Sebaran Spasial Suhu, Salinitas dan Densitas di Perairan Kepulauan Sangihe Talaud Sulawesi Utara

The Sangihe Talaud waters are part of the toll road of the Indonesian Throughflow, which has an important role in the transport of seawater properties from the Pacific Ocean to the Indian Ocean. To understand the distribution pattern of physical oceanography parameters namely temperature, salinity, density around the waters of Sangihe Talaud, the research expedition Widya Nusantara Expedition (EWIN) has been conducted using the research vessel Baruna Jaya VIII. The temperature, salinity, and density of the seawater were measured using the CTD Seabird 911plus instrument at 33 stations distributed on the Sangihe Talaud waters. The results of the temperature analysis showed the presence of surface temperature zoning between the Sulawesi Sea and the north of the Maluku Sea, while the salinity distribution showed a low to high salinity gradient from the east to the west side of the Sangihe Talaud waters. The density distribution represents three zones of surface density detected in the north of the Maluku Sea, the northeast side and the west side of the Sangihe and Talaud waters.  Perairan kepulauan Sangihe Talaud merupakan bagian dari jalur tol laut Arus Lintas Indonesia yang memiliki peran penting dalam transpor properti air laut dari Samudera Pasifik ke Samudera Hindia. Untuk mengungkap pola sebaran parameter oseanografi fisik seperti suhu, salinitas dan densitas laut di perairan kepulauan Sangihe Talaud, telah dilakukan kegiatan penelitian Ekspedisi Widya Nusantara (EWIN) dengan menggunakan kapal riset Baruna Jaya VIII. Suhu, salinitas, dan densitas air laut diukur dengan menggunakan instrumen CTD Seabird 911Plus pada 33 stasiun pengamatan yang tersebar di perairan Kepulauan Sangihe Talaud. Hasil Analisa suhu menunjukan adanya zonasi sebaran suhu permukaan antara laut Sulawesi dan utara Laut Maluku, adapun sebaran salinitas menunjukan adanya gradien salinitas rendah ke tinggi dari sisi timur ke sisi barat perairan kepulauan Sangihe Talaud. Sedangkan sebaran densitas laut memperlihatkan adanya tiga zonasi densitas permukaan yang terdeteksi di utara Laut Maluku, sisi timur laut dan sisi barat perairan kepulauan Sangihe Talaud

Remote sensing of upwelling off Australia's north-east coast

Cross-shelf processes drive the exchange of water between the continental shelf and western boundary currents, leading to the import and export of heat, freshwater, sediments, nutrients, plankton, fish larvae, and other properties. Upwelling is an important process which modulates those exchanges. It regulates primary productivity, which in turn promotes higher trophic levels and fisheries. In this paper, we investigate upwelling events in the East Australian Current (EAC) intensification zone off Southeast Queensland through the analysis of remotely-sensed Chlorophyll-a (Chl-a) and Sea Surface Temperature (SST) as well as wind and ocean reanalysis products. A particular focus is on identifying the likely mechanisms that drive upwelling events during the austral autumn to winter which are evident from cold SST and enhanced Chl-a concentrations. Four complementary Upwelling Indices (UIs) are derived. Chl-a (UIChla) and SST (UISST) based indices characterize the oceanic response to upwelling, while indices based on wind (UIw) and current (UIc) data capture the forcing of upwelling. The spatial and temporal variability of all UIs is examined over the continental shelf. It reveals distinct seasonal patterns. For the northern region, UIs identify the well-known Southeast Fraser Island Upwelling System. It prevails during the austral spring to early summer and is driven by current- and upwelling favourable wind. In contrast, upwelling is enhanced over the southern shelf during austral autumn to winter. About 70% of all UISST and UIChla identified upwelling events occur during this period. A case study is presented that provides observational evidence for the existence of a shelf-break upwelling. Simultaneous downwelling favourable wind stress and upwelling favourable current-driven bottom stress establish a flow convergence in the bottom boundary layer (BBL). These convergent BBL flows force upwelling of cold and nutrient-rich slope waters as evident from negative SST anomaly and enhanced Chl-a in austral autumn to winter. It is evident from these results that the shelf region is characterised by two distinct seasonally reoccurring upwelling regimes

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)

