Just as growth rings from trees offer clues to past climate change, corals can do the same for changes in the ocean.
Scientists know that ice sheets wax and wane as the concentration of CO2 decreases and increases in the atmosphere. Researchers believe that the deep ocean—which stores 60 times more inorganic sources of carbon than is found in the atmosphere—must play a vital role in this shift.
To investigate this, the researchers analyzed the calcium carbonate skeletons of corals collected from deep in the North Atlantic Ocean. The corals were built up from 11,000 to 18,000 years ago out of CO2 dissolved in the ocean.
“We used a new technique that has been developed at Caltech, called clumped isotope thermometry, to determine what the temperature of the ocean was in the location where the coral grew,” says Nivedita Thiagarajan, a postdoctoral scholar in geochemistry at California Institute of Technology (Caltech) and lead author of the paper published in the journal Nature.
“We also used radiocarbon dating and uranium-series dating to estimate the deep-ocean ventilation rate during this time period.”
Warm water under cold water
The deep ocean started warming before the start of a rapid climate change event about 14,600 years ago. During this time, the Earth was transitioning from a glacial period—when ice sheets covered a large portion of Earth—to the current interglacial period.
“We found that a warm-water-under-cold-water scenario developed around 800 years before the largest signal of warming in the Greenland ice cores, called the Bølling–Allerød,” says Jess F. Adkins, professor of geochemistry and global environmental science.
“CO2 had already been rising in the atmosphere by this time, but we see the deep-ocean reorganization brought on by the potential energy release to be the pivot point for the system to switch from a glacial state, where the deep ocean can hold onto CO2, and an interglacial state, where it lets out CO2.”
“Studying Earth’s climate in the past helps us understand how different parts of the climate system interact with each other,” says Thiagarajan. “Figuring out these underlying mechanisms will help us predict how climate will change in the future.”
Other authors of the paper are from Caltech and from UC Irvine.