Sumba Strait Research Articles

First occurrence of planktonic foraminiferal species Boliella adamsii as a marker for the Pleistocene-Holocene Boundary in the sea around Sumba Island

The expensive cost of Accelerator Mass Spectrometry radiocarbon dating (AMS 14C), the main tool for geochronology in Late Pleistocene-Holocene paleoclimate and paleoceanography study using marine sediment cores, hinders Indonesian researchers to produce competing research outputs. The first occurrences of planktonic foraminiferal species which have been applied as Pleistocene-Holocene Boundary markers in previous Quarternary marine sediment studies in the Indonesian region need to be confirmed as these species might actually occur since the Late Pleistocene. Quantitative foraminifera determination and oxygen isotope (δ18O) analysis of planktonic foraminiferal species Globigerinoides (Gs.) ruber have been carried out in marine sediment cores ST10 (off south Sumba) and ST14 (Sumba strait). δ18O of Gs. ruber was correlated to North Greenland Ice Core Project (NGRIP) Greenland Ice Core Chronology 2005 (GICC05) δ18O to determine the depth of the Pleistocene-Holocene Boundary (11653 BP) in core ST10 and ST14. Pleistocene-Holocene Boundary depth in core ST10 (31 cm) and ST14 (28 cm) are nearly coeval with the First occurrence (FO) of planktonic foraminifera Boliella adamsii, which at 34-35 cm depth interval in core ST10 and at 26-27 cm depth interval in core ST14. This indicated the practicality of Boliella adamsii FO as a Pleistocene-Holocene Boundary marker in the sea around Sumba Island, in case radiocarbon ages and proper planktonic foraminiferal δ18O data are not available. Future studies using a similar method in other Indonesian regions are needed to confirm the practicality of Boliella adamsii FO as a Pleistocene-Holocene Boundary marker in the Indonesian region.

EA SURFACE PALEOPRODUCTIVITY RECONSTRUCTION BASED ON FORAMINIFERAL ACCUMULATION RATE IN THE WESTERN SAVU STRAIT SINCE THE LAST GLACIAL MAXIMUM (~23 KA BP)

Despite its importance, sea surface paleoproductivity of the western Savu Strait is not well studied. Results from previous studies at the nearby Southwest Sumba and Sumba Strait might not be applicable due to the oceanographic difference. Foraminiferal proxies from gravity core ST10 were applied to generate sea surface paleoproductivity and thermocline depth reconstruction. Foraminiferal Accumulation Rate and Benthic Foraminiferal Accumulation Rate were used as paleoproductivity proxies while the thermocline dwellers’ relative abundance was applied as the thermocline depth proxy. This study suggested paleoproductivity increase during the Last Glacial Maximum (LGM)–~16 ka BP and Holocene (after ~11.65 ka BP) in the western Savu Strait. Thermocline depth was relatively shallower during the LGM–Last Deglaciation and became deeper afterwards. Paleoproductivity increase at LGM–~16 ka BP was caused by the Australian-Indonesian winter monsoon (AIWM)-like condition, characterized by intense coastal upwelling while the Holocene paleoproductivity increase was related to the abrupt rainfall increase which enhanced terrestrial/riverine input. Thermocline depth variability in the western Savu Strait is in-phase with thermocline depth variability in the Java upwelling region, characterized by a shallower thermocline during the LGM–Last Deglaciation (before ~11.65 ka BP) and a deeper thermocline during the Holocene (after ~11.65 ka BP). This thermocline depth shifting indicates a strong Australian-Indonesian Monsoon (AIM) influence on the paleoceanography of the western Savu Strait since LGM.

Australian–Indonesian monsoon rainfall responses to the northern hemisphere climatic changes prior to the Last Glacial Maximum: an early indication

