A new study published recently in the journal Nature Geoscience looks at the connection between Atlantic Ocean currents and our planet’s climate history. Led by researchers at Columbia University's Lamont-Doherty Earth Observatory, the study analyzed the Atlantic meridional overturning circulation (AMOC) current system and was able to correlate a sudden slow-down of the AMOC that occurred 950,000 years ago with a massive buildup of carbon in the deep Atlantic.
Let’s put some context to this event. The scientists figured out about the AMOC weakening and slow-down by analyzing cores of deep-sea sediments from the south and north Atlantic. The subsequent result was the deep ocean absorbing approximately 50 billion tons more carbon than it had during any past glaciations. That’s a huge number, roughly equal to one-third of the human emissions that all the world's oceans have so far absorbed today, according to Science Daily.
The buildup of carbon into the ocean almost one million years ago meant a reduction of carbon in the air at that same time and scientists think that this played a role in the Mid-Pleistocene Transition, which refers to the period when ice ages began happening every 100,000 years instead of every 40,000 years. While scientists still don’t understand why the pattern of ice ages every 100,000 years has continued, this study at least clears up the link between the carbon buildup in the ocean and correlating reduction in the air.
"It's a one-to-one relationship. It was like flipping a switch," said lead author Jesse Farmer. "It shows us that there's an intimate relationship between the amount of carbon stored in the ocean, and what the climate is doing."
One of the reasons scientists are so key to understand these past patterns is because the AMOC is currently undergoing a slow-down which researchers believe may be similar to the one it experienced almost a million years ago. While the strength of the AMOC is thought to fluctuate naturally, it seems to have weakened 15% since the mid-20th century. It is still unclear if the trend will continue and what impacts it will have, though the researchers are quick to say it will certainly not be the savior for climate change.
However, in order to better understand how the AMOC patterns come into play in climate history and climate future, scientists will also have to learn more about the carbon dynamics of the rest of the oceans, for example, the Indian and Pacific oceans which make up part of the Great Ocean Conveyor. The team plans to continue their work on carbon chronologies in attempts to fill in gaps in all the oceans.