The presence of a southward-moving undercurrent along the west coast of South America, underlying the Peru Current at depths of several hundred meters, has been established by direct measurements with parachute drogues, by calculations of geostrophic motion, and by analysis of the distributions of salinity and dissolved oxygen....
Wooster, Warren S., and Malvern Gilmartin. 1961. "The Peru-Chile undercurrent." Journal of Marine Research 19, (3). https://elischolar.library.yale.edu/journal_of_marine_research/967