Océan Pacifique

Résumé

L'océan Pacifique est l'océan le plus vaste du globe terrestre. Le Pacifique fait partie de l'océan mondial et il comporte deux océans : le Pacifique Nord et le Pacifique Sud. Le Pacifique s'étend sur une surface de , soit environ un tiers de la surface totale de la Terre et de plus que la surface totale de la planète Mars. Sa superficie est également supérieure à celle de l'ensemble des terres émergées de la planète. Il comprend l'Océanie dans sa totalité et quelques autres îles et archipels qui font traditionnellement partie de l'Asie (Japon, Philippines, Insulinde). Il est entouré par l'Amérique, le continent Antarctique, l'Australie, la Nouvelle-Guinée et l'Asie. La ligne de changement de date le traverse aux alentours du . Sa plus grande dimension en longitude est de depuis le tanjung Sopi, sur l'île de Morotai (Indonésie), jusqu'aux côtes colombiennes (El Naranjo). Toponymie Le qualificatif de Pacifique est donné à cet océan par le navigateur portugais Fernand de

Source officielle

https://fr.wikipedia.org/wiki/Oc%C3%A9an_Pacifique

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Model Analysis of Ocean Compound Extreme Events in the North-Eastern Pacific

Joëlle Perreten

2021

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Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs

Hélène Paule Angot

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

National Academy of Sciences2022

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Background Two porphyry copper mines located in southern Peru initiated the discharge of mine wastes (tailings) for a final shore deposition in the Bay of Ite (Pacific Ocean). 780 millions metric tons of tailings were deposited, which formed a delta with a surface of ca. 16 km2. A low-pH oxidation zone characterized by the presence of iron hydroxides developed on the surface, along with a strong build-up of efflorescent salts rich in heavy metals. Objectives A 3 years investigation was carried out in order to understand the biogeochemical processes resulting from the remediation of the oxidizing tailings by the implementation of a wetland cover1. Methods Analysis of the bacterial communities was carried out by molecular techniques (T-RFLP and cloning-sequencing). A combination of physical, chemical and mineralogical methods was applied for the characterization of solid tailings and water samples. Results The non-remediated tailings was characterized by a low-pH oxidation zone (pH 3 – 4), in which the oxidative dissolution of sulphide was identified as the dominant process, carried out mainly by Leptospirillum spp, Acidithiobacillus spp and Sulfobacillus spp. This dissolution led to an increase in metal concentrations in the pore water. Below the oxidation zone, the neutrophilic primary zone was characterized by SO42- and Fe reductions induced by sulphate- and iron-reducing bacteria (SRB and FeRB). Drastic changes were observed along the remediation process, as the heavy metal concentrations decreased progressively close or below the detection limits together with the gradual installation of a near neutral pH and more reducing conditions. SO42- and Fe reductions were still observed in the deep section of the remediated tailings. Close to the surface, the presence of lithoautotrophic neutrophilic iron oxidizing bacteria such as Mariprofundus ferroxidans, Galionella spp, Leptotrix mobilis suggested that iron oxidation played an important role in the iron cycle. Other ubiquitous bacteria related to fresh water and marine environment were also detected in the wetland. Conclusions The implementation of a wetland promoted neutralization of the acid mine drainage and induced favourable geochemical conditions for the development of both SRB and FeRB, which lead to the metal removal from solution. References Diaby, N. 2009. Biogeochemical evolution of a marine shore tailings deposit during bioremediation. Ph. D. Thesis, University of Lausanne, Switzerland. 217 pp.

2009

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2009