico all these phenomena are already occurring naturally, providing a laboratory from which to explore ocean biogeochemical dynamics that are predicted under future anthropogenic forcing conditions. Here, seasonally anomalous surface tropical waters were detected as a result of the developing “Godzilla El Niño 2015–2016.” The incursion of this oxygenated water modified the local structure of an intense and shallow oxygen minimum zone (OMZ), partially eroding and intensifying the oxycline while having an associated impact on the carbon maximum zone. The core of the OMZ (<4.4 μmol kg–1) was centered around 474 m, with a variant upper level between 50 and 360 m depth. Below the dominance of Tropical Surface Waters, the thickness of the oxycline varied between 10 and 325 m, with intensity values up to 11 μmol kg–1 m–1. The change in dissolved inorganic carbon (DIC) and apparent oxygen utilization yielded a molar ratio of δDIC = 0.98 × δAOU during June 2015 and of δDIC = 1.08 × δAOU for March 2016. A further decrease in the average content of DIC was observed in the carbon maximum zone for 2016. Traditionally, different explanations have been proposed to account for changing oxygen concentrations in the ocean rather than considering the interactions between multiple forcing factors. Our results highlight the significance of an episodic event like El Niño in the distribution and concentration of O2 and DIC and as a plausible mechanism of ventilation and increased oxygen availability in the upper OMZ of the tropical Pacific off central Mexico.
2296-7745
Trucco-pignata, Pablo N.
3a82ee58-cff6-42fa-a5e6-3cb629ba22de
Hernández-ayón, José Martín
9db81611-c129-485c-8f63-116723e8dc8b
Santamaria-del-angel, Eduardo
6992c1e1-56d0-43b9-af33-3c482124d966
Beier, Emilio
b48d75af-03b4-4c44-a8b9-b61dbe0234ab
Sánchez-velasco, Laura
4e3a2370-2631-45c3-ae5e-f84d073ca4a5
Godínez, Victor M.
893637de-366d-4ac0-bca7-186df8804ec4
Norzagaray, Orión
e2b1faa8-c157-40e6-a2a3-956b1e5da071
Trucco-pignata, Pablo N.
3a82ee58-cff6-42fa-a5e6-3cb629ba22de
Hernández-ayón, José Martín
9db81611-c129-485c-8f63-116723e8dc8b
Santamaria-del-angel, Eduardo
6992c1e1-56d0-43b9-af33-3c482124d966
Beier, Emilio
b48d75af-03b4-4c44-a8b9-b61dbe0234ab
Sánchez-velasco, Laura
4e3a2370-2631-45c3-ae5e-f84d073ca4a5
Godínez, Victor M.
893637de-366d-4ac0-bca7-186df8804ec4
Norzagaray, Orión
e2b1faa8-c157-40e6-a2a3-956b1e5da071

Trucco-pignata, Pablo N., Hernández-ayón, José Martín, Santamaria-del-angel, Eduardo, Beier, Emilio, Sánchez-velasco, Laura, Godínez, Victor M. and Norzagaray, Orión (2019) Ventilation of the upper oxygen minimum zone in the coastal region off Mexico: Implications of El Niño 2015–2016. Frontiers in Marine Science, 6. (doi:10.3389/fmars.2019.00459).

Record type: Article

Abstract

As a result of anthropogenic activities, it has been predicted that the ocean will be challenged with rising temperature, increased stratification, ocean acidification, stronger more frequent tropical storms, and oxygen depletion. In the tropical Pacific off central Mexico all these phenomena are already occurring naturally, providing a laboratory from which to explore ocean biogeochemical dynamics that are predicted under future anthropogenic forcing conditions. Here, seasonally anomalous surface tropical waters were detected as a result of the developing “Godzilla El Niño 2015–2016.” The incursion of this oxygenated water modified the local structure of an intense and shallow oxygen minimum zone (OMZ), partially eroding and intensifying the oxycline while having an associated impact on the carbon maximum zone. The core of the OMZ (<4.4 μmol kg–1) was centered around 474 m, with a variant upper level between 50 and 360 m depth. Below the dominance of Tropical Surface Waters, the thickness of the oxycline varied between 10 and 325 m, with intensity values up to 11 μmol kg–1 m–1. The change in dissolved inorganic carbon (DIC) and apparent oxygen utilization yielded a molar ratio of δDIC = 0.98 × δAOU during June 2015 and of δDIC = 1.08 × δAOU for March 2016. A further decrease in the average content of DIC was observed in the carbon maximum zone for 2016. Traditionally, different explanations have been proposed to account for changing oxygen concentrations in the ocean rather than considering the interactions between multiple forcing factors. Our results highlight the significance of an episodic event like El Niño in the distribution and concentration of O2 and DIC and as a plausible mechanism of ventilation and increased oxygen availability in the upper OMZ of the tropical Pacific off central Mexico.

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Published date: 24 July 2019

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Local EPrints ID: 432727
URI: https://eprints.soton.ac.uk/id/eprint/432727
ISSN: 2296-7745
PURE UUID: 092d9f77-cc3b-43dd-bd77-4532c9248e2d

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Date deposited: 25 Jul 2019 16:30
Last modified: 09 Dec 2019 17:33

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Author: José Martín Hernández-ayón
Author: Eduardo Santamaria-del-angel
Author: Emilio Beier
Author: Laura Sánchez-velasco
Author: Victor M. Godínez
Author: Orión Norzagaray

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