Investigasi Arus Sejajar Pantai (Longshore Current) di Daerah Abrasi Bengkulu Utara

The coastal area of Serangai Village is directly facing the open sea; as a result it is vulnerable to coastal abrasion. Longshore currents can accelerate the process of coastal abrasion. The study was aimed to determine the speed and direction of current as well as the existence of the longshore current at the Serangai. Field observation was conducted on 5-7 November 2018. The results showed that the frequency distribution of current at speed of 0-10 cm/s reached 69%, and at speed of 10-20 cm/s reached 25%. The highest speed of 20-30 cm/s has a frequency of 6 %. Moreover, the direction of the majority of ocean currents is to the southeast (120o-150o), showing that the current is more likely to be parallel to the shoreline called longshore current that can accelerate shoreline Serangai Village, Bengkulu. However, further research is needed to see variability of current associated with the season (monsoon). Wilayah pesisir Desa Serangai berhadapan langsung dengan laut lepas; sehingga rentan terhadap abrasi pantai. Arus sejajar pantai dapat mempercepat proses abrasi pantai. Penelitian bertujuan untuk mengetahui kecepatan dan arah arus serta keberadaan arus sejajar pantai di Serangai. Pengamatan lapangan dilakukan pada tanggal 5-7 November 2018. Hasil penelitian menunjukkan bahwa distribusi frekuensi arus pada kecepatan 0-10 cm/s mencapai 69%, dan pada kecepatan 10-20 cm/s mencapai 25%. Kecepatan tertinggi 20-30 cm/s memiliki frekuensi 6%. Selain itu, arah arus laut mayoritas ke arah tenggara (120o-150o), menunjukkan bahwa arus lebih cenderung sejajar dengan garis pantai yang disebut arus sejajar pantai yang dapat mempercepat garis pantai Desa Serangai, Bengkulu. Namun, penelitian lebih lanjut diperlukan untuk melihat variabilitas arus yang terkait dengan musim (monsun)

Observation of Coastal Front and Circulation in the Northeastern Java Sea, Indonesia

The structure and spatial extent of a coastal front and circulation in the shallow (<55 m depth) northeastern Java Sea in Indonesia was investigated with a new dataset of high-resolution conductivity-temperature-depth (CTD) and along-track shipboard acoustic Doppler current profiler (SADCP) during a DIKTI-LIPI 2010 joint research cruise on R.V. Baruna Jaya 8. The coastal front separates fresh warm coastal water derived mainly from Barito River discharge and the saline, cool Java Sea water. The surface fresh water plume extends approximately 760 km from the Barito River estuary to the south, and its thickness varies from the surface to 10 m and 20 m depth, depending on its proximity to the fresh water source. The front is aligned a northeast and east direction, probably related to a meandering of strong northeastward monsoon current in the eastern part of the Java Sea during the observation time

Perubahan Spasial dan Temporal Luas Wilayah untuk Pengembangan Wisata Bahari di Bagaian Barat Pulau Gili Ketapang Probolinggo Jawa Timur

Pulau Gili Ketapang yang berpenduduk padat, dengan kepadatan mencapai 12.356 jiwa/ km2 dan mempunyai luasan sebesar 68 hektar atau 0,68 km2 termasuk katagori pulau kecil. Dengan adanya Perda Kab. Probolinggo no15 th.2001 menjadika Pulau Gili Ketapang menjadi salah satu destinasi wisata bahari di Kab.Probolinggo, pesona pasir putih di barat wilayah dari Pulau Gili Ketapang yang menjadi salah satu daya tarik wisatawan. Perubahan luasan wilayah hamparan pasir putih tersebut akan mengurangi wilayah hamparan pasir putih tersebut karena kehilangan hamparan pasir tersebut akan mengurangi keragaman destinasi wisata. Metoda penelitian menggunakan google earth image digunakan sebagai sumber masukan utama untuk membuat peta perubahan wilayah selain penelitian lapangan yang berupa pengukuran garis pantai, batimetri dan pola arus di wilayah perairan Gili Ketapang. Dari data citra Satelit dari tahun 2004 sampai tahun 2018 terjadi penyusutan luas wilayah untuk pasir putih di Barat Pulau Gili Ketapang sebesar 0.288 Ha. Batimetri Perairan Gili Ketapang secara umum memiliki kedalaman terukur antara 0-34 meter, Daerah terdalam terdapat disebelah utara Pulau Gili Ketapang dengan jarak sekitar 1.700 m. Sebelah Barat dari Pulau Gili Ketapang memiliki dasar laut yang agak dangkal kurang dari 20 m sehingga sangat cocok untuk dikembangkan menjadi daerah wisata bahari

