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2009-03-09 – L’inquinamento “corrode” la vita marina (Acid Ocean, thinner shells)

L’acidificazione degli oceani dovuta al crescente aumento di CO2 nell’atmosfera, ha comportato una riduzione del 35% nello spessore della conchiglia nel foraminifero Globigerina bulloides dal periodo pre-industiale ad oggi.

Ciò oltre ad alterare l’equilibrio della vita marina è una brutta notizia anche per noi esseri umani in quanto una riduzione di spessore nelle conchiglie significa una maggior quantità di CO2 che non viene fissato dagli organismi nelle loro conchiglie e che quindi rimane ad intossicare l’aria che respiriamo.

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Proof on the Half Shell: A More Acid Ocean Corrodes Sea Life

Ocean acidification is taking a toll on tiny shell-building animals

By David Biello  

SHELL GAME: Foramnifera, like Globigerina bulloides pictured here, are having a harder time building big shells in a more caustic Southern Ocean. COURTESY OF ANDREW MOY

SHELL GAME: Foramnifera, like Globigerina bulloides pictured here, are having a harder time building big shells in a more caustic Southern Ocean. COURTESY OF ANDREW MOY

 

The shells of tiny ocean animals known as foraminifera—specifically Globigerina bulloides—are shrinking as a result of the slowly acidifying waters of the Southern Ocean near Antarctica. The reason behind the rising acidity: Higher carbon dioxide (CO2) levels in the atmosphere, making these shells more proof that climate change is making life tougher for the seas’ shell-builders.

Marine scientist Andrew Moy at the Antarctic Climate & Ecosystems Cooperative Research Center (ACE) in Hobart, Tasmania, and his Australian colleagues report in Nature Geoscience this week that they made this finding after comparing G. bulloides shells in ocean cores collected along the South Tasman Rise in 1995 with samples from traps collected between 1997 and 2004. The cores provide records that stretch back 50,000 years.

“We knew there were changes in carbonate chemistry of the surface ocean associated with the large-scale glacial-interglacial cycles in CO2 [levels], and that these past changes were of similar magnitude to the anthropogenic changes we are seeing now,” says study co-author William Howard, a marine geologist at ACE. “The Southern [Ocean] works well [to study this issue] as it is a region where anthropogenic CO2 uptake, and thus acidification, has progressed more than in other regions. Other variables, such as temperature, have changed, but not as much.”

The researchers found that modern G. bulloides could not build shells as large as the ones their ancestors formed as recently as century ago. In fact, modern shells were 35 percent smaller than in the relatively recent past—an average of 17.4 micrograms compared with 26.8 micrograms before industrialization. (One microgram is one millionth of a gram; there are 28.3 grams in an ounce.)

“We don’t yet know what impact this will have on the organisms’ health or survival,” Howard says, but one thing seems clear: the tiny animals won’t be storing as much CO2 in their shells in the form of carbonate. “If the shell-making is reduced, the storage of carbon in the ocean might be, as well.”

That’s bad news for the climate, because the ocean is responsible for absorbing at least one quarter of the CO2 that humans load into the air through fossil fuel burning and other activities—and it is the action of foraminifera and other tiny shell-building animals, along with plants like algae that lock it away safely for millennia.

It will be harder to get such a clear sign in a shell from other ocean regions—as variables like temperature and the amount of minerals available can significantly change the chemistry of a given ocean region. As Howard noted, the Southern Ocean has absorbed lots of manmade CO2 while temperatures and nutrients have not changed as much, making it more ideal for studying ocean acidification than other areas. Scientists examining foraminifera in the Arabian Sea, however, have found similar results, and Howard speculates the situation may be similar in the North Atlantic region, because it also absorbs a significant chunk of manmade CO2.

Howard says that CO2 emissions must be cut or captured and stored permanently in some fashion to halt this gradual acidification of the world’s oceans. In the meantime, he adds, it’s likely that many of the other shell-building oceanic animals are suffering similar fates as G. bulloides.

source: http://www.sciam.com/article.cfm?id=more-acid-ocean-corrodes-sea-life

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ABC Science Online – ‎12 ore fa‎
“The ocean is currently taking up somewhere in the neighbourhood of a third of our fossil fuel emissions,” says Howard, a palaeo-climatologist.
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Reduced calcification in modern Southern Ocean planktonic foraminifera

 

Andrew D. Moy, William R. Howard, Stephen G. Bray & Thomas W. Trull

Abstract: Anthropogenic carbon dioxide has been accumulating in the oceans, lowering both the concentration of carbonate ions and the pH (ref. 1), resulting in the acidification of sea water. Previous laboratory experiments have shown that decreased carbonate ion concentrations cause many marine calcareous organisms to show reduced calcification rates2, 3, 4, 5. If these results are widely applicable to ocean settings, ocean acidification could lead to ecosystem shifts. Planktonic foraminifera are single-celled calcite-secreting organisms that represent between 25 and 50% of the total open-ocean marine carbonate flux6 and influence the transport of organic carbon to the ocean interior7. Here we compare the shell weights of the modern foraminifer Globigerina bulloides collected from sediment traps in the Southern Ocean with the weights of shells preserved in the underlying Holocene-aged sediments. We find that modern shell weights are 30–35% lower than those from the sediments, consistent with reduced calcification today induced by ocean acidification. We also find a link between higher atmospheric carbon dioxide and low shell weights in a 50,000-year-long record obtained from a Southern Ocean marine sediment core. It is unclear whether reduced calcification will affect the survival of this and other species, but a decline in the abundance of foraminifera caused by acidification could affect both marine ecosystems and the oceanic uptake of atmospheric carbon dioxide.

Correspondence to: William R. Howard1 e-mail: Will.Howard@utas.edu.au

Link: nature.com – supplementary information

Nature Geoscience  – Published online: 8 March 2009 | doi:10.1038/ngeo460

marzo 9, 2009 - Posted by | Articolo sc. di riferimento, Attuale, Bio-Zoology / Bio-Zoologia, Bl - Top posts, Geology - Geologia, Italiano (riassunto), X - Nature | , , , , , , , ,

2 commenti »

  1. […] 2009-03-09 – L’inquinamento “corrode” la vita marina (Acid Ocean, thinner shells) […]

    Pingback di 2009-04-06 - Plymouth ENG: Plymouth Ocean Acidification Meeting « Paleonews | aprile 6, 2009

  2. Ciao

    Nice site!

    David
    (palaeontologist)

    Commento di David Mayhew | novembre 9, 2009


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