Oxygen levels fell in Ice Age oceans

MCGILL (CAN) — Data from the end of the last Ice Age confirm that a changing climate lowers the amount of oxygen in the water.

The first comprehensive study of changes in the oxygenation of oceans at the end of the last Ice Age (between about 10 to 20,000 years ago) has implications for the future of our oceans under global warming.


The study, which was co-authored by Eric Galbraith, assistant professor of earth and planetary sciences at McGill University, looked at marine sediment and found that that the dissolved oxygen concentrations in large parts of the oceans changed dramatically during the relatively slow natural climate changes at the end of the last Ice Age.

This was at a time when the temperature of surface water around the globe increased by approximately 2 °C over a period of 10,000 years.
A similar rise in temperature will result from human emissions of heat-trapping gases within the next 100 years, if emissions are not curbed, say the researchers, whose findings are published in the journal Nature Geoscience.

Most of the animals living in the ocean, from herring to tuna, shrimp to zooplankton, rely on dissolved oxygen to breathe. The amount of oxygen that seawater can soak up from the atmosphere depends on the water temperature at the sea surface. As temperatures at the surface increase, the dissolved oxygen supply below the surface gets used up more quickly.

Currently, in about 15 percent of the oceans—in areas referred to as dead zones—dissolved oxygen concentrations are so low that fish have a hard time breathing at all. The findings from the study show that these dead zones increased significantly at the end of the last Ice Age.

“Given how complex the ocean is, it’s been hard to predict how climate change will alter the amount of dissolved oxygen in water. As a result of this research, we can now say unequivocally that the oxygen content of the ocean is sensitive to climate change, confirming the general cause for concern,” says Galbraith.

This research was funded by the Natural Sciences and Engineering Research Council of Canada and the Canadian Institute for Advanced Research.

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