[A-OS14] [EE] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS14-09] Possible uncertainty in CMIP5 projections of low-oxygen water volume in the Eastern Tropical Pacific

*Masahito Shigemitsu¹, Akitomo Yamamoto², Akira Oka², Yasuhiro Yamanaka³ (1.Japan Agency for Marine-Earth Science and Technology, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.Hokkaido University)

Keywords:low-oxygen water volume, global warming, Eastern Equatorial Pacific

Using the results from nine Earth system models submitted to the Coupled Model Intercomparison Project Phase 5 (CMIP5), we identify the Eastern Tropical Pacific (ETP) as the region with the greatest uncertainty of future changes in oxygen-deficient (< 30μM) water volumes, since different models variously project both positive and negative changes in the oxygen-deficient volume and export flux there. We investigate the factors controlling future changes in oxygen-deficient volume in the ETP with global warming, using a single offline biogeochemical model. Oxygen budget analysis clarifies that the Equatorial Undercurrent (EUC) is the key mechanism controlling future variations in the oxygen-deficient volume in the ETP in our model. From the outputs of all of the CMIP5 models, we identify a significant negative relationship between changes in the EUC volume transport and the oxygen-deficient water volume from the present to the end of the 21^st century, which indicates that the response of the EUC to global warming leads to one possible uncertainty in future projections of oxygen-deficient volume in the ETP.