The evidences of Australian-Indonesian monsoon (AIM) rainfall response to the northern hemisphere climatic changes from both marine and terrestrial proxies are well established for the Last Glacial Maximum (LGM) – Deglaciation time interval but not in the previous time interval. Sediment cores from off south Sumba (ST10) and off north Sumba (Sumba strait) (ST14) were analyzed using X-Ray Fluorescence method to obtain elemental proxies. Elemental ratios which reflect terrigenous input (Ti/Ca and K/Ca) are used to infer the AIM rainfall changes since ~42 ka BP. AIM rainfall changes indicate a clear response to the Heinrich Events prior to the LGM (H2, H3, and H4). H2 and H3 are corroborated with the AIM rainfall increases in off south Sumba (~24 – 26 ka BP and ~30 – 31 ka BP) while the AIM rainfall increase (~39 – 41 ka BP) in the Sumba strait indicates a response to H4. The cooler temperature during the Heinrich Events could enhance the Northern Hemisphere (NH) cold surges which eventually pushed the Austral summer Intertropical Convergence Zone (ITCZ) southward in a similar fashion to the Last Deglaciation period (~18 – 11 ka BP). The southward movement of Austral summer ITCZ should increase the research area’s exposure time to the Tropical Rain Belt (TRB) during the Australian – Indonesian summer monsoon (AISM) which eventually triggers the AIM rainfall increase. The Sumba strait AIM rainfall unresponsiveness to H2 and H3 could be related to the constant exposure time to the TRB which indicates that the southern limit of Austral summer ITCZ during its northernmost shift didn’t reach the latitude of Sumba Strait. Comparison with other proxies from the same site and other rainfall proxies from southern Indonesia and the northern Australia regions is needed to confirm the spatial extend of those responses.

Part I: Hydrological properties within the eastern Indonesian throughflow region during the INDOMIX experiment

The Indonesian Mixing (INDOMIX) cruise of July 2010, resolves the Pacific Ocean water masses spreading from the Halmahera Sea through the Seram Sea, Manipa Strait, Banda Sea, to the Ombai Strait, and along the southern margin of Lesser Sunda Arc across the northern Savu Sea, Sumba Strait, and south of Lombok Strait. This paper focuses on the characteristics and stratification of the water masses, along this path and Part II of this study discusses the biogeochemical aspects. Two companion papers on quantification of turbulent mixing have been published elsewhere. We find: a) A marked transformation of South Pacific (SP) thermocline water within a sharp salinity front between the Halmahera Seram Seas. Tidally induced vertical mixing is the main process weakening the SP stratification, as suggested by a simple 1-dimensional diffusion model forced by vertical diffusivity of INDOMIX vertical microstructure profiler dataset. The transformation of SP water by vertical mixing can occur after 3 days, which is in good agreement with previously reported water mass residence times. Lateral advection plays a minor role; b) Interleaving salinity structure within the thermocline of the central Halmahera Sea and two deeper inflow channels. The interleaving salinity features within the central Halmahera Sea thermocline occurs where vertical diffusivity is relatively weak, compared to the vertical mixing at entry/exit portal that removes the interleaving salinity features. Two deeper inflow channels (about 950 m and 740 m depth) in the entry portal of the Halmahera Sea are mapped from the multi-beam echo sounder measurement, where both channels allow the renewal of SP thermocline water and salinity interleaving processes; c) Northward flow of thermocline water (100–200 m depth) in the Manipa Strait that injects Banda homogeneous salinity water into Seram Sea that erode Halmahera salty water via strong diapycnal mixing; d) Cyclonic upper layer circulation in Banda where eastward (westward) flow occurs in the northern (southern) Banda, confirmed by recent modeling study; and e) Relative salty Indian Ocean intermediate water flowing along southern margin of the Lesser Sunda Arc, within the South Java Undercurrent. Two distinct upper thermocline water, due to different source of Indonesian Throughflow (ITF) water, are found in the Banda Sea: fresher and colder water contrasting to saltier and warmer water that converge in this confluence region. Beneath it, Banda intermediate homogeneous salinity water and low dissolved oxygen water is dominant.

Studi Pendahuluan Variasi Suhu Permukaan Laut dan Sebaran Aerosol di Laut Sawu

Research related to aerosols in Indonesia is still very minimal compared to sea surface temperature parameters and other oceanographic parameters. This study is a preliminary study that aims to determine the variation in aerosol distribution and its influence by variations in sea surface temperatures in the areas crossed by Arlindo, especially the savu sea. Savu sea surrounded by Flores islands (Sumba Regency, Kupang Regency, and Manggarai Regency) has a variation of SPL from 22 - 30 °C, where in the wetar strait, ombai strait, and sumba strait in the northwest part of sawu often occur low temperatures. While the value of aerosol spread is ranging from 0 - 0.3. Thus, a numerical model is needed that can help in analyzing the results that currently exist.

