Ancient global warming ‘triggered’ by volcanoes

Massive volcanic eruptions about 55 million years ago near Greenland and Europe triggered a period of global warming, scientists said today.

During this period, known as the Paleocene-Eocene thermal maximum (PETM), sea surface temperatures rose by five degrees C in the tropics and more than six degrees C in the Arctic.

PETM lasted for 220,000 years and the eruptions, which pushed Greenland and north-west Europe apart to create the north Atlantic ocean, also resulted in increased acidification of the world’s oceans and the extinction of numerous deep-sea species.

inthenews.co.uk, 27 April 2007. Article.

Huîtres et moules vont pâtir de l’acidification des océans

La concentration du gaz carbonique (CO2) dans les eaux superficielles des océans augmente, et avec elle l’acidité de ce milieu. Les conséquences de cette acidification pour les organismes marins tels que le corail, le plancton, les algues et nombre de micro-organismes à coquille risquent d’être dévastatrices : le calcaire dont est constitué leur squelette est plus difficile à former lorsque le pH de l’eau baisse.

Pour certains mollusques d’intérêt commercial, telles l’huître ou la moule, l’impact ne sera pas non plus anodin, comme le montre une étude à paraître dans la revue Geophysical Research Letters. En modifiant la concentration en CO2 dans des aquariums abritant des moules comestibles (Mytilus edulis) et des huîtres du Pacifique (Crassostrea gigas), une équipe internationale a constaté que la vitesse de fabrication des coquilles était respectivement diminuée de 25 % et 10 % lorsqu’on atteignait un taux de CO2 correspondant à un scénario moyen prévu pour 2100.

“Il s’agit de mesures à court terme, note Jean-Pierre Gattuso, du laboratoire d’océanographie de Villefranche-sur-Mer (CNRS, université Pierre-et-Marie-Curie), cosignataire de l’article. On ignore si cela conduira à une croissance plus lente, à une coquille plus fragile, ou si cela induira un mécanisme d’adaptation à long terme.”

L’aquaculture des mollusques représente un marché mondial annuel de 7,9 milliards d’euros. Outre leur intérêt commercial, ces animaux jouent un rôle de filtration des eaux. Leur déclin aurait un impact sur l’ensemble des écosystèmes côtiers.

Le Monde, Hervé Morin, 20 Mars 2007. Article (subscription required).

Ocean Acidification

In addition to climate change, another concern about increasing atmospheric CO2 is its potential impact on the chemistry of the world’s oceans. Higher CO2 concentrations cause ocean waters to become more acidic. In a more acidic ocean, calcium carbonate, the foundation of the shells and skeletons of many aquatic organisms, starts to dissolve.

In the past 5-10 years, scientists have begun to demonstrate changes in ocean chemistry and to observe the impacts of chemical changes on marine plants and animals. To better understand this phenomenon, let’s briefly look at the global carbon cycle and the carbonate system of seawater.

Educational web site

Late Early Triassic climate change: Insights from carbonate carbon isotopes, sedimentary evolution and ammonoid paleobiogeography

The late Early Triassic sedimentary-facies evolution and carbonate carbon-isotope marine record (delta C-13(carb)) of ammonoid-rich, outer platform settings show striking similarities between the South ChinaBlock (SCB) and the widely distant Northern Indian Margin (NIM). The studied sections are located within the Triassic Tethys Himalayan belt (Losar section, Himachal Pradesh, India) and the Nanpanjiang Basin in the South China Block (Jinya section, Guangxi Province), respectively. Carbon isotopes from the studied sections confirm the previously observed carbon cycle perturbations at a time of major paleoceanographic changes in the wake of the end-Permian biotic crisis. This study documents the coincidence between a sharp increase in the carbon isotope composition and the worldwide ammonoid evolutionary turnover (extinction followed by a radiation) occurring around the Smithian-Spathian boundary.

Based on recent modeling studies on ammonoid paleobiogeography and taxonomic diversity, we demonstrate that the late Early Triassic (Smithian and Spathian) was a time of a major climate change. More precisely, the end Smithian climate can be characterized by a warm and equable climate underlined by a flat, pole-to-equator, sea surface temperature (SST) gradient, while the steep Spathian SST gradient suggests latitudinally differentiated climatic conditions. Moreover, sedimentary evidence suggests a transition from a humid and hot climate during the Smithian to a dryer climate from the Spathian onwards. By analogy with comparable carbon isotope perturbations in the Late Devonian, Jurassic and Cretaceous we propose that high atmospheric CO2 levels could have been responsible for the observed carbon cycle disturbance at the Smithian-Spathian boundary. We suggest that the end Smithian ammonoid extinction has been essentially caused by a warm and equable climate related to an increased CO2 flux possibly originating from a short eruptive event of the Siberian igneous province. This increase in atmospheric CO2 concentrations could have additionally reduced the marine calcium carbonate oversaturation and weakened the calcification potential of marine organisms, including ammonoids, in late Smithian oceans.

Galfetti T, Bucher H, Brayard A, Hochuli PA, Weissert H, Guodun K, Atudorei V, Guex J, 2007. Late Early Triassic climate change: Insights from carbonate carbon isotopes, sedimentary evolution and ammonoid paleobiogeography, Palaeogeography, Palaeoclimatology, Palaeoecology 243 (3-4): 394-411. Article

What Corals Are Dying to Tell Us about CO2 and Ocean Acidification

What Corals Are Dying to Tell Us about CO2 and Ocean Acidification

Speaker: Ken Caldeira, Ph.D.
Dept. of Global Ecology, The Carnegie Institution

Monday, March 5, 2007 5:30 PM. Smithsonian National Museum of Natural History. Link.

An estimate of anthropogenic CO2 inventory from decadal changes in oceanic carbon content

Increased knowledge of the present global carbon cycle is important for our ability to understand and to predict the future carbon cycle and global climate. Approximately half of the anthropogenic carbon released to the atmosphere from fossil fuel burning is stored in the ocean, although distribution and regional fluxes of the ocean sink are debated. Estimates of anthropogenic carbon (Cant) in the oceans remain prone to error arising from (i) a need to estimate preindustrial reference concentrations of carbon for different oceanic regions, and (ii) differing behavior of transient ocean tracers used to infer Cant. We introduce an empirical approach to estimate Cant that circumvents both problems by using measurement of the decadal change of ocean carbon concentrations and the exponential nature of the atmospheric Cant increase. In contrast to prior approaches, the results are independent of tracer data but are shown to be qualitatively and quantitatively consistent with tracer-derived estimates. The approach reveals more Cant in the deep ocean than prior studies; with possible implications for future carbon uptake and deep ocean carbonate dissolution. Our results suggest that this approach applied on the unprecedented global data archive provides a means of estimating the Cant for large parts of the world’s ocean.

Tanhua T., Körtzinger A., Friis K., Waugh D. W., and Wallace D. W. R., 2007. An estimate of anthropogenic CO2 inventory from decadal changes in oceanic carbon content. Proceedings of the National Academy of Science of the USA. doi:0.1073/pnas.0606574104. Article.

Climate change already affecting UK’s marine life

… Oceans around the world are becoming more acid as a result of the increased concentration of carbon dioxide being absorbed at the sea surface. Computer models suggest that the increased acidity of British coastal waters will surpass the maximum acidity of existing levels.

"The full impacts of acidification remain largely unknown but organisms such as corals, some plankton, shellfish and sea urchins are expected to become less able to produce calcareous parts, such as shells, by the middle of the century," the report says.

The Independent Online, 29 November 2006. Article.


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

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