The first comprehensive study of changes in the oxygenation of oceans at
the end of the last Ice Age (between about 10,000 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, of McGill's Department
of Earth & Planetary Sciences, 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, giving cause for concern.
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 per cent 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.
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