Glaciation not related to carbon isotopic ratio change prior to 'snowball earth'

The study was conducted by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science. The large changes in the carbon isotopic composition of carbonates

which occurred prior to the major climatic event more than 500 million years ago, known as ‘Snowball Earth,’ are unrelated to worldwide glacial events, a new study has suggested. The study

was conducted by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science. “Our study suggests that the geochemical record documented in rocks prior to

the Marinoan glaciation or ‘Snowball Earth’ are unrelated to the glaciation itself,” said UM Rosenstiel professor Peter Swart, a co-author of the study. “Instead the changes in the carbon

isotopic ratio are related to alteration by freshwater as sea level fell,” Swart stated. In order to better understand the environmental conditions prior to ‘Snowball Earth’, the research

team analysed geochemical signatures preserved in carbonate rock cores from similar climactic events that happened more recently — two million years ago — during the Pliocene-Pleistocene

period. The team analysed the ratio of the rare isotope of carbon (13C) to the more abundant carbon isotope (12C) from cores drilled in the Bahamas and the Enewetak Atoll in the Pacific

Ocean. The geochemical patterns that were observed in these cores were nearly identical to the pattern seen prior to the Marinoan glaciation, which suggests that the alteration of rocks by

water, a process known as diagenesis, is the source of the changes seen during that time period. Prior to this study, scientists theorized that large changes in the cycling of carbon between

the organic and inorganic reservoirs occurred in the atmosphere and oceans, setting the stage for the global glacial event known as ‘Snowball Earth’. “It is widely accepted that changes in

the carbon isotopic ratio during the Pliocene-Pleistocene time are the result of alteration of rocks by freshwater,” said Swart. “We believe this is also what occurred during the

Neoproterozoic. Instead of being related to massive and complicated changes in the carbon cycle, the variations seen in the Neoproterozoic can be explained by simple process which we

understand very well,” he added. Scientists acknowledge that multiple sea level fluctuations occurred during the Pliocene-Pleistocene glaciations resulting from water being locked up in

glaciers. Similar sea-level changes during the Neoproterozoic caused the variations in the global carbon isotopic signal preserved in the older rocks, not a change in the distribution of

carbon as had been widely postulated. The study was published in the journal Geology.