Preprints
https://doi.org/10.5194/egusphere-2024-451
https://doi.org/10.5194/egusphere-2024-451
28 Feb 2024
 | 28 Feb 2024
Status: this preprint is open for discussion.

Signatures of Oxygen-Depleted Waters along the Sumatra-Java Coasts in the Southeastern Tropical Indian Ocean

Faisal Hamzah, Iis Triyulianti, Agus Setiawan, Intan Suci Nurhati, Bayu Priyono, Dessy Berlianty, Muhammad Fadli, Rafidha D. Ahmad Opier, Teguh Agustiadi, Marsya J. Rugebregt, Weidong Yu, Zexun Wei, Huiwu Wang, R. Dwi Susanto, and Priyadi D. Santoso

Abstract. A prominent ocean region exhibiting depleted oxygen concentration is the northern Indian Ocean, whose projected deoxygenation trend in response to climate change requires a comprehensive understanding of the roles of ocean dynamics. We present newly compiled in situ data across platforms (e.g. cruises, Argo, buoy) in the Indonesian coasts of Sumatra and Java between 2010–2022. Combined with reanalysis products, our data detect oxygen-depleted waters attributed to the eastward advection of the northern Indian Ocean waters and monsoon-driven coastal upwelling. Oxygen limited zones (OLZs, DO < 60 μmol kg-1) occupy various depths off the Sumatra-Java coasts, in which dissolved oxygen (DO) reaches ~40 μmol kg-1 in northwest Sumatra. The eastward propagating Equatorial Counter Current plays a major role in delivering the oxygen-depleted waters during the boreal summer; similarly, the South Equatorial Counter Current in the winter monsoon and the Wyrtki Jet during the transition months. Coastal upwelling regulates DO variations via primary production and the respiration of organic matter at intermediate depths in southern Java as the upwelled waters being advected westward towards Sumatra in the summer monsoon. Indonesian Throughflow with enriched organic matter modifies the oxygenated-depleted waters at its outlets. We observe a trend towards deepened OLZ in western Sumatra, while positive Indian Ocean Dipole events (2006, 2012, 2015, 2019) lower DO in the thermocline depths of southern Java on the interannual timescale. Altogether, high-resolution observational biogeochemical data are key to advance our understanding of dynamical DO changes in the southeastern tropical Indian Ocean under the global deoxygenation trend.

Faisal Hamzah, Iis Triyulianti, Agus Setiawan, Intan Suci Nurhati, Bayu Priyono, Dessy Berlianty, Muhammad Fadli, Rafidha D. Ahmad Opier, Teguh Agustiadi, Marsya J. Rugebregt, Weidong Yu, Zexun Wei, Huiwu Wang, R. Dwi Susanto, and Priyadi D. Santoso

Status: open (until 16 May 2024)

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Faisal Hamzah, Iis Triyulianti, Agus Setiawan, Intan Suci Nurhati, Bayu Priyono, Dessy Berlianty, Muhammad Fadli, Rafidha D. Ahmad Opier, Teguh Agustiadi, Marsya J. Rugebregt, Weidong Yu, Zexun Wei, Huiwu Wang, R. Dwi Susanto, and Priyadi D. Santoso
Faisal Hamzah, Iis Triyulianti, Agus Setiawan, Intan Suci Nurhati, Bayu Priyono, Dessy Berlianty, Muhammad Fadli, Rafidha D. Ahmad Opier, Teguh Agustiadi, Marsya J. Rugebregt, Weidong Yu, Zexun Wei, Huiwu Wang, R. Dwi Susanto, and Priyadi D. Santoso

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Short summary
We provide new insights on the presence of oxygen-depleted waters along the Indonesian coasts of Sumatra and Java attributed to the eastward advection of the northern Indian Ocean waters and monsoon-driven upwelling. Combined in situ and reanalysis data elucidate the complex interplay of oceanographic processes responsible for the observed oxygen in the region. The knowledge is crucial for research and management strategies to mitigate deoxygenation impacts on marine ecosystems in Indonesia.