Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 12, issue 18
Biogeosciences, 12, 5429-5454, 2015
https://doi.org/10.5194/bg-12-5429-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Low oxygen environments in marine, fresh and estuarine...

Biogeosciences, 12, 5429-5454, 2015
https://doi.org/10.5194/bg-12-5429-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Sep 2015

Research article | 21 Sep 2015

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

A. Cabré1, I. Marinov1, R. Bernardello1,2, and D. Bianchi3,4 A. Cabré et al.
  • 1Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, USA
  • 2National Oceanographic Centre, Southampton, UK
  • 3School of Oceanography, University of Washington, Seattle, USA
  • 4Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, USA

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.

Publications Copernicus
Special issue
Download
Short summary
We analyze 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, climate change projections, and interannual variability. We analyse biases with respect to observations and consistency of results across simulations.
We analyze simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system...
Citation
Share