Earth’s Coldest Ocean Temperatures Measured from ‘Snowball Earth’ Period
Scientists have, for the first time, quantitatively measured ocean temperatures from the “Snowball Earth” period, approximately , revealing conditions far colder than previously understood. The research, led by an international team including Chinese scientists, indicates that ocean temperatures at continental margins – areas crucial for early life – plummeted to between -22°C and -8°C. This discovery provides critical insight into how life persisted during a time when ice sheets are believed to have extended from the poles to the equator.
The study, recently published in the journal Nature Communications, focused on analyzing iron formations – distinctive rusty red rocks deposited where ancient glaciers met the ice-covered seas. These formations hold a key to unlocking the secrets of this extreme period in Earth’s history. The team developed a novel method utilizing iron isotopes as a “thermometer” to determine the temperature of the ancient oceans.
Iron isotopes, variants of the element differing in neutron count, exhibit variations in atomic abundance that are sensitive to temperature. By analyzing the isotopic composition of iron in these formations, researchers were able to reconstruct the ocean temperatures with unprecedented accuracy. “As the first measured ocean temperature during the Snowball Earth period, this discovery offers new insights into understanding the mechanisms by which early life survived in such extreme climates and sheds light on Earth’s dramatic climate changes,” explained Lu Kai, the study’s first author and a postdoctoral researcher at the Institute of Geology and Geophysics of the Chinese Academy of Sciences.
The measured temperatures are significantly colder than today’s average ocean surface temperature of 17°C, and even surpass the frigid conditions found in modern Antarctic environments. Lu Kai noted that the temperatures are colder than the -13°C salty slush found in ice-covered Lake Vida in Antarctica, making this the coldest measured ocean temperature in Earth’s history.
High Salinity as an ‘Antifreeze’
Despite the extreme cold, the seawater remained liquid, a phenomenon the researchers attribute to exceptionally high salinity levels. The study suggests that the seawater during the Snowball Earth period was up to four times saltier than modern ocean water, reaching 150 practical salinity units. This high salinity acted as a natural antifreeze, lowering the freezing point of water and allowing it to remain in a liquid state at temperatures well below 0°C.
“The results showed that the surface seawater temperature during that period was significantly lower than today’s 17 C, yet it remained unfrozen,” Lu said, attributing this to the high salinity. This finding challenges previous assumptions about the extent of ice cover during the Snowball Earth period and suggests that pockets of liquid water may have been more widespread than previously thought.
Ice Shelves and Brine Formation
The extreme conditions are believed to have formed at the base of massive ice shelves, mirroring a process known as “ice pump” circulation observed beneath modern Antarctic ice shelves. This process involves the repeated melting and freezing of ice, which expels salts and creates dense brine layers with extremely low temperatures and high salinity. The researchers suggest that similar dynamics were at play during the Snowball Earth period, contributing to the formation of the exceptionally cold and salty ocean conditions.
The formation of these brine pools is crucial to understanding the geochemical signatures found in the iron formations. The temperature-dependent fractionation of iron isotopes, where colder temperatures lead to more positive δ56Fe values, allowed the team to accurately estimate the ocean temperatures. This process, detailed in related research published in , had not been observed in earlier anoxic Archaean oceans, making the Snowball Earth iron formations particularly valuable for paleoclimate reconstruction.
Implications for Early Life and Climate Change
This research provides the first quantitative evidence of the marine environment during the Snowball Earth period, offering a valuable reference point for understanding the dramatic climate changes of that era. It also sheds light on the resilience and tolerance of early microorganisms that managed to survive in such extreme conditions. “This study provides the first quantitative evidence of the marine environment during the Snowball Earth period and serves as a valuable reference for understanding the dramatic climate changes of that era, as well as the tolerance and resilience of early microorganisms,” Lu Kai stated.
The findings contribute to a broader understanding of Earth’s climate history and the factors that have shaped the planet’s environment over billions of years. Further research will likely focus on refining the iron isotope thermometer and applying it to other ancient geological formations to reconstruct a more complete picture of Earth’s past climates.
