Snowball Earth: Asynchronous coupling of sea‐glacier flow with a global climate model

Abstract

During Snowball Earth episodes of the Neoproterozoic and Paleoproterozoic, limited amounts of tropical open ocean (Jormungand), or tropical ocean with thin ice cover, would help to explain (1) vigorous glacial activity in low latitudes, (2) survival of photosynthetic life, and (3) deglacial recovery without excessive buildup of atmospheric CO2. Some previous models have suggested that tropical open ocean or thin‐ice cover is possible; however, its viability in the presence of kilometer‐thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively. Here we describe a new method of asynchronously coupling a zonal sea‐glacier model with a 3‐D global climate model and apply it to Snowball Earth. Equilibrium curves of ice line versus CO2 are mapped out, as well as their dependence on ocean heat transport efficiency, sea‐glacier flow, and other model parameters. No climate states with limited tropical open ocean or thin ice are found in any of our model runs, including those with sea glaciers. If this result is correct, then other refugia such as cryoconite pans would have been required for life to survive. However, the reasons for the differences between our results and others should first be resolved. It is suggested that small‐scale convective dynamics, affecting fractional snow cover in low latitudes, may be a critical factor accounting for these differences.

Neoproterozoic glacial origin of the Great Unconformity

“…The extent of ice-free ocean available to sustain hydrological cycling during such global glaciation is controversial (41, 44). However, precipitation rates driven by sublimation alone appear sufficient for the development of localized wet-based ice streams with high basal sliding velocities and consequent erosive potential (40); evaporation from cryoconite ponds [a notable sink for solar radiation in a snowball state (45)] might further enhance hydrological cycling.…”

Ocean bays surrounded by desert land could support photosynthetic life on Snowball Earth

“…Pollard and Kasting (2005) tried to find a thin-ice solution that would even hold off sea glaciers, and succeeded only when three parameters were pushed beyond their acceptable limits (Warren and Brandt, 2006). An improved model (Pollard et al, 2017) convincingly rejected the thin-ice solution.…”

Neoproterozoic glacial origin of the Great Unconformity

“…Such a configuration would provide a large gravitational potential energy gradient to drive erosion, while isostatically permitting more than 12 km vertical erosion of typical continental crust by a 2 km ice sheet. The extent of ice-free ocean available to sustain hydrological cycling during such global glaciation is controversial (41,44). However, precipitation rates driven by sublimation alone appear sufficient for the development of localized wetbased ice streams with high basal sliding velocities and consequent erosive potential (40); evaporation from cryoconite ponds (a notable sink for solar radiation in a Snowball state (45)) might further enhance hydrological cycling.…”