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Event

 
Warmer seas will wipe out plankton, source of ocean life

By Steve Connor, Science Editor
Published: 19 January 2006
http://news.independent.co.uk/environment/article339596.ece

The microscopic plants that underpin all life in the oceans are likely 
to be destroyed by global warming, a study has found.

Scientists have discovered a way that the vital plankton of the oceans 
can be starved of nutrients as a result of the seas getting warmer. They 
believe the findings have catastrophic implications for the entire 
marine habitat, which ultimately relies on plankton at the base of the 
food chain.

The study is also potentially devastating because it has thrown up a new 
"positive feedback" mechanism that could result in more carbon dioxide 
ending up in the atmosphere to cause a runaway greenhouse effect.

Scientists led by Jef Huisman of the University of Amsterdam have 
calculated that global warming, which is causing the temperature of the 
sea surface to rise, will also interfere with the vital upward movement 
of nutrients from the deep sea.

These nutrients, containing nitrogen, phosphorus and iron, are vital 
food for phytoplankton. If the supply is interrupted the plants die off, 
which prevents them from absorbing carbon dioxide from the atmosphere.

"Global warming of the surface layers of the oceans reduces the upward 
transport of nutrients into the surface layers. This generates chaos 
among the plankton," the professor said.

The sea is one of nature's "carbon sinks", which removes carbon dioxide 
from the atmosphere and deposits the carbon in a long-term store - 
dissolved in the ocean or deposited as organic waste on the seabed. The 
vast quantities of phytoplankton in the oceans absorb huge amounts of 
carbon dioxide. When the organisms die they fall to the seabed, carrying 
their store of carbon with them, where it stays for many thousands of 
years - thereby helping to counter global warming.

"Plankton... forms the basis of the marine food web. Moreover, 
phytoplankton consumes the greenhouse gas carbon dioxide during 
photosynthesis," Professor Huisman said. "Uptake of carbon dioxide by 
phytoplankton across the vast expanses of the oceans reduces the rising 
carbon dioxide levels in the atmosphere."

Warmer surface water caused by global warming causes greater temperature 
stratification, with warm surface layers sitting on deeper, colder 
layers, to prevent mixing of nutrients.

Professor Huisman shows in a study published in Nature that warmer sea 
surfaces will deliver a potentially devastating blow to the supply of 
deep-sea nutrients for phytoplankton.

His computer model of the impact was tested on real measurements made in 
the Pacific Ocean, where sea surface temperatures tend to be higher than 
in other parts of the world. He found that his computer predictions of 
how nutrient movement would be interrupted were accurate.

"A larger temperature difference between two water layers implies less 
mixing of chemicals between these water layers," he said. "Global 
warming of the surface layers of the oceans, owing to climate change, 
strengthens the stratification and thereby reduces the upward mixing of 
nutrients."

Scientists had believed phytoplankton, which survives best at depths of 
about 100 metres, is largely stable and immune from the impact of global 
warming. "This model prediction was rather unexpected," Professor 
Huisman said.

"Reduced stability of the plankton, caused by global warming of the 
oceans, may result in a decline of oceanic production and reduced 
sequestration of the greenhouse gas carbon dioxide into the oceans."

Vital link in the food chain

Microscopic plankton comes in animal and plant forms. The plants are 
known as phytoplankton. They lie at the base of the marine food chain 
because they convert sunlight and carbon dioxide into organic carbon - 
food for everything else.

Smaller animals such as shrimp-like krill feed on plankton and are 
themselves eaten by larger organisms, from small fish to the biggest 
whales. Without phytoplankton, the oceans would soon because marine 
deserts. Phytoplankton are also important because of the role they play 
in the carbon cycle, which determines how much carbon dioxide - the most 
important greenhouse gas - ends up in the atmosphere to cause global 
warming. Huge amounts of carbon dioxide from the atmosphere, which 
dissolves in the oceans, are absorbed by phytoplankton and converted to 
organic carbon. When the phytoplankton die, their shells and bodies sink 
to the seabed, carrying this carbon with them.

Phytoplankton therefore acts as a carbon "sink" which takes carbon 
dioxide from the atmosphere and deposits the carbon in long-term stores 
that can remain undisturbed for thousands of years. If the growth of 
phytoplankton is interrupted by global warming, this ability to act as a 
buffer against global warming is also affected - leading to a 
much-feared positive feedback.