CHANGES OF THERMOCLINE DEPTH AT THE SUMBA ISLAND OFFSHORE BASED ON PLANKTONIC FORAMINIFERAL ASSEMBLAGES AND ITS IMPLICATION TO EUTROPHICATION SINCE THE LAST DEGLACIATION (~18 ka BP): A PRELIMINARY STUDY

Changes of the thermocline depth (DOT) at the Sumba Island offshore are not well-known compared to the DOT changes in the Timor Sea, the main exit passage of the Indonesian Through-flow (ITF). Planktonic foraminiferal assemblages in cores collected from the southwest Sumba offshore (ST08) and Sumba Strait (ST12, ST13, and ST14) were used as a tool to infer the DOT and paleoproductivity changes at the Sumba Island offshore. The DOT changes were indicated from the thermocline and mixed layer dwellers’ relative abundance while the paleoproductivity changes were indicated from the relative abundance of Neogloboquadrina dutertrei. This study suggests a contrast between the DOT pattern at the Sumba Island offshore and the DOT pattern in the Timor Sea during the Last Deglaciation–Holocene. The contrast DOT pattern indicated that the multi-millennial changes of the Australian-Indonesian monsoon (AIM) during the Last Deglaciation– Holocene were the main factors behind the DOT changes in this region while the effects of El Niño Southern Oscillation (ENSO) –like, Indian Ocean Dipole (IOD) –like, and ITF to DOT changes were minimal. Paleoproductivity enhancement at the Sumba Island offshore was not solely related to the monsoon-driven coastal upwelling intensification, which resulted in the DOT shoaling and eutrophic condition. The increase of nutrient availability in surface water due to river runoff increase and changes in the lifted water mass nature were also able to enhance productivity in this region.

Characteristics of Quaternary Deep Sea Sediment in the Sumba Strait based on Grain Size and LoI (Lost on ignition Analysis)

This research was conducted in the Sumba Strait, southwest of Sumba East Nusa Tenggara. The Purpose of this study is to determine the depositional facies characteristics of the Quaternary deep sediment. The sample was taken at a depth of 1858 m by gravity core in board of RV Baruna Jaya VII by the geology team of Ekspedisi Widya Nusantara LIPI 2016. The length of the sample was 246 cm. Sedimentology analysis was conducted to measure grain size distribution, organic material and carbonate content in the core. The characteristics of the sediment were dominated by coarse silt, poorly sorted, symmetrical skewness and mesokurtic kurtosis. Generally, the percentage of carbon and carbonate is 20.09% carbon and 9.67% carbonate; it shows that grain size is very influential on organic material in the sediment. The finer the grain of sediment the higher the organic material, which in the sediment results from the grain size analysis indicates the dominant grain size of the fine (Coarse silt).

Holocene climate dynamics in Sumba Strait, Indonesia: a preliminary evidence from high resolution geochemical records and planktonic foraminifera

The dynamics of climatic conditions during the Holocene in the Sumba Strait is not well known, compared with in the Indian Ocean. The aim of this paper is to identify the possible Holocene climate dynamics in Sumba Strait, eastern Indonesia by using deep-sea core sediments. A 243 cm core was taken aboard RV Baruna Jaya VIII during the Ekspedisi Widya Nusantara 2016 cruise. The core was analyzed for elemental, carbonate and organic matter content, and abundance of foraminifera. Based on geochemical and foraminifera data, we were able to identify at least six climatic changes during the Holocene in the Sumba Strait. By using the elemental ratio of terrigenous input parameter, we infer to interpret that the precipitation in the Sumba Strait during the Early Holocene was relatively higher compared with the Mid to Late Holocene.

Internal solitary wave observations in the Flores Sea using the Himawari-8 geostationary satellite

ABSTRACT The Japanese Meteorological Agency’s geostationary satellite Himawari-8/Advanced Himawari Imager (AHI) images, acquired over the Flores Sea in Indonesia, observed that long internal solitary waves (ISWs) seem to be generated from the Sape Strait, which then propagates through the Java Sea, the Sumba Strait, and the Savu Sea. Shallow water wave refraction behaviour is present during the observations. These important parameters related to the ISW propagation (wavelength, soliton number, first crest length, propagation direction, and phase speed) could also be estimated using Himawari-8 images. These observational results were also compared with Moderate Resolution Imaging Spectroradiometer (MODIS) images, Sentinel-1A Synthetic Aperture Radar (SAR) images, and the Korteweg-de Vries (KdV) equation. The geostationary satellite Himawari-8 showed great potential and was very helpful in observing the ISW propagation parameters, spatially and temporally, in the Flores Sea in detail.

