Introduction

The Indonesian Throughflow (ITF) is an integral part of the global thermohaline circulation and climate system (see Gordon, 2001; Sprintall et al., 2001 for recent overviews), providing a low-latitude pathway for the transfer of warm, low-salinity Pacific waters into the Indian Ocean. The heat and freshwater carried by the ITF impacts the basin budgets of both the Pacific and the Indian Oceans (Bryden and Imawaki, 2001; Wajsowicz and Schneider, 2001; Wijffels et al., 2001). Within the internal Indonesian seas, observations and models indicate that the primary ITF source is north Pacific thermocline water flowing through Makassar Strait (sill depth 650 m) (Fig. 1). Additional ITF contributions of lower thermocline water and deep water masses of direct south Pacific origin are derived through the eastern routes, via the Maluku and Halmahera Seas, with dense water overflow at the Lifamatola Passage (sill depth 1,940 m). The ITF exits into the eastern Indian Ocean through the major passages along the Lesser Sunda Island chain: Ombai Strait (sill depth 3,250 m), Lombok Strait (300 m), and Timor Passage (1,890 m). The complex geography of the region, with multiple narrow constrictions connecting a series of large, deep basins, leads to a circuitous ITF pathway within the Indonesian seas. En route, the Pacific inflow waters are modified due to mixing, upwelling, and air—sea fluxes before export to the Indian Ocean.

In recent years, a number of monitoring programs have measured aspects of the ITF from its Pacific source, through the internal seas, to the exit passages. The programs range from individual year-long mooring deployments in Makassar, Timor, and Ombai Straits, a 3-year shallow pressure gauge array (SPGA) in the exit passages, to decade long expendable bathythermograph (XBT) transects within the Indonesian region and five full-depth hydrographic CTD/ADCP sections between Australia and Indonesia.

In Section 2, we detail the progress toward understanding the mean and time-dependent throughflow dynamics made to date from these recent observations, and discuss some of the still outstanding issues toward a

110'E f20'E 130'E

Figure 1: Schematic of Indonesian throughflow pathways (Gordon, 2001; reprinted with permission from Elsevier). The solid arrows represent north Pacific thermocline water; the dashed arrows are south Pacific lower therm-ocline water. Transports in Sv (106m3/s) are given in red. The 10.5 Sv in italics is the sum of the flows through the Lesser Sunda passages. ME is the Mindanao Eddy; HE is the Halmahera Eddy. Superscript refers to reference source: 1, Makassar Strait transport in 1997 (Gordon et al., 1999); 2, Lombok Strait (Murray and Arief, 1988; Murray et al., 1990) from January 1985 to January 1986; 3, Timor Passage (between Timor and Australia) measured from March 1992 to April 1993 (Molcard et al., 1996); 4, Timor Passage, between October 1987 and March 1988 (Cresswell et al., 1993); 5, Ombai Strait (north of Timor, between Timor and Alor Island) from December 1995 to December 1996 (Molcard et al., 2001); 6, between Java and Australia from 1983 to 1989 XBT data (Meyers et al., 1995; Meyers, 1996); 7, Upper 470 m of the South Equatorial Current in the eastern Indian Ocean in October 1987 (Quadfasel et al., 1996); 8, Average ITF within the South Equatorial Current defined by five WOCE WHP sections (Gordon et al., 1997). The hollow arrow represents overflow of dense Pacific water across the Lifamatola Passage into the deep Banda Sea, which may amount to about 1 Sv (van Aken et al., 1988). Inserts A-D show the positions of the INSTANT moorings. Insert A: position of the two Makassar Strait inflow moorings (US, red diamond) within Labani Channel. Insert C: position of the Netherland's mooring within the main channel of Lifamatola Passage (yellow triangle). Insert B, D: position of the Sunda moorings in Ombai Strait, Lombok strait, and Timor Passage (US, red diamonds; French, purple square; Australian, green circles). The positions of the shallow pressure gauge array (SPGA) (US, green X). The 100, 500, and 1,000 m isobaths are shown in the inserts (For colour version, see Colour Plate Section).

comprehensive understanding of the dynamics of the ITF and its associated property fluxes. Historic data from moorings, pressure gauges and other stationary measurement systems suggest that large-scale and remotely forced wave interactions play an important role in the dynamics of the ITF. After a brief description in Section 3 of the model and data used here, the large-scale wave dynamics is explored in more detail in Section 4. We compare observed and simulated temperature responses to remote and local wind forcing within the Indonesian region. Section 5 contains a discussion and the conclusions.

Was this article helpful?

0 0

Post a comment