Deep Topographic Barriers Within the Indonesian Seas

Home , Banda Sea, Flores Sea, Halmahera Sea, Lombok Strait, Ombai Strait, Savu Sea

Deep-Sea Research II 50 (2003) 2205–2228

Deep topographic barriers within the Indonesian seas

Arnold L.Gordon a,*, Claudia F.Giulivi a, A.Gani Ilahude b a Lamont-Doherty Earth Observatory, Palisades, New York, 10964-8000 USA b Pusat Penelitian Oseanograﬁ, LIPI, J1. Pasir Putih 1, Ancol Timur, Jakarta 14430, Indonesia

Accepted 10 November 2002

Abstract

Whereas at the surface and at thermocline depth the Indonesian throughflow can weave its way between basins towards the Indian Ocean on a quasi-horizontal plane, at greater depth numerous sills are encountered, resulting in circulation patterns governed by density-driven overflow processes.Pacific water spills over deep topographic barriers into the Sulawesi Sea and into the Seram and Banda seas.The western-most throughflow path flowing through Makassar Strait encounters shallower barriers than does the eastern path.The first barrier encountered by Pacific water directed towards Makassar Strait is the 1350-m deep Sangihe Ridge, providing access to the Sulawesi Sea.The 680-m deep Dewakang Sill separating the southern Makassar Strait from the Flores Sea is a more formidable barrier.Along the eastern path, Pacific water must flow over the 1940 m barrier of the Lifamatola Passage before passing into the deep levels of the Seram and Banda Seas.The deepest barrier encountered by both the western and eastern paths to the Indian Ocean is the 1300–1450 m (perhaps as deep as 1500 m) sill of the Sunda Arc near Timor.The Savu Sea while connected to the Banda Sea down to 2000 m depth, is closed to the Indian Ocean at a depth shallower than the Timor Sill.The density-driven overflows force upwelling of resident waters within the confines of the basins, which is balanced by diapycnal mixing, resulting in an exponential deep-water temperature profile.A scale depth ( Z¼Kz=w)of 420–530 m is characteristic of the 300–1500 m depth range, with values closer to 600 m for the deeper water column. The upwelled water within the confines of the Banda Sea, once over the confining sill of the Sunda Arc, may contribute 1.8–2.3 Sv the interocean throughflow. r 2003 Elsevier Science Ltd.All rights reserved.

1. Introduction salinity and oxygen standardization (Fig.1 ).The Arlindo CTD stations extend to the sea ﬂoor or to As part of the Arlindo Project, a joint oceano- 3000 decibars (dbar; the shallower of the two), graphic research endeavor of Indonesia and the were obtained in four periods: using the Indone- United States, proﬁles of temperature, salinity and sian research vessel Baruna Jaya I, during the oxygen were obtained within the Indonesia seas South East Monsoon of 1993 (August and with CTD equipment and water samples for September) and reoccupied during the North West Monsoon of 1994 (January and March); additional CTD stations were obtained from the vessel *Corresponding author.Tel.:+1-845-365-8325; fax: +1- 845-365-8157. Baruna Jaya IV in November–December 1996 and E-mail address: [email protected] February 1998.The Arlindo data were used to (A.L. Gordon). investigate the water mass composition and mixing

Fig.1. Map showing the major bathymetric features of the Indonesian Seas and the position of CTD stations taken during the Arlindo cruises.Connected symbols by a solid black line represent the western and eastern sections shown in Figs.5 and 6 .Sea ﬂoor bathymetry (contours every 1000 m, gray shading for depths deeper than 2000 m) has been extracted from Smith and Sandwell (1997).

within the thermocline of the Indonesian Seas Whereas the surface and thermocline water (Gordon, 1995; Gordon and Fine, 1996; Ilahude component of the Indonesian Throughflow (ITF) and Gordon, 1996a, b; Ffield and Gordon, 1996). can weave its way between the multitude of The objectives of this paper are to combine the Indonesian Islands towards the Indian Ocean on Arlindo data with archived data (Conkright et al., an approximate horizontal plane, without signifi- 1998) to: (1) determine the effective sill depths of cant impedance by topography, below thermocline the ridges segmenting the primary Indonesian depths numerous sills are encountered.This basins, and (2) investigate the stratification within induces deep circulation patterns governed by the intermediate and deep-water layers of the density-driven overflow processes, in which resi- Indonesian Seas.Correct sill depths are essential dent deep water, continuously made less dense by for proper model simulation of stratification and downward eddy diffusion of buoyancy, is dis- interocean transport characteristic of the Indone- placed upward.Overflow of Pacific water into the sian Seas (Gordon and McClean, 1999). northern Banda Sea through the Lifamatola A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2207