A Maluku Sea intermediate western boundary current connecting Pacific Ocean circulation to the Indonesian Throughflow

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Yuan, D., Yin, X., Li, X., Corvianawatie, C., Wang, Z., Li, Y., Yang, Y., Hu, X., Wang, J., Tan, S., Surinati, D., Purwandana, A., Wardana, A., Ismail, M., Budiman, A., Bayhaqi, A., Avianto, P., Santoso, P., Kusmanto, E., Dirhamsyah, Arifin, Z., & Pratt, L. A Maluku Sea intermediate western boundary current connecting Pacific Ocean circulation to the Indonesian Throughflow. Nature Communications, 13(1), (2022): 2093, https://doi.org/10.1038/s41467-022-29617-6.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.This study is supported by NSFC (D.Y., Z.W., Y.L., Y.Y., S.T., J.W., and X.L.: 41720104008; D.Y., J.W., Y.L., X.L., Y.Y., S.T., X.H., and X.Y.: 91858204), the National Key Research and Development Program of China (D.Y. and X.L.: 2020YFA0608800), CAS (D.Y., Z.W., J.W., and Y.L.: XDB42000000), projects. Affiliations 1 and 2 share the first position. D.Y. is supported by QMSNL (2018SDKJ0104-02), and Shandong Provincial (U1606402) and the “Kunpeng Outstanding Scholar Program” of the FIO/NMR of China, J.W. supported by NSFC (41776011), Z.W. by NSFC (41876025)

Arus Rip di Perairan Pesisir Pangandaran, Jawa Barat (Rip Current in Pangandaran Coastal Water, West Java)

Perairan pesisir Pangandaran adalah bagian dari perairan pesisir Teluk Parigi dan merupakan bagian yang paling tenang. Keadaan tersebut menyebabkan pantai Pangandaran berkembang menjadi tempat tujuan wisata pantai yang terkenal. Penelitian dilakukan di bagian pantai dimana arus rip diketahui sering terjadi. Gambaran tentang arus rip dilakukan dengan pengamatan visual dan pendekatan analisis kondisi morfologi pantai, batimetri atau morfologi dasar laut, kondisi gelombang, kecepatan dan arah arus, serta kekeruhan. Hasil penelitian ini menunjukkan bahwa arus rip merupakan kejadian yang umum di kawasan pesisir Teluk Parigi, dan sering muncul di bagian tertentu pantai Pangandaran yang telah dipandang aman. Swell dengan kisaran periode 6,57– 8,91 dt dari Samudera Hindia dengan arah hampir tegak lurus garis pantai diduga merupakan gelombang pencetusnya. Hasil penelitian menunjukkan enam arus rip dengan kecepatan berkisar dari 0,8–1 m.dt-1. Rekaman data kekeruhan membuktikan arus rip tersebut membawa muatan sedimen dari tepi pantai ke tengah laut. Data batimetri di lokasi penelitian memperlihatkan adanya morfologi dasar laut yang bergelombang membentuk punggungan dan lembah memanjang dari pantai ke arah laut lepas. Posisi kejadian arus rip yang tidak spesifik di lembah atau punggungan menunjukkan tidak adanya kontrol morfologi dasar laut terhadap kejadian arus rip. Kata kunci: arus rip, swell, pantai pasir, perairan pesisir, Pangandaran Pangandaran coastal waters is coastal tourism site that situated at the calmest part of Parigi Bay coastal waters. The favorable coastal area condition has made the coastal zone growth to be favorite coastal tourism site. The study site was coastal segment where rip currents frequently occur. This research was conducted by visual observation of rip currents and coastal morphology analysis approach, bathymetry survey, wave conditions, the speed and direction of currents, and turbidity. Results of this study indicate that rip currents are common phenomena at the Parigi Bay coastal area, and the currents frequently occur at several parts of the Pangandaran coastal zone, which are supposed to be safe. The rip currents could be identified visually. Swell with periods of 6.57 to 8.91 s propagating from the Indian Ocean in nearly normal direction to the coastline of Pangandaran could be the cause of rip currents. During field work of this study, it was recorded the existing of six rip currents with speeds in the range of 0,8–1 m.s-1. Obtained backscatterance records indicated that the recorded rip currents transport sediment load seaward from swash zone. Bathymetry data records of the study area showed an existing of undulating submarine morphology with axis lines normal to coastline. However, position of the rip current occurrence had no a good correlation with the undulating morphology. The facts indicate that no control of seabed morphology on rip current occurrence.   Keywords: rip current, swell, sandy beach, coastal waters, Pangandara

