1,2,3,3,1- 1Instituto de Astrofísica e Ciências do Espaço (IA) and Physics Department, Faculty of Sciences, University of Lisbon, Campo Grande, PT1749-016 Lisbon, Portugal (dfquirino@fc.ul.pt)
- 2Instituto Dom Luiz (IDL) and Geology Department, Faculty of Sciences, University of Lisbon, Campo Grande, PT1749-016 Lisbon, Portugal
- 3School of Ocean Sciences, Bangor University Menai Bridge, LL59 5AB, UK
- 4NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- 5Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, SE-75120, Sweden
- 6GSFC Sellers Exoplanet Environments Collaboration, NASA Goddard Space Flight Center, MD, USA
The modern atmosphere of Venus shows a substantially lower abundance of water vapour [1-3] and a high deuterium to hydrogen ratio (D/H) compared to Earth [3, 4]. This high D/H ratio suggests a significantly larger initial water reservoir than today. Some climate modelling studies suggest that early Venus might have had an initial benign climate, with the dayside cloud-albedo feedback supporting early and prolonged surface Habitability – also based on the planet’s slow-rotation [5, 6, 7]. According to this hypothesis, this benign early climate is theorised to end by large-scale volcanism in the form of multiple large igneous provinces, eventually leading to the present runaway greenhouse state we currently observe on modern Venus [8]. Water vapour photodissociation and preferential loss of the lighter hydrogen would explain the observed D/H ratio [9]. Other climate modelling studies claim that warming from nightside stratospheric clouds could prevent water condensation in the first place [10].
Assuming surface water condensation from the steam atmosphere in the first place, we simulate a hypothetical ocean on Venus at 2.9 Ga by using a 3D General Circulation model (GCM). We use the 3D GCM ROCKE-3D (Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics), developed at the NASA Goddard Institute for Space Studies [11]. The simulations use a spatial resolution of 4ºx5º (latitude x longitude), a 40-layer atmosphere (with a top pressure: 0.1-hPa) and a 13-layer fully dynamic ocean [12] coupled to the atmosphere. For the reference simulation, we select a modern Venus topography following the NASA/Magellan archive. We simulate a 310-m global equivalent layer (GEL), covering ~60% of the surface of Venus. Ocean volume is 1.4 x 1017 m3, one order of magnitude below that of modern Earth’s Ocean [5]. We set insolation to 2001 W/m2 or 1.47 times that of modern Earth, representing conditions at 2.9 Ga. The atmospheric composition was set to be Archean Earth-like (1.013 bar N2, 400 ppm CO2, 1 ppm CH4) [6]. Other planetary parameters follow the modern values of Venus’s surface gravity, radius, obliquity, eccentricity and rotation rate (retrograde slow-rotator: -243 days) [5].
We will discuss the main physical oceanographic parameters (e.g., potential temperature, salinity, potential density) and ocean circulation. Our simulations point to the existence of a significant monthly-long diurnal cycle, allowing for the development of a considerable mixed layer depth at the equator during the nighttime. This diurnal cycle results in the inversion of the equatorial surface current, from a -125 cm/s westward at midday to 50 cm/s eastward at the evening terminator. The highly saline Southern Ocean is controlled by a mass balance that favours evaporation, and is influenced by a limited exchange due to the presence of a strait-like feature preventing denser water to cross the sill. In addition, the model shows the development of a complex «meridional overturning circulation», controlled by the bathymetry and a southern «closed» basin. We will compare this ocean circulation results with a simulation of a deeper ocean on the paleo-Venus, assuming a 1000-m GEL with a modern Venus-like topography.
Moreover, we will study the impact of the paleo bathymetry/topography in the ocean circulation and tidal dissipation. Initial simulations are based on the NASA/Magellan altimetry database. However, modern volcanic rises might not have been present in the early Venus. Venusian tides are simulated using the portable Oregon State University Tidal Inversion Software (OTIS), a model extensively used for deep-time, present-day and future tides on Earth [13 – 16] and on Venus with a modern topography [17]. We will draw conclusions for the importance of studying ocean circulation, landmass configuration, and interactions between atmosphere-ocean for Earth-sized exoplanets located in the vicinity of the inner edge of the Habitable Zone.
References: [1] Bézard B., et al.,2011.Icarus.216:173; [2] Cottini et al.,2015. Space Sci.113:219; [3] Encrenaz T, et al.,2015. Space Sci.113:275; [4] Krasnopolsky V, et al.,2013.Icarus.224:57; [5] Way M.J., et al.,2016.GRL.43; [6] Way M.J. & Del Genio A.D. (2020).JGR:Planets.125; [7] Yang J, et al., 2014, ApJL., 787, L2 [8] Way M, et al.,2022. Sci. J.3:92; [9] Chaffin M, et al.,2024.Nature.629:307; [10] Turbet M., et al.,2021.Nature.598:276; [11] Way M.J., et al.,2017.ApJS.213:12; [12] Russell G.L., et al.,1995.Atmos-Ocean.33:683 ; [13] Egbert, G.D., et al., 2004, JGRC, 109, C03003 ; [14] Green, J., et al., 2017, E&PSL, 461,46 ; [15] Green, et al., 2018, GeoRL, 45, 3568 ; [16] Wilmes, S.-B., 2017, JGRC, 122, 8354 ; [17] Green, et al., 2019, ApJL,876, L22.
Funding: DQ acknowledges FCT a PhD fellowship 2023.05220.BD
How to cite: Quirino, D., Way, M. J., Green, J. A. M., Duarte, J. C., and Machado, P.: Ocean circulation and tides on a temperate paleo-Venus, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-1577, https://doi.org/10.5194/epsc-dps2025-1577, 2025.
