Pathways and variability of the Antarctic Intermediate Water in the western equatorial Pacific Ocean.

• Published in: Progress in Oceanography
• Main Authors: Zenk, Walter, Siedler, Gerold, Ishida, A., Holfort, J., Kashino, Y., Kuroda, Y., Miyama, T., Müller, Thomas J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2005
• Subjects: Antarctic; Bismarck; Pacific; The Antarctic; Antarc*
• Online Access: https://oceanrep.geomar.de/id/eprint/8313/; https://oceanrep.geomar.de/id/eprint/8313/1/Path.pdf; https://doi.org/10.1016/j.pocean.2005.05.003

In the western equatorial Pacific the low-salinity core of Antarctic Intermediate Water (AAIW) is found at about 800 m depth between potential density levels σθ = 27.2 and 27.3. The pathways of AAIW and the degradation of its core are studied, from the Bismarck Sea to the Caroline Basins and into the zonal equatorial current system. Both historical and new observational data, and results from numerical circulation model runs are used. The observations include hydrographic stations from German and Japanese research vessels, and Eulerian and Lagrangian current measurements. The model is the JAMSTEC high-resolution numerical model based on the Modular Ocean Model (MOM 2). The general agreement between results from the observations and from the model enables us to diagnose properties and to provide new information on the AAIW. The analysis confirms the paramount influence of topography on the spreading of the AAIW tongue north of New Guinea. Two cores of AAIW are found in the eastern Bismarck Sea. One core originates from Vitiaz Strait and one from St. George’s Channel, probably arriving on a cyclonic pathway. They merge in the western Bismarck Sea without much change in their total salt content, and the uniform core then increases considerably in salt content when subjected to mixing in the Caroline Basins. Hydrographic and moored current observations as well as model results show a distinct annual signal in salinity and velocity in the AAIW core off New Guinea. It appears to be related to the monsoonal change that is typically found in the near-surface waters in the region. Lagrangian data are used to investigate the structure of the deep New Guinea Coastal Undercurrent, the related cross-equatorial flow and eddy-structure, and the embedment in the zonal equatorial current system. Results from 17 neutrally buoyant RAFOS floats, ballasted to drift in the AAIW core layer, are compared with a numerical tracking experiment. In the model 73 particles are released at five-day intervals from Station J (2.5°N, 142°E), ...