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Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends

Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak.

At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific.

Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature.
1726-4170
5429-5454
Cabré, A.
56f47ddf-acec-44d6-9d62-fae8dc4ee4eb
Marinov, I.
f82e7a23-9a7b-46bf-8702-3ce4660ebe23
Bernardello, R.
7db9abe7-7079-4f14-8397-6371d96e2420
Bianchi, D.
a8ad2342-66b4-4871-ae59-6efd945f321a
Cabré, A.
56f47ddf-acec-44d6-9d62-fae8dc4ee4eb
Marinov, I.
f82e7a23-9a7b-46bf-8702-3ce4660ebe23
Bernardello, R.
7db9abe7-7079-4f14-8397-6371d96e2420
Bianchi, D.
a8ad2342-66b4-4871-ae59-6efd945f321a

Cabré, A., Marinov, I., Bernardello, R. and Bianchi, D. (2015) Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends. Biogeosciences, 12 (18), 5429-5454. (doi:10.5194/bg-12-5429-2015).

Record type: Article

Abstract

We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak.

At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific.

Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature.

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Published date: 21 September 2015
Organisations: Marine Biogeochemistry

Identifiers

Local EPrints ID: 382274
URI: http://eprints.soton.ac.uk/id/eprint/382274
ISSN: 1726-4170
PURE UUID: ef97e898-552e-4d97-ba4b-b3e1fb40f5c7

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Date deposited: 02 Oct 2015 08:48
Last modified: 16 Dec 2019 20:13

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