Suhu dan Salinitas Permukaan Merupakan Indikator Upwelling Sebagai Respon Terhadap Angin Muson Tenggara di Perairan Bagian Utara Laut Sawu (Surface Temperature and Salinity are Indicators of Upwelling In Response to Southeast Moonson in the Savu Sea)

Laut Sawu merupakan bagian perairan Indonesia yang secara langsung berbatasan dengan Samudera Hindia. Di bagian utara, terutama perairan selatan Selat Flores, Selat Lamakera dan Selat Alor merupakan perairan dinamik dengan perubahan suhu dan salinitas permukaan yang signifikan pada musim angin muson tenggara. Dinamika perairan tersebut terutama di lapisan permukaan sangat dipengaruhi pola tiupan angin muson. Pada bulan Juni-Juli angin muson tenggara bertiup dengan kekuatan maksimum di sebagian wilayah Indonesia termasuk di bagian utara Laut Sawu. Tiupan angin tersebut menyebabkan pergerakan massa air permukaan cenderung bergerak ke arah barat. Keadaan tersebut menyebabkan terjadinya pengangkatan massa air lapisan dalam ke permukaan di bagian utara Laut Sawu. Suhu permukaan laut di laut Flores berkisar antara 27,45-27,79 oC dengan rerata 27,62±0,14 oC, sedangkan pada stasiun pengamatan di bagian selatan dan berhubungan langsung dengan Laut Sawu, suhu perairan berkisar 25,25-26,75 oC dengan rerata 25,90±0,43oC. Secara umum sebaran suhu pada lapisan permukaan laut pada kedalaman 0-5 m menunjukkan semakin ke selatan massa air permukaan laut semakin dingin. Pusat konsentrasi massa air dengan suhu terendah di selatan Selat Alor berkisar antara 25,25-25,89oC. Dinginnya massa air perairan bagian utara Laut Sawu mengindikasikan kemungkinan terjadi pengangkatan massa air dalam ke permukaan pada perairan tersebut. Kata kunci: Laut Sawu, upwelling, salinitas, suhu permukaan laut, termoklin Savu Sea waters are part of Indonesia waters which is located directly adjacent to Indian Ocean. The northern part of Savu Sea particularly in the south of Flores Strait, Lamakera Strait and the Strait of Alor waters are dynamic with changes in temperature and salinity of the surface which is significant at southeast monsoon season. The dynamics of these waters, especially in the surface layer is strongly influenced by the monsoon wind patterns. In June-July, the monsoon winds blowing from southeast with maximum strength in parts of Indonesia, including in the waters of the northern Sea Savu. The wind causes the movement of surface water masses tend to move westward. These circumstances would to bring deeper and colder waters to the surface layer in the northern part of Savu Sea. Sea surface temperature in the Flores Sea ranged from 27.45 to 27.79°C with a mean 27.62 ± 0.14°C, whereas the observation stations located in the south and deal directly with the Savu Sea, water temperatures in the range 25.25 to 26.75°C with a mean 25.90 ± 0.43°C. In general, the temperature distribution on the surface layer of the ocean at a depth of 0-5 m to the south indicates that the mass of sea water gets colder. Central mass concentration of water with the lowest temperature in the southern Strait of Alor range from 25.25 to 25.89°C. The cold waters of the northern part of the Savu Sea water mass indicates the possibility upwelling of water mass in the Savu waters. Key words: Savu sea, upwelling, salinity, sea surface temperature, thermoclin

