The Indonesian Throughflow plays an important role in the global ocean circulation and climate. Existing studies of the Indonesian Throughflow have focused on the Makassar Strait and the exit straits, where the upper thermocline currents carry North Pacific waters to the Indian Ocean. Here we show, using mooring observations, that a previous unknown intermediate western boundary current (with the core at ~1000 m depth) exists in the Maluku Sea, which transports intermediate waters (primarily the Antarctic Intermediate Water) from the Pacific into the Seram-Banda Seas through the Lifamatola Passage above the bottom overflow. Our results suggest the importance of the western boundary current in global ocean intermediate circulation and overturn. We anticipate that our study is the beginning of more extensive investigations of the intermediate circulation of the Indo-Pacific ocean in global overturn, which shall improve our understanding of ocean heat and CO2 storages significantly.
Hydrodynamical condition of Java sea as a part of Indian-Pacific throughflow system which is influenced by monsoon will affect the condition of Banten bay such tidal current. Bordered by Java sea makes Banten bay preoccupied with fisheries and shipping activities, so the information of current pattern e.g. tidal current is very necessary. This study aims to simulate the tidal current pattern using flow model fm as a numerical approach. Two-dimensional hydrodynamic model was employed to perform the simulation of tidal current. Model was validated by using current and tidal observation data which was taken on September 2015 and April 2016. The result shows that the current moved southwestern toward the land during high neap and high spring tidal conditions which ranged 0 – 0.142 m/s at the first transitional monsoon and 0-0.153 m/s at second transitional monsoon. During low spring tidal condition for both transitional monsoon, the current flowed northwestward on west side and northeastward on east side within the bay which ranged 0 – 0.137 m/s and 0 – 0.127 m/s respectively. The hydrodynamic conditions of Banten Bay are severe different between 2 transitional seasons, especially for the current speed and direction. It induces a different transport mechanism, resulting the unstable accretion and abrasion along Banten Bay coast.
The ocean currents in the Halmahera Sea are studied using a subsurface mooring deployed in the Jailolo Strait from November 2015 to October 2017. The subtidal currents of the mooring measurements are characterized by a two-layer system, with the current variability below about 200 m in opposite phases to that in the upper layer. The mean along-strait velocity (ASV) is toward the Indonesian seas in the whole water column, producing an estimated mean transport of 2.44 ± 0.42 Sv (1 Sv ≡ 106 m3 s−1). The errors of the transport calculation based on the single mooring measurements are estimated to be less than 15% using simulations of high-resolution ocean models. A weak current is observed to flow northward during 2017 at the bottom of the strait. The ASV variability is found to be dominated by an annual cycle both in the upper and lower layers. The total transport, however, is dominated by semiannual variability because of the cancelation of the annual transports in the upper and lower layers. The variability of the transport is suggested to be driven by the pressure difference between the Pacific Ocean and the Indonesian seas, as evidenced by the agreement between the satellite pressure gradient and the two-layer transports. The transport of the Jailolo Strait during the 2015/16 super El Niño is found to be nearly the same as that during the 2016 La Niña, suggesting that the interannual variability of the transport is much smaller than the seasonal cycle.
<p><strong><em>Abstract. </em></strong><em>Erosion or sedimentation process is an important thing to know the condition of beach. That process can be noticed from sediment’s feature. Meanwhile, the particle size of sediment is of paramount thing than other feature such as speed of deposition and mass density. This study was conducted to find out distribution of particle size in Dalegan beach. Samples were collected from 15 sampling sites in different zones (zone A: lowest tide zone, zone B: 5 meters from zone A, zone C: 5 meters from zone B) with purposive sampling method. Sediments were grouped by Wentworth scale. Sieve and Granulometry analysis were used in this research to know type of sediment and its distribution. Results of study showed that the dominant of sediment type is fine sand. The spreading of this type be more dominant to the open sea and west direction along the coast. The condition of this spreading can be potential to make a change of beach condition.</em><em></em></p><p><strong><em>Keywords</em></strong><em>: </em><em>Particle size; Sediment; Fine Sand; Granulometry</em><em></em></p><p><strong>Abstrak. </strong>Proses erosi dan sedimentasi adalah hal yang penting untuk mengetahui kondisi pantai. Proses tersebut dapat diketahui dengan sifat-sifat sedimen. Ukuran butir sedimen merupakan hal yang terpenting diantara sifat-sifat sedimen yang lainnya seperti kecepatan endap dan kepadatan massa. Tujuan penelitian ini ialah untuk mengetahui distribusi ukuran butir sedimen di Pantai Dalegan. Sampel dikumpulkan dari 15 titik sampling yang berbeda dari 3 zona (zona A : zona surut terendah, zona B : zona 5 meter dari zona A dan zona C : zona 5 meter dari zona B) menggunakan purposive sampling method. Sedimen dikelompokkan dengan skala Wenworth. Analisis ayakan dan granulometri digunakan untuk mengetahui jenis sedimen dan penyebaran ukuran butirnya. Hasil penelitian menunjukkan bahwa jenis sedimen yang mendominasi adalah pasir halus. Penyebaran jenis sedimen ini lebih cenderung dominan ke arah laut terbuka dan semakin ke barat dari pantai. Kondisi penyebaran distribusi ukuran butir sedimen dapat berpotesi membuat perubahan pada kondisi pantai.</p><div><p><strong>Kata kunci</strong> : Ukuran Butir; Sedimen; Pasir Halus; Granulometri</p></div>
Hydrographic measurements recently acquired along the thalweg of the Lifamatola Passage combined with historical moored velocity measurements immediately downstream of the sill are used to study the hydraulics, transport, mixing, and entrainment in the dense overflow. The observations suggest that the mean overflow is nearly critical at the mooring site, suggesting that a weir formula may be appropriate for estimating the overflow transport. Our assessment suggests that the weir formulae corresponding to a rectangular, triangular, or parabolic cross section all result in transports very close to the observation, suggesting their potential usage in long-term monitoring of the overflow transport or parameterizing the transport in numerical models. Analyses also suggest that deep signals within the overflow layer are blocked by the shear flow from propagating upstream, whereas the shallow wave modes of the full-depth continuously stratified flow are able to propagate upstream from the Banda Sea into the Maluku Sea. Strong mixing is found immediately downstream of the sill crest, with Thorpe-scale-based estimates of the mean dissipation rate within the overflow up to 1.1 × 10−7 W kg−1 and the region-averaged diapycnal diffusivity within the downstream overflow in the range of 2.3 × 10−3 m2 s−1 to 10.1 × 10−3 m2 s−1. Mixing in the Lifamatola Passage results in 0.6-1.2 Sv entrainment transport added to the overflow, enhancing the deep-water renewal in the Banda Sea. A bulk diffusivity coefficient estimated in the deep Banda Sea yields 1.6 × 10−3 ± 5 × 10−4 m2 s−1, with associated downward turbulent heat flux of 9 W m−2.
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