Another iron in the fire

Two weeks ago, I mentioned that scientists had discovered the whereabouts of "missing" carbon dioxide: It had been absorbed by the oceans. At the time, I noted that some scientists, while saying that this absorption had ameliorated the effects of global warming, could spell trouble for some shell-forming marine animals - which could cause other trouble in the future.

Add another creature and another potential problem to that list, said the BBC on August 29.

The increasing acidity of the world's oceans could banish all coral by 2065, a leading marine expert has warned.

Professor Katherine Richardson said sea organisms that produced calcareous structures would struggle to function in the coming decades as pH levels fell

The expert, based in Denmark, told the EuroScience Open Forum 2004 that human-produced carbon dioxide was radically changing the marine environment.

Ice cores show current carbon dioxide levels are higher now than they have been in the last 440,000 years.

Most of it will eventually be absorbed by seawater, where it will react to form carbonic acid.

The oceans currently have a pH of about 8, but experts predict this could drop to pH 7.4. ...

Carbon dioxide is removed from the atmosphere by microscopic ocean-dwelling plants called phytoplankton, through photosynthesis. But one group, called the coccolithophorids, also produce calcium carbonate platelets, called liths.

Each lith is only about 2.5 micrometres (millionths of a metre) across but a very great many are produced each year.

It is estimated that blooms of the dominant species, Emiliania Huxleyi, annually cover about 1.4 million sq km of the ocean.

When they die, they rain down to the ocean floor, in the process locking carbon away in a vast sediment store. This biological pump helps to control the exchange of carbon between the oceans and atmosphere.

"E. Huxleyi has dominated the world's oceans since the Holocene, but prior to that a different species was responsible for moving all the carbon to the bottom," explained Professor Richardson.

"It's anyone's guess if another species would step in if E. Huxleyi can't tolerate the more acidic conditions."

In other words, they go, we have no clue what happens - except that if no other creature "steps in," atmospheric CO₂ skyrockets. Terrific.

Footnote: The Holocene is the present era, encompassing the period since the last ice age, or about 11,000 years.