Ocean bays surrounded by desert land could support photosynthetic life
on Snowball Earth
Abstract
Photosynthetic eukaryotic algae survived the Neoproterozoic Snowball
Earth events, indicating that liquid-water refugia existed somewhere on
the surface. We examine the potential for refugia at the coldest time of
a snowball event, before CO2 had risen and with high-albedo ice on the
frozen ocean, before it became darkened by dust deposition. We use the
Community Earth System Model to simulate a “modern” Snowball Earth
(i.e., with continents in their current configuration), in which the
ocean surface has frozen to the equator as “sea glaciers”, hundreds of
meters thick, flowing like ice shelves. Despite global mean surface
temperatures below -60°C, some areas of the land surface reach
above-freezing temperatures because they are darker than the ice-covered
ocean. With low CO2 (10 ppm) and land-surface albedo 0.4 (characteristic
of bright sand-deserts), 0.1 percent of the land surface could host
liquid water seasonally; this increases to 12 percent for darker land of
albedo 0.2, characteristic of polar deserts. Narrow bays intruding from
the ocean to these locations (such as the modern Red Sea) could provide
a water source protected from sea-glacier invasion, where photosynthetic
life could survive. The abundance of potential refugia increases more
strongly in response to reducing the land albedo than to increasing the
CO2, for the same global radiative forcing.