The microscopic plants that underpin all life in the oceans are likely 
to be destroyed by global warming, a study has found.

Scientists have discovered a way that the vital plankton of the oceans 
can be starved of nutrients as a result of the seas getting warmer. They 
believe the findings have catastrophic implications for the entire 
marine habitat, which ultimately relies on plankton at the base of the 
food chain.

The study is also potentially devastating because it has thrown up a new 
"positive feedback" mechanism that could result in more carbon dioxide 
ending up in the atmosphere to cause a runaway greenhouse effect.

Scientists led by Jef Huisman of the University of Amsterdam have 
calculated that global warming, which is causing the temperature of the 
sea surface to rise, will also interfere with the vital upward movement 
of nutrients from the deep sea.

These nutrients, containing nitrogen, phosphorus and iron, are vital 
food for phytoplankton. If the supply is interrupted the plants die off, 
which prevents them from absorbing carbon dioxide from the atmosphere.

"Global warming of the surface layers of the oceans reduces the upward 
transport of nutrients into the surface layers. This generates chaos 
among the plankton," the professor said.

The sea is one of nature's "carbon sinks", which removes carbon dioxide 
from the atmosphere and deposits the carbon in a long-term store - 
dissolved in the ocean or deposited as organic waste on the seabed. The 
vast quantities of phytoplankton in the oceans absorb huge amounts of 
carbon dioxide. When the organisms die they fall to the seabed, carrying 
their store of carbon with them, where it stays for many thousands of 
years - thereby helping to counter global warming.

"Plankton... forms the basis of the marine food web. Moreover, 
phytoplankton consumes the greenhouse gas carbon dioxide during 
photosynthesis," Professor Huisman said. "Uptake of carbon dioxide by 
phytoplankton across the vast expanses of the oceans reduces the rising 
carbon dioxide levels in the atmosphere."

Warmer surface water caused by global warming causes greater temperature 
stratification, with warm surface layers sitting on deeper, colder 
layers, to prevent mixing of nutrients.

Professor Huisman shows in a study published in Nature that warmer sea 
surfaces will deliver a potentially devastating blow to the supply of 
deep-sea nutrients for phytoplankton.

His computer model of the impact was tested on real measurements made in 
the Pacific Ocean, where sea surface temperatures tend to be higher than 
in other parts of the world. He found that his computer predictions of 
how nutrient movement would be interrupted were accurate.

"A larger temperature difference between two water layers implies less 
mixing of chemicals between these water layers," he said. "Global 
warming of the surface layers of the oceans, owing to climate change, 
strengthens the stratification and thereby reduces the upward mixing of 
nutrients."

Scientists had believed phytoplankton, which survives best at depths of 
about 100 metres, is largely stable and immune from the impact of global 
warming. "This model prediction was rather unexpected," Professor 
Huisman said.

"Reduced stability of the plankton, caused by global warming of the 
oceans, may result in a decline of oceanic production and reduced 
sequestration of the greenhouse gas carbon dioxide into the oceans."

Vital link in the food chain

Microscopic plankton comes in animal and plant forms. The plants are 
known as phytoplankton. They lie at the base of the marine food chain 
because they convert sunlight and carbon dioxide into organic carbon - 
food for everything else.

Smaller animals such as shrimp-like krill feed on plankton and are 
themselves eaten by larger organisms, from small fish to the biggest 
whales. Without phytoplankton, the oceans would soon because marine 
deserts. Phytoplankton are also important because of the role they play 
in the carbon cycle, which determines how much carbon dioxide - the most 
important greenhouse gas - ends up in the atmosphere to cause global 
warming. Huge amounts of carbon dioxide from the atmosphere, which 
dissolves in the oceans, are absorbed by phytoplankton and converted to 
organic carbon. When the phytoplankton die, their shells and bodies sink 
to the seabed, carrying this carbon with them.

Phytoplankton therefore acts as a carbon "sink" which takes carbon 
dioxide from the atmosphere and deposits the carbon in long-term stores 
that can remain undisturbed for thousands of years. If the growth of 
phytoplankton is interrupted by global warming, this ability to act as a 
buffer against global warming is also affected - leading to a 
much-feared positive feedback.
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