04 Oct 2023
 | 04 Oct 2023

Sea-ice thermodynamics can determine waterbelt scenarios for Snowball Earth

Johannes Hörner and Aiko Voigt

Abstract. Snowball Earth refers to multiple periods in the Neoproterozoic during which geological evidence indicates that Earth was largely covered in ice. A Snowball Earth results from a runaway ice-albedo feedback, but there is an ongoing debate about how the feedback stopped: with fully ice-covered oceans or with a narrow strip of open water around the equator. The latter states are called waterbelt states and are an attractive explanation for Snowball Earth events because they provide a refugium for the survival of photosynthetic aquatic life, while still explaining Neoproterozoic geology. Waterbelt states can be stabilized by bare sea ice in the subtropical desert regions, which lowers the surface albedo and stops the runaway ice-albedo feedback. However, the choice of sea-ice model in climate simulations significantly impacts snow cover on ice and, consequently, surface albedo.

Here, we investigate the robustness of waterbelt states with respect to the thermodynamical representation of sea ice. We compare two thermodynamical sea-ice models, an idealized 0-layer Semtner model, in which sea ice is always in equilibrium with the atmosphere and ocean, and a 3-layer Winton model that is more sophisticated and takes into account the heat capacity of ice. We deploy the global climate model ICON-A in an idealized aquaplanet setup and calculate a comprehensive set of simulations to determine the extent of the waterbelt hysteresis. We find that the thermodynamic representation of sea ice strongly influences snow cover on sea ice over the range of all simulated climate states. Including heat capacity by using the 3-layer Winton model increases snow cover and enhances the ice-albedo feedback. The waterbelt hysteresis found for the 0-layer model disappears in the 3-layer model and no stable waterbelt states are found. This questions the relevance of a subtropical bare sea-ice region for waterbelt states and might help explain drastically varying model results on waterbelt states in the literature.

Johannes Hörner and Aiko Voigt

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2073', Stephen Warren, 29 Oct 2023
  • RC2: 'Comment on egusphere-2023-2073', Yonggang Liu, 04 Nov 2023

Johannes Hörner and Aiko Voigt

Johannes Hörner and Aiko Voigt


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Short summary
Snowball Earth refers to a climate in the deep past of Earth where the whole planet was covered in ice. Waterbelt states, where a narrow region of open water remains at the equator, have been discussed as an alternative scenario, which might explain how life was able to survive these periods. Here, we demonstrate how waterbelt states are influenced by the thermodynamical sea-ice model used. The sea-ice model modulates snow on ice, ice albedo and ultimately the stability of waterbelt states.