Page - June 16, 2008
The world’s climate is changing, and our oceans are feeling the heat. Oceans cover 70 per cent of the Earth’s surface, and small changes in the oceans’ temperature mean severe and wide-ranging impacts on the climate and marine ecosystem stability.
Simplified diagram of the Great Ocean Conveyor Belt, courtesy of the Arctic Climate Impact Assessment (ACIA), "Arctic Climate Change and Its Impacts" report.
Missing links in the conveyor belt
The water in our oceans is constantly moving, not just on the
surface, but deep below in a global ocean 'conveyor belt' that
slowly circulates warm and cold waters around the globe. This
process, known as thermohaline circulation (THC) is powered by
differences in water temperatures and salinity and redistributes
heat and nutrients so that life in the marine environment can
thrive. It also helps regulate the earth's climate, transporting
heat absorbed at the equator toward the poles.
In the Arctic, ice shelves and glaciers are melting at an
unprecedented rate and dumping huge amounts of fresh water into the
North Atlantic Ocean. The North Atlantic is a vital point in ocean
circulation, where water that has been pushed north by the North
Atlantic Current is cooled and sinks up to four kilometres in a
giant underwater waterfall. The sinking water then begins a long
journey south, deep beneath the ocean's surface.
Disruption of this process could have very serious implications
for marine ecosystem health. Deep cold water is richer in nutrients
than warm surface water, which is in turn richer in oxygen. Ocean
circulation causes upwellings of nutrient-rich cold water to
surface animals such as plankton, which forms the basis of the
marine food chain. Without these upwellings, vertical
stratification can occur, which essentially suffocates the bottom
layers of the ocean, while depriving the top layers of
nutrients.
Through the process of THC, the ocean has also been able to
absorb and sequester a large amount of the CO2 that
humans have emitted over the last two centuries. But our oceans
have reached a point where they can no longer keep up with the rate
that CO2 is being emitted into the atmosphere, leading
to an upset in its pH balance and acidification of our oceans.
Through chemical processes, CO2 is converted to carbonic
acid when it dissolves. This can lead to corrosion of the limestone
structure of existing coral reefs, and prevent the formation of new
corals and shelled organisms.
Impacts of warmer water