Investigating ocean deoxygenation and the oxygen minimum zone in the Central Indo Pacific region based on the hindcast datasets.

Deoxygenation is increasingly recognized as a significant environmental threat to the ocean following sea temperature rises due to global warming and climate change. Considering the cruciality of the deoxygenation impacts, it is important to assess the current status and predict the future possibility of ocean deoxygenation, for instance, within the Central Indo Pacific (CIP) regions represent climate-regulated marine areas. This study divided CIP into five regions then investigated the deoxygenation parameters (dissolved oxygen, temperature, salinity, and pH) collected from 1993 to 2021 sourced from in situ measurement and long-term hindcast data. The overall error statistics indicate a good accuracy of hindcast data and are comparable to the in situ values. The surface waters were identified to have the most fluctuated seasonal pattern of dissolved oxygen (DO) concentration compared to other water columns. However, DO fluctuation occurred in a different pattern in each region. The study shows ocean deoxygenation is accelerated in all five regions over decades. The strongest oxygen minimum zone (OMZ) is identified in the Bay of Bengal and the Arafura Sea with the lowest oxygen concentration less than 0.5 mmol/m3, while the weakest OMZ is located in the South China Sea with 60 mmol/m3 of DO concentration. The deoxygenation rates in CIP regions are varied by 0.09-2.75 mmol/m3/year depending on the different controlling factors that work in the five regions. Our results indicate that deoxygenation is attributed to ocean warming, seawater salinity increases, and ocean acidification and possibly continue in the future with continued global changes.

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

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.

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.