Contents lists available at ScienceDirect Progress in Oceanography journal homepage: www.elsevier.com/locate/pocean Spatial structure of turbulent mixing inferred from historical CTD datasets in the Indonesian seas Adi Purwandana a,b, ⁎ , Yannis Cuypers a , Pascale Bouruet-Aubertot a , Taira Nagai c , Toshiyuki Hibiya c , Agus S. Atmadipoera d a Laboratoire d'Océanographie et de Climatologie par Expérimentation et Approche Numérique (LOCEAN), Sorbonne Université, Paris, France b Research Center for Oceanography, Indonesian Institute of Sciences (RCO-LIPI), Jakarta, Indonesia c Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan d Department of Marine Sciences and Technology, Faculty of Fisheries and Marine Sciences, Bogor Agricultural University, Bogor, Indonesia ARTICLEINFO Keywords: Internal tide Indonesian seas Dissipation rates Vertical mixing Indonesian throughflow ABSTRACT Turbulent kinetic energy dissipation rates and vertical diffusivities in the Indonesian seas are inferred from historical CTD measurements gathering for the first time data from Indonesian and international cruises. Dissipation rates are inferred from the CTD using an improved Thorpe scale method, which is validated against microstructure measurements. Elevated dissipation rates ~[10 -6 –10 -7 ]m 2 s -3 , were observed in the near field stations, such as in the straits, narrowing passages and shallowing topography where internal tides are generated and Indonesian throughflow (ITF) is intense, while lower dissipation rates ~[10 -8 –10 -10 ]m 2 s -3 were ob- served in the far field stations and below the pycnocline. The main mixing hot spots are located in the Labani Channel and shallowing topography of the Dewakang waters for the western route of ITF, i.e. the passage that connects the north Pacific source via Sulawesi Sea, Makassar Strait and Flores Sea; in the straits of Halmahera, Lifamatola, and Buru for the eastern route of ITF, i.e. the passage that connects the south Pacific source via Halmahera Sea, Maluku Sea, Seram Sea; and in the ITF exit passages, i.e. the Lombok, Sape and Ombai Straits. The eastern route is more dissipative than the western route, which is consistent with the stronger erosion of the salinity peak of the Pacific waters along the eastern route. We found that tidal variations influence the dis- sipation rates and diffusivities as has been suggested from the yoyo profiling datasets. The spatial pattern of dissipation rates inferred from the high-resolution 3D hydrodynamics model output of Nagai and Hibiya (2015) shows a general agreement with the observations in the location of the mixing hot spots and suggests that the M 2 internal tide is the dominant factor driving the turbulent kinetic energy dissipation rates in the Indonesian seas. Yet the model also shows a bias toward lower dissipation rate in the pycnocline, that we attribute to the lack of representation of the ITF and mesoscale circulation and a bias toward higher dissipation rate in the weak mixing region, suggesting an overestimation of the background dissipation rate in calm waters. 1. Introduction The Indonesian seas is the only low latitude passage connecting the Pacific and Indian Oceans. The flow, from the Pacific to the Indian Ocean, is known as the Indonesian throughflow (ITF) (Sprintall et al., 2003, 2004), and drives the transport of Pacific thermocline layer water masses (i.e. North Pacific Subtropical Water, NPSW, and South Pacific Subtropical Water, SPSW) and Pacific intermediate layer water masses (i.e. North Pacific Intermediate Water, NPIW, and South Pacific Inter- mediate Water, SPIW) into the Indian Ocean (Bingham and Lukas, 1994; Fine et al., 1994; Tsuchiya et al., 1989; Wyrtki, 1961). The general current system in the Indonesian seas, with its main branches, is shown in Fig. 1. There are two main ITF routes connecting the two oceans, i.e. the western route and the eastern route. The western route of ITF is the main pathway of North Pacific water masses, comprising the Sulawesi Sea, Makassar Strait, and Flores Sea. While the eastern route is understood to be the main pathway of South Pacific water masses, comprises the Halmahera Sea, Maluku Sea, Banda Sea and Seram Sea. Along the western route, the North Pacific water masses flow through the Mindanao Strait/Sangihe Passage, enter the Sulawesi Sea and Makassar Strait, and then bifurcate in the Dewakang waters where one portion exits through the Lombok Strait and the other is deflected eastward and enters the Flores and the Banda Sea. Through the eastern route, the South Pacific water masses flow through the https://doi.org/10.1016/j.pocean.2020.102312 Received 19 June 2019; Received in revised form 25 December 2019; Accepted 10 March 2020 ⁎ Corresponding author. E-mail address: adi.purwandana@lipi.go.id (A. Purwandana). Progress in Oceanography 184 (2020) 102312 Available online 14 March 2020 0079-6611/ © 2020 Elsevier Ltd. All rights reserved. T