06 Jan 2023
 | 06 Jan 2023

Stirring across the Antarctic Circumpolar Current's Southern Boundary at the Greenwich Meridian, Weddell Sea

Ria Oelerich, Karen J. Heywood, Gillian M. Damerell, Marcel du Plessis, Louise C. Biddle, and Sebastiaan Swart

Abstract. At the Southern Boundary of the Antarctic Circumpolar Current (ACC), relatively warm ACC waters encounter the colder waters surrounding Antarctica. Strong density gradients across the Southern Boundary indicate the presence of a frontal jet and are thought to modulate the southward heat transport across the front. In this study, the Southern Boundary in the Weddell Sea sector at the Greenwich Meridian is surveyed for the first time in high resolution over an entire austral summer with underwater gliders transecting the front on 5 occasions. The 5 transects show that the frontal structure (i.e., hydrography, velocities and lateral density gradients) varies temporally. The results demonstrate significant, quite rapid (a few weeks) variability of the Southern Boundary and its frontal jet in location, strength and width. A mesoscale cold-core eddy is identified to disrupt the Southern Boundary’s frontal structure and strengthen lateral density gradients across the front. The front’s barrier properties are assessed using mixing length scales and potential vorticity to establish the cross-frontal exchange of properties between the Southern Boundary and the Weddell Gyre. The results show that stronger lateral density gradients caused by the mesoscale eddy strengthen the barrier-like properties of the front through reduced mixing length scales and pronounced gradients of potential vorticity. In contrast, the barrier-like properties of the Southern Boundary are reduced when no mesoscale eddy is influencing the density gradients across the front. Using altimetry, we further demonstrate that the barrier properties over the past decade have strengthened as a result of increased meridional gradients of absolute dynamic topography and increased frontal jet speeds in comparison to previous decades. Our results emphasize that locally and rapidly changing barrier properties of the Southern Boundary are important to quantify the cross-frontal exchange, which is particularly relevant in regions where the Southern Boundary is located near the Antarctic shelf break (e.g. in the West Antarctic Sector).

Ria Oelerich et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1527', Kaihe Yamazaki, 12 Jan 2023
    • AC1: 'Reply on RC1', Ria Oelerich, 21 May 2023
  • RC2: 'Comment on egusphere-2022-1527', Anonymous Referee #2, 09 Apr 2023
    • AC2: 'Reply on RC2', Ria Oelerich, 30 May 2023

Ria Oelerich et al.

Ria Oelerich et al.


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Short summary
At the Southern Boundary of the Antarctic Circumpolar Current, relatively warm waters encounter the colder waters surrounding Antarctica. Observations from underwater vehicles and altimetry show that medium-sized cold-core eddies influence the Southern Boundary’s barrier properties by strengthening the slopes of constant density lines across it and amplifying its associated jet. As a result, the ability of exchanging properties, such as heat, across the Southern Boundary is reduced.