Having used a set of samples gathered at three different locations, a team of Princeton University researchers have created an unprecedented record of ocean nitrogen and oxygen levels starting from 70 million years ago, shortly before the dinosaurs became extinct, up until 30 million years ago, showing a major shift in ocean chemistry after the India-Asia collision, according to the abstract of their findings published in the magazine Science.
When the landmass that now constitutes the Indian subcontinent slammed into Asia about 50 million years ago, the collision drastically altered the configuration of the continents, the landscape, along with climate conditions and so on. With regard to this, scientists have identified one essential effect: the oxygen in the world’s oceans increased, resulting in sweeping changes in living conditions:
“These results are different from anything people have previously seen,” said Emma Kast, a graduate student in geosciences and the lead author of the paper. “The magnitude of the reconstructed change took us by surprise.”
Another shift notably came 35 million years ago, when Antarctica started to accumulate ice, causing global sea levels to fall.
To create these images, Kast used paleogeographic reconstructions with credit to Deep Time Maps and also looked into minute shells to come up with a record of ocean nitrogen over the afore-mentioned period.
The findings indicate that 10 million years after the giant reptiles vanished from the continents, the 15N-to-14N nitrogen ratio was high, suggesting that ocean oxygen levels were low.
The researchers initially thought that the warm climate accounted for this, as oxygen is less soluble in warmer water; however, the timing hinted at the possibility that the shift to a greater amount of ocean oxygen occurred around 55 million years ago, when a warmer climate set in.
According to John Higgins, an associate professor of geosciences at Princeton and a co-author on the paper, the finding is an invaluable contribution in the field of global climate studies:
“In our field, there are records that you look at as fundamental, that need to be explained by any sort of hypothesis that wants to make biogeochemical connections,” Higgins remarked.
“Those are few and far between, in part because it’s very hard to create records that go far back in time. Fifty-million-year-old rocks don’t willingly give up their secrets. I would certainly consider Emma’s record to be one of those fundamental records. From now on, people who want to engage with how the Earth has changed over the last 70 million years will have to engage with Emma’s data,” he concluded.
