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WANG Yu, LI Yuanlong, WEI Chuanjie. Subtropical sea surface salinity maxima in the South Indian Ocean[J]. Journal of Oceanology and Limnology, 2020, 38(1): 16-29

Subtropical sea surface salinity maxima in the South Indian Ocean

WANG Yu1, LI Yuanlong2,3, WEI Chuanjie3,4,5
1 North China Sea Offshore Engineering Survey Institute, North China Sea Branch of Ministry of Natural Resources, Qingdao 266061, China;
2 Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;
3 Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China;
4 Engineering and Technology Department, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;
5 University of Chinese Academy of Sciences, Beijing 100049, China
Subtropical sea surface salinity (SSS) maximum is formed in the subtropical South Indian Ocean (SIO) by excessive evaporation over precipitation and serves as the primary salt source of the SIO. Spaceborne SSS measurements by Aquarius satellite during September 2011-May 2015 detect three disconnected SSS maximum regions (>35.6) in the eastern (105°E-115°E, 38°S-28°S), central (60°E-100°E, 35°S-25°S), and western (25°E-40°E, 38°S-20°S) parts of the subtropical SIO, respectively. Such structure is however not seen in gridded Argo data. Analysis of Argo profile data confirms the existence of the eastern maximum patch and also reveals SSS overestimations of Aquarius near the western and eastern boundaries. Although subjected to large uncertainties, a mixed-layer budget analysis is employed to explain the seasonal cycle of SSS. The eastern and central regions reach the highest salinity in February-March and lowest salinity in August-September, which can be well explained by surface freshwater forcing (SFF) term. SFF is however not controlled by evaporation (E) or precipitation (P). Instead, the large seasonal undulations of mixed layer depth (MLD) is the key factor. The shallow (deep) MLD in austral summer (winter) amplifies (attenuates) the forcing effect of local positive E-P and causes SSS rising (decreasing). Ocean dynamics also play a role. Particularly, activity of mesoscale eddies is a critical factor regulating SSS variability in the eastern and western regions.
Key words:    sea surface salinity (SSS)|subtropical salinity maximum|Aquarius|Argo float|freshwater flux   
Received: 2018-09-24   Revised:
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