Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctic Intermediate Water - Role of Mesoscale Eddies in Ventilation

According to the authors¹ debate continues over the Antarctic Intermediate Water (AAIW) distribution of formation, some studies suggesting formation of AAIW occurs in a pattern that is circumpolar, while other studies favour a formation that is more localised, particularly in the southeast Pacific Ocean. In this study the authors¹ demonstrate that AAIW formation patterns and magnitude are affected, substantially, by mesoscale eddies. The authors¹ constructed global CFC-11 simulations in 2 versions of the ocean global circulation model OPA9, a non-eddying version at coarse resolution (2^ocosϕ×2^o, ORCA2) and the eddying or eddying-permitting version (½^o cos φ x ½^o,  ORCA05). AAIW subducts in a circumpolar pattern that is close to homogeneous in the non-eddying simulation; the distribution of AAIW ventilation is patchier in the eddying simulation. In the Indian Ocean sector the AAIW layer thins by 32% on average with increasing resolution, though by 11% in the Pacific Ocean sector. The zonal wind stress appears to be the cause of the patchiness, the zonal wind stress being weak over the Pacific and the southwest Atlantic, though it is strong over the Indian Ocean sector. The largest effect of the eddies is consequently in the Indian Ocean, moderate in the Atlantic Ocean and it has its smallest effect in the Pacific Basin. In contrast with the observations applying the Gent & McWilliams (GM) parameterisation in the non-eddying model of the authors¹ still results in almost uniform AAIW circumpolar ventilation distribution, though in the Southern Ocean it improves the overall vertical density structure.

Sources & Further reading

1. Lachkar, Zouhair, James C. Orr, Jean-Claude Dutay, and Pascale Delecluse. "On the Role of Mesoscale Eddies in the Ventilation of Antarctic Intermediate Water." Deep Sea Research Part I: Oceanographic Research Papers 56, no. 6 (6// 2009): 909-25.