Investigating the influence of atmospheric CO2, bathymetry, and salinity on Archean Ocean circulation

Abstract

During part of the Archean Eon (4 to 2.5 billion years ago), it is estimated that Earth experienced near-global ocean coverage. Little is known about the ocean during this time,but it coincides with—and may have been instrumental in—the earliest development of life on our planet. It is therefore essential to understand what the ocean’s physical environment could have been within the early Archean Eon, as it can help us better understand the background under which life on our planet evolved. However, modeling this environment requires constraints on the atmospheric and oceanic conditions at the time, many of which span wide ranges (e.g., atmospheric CO2 and other greenhouse gases, and ocean salinity) or have almost no constraints at all, such as ocean depth and bathymetry. Here we use the ROCKE-3D coupled atmosphere-ocean general circulation model configured for the early Archean environment to explore the ocean properties and circulation under a range of atmospheric and oceanographic parameters. Specifically, a suite of simulations is performed to understand how atmospheric CO2 concentration,ocean salinity, and simplified ocean bathymetry could have impacted ocean circulation and heat transport. We find that 1) altering the atmospheric CO2 concentration results in different ocean states ranging from cold, fully ice-covered, to warm, fully ice-free; 2) the addition of bathymetry leads to changes in both ocean density and the overturning circulation, but the strength of the changes depends on the specifics of the bathymetry; and 3) the influence of increased salinity is larger in a colder ocean with sea ice present compared to a warmer ocean with no sea ice.