Decoupled freshwater transport and meridional overturning in the South Atlantic

Mignac, D., Ferreira, D. ORCID: https://orcid.org/0000-0003-3243-9774 and Haines, K. ORCID: https://orcid.org/0000-0003-2768-2374 (2019) Decoupled freshwater transport and meridional overturning in the South Atlantic. Geophysical Research Letters, 46 (4). pp. 2178-2186. ISSN 0094-8276 doi: 10.1029/2018GL081328

Abstract/Summary

Freshwater transports (F_ov) by the Atlantic Meridional Overturning Circulation (AMOC) are sensitive to salinity distributions and may determine AMOC stability. However, climate models show large salinity biases, distorting the relation between F_ov and the AMOC. Using free-running models and ocean reanalyses with realistic salinities but quite different AMOCs, we show that the fresh Antarctic Intermediate Water (AAIW) layer eliminates salinity differences across the AMOC branches at ~1200 m, ∆S_1200m, which decouples F_ov from the AMOC south of ~10˚N. As AAIW disappears north of ~10˚N, a large ∆S_1200m allows the AMOC to drive substantial southward F_ov in the North Atlantic. In the South Atlantic the 0-300 m zonal salinity contrasts control the gyre freshwater transports F_gyre, which also determine the total freshwater transports. This decoupling makes the southern F_ov unlikely to play any role in AMOC stability, leaving indirect F_gyre feedbacks or F_ov in the north, as more relevant factors.