Passage with a sill depth near 1940 m is a well- report on the results of a JADE 1-year mooring known example of such a process within the beginning in late November 1995 in Ombai Indonesian seas (Wyrtki, 1961; Broecker et al., Strait, a 30-km wide and 3250 m deep passage 1986; Van Aken et al., 1988).Based on a 3-month separating Timor from islands just north of it. current meter record, from January to March The estimated transport is 4–6 Sv.Between 680 1985, in the deep axis of the Lifamatola Passage and 1200 m the transport is estimated as 0.6 the estimated overflow transport through the and 0.8 Sv. From the JADE data we may expect passage deeper than 1500 m was 1.5 Sv that the total throughflow below the Makassar sill (1 Sv=106 m3/s), which is sufficient to force a 29- depth into the Indian Ocean is 1.8–2.3 Sv. All the year residence time for the Banda Sea below connections between the interior Indonesian Seas 1500 m, corresponding to an upwelling across a and the Indian Ocean to the west of Timor are 1500 m horizon of 75 m/year or 2.38 Â 10À6 m/s shallower than 680 m.The Van Aken et al.(1988) (Van Aken et al., 1988, 1991).This overflow speed transport of 1.5 Sv deeper than 1500 m can explain of Van Aken et al.(1988) is about 3 times roughly all but 0.5 Sv of the >680 m export to the (residence time 1/3) that found by Broecker et al. Indian Ocean.Noting the short time span of the (1986) based on a 1-month current meter record Lifamatola moorings, an additional 0.5 Sv of obtained in Lifamatola Passage in January/Feb- Lifamatola Passage overflow required to close ruary 1976. Postma and Mook (1988) using the deep throughflow budget, is reasonable.Of Carbon-14 (14C) find a flushing rate in the eastern course the Timor Passage, Ombai Strait and Indonesian seas of 10–140 years, with values closer Lifamatola Passage measurements were made at to 10 years in the western and northern Banda Sea different times, and the assumptions of a steady- and Seram Sea, and a basin-wide average of 25 state system does not necessarily apply in this case, years. Wyrtki (1961) noted that the relatively high but the near balance is instructive. Van Bennekom oxygen within the deep waters suggests good (1988) using silicate distribution surmise that some ventilation of these waters, but cautioned that it of the water leaving the Banda Sea near 1000 m may also be the result of very low rates of oxygen depth just to the east of Sunda chain Island of consumption. Wetar then turn eastward (therefore do not pass Makassar contribution to the throughflow is across the JADE moorings) to flow along the blocked by the Dewakang Sill, named after the Outer Banda Arc (Fig.1 ), thus forming a large re- local island group, with a 680-m sill depth, as circulating loop. determined from depths shown on Indonesian The Timor Passage and Ombai Strait total navigation charts (Ilahude and Gordon, 1996a). transport between the sea surface and 680 m from Throughflow contribution below 680 m must be the Molcard et al.(1996; 2001) JADE results is derived solely from the eastern throughflow between 5.6 and 9.0 Sv. Adding the estimated channels including the Lifamatola Passage over- Lombok Strait transport of 1.7 Sv (Murray and flow to the deep Banda Sea.From March 1992 to Arief, 1988, measured in 1985) we arrive at 7.3– April 1993 the average transport within the Timor 10.7 Sv, which is not significantly different than Passage (south of Timor) measured during the the Makassar Strait transport of 9.372.5 Sv JADE French–Indonesian program, from the (Gordon et al., 1999).This suggests that the surface to 1250 m was 3.4–5.3 Sv (Molcard et al., Makassar throughflow may provide all of the 1996). Of this amount, 1.2–1.5 Sv occurs between export to the Indian Ocean for the water column 680 and 1250 m.An additional transport of 0.5Sv from the sea surface to 680 m, with the Lifamatola is estimated between 1250 and 1550 m, but this is Passage overflow providing the deeper through- believed to be a return of Indian Ocean deep water flow. that passed to the east within the deep channel axis The Arlindo and JADE Helium-3 (3He) data are (about 1800 m), inhibited from entering the Banda used to trace deep-water movements within the Sea which has a approximate sill depth of 1450 m Indonesian seas (Top et al., 1997). 3He sources in (Van Aken et al., 1988). Molcard et al.(2001) the Sulawesi Sea and in Makassar Strait are found, 2208 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 but these are prevented from spreading into the deepest path between basins as might be deter- Banda Sea and Indian Ocean by blocking sills.A mined by a bathymetric survey. major mantle source is identified below 2000 m in The primary deep sills between the Pacific and the Banda and Flores Seas.Higher-than-ambient Indonesian seas within the northern Indonesian 3He on the Indian Ocean side of the Lesser Sunda seas are: Island chain indicates a deep outflow of Flores and Banda Sea water into the Indian Ocean near 1.Sangihe Ridge stretching from Sulawesi to 1300 m. Mindanao, which limits deep water access to the Sulawesi Sea and Makassar Strait; 2.Halmahera Sea sill depth controlling direct 2. The topographic divides access of South Pacific water to the Indonesian Seas; and The depths of the critical sills that govern deep 3.Lifamatola Passage, which links the Maluku inter-basin exchange of water masses within the Sea to the Banda Sea. Indonesian seas can be estimated by comparing the profiles of temperature on either side of the The Inner and the Outer Banda Arcs cut by topographic barrier.This classic oceanographic numerous deep channels leading to passages both method provides what is called the thermometric north (Ombai Passage) and south (Timor Passage) sill depth.It is determined by comparing the of Timor separate the Indian Ocean from the bottom temperature on the overflow side of a sill southern Indonesian Seas.The Torres Strait is with the temperature profile on the upstream side the shallow connection of the South Pacific to the of the sill.Effective sill depths also can be Indonesian Seas between Australia and New estimated from other parameters, such as salinity Guinea.It is less than 10 m deep with the presence or oxygen, but generally the temperature profile of numerous islands and reefs.From 5 months of has the best dynamic range and affords the best current observations, Wolanski et al.(1988) found estimate of sill depths.However, there are a strong tidal flow, but no evidence of a mean flow measurement errors and real temporal variability through Torres Strait. of the temperature (and other parameter) profiles. The Arlindo data is limited to the upper 3000 m, The accuracy of a thermometric or effective sill deep enough to reach the sill depths, but not depth depends on the scatter of points defining deep enough to resolve the deep-water properties the mean profile, which generally is larger for the on the overflow side of the sill, as required to shallower levels.In the discussion to follow estimate effective sill depths.Therefore, archived the scatter shown in Figs.2 and 3 allows an regional data (Conkright et al., 1998) are added estimate of sill depth to within 5–10% of the sill to the Arlindo stations to determine the control- depth for sills deeper than 1000 m, 10–20% for sills ling sill depths.Effective sill depths are determined shallower than 1000 m.The thermometric or by matching the bottom potential temperature effective depth does not need to be equal to the and salinity point within the enclosed basin with depth of the deepest saddle of a ridge.The the stratification on the open ocean side of the overflow water is expected to be a blend of sill.The water within the enclosed basins, but characteristics over a layer of the inflowing water below sill depth is made more buoyant than the column from the deepest sill up to some shallower overflow water by vertical mixing; this process depth.The thickness of the overflow layer is allows open-ocean water at the sill depth to determined by the sill topography (for example, a continually renew the bottom water of the broad u-shaped gap versus a more restrictive v- enclosed basin.In the mean, diapycnal mixing shaped gap) and mixing, such as entrainment and rate within the isolated basin essentially deter- shear induced turbulence, including the effects of mines the rate of renewal of deep basin water. internal wave at the sill.The effective sill depth is Transient effects at the sill may lead to sporadic expected to be somewhat shallower than the actual overflow. olwn aawr sd(hpnmsaei tlc;epdto ae r ncptlltes nprnhssi h ubro ttos:IDE 6;S d (6); Arlindo 7 INDLEG m).Besides 1000 stations): every of number (contours the bathymetry is floor parenthesis sea in letters; and capital data in the are of names expedition location italics; the in show are (13); maps names WEPOCS (ship inset used m.The 1650 were data of following depth sill Passage, Lifamatola i..Tmeaue aiiyadoye rfie enn h otoln ildph ewe h otenIdnsa es(pnsmos n Pacific and symbols) (open Seas Indonesian northern the between depths ( sill data controlling regional archived the and data defining Arlindo profiles on based oxygen symbols) and salinity Temperature, Fig.2.

Pressure (dbar) (a) 4500 4000 3500 3000 2500 2000 1500 1000 7000 6500 6000 5500 5000 500 auoMaru Hakuho

2 Pacific Morotai Basin Karakelong Basin Potential Temperature( 3 (1);

4 Sulawesi Sea 2 4N 6N N 0Ê

Kaiyo 122E 5 4000 (13); 6 124E Priliv o C)

5000 7 (3);

1 000 126E 8 yf Maru Ryofu okih ta. 1998 al., et Conkright

2000 3000

1000

2000

3 000 128E (20); 34.5 Samudera 130E :()SnieRde ildpho 30m b amhr e,sl et f50mad(c) and m 580 of depth sill Sea, Halmahera (b) m; 1350 of depth sill Ridge, Sangihe (a) ): Salinity

(23); Sulawesi Sea 34.6

in a Hong Yan Xiang Karakelong Basin Morotai Basin 34.7 Pacific (4).