Studi Arus Sejajar Pantai dan Variasi Arus Laut Terhadap Kedalaman di Daerah Perairan Pantai Pasar Palik, Bengkulu Utara

Kajian arus sejajar pantai serta variasi arus kedalaman telah dilakukan di wilayah pesisir Pantai Pasir Palik dimana daerah ini merupakan salah satu wilayah pesisir yang paling rawan terhadap abrasi pantai di Provinsi Bengkulu Utara. Pengumpulan data arus laut beserta arahnya pada tiga lokasi berbeda dilakukan pada 6 - 8 November 2018 dengan menggunakan peralatan RCM Seaguard Aanderaa. Untuk mengetahui keberadaan arus sejajar pantai, data arus pada dua lokasi dianalisis dengan current rose. Data arus dari lokasi ketiga juga telah dianalisis untuk mempelajari variabilitas arus terhadap kedalaman. Hasil penelitian menunjukkan bahwa kecepatan arus rata-rata pada lokasi 1 adalah 7,1 cm/s, dan lokasi 2 adalah 12,4 cm/s. Arah arus di lokasi 1 dan lokasi 2 dominan ke arah tenggara dan selatan-tenggara. Selain itu, variasi arus terhadap kedalaman di daerah pesisir Pantai Pasir Palik telah diamati baik besaran maupun arahnya dengan kecepatan arus rata-rata setiap kedalaman berkisar antara 12,55-44,35 cm/s. Arah dominan arus laut yang teramati sejajar dengan garis pantai, menunjukkan keberadaan arus sejajar pantai di daerah Pantai Pasar Palik, Lais, Bengkulu Utara. Fenomena ini mungkin berhubungan dengan peristiwa abrasi pantai di sepanjang pantai karena arus sejajar pantai dapat menyebabkan erosi dan mengalirkan sedimen ke arah tenggara dan selatan-tenggara menuju Kota Bengkulu

The sediments of Lake Singkarak and Lake Maninjau in West Sumatra reveal their earthquake, volcanic and rainfall history

International audienceNatural hazards such as earthquakes, volcanic activity, and heavy rainfall causing floods and debris avalanches are common phenomena in many tropical settings, including the island of Sumatra, located in the Indonesian archipelago. To enhance our understanding of the recurrence of these often destructive events, we studied the sedimentary infill of two lakes in the Padang highlands, West Sumatra. This includes Lake Singkarak, a tectonically-formed lake located on a step-over of a major strike-slip fault system (the Sumatran Fault), and Lake Maninjau, a caldera lake. Both lakes are located -300 km from the Sunda subduction trench and surrounded by steep slopes and a chain of active volcanoes. Hence, considering their unique tectonic setting, these lakes may potentially record a wide range of natural hazards that affect the region. A combination of seismic-reflection pro¬files and short sediment cores revealed that both lakes indeed record various types of natural hazards, each with their own sedimentary response to a specific type of event. Lake Singkarak can be used to study past floods and major debris avalanches in addition to high-magnitude megathrust earthquakes, while traces of past intraplate earthquakes have been identified in both lakes. Furthermore, we argue that Lake Singkarak is an ideal recorder of volcanic activity in the region, while Lake Maninjau itself can pose a volcanic hazard toits surroundings as demonstrated by potential activity of the volcano below the lak