Journal cover Journal topic
Ocean Science An interactive open-access journal of the European Geosciences Union
Ocean Sci., 13, 521-530, 2017
https://doi.org/10.5194/os-13-521-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
06 Jul 2017
Freshening of Antarctic Intermediate Water in the South Atlantic Ocean in 2005–2014
Wenjun Yao1, Jiuxin Shi1, and Xiaolong Zhao2 1Physical Oceanography Laboratory/CIMST, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
2North China Sea Marine Forecasting Center, State Oceanic Administration, Qingdao, 266061, Shandong, China
Abstract. Basin-scale freshening of Antarctic Intermediate Water (AAIW) is reported to have occurred in the South Atlantic Ocean during the period from 2005 to 2014, as shown by the gridded monthly means of the Array for Real-time Geostrophic Oceanography (Argo) data. This phenomenon was also revealed by two repeated transects along a section at 30° S, performed during the World Ocean Circulation Experiment Hydrographic Program. Freshening of the AAIW was compensated for by a salinity increase of thermocline water, indicating a hydrological cycle intensification. This was supported by the precipitation-minus-evaporation change in the Southern Hemisphere from 2000 to 2014. Freshwater input from atmosphere to ocean surface increased in the subpolar high-precipitation region and vice versa in the subtropical high-evaporation region. Against the background of hydrological cycle changes, a decrease in the transport of Agulhas Leakage (AL), which was revealed by the simulated velocity field, was proposed to be a contributor to the associated freshening of AAIW. Further calculation showed that such a decrease could account for approximately 53 % of the observed freshening (mean salinity reduction of about 0.012 over the AAIW layer). The estimated variability of AL was inferred from a weakening of wind stress over the South Indian Ocean since the beginning of the 2000s, which would facilitate freshwater input from the source region. The mechanical analysis of wind data here was qualitative, but it is contended that this study would be helpful to validate and test predictably coupled sea–air model simulations.

Citation: Yao, W., Shi, J., and Zhao, X.: Freshening of Antarctic Intermediate Water in the South Atlantic Ocean in 2005–2014, Ocean Sci., 13, 521-530, https://doi.org/10.5194/os-13-521-2017, 2017.
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Short summary
Antarctic Intermediate Water (AAIW) in the South Atlantic Ocean has experienced basin-scaled freshening from 2005 to 2014, reflected by the Argo gridded products. Two zonal sections of WOCE observation also revealed a similar quasi-decadal signal. Our analysis revealed that such freshening was induced by the increase of freshwater input in the AAIW ventilation region and the decrease of Agulhas Leakage transport.
Antarctic Intermediate Water (AAIW) in the South Atlantic Ocean has experienced basin-scaled...
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