Variability of Indonesian Throughflow Transport in the Indonesian Seas during Triple-Dips La Nina
Naffisa Adyan Fekranie(1,2,*), Agus Setiawan(2,*), Mutiara Rachmat Putri(3)

1) Study Program of Oceanography, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Labtek XI (^Labtek Biru^) 2nd Floor, Jl. Ganesha No 10, Bandung, 40132, Jawa Barat, Indonesia

2) Research Centre for Deep Sea, Research Organisation for Earth Sciences and Maritime, National Research and Innovation Agency, Indonesia

3) Research Group of Oceanography, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Labtek XI (^Labtek Biru^) 2nd Floor, Jl. Ganesha No 10, Bandung, 40132, Jawa Barat, Indonesia

Abstract

The Indonesian Seas serve as an important conduit for the Indonesian Throughflow (ITF), a critical system of warm water and freshwater transport connecting the Pacific and Indian Oceans. El Nino-Southern Oscillation (ENSO) significantly impacts the regional variability in the Pacific and exerts a profound influence on water mass transport from the Pacific to the Indian Ocean. This study focuses on the influence of triple-dips La Nina events during two distinct periods (1998 - 2001 and 2020 - 2023) on the variability of ITF transport in key areas of the Indonesian Seas, including the Makassar, Lombok, and Ombai Straits, Flores and Banda Seas, and Timor Passage.

Using forecast and reanalysis data from the Copernicus Marine Environment Monitoring Service (CMEMS), transport calculations are conducted across cross-sectional profiles representing the study areas. The results reveal that the volume transport is significantly higher at depths ranging from ~50 - 300 m. It also shows seasonal fluctuations in volume transport across all regions, with lower transport during winter (DJF) and higher transport during summer (JJA) and transition period (SON) in the Makassar and Lombok Straits. In the Flores and Banda Seas, Ombai Strait, and Timor Passage, the surface transport volume follows seasonal patterns, while transport volume at deeper depths (~50 - 300 m and 300 - 800 m) exhibits distinct fluctuations compared to the surface.

Triple-dips La Nina events lead to an overall increase in transport volume during both periods, with the 2019 - 2023 period showing larger transport values (~ 19 Sv) compared to the 1997 - 2001 period (~14 Sv). The strengthened ocean current velocity during Triple-Dips La Nina events results in more significant variations in total transport, leading to larger differences between minimum and maximum transport values during these periods.

Keywords: ITF, Triple-Dips La Nina, volume transport, ENSO

Topic: Ocean-Atmosphere Dynamics