Origin and mechanism of Antarctic Intermediate Water formation and transformation in the Southern Atlantic Ocean: A Lagrangian analysis based on Argo data
Abstract
Recent studies using Argo floats (Schmid and Garzoli, 2009) and a model (Garzoli and Matano, 2011) indicate that South Atlantic is not just a passive conduit for the passage of water masses formed in other regions of the world ocean, but instead actively participates in their transformation. By analyzing salinity, temperature, and absolute geostrophic velocity fields derived from Argo float vertical profiles and deep displacements at 1000 m, Rusciano et al. (2012) recently showed that three different regional varieties of intermediate water converge in the southeast Atlantic: Atlantic AAIW (A-AAIW, characterized by S ≤ 34.2), Indian AAIW (I-AAIW, characterized by S ≥ 34.3), and a previously undefined Indo-Atlantic intermediate water (IA-AAIW, characterized by 34.2 < S < 34.3). Corroborative results were obtained by Rimaud et al. (2012) who discussed the results of a regional ocean model run around Southern Africa and emphasized the strength and potential of a Lagrangian analysis to describe the properties and dynamics of AAIW. In this new study, we propose a qualitative description of AAIW over the whole South Atlantic and South East Indian oceans, based on an extension of our Argo-derived 1°x1° gridded temperature and salinity data set. Higher salinity AAIW is found to the north of the domain, bounded by the Subtropical Front. AAIW salinity decreases southward with minimum values south of the Polar Front. The IA-AAIW is confined north of the Subtropical Front between 70°W and 10°E. To the east of 10°E the IA-AAIW is confined between the Subtropical Front and the Subantarctic Front. The ARIANE diagnostic tool is adapted to the analysis of the tracer and velocity fields derived from Argo float data. The careful construction of the 3D absolute geostrophic velocity field with suitable constraints on the vertical velocity component allows direct investigation of Lagrangian variations of salinity and temperature. We present transport estimates, water mass fates and origins, and water mass conversions for the ocean circulation related to AAIW pathways in the South Atlantic. The analysis is performed between several sets of initial and final control sections over which the AAIW flow can be described with several hundred of thousands of individual numerical parcels transported by the reconstructed 3D velocity field.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSMOS31C..01R
- Keywords:
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- 4500 OCEANOGRAPHY: PHYSICAL