2 Sulawesi Sea

Oxy Karakelong Basin g en (ml/l) 3 Morotai Basin

Pacific ELU (20); 2 NELLIUS 4 ca (solid Ocean t the ata

2209 ..Gro ta./De-e eerhI 0(03 2205–2228 (2003) 50 II Research Deep-Sea / al. et Gordon A.L. (b) Pressure (dbar) 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500

2 Pacific Potential Temperature( 3 4 2N 4N 2S 0 126E Ê 5

3000

6 2000 3000 128E o

7 3000

1000 0

000 4000 130E 8 Halmahera Sea

4 000 132E

4000 4000 34.5 i. ( Fig.2 134E continued

Salinity Halmahera Sea 34.6 ). 34.7 Pacific 2 Oxygen (ml/l) 3 Halmahera Sea

Pacific 4

2210 ..Gro ta./De-e eerhI 0(03 2205–2228 (2003) 50 II Research Deep-Sea / al. et Gordon A.L. (c) 500

1000

1500 ..Gro ta./De-e eerhI 0(03 2205–2228 (2003) 50 II Research Deep-Sea / al. et Gordon A.L.

2000

2500

3000

3500 Maluku Sea Sea Seram 124E 126E 128E 130E Pressure (dbar) Seram Sea Seram Seram Sea Seram Maluku Sea 4000 0Ê Maluku Sea

3000

1000 4500 2S 0 2000 000 4 3 000

0 5000 1000 4S 3000 5500

6000 2 3 4 5 6 7 8 34.5 34.6 34.7 2 3 4 5 Potential Temperature (oC) Salinity Oxygen (ml/l) Fig.2 ( continued). 2211 i..Tmeaue aiiyadoye rﬁe costeinradotrSnaAc ewe h ad e oe ybl)adIda ca TmrSea (Timor Ocean Indian and symbols) (open Sea Banda ( the data between regional Arcs archived Sunda and outer and data inner Arlindo the on across based proﬁles symbols) oxygen and salinity Temperature, Fig.3. xeiinnmsaei aia etr;i aetei stenme fsain) NLG7() NLIS2(8); 2 SNELLIUS (5); 7 INDLEG stations): of number the is parenthesis in letters; capital in are names expedition

Pressure (dbar) 2000 1500 1000 6000 5500 5000 4500 4000 3500 3000 2500 500 2 Banda Sea Timor Sea Potential Temperature( 3 10S 8S 6S 4S Savu Sea 4 122E

0 5

124E 6

5000

4 000 o

1 C)

000 7

126E 3000 8

1000

0 3000 0

30 okih ta. 1998 al., et Conkright

0 2000

128E 1000

2 000 34.5 130E

4000

3000 6000 Salinit

.eie rid aatefloigdt eeue si ae r nitalics; in are names (ship used were data following the data Arlindo ).Besides 5000 34.6 132E 4000 y 34.7

Indian Ocean Deep Water Jalanidhi 2 (6); Samudera Ox yg en (ml/l) 3 (1). 4 (solid )

2212 ..Gro ta./De-e eerhI 0(03 2205–2228 (2003) 50 II Research Deep-Sea / al. et Gordon A.L. A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2213

