Antarctic intermediate water in the South Pacific Ocean

Graduation date: 1972The distribution of Antarctic Intermediate Water in the South\ud Pacific has been examined using a model of horizontal advection,\ud along the Sigma-t surface 27.10, with three point vertical mixing.\ud The core of the Antarctic Intermediate Water mass was traced\ud from the Antarctic Convergence northward. The charts used to\ud describe the distribution were those of core depth, salinity, percentage\ud composition, Equivalent Thickness, and acceleration potential.\ud The percentage composition of Antarctic Intermediate Water\ud in the entire water column for all stations was computed and the\ud Equivalent Thickness determined. Intermediate water volume for\ud the South Pacific was then calculated. North-South geostrophic\ud velocities and transports were computed for two zonal sections.\ud The model agreed quite well with the flow patterns reported by\ud other investigators. The broad counterclockwise gyre in the central\ud South Pacific, the flow into the Tasman and Coral Seas, the localized flow near New Zealand, and the suggestion of southward flow near\ud the South American Coast are all indicated by the model. A previously\ud unreported small, counterclockwise gyre in the southeast\ud South Pacific was detected. The circulation within the small gyre\ud is consistent wity flow over a variable bottom in the Southern Hemisphere.\ud Antarctic Intermediate Water transport across selected\ud sections indicate a northward flow of 10 x 10⁶ m³ sec⁻¹. A low\ud salinity tongue was found on the salinity chart. This tongue extended\ud northward, then westward, into the northern Tasman Sea. The\ud salinity was over 34.50°/₀₀ in the center of this counterclockwise\ud motion east of New Zealand. The isohalines in the southeast Pacific\ud suggest the presence of the small counterclockwise gyre. A 20\ud percent drop in core percentage composition was noted in the 10 degrees\ud north of the Antarctic Convergence. A large uniform area\ud between 80 percent and 70 percent over the central portion of the\ud central South Pacific was bounded on the north by a 20 percent drop\ud near the equator, again supporting the general counterclockwise\ud circulation.\ud The Equivalent Thickness distribution showed a general lenticular\ud shape, the thickest part lying in the center of the counterclockwise\ud gyre east of New Zealand. The Equivalent Thickness distribution,\ud as well as the core percentage, supported the hypothesis of\ud little or no flow into the Tasman Sea from the south. The volume of intermediate water obtained from surface area integration of the\ud Equivalent Thickness distribution was 59.44 x 10⁶ km³. This is\ud approximately 16% of the water volume in the South Pacific