Brief Cruise Summary

Scientific work for the first portion of the TUNES-2 Expedition (Section P17S) was proposed by Lynne Talley and Mizuki Tsuchiya (both SIO); the second portion (P16S) was planned by James Swift (SIO). The overall purpose of both sections was to contribute to a planned WOCE Hydrographic Program multi-cruise examination of the meridional circulation and water mass transportation in the Pacific Ocean, in this case emphasizing the central subtropical gyros of the North and South Pacific.

After departure from Papeete, Tahiti, on July 16, 1991, WOCE Section P17S began on July 21, 1991, with the occupation of Station 124 at 6^oS and 135^oW and continued south along 135^oW meridian with stations every 30 nm. The P17S track, which followed the ridge extending from the East Pacific Rise to the Tuanotu Islands, was shifted slightly to the east, then back again, in order to cross the rise at a saddle (Fig. 1). The planned southern Station 179 (33^o 03'S and 135^o 01'W) of the P17S line was reached without major problems on August 8, 1991, and the vessel steamed for 83 hours to the southern end of the P16S line. In general, the weather was relatively good during the work on the P17S line. A total of 56 stations were occupied.

WOCE Section P16S began on August 11, 1991, with the occupation of Station 180 at 37^o 30'S and 150^o 28'W, and continued north along 150^oW meridian with stations spaced every 30 nm. The weather was still remarkably favorable considering that operations were being carried out during the middle of the austral winter. Although some instrument problems that could potentially affect CTD data quality occurred during this section of the cruise, researchers managed to complete every planned station. The last station of the TUNES-2 Expedition, station 210, was occupied on August 25, 1991, at 17^o 31'S and 150^o 30'W, and the same day R/V Thomas Washington arrived back at Papeete, Tahiti. A total of 41 stations were occupied during Section P16S.