Velocity and transport of the Makassar Strait throughflow

Abstract

Analyses of ocean current measurements from two moorings in the Makassar Strait (MAK‐1, December 1996 to July 1998, and MAK‐2, December 1996 to February 1998) with newly processed acoustic Doppler current profiler (ADCP) data provide a new estimate of transport and vertical velocity structure for this important passageway of the Indonesian Throughflow. The 7‐month record of the MAK‐1 ADCP and the 3‐month record of the MAK‐2 ADCP, nominally set at depths of 150 m, are extrapolated to the end of the mooring period using a surface layer relationship to the shallowest current meter at 200 m and to the regional winds. The southward transport within Makassar Strait is confined for the most part to the upper 750 m, above the blocking topographic sill of Makassar Strait. The transport maximum occurs within the thermocline (100–300 m). After the temporal mean flow has been removed, the vertical structure of the along channel flow in the upper 750 m is decomposed using the empirical orthogonal function (EOF) method. The first two modes contain 91% of the total variance. For the entire mooring period, the total depth‐integrated transport was 8.1 ± 1.5 Sv (Sv = 1 × 106 m3/s), with 7.9 ± 1.2 Sv for calendar year1997. During the peak of 1997/1998 El Niño from September 1997 to mid‐February 1998, the first mode time series displays northward flow, enhancing the vertical shear within the thermocline and reducing the mean throughflow to 4.6 ± 0.9 Sv.

On the Indonesian Throughflow in the OCCAM 1/4 degree ocean model

“…In the north the most striking difference is in the Makassar Channel, where the model gives values of 5.7 and 5.9 Sv for the two runs. These are lower than Susanto and Gordon's (2005) estimate of 7 to 11 Sv. There is also a marked difference in the Halmahera Sea where the model shows transports of 1.6 and 3.4 Sv.…”

“…In the north there have been moorings in the Makassar Strait from December 1997 to July 1998 (Gordon et al, 1999;Susanto and Gordon, 2005) and the Lifamatola Passage overflow, at the southern end of the Molucca Sea, from January to March 1985 (van Aken et al, 1988(van Aken et al, , 1991.…”

M2 Baroclinic Tides in the Indonesian Seas

“…The uppermost current meter on the western Makassar mooring (1), was near its target depth of 200 m for only 6% of the record, whereas the uppermost meter on the eastern Makassar mooring (2) was near its target depth of 205 m for 32% of the record and the next lower current meter on that mooring was near its target depth of 255 m for 85% of the record (Susanto and Gordon, 2005).…”

Oceanography of the Indonesian Seas and Their Throughflow

“…Modifi ed from Gordon and Fine (1996). Makassar moorings: Dec 96 -Jul 98 7 -11 Sv (ARLINDO: Gordon et al, 1999;Susanto and Gordon, 2005) Ombai Strait (north of Timor): Nov 95 -Nov 96 4 -6 Sv (JADE: Molcard et al, 2001) Timor Passage: Aug 89 -Sep 90 3 -6 Sv (JADE: Molcard et al, 1994) Timor Passage (south of Timor) 0-1250 m: Mar 92 -Apr 93 3.4 -5.3 Sv (JADE: Molcard et al, 1996) Lombok Strait: Jan 85 -Jan 86 1.7 Sv (Murray and Arief, 1988) Lifamatola Meyers, 1996;Hautala et al, 2001;England and Huang, 2005), the assumption of a steady-state system does not necessarily apply.…”