ANALISIS SPASIAL PERUBAHAN GARIS PANTAI DI PESISIR KABUPATEN SUBANG, JAWA BARAT

Pengamatan mengenai perubahan garis pantai di pesisir Kabupaten Subang, Jawa Barat telah dilakukan dengan menggunakan program Digital Shoreline Analysis System berdasarkan citra satelit Landsat TM dari tahun 1996–2010. Tujuan dari penelitian ini adalah untuk mengetahui besar perubahan garis pantai di Kabupaten Subang serta zonasi kawasan yang mengalami perubahan garis pantai tersebut. Metode yang digunakan adalah pemprosesan citra dan survey lapangan. Hasil dari penelitian ini menunjukkan bahwa dari tahun 1996–2010 perairan pesisir Kabupaten Subang mengalami perubahan garis pantai oleh adanya akresi dan abrasi yang maksimalnya sejauh lebih dari 1 km. Hasil analisis regresi antara perubahan waktu dengan akresi serta abrasi memberikan nilai positif. Secara keseluruhan, lebih dari 50% panjang pesisir Kabupaten Subang dikategorikan dalam kerusakan yang parah. Perubahan garis pantai di Pesisir Kabupaten Subang terjadi terutama karena kegiatan pembangunan di sekitar pesisir seperti pembukaan lahan mangrove menjadi tambak dan sawah, pembangunan pemukiman, serta transpor sedimen dari sungai-sungai di kawasan pesisir Kabupaten Subang. Kata kunci: perubahan garis pantai, Kabupaten Subang, citra satelit, akresi, abrasi.   Observation of coastal shoreline changes in the Subang District was conducted using Digital Shoreline Analysis System Program based on the satellite images of Landsat TM from 1996 to 2010. The purpose of this study was to determine the distance of shoreline change and the zoning area in the Coastal of Subang District. Methods used in this study were images processing and field survey. The results of the study indicated the presence of shoreline changes which experienced maximum accretion and abrasion of more than 1 km between 1996 to 2010. The results of regression analysis between time and accretion as well as time and abrasion showed positive correlation. More than 50% the coastal area of Kabupaten Subang was in severely damaged con­dition. Coastal shoreline change in Kabupaten Subang occurred mainly due to the developmental activities such as residential construction, coastal mangrove conversion to ponds and rice paddies and sediment transport from the river around Kabupaten Subang. Keywords: shoreline change, Subang District, satellite images, accretion, abrasion

On the cross-shelf exchange driven by frontal eddies along a western boundary current during austral winter 2007

Western boundary currents are characterized by high mesoscale eddy activity including that of cyclonic frontal eddies (CFEs). These form frequently adjacent to the shelf-break, export coastal water and affect biological productivity. Here, we study the physical properties of eddies identified within the intensification zone of the East Australian Current (EAC) through the analysis of remotely sensed data, the application of an ocean circulation model and the evaluation of Lagrangian simulations during austral winter 2007. We examine the spatial and temporal evolution of identified eddies, investigate their formation mechanism, and quantify the contribution made to cross-shelf exchanges. The mesoscale eddies are tracked from generation to decay using an eddy detection and tracking method. In this case study, we identify two CFEs referred to as C1 and C2 with lifetimes of 11 and 38 days and radii of 45 and 70 km, respectively, and one anticyclonic eddy (ACE) with a lifetime of 62 days and a radius of 60 km. Both CFEs interact with the ACE leading to quasi-stationary dipole-eddies located in the vicinity of the shelf. This is the first time dipole-eddies are reported for the intensification zone of the EAC. The location of CFEs characterised by negative sea surface height anomaly (SSHA) and clockwise rotation coincides with remotely-sensed sea surface temperature (SST) and chlorophyll-a (Chl-a) anomalies. CFEs C1 and C2 appear to contribute in different ways to the cross-shelf transport along the shelf-break. CFE C1 drives a stronger onshore transport, while CFE C2 appears to enhance the offshore transport. The estimated daily cross-shelf export of shelf water associated with CFE C2 is estimated with about 1.23 Sv (~106 km3 day-1). It renews the regional shelf water in about 7 days. The lifetime of CFE C2 is about 38 days, thus the eddy had the potential to flush the shelf at least five times. The transient CFEs were found for the first time to intensify the cross-shelf exchange that is due to the wind-driven cyclonic circulation of the Fraser Gyre. This seasonally occurring gyre dominates the local shelf during austral autumn and winter. The results from this study demonstrate the importance of CFEs in exporting cooler and Chl-a enriched shelf water into the warmer and oligotrophic waters of the southward-flowing EAC

