Agus S Atmadipoera
Fakultas Perikanan dan Ilmu Kelautan, Intitut Pertanian Bogor Kampus IPB Darmaga, Bogor 16680

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Distribusi Percampuran Turbulen di Perairan Selat Alor (Distribution of Turbulence Mixing in Alor Strait) Purwandana, Adi; Purba, Mulia; Atmadipoera, Agus S
ILMU KELAUTAN: Indonesian Journal of Marine Sciences Vol 19, No 1 (2014): Jurnal Ilmu Kelautan
Publisher : Marine Science Department Diponegoro University

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Abstract

Selat Alor merupakan kanal terdalam setelah Selat Ombai di kepulauan Alor. Kontribusinya sebagai salah satu celah keluar Arus Lintas Indonesia (Arlindo) belum banyak dikaji hingga saat ini. Selat Alor memisahkan Laut Flores dan Laut Sawu, dan memiliki sill yang tinggi di dalamnya, diduga turbulensi akibat interaksi antara aliran selat dengan topografi dasar dapat memicu percampuran dan memodifikasi properti massa air yang melaluinya. Tujuan dari penelitian ini adalah untuk mengkuantifikasi transformasi massa air yang melalui Selat Alor dan mengkaji kemungkinan percampuran di dalam selat berdasarkan estimasi sesaat properti percampuran, yakni percampuran turbulen menggunakan metode skala Thorpe. Penurunan CTD dilakukan di 15 stasiun di perairan Selat Alor. Diperoleh hasil bahwa kontur kedalaman yang menghubungkan Laut Flores dengan Laut Sawu adalah ~300 m pada kanal utama. Salinitas maksimum massa air Subtropis Pasifik Utara (NPSW) dar i Laut Flores di Selat Alor banyak mengalami reduksi akibat intensifnya percampuran yang diduga dipicu oleh topografi dasar dan aliran selat yang menghasilkan turbulensi. Lapisan salinitas maksimum Massa Air Subtropis Samudera Hindia Utara (NISW) pada σθ = 23,5-24,5 terdeteksi di bagian selatan selat (Laut sawu). Jejak massa air NISW menurun dan banyak tereduksi mendekati pintu selatan selat. Intrusi Massa Air Lapisan Menengah Samudera Hindia Utara (NIIW) juga dijumpai di lapisan bawah Laut Sawu, konsisten dengan profil arus pada lapisan bawah. Rata-rata nilai difusivitas vertikal eddy (Kρ)  di Selat Alor bagian utara memiliki orde of 10-3 m2 s-1, dan di bagian selatan memiliki orde bervariasi, 10-6-10-4 m2 s-1. Penyempitan celah Selat Alor diduga merupakan pemicu turbulensi tinggi aliran yang berkontribusi pada tingginya nilai difusivitas vertikal. Kata kunci: Arlindo, percampuran turbulen, difusivitas vertikal, Selat Alor Alor Strait is the deepest channel in Alor islands after Ombai Strait. Contribution of the strait as one of the secondary exit passages of Indonesian Throughflow (ITF) has not been studied yet. The strait separates Flores Sea and Sawu Sea, and is featured by the existence of high sill within the strait, suggested that turbulence due to interaction between strait flow and bottom topography could drive mixing and then modify the water mass properties. The purpose of this study is to investigate transformation of ITF water mass and turbulent mixing process with Thorpe scale method. A hydrographic survey has been carried out in July 2011, in which 15 CTD casts were lowered in the strait. The results show that Alor sill depth is about 300 ms in the main gate. Maximum salinity of NPSW from Flores Sea within Alor Strait is significantly reduced due to strong mixing, perhaps driven by bottom topography and strait flow which creates turbulence. NISW (Northern Indian Subtropical Water) with maximum salinity layer at σθ = 23,5-24,5 is dominant in the southern part of Alor Strait (i.e. Sawu Sea). The existence of NIIW (North Indian Intermediate Water) is also found in the deeper layer of Sawu Sea. The average value of vertical eddy diffussivity (Kρ) estimate in the thermocline layer and deep layer in northern part and central part of strait channel is within the order of 10-3 m2 s-1. Lower order of Kρ in the thermocline layer and deep layer were found in southern part of the Strait (Sawu Sea), ranging from 10-6 to 10-4 m2 s-1. These indicate that the existence of sills in the northern part and central part of Alor Strait could drive mixing significantly. Narrowing passage of Alor Strait probably contribute to the high value of vertical eddy diffusivity due to highly turbulence flow. Keywords: Indonesian Throughflow (ITF), turbulent mixing, vertical diffussivity, Alor Strait
PERGESERAN HALMAHERA EDDY KAITANNYA DENGAN PRODUKTIVITAS TANGKAPAN IKAN CAKALANG DI PERAIRAN SEKITARNYA Harsono, Gentio; Supartono, Supartono; Manurung, D; Atmadipoera, Agus S; Syamsudin, Fadlt; Baskoro, Mulyono S
Jurnal Teknologi Perikanan dan Kelautan Vol 5, No 2 (2014): NOVEMBER 2014
Publisher : Fakultas Perikanan dan Ilmu Kelautan

