Southern Makassar Strait Research Articles

Regional Depositional Model Of South Makassar Basin Depocenter, Makassar Strait, Based On Seismic Facies

South Makassar Basin Depocenter (SMBD) is located in Southern Makassar Strait which has petroleum potential by the presence of oil and gas indications within the area based on Airborne Laser Fluorescence survey. However, detail studies within this area are not developed well. One of the studies which can be utilized for further discoveries of oil and gas field in SMBD is a study of depositional model using seismic facies method to maximize limited seismic and well data. Interpretation of depositional model in Eocene (syn-rift phase) was varied from alluvial plain and alluvial fan complex, continued gradually to platform. In Oligocene time (post-rift phase), massive transgression caused a major deepening in entire SMBD where the depositional environment changed to basinal plain. In early Miocene – recent interval (syn-orogenic phase), SMBD was relatively in stable condition at basinal plain environment. Lower Tanjung Sequence will be the most prolific petroleum play in SMBD due to its adequate source rock, reservoir rock and seal rock as well. Keywords: South Makassar basin, depositional model, seismic facies

A NUMERICAL MODELING STUDY ON UPWELLING MECHANISM IN SOUTHERN MAKASSAR STRAIT

<p><strong><em>ABSTRACT</em></strong></p> <p><em>While it has been well documented in the previous studies that upwelling events in the southern Makassar Strait (MAK) during the Southeast Monsoon (SEM) period are associated with low sea surface temperature (SST) and high chlorophyll-a (Chl-a) concentrations in the seawater, the dynamic and physical processes that trigger these upwelling events are still less well understood. In the present study we proposed a mechanism of the upwelling event using a numerical model of the Regional Ocean Modeling System (ROMS). Model validations showed a high correlation of SST climatology between the model and the NOAA-AVHRR satellite data. Moreover, </em><em>velocity fields of the Indonesian Throughflow (ITF) Makassar in Libani Channel was well reproduced by proposed model, revealing an intensification of the flow centered near 120 m depth, which is in good agreement with the observation data. </em><em>The model demonstrated that during the SEM period strong southeasterly winds that blow over southern Sulawesi Island can increase high vertical diffusivity and heat loss through heat flux. Hence, these physical processes lead to increased vertical mixing that, in turn, generates low SST, as a proxy of upwelling event. Furthermore, the upwelling process is enhanced by the ITF Makassar jet that creates large circular eddies flow due to complex topographic within the triangle area of southern Makassar - eastern Java Sea - western Flores Sea. The eddies generate the area of convergence offshore along the ITF pathways and divergence area in the coastal waters close to southern Sulawesi Island. Model experiment with closing/opening Selayar Strait revealed a change of intensity and area of upwelling, suggesting that the Selayar Island forms a barrier for the outflow from MAK to northern part of Flores Sea.</em><em> </em></p> <p><em> </em></p> <strong><em>Keywords: </em></strong><em>Upwelling, ITF Makassar, SE monsoon winds, ROMS-AGRIF, Makassar Strait.</em>

A NUMERICAL MODELING STUDY ON UPWELLING MECHANISM IN SOUTHERN MAKASSAR STRAIT

ABSTRACT While it has been well documented in the previous studies that upwelling events in the southern Makassar Strait (MAK) during the Southeast Monsoon (SEM) period are associated with low sea surface temperature (SST) and high chlorophyll-a (Chl-a) concentrations in the seawater, the dynamic and physical processes that trigger these upwelling events are still less well understood. In the present study we proposed a mechanism of the upwelling event using a numerical model of the Regional Ocean Modeling System (ROMS). Model validations showed a high correlation of SST climatology between the model and the NOAA-AVHRR satellite data. Moreover, velocity fields of the Indonesian Throughflow (ITF) Makassar in Libani Channel was well reproduced by proposed model, revealing an intensification of the flow centered near 120 m depth, which is in good agreement with the observation data. The model demonstrated that during the SEM period strong southeasterly winds that blow over southern Sulawesi Island can increase high vertical diffusivity and heat loss through heat flux. Hence, these physical processes lead to increased vertical mixing that, in turn, generates low SST, as a proxy of upwelling event. Furthermore, the upwelling process is enhanced by the ITF Makassar jet that creates large circular eddies flow due to complex topographic within the triangle area of southern Makassar - eastern Java Sea - western Flores Sea. The eddies generate the area of convergence offshore along the ITF pathways and divergence area in the coastal waters close to southern Sulawesi Island. Model experiment with closing/opening Selayar Strait revealed a change of intensity and area of upwelling, suggesting that the Selayar Island forms a barrier for the outflow from MAK to northern part of Flores Sea. Keywords: Upwelling, ITF Makassar, SE monsoon winds, ROMS-AGRIF, Makassar Strait.

