A Simple Model for Multiple Equilibria in Ice-Covered Oceans

• Published in: Journal of physical oceanography Vol. 54; no. 10; pp. 2087 - 2097
• Main Author: Spall, Michael A.
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.10.2024
• Subjects: Albedo; Atmosphere; Atmospheric cooling; Atmospheric forcing; Atmospheric temperature; Basins; Diapycnal mixing; Dimensionless numbers; Equilibrium; Evaporation; Feedback; Heat exchange; Ice; Ice cover; Ocean basins; Ocean dynamics; Oceans; Parameter identification; Parameter sensitivity; Radiation; Rivers; Runoff; Salinity; Solar radiation; Temperature dependence; Water; Water masses; Arctic Ocean; Labrador Sea; Arctic region; Greenland; Bering Strait
• ISSN: 0022-3670; 1520-0485
• DOI: 10.1175/JPO-D-24-0022.1

The existence of multiple equilibria (ice-covered and ice-free states) is explored using a set of coupled, nondimensional equations that describe the heat and salt balances in basins, such as the Arctic Ocean, that are subject to atmospheric forcing and two distinct water mass sources. Six nondimensional numbers describe the influences of atmospheric cooling, evaporation minus precipitation, solar radiation, atmospheric temperature, diapycnal mixing, and the temperature contrast between the two water masses. It is shown that multiple equilibria resulting from the dependence of albedo on ice cover exist over a wide range of parameter space, especially so in the weak mixing limit. Multiple equilibria can also occur if diapycnal mixing increases to O (10 −4 ) m 2 s −1 or larger under ice-free conditions due to enhanced upward mixing of warm, salty water from below. Sensitivities to various forcing parameters are discussed.