2.1. Northern access Fig.2a ) with an effective sill depth of 2800 m separating it from the open Pacific Ocean. Sangihe Ridge: The Sangihe Ridge spans the Halmahera Sea: The Halmahera Sea is exposed distance between the northeastern tip of Sulawesi at its northern end to the South Pacific water to the southern end of Mindanao (Fig.2a ).It is advected into the region by the New Guinea broken by three channels, which Mammericks et al. Coastal Current (Gordon, 1995; Ilahude and (1976) show to lie each between 1000 and 1500 m. Gordon, 1996a, b).The South Pacific water We name each after the adjacent island: the Kawio column may spread into the southern Halmahera sill in the north at 5100N and two sills in the Sea across a sill near 0.5N.The salinity and southern end of the ridge: Biaro sill at 2000N oxygen stratification do not display enough range and the Ulu Siau sill at 2300N.The comparison amid the scatter to help define a sill depth, but of the stratification in the Sulawesi Sea with that the temperature field does a bit better (Fig.2b ). to the Pacific Ocean side of the ridge (Fig.2 ) The Halmahera thermal stratification deviates indicates that at depths deeper than roughly from the Pacific Ocean with increasing depth 1000 m, profiles of potential temperature, salinity below 490 m.Bottom-water potential temperature and oxygen from opposites sides of the ridge of 7.6C and salinity of 34.6 in the Halmahera Sea diverge from each other with increasing suggest complete blockage near 580 m.Bottom depth.This indicates restricted communication water at near 2000 m is matched by bottom water between the water bodies on either side of the ridge near 800 m (Fig.2b ), probably just to the overflow below 1000 m.The bottom water (potential side of the effective sill.The shallow Halmahera temperature of 3.34C and salinity of 34.59) in Sea sill allows saline South Pacific lower thermo- the Sulawesi Sea near 4500 m matches the Pacific cline water to enter the Seram Sea (Ilahude and values east of the Sangihe Ridge at a depth of Gordon, 1996a, b), but prohibits deeper water 1350 m.Therefore, 1350 m is assigned as the depth from entering the Indonesian seas, which have of the effective sill depth across the Sangihe Ridge. access to the interior seas only through the The Sulawesi bottom water oxygen is slightly Sulawesi and Maluku Seas, with the Sulawesi lower, 0.15 ml/l, than the oxygen concentrations pathway blocked near 680 m by the sill in the on the Pacific side of the effective sill.This oxygen southern Makassar Strait. decrease is governed by the residence time of Lifamatola Passage: The Lifamatola Passage is Sulawesi bottom water.The data are not sufficient the deepest entry passage for Pacific water into the to determine which sill is the primary pathway. interior Indonesian seas.A sill depth of 1940 m at Entry into the Sulawesi Sea does not insure 1.81S, 126.95E has been determined by careful spreading at depth into the Flores and Banda bathymetric survey (Van Aken et al., 1988).Water Seas, because in the southern Makassar Strait the profiles (Fig.2c ) reveal that deviation occurs at Dewakang Sill near 680 m (and Ilahude and depths greater than approximately 1400 m, which Gordon, 1996a; Waworuntu et al., 2000) blocks may be taken as the depth at which restriction of all but the upper layers to free communication free access begins.Comparison of bottom water in with the Flores Sea. the Seram Sea (2.65C and 34.62C) with the Differences in the profiles that are situated in the Maluku Sea water column suggests an effective sill Karakelong Basin between the Sangihe Ridge and depth at 1650 m, about 300 m shallower than the Karakelong Ridge (see Fig.1 ; named for the surveyed sill depth.The shallow sill relative to Island near 4N, 126.6E; +symbol on Fig.2a ) the bathymetric survey is likely a consequence of are observed below a depth of 1700 m (Fig.2a ). strong mixing due to internal wave energy at the The stations in that basin indicate isolation from sill (Van Aken et al., 1988; Ffield and Gordon, the open Pacific Ocean below the effective sill 1996), which act to dilute the sill depth water with depth of 2000 m.East of Karakelong Ridge is the overlying warmer water before descending to the Morotai Basin that leads into the Maluku Sea (see floor of the Seram Sea.A sill depth of 1940 m Fig.1 ; stations denoted by a solid triangle in would produce Seram Sea bottom water potential 2214 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 temperature of 2.20C, 0.45C colder than ob- Table 1 a served, if the Lifamatola Passage overflow were Sill depths (see Fig.1 for locations) laminar.The Seram Sea bottom oxygen is only Sill Separating Sill depth (m) 0.10 ml/l, slightly lower than the Maluku Sea Sangihe Ridge Sulawesi—Pacific 1350 oxygen at the water property determined sill Karakelong Ridge Karakelong—Pacific 2000 depth.As the Lifamatola Passage is the deepest Morotai Basin Maluku—Pacific 2800 passage connecting the Pacific Ocean to the Halmahera Sea Seram—Pacific 580 Indonesian Sea, it provides all of the bottom Lifamatola Passage Maluku—Banda 1940 water of the expansive Seram, Banda and Flores Lombok Strait Flores—Indian 300 Timor Sea Banda—Indian 1300–1500 seas.The Seram Sea is a relatively small basin (a vestibule to the Banda Sea), with an expected short a Accuracy of the sill depth determinations is estimated to be deep residence time. Postma and Mook (1988), within 5–10% of the sill depth for sills deeper than 1000 m, 10– 20% for sills shallower than 1000 m. using 14C, estimated the residence time of deep water in the Seram Sea and northern Banda Sea as less than 10 years. Indian Ocean (Fieux et al., 1996).Available data 2.2. Southern access suggest that exchange between the Banda and Timor Seas becomes increasingly restricted below Timor Sea Sill: The deepest link between the 1300 m.Exchange is blocked below 1450 m or Indian Ocean and Indonesian Seas and the perhaps as deep as 1500 m. majority of export of Indonesia Sea water occurs The Savu Sea profile (the +symbol on Fig.3 )is in the vicinity of Timor involving an array of warmer than the Banda Sea profile below 1900– passages along the Timor Passage and across the 2000 m, this is indicative of a sill of approximately Outer Banda Arc (see Mammericks et al., 1976). that depth between these two seas.However, the Secondary export of water to the Indian Ocean lack of the cooler deep Indian Ocean water in the also occurs in Lombok Strait, which has a sill Savu Sea indicates that the connection of the Savu depth of about 300 m (Murray and Arief, 1988; Sea to the open Indian Ocean is shallower than the Murray et al., 1990). Fieux et al (1996) state that 1300 m sill depth of the Timor Sea (Table 1). the sill depth near Timor is between 1200 and 1300 m. Van Aken et al.(1988) found a sill near 7.5S and 132.3E of 1450 m.As these are both 3. Deep-water upwelling shallower than the Lifamatola Passage, the southern access passages are not the controlling sill for Van Aken et al.(1988, 1991) investigated the renewal of deep water in the Banda Sea.Therefore, exponential form of the temperature, oxygen, comparison of bottom water on the overflow side phosphate, silica and 14C profiles in the deep to the upstream profiles does not define an Banda Sea.They noted that the overflow from the effective sill depth; however, they do fix the limits Lifamatola Passage has no other escape route than of the sill depth limiting exchange of waters upwelling to the depth of the outflow sill (1300– between the Banda Sea and the Indian Ocean. 1500 m, see above) into the Indian Ocean.They Within the Timor Sea (solid symbols in Fig.3 ) explored the Munk abyssal recipe (Munk, 1966)of divergence of the temperature, salinity and oxygen vertical balance of upwelling, w; to the kinematic profiles relative to the Banda Sea stratification is vertical mixing coefficient, Kz (the diffusivity first noticed at 1300 m (near 3.8C, 34.62, 2.4 ml/l), divided by the water density) for the Banda Sea. À4 2 though more striking below 1500 m.This indicates They found a relatively large Kz of 13.0 Â 10 m / that below 1300 m, communication between the s, which they attributed to tidally driven bound- Banda Sea and Timor Sea is restricted.The cooler, ary-layer mixing.For comparison we now deter- more saline and better oxygenated deep water in mine the Z* (scale height) for the Arlindo CTD Timor Passage below 1500 m is derived from the data in the deep Banda and Seram Seas for the A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2215

Table 2 Scale height of deep water in the Banda and Seram seas below 1300 m

Parameter Western Banda Central Banda Eastern Banda Seram

Number of profiles 7 11 5 9 Z* (m)a 582 542 526 608 Std (m)b 72 92 57 160 w (m/s)c 2.38 Â 10À6 2.38 Â 10À6 2.38 Â 10À6 2.38 Â 10À6 2 d À4 À4 À4 À4 Kz (m /s) 13.9 Â 10 12.9 Â 10 12.5 Â 10 14.5 Â 10 a Scale height in meters. b Standard deviation in meters. c w=vertical velocity, m/s.The value is taken from Van Aken et al.(1991) for the upwelling velocity across the top of the confined Banda Sea d Kz=vertical eddy mixing coefficient.

Eastern Banda Central Banda Western Banda Seram 0

500

1000

1500

Depth (m) 2000

2500

3000 Z* (m) Z* (m) Z* (m) Z* (m) 531 503 424 450 526 542 582 608

3500 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12

Potential Temperature (oC) 300-1500 Depths (m) > 1300 Fig.4. Temperature proﬁles for the Banda and Seram Seas based on Arlindo 1993, 1996 and 1998 data. Solid black dots for the observations, the red line indicates the exponential ﬁt according to Eq.(1) (see text) for data between 300 and 1500 m depths (red) and for depths deeper than 1300 m (blue), also shown respectively in red or blue, Z*(Kz=w) values. 2216 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228

Table 3 Scale height of deep water in the Banda and Seram seas between 300 and 1500 m