Occurrence and Molecular Identification of Anisakis Dujardin, 1845 from Marine Fish in Southern Makassar Strait, Indonesia

Anisakis spp. (Nematoda: Anisakidae) parasitize a wide range of marine animals, mammals serving as the definitive host and different fish species as intermediate or paratenic hosts. In this study, 18 fish species were investigated for Anisakis infection. Katsuwonus pelamis, Euthynnus affinis, Caranx sp., and Auxis thazard were infected with high prevalence of Anisakis type I, while Cephalopholis cyanostigma and Rastrelliger kanagurta revealed low prevalence. The mean intensity of Anisakis larvae in K. pelamis and A. thazard was 49.7 and 5.6, respectively. A total of 73 Anisakis type I larvae collected from K. pelamis and A. thazard were all identified as Anisakis typica by PCR-RFLP analysis. Five specimens of Anisakis from K. pelamis and 15 specimens from A. thazard were sequenced using ITS1-5.8S-ITS2 region and 6 specimens from A. thazard and 4 specimens from K. pelamis were sequenced in mtDNA cox2 region. Alignments of the samples in the ITS region showed 2 patterns of nucleotides. The first pattern (genotype) of Anisakis from A. thazard had 100% similarity with adult A. typica from dolphins from USA, whereas the second genotype from A. thazard and K. pelamis had 4 base pairs different in ITS1 region with adult A. typica from USA. In the mtDNA cox2 regions, Anisakis type I specimens from A. thazard and K. pelamis showed similarity range from 94% to 99% with A. typica AB517571/DQ116427. The difference of 4 bp nucleotides in ITS1 regions and divergence into 2 subgroups in mtDNA cox2 indicating the existence of A. typica sibling species in the Makassar Strait.

Abrupt increase in east Indonesian rainfall from flooding of the Sunda Shelf ∼9500 years ago

We present a precisely dated, multi-proxy stalagmite record from Liang Luar Cave, Flores (southeast Indonesia) that reveals a rapid increase in Indonesian monsoon rainfall at ∼9.5 ka. A “ramp-fitting” method for detecting statistically significant inflections in a time-series was applied to the stalagmite δ18O, Mg/Ca, and Sr/Ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of ∼350 years. Previously published lake-level records from the monsoon-affected Australian interior show a sudden intensification of the Australian monsoon at ∼14 ka. However, our records indicate that monsoon intensification in Flores occured ∼4–5 kyr later. The timing of the monsoon shift in Flores is synchronous with the rapid expansion of rainforest in northeast Australia and regional freshening of the southern Makassar Strait which, under present-day conditions, is sensitive to monsoon variability. The freshening of southern Makassar was coeval with an abrupt ∼1.5 °C cooling in the upper thermocline of the Timor Sea ∼9.5 ka, indicative of reduced surface heat transport by the Indonesian Throughflow (ITF) when the Java Sea opened during postglacial sea-level rise. This suggests that the abrupt increase in monsoon rainfall on Flores was not due to a change in the ITF – because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures (SSTs) – but rather by the sudden increase in ocean surface area and/or temperature in the monsoon source region as the Sunda Shelf flooded during deglaciation. We propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the ITF following the flooding of the Sunda Shelf at ∼9.5 ka.

PRODUKTIFITAS PRIMER DAN KELIMPAHAN IKAN LAYANG (Decapterus spp.) HUBUNGANNYA DENGAN FENOMENA ENSO, DI SELAT MAKASSAR BAGIAN SELATAN

Two species of scad fish (Decapterus russelli and D. macrosoma) is a major catch of purse seine in almost fishing area, its contributed approximately 58%. Production data of scad fish is based on catch data of purse seine which having fishing base in Java (2006-2007). Chlorophyll-a concentration, sea surface temperature and Photosyntetic Available Radiation (PAR) was derived from satellite imagery AQUA MODIS. That data is used to estimate primary productivity with Vertically Generalized Production Model (VGPM). The effect of ENSO (El Niño-Southern Oscillation) to scad fish fisheries also discussed. This research is aimed to get information about the effects of ENSO to primary productivity and abundance of scads in the southern part of Makassar Strait. Results showed scad fish abundance in the waters of the southern Makassar Strait fluctuates according to season, the peak abundance lasted for three months between November to January. Utilization of scad fish as 3th tropic level component showed percentage of utilization is 8,93% in 2006 and 14,59% in 2007. AQUA MODIS image data showed the highest chlorophyll concentrations occurred between February to April each year. While the highest sea surface temperature occurs in November-January period. There are indication that ENSO have indirect effect to chlorophyll-a consentrations and sea surface temperature. Both of them having relations with scad fish abundance in Makassar Strait.

