Abstract. An array of shallow pressure gauge pairs is used to determine shallow geostrophic flow relative to an unknown mean velocity in the five principal straits that separate the eastern Indian Ocean from the interior Indonesian seas (Lombok Strait, Sumba Strait, Ombai Strait, Savu/Dao Straits, and Timor Passage). Repeat transects across the straits over several tidal cycles with a 150-kHz acoustic Doppler current profiler were made during three separate years, and provide a first look at the lateral and vertical structure of the upper throughflow in these straits as well as a means of "leveling" the pressure gauge data to determine the mean shallow velocity and provide transport estimates. We estimate a total 2-year average transport for 1996-1997 through Lombok,

Abstract.A

A conductivity-temperature-depth/hydrographic survey in January-February 1994 and a 17-month deployment of current meter moorings from September 1992 to March 1994 were carried out to determine the volume transport, water mass characteristics, and diathermal fluxes of northward flowing abyssal waters in the Samoan Passage and adjacent regions of the South Pacific Ocean. Geostrophic calculations relative to 1.2øC potential temperature indicated northward transport of 7.8 Sv in the Samoan Passage, 1.1 Sv through a gap in Robbie Ridge, and 2.8 Sv along the eastern flank of the Manihiki Plateau. All of the total of 11.7 Sv of northward geostrophic transport was in waters colder than 1.1øC. The northward transport distribution was bimodal in temperature, with a cold mode of 3.6 Sv in the range 0.65ø-0.70øC occurring entirely in the Samoan Passage and a warm mode of 3.0 Sv in the range of 0.80ø.-0.85øC occurring mainly along the Manihiki Plateau. Within the Samoan Passage, 7.1 Sv of the northward transport was below 4000 rn where the geostrophic calculation was confirmed by an equal estimate of transport from current meters during the simultaneous 3-day period. The 17month mean transport from the moored array was 6.0 Sv _ 0.5. By using the observed temporally varying flow within the Samoan Passage together with the hydrographic snapshot across the region, an estimate of the total mean northward transport of 10.6 Sv +_ 1.7 was obtained. Estimates of the flow across near-bottom potential temperature surfaces indicate extraordinarily high rates of mixing, with heating of the abyssal layer up to 20 W m -2, corresponding to diffusivities up to 10 -1 m 2 s -•. Introduction The abyssal waters of the world's oceans are formed only in the northern North Atlantic and the Southern Ocean. There is no abyssal source in the North Pacific, and the bottom waters there are renewed by flow from the south. This northward flowing Pacific limb of the global thermohaline circulation carries relatively cold and saline waters that have less inorganic nutrients and higher dissolved oxygen concentration than the overlying deep water masses. The volume transport, property fluxes, and temporal variability of the abyssal flow contain vital clues not only to the renewal of the deep waters of the North Pacific but also to the overall role of the ocean in the Earth's climate system and to the mixing and dynamics of the deep oceans. The present experiment focuses on the Samoan Passage and adjacent regions: the Robbie Ridge to the west and the Penrhyn Basin to the east (Figure 1). Previous studies [Reid and Lonsdale, 1974; Wunsch et al., 1983; Taft et al., 1991] have indicated that the northward flowing abyssal layer is predominantly at potential temperature less than 1.0øC. The geo-Paper number 96JC00797. 0148-0227/96/96J C-00797509.00 graphic advantage exploited by the new measurements described here is that, while sampling only about one quarter of the full width of the Pacific Ocean, all water colder than about 1.2øC is spanned. The East Pacific Ri...

To set the WOCE PX37 data into its broader context, in-13,055

The salinity and dissolved oxygen of water masses in the Indonesian Seas, from historical hydrographic data, are examined on isopycnal surfaces. We focus primarily on the Banda Sea, from which the bulk of the throughflow transport flows into the Indian Ocean. Dissolved oxygen proves to be a problematic conservative tracer in this region due to biological consumption in the upwelling regime of the Arafura Sea and the subsequent spreading of relatively low oxygen water over a broad area. The remaining analysis is thus restricted to salinity. We first consider a hypothesis of simple isopycnal advection and mixing between North and South Pacific low-latitude western boundary current sources. Three regimes are apparent. The surface and upper thermocline layers, down to 25.8rr0, are too fresh to fit the hypothesis. Vertical mixing of surface precipitation and runoff excesses down into the water column must be invoked. Vertical mixing is also apparent on deeper isopycnals, below 27.0rr0, where a contribution from the deep Indian Ocean can be discerned. In between, in the lower thermocline, the 0-S data are consistent with the hypothesis of purely isopycnal spreading, given a simple variation in the ratio of sources toward increasing South Pacific contribution with depth. In this regime the juxtaposition of sources leads to relatively strong gradients in water mass properties across the Banda Sea. This gradient translates into a difference in outflow characteristics between Timor and Ombai Straits, which appear to draw their waters, respectively, from the eastern and western Banda Sea. We then consider how the presence of vertical mixing modifies our inferred water mass ratio under a variety of boundary conditions. Vertical mixing effects are particularly important in the upper thermocline. In the Banda Sea, on all isopycnals down to rr 0 = 26.5, an increase in the degree of vertical mixing tends to decrease the relative importance of the North Pacific source. The sensitivity of the water mass ratio to degree of vertical mixing decreases with depth, and the tendency is reversed below 26.5rr 0. In the Banda Sea, for •lausible values of throughflow residence time and verticaldiffusivity (h = (Kt) •/ < 100 m), the North Pacific contributes 80-90% of the water mass at 26rr0, 50-60% at 26.5rr0, and only 10-30% at 27rr 0. This large South Pacific contribution in the lower thermocline is supported by other studies.