Characteristics of Grain Size Distribution on Beaches Sediment of Sumba Island, Nusa Tenggara Timur Based on Grainsize and Geochemical Data

Study of beaches sediment characteristics were conducted on three beaches on Sumba Island, East Nusa Tenggara.The research is a part of Widya Nusantara Expedition which conducted by using Research Vessel of Baruna Jaya VIII. The aim of this study is to determine the characteristics of coastal deposits through the observation of grain size by using the grain size trend analysis approach (Grain Size Trend Analysis, commonly abbreviated as GSTA) and geochemical analysis. A total of 36 samples were taken on each coast representing high tide, transition and low tide along the coast. A grain size analysis was performed using a Malvern Mastersizer 2000 that was processed with Gradistat 4.0 software. Geochemical analysis was carried out using X-ray fluorescence spectrometry (XRF). The distribution of beach sediments is dominated by moderate sand - coarse sand and differences on content of geochemical elements (Ca, Sr, Fe, K, and Ti). The coastal conditions that are connected to the Indian Ocean (B1) have different characteristics from the beach that connected to the Sumba strait (B5 and B7). GSTA analysis showed sediment of Laboya Beach finer than sediment on Waikelo and Melolo Beach. Geochemical elements on Laboya Beach indicates different values than others. It indicates there are differences in the provenance and composition of sediment on the all three beaches. The supply of coastal deposits on these three beaches is influenced by the mechanism of precipitation of the walls and the processes of waves and rivers.Keywords: distribution, sediment, grainsize, geochemical, XRF, beach sediment.

Characteristics of Grain Size Distribution on Beaches Sediment of Sumba Island, Nusa Tenggara Timur Based on Grainsize and Geochemical Data

Study of beaches sediment characteristics were conducted on three beaches on Sumba Island, East Nusa Tenggara.The research is a part of Widya Nusantara Expedition which conducted by using Research Vessel of Baruna Jaya VIII. The aim of this study is to determine the characteristics of coastal deposits through the observation of grain size by using the grain size trend analysis approach (Grain Size Trend Analysis, commonly abbreviated as GSTA) and geochemical analysis. A total of 36 samples were taken on each coast representing high tide, transition and low tide along the coast. A grain size analysis was performed using a Malvern Mastersizer 2000 that was processed with Gradistat 4.0 software. Geochemical analysis was carried out using X-ray fluorescence spectrometry (XRF). The distribution of beach sediments is dominated by moderate sand - coarse sand and differences on content of geochemical elements (Ca, Sr, Fe, K, and Ti). The coastal conditions that are connected to the Indian Ocean (B1) have different characteristics from the beach that connected to the Sumba strait (B5 and B7). GSTA analysis showed sediment of Laboya Beach finer than sediment on Waikelo and Melolo Beach. Geochemical elements on Laboya Beach indicates different values than others. It indicates there are differences in the provenance and composition of sediment on the all three beaches. The supply of coastal deposits on these three beaches is influenced by the mechanism of precipitation of the walls and the processes of waves and rivers.Keywords: distribution, sediment, grainsize, geochemical, XRF, beach sediment.

The Variability of Indonesian Throughflow in Sumba Strait and Its Linkage to the Climate Events

As one of the Indonesian Throughflow (ITF) outflow passages, the Sumba Strait is a meeting point for the Pacific and the Indian Ocean water mass. In order to study the long-term variability of ITF flowing via Sumba Strait, this research uses observational data from the Ekspedisi WIdya Nusantara (EWIN) research cruise conducted in August 2016 to validate the altimetric geostrophic surface current by referencing the shear velocity. Stating the referenced level to 700 m, geostrophic transport is calculated using the Monthly Isopycnal/Mixed-Layer Ocean Climatology (MIMOC) data. Over the period of 1993-2016, the results demonstrate a dominant seasonal pattern for the geostrophic variability. While the total geostrophic transport shows a main westward direction towards the Indian Ocean, the Sumba Strait provides only a small portion (less than 0.1 Sv) for westward ITF geostrophic current. Intraseasonally, the maximum transport occurs during the southeast monsoon. The reversal of South Java Current (SJC), which flows with the eastward direction heading to the Savu Sea, is observed as the intrusion for westward ITF in almost every monsoon season. Despite having an unclear year to year cycle, climate mode of the Indian Ocean may have more influence on the surface geostrophic variability at the Sumba Strait. On the other hand, ocean-atmosphere coupling in the Pacific Ocean has a role in regulating geostrophic transport variation within the Sumba Strait. Using a statistical approach, the findings emphasize that the throughflow may well be impacted as well as feedback on both ENSO and IOD since there is robustness in those variables.

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait.

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait. DOI: 10.33332/jgsm.2019.v20.1.17-26

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait.

