The Effect of Ocean Salinity on Climate and Its Implications for Earth's Habitability

TL;DR

This study uses climate modeling to show that ocean salinity significantly influences Earth's climate and habitability, affecting sea ice extent and glaciation thresholds in both present-day and early Earth scenarios.

Contribution

It is the first to systematically analyze how variations in ocean salinity impact Earth's climate and its implications for planetary habitability using advanced climate models.

Findings

Saltier oceans reduce sea ice cover significantly.

Higher salinity lowers the CO2 threshold for Snowball glaciation.

Saltier oceans can maintain warm climates on early Earth despite lower solar energy.

Abstract

The influence of atmospheric composition on the climates of present-day and early Earth has been studied extensively, but the role of ocean composition has received less attention. We use the ROCKE-3D ocean-atmosphere general circulation model to investigate the response of Earth's present-day and Archean climate system to low vs. high ocean salinity. We find that saltier oceans yield warmer climates in large part due to changes in ocean dynamics. Increasing ocean salinity from 20 g/kg to 50 g/kg results in a 71% reduction in sea ice cover in our present-day Earth scenario. This same salinity change also halves the pCO$_2$ threshold at which Snowball glaciation occurs in our Archean scenarios. In combination with higher levels of greenhouse gases such as CO$_2$ and CH$_4$, a saltier ocean may allow for a warm Archean Earth with only seasonal ice at the poles despite receiving 20% less energy from the Sun.