Glacial flow of floating marine ice in “Snowball Earth”

Abstract

Simulations of frigid Neoproterozoic climates have not considered the tendency of thick layers of floating marine ice to deform and spread laterally. We have constructed a simple model of the production and flow of marine ice on a planetary scale, and determined ice thickness and flow in two situations: when the ocean is globally ice‐covered (“hard snowball”) and when the tropical waters remain open (“soft snowball”). In both cases, ice flow strongly affects the distribution of marine ice. Flowing ice probably carries enough latent heat and freshwater to significantly affect the transition into a Snowball Earth climate. We speculate that flowing marine ice, rather than continental ice sheets, may be the erosive agent that created some Neoproterozoic glacial deposits.

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.…”

“…In a possible Snowball Earth climate, ocean circulation and mixing processes would have determined the melting and freezing rates that determine ice thickness 5,6 , influenced the survival of photosynthetic life 4,5,7-9 , and may provide important constraints for the interpretation of geochemical and sedimentological observations 4,10 . Here we show that in a Snowball Earth, the ocean would have been well mixed and characterized by a dynamic circulation 11 , with vigorous equatorial meridional overturning circulation, zonal equatorial jets, a well-developed eddy field, strong coastal upwelling and convective mixing.…”

“…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 .…”