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait. DOI: 10.33332/jgsm.2019.v20.1.17-26

Analysis of Waikelo Port Breakwater Failure through 2D Wave Model

Waikelo Port is located in South West Sumba of East Nusa Tenggara. The port facilities are protected by breakwater with a vertical wall construction and it was built in a relatively deep ocean at -15m of Low Water Sea Level (LWS). On 21 of January 2012, an earthquake with magnitude of 6.3 Richter scale occurred around Sumba Island and it caused cracking in the concrete wall of breakwater. Then, 4 days after on 25 st January 2012, a heavy wind of 20–23 knots generated a high wave around 4.0–5.0m in Sumba strait. These high waves caused a critical damage on the west part of the breakwater. The damage of port facilities were getting worse when a storm called Lua hit on March 2012. This study was conducted to observe the effect of the extreme event in the failure of breakwater. The result of two-dimensional (2D) wave model shows that the wave heights in the area of breakwater are varied 3.80 to 4.0m. It is quite greater than the wave design of 50 years return period (= 2.00m) which was used in breakwater design and calculation. This observable fact confirms that the failure of breakwater was caused by the continuous extreme events that exceed the design criteria

Water mass characteristic in the outflow region of the Indonesian throughflow during and post 2016 negative Indian ocean dipole event

Strong El Niño and positive Indian Ocean Dipole (pIOD) events in 2015/2016 followed by relatively strong negative Indian Ocean Dipole (nIOD) and weak La Niña in 2016 events have affected hydrography conditions in the Indonesian Throughflow (ITF) region. Two research cruises were conducted using RV Baruna Jaya VIII in August and November 2016. These cruises aim to evaluate possible impact of those two climate mode events on the water mass characteristic in the outflow region of the ITF. Hydrographic data from those two cruises were combined with the sea surface temperature (SST) from the Advanced Very High Resolution Radiometer (AVHRR) and surface wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF). The results showed that in the 2016 anomaly year, the cooler sea surface temperature was observed during the negative IOD (nIOD) event while the warmer temperature was found in the post of nIOD event. The observed water mass characteristics in the outflow region of the ITF revealed that the upper layer was dominated by the Indian Ocean water mass, while the Pacific Ocean water mass was observed in the deeper layer. The observed current data across the Sumba Strait showed that the South Java Coastal Current (SJCC) was observed in the upper layer, propagating eastward toward the Savu Sea. A few days later, the observed currents in the upper layer of the Ombai Strait revealed the ITF flow towards the Indian Ocean. Meanwhile, the lower layer showed an eastward flow towards the Ombai Strait.

Distribusi Sedimen Permukaan Dasar Laut Perairan Sumba, Nusa Tenggara Timur

<strong>Subsurface sediment distribution in the Sumba Waters, East Nusa Tenggara.</strong> Marine geological survey of the Ekspedisi Widya Nusantara 2016 was conducted in the Sumba Waters on 4 to 26 August 2016 using Baruna Jaya VIII research vessel. The aim of this survey was to reveal the type and characteristics of the subsurface sediments of the Sumba Waters. A total of 13 samples were taken from the different depth in the subsurface bottom of the sea using grabbing methode with box corer. Grain size analysis were conducted using Mastersizer 2000 to understand the characteristics and the sediment type distribution. In general, the type of the subsurface sediment in the Sumba Waters is ranging from medium to very coarse sandy silt. Distribution of the subsurface sediments is correlated to depths. Grain size of the sediments in the Sumba Strait is coarser than in the western and southern of Sumba Island that directly connected to the Indian Ocean. Distribution of the subsurface sediment showing that the sediment, which are distributed further away from the coast is poorly sorted. The deposition of the subsurface-sea sediment is interpreted to represent a calm, and slow sedimentation mechanism under uniform suspension process.

Pathways of intraseasonal Kelvin waves in the Indonesian Throughflow regions derived from satellite altimeter observation

AbstractThe gridded sea level anomaly (SLA) data-set provided by AVISO is used to track the propagation of intraseasonal Kelvin waves in the Indonesian Throughflow (ITF) region. The large root mean square of intraseasonal SLA along the Sumatra and Java coast is closely related to the propagation of intraseasonal Kelvin waves that derive from the equatorial Indian Ocean. These Kelvin waves are further found to propagate following different pathways at the Lombok Strait. Pathway A propagates eastward throughout the Sumba Strait and Savu Sea to reach the Ombai Strait. Pathway B penetrates into Lombok and propagates northward to reach the Makassar Strait. Pathway C propagates southeastward along the southwest coast of the Sumba Island. The equatorial Kelvin waves take around 15 days to travel from the equatorial Indian Ocean to Lombok Strait, and around 5 days to penetrate into the Makassar and Ombai straits. The Kelvin wave-induced SLA persists in the ITF region for an additional 5 days and then diminishes s...