Observations of the vertical and temporal evolution of a Natal Pulse along the Eastern Agulhas Bank

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Pivan, Xavier, Krug, Marjolaine, Herbette, Steven
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Geophysical Union 2016
• Subjects: Agulhas Current; Natal Pulse; Lagrangian floats; Antarctic; Indian; Antarc*
• Online Access: https://archimer.ifremer.fr/doc/00350/46162/45860.pdf; https://doi.org/10.1002/2015JC011582; https://archimer.ifremer.fr/doc/00350/46162/

This study re-investigates the work of Lutjeharms et al. [2001,2003] who documented the properties of a Natal Pulse using isopycnal Lagrangian floats. We combined Lagrangian analyses and Eulerian maps derived from objective analysis to better describe the evolution of a Natal Pulse along three density surfaces referred to as the surface (satellite-observed), shallow (isopycnal-1026.8 kg.m−3) and deep (isopycnal-1027.2 kg.m−3) layer. Our observations show that this Natal Pulse extended to a depth of 1000m and was associated with cyclonic relative vorticity values of about 6.5 to 8.5x10−5.s−1 in the surface and shallow layer and 4x10−5.s−1 in the deep layer. This Natal Pulse contributed to cross-shelf exchange through the offshore advection of Eastern Agulhas Bank water near the surface, onshore advection of South Indian Central Water and/or Indian Equatorial Water in the shallow layer and Antarctic Intermediate Water in the deep layer. Sea Surface Temperature maps showed that the downstream progression of the Natal Pulse along the 3000m isobath was related to a readjustment of its rotation axis. This readjustment advected Eastern Agulhas Bank water into the Natal Pulse eddy and triggered a SST cooling of about 3°C in the cyclonic area. The importance of a warm recirculating Agulhas plume originating from the Natal Pulse was highlighted. This warm water plume extended to a depth of 700m and was associated with onshore velocities exceeding those experienced within the Natal Pulse eddy by a factor of two. Our observations indicate that the June/July 1998 Natal Pulse and its associated plumes enhanced cross-shelf exchanges. This article is protected by copyright. All rights reserved.