Monsoon versus ocean circulation controls on paleoenvironmental conditions off southern Sumatra during the past 300,000 years

A multiproxy record has been acquired from a piston core (SO139‐74KL) taken offshore southern Sumatra, an area which is situated in the southwestern sector of the tropical Indo‐Pacific Warm Pool. The high‐resolution data sets (X‐ray fluorescence, total organic carbon, and C37 alkenones) were used to track changes in paleoproductivity, freshwater budget, and sea surface temperature (SST) of the tropical climate system at orbital time scales over the past 300 ka. Our paleoclimatic data show that enhanced marine paleoproductivity was directly related to strengthening of coastal upwelling during periods of increased boreal summer insolation and associated SE monsoon strength with a precessional cyclicity. Changes in freshwater supply were primarily forced by precession‐controlled changes in boreal NW winter monsoon rainfall enclosing an additional sea level component. SST variations of 2°–5°C occurred at eccentricity and precessional cyclicity. We suggest that the sea surface temperature variability off southern Sumatra is predominantly related to three major causes: (1) variations in upwelling intensity; (2) an elevated freshwater input into the southern Makassar Strait leading to reduced supply of warmer surface waters from the western Pacific and increased subsurface water transport via the Indonesian Throughflow into the Indian Ocean; and (3) long‐term changes in the intensity or frequency of low‐latitude climate phenomena, such as El Niño–Southern Oscillation.

Transformation of the Indonesian Throughflow Water by Vertical Mixing and Its Relation to Tidally Generated Internal Waves

Numerical experiments with two-dimensional nonhydrostatic model have been performed to investigate tidally generated internal waves at the Dewakang sill at the southern Makassar Strait where two large-amplitude “bumps” of relatively shallow water exist. We investigate the effect of these features on vertical mixing, with emphasis on the transformation of the Indonesian throughflow (ITF) water properties. The result shows that large-amplitude internal waves are generated at both bumps by the predominant M2 tidal flow, even though the condition of the critical Froude number and the critical slope are not satisfied. The internal waves induce such vigorous vertical mixing in the sill region that the vertical diffusivity attains a maximum value of 6 × 10−3 m2s−1 and the salinity maximum and minimum core layers characterizing the ITF thermocline water are considerably weakened. Close examination reveals that bottom-intensified currents produced mainly by the joint effect of barotropic M2 flow and internal tides generated in the concave region surrounding both bumps can excite unsteady lee waves (Nakamura et al., 2000) on the inside slopes of the bumps, which tend to be trapped at the generation region and grow into large-amplitude waves. Such generation of unsteady lee waves does not occur in case of one bump alone. Trapping and amplification of the waves in the sill region induce large vertical displacements (∼60 m) of water parcels during one tidal period, leading to strong vertical mixing there. Since the K1 tidal currents are relatively weak, large-amplitude internal waves causing intense vertical mixing are not generated.

Cool Indonesian throughflow as a consequence of restricted surface layer flow.

Approximately 10 million m3 x s(-1) of water flow from the Pacific Ocean into the Indian Ocean through the Indonesian seas. Within the Makassar Strait, the primary pathway of the flow, the Indonesian throughflow is far cooler than estimated earlier, as pointed out recently on the basis of ocean current and temperature measurements. Here we analyse ocean current and stratification data along with satellite-derived wind measurements, and find that during the boreal winter monsoon, the wind drives buoyant, low-salinity Java Sea surface water into the southern Makassar Strait, creating a northward pressure gradient in the surface layer of the strait. This surface layer 'freshwater plug' inhibits the warm surface water from the Pacific Ocean from flowing southward into the Indian Ocean, leading to a cooler Indian Ocean sea surface, which in turn may weaken the Asian monsoon. The summer wind reversal eliminates the obstructing pressure gradient, by transferring more-saline Banda Sea surface water into the southern Makassar Strait. The coupling of the southeast Asian freshwater budget to the Pacific and Indian Ocean surface temperatures by the proposed mechanism may represent an important negative feedback within the climate system.

Deep topographic barriers within the Indonesian seas

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 (Z*=Kz/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.

Tidal currents in the Indonesian Seas and their effect on transport and mixing

We have investigated the characteristics of tides and tidal currents in the Indonesian Seas, with particular emphasis on the predominant constituents, the barotropic M2 and K1 components. The calculated harmonic constants of the M2 and K1 tides agree well with those obtained from extensive tide gauge observations: the mean root‐mean‐square errors between models and observations for M2 and K1 over the entire Indonesian Seas are 11.2 and 8.65 cm, respectively, smaller than previous studies. The features of the tidal current field are qualitatively similar to those reported by Wyrtki [1961]. Relatively strong tidal currents are found in the Java Sea and in the vicinities of the narrow straits, such as the Lombok and Malacca Straits. Tracking of numerous labeled particles in the calculated velocity field clearly shows that the tidal currents play essential roles in the transport and mixing processes in the Indonesian Seas. For example, in the eastern Indonesian Seas a significant clockwise residual circulation appears around Buru Island, due primarily to the tidal rectification over variable bottom topography, with a minor impact from the nonlinear effects around narrow straits. The tide‐induced residual transport from the Seram Sea to the eastern Banda Sea attains about 3.8 Sv (1 Sv = 106 m3 s−1), comparable to that of the Indo‐Pacific throughflow along the eastern route. In the western Indonesian Seas (the Java Sea and the Makassar Strait) the residual transport is much smaller than the throughflow transport along the western route. Our result suggests, however, that the properties of water flowing through this route could be modified by strong tidal mixing around the shelf of the southern Makassar Strait and the Lombok Strait.