Parameter Western Banda Central Banda Eastern Banda Seram

Number of profiles 7 11 5 9 Z*a 424 503 531 450 Stdb 77 88 54 59 w (m/s)c 2.38 Â 10À6 2.38 Â 10À6 2.38 Â 10À6 2.38 Â 10À6 2 À4 À4 À4 À4 Kz (m /s) 9.8 Â 10 11.6 Â 10 13.0 Â 10 10.1 Â 10 d À6 À6 À6 w (m/s) 1.39 Â 10À6 1.39 Â 10 1.39 Â 10 1.39 Â 10 2 À4 À4 À4 À4 Kz (m /s) 5.7 Â 10 6.8 Â 10 7.3 Â 10 6.2 Â 10 w (m/s)e 0.24 Â 10À6 0.21 Â 10À6 0.19 Â 10À6 0.23 Â 10À6 2 À4 À4 À4 À4 Kz(m /s) 1 Â 10 1 Â 10 1 Â 10 1 Â 10 a Scale height in meters. b Standard deviation in meters. c Determination of Kz from the Z* value using the deep upwelling velocity required to compensating the Lifamatola overflow (Van Aken et al., 1991). d Determination of Kz from the Z* value using the Ekman-induced upwelling in Banda Sea (Gordon and Susanto, 2001). e Determination of vertical velocity using the canonical vertical mixing coefficient of 10À4 m2/s. simple one-dimensional vertical balance determined by Van Aken et al.(1991) .This value represents a regional average.Most of the mixing y ¼ y expÀZ=Z ; ð1Þ 0 is expected to be accomplished along the sidewalls. Based on near bottom Radon profiles in the Banda Z ¼ Kz=w: ð2Þ Sea, the Kz is found to vary from 46 to For the Arlindo temperature data deeper than 64 Â 10À4 m2/s, reaching 83–2000 Â 10À4 m2/s over 1300 m and for those stations that reach to at least rough topography and sills (Berger et al., 1988), 2000 m, the Z* was determined for the western, with similar values found from the deep silicate central, eastern Banda Sea and for the Seram Sea distribution (Van Bennekom, 1988). (Table 2; Fig.4 ).The regional average Z* is 565 m. The regional variability of Kz; highest in the Van Aken et al.(1991) calculated a Z* of 560 m. Seram Sea and in the western Banda Sea, agree Wyrtki (1961) also noted the exponential nature of with the spatial variability of the 14C derived deep- the temperature profile below 1500 m within the water residence time of Postma and Mook (1988), Banda Sea, but arrived at a larger value of Z* lower residence time for areas of greater vertical (714 m; converted from the value in Table 8 of mixing.However, in view of the relatively large Wyrtki, 1961).Using the upwelling rate of standard deviations of the Z* determinations 2.38 Â 10À6 m/s across 1500 m that Van Aken between the profiles used in the calculations, these et al.(1991) determined from the Lifamatola spatial variations are not significant. overflow rate, the Kz value derived from the While the simple balance rigorously applies to Arlindo data in the Banda and Seram Seas is the water column deeper than 1300 m, a reason- 13.3 Â 10À4 m2/s, essentially the same as the value able exponential fit to the temperature profile

Fig.5. Western throughﬂow pathway.Vertical sections: (a) contours of potential temperature combining 1993 and 1994 Arlindo data; the inset map shows the location of the section based on the Arlindo data and in small solid circles the location of the archived data; (b) upper panel: contours of salinity only for 1993 Arlindo data; the inset potential temperature versus salinity for both 1993 and 1994 Arlindo data; (c) contours of salinity for the upper 2500 m of 1994 Arlindo data; (d) contours of oxygen (ml/l) combining 1993 and 1994 Arlindo data, the inset, potential temperature versus oxygen for both 1993 and 1994 Arlindo data.The bottom topography along the section is generalized to show only the major basins and topographic barriers.The values shown in most of deep basins represent a spatial/temporal average of archived data (Conkright et al., 1998) found within 50 km from the cruise track.For all sections solid symbols represent Arlindo 1993 data and open symbols, Arlindo 1994 data.

A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2217

7 1 7 7 7 6

8 7 71 7

.79 .7 .7 .7 .76

2. 2 2 2 2. 2 2 2. 2.76

8 3

2400

7 8

.81 .79 .79 .78 .78

2 2 2 2. 2 2 2.

2 9

9 2200

84 79

. 3.2 .

2 2.8 2.7 2.7 2 3.6

3.4 3.8

4.8 4 4.4 4.2

1 2000

2 2.81

8 7

9 6 5

1800

0 9 9 9 9

0 9 9 9

. . . .

3.01 3 2 2 2.9 2

2 .98

8 5

15 2 20

3.6

3. 3.2 3.

0 0 0 0 0 0 0 9

02 0

Flores Banda 0 . . . .0

3 3.02 3.0 3.0 3 3.0 3.0 3 3

2.9 1600

4 4.8

1400 4

1993 1994 Potential Temperature 1993 1994 Potential

Sill

Dewakang 132E 5

9 8 7 6

3.4 1200

3.2 6

Distance (km) 3. 71

.4 128E

4 4.2 3.8 82 1000 9087

4.8

. 4 124E 26 93 95 24

800 4 21

98 98 98 98 23 3. 10 17 120E 16 11 10 10 10 13

5 4

20 15 10 3.6 600 116E Ê 0

8 2

9 8 3 4. 4.4 4. 4S 8S

400

2 3

4.6 .

3.3 3

3 3.34 200

.6 26 24 23 21 18 17 16 13 11 10 7 98 95 93 90 87 82 3 Sulawesi Makassar 0 181 183 184186189 190 191 194 200 202 203 109 114 116 119 122 136 138 0

500

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Depth (m) Depth (a) 2218 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228

2 2 2

34.6 34.62 34.6 34.62 34.6 34.62 34. 34.62 34.62

34.6 34.62

34.45

2200

2 1

34.6 34.61 34.6 34.61

2 2 2

34.6 34.62 34.62 34.6 34.6

2000 2

34.4

34.6 34.62

34.

34.56

34.6

34.55 34.

1800 34.54

34.45

1600

1 1 0 0

60 58

Flores Banda

34.5 34.6

34.61 34.6 34.61 34.6 34.60 34.6 34.60 34. 34.6 34.58 34.

5 85

1400 5

Aug-Sep 1993 Salinity Aug-Sep

34.58

34.4 34.

55 .5 .3

7.1 7.4

27 2 27 2

34.56 34.

27.2 27 27.6 1200 0

34.65

Sill Sill σ Dewakang continued Distance (km)

34.54 34.54 Fig.5 ( 34.60

1000

4 3 34.45

34.58 7

62 34.55 .

Salinity 4 34.58

800

3 34.5

6 34. 34.

55 34.50 34.54 34.45

34. 34.56 600

34.62 34.5

34.62 34.45

8 7 6 5 4 3 2 Potential Temperature Potential 400

34.5434.5534.56 34.54

585 .

34.4 4

34.6

34.

34.4 34.58 34.585 3 200 Sulawesi Makassar 0 26 24 23 21 18 17 16 13 11 10 7 98 95 93 90 87 82 0

500

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Depth (m) Depth (b) A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2219

2400 34.5

.54

2200

34.56

.58

34.54

5 34

2000

34.55

34.56

34.55 34.55

1800

34.54 34.54

Flores Banda 34.45

1600

.56

.58

.6 34

85 34.54 3 5

1400

34.

3 34.55

Sill Dewakang 203 109 114 116 119 122 136 138

34.5 1200 continued Distance (km)

34.45 34.5 Fig.5 ( 34.4 1000

34.2 34.45 5 Jan-Feb 1994 Salinity

.58 34.58

34 34.56 800 34.54

.45

34.55

3 600

34 34.45 400

.585

6 58

34.

