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The extreme conditions of the deep-sea environment, including limited light, low oxygen levels, high pressure, and nutrient scarcity, create a natural habitat for deep-sea bacteria. These remarkable microorganisms have developed unique strategies to survive and adapt to their surroundings. However, research on the diversity of deep-sea bacteria, both culture-dependent and culture-independent, in Indonesian waters remains insufficient. This study focused on exploring the biodiversity of deep-sea bacteria, specifically in the Makassar and Lombok Strait, the main Indonesian throughflow pathway characterized by relatively fertile water, which serves as an important deep-sea region. High-throughput DNA sequencing of full-length 16S rRNA was employed to construct a genomic database. The results of the bioinformatic analysis revealed that two stations, 48 and 50 (Makassar Strait), exhibited a more similar community structure of deep-sea bacteria than did station 33 (Lombok Strait). Among the predominant phyla found at a depth of 1000 m, the top ten were Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Planctomycetes, Acidobacteria, Nitrospinae, Verrucomicrobia, Candidatus Melainabacteria, and Cyanobacteria. Furthermore, the genera Colwellia, Moritella, Candidatus Pelagibacter, Alteromonas, and Psychrobacter consistently appeared at all three stations, albeit with varying relative abundance values. These bacterial genera share common characteristics, such as psychrophilic, halophilic, and piezophilic tendencies, and are commonly found in deep-sea ecosystem. The environmental conditions at a depth of 1000 m were relatively stable, with an average pressure 10 MPa, temperature 4.68 °C, salinity 34.58 PSU, pH 8.06, chlorophyll-a 0.29 µg/L, nitrate 3.19 µmol/L, phosphate 6.32 µmol/L and dissolved oxygen (DO) 2.90 mg/L. The bacterial community structures at the three sampling stations located at the same depth (1000 m) exhibited similarities, as indicated by the closely aligned similarity index values. 

Zooplankton are vulnerable to microplastics in the waters due to their indiscriminate feeding habits. Zooplankton consumption of microplastics affects microplastic accumulation and transmission in the marine ecosystem. Therefore, it is essential to know the intake and transmission by different group sizes of zooplankton in natural seawater. This study documented for the first time the levels of microplastics found in three sizes of copepods along the Indonesian Throughflow (ITF) pathways. The ingestion rates were 0.028, 0.023 and 0.016 n/ind for group sizes copepod 1000-2000 µm, 500-1000 µm and 200-500 µm, respectively. There was no significant distinction in the microplastics concentrations of the three groups of copepod classes along the ITF pathway (p>0.005). Fiber microplastics were the most dominant in the body of copepods, constituting 87.22% of ingested microplastics. In terms of the chemical composition of the microplastic, a total of 7 polymers were detected in copepods in the ITF pathway. The three predominant polymer types identified were polyvinyl butyral (PVB), polyvinyl ether maleic anhydride (PVEMA) and polyester (PES) (27%, 27% and 20%, respectively). This study provides the critical parameters of the microplastic in copepods in the ITF pathway and is an essential basis for further ecological risk assessments of microplastics in biota species. 

Abstract The Indonesian seas, with their complex passages and vigorous mixing, constitute the only route and are critical in regulating Pacific–Indian Ocean interchange, air–sea interaction, and global climate events. Previous research employing remote sensing and numerical simulations strongly suggested that this mixing is tidally driven and localized in narrow channels and straits, with only a few direct observations to validate it. The current study offers the first comprehensive temporal microstructure observations in the south of Lombok Strait with a radius of 0.05° and centered on 115.54^oE and 9.02^oS. Fifteen days of tidal mixing observations measured potential temperature and density, salinity, and turbulent energy dissipation rate. The results revealed significant mixing and verified the remotely sensed technique. The south Lombok temporal and depth averaged of the turbulent kinetic energy dissipation rate, and the diapycnal diffusivity from 20 to 250 m are$$\varepsilon$$ $\epsilon$ = 4.15 ± 15.9) × 10^–6W kg^–1and$$K\rho$$ $K\rho$= (1.44 ± 10.7) × 10^–2m²s^–1, respectively. This$$K\rho$$ $K\rho$is up to 10⁴times larger than the Banda Sea [$$K\rho$$ $K\rho$ = (9.2 ± 0.55) × 10^–6m²s^–1] (Alford et al. Geophys Res Lett 26:2741–2744, 1999) or the “open ocean”$$K\rho$$ $K\rho$= 0.03 × 10^–4 m²s⁻¹within 2° of the equator to (0.4–0.5) × 10^–4m²s⁻¹at 50°–70° (Kunze et al. J Phys Oceanogr 36:1553–1576, 2006). Therefore, nonlinear interactions between internal tides, tidally induced mixing, and ITF plays a critical role regulating water mass transformation and have strong implications to longer-term variations and change of Pacific–Indian Ocean water circulation and climate. 

Even though Pacific – Indian Ocean exchange [Indonesian Throughflow (ITF)] has been measured for the last three decades, the measurements of microplastic in the region is very limited. This study was the initial investigation of the vertical distribution of microplastic in the deep-sea areas across the ITF Pathway. Niskin water samples were utilized to obtain the samples from a water column in a range of 5 to 2450 m. A total of 924 microplastic particles with an average abundance of 1.062 ± 0.646. n/L were found in the water column. Our findings indicate that water temperature and water density are the most significant factors correlated to the microplastic concentration. This study will be the first report discussing the distribution of microplastics in the deep-sea water column that could be highly significant in determining the fate and transport of microplastic within Indonesian waters that exits into the Indian Ocean.