Effects of mixed layer depth on the changes in the sea surface temperature under global warming in CMIP5 models

Abstract

We analyzed two simulations, the control simulation using industrial greenhouse gas concentrations (historical run) and the experiment simulation using doubled CO2 concentrations (RCP4.5 run) to investigate relationship of changes in the MLD with SST changes under the anthropogenic climate change in selected data set from CMIP5 simulations. The shallow MLD group simulated higher SST compared to the deep group in all equatorial Pacific regions except eastern equator and near the coast during historical period. The region has high value of SST difference along the off equator in mid Pacific consisted with maximum value of MLD difference. Therefore, it proved that MLD shoaling enhances stratification in the upper ocean and then it leads to SST warming. The projected changes in SST as well as MLD are larger at the deep group than the shallow group, and thus it allows us to expect that MLD in deep group might become much shallow and result in steep SST warming. However, the ratio of SST difference and MLD difference in all period showed the higher value in shallow group than deep group, implying that models with shallow MLDs have a substantial SST increase, thus enhancing surface stratification in the ocean and this process constitutes a positive feedback between MLD and SST. Therefore, to confirm this feedback, the future study about the stratification in the CMIP5 model will be necessary.D with SST changes under the anthropogenic climate change in selected data set from CMIP5 simulations. The shallow MLD group simulated higher SST compared to the deep group in all equatorial Pacific regions except eastern equator and near the coast during historical period. The region has high value of SST difference along the off equator in mid Pacific consisted with maximum value of MLD difference. Therefore, it proved that MLD shoaling enhances stratification in the upper ocean and then it leads to SST warming. The projected changes in SST as well as MLD are larger at the deep group than the shallow group, and thus it allows us to expect that MLD in deep group might become much shallow and result in steep SST warming. However, the ratio of SST difference and MLD difference in all period showed the higher value in shallow group than deep group, implying that models with shallow MLDs have a substantial SST increase, thus enhancing surface stratification in the ocean and this process constitutes a positive feedback between MLD and SST. Therefore, to confirm this feedback, the future study about the stratification in the CMIP5 model will be necessary.