Regional Studies in Marine Science 52 (2022) 102336 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Water exchange across the Strait of Hormuz. Effects of tides and rivers runoff Edmo J.D. Campos a,b,∗ , Björn Kjerfve c , Geórgenes Cavalcante a,d , Filipe Vieira a , Mohamed Abouleish a a College of Arts and Sciences, American University of Sharjah, University City, PO Box 26666, Sharjah, Sharjah, United Arab Emirates b Oceanographic Institute of the University of São Paulo, Praça do Oceanográfico, 191, Cidade Universitária, São Paulo, 05508-120, SP, Brazil c School of the Earth, Ocean and the Environment, Univ. South Carolina, USA d Institute of Atmospheric Science, Federal Univ. Alagoas, Brazil article info Article history: Received 5 October 2021 Received in revised form 10 March 2022 Accepted 19 March 2022 Available online 28 March 2022 Keywords: Persian Gulf Arabian Gulf Freshwater budget Strait of Hormuz abstract The Persian Gulf exchanges water with the Arabian Sea by means of an inverse-estuary circulation. Fresher surface waters are imported while heavier, saltier waters are exported near the bottom. This mechanism compensates for the loss of freshwater by excess evaporation, maintaining the Gulf’s environmental conditions. To assess the effects of climate change and local anthropogenic stressors, the salt budget driven only by natural mechanisms must be well understood. A previous study with the Hybrid Coordinate Ocean Model (HYCOM), showed that the salt, or equivalent-freshwater, exchange through the Strait of Hormuz is composed of overturning and horizontal components, both well correlated with the basin-averaged net evaporation in the Gulf. Tidal forcing and river runoff inside the Gulf were not considered. Here we report results of experiments with a newer, higher-resolution implementation of HYCOM, forced with the same atmospheric products but including the tidal forcing and riverine inflow in the Gulf’s basin. We found that the mean exchange across a vertical section in the Strait of Hormuz is significantly sensitive to the addition of rivers and tides. In the numerical simulations, river runoff inside the Gulf tends to increase the freshwater exchange while the tides lead to appreciable reduction in the net transport. © 2022 Elsevier B.V. All rights reserved. 1. Introduction The Persian or Arabian Gulf, hereinafter referred as the Gulf, is a semi-enclosed sea located between latitudes 24 ◦ and 31 ◦ N and longitudes 48 ◦ and 56 ◦ E, connected to the northern Indian Ocean via the Strait of Hormuz and the Gulf of Oman (Fig. 1). The Gulf is a shallow basin, with an approximate length of 1000 km and mean depth of 36 m. At its northern boundary, there is a mean riverine inflow of approximately 3000 m 3 s −1 (Barron and Smedstad, 2002). However, the evaporation over the Gulf is much greater than the freshwater input by rivers and precipita- tion. This makes it a hypersaline basin, with an inverse-estuary circulation: fresher waters from the Indian Ocean enter the Gulf near the surface while denser, saltier waters are exported in the deeper layers to the Gulf of Oman and beyond (Johns et al., 2003; ∗ Corresponding author at: Oceanographic Institute of the University of São Paulo, Praça do Oceanográfico, 191, Cidade Universitária, São Paulo, 05508-120, SP, Brazil. E-mail addresses: edmo@usp.br (E.J.D. Campos), bjornkjerfve@gmail.com (B. Kjerfve), georgenes.cavalcante@icat.ufal.br (G. Cavalcante), filipebvieira@yahoo.com (F. Vieira), mabouleish@aus.edu (M. Abouleish). URL: https://io.usp.br/index.php/perfil/userprofile/edmo (E.J.D. Campos). Campos et al., 2020a). The absence of a significant sill at the Gulf’s entrance, as compared with the Red Sea (Cember, 1988), and the increasing depths towards the Strait of Hormuz make the residence time relatively short. Changes within the Persian Gulf are communicated directly to the Arabian Sea on time scales ranging from 1 to 5 years (Reynolds, 1993; Xue and Eltahir, 2015; Alosairi et al., 2011). The climatological conditions, the variability of the Gulf’s cir- culation, and the exchange of water through the Strait of Hormuz have been investigated by modeling and observational studies in the past few decades (Johns et al., 2003; Campos et al., 2020a; Yao and Johns, 2010a,b; Thoppil and Hogan, 2010; Pous et al., 2004a, 2012, 2015; Vasou et al., 2020; Lorenz et al., 2019). Tidal forcing impacts the overall instantaneous circulation with weak residual effect on the mean currents (Pous et al., 2004b, 2012, 2015). Wind forcing is significant, particularly the Shamal weather phe- nomenon (Johns et al., 2003; Campos et al., 2020a; Alosairi et al., 2011). Due to the large excess evaporation, the air–sea fluxes over the Gulf and the salt exchanges across the Strait of Hormuz play a central role in the mean circulation and its variability (Johns et al., 2003; Campos et al., 2020a; Thoppil and Hogan, 2010; Pous et al., 2004a,b; Lorenz et al., 2021; Ghazi et al., 2017). Within the Gulf, https://doi.org/10.1016/j.rsma.2022.102336 2352-4855/© 2022 Elsevier B.V. All rights reserved.