A Deep Eddy in the Antarctic Intermediate Water North of the Chatham Rise

Abstract

In mid-1996, a hydrographic survey was made over the Chatham Rise, near New Zealand. A deep isolated eddy of Antarctic Intermediate Water was found north of the rise between 1200 and 1800 dbar. It was widest on a potential density surface (σ1) of 32.1. Potential-temperature salinity and potential-temperature oxygen characteristics identify the eddy as having a source south of the Chatham Rise. This eddy was too deep to have passed over the Chatham Rise, and the only way it could have reached this position was by flowing around the eastern end of the Chatham Rise. The authors hypothesize that the intrusion may have been generated by a similar mechanism to that proposed for Mediterranean eddies, so that eddies are formed by separation of a frictional boundary layer at the end of the Chatham Rise. Once the intrusion is formed, it was most likely advected to its observed position, 500 km from the generation region, by recirculation within a much larger-scale permanent eddy found off the south east of the North Island (the Wairarapa Eddy).