Middepth decadal warming and freshening in the South Atlantic
2017
Giglio, Donata | Johnson, Gregory C.
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 10² 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.
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