The Indonesian throughflow during 2004–2006 as observed by the INSTANT program
Section snippets
Introduction to the Indonesian throughflow
The Indonesian seas represent a complex array of passages linking shallow and deep seas (Fig. 1). The literature, dating to 1961 (Wyrtki, 1961), offers a wide range of annual mean transport values for the ITF, from near zero to 25 Sv (Sv = 106 m3/s). Estimates based on observations obtained from the mid-1980s and mid-1990s suggest a mean ITF of ∼10 Sv (Gordon, 2005; Fig. 1) with interannual and seasonal fluctuations, as well as energetic intraseasonal (<90 days) variability and tides (Gordon, 2005,
International Nusantara Stratification and Transport (INSTANT) program
In the past, the main throughflow passages have been measured over different years and for varied lengths of time, making it impossible to assemble a reliable synoptic picture of the ITF. The transports reported in the literature for the primary ITF passages and the time interval over which the transport is based is shown in Fig. 1. Historically, the transport through Makassar Strait is estimated as 9.2 Sv (Gordon et al., 1999, Susanto and Gordon, 2005), and the overflow in the Lifamatola
INSTANT along-channel speeds
A composite view of the along-channel velocity time series at various depths reveals much variability (Fig. 3). Detailed analysis of the along-channel flow is presented in the INSTANT publications mentioned above. Here we offer a qualitative comparison of the features revealed by simple inspection of the time series from the INSTANT passages.
At all levels Makassar and Timor throughflow are relatively steady, in comparison to Lombok and Ombai, which are rich in intraseasonal oscillations. The
INSTANT transports
The ITF transports within the passageways observed by INSTANT for 2004–2006 (Fig. 1; Table 1) are reported by Gordon et al. (2008) (Makassar Strait); Van Aken et al. (2009) (Lifamatola Passage) and Sprintall et al. (2009) (Lombok Strait, Ombai Strait and Timor Passage). The reader is referred to these papers for specifics on the data set and methods used in determining the velocity field and associated transport. In the above mentioned publications, the authors present what they consider are
Inflow–outflow convergence
The Pacific water entering the Indonesian seas is modified within the interior seas before export to the Indian Ocean. Using the most reasonable transport profile for the passages carefully derived by the INSTANT program investigators (Gordon et al., 2008, Van Aken et al., 2009, Sprintall et al., 2009), here we estimate the inflow–outflow convergence profile (Table 2a, Table 2b), along with the resultant vertical velocity and downward heat fluxes within the interior seas as required for an
Conclusions
The 3-year mean ITF transport recorded during INSTANT via the primary deep outflow passages of the Sunda archipelago (Lombok Strait, Ombai Strait and Timor Passage) into the Indian Ocean is 15 × 106 m3/s. This is about 25–30% greater than the values from non-simultaneous measurements made prior to 2000, a period dominated by El Niño conditions.
The form of the along-channel time series within each of the INSTANT observed passages differ. The Makassar and Timor throughflow are relatively steady, in
Acknowledgments
The professionalism and support of the R/V Baruna Jaya I and VIII officers and crew to a large measure led to the success of INSTANT. We thank the capable mooring teams: P. Adams, M. Bakker, P.J. Harvey, B. Huber, S. Kawamoto, A. Lourenco, C. Marec, D. McLaughlan, K. Miller, L. Pender, and J. Schilling. Bruce Huber prepared Fig. 3. The Lifamatola mooring was funded with grants from the Netherlands Organisation for Scientific Research (NWO) and the International Research School for Cooperation
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