Scientists from the University of Tasmania and Canada have gained new insights into the last global ice age by collating research on ocean temperatures and carbon dioxide levels.
Institute of Marine and Antarctic Studies associate professor Zanna Chase was part of the team that examined data, to get a “big picture” of the ocean during the last ice age.
“We have known for a long time that the carbon dioxide in the atmosphere was lower during the last ice age and there’s been a lot of debate about why that was and a lot of theories,” she said.
“We know it had something to do with the ocean ... but we wanted to look at the timing of the changes, so how the changes in the ocean lined up with the changes in the CO2.”
The team focussed on two big drops in carbon dioxide levels, which were measured in bubbles trapped in Antarctic ice, one about 115,000 years ago and then another at about 70,000 years ago.
“The beginning of the last ice age, when it started to cool, was about 130,000 years ago and then around 115,000 years ago there was the first big drop in CO2 … the other thing that happened at that time was there was a big increase in the sea’s ice around Antarctica,” associate professor Chase said.
“That first drop in CO2 was most likely because of the sea ice, the sea ice kind of acts like a lid and prevents the CO2 that’s in the ocean from getting into the atmosphere.”
The second big drop in carbon dioxide was attributed to another reason.
“Then we see there was another big cooling in the ocean's surface, but at that point we see a big reorganisation of the deep ocean circulation, so we were able to separate the two effects; due to the sea ice and the deep ocean circulation,” associate professor Chase said.
She added they were unsure why there was such a large gap, 45,000 years, between these two events.
They could also not determine what caused the changes in the deep ocean circulation.
The results of the research could help improve understanding about ocean and climate into the future.
“We’ve identified feedbacks between the ocean and carbon and it’s really important to include these feedbacks in climate models that try to predict future levels of carbon in the atmosphere,” associate professor Chase said.
Both of those things would be .... things you might expect to see in the future.Zanna Chase
“Both of those things would be, changes in both the sea ice and the deep ocean circulation, things you might expect to see in the future, the other side of the cooling is they could be affected by warming.”
The researchers will now test their models.