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Ocean floor reveals past climate changes

Invaluable resource

Lamont-Doherty oceanographic vessels started collecting these samples more than 50 years ago, at a time when no one was sure what they would be used for.

“The first director, Maurice Ewing, had the sense that these cores had to contain important information and it turns out they do," Raymo says. "They’ve been an invaluable resource in studying past climate change, past ocean circulation, past ocean temperatures, the evolution of life in the ocean in the past, and they are an incredible archive of the evolution of life in the ocean in the past.”

The core samples provide a reliable record partly because the deep ocean is a very peaceful place, compared to the shoreline.

“It’s very far away from the margins where there is a lot of erosional material coming in, where there are lots of waves breaking on the shores and on the continental shelf. Material that settles through the water column just gently layers on the bottom, layer by layer by layer, and it can just be undisturbed for millions of years.”

Vital clues

According to Raymo, the types of species one finds along a length of core reveal vital clues about past environmental changes where the sample was taken. She asks us to imagine a core sample from the middle of the North Atlantic Ocean:

“And you go down your core and you see these kind of sub-polar species, temperate species. Then all of a sudden, you see species that only live in sea ice or next to sea ice. And that tells you that at that location, at that time in the past, sea ice covered that part of the North Atlantic. Because you only see these polar species of plankton. You could go further south and look at a core and see it varying between tropical species and subtropical species, and that’s directly reflective of how the sea surface temperature was changing through time.”