Tracking the pumice rafts from the Fukutoku-Okanoba submarine volcano with Satellites and a Lagrangian Particles trajectory model.

On August 13th, 2021, the Fukutoku-Okanoba, a submarine volcano in the Northwest Pacific Ocean, erupted. Satellites detected various pumice rafts that had drifted westward to reach southern Japan over two months. To cope with the potential danger from pumice rafts, predicting their trajectories is crucial. Using a Lagrangian particle tracking model, the trajectories of the rafts were investigated. The model results showed strong sensitivity to the windage coefficient of pumice rafts, which is uncertain and could cause significant errors. An optimal windage coefficient was estimated by comparing the model results with satellite images using a skill score based on the distance between simulated particles and the nearest observed rafts divided by the travel distance of the particles. The optimal windage coefficients ranged between 2 and 3 % and produced pathways comparable to the observations from satellites. The simulation results showed that the pumice rafts moved from Fukutoku-Okanoba toward the Ryukyu Islands for approximately two months prior to being pushed by the north-easterly wind toward Taiwan against the Kuroshio. The methods presented here may become a valuable tool in managing coastal hazards due to diverse marine debris.

Change in Salinity of Indonesian Upper Water in the Southeastern Indian Ocean during Argo Period.

The change in salinity of Indonesian Upper Water (IUW) in the Indian Ocean has been examined during 2004-2020 based on the Argo product. Monthly salinity fields reveal a contrast of IUW salinity changes between two time periods (2004-2013 and 2014-2020) in the outflow of Indonesian Throughflow (ITF) in the Indian Ocean. Freshening of IUW has been observed in the Indian Ocean from 2004-2013 on a basin scale. The opposite changes appear from 2014-2020, when IUW shows a general increase in salinity. The present study shows that oceanic-atmospheric processes in the Maritime Continent influence the changes in the IUW salinity in the southeastern Indian Ocean. The salinity changes are connected to the alteration of the freshwater flux in the Maritime Continent. The ITF enhances subsequent salinity transport into the southeastern Indian Ocean. Zonal atmospheric circulation strength in the tropical region is linked to the shift of the large freshwater flux in the Maritime Continent.

Spatio-temporal variation and seasonal dynamics of stranded beach anthropogenic debris on Indonesian beach from the results of nationwide monitoring.

The first stranded macrodebris study on a national scale in Indonesia was conducted on 18 beaches from February 2018 to December 2019. The average weight and abundance of beach debris were higher between October and February (rainy season). The highest stranded macrodebris was located in Ambon, Manado, Takalar, and Padang. Plastic (46.38 %) was the most prevalent type of debris across all macrodebris categories, with single-use plastics such as plastic sachets, plastic bags, and plastic bottles being the dominant macroplastic debris (64.64 %). Based on CCI, HII, and BGI, 18 beaches are "moderately clean," with few hazardous items observed, and "Good." This anthropogenic macrodebris is thought to be more localized (55 %) than transboundary macrodebris. Litter control and environmental quality of this Indonesian coastal region should be improved through a proactive and flexible approach. Finally, extensive stranded beach debris monitoring is recommended to better understand the distribution of macrodebris in the region.

Pathways of floating marine debris in Jakarta Bay, Indonesia.

Jakarta is the capital of Indonesia with a high population density, which affects the amount of waste generated. The waste that ends up in Jakarta Bay has become an environmental problem. Understanding the pathway of marine debris in the ocean is important to identify the mitigation strategies. Before this study, the pathways and sources of marine debris in Jakarta Bay were unknown. By using virtual floating marine debris particles in a high-resolution ocean model, the fate of marine debris based on the pathways of particles released in Jakarta Bay in both forward and backward tracking experiments was analyzed. It was found that most of the particles from Jakarta Bay flow toward the Indian Ocean in all seasons. They flow off through the Sunda Strait and reach the open Indian Ocean after a few weeks. With regard to the source location, most particles that end up in Jakarta Bay come from the north of Java Island locally and from the Gulf of Thailand, Sumatra, and Kalimantan coasts. The particles do not appear to vary significantly across all seasons and identifying the pathway of marine debris might be useful in pollution reduction.

Marine heatwaves of sea surface temperature off south Java.

The frequency of marine heatwaves (MHWs) events has been rising globally in recent years, and this trend is expected to continue in the region off the coast of south Java Island. These oceanic extreme events may have the potential to devastate marine habitats, ecosystems and fisheries. This paper characterized MHWs off south Java from 1982 to 2019 using satellite-observed sea surface temperature. The aim of this study was to examine the dynamics of MHWs in one of Indonesia's most important fisheries hotspots, located in the southeast of the tropical Indian Ocean. We have identified two strong MHWs events in 1998 and 2016, both of which started in the austral winter months. Both events were lasted through the spring before dissipating in the early austral winter. These intense MHWs were likely related to a strong El Niño and decreased monsoon activity.