The clay protects foraminifera from surrounding water and the sediments that might otherwise infiltrate and erode the shell.
Pearson's team discovered Tanzanian shells from the Late Cretaceous epoch had much higher concentrations of the oxygen 16 isotope than shells of similar age collected from deep-sea cores. The high oxygen 16 concentrations are a signature of shells that originally grew in warm waters.
The oxygen profile of the Tanzanian shells indicated that tropical sea surface temperatures were between 28 and 32 degrees Celsius (82 and 89 degrees Fahrenheit), which are consistent with climate predictions for the Late Cretaceous period. Analysis of deep-sea foraminifera suggests much colder temperatures: 15 to 23 degrees Celsius.
"This paradox has been a serious impediment to progress," said Kump. Considerable effort has been spent to resolve this paradox by reshaping climate models to account for the cool-tropics phenomenon.
"Researchers tried to make models fit the data by taking into consideration cloud cover and ocean currents that may have led to cooler tropical waters, but these creative ideas are hard to substantiate," said Kump.
"The new data rids us of this paradox so we can move on," says Kump.
The new study also improves confidence in the ability of climate models to predict greenhouse-induced changes as carbon dioxide levels rise.
Kump anticipates that this new study will be met with considerable resistance. "Decades of climate research are based on deep-sea planktonic foraminifera, now much of this research is of dubious value and may be thrown away," said Kump.
Although further studies are needed to verify these results, "researchers will undoubtedly need to choose their sample more carefully, looking for those that are unaffected by local conditions," he said.
