Abstract
When a snowball Earth deglaciates through a very high atmospheric CO2 concentration, the resulting inflow of freshwater leads to a stably stratified ocean, and the strong greenhouse conditions drive the climate into a very warm state. Here, we use a coupled atmosphere-ocean general circulation model, applying different scenarios for the evolution of atmospheric CO2, to conduct the first simulation of the climate and the three-dimensional ocean circulation in the aftermath of the Marinoan snowball Earth. The simulations show that the strong freshwater stratification breaks up on a timescale in the order of 103 years, mostly independent of the applied CO2 scenario. This is driven by the upwelling of salty waters in high latitudes, mainly the northern hemisphere, where a strong circumpolar current dominates the circulation. In the warmest CO2 scenario, the simulated Marinoan supergreenhouse climate reaches a global mean surface temperature of about 30 °C under an atmospheric CO2 concentration of 15 × 103 parts per million by volume, which is a moderate temperature compared to previous estimates. Consequently, the thermal expansion of seawater causes a sea-level rise of only 8 m, with most of it occurring during the first 3000 years. Our results imply that the surface temperatures of that time were potentially not as threatening for early metazoa as previously assumed. Furthermore, the short destratification timescale found in this study implies a very rapid accumulation of Marinoan cap dolostones, given that they were deposited in a freshwater environment.
Highlights
15 We apply a coupled atmosphere-ocean general circulation model (AOGCM) to study the transient period after the deglaciation of the Marinoan snowball Earth, including, for the first time, the three-dimensional ocean circulation
In the warmest CO2 scenario, the simulated Marinoan supergreenhouse climate reaches a global mean surface temperature of about 30◦C under an atmospheric CO2 concentration of 15×103 parts per million by volume, which is a moderate temperature compared to previous estimates
The short destratification timescale found in this study implies a very rapid accumulation of Marinoan cap dolostones, given that they were deposited in a freshwater environment
Summary
15 We apply a coupled atmosphere-ocean general circulation model (AOGCM) to study the transient period after the deglaciation of the Marinoan snowball Earth, including, for the first time, the three-dimensional ocean circulation. During the globally frozen state kilometer-scale continental ice sheets and a several hundred meter, up to one kilometer, thick layer of sea ice formed (Hoffman, 2011; Abbot et al, 2013). Beneath this global ice cover the ocean was hypersaline, geochemically evolved through ridge volcanism and well mixed (Le Hir et al, 2008b; Gernon et al, 2016; Ashkenazy et al, 2013). The subsequent transition from the cold snowball to a warm greenhouse climate was rapid and globally synchronous, as can be inferred from the sharp contact between the glacial deposits 30 of the panglacial state and the overlying carbonate formations (Kennedy, 1996; Hoffman et al, 1998; Calver et al, 2013; Hoffman, 2011). The partial pressure of CO2 is expected to have reached 0.01-0.1 bar at the end of the Marinoan snowball Earth (Kasemann et al, 2005; Le Hir et al, 2008c; Abbot et al, 2012), promoting very 35 high temperatures in its aftermath
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
