Most people around Madison are familiar with the idea that when you "over fertilize" our lakes with nutrients like phosphorus, it causes an algae bloom. First the lake turns green-- then the algae run out of food and die. Often fish die, because all the oxygen gets used up when the algae rots.
I've reported before how you can get algae blooms in the ocean. These, too, sometimes cause die-offs. For example, there's the "infamous dead zone in the Gulf of Mexico created by farm runoff carried down the Mississippi River."
The mother of all algae blooms
A scientist at Stanford University, Katja Meyer, has been studying the Earth's largest period of extinction, which happened 250,000 years ago. It's cause hasn't been pinned down for sure, but it may have been caused by a period of massive lava flows, which belched poisonous gasses and carbon dioxide into the atmosphere.
Dr. Meyer's research explains why it took life millions of years for larger forms of sea life to recover from the extinction. Basically, larger forms like fish couldn't live in the ocean, because oxygen was depleted by an algae bloom lasting millions of years.
"The driver of the ongoing population boom appears to have been the massive amounts of carbon dioxide pumped into the atmosphere during the volcanism, Meyer said, which caused the world to warm.
'More warmth means... more rain and this rain is also more acidic because there is more carbon dioxide dissolved in the rain,' Meyer said.
The increased amounts of more acidic rain increased weathering of the land surface, which sent more nutrients into the ocean, which fueled explosions of life such as algae blooms.
'It is kind of counter intuitive that high productivity on the part of algae and bacteria would likely be generating these toxic geochemical conditions that prevent most of animal life from recovering from mass extinction,' Meyer said."
But the process, she said, is basically the same as when excess runoff from fertilizers goes into a body of water...."