Snowball Earth: A thin‐ice solution with flowing sea glaciers

Abstract

[1] The late Neoproterozoic era, $600-800 Myr ago, was marked by at least two intervals of widespread cold that left glacial deposits at low paleolatitudes. Both ''Snowball'' solutions with global ice cover and ''Slushball'' solutions with ice-free tropical oceans have been proposed to explain the paleomagnetic data. The Snowball model is best able to explain the auxiliary geological evidence, particularly the existence of cap carbonates, but it implies drastic survival pressure on the photosynthetic biota if the ice cover was everywhere thick enough to prevent sunlight from reaching the underlying ocean. A ''thin ice'' solution that avoids this problem has been proposed but is thought to be inconsistent with realistic optical properties of sea ice and with the equatorward flow of sea glaciers. Here we use a coupled energy-balance climate/sea-glacier model to argue that these apparent difficulties can be overcome and that thin tropical ice may have prevailed during these remarkable glacial episodes. We also suggest that (1) some processes beyond the scope of zonal mean energy-balance models may significantly affect the solutions and (2) thin ice could have prevailed on low-latitude seas (or large lakes) protected from large-scale sea-glacier flow by surrounding land even if most of the Earth was in a ''hard Snowball'' state.

Dynamics of a Snowball Earth ocean

“…1e) is quite uniform, varying from 1120 to 1200 m, due to the homogenizing effect of the ice flow 6 , consistent with previous studies 7,15 . High latitude basal freezing and low latitude melting rates are balanced by an equatorward ice flow and are comparable to, if not larger than, the ice surface sublimation and precipitation rates (Fig.…”

“…2e), about ten times larger than the maximum melting rates calculated by coarse model runs 6,7 . This warmer area is due to a concentrated coastal upwelling of deep water heated by geothermal heating.…”

“…Our model couples the state--of--the--art ocean general circulation model, MITgcm 28 , which can simulate thick ice shelves 29 , with a recently developed two--dimensional (2D, latitude--longitude) ice flow model 15 , extending previous 1D flow models 6,7 . The model is run here in Sensitivity experiments to the location and amplitude of the enhanced heating, and to the topography in both the 2D and 3D models, show our solution to be very robust.…”

“…Our model couples the state--of--the--art ocean general circulation model, MITgcm 28 , which can simulate thick ice shelves 29 , with a recently developed two--dimensional (2D, latitude--longitude) ice flow model 15 , extending previous 1D flow models 6,7 . The model is run here in …”

“…The flow of thick ice over a Snowball ocean ("sea glaciers", characterized by very different dynamics from thinner sea ice 14 ), has received significant attention over the past few years [5][6][7]9,14,15 . Similarly, the role and dynamics of atmospheric circulation and heat transport, CO2 concentration, cloud feedbacks, and continental configuration have been studied [16][17][18] , as has the role of dust over the Snowball ice cover 17,19 .…”