L’acidification des océans : vérité ou intox ? (in French)

La communication sur « le développement durable », souvent réduite à sa dimension environnementale, a choisi de dramatiser les enjeux, quitte à les grossir, voire parfois à les caricaturer.

Après le réchauffement climatique et la mise en cause des rejets de dioxyde de carbone par l’homme, les médias nous alertent sur un problème beaucoup plus préoccupant: l’acidification des océans. Vérité ou intox?

A côté des méthodes qui privilégient la peur, l’émotion ou la mauvaise conscience, il existe la voie de l’information contradictoire et de la responsabilisation des citoyens.

Mission: à partir des différentes ressources qui vous sont proposées, votre dasse est chargée de présenter une exposition au CDI sur l’acidification des oceans.

Changes in depth-transect redox conditions spanning the end-Permian mass extinction and their impact on the marine extinction: evidence from biomarkers and sulfur isotopes

Changes in redox conditions during the Changhsingian to Griesbachian spanning the end-Permian mass extinction were recently reported based on analyses of organic molecules. We provide more precise organic-molecular data, that details redox conditions spanning the end-Permian mass extinction at different palaeowater depths in the neritic Palaeotethys (estimated water depths: 10, 40, 100, and 200 m; Bulla, Huangzhishan, Meishan, and Chaohu sections, respectively) during this period. Here we propose that a change from occasional euxinia to anoxia in the shallow Palaeotethys occurred at the time of the mass extinction intercalated with oxic pulses. The second extinction at 0.7 m.y. after the main extinction was also caused by anoxia. New and published sulfur-isotope ratios (³⁴S/³²S) measured in carbonate-associated sulfate from the neritic Palaeotethys and in sulfide from pelagic central Panthalassa sediments show high values during the Changhsingian, consistent with the development of euxinia. The mass extinction coincided with a global fall in δ³⁴S values, as well as a shift in δ¹³C values, indicating a global oxidation of H₂S. This organic and isotopic geochemistry implies that accumulation of hydrogen sulfide in intermediate and deep waters followed by oxidation of hydrogen sulfide led to dissolved oxygen consumption, surface-water anoxia, and acidification, resulting in the end-Permian mass extinction in the seas.

Rapidly rising ocean acidity threatens marine life

Carbon dioxide causes global warming, but it also is the reason behind another problem: ocean acidification. The ocean absorbs carbon dioxide that would otherwise contribute to global warming, but it’s not all good news. This additional CO2 changes water’s chemistry, making it more acidic, which will vastly alter marine life in the next several decades and force extinction of many species.

This problem has only been on scientists’ radar for the past five or so years, and much of the public remains unaware. Every day, approximately 22 million tons of carbon dioxide from the atmosphere is absorbed into ocean waters. Since the Industrial Revolution, humans have increased ocean acidity by 30 percent, and it’s expected to double by the end of the century.