BOTTOM WATER VARIABILITY IN THE SAMOA PASSAGE

The Samoa Passage (near 10S, 170W) is the channel through which the co ldest, saltiest, densest bottom water approaches the North Pacific Oce an from its southern source. Over the past 25 years, three hydrographi c sections have been made across the passage. A section occupied in 19 68 shows little sign of modified North Atlantic Deep Water (NADW) with in the northward flowing Lower Circumpolar Water (LCPW). In contrast, a section occupied in 1987 shows a strong negative curvature in theta- S (potential temperature-salinity) and a local maximum in salinity cha racteristic of NADW. A third section occupied in 1992 reveals a margin al NADW signature. The three sections are objectively mapped and very fine-scale bivariate areal theta-S censuses are made for a quantitativ e comparison of differences in water-mass structure. The strength of t he NADW signature could fluctuate over a wide range of time-scales. Ho wever, these data are consistent with decadal variability, with no NAD W signal in the passage in 1968, a strong signal in 1987, and a weak o ne in 1992. The geostrophic volume transport through the passage is 1. 0 +/- 0.2, 5.6 +/- 1.3, and 4.8 +/- 0.6 x 10(6) m3 s-1 below a zero-ve locity surface (ZVS) of theta = 1.2-degrees-C for the 1968, 1987, and 1992 sections respectively. The transport estimates, made for comparis on with those from velocity data presently being collected by a curren t meter array in the passage, are sensitive to variations in the choic e of ZVS.