Frontal eddies along a western boundary current

Cyclonic frontal eddies are distinguishable from the surrounding water due to their unique biological and physical characteristics and have been observed in all western boundary current regions. These eddies spawn from cut-off meanders and are found on the landward side of the current. Here, we report for the first time observed frontal eddies for the intensification zone (north of 28 oS) of the East Australian Current (EAC) off Southeast Queensland, Australia, by analysing remotely sensed sea surface temperature (SST) and chlorophyll-a (Chl-a) data. The frontal eddies were detected initially in the analysis of satellite tracked surface drifters. The shelf-crossing cyclonic drifter pathways indicated the presence of drifter-trapping cyclonic frontal eddies. The subsequent analysis of satellite images allows to quantify key eddy characteristics, cross-shelf volume transports associated with eddy filaments, eddy-driven shelf water renewal time scales, and export of total Chl-a and carbon per day. The observed frontal eddies have core radii of approximately 13 km and 15 km. The cold core surface SST anomaly and elevated chl-a indicates eddy entrainment of shelf water. The translational or core displacement velocity is estimated with 0.17 m.s-1 or 15 km per day and the tangential velocity quantified from tracking surface drifters is 0.28 m.s-1 to - 0.5 m.s-1. This results in a rotational period of 1.9 days to 3.9 days. We use maximum Chl-a and SST gradients to approximate the width of importing and exporting filaments associated with the frontal eddy to derive volume transports of 1.5 Sv and 1.9 Sv (import) and 0.3 Sv and 1.8 Sv (export), respectively. Chl-a concentrations of the exporting filaments are about 0.4 mg.m-3 to 0.6 mg.m-3 yielding a total export of 13 t to 78 t of Chl-a per day. The frontal eddy induced on-shelf transport of 130 km3 - 160 km3 per day represents between 18 % and 22 % of the shelf volume. Therefore, it would take approximately five days to renew all shelf water. We conclude that the observed frontal eddies of the northern intensification zone of the EAC potentially play an important role in determining cross-shelf exchanges, contribute to on-shelf marine conditions, enhancing coastal primary productivity and are possibly important to the export of shelf water properties such as the fish larvae of subtropical species via entrainment

The Fraser Gyre: a cyclonic eddy off the coast of eastern Australia

This paper examines the on-shelf circulation of the eastern Australian continental shelf for a region off southeast Queensland. We identify a characteristic seasonally reoccurring wind-driven cyclonic flow. It influences the cross-shelf exchange with the East Australian Current (EAC), which is the western boundary current of the South Pacific Ocean. We refer to this cyclonic circulation as the Fraser Gyre. It is located south of Fraser Island between about 25oS and 27oS. The region is adjacent to the intensification zone of the EAC where the current accelerates and establishes a swift, albeit seasonally variable southward boundary flow. Through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly, satellite tracked surface drifters, ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry, we find that the on-shelf Fraser Gyre develops during the southern hemisphere autumn and winter months. The gyre is associated with a longshore near-coast northward flow. Maximum northward on-shelf depth averaged velocities are estimated with about 0.15 – 0.26 ms-1. The flow turns eastward just to the south of Fraser Island and joins the persistent southward EAC flow along the shelf break. The annual mean net cross-shelf outward and inward flow associated with the gyre is about -1.17 ± 0.23 Sv in the north and 0.23 ± 0.13 Sv (1 Sv =.106 m3s-1) in the south. Mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3.3 days due to the Fraser Gyre retaining water over the shelf, however, monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter. The southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing Fraser Gyre. The conceptual model of the Fraser Gyre is consistent with general physical principals of the coastal shelf circulation. A southerly wind is associated with surface layer flow toward the coast, a near coast positive SSHa with a current in the direction of the wind, down-welling and export of shelf water. The Fraser Gyre influenced cross-shelf exchanges are possibly facilitating the offshore transport of fish larvae, sediments, nutrients, river discharges, and other properties across the shelf break and into the southward flowing EAC during the austral autumn and winter

Propagation of tropical squall line-induced storm coastal inundation episodes in Java-Bali, Indonesia

The short-lived tropical squall lines could trigger weather-related hazards to the northern part of the Indonesia Maritime Continent (IMC), such as Sumatra and Kalimantan. Herein, we investigated the rare propagation event of the long-lived Sumatra squall line associated with a severe storm surge that induced coastal inundation in Java-Bali with devastating impacts from 22 May–2 June 2020. With a comprehensive approach combining observational, numerical, and analytical studies, for the first time, we proposed the possible mechanism related to the long-lived squall line over the IMC, which represents the largest equatorial tropical region with the most complicated air-sea interaction area in the world. Our findings suggest that the long-lived squall line related to the supercell-like thunderstorm initiated from multicell over central Sumatra on May 20, 2020, continuously propagated southeastward until several days later reached Bali. The near-quasi steady convective line has 6 hours of time travel from central Sumatra to west Java. The supercell-like rapidly develops from multicell with a deep convective updraft under the strong and fast cold pool (∼13.8 m s−1). The further southeastward propagation of squall line with broken line type seems reinforced by low-level moist transport from the Java Sea. This study also suggested that this unusual event of a long-lived squall line might occur more frequently in the warming upper ocean in the IMC