Neoproterozoic Snowball Earth oceans

Snowball Earth episodes during the Neoproterozoic era (~1000–541 million years ago) represent some of the most extreme climates our planet has experienced. Geological evidence suggests that ice advanced to very low latitudes, raising a long-standing question: were the oceans completely sealed beneath ice, or did regions of open water persist? One of the most intriguing clues comes from the reappearance of banded iron formations (BIFs) during these intervals, which are often cited as evidence for fully ice-covered, or “hard snowball,” oceans.

In my doctoral work, I revisited this interpretation by focusing on the ocean itself. I developed a biogeochemistry module within the MITgcm tailored to Neoproterozoic conditions and ran near-global simulations under Snowball-like forcing. These experiments showed that nutrient-depleted, partially ice-covered oceans, often referred to as “soft snowball” or “waterbelt” states, can produce patterns of iron deposition similar to those observed in the geological record. Limited nutrient availability suppresses cyanobacterial productivity, leading to low oxygen levels and favoring iron accumulation and mobility. In other words, a completely frozen ocean is not required to explain several of the geochemical signals that have traditionally been associated with a hard snowball climate.

This result shifts how we think about Snowball Earth climates. Rather than a static, sealed system, the ocean may have remained dynamically active, with circulation and chemical gradients playing a central role in shaping redox conditions and nutrient availability. It also highlights how tightly coupled physical circulation and biogeochemistry become in extreme environments, where relatively small changes in circulation can have outsized chemical consequences.

Looking ahead, an important next step is to add more physical and chemical realism to Snowball Earth simulations. Incorporating thick marine ice dynamics alongside a more complete treatment of ocean biogeochemistry would make it possible to explore how Snowball climates influenced Earth’s oxygen and carbon cycles across glacial and post-glacial transitions. Approaching the problem this way creates a clearer link between paleo-proxies and the physical and chemical processes that govern long-term climate stability, while also pushing general circulation models into regimes far outside the modern climate system.

More broadly, Snowball Earth offers a natural testbed for developing intermediate-complexity modeling frameworks that sit between idealized models and full Earth system models. These frameworks can help bridge insights from ancient extreme climates to more familiar problems in Earth’s climate system, such as ocean carbon uptake and long-term climate variability.