Middepth decadal warming and freshening in the South Atlantic. Issue 2 (7th February 2017)

• Record Type: Journal Article
• Authors: Giglio, Donata; Johnson, Gregory C.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 2(2017)
• Page Start: 973
• Page End: 979
• Publication Date: 2017-02-07
• Subjects: ocean warming -- ocean freshening -- temperature trend -- AMOC changes -- South Atlantic -- Argo; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012246
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: South Atlantic Ocean middepth water property (temperature, salinity, oxygen, nutrients, etc.) distributions are set by salty, well‐ventilated, and relatively nutrient‐poor North Atlantic Deep Water (NADW) spreading southward toward the Southern Ocean underneath fresher, well‐ventilated, and relatively nutrient‐poor northward spreading Antarctic Intermediate Water (AAIW). The layer between the NADW and AAIW is oxygen‐poor and nutrient‐rich, with small vertical temperature gradients. Salinity stratification dominates the vertical density gradient, hence the layer is referred to as Salinity Stratified Layer (SSL). Decadal warming (0.044 ∘C decade −1 ) and freshening (0.006 g kg −1 decade −1 ) of this layer are analyzed using Argo data, a climatology, and repeat hydrographic sections. Warming within the SSL accumulates heat at a rate of ∼20 TW, is unlikely to be caused by vertical heave, and is consistent with anomalous southward advection of order 10 2 km decade −1 in the Atlantic Meridional Overturning Circulation. Salinity changes within the SSL are consistent with a downward velocity anomaly of order 10 m decade −1 . Key Points: The middepth oxygen‐poor layer in the South Atlantic is salinity stratified This layer warms over the past few decades and freshens over the last decade This warming could result from very small changes in meridional velocities