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

2015 ◽  
Vol 12 (8) ◽  
pp. 6525-6587 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. 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 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 a too large biologically-driven downward flux of particulate organic carbon at depth, caused by too high particle export from the euphotic layer and too weak remineralization in the upper ocean. 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, deep and high latitudes ocean due to an overall slow-down of ventilation and increased temperature.

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

2015 ◽  
Vol 12 (18) ◽  
pp. 5429-5454 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

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.

scholarly journals Response of ENSO and the Mean State of the Tropical Pacific to Extratropical Cooling and Warming: A Study Using the IAP Coupled Model

2009 ◽  
Vol 22 (22) ◽  
pp. 5902-5917 ◽  
Author(s):  
Y. Yu ◽  
D-Z. Sun
Keyword(s):  
Climate Change ◽  
Climate Modeling ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Equatorial Region ◽  
Upper Ocean ◽  
Central Pacific ◽  
Intergovernmental Panel ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract The coupled model of the Institute of Atmospheric Physics (IAP) is used to investigate the effects of extratropical cooling and warming on the tropical Pacific climate. The IAP coupled model is a fully coupled GCM without any flux correction. The model has been used in many aspects of climate modeling, including the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) climate change and paleoclimate simulations. In this study, the IAP coupled model is subjected to cooling or heating over the extratropical Pacific. As in an earlier study, the cooling and heating is imposed over the extratropical region poleward of 10°N–10°S. Consistent with earlier findings, an elevated (reduced) level of ENSO activity in response to an increase (decrease) in the cooling over the extratropical region is found. The changes in the time-mean structure of the equatorial upper ocean are also found to be very different between the case in which ocean–atmosphere is coupled over the equatorial region and the case in which the ocean–atmosphere over the equatorial region is decoupled. For example, in the uncoupled run, the thermocline water across the entire equatorial Pacific is cooled in response to an increase in the extratropical cooling. In the corresponding coupled run, the changes in the equatorial upper-ocean temperature in the extratropical cooling resemble a La Niña situation—a deeper thermocline in the western and central Pacific accompanied by a shallower thermocline in the eastern Pacific. Conversely, with coupling, the response of the equatorial upper ocean to extratropical cooling resembles an El Niño situation. These results ascertain the role of extratropical ocean in determining the amplitude of ENSO. The results also underscore the importance of ocean–atmosphere coupling in the interaction between the tropical Pacific and the extratropical Pacific.

scholarly journals ENSO Amplitude Changes due to Climate Change Projections in Different Coupled Models

2007 ◽  
Vol 20 (2) ◽  
pp. 203-217 ◽  
Author(s):  
Sang-Wook Yeh ◽  
Ben P. Kirtman
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Skewed Distribution ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Coupled Models ◽  
Climate Change Projections ◽  
State Changes ◽  
The Mean ◽  
Gfdl Model ◽  
Mean State

Abstract Four climate system models are chosen here for an analysis of ENSO amplitude changes in 4 × CO2 climate change projections. Despite the large changes in the tropical Pacific mean state, the changes in ENSO amplitude are highly model dependant. To investigate why similar mean state changes lead to very different ENSO amplitude changes, the characteristics of sea surface temperature anomaly (SSTA) variability simulated in two coupled general circulation models (CGCMs) are analyzed: the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) models. The skewed distribution of tropical Pacific SSTA simulated in the MRI model suggests the importance of nonlinearities in the ENSO physics, whereas the GFDL model lies in the linear regime. Consistent with these differences in ENSO regime, the GFDL model is insensitive to the mean state changes, whereas the MRI model is sensitive to the mean state changes associated with the 4 × CO2 scenario. Similarly, the low-frequency modulation of ENSO amplitude in the GFDL model is related to atmospheric stochastic forcing, but in the MRI model the amplitude modulation is insensitive to the noise forcing. These results suggest that the understanding of changes in ENSO statistics among various climate change projections is highly dependent on whether the model ENSO is in the linear or nonlinear regime.