34.45 34 34.585

200 34.6

Sulawesi Makassar

.56 34.58

3 34.55

34.54 34.54 0 181 183 184186189 190 191 194 200 202 0

500

1000 1500 2000 2500 Depth (m) Depth (c) 2220 Sill (d)

Sulawesi Makassar Dewakang Flores Banda 181 183 184186189 190 191 194 200 202 203 109 114 116 119 122 136 138 26 24 23 21 18 17 16 13 11 10 7 98 95 93 90 87 82 71 0 4.5 4 4 3.5 3.5 3.5 3.5 3 3 2.6 2.6 2.6 2.45 2.5 2.5 2.5 2.4 2.35 2.4 2.3 2.35 2.42.3 2.25 2.32.3 2.25 2.25 2.25 2.2 2.2 500 2.15

2.2 2.1 2.2 2.15

1000 2 .1 5 2.15 2.25 2205–2228 (2003) 50 II Research Deep-Sea / al. et Gordon A.L. 2.2 2.25

2.2

1500 2.3

2.2 5 2.1 2.35 2000 2.2

2.15 2.15 2.2

2500 2.2 2.3

2.25

2.4 8 2.31 2.29 2.40 2.41 2.44 2.42 Depth (m) 3000 2.29 2.27 2.39 2.42 2.42 7 2.41 2.42

3500 2.41 6

5 4000

4 Potential Temperature Potential

4500 3

2 2.0 2.1 2.2 2.3 2.4 2.5 5000 Oxygen 1993 1994 Oxygen

5500 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 Distance (km) Fig.5 ( continued). A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2221 occurs for the water column deeper than 3 Seram Sea, into Banda Sea where it crosses the 00 m (Fig.4 ).We fit an exponential to the interval western pathway section, extending into the Timor 300–1500 m to determine the scale height for the Sea and Indian Ocean.The thermocline stratifica- depth range above the export of Lifamatola tion based on the Arlindo data is described by overflow (Table 3).The average scale height Z* Ilahude and Gordon (1996a, 1996b), Ffield and is 477 m.To convert Z* to a mixing coefficient Gordon (1992) and with archived data by Hautala requires knowledge of the upwelling rate (or et al.(1996) , and will not be repeated here.The conversely knowledge of Kz is needed to calculate focus of this work is on the deeper, subthermocline upwelling).Above the confines of the isolated stratification, supplementing the excellent series of Banda Basin the vertical velocity is not known. papers derived from the Snellius II expedition of Therefore, a reasonable range of vertical velocities 1984–1985 (see Van Aken et al., 1988, 1991). is offered.If the Lifamatola overflow upwelling value is applied across the full 300–1500 m 4.1. Western pathway À4 2 interval, the resultant Kz is 11.4 Â 10 m /s.If the Ekman-induced upwelling in the Banda Sea The controlling sill depth between Makassar average of 1.39 Â 10À6 m/s, upwelling value nom- Strait and the Flores Sea is the 680 m deep, rather inally at 100 m (Gordon and Susanto, 2001), is broad, Dewakangs sill (Ilahude and Gordon, applied across the full 300–1500 m range, the Kz is 1996a).As the deep water is ventilated by Pacific 6.6 Â 10À4 m2/s. waters from both sides (from the Banda Sea fed by À4 2 The canonical Kz value of 1 Â 10 m /s implies the Lifamatola Passage overflow and from the an average upwelling of 0.21 Â 10À6 m/s.While the Sulawesi Sea fed by the Sangihe Ridge overflow), thermocline is in the 100–200 m interval, shallower there is not a sharp discontinuity of stratification than the exponential profile, the use of a typical on either side of the Dewakang Sill.However, with À4 2 thermocline Kz value of 0.1Â 10 m /s (Ledwell increasing depth, differences in temperature and et al., 1993, 1998) results in an upwelling rate of salinity as revealed in the y=S scatter (Fig.5b ) 0.21 Â 10À7 m/s. Alford et al.(1999) find begin to emerge near the 5.5C (at 750 m), À4 2 Kz ¼ 0:92 Â 10 m /s in the Banda Sea near becoming more pronounced near 4.2 C (at 100 m depth averaged over a 2 week cruise, but 1200 m) with the Banda side being slightly saltier that period was one of minimal tidal activity, which and cooler.During the southeast monsoon may boost diapycnal mixing (Ffield and Gordon, (August–September 1993; Fig.5c ) the deep water 1992, 1996). on the Makassar Strait side of Dewakang Sill is slightly (less than 0.01) fresher than that found during the northwest monsoon season of January– 4. Intra-basin exchange and subthermocline water February 1994 (Fig.5b ). masses The deep temperature and salinity indicate the presence of a deep topographic barrier of about For completeness we offer sections of tempera- 2300 m depth between the Banda Sea and Flores ture, salinity and oxygen composed of August Sea.This sill blocks water colder than 3.0 C from 1993 and February 1994 Arlindo data (Fig.1 ) flowing freely into the Flores Sea from the Banda supplemented with data below 3000 m depth Sea. Gordon et al.(1994 ; also see Top et al., 1997) drawn from archived data (Conkright et al., describe a deep circulation pattern in the Flores 1998), for the western and eastern ITF paths. Sea in which deep water from the Banda Sea, fed The western section (Fig.5 ) stretches from the by Lifamatola overflow, spreads westward reach- Sulawesi Sea, through the Makassar Strait and ing the southern flank of Dewakang Sill, where it Flores Sea and into the southern Banda Sea.This upwells and returns to the east above the 1200 m is considered to be the main ITF path for depth range, though some may occasionally over- thermocline water.The eastern section ( Fig.6 ) flow the Dewakang Sill into the southern Makas- transverses the region from the Maluku Sea, the sar Strait (an inference drawn from the Arlindo 2222 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228

