Interannual Variability of Antarctic Intermediate Water in the Tropical North Atlantic

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Fu, Yao, Wang, Chunzai, Brandt, Peter, Greatbatch, Richard J.
• Format: Report
• Language: English
• Published: AMER GEOPHYSICAL UNION 2019
• Subjects: Oceanography; interannual variability of Antarctic Intermediate Water in the tropical North Atlantic; meridional propagating AAIW salinity anomalies associated with the western boundary transport; zonal propagating AAIW anomalies related to baroclinic Rossby wave propagation; MERIDIONAL OVERTURNING CIRCULATION; PLANETARY WAVE-PROPAGATION; OXYGEN-MINIMUM ZONES; VARYING MEAN FLOW; BRAZIL CURRENT; AGULHAS LEAKAGE; BOTTOM TOPOGRAPHY; DECADAL CHANGES; TRANSPORT; OCEAN; Antarctic; Curl; Antarc*; North Atlantic
• Online Access: http://ir.gig.ac.cn/handle/344008/41482; https://doi.org/10.1029/2018JC014878

Interannual variability of Antarctic Intermediate Water (AAIW) in the tropical North Atlantic is investigated using the GECCO2 ocean state estimate and Argo data. AAIW salinity variability near the western boundary is highly correlated with the transport along the western boundary on interannual timescales. Northward propagating anomalies are associated with the western boundary transport variability that, to some extent, is related to the large-scale wind stress curl forcing by means of the Sverdrup balance. AAIW anomalies also propagate westward with the speed of baroclinic Rossby waves, indicating that the displacement of the meridional salinity gradient by westward propagation of baroclinic Rossby waves plays a role in the variability of AAIW characteristics. Slower eastward spreading of AAIW anomalies is identified on decadal timescales likely associated with the advection of salinity anomalies by weak eastward current bands. Understanding the observed interannual and decadal variability of AAIW salinity is important to properly interpret salinity changes reported in response to changes in the hydrological cycle. Plain Language Summary Antarctic Intermediate Water (AAIW) is characterized by its low salinity in the ocean. Here we examine the variability of AAIW in the tropical North Atlantic on interannual timescales by using an ocean assimilation product (GECCO2) and Argo data. The analysis of these data shows that in the tropical northwestern Atlantic, variability of the AAIW salinity is associated with the transport variability near the western boundary and with the westward propagation of planetary waves. Decadal AAIW signals propagate eastward, which is indicative of eastward spreading of water mass anomalies with the weak circulation at intermediate depths. The identified AAIW water mass variability in the tropical North Atlantic has implications for the transport of tracers and particularly the ventilation of the oxygen minimum zone of the eastern tropical North Atlantic.