Ocean Surfaces on Snowball Earth

Intellectual merit: Evidence of episodes of extreme glaciation during the Neoproterozoic time (600-800 million years ago) lead to formulation of the Snowball Earth hypothesis in the early 1990’s. A central but controversial idea of this hypothesis is that ice covered nearly the entire ocean for periods of up to several million years. Climate models differ greatly in their simulations of this time period suggesting everything from an ice free tropical ocean, to a “hard” snowball or fully frozen ocean to “slushy” scenario in between. It is known that climate models are highly sensitive to prescribed albedos although modelers have yet to settle on a preferred treatment in part because the full spectral albedos of the likely surfaces are uncertain. To provide clearer guidance in this realm, the Office of Polar Programs, Antarctic Integrated System Science Program has made this award to study the albedo of snow and ice surfaces that may have been pivotal to initiation and maintenance of an ice-covered ocean. Albedo may have also been key factor in determining sea ice thickness, thus light transmission to the water below and so governing possible refugia for the more delicate eukaryotic life forms that are known to have survived this time period. It is argued that today only Antarctica provides sufficiently analogous ice surfaces to the specialized ones that are thought to have occurred under a Snowball Earth scenario. A combination of field observations of cold (meaning less than -23C) snow-free sea ice, salt encrusted sea-ice surfaces and blue (subject to net ablation) glacial ice, laboratory experiments (various salt encrusted ice surfaces) and modeling (of radiative transfer and conditions required for potential refugia under thin, light transmitting ice in marginal seas such as the Mediterranean) will be carried out to test the viability of the Snowball Earth hypothesis. In collaboration with climate modelers, the field and laboratory results will be applied to better constraining global scale models of Snowball Earth.

Broader impacts: This basic research program is aimed at understanding past extreme climate conditions on Earth. Such conditions have implications for biological evolution; while prokaryotes could readily survive the challenge, it is not clear how the more susceptible eukaryotes did. The measurements should also provide information for sea-ice and glacial-ice in the modern environment that may be relevant to projecting future climate. They might also provide insights for the understanding of ice and salts surfaces on the moons of Jupiter and Saturn. The project will involve an undergraduate in laboratory observations and a graduate student whose PhD thesis will derive from this study. This research program integrates the expertise of an atmospheric scientist, sea-ice scientist and glaciologist. One of the coPIs is a member of an underrepresented group (female) in sea ice physics. The sea-ice component is collaborative with a New Zealand International Polar Year project focused on seasonal evolution of sea-ice properties.