scholarly journals Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0

2020 ◽  
Author(s):  
Kai Wang ◽  
Xiujun Wang ◽  
Raghu Murtugudde ◽  
Dongxiao Zhang ◽  
Rong-Hua Zhang
Keyword(s):  
Model Simulation ◽  
Tropical Pacific ◽  
Scale Model ◽  
Oxygen Minimum Zones ◽  
The North ◽  
Basin Scale ◽  
Dominant Process ◽  
Fully Coupled ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. The tropical Pacific Ocean holds the world’s two largest Oxygen Minimum Zones (OMZs), showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the equator. However, there is a lack of quantitative assessments of physical and biological regulations on the asymmetry of tropical Pacific OMZs. Here, we apply a fully coupled basin-scale model (OGCM-DMEC V1.0) to investigate the impacts of physical supply and biological consumption on the dynamics of OMZs in the tropical Pacific. We first utilize observational data to evaluate and improve our model simulation, and find that mid-depth DO is more sensitive to the parameterization of background diffusion. Enhanced background diffusion results in higher DO concentrations at mid-depth, leading to significant improvement of our model capability to reproduce the asymmetric OMZs. Our study shows that while physical supply of DO is increased in majority of the tropical Pacific due to enhanced background diffusion, there is little increase in the largest OMZ to the north. Interestingly, enhanced background diffusion results in lower rates of biological consumption over ~ 300–1000 m in the entire basin, which is associated with redistribution of dissolved organic matter (DOM). Our analyses demonstrate that weaker physical supply in the ETNP is the dominant process responsible for the asymmetric DO in the core OMZs (~ 200–600 m) while higher biological consumption to the north plays a larger role in regulating DO concentration beneath the OMZs (~ 600–800 m), with implication for the asymmetric OMZs. This study highlights the roles of physical supply and biological consumption in shaping the asymmetric OMZs in the tropical Pacific, underscoring the need to understand both physical and biological processes for accurate projections of DO variability.

scholarly journals Sensitivity of asymmetric Oxygen Minimum Zones to remineralization rate and mixing intensity in the tropical Pacific using a basin-scale model (OGCM-DMEC V1.2)

2021 ◽  
Author(s):  
Kai Wang ◽  
Xiujun Wang ◽  
Raghu Murtugudde ◽  
Dongxiao Zhang ◽  
Rong-Hua Zhang
Keyword(s):  
Vertical Mixing ◽  
Tropical Pacific ◽  
Scale Model ◽  
Oxygen Minimum Zones ◽  
The North ◽  
Basin Scale ◽  
Dominant Process ◽  
Fully Coupled ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. The tropical Pacific Ocean holds the world’s two largest Oxygen Minimum Zones (OMZs), showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the equator. However, many models have difficulties in reproducing the observed asymmetric OMZs in the tropical Pacific. Here, we apply a fully coupled basin-scale model (OGCM-DMEC V1.2) to evaluate the impacts of remineralization rate and the intensity of vertical mixing on the dynamics of OMZs in the tropical Pacific. We first utilize observational data of dissolved oxygen (DO), dissolved organic nitrogen (DON) and oxygen consumption to calibrate and validate the basin-scale model. Our model experiments demonstrate that enhanced vertical mixing combined with reduced remineralization rate can significantly improve our model capability of reproducing the asymmetric OMZs. Our study shows that DO is more sensitive to biological processes over 200–400 m but to physical processes over 400–1000 m. Enhanced vertical mixing not only causes an increase in DO supply at mid-depth, but also results in lower rates of biological consumption in the OMZs, which is associated with redistribution of DON. Our analyses demonstrate that weaker physical supply in the ETNP is the dominant process responsible for the asymmetry of the lower OMZs whereas greater biological consumption to the north plays a larger role in regulating the upper OMZs. This study highlights the complex roles of physical supply and biological consumption in shaping the asymmetric OMZs in the tropical Pacific.

scholarly journals Rectification of El Niño–Southern Oscillation into Climate Anomalies of Decadal and Longer Time Scales: Results from Forced Ocean GCM Experiments