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Abstract

Perairan antara Mindanao dan Papua merupakan salah satu wilayah potensial perikanan cakalang (Katsuwanus pelamis) yang paling maju di Pasifik barat. Sebagian besar industri perikanan jenis ini didominasi oleh kapal jenis purse-seine dengan ukuran besar (50-100 GT). Peran arus pusar Halmahera menjadi penting dalam dinamika perikanan di wilayah ini, namun belum ada yang menjelaskannya. Seri data penangkapan cakalang Catch per Unit Effort (CPUE) dari Western Central Pacific Fisheries Commission (WCPFC) selama satu dekade periode Juli 2002-Desember 2012 dianalisis guna melihat hubungan antara pergeseran Halmahera Eddy dengan produktivitas ikan cakalang di wilayah studi. Hasilnya menunjukkan bahwa produktivitas ikan cakalang di wilayah studi berkorelasi kuat terhadap pergeseran meridional Halmahera Eddy di mana CPUE cakalang memperlihatkan peningkatan dengan jeda waktu 2 bulan setelah pusat Halmahera Eddy bergeser ke utara sedangkan untuk pergeseran zonalnya mempunyai korelasi yang lemah.
SEBARAN LOGAM BERAT TERLARUT DAN TERENDAPKAN DI PERAIRAN TELUK JAKARTA Kusuma, Anma Hari; Prartono, Tri; Atmadipoera, Agus S; Arifin, Taslim
Jurnal Teknologi Perikanan dan Kelautan Vol 6, No 1 (2015): MEI 2015
Publisher : Fakultas Perikanan dan Ilmu Kelautan

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Abstract

Teluk Jakarta merupakan kawasan padat dengan berbagai aktivitas sehingga menjadi tempat berkumpulnya polutan dari daratan yang ditransport melalui 13 sungai yang mengalir di wilayah DKI Jakarta. Tujuan dari penelitian ini adalah menjelaskan proses dan sumber logam berat melalui perbandingan profil sebaran logam berat terlarut dan terendapkan pada bulan September di Perairan Teluk Jakarta. Penelitian logam berat terlarut dan terendapkan di perairan Teluk Jakarta telah dilakukan pada bulan September 2014. Analisis logam berat terlarut dan sedimen mengikuti prosedur (APHA 2012). Hasil penelitian menunjukkan kondisi fisika-kimia perairan Teluk Jakarta untuk suhu berkisar 28,9-30,2 ºC, salinitas berkisar 29,5-30,6 psu, derajat keasaman (pH) berkisar 7,80-8,17 dan partikel tersuspensi (TSS) berkisar 25-68 mg/l. Logam berat terlarut untuk Pb berkisar 0,006-0,016 ppm, Cd berkisar 0,001-0,003 ppm, Cu berkisar 0,001-0,005 ppm, Ni berkisar 0,001-0,016 ppm dan Zn berkisar 0,003-0,097 ppm. Logam berat sedimen untuk Pb berkisar 24,86-59,32 ppm, Cd berkisar 0,32-3,49 ppm, Cu berkisar 11,42-67 ppm, Ni berkisar 19,80-39,85 ppm dan Zn berkisar 26,14,8-241,01 ppm. Sebaran logam berat terlarut yang diperkuat dengan sebaran logam berat dalam sedimen mengindikasikan sumber logam berat di perairan Teluk Jakarta sebagian besar berasal dari input materi dari daratan.
INTRA-SEASONAL VARIABILITY OF NEAR-BOTTOM CURRENT IN THE HALMAHERA SEA Wattimena, Marlin C; Atmadipoera, Agus S; Purba, Mulia; Koch-Larrouy, Ariane
Jurnal Ilmu dan Teknologi Kelautan Tropis Vol 6, No 2 (2014): Electronik Jurnal Ilmu dan Teknologi Kelautan Tropis
Publisher : Bogor Agricultural University

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Abstract

The secondary entry portal of the Indonesian Throughflow (ITF) from the Pacific to Indian Oceans is considered to be via the Halmahera Sea (HS). However, few ITF studies have been done within the passage. This motivated the Internal Tides and Mixing in the Indonesian Througflow (INDOMIX) program to conduct direct measurements of currents and its variability across the eastern path of the ITF. This study focused on the intra-seasonal variability of near-bottom current in HS (129°E, 0°S), its origin and correlation with surface zonal winds and sea surface height over the equatorial Pacific Ocean. The result showed a strong northwestward mean flow with velocity exceeding 40 cm/s, which represented the current-following topography with the northwest orientation. Meridional current component was much stronger than the zonal component. The energy of power spectral density (PSD) of the current peaked on 14-days and 27-days periods. The first period was presumably related to the tidal oscillation, but the latter may be associated with surface winds perturbation. Furthermore, cross-PSD revealed a significant coherency between the observed currents and the surface zonal winds in the central equatorial Pacific zonal winds (180°E-160°W), which corroborates westward propagation of intra-seasonal sea surface height signals along the 5°S with its mean phase speeds of 50 cm/s, depicting the low-latitude westward Rossby waves on intra-seasonal band. Keywords: current, equatorial Pacific Ocean,  zonal winds, sea surface height, Halmahera Sea
A NUMERICAL MODELING STUDY ON UPWELLING MECHANISM IN SOUTHERN MAKASSAR STRAIT Atmadipoera, Agus S; Widyastuti, Priska
Jurnal Ilmu dan Teknologi Kelautan Tropis Vol 6, No 2 (2014): Electronik Jurnal Ilmu dan Teknologi Kelautan Tropis
Publisher : Bogor Agricultural University

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Abstract

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.