CFC, Waworuntu et al., 2000).The linear y=S seas through the Halmahera Sea.It spreads both scatter between 4.2C and 5.5C represents a northward in the Maluku and southward into the mixture of Banda deep and Makassar throughflow Banda Sea, with much more pervasion during the water.For water colder than the 4.2 C end- northwest monsoon phase (January/February member, the Flores Sea y=S is identical to the 1994).In the central and southern Banda Sea the Banda Sea deep water. South Pacific lower thermocline water is replaced The oxygen distribution (Fig.5d ) shows that the by the lower salinity North Pacific thermocline deep water with the highest oxygen is found in the water drawn through the Makassar Strait. Banda Sea, roughly at 2000 m near the 3.1C Antarctic Intermediate Water is observed within isotherm.This oxygen maximum slowly yields to the Maluku and Seram Seas as a salinity-minimum lower values as the Banda Sea deep water spreads and oxygen-minimum between 600 and 1000 m. into the Flores Sea, though the Flores Sea deep This core layer attenuates in the Seram Sea and water remains higher in oxygen than the deep disappears within the northern Banda Sea. Wyrtki water on the Makassar side of Dewakang Sill.The (1961, Plates 28–30) does not show an Antarctic better-ventilated deep water is derived from the Intermediate Water spreading path from the Lifamatola overflow.The lowest oxygen concen- Maluku Sea into the Banda Sea.The August/ trations are found in Makassar Strait and between September 1993 low salinity (Fig.6b ) core layer 500 and 2000 m in the Flores Sea.The oxygen near 700 m in the central and southern Banda Sea distribution is consistent with the deep circulation (stations 62–71) may also be a remnant of scheme of the Flores Sea presented by Gordon Antarctic Intermediate Water but it is not et al.(1994) based on 1991 (pre-Arlindo) data. contiguous with the Maluku Sea Antarctic Inter- mediate Water salinity minimum.In February 4.2. Eastern pathway 1994 (Fig.6c ) the salinity pattern displays weak- ening of the vertical gradient in the 500–700 m The eastern path (Fig.6 ) provides a deeper interval.It is suggested that ‘‘trace’’ presence throughflow route than the western section.Below of Antarctic Intermediate Water in the central the thermocline, South Pacific characteristics and southern Banda Sea is derived from the become more pervasive within the Indonesian seas Makassar Strait, which is consistent with the as the main access path of North Pacific along the thermocline flow lines presented by Gordon and pathway is limited by the 680 m Dewakang Sill, Fine (1996). and constituting the deep-water component of the The Lifamatola Passage surveyed sill depth is throughflow (Wyrtki, 1961; Hautala et al., 1996). 1940 m (Van Aken et al., 1988), but the water Within the depth range from 200 to 600 m in the spilling into the Seram and Banda Seas represents Maluku, Seram and to the northern boundary of a mixture of the lower 500 m of the Lifamatola the Banda Sea, a salinity maximum greater than water column (Van Aken et al., 1988; Ffield and 34.6 marks the signature of the South Pacific lower Gordon, 1996).This is due to mixing at the sill, as thermocline water (Gordon and Fine, 1996; mentioned above.The Arlindo data suggest that Ilahude and Gordon, 1996a, b) into the Indonesian this is a variable process.Stations 48 (August

Fig.6. Eastern throughﬂow pathway.Vertical sections: (a) contours of potential temperature combining 1993 and 1994 Arlindo data, on the upper right, map showing the location of the section based on the Arlindo data and in small solid circles the location of the archived data, middle right potential temperature versus salinity for both 1993 and 1994 Arlindo data and on the lower right potential temperature versus oxygen for both 1993 and 1994 Arlindo data (b) contours of salinity only for 1993 Arlindo data; (c) contours of salinity for the upper 2500 m 1994 Arlindo data; (d) contours of oxygen (ml/l) combining 1993 and 1994 Arlindo data.The bottom topography along the section is generalized to show only the major basins and topographic barriers.The values shown in most of deep basins represent a spatial/temporal average of archived data (Conkright et al., 1998) found within 50 km from the cruise track.For all sections solid symbols represent Arlindo 1993 data and open symbols, Arlindo 1994 data. 33

(a) Passage 35 Maluku Lifamatola Seram Banda Timor 0Ê 36 173 171 170 169 168 167 154 153 152 151 150 148 147 141 140 139 138 137 135 132131130 129 128 3738 33 35 36 3738 39 48 49 50 5158 596061149 63 62 64 66 70 71 72 8079 7776757473 39 48 0 49 25 5150 20 58 596061 15 4S 63 62 10 64 9 9 66 8 8 70 500 71 7 7 72 8079 8S 78 6 77 6 7675 7473

5 5 2205–2228 (2003) 50 II Research Deep-Sea / al. et Gordon A.L. 4.8 4.8 1000 4.6 4.6 116E 120E 124E 128E 132E 4.4 4.4 4.2 4.2 4 8 σ 3.8 4 0 .1 3.6 3.8 27 3.4 3.6 1500 7 2.8 3.4 27.2 3 3 2.6 .2 3.2 6 27.3 2000

2.8 27.4 3 5

.5 27 2500 4 Potential Temperature Potential 27.6

4 1 1 3 0 9 4 3 1.6 1.8 1.8 2.3 2.80 2.8 2.86 2.8 2.8 2.84 2.83 2.83 2.92 .8 Depth (m) 3000 2 27.7 35 1 82 3 1 81 91 1.64 1.79 1.79 2. 2.7 2.72 2. 2.89 2.82 2.8 2.8 2. 2. 2 9 9 2 9 7 7 34.50 34.55 34.60 34.65 34.70 1.7 1.7 2.3 2.68 2.6 2.78 2.7 2.78 2.80 2.7 2.81 8 Salinity 7 7 8 0 7 9 3500 1.79 1.78 2.6 2.68 2.7 2.7 2.8 2.7 2.7

6 .66 7 7 .77 .78 1.78 2.6 2 2.7 2.7 2 2 7 5 7 7 7 1.78 2.6 2.65 2.7 2.7 2.7 2.78 4000 8 4 7 7 1.7 2.64 2.6 2.7 2.7 2.78 6

4 6 1.78 2.6 2.64 2.7 2.79 5 3 6 4500 1.78 2.6 2.63 2.7

3 .63 .76 1.78 2.6 2 2 4

2 Temperature Potential 2.6 5000 3 1993 1994 Potential Temperature 2 5500 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

Oxygen 2223 Distance (km) 2224 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 Passage

(b) Maluku Lifamatola Seram Banda Timor 33 35 36 373839 48 49 5051 58 596061 63 62 64 66 70 71 72 8079 78 7776757473 0 34.45 34.4 585 34.5 34.45 34. 34.34.54 34.62 5534.56 34 .58 34.585 34.54 6 34.55 34. 34.56 3 500 4.58 .58 34

6 34.585 34.

1000 5 58 34. 34.58

34.6 1500

34.62

2000

34.

62 2500

34.66 34.65 34.65 34.64 34.62 34.62 34.62 34.62 34.62 34.62 34.62 34.61

Depth (m) 3000 34.66 34.65 34.65 34.65 34.62 34.62 34.61 34.62 34.62 34.62 34.62 34.62

34.65 34.65 34.65 34.62 34.61 34.61 34.62 34.62 34.62 34.62 34.62

34.66 34.65 34.62 34.61 34.62 34.62 34.62 34.62 3500 34.62

34.65 34.62 34.61 34.62 34.62 34.62

34.65 34.62 34.61 34.62 34.62 34.62 4000 34.65 34.62 34.61 34.62 34.62

34.7 34.65 34.62 34.62 34.62

4500 34.65 34.62 34.62

34.65 34.62 34.62

34.62 5000

Aug-Sep 1993 Salinity

5500 0 200 400 600 800 1000 1200 1400 1600 Distance (km) Fig.6 ( continued). A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2225 Passage

173 171 170 169 168167154 153 152151 150149 148 147 141 140 139 138 137 135134133132131130129128 0 34.4 34.5 34.45 34.55 34.62 34.58

34.62 34.6 34.54 34.58 34.55 34. 500 34.58534.6 56

34.58

34.5 85 1000 34.6 34.585

1500 Depth (m)

34.62

2000

2500 Feb 1994 Salinity

0 200 400 600 800 1000 1200 1400 1600 Distance (km) Fig.6 ( continued).