2014 ◽  
Vol 27 (7) ◽  
pp. 2545-2561 ◽  
Author(s):  
De-Zheng Sun ◽  
Tao Zhang ◽  
Yan Sun ◽  
Yongqiang Yu
Keyword(s):  
Climate Change ◽  
Time Scales ◽  
Wind Stress ◽  
Surface Wind ◽  
Tropical Pacific ◽  
Surface Wind Stress ◽  
Interannual Fluctuations ◽  
Mean State ◽  
The Tropical Pacific

Abstract To better understand the causes of climate change in the tropical Pacific on the decadal and longer time scales, the rectification effect of ENSO events is delineated by contrasting the time-mean state of two forced ocean GCM experiments. In one of them, the long-term mean surface wind stress of 1950–2011 is applied, while in the other, the surface wind stress used is the long-term mean surface wind stress of 1950–2011 plus the interannual monthly anomalies over the period. Thus, the long-term means of the surface wind stress in the two runs are identical. The two experiments also use the same relaxation boundary conditions, that is, the SST is restored to the same prescribed values. The two runs, however, are found to yield significantly different mean climate for the tropical Pacific. The mean state of the run with interannual fluctuations in the surface winds is found to have a cooler warm pool, warmer thermocline water, and warmer eastern surface Pacific than the run without interannual fluctuations in the surface winds. The warming of the eastern Pacific has a pattern that resembles the observed decadal warming. In particular, the pattern features an off-equator maximum as the observed decadal warming. The spatial pattern of the time-mean upper-ocean temperature differences between the two experiments is shown to resemble that of the differences in the nonlinear dynamic heating, underscoring the role of the nonlinear ocean dynamics in the rectification. The study strengthens the suggestion that rectification of ENSO can be a viable mechanism for climate change of decadal and longer time scales.

scholarly journals Oxygen minimum zone variations in the tropical Pacific during the Holocene

2015 ◽  
Vol 42 (20) ◽  
pp. 8530-8537 ◽  
Author(s):  
Xu Xu ◽  
Joachim Segschneider ◽  
Birgit Schneider ◽  
Wonsun Park ◽  
Mojib Latif
Keyword(s):  
Oxygen Minimum Zone ◽  
Tropical Pacific ◽  
The Holocene ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
The Tropical Pacific

scholarly journals Impact of Resolution on the Tropical Pacific Circulation in a Matrix of Coupled Models

2009 ◽  
Vol 22 (10) ◽  
pp. 2541-2556 ◽  
Author(s):  
Malcolm J. Roberts ◽  
A. Clayton ◽  
M.-E. Demory ◽  
J. Donners ◽  
P. L. Vidale ◽  
...  
Keyword(s):  
Coupled Model ◽  
Walker Circulation ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Coupled Models ◽  
Model Stability ◽  
The Mean ◽  
The Impact ◽  
Mean State ◽  
The Tropical Pacific

Abstract Results are presented from a matrix of coupled model integrations, using atmosphere resolutions of 135 and 90 km, and ocean resolutions of 1° and 1/3°, to study the impact of resolution on simulated climate. The mean state of the tropical Pacific is found to be improved in the models with a higher ocean resolution. Such an improved mean state arises from the development of tropical instability waves, which are poorly resolved at low resolution; these waves reduce the equatorial cold tongue bias. The improved ocean state also allows for a better simulation of the atmospheric Walker circulation. Several sensitivity studies have been performed to further understand the processes involved in the different component models. Significantly decreasing the horizontal momentum dissipation in the coupled model with the lower-resolution ocean has benefits for the mean tropical Pacific climate, but decreases model stability. Increasing the momentum dissipation in the coupled model with the higher-resolution ocean degrades the simulation toward that of the lower-resolution ocean. These results suggest that enhanced ocean model resolution can have important benefits for the climatology of both the atmosphere and ocean components of the coupled model, and that some of these benefits may be achievable at lower ocean resolution, if the model formulation allows.

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