1993, Fig.6a ; latitude: 1.846S, longitude: responsible for the mean overflow temperature of 126.994E, close to the Lifamatola sill; station 48 2.78C. deepest measurement is at 1990 m with a water The Seram and Banda seas display an oxygen depth of 2122 m) and 154 (February 1994, Fig.6a ; maximum from 2000 to 2600 m.A possible latitude: 1.848S; longitude: 126.993E; station explanation is as follows.Relatively high-oxygen 154 deepest measurement is at 2029 m with a water water at the Lifamatola sill overflows into the deep depth of 2045 m) are in the Lifamatola Passage, Banda Sea and then upwells slowly within the slightly on the Seram Sea ‘‘spill-over’’ side of the confines of the deep basin as required to balance passage.They show significantly different bottom downward eddy diffusion of buoyancy and ‘‘make temperature.The bottom potential temperature at room’’ for a continued overflow from Lifamatola. station 48 is 2.714C, but at station 154 it is At the shallower level of the confined basin the 2.460C, a difference of 0.25C.The bottom lowest oxygen is expected, as this water has been temperature of the Banda Sea from the archived resident for the longest time.However, in the data is 2.78C, close to the bottom temperature at Banda Sea, above the Lifamatola sill depth, station 48.The fluctuation in the temperature of relatively oxygenated water spreads southward the overflow may be a product of internal waves from the Maluku Sea on a more horizontal plane and tides, which produce heave of the isopycnals into the Banda Sea, producing a slight oxygen at the sill depth.The average overflow, over the maximum near and slightly shallower than the 40-year residence time of the Banda Sea, is controlling sill depth. 2226 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228

(d) Passage Timor Maluku Lifamatola Seram Banda 2 0 173 171 170 169 168167 154 153 151 15 149 148 147 141 140 139 138 137 135 132 131 130129 128 33 35 36 3738 39 48 49 505115 58 596061 63 62 64 66 70 71 72 8079 7776757473 0 4 3.5 3.5 3 2.6 2.5 2.5 2.6 2.5 2.45 2.45 2.45 2.4 2.35 500 2. 4 2.3 2.25 2. 35

2.25

1000 2.4 2.3 2.35 2.35

2.4 2.45 2.45

1500 2.5

2.5 2000 2.4 5

2. 2500 6

3.06 2.85 2.84 2.75 2.54 2.54 2.49 2.44 2.45 2.44 2.44 2.43 2.41

Depth (m) 3000 3.06 2.92 2.52 2.53 2.47 2.42 2.41 2.44 2.44 2.43 2.40

2.93 2.53 2.52 2.26 2.44 2.44 2.43 2.39

3500 2.93 2.53 2.26 2.44 2.44 2.39

2.95 2.21 2.43 2.37

2.94 2.21 2.43 2.37 4000 2.94 2.46 2.39

2.94 2.43

4500 2.98

2.98

5000

1993 1994 Oxygen

5500 0 200 400 600 800 1000 1200 1400 1600 Distance (km) Fig.6 ( continued). A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228 2227

5. Summary suggested for the water column shallower than 680 m (Dewakang Sill).Below 680 m the export in Transfer of water from the Pacific Ocean to the the passage on either side of Timor is estimated as Indian Ocean through the Indonesian seas is 1.8–2.3 Sv, which matches the estimated flow accomplished mainly in the thermocline layer though Lifamatola Passage. (Gordon et al., 1999).However, water properties Water overflowing into the depths of an isolated that reveal significant contribution to the inter- basin displaces the resident water made less dense ocean throughflow may be derived from the deeper by vertical mixing processes (and perhaps geother- layer.Below the thermocline, numerous topo- mal heat flux).In this way the density-driven graphic barriers or sills separating the basins of overflow is balanced by compensated upwelling the Indonesian seas impede throughflow.This within the confines of the basins.The profiles of results in a deep circulation pattern governed by temperature within the deep Banda and Seram density-driven overflow processes.While a few sills Seas conform very closely to an exponential form, have been surveyed by sonic means, most have which is expected from a simple vertical balance of not.For these, comparison of temperature and upwelling with vertical mixing.A scale depth ( Z*) salinity of the water column on either side of a sill of 477 m is characteristic of the 300–1500 m depth allows estimation of the effective depth of the sill. range, with a value of 565 m for the water column Pacific water may follow three possible paths deeper than 1300 m.Deep vertical mixing coeffi- into the northern Indonesian seas.A 1350 m deep cients as high as 10–15 Â 10À4 m2/s are implied. sill in the Sangihe Ridge blocks the flow into the Sulawesi Sea.The shallowest barrier is found between the Halmahera Sea and Seram Sea, with a Acknowledgements sill depth of 580 m.The deepest occurs between the Maluku Sea and the Seram Sea, within the Analysis of the Arlindo data set is derived from Lifamatola Passage, with a depth of 1940 m. NSF Grant OCE00-99152.We are greatly appre- Escape to the Indian Ocean occurs over the Sunda ciative of the comments of the anonymous Arc.The deepest sill is near Timor and is estimated reviewers whose careful reading and insightful to be from 1300 to 1450 m deep, possibly as deep comments improved the manuscript.LDEO Con- as 1500 m.However, the bulk of the throughflow tribution Number 6360. does not necessarily follow the deepest route.The main throughflow path is accomplished within the thermocline layer passing through the Makassar References Strait.The southern end of the Makassar Strait is marked by a relatively shallow sill, the 680-m-deep Alford, M., Gregg, M., Ilyas, M., 1999. Diapycnal mixing in the Dewakang Sill, which limits the continuation of Banda Sea: results of the first microstructure measurements in the Indonesian throughflow.Geophysical Research throughflow into the Flores Sea.Some through- Letters 26, 2741–2744. flow water escapes to the Indian Ocean through Berger, G.W., Van Bennekom, A.J., Kloosterhuis, H.J., 1988. the 300 m deep Lombok Strait, but most passes to Radon profiles in the Indonesian archipelago.Netherlands the Banda Sea to cross into the Indian Ocean over Journal of Sea Research 22, 395–402. the deeper gaps of the Lesser Sunda Arc near Broecker, W.S., Patzert, W.C., Toggweiler, R., Stuiver, M., 1986.Hydrography, chemistry and radioisotopes in the Timor.Throughflow water found deeper than southeast Asian basins.Journal of Geophysical Research 91 roughly 680 m must enter the Banda Sea from (C12), 14345–14354. the eastern channels, including overflow within the Conkright, M.E., Levitus, S., O’Brien, T., Boyer, T.P., Lifamatola Passage. Antonov, J.I., Stephens, C., 1998. World ocean atlas CD- Using transport values obtained at various sites, ROM data set documentation.NODC Internal Report 15, Silver Spring, MD, 16pp. at different times, an approximate balance of the Ffield, A., Gordon, A.L., 1992. Vertical mixing in the inflow and outflow of Indonesian waters is found. Indonesian thermocline.Journal of Physical Oceanography Export to the Indian Ocean of 7.3–10.7 Sv is 22 (2), 184–195. 2228 A.L. Gordon et al. / Deep-Sea Research II 50 (2003) 2205–2228

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