Archive for February, 2011

L’homme, prédateur indirect des coraux (in French)

Selon une étude, la totalité des massifs coralliens est menacée de disparition d’ici à 2050 en raison des activités humaine

D’ici à 2050, l’un des spectacles les plus éblouissants du monde sous-marin, par ailleurs immense réservoir de biodiversité et source de revenus importante pour des centaines de milliers d’habitants des zones côtières, sera menacé de disparition, selon une étude publiée par le World Resources Institute (WRI), mercredi 23 février.

Cette organisation non gouvernementale américaine prévoit un avenir plus sombre que jamais pour les récifs coralliens, souvent qualifiés d’équivalent marin des forêts tropicales. Quelque 800 espèces de coraux ont été décrites, et les récifs calcaires qu’ils construisent hébergent un quart des espèces marines connues.
Continue reading ‘L’homme, prédateur indirect des coraux (in French)’

Ocean acidification impacts

Impacts on tropical tuna

The unaccounted impacts of ocean acidification (and warming) upon tuna stocks in the Pacific (and globally) represent a serious risk to the achievement of sustainability based management objectives for both Regional Fisheries Management Organisations (RFMOS) and for the policies of sovereign states responsible for tuna fisheries management in the Pacific region. Research has demonstrated that the early life history stages of some fish species (and numerous other marine organisms) are sensitive to ocean acidification levels that are projected to occur by the end of this century. Those findings have significant implications for future recruitment success and population levels for those species. Utilising the long established expertise and unique facilities at the IATTC’s Achotines Laboratory in Panama, the first year of this project aims to elucidate the impacts of projected ocean acidification levels upon processes and life history stages of yellowfin tuna (Thunnus albacores) that are considered critical to recruitment success: sperm motility, fertilisation rates, embryonic development, hatching rates, condition, development, growth and survival in pre- and post-feeding larvae. Empirical results from the laboratory trials will then be used, in conjunction with physical oceanographic data from ocean acidification projection models, to parameterise the SEAPODYM model and evaluate the impact of ocean acidification upon the distribution and abundance of yellowfin tuna in the Pacific Ocean. The outputs from this project will reduce uncertainty regarding future stock trends as provided to tuna RFMOs in the Pacific, increasing the likelihood that these organisations can make decisions that ultimately achieve sustainability based management objectives.
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Trajectories of Late Permian – Jurassic radiolarian extinction rates: no evidence for an end-Triassic mass extinction

The hypothesis that ocean acidification was a proximate trigger of the marine end-Triassic mass extinction rests on the assumption that taxa that strongly invest in the secretion of calcium-carbonate skeletons were significantly more affected by the crisis than other taxa. An argument against this hypothesis is the great extinction toll of radiolarians that has been reported from work on local sections. Radiolarians have siliceous tests and thus should be less affected by ocean acidification. We compiled taxonomically vetted occurrences of late Permian and Mesozoic radiolarians and analyzed extinction dynamics of radiolarian genera. Although extinction rates were high at the end of the Triassic, there is no evidence for a mass extinction in radiolarians but rather significantly higher background extinction in the Triassic than in the Jurassic. Although the causes for this decline in background extinction levels remain unclear, the lack of a major evolutionary response to the end-Triassic event, gives support for the hypothesis that ocean acidification was involved in the dramatic extinctions of many calcifying taxa.
Continue reading ‘Trajectories of Late Permian – Jurassic radiolarian extinction rates: no evidence for an end-Triassic mass extinction’

Compensatory response of the unicellular-calcifying alga Emiliania huxleyi (Coccolithophoridales, Haptophyta) to ocean acidification

Ocean acidification damages calcareous organisms, such as calcifying algae, foraminifera, corals, and shells. In this study, we made a device equipped with a Clark-type oxygen electrode and a pH-stat to examine how the most abundant calcifying phytoplankton, the coccolithophorid Emiliania huxleyi, responded to acidification and alkalization of the seawater medium. When E. huxleyi was incubated at pH 8.2, close to oceanic pH, the medium was alkalized during photosynthesis, and the alkalization rate [determined as μmol HCl added (mg Chl)−1 h−1] was identical to the activity of photosynthesis [determined as μmol O2 evolved (mg Chl)−1 h−1]. When pH was maintained at 7.2 by the pH-stat, alkalization activity was stimulated and exceeded photosynthetic activity, resulting in an increase in the ratio of alkalization to photosynthesis (Alk/PS). On the other hand, no alkalization and photosynthesis were observed at pH 9.2. In contrast, acidification of seawater was observed in the dark because of the release of respiratory CO2 from cells at pH 8.2–9.2, but not at pH 7.2. When orthophosphate was rapidly depleted within a day in the batch culture, intracellular calcification gradually increased, and both photosynthesis and alkalization decreased gradually. During the period the Alk/PS ratio also decreased gradually. These results indicate that E. huxleyi possesses an ability to compensate for the acidification of seawater when photosynthesis is more actively driven than respiration. These results suggest that the E. huxleyi cells may not be severely damaged by oceanic acidification during photosynthesis because of their homeostatic function to avoid negative effects on cellular activity. Finally, we concluded that E. huxleyi cells possess a buffering ability to reduce acidification effects when photosynthesis is actively driven.
Continue reading ‘Compensatory response of the unicellular-calcifying alga Emiliania huxleyi (Coccolithophoridales, Haptophyta) to ocean acidification’

Distal “impact” layers and global acidification of ocean water at the Cretaceous-Paleogene boundary (KPB)

The KPB sections at Højerup in Denmark, Agost and Caravaca in Spain and El Kef in Tunisia and (elsewhere in the world) consists of a very thin reddish biogenic calcite-poor smectite-rich “impact” layer overlain by a thicker smectite-rich marl. The massive amount of impact-generated atmospheric CO2 at KPB would have accumulated globally in the ocean surface, leading to acidification and CaCO3 undersaturation. These chemical changes would have induced a low biocalcification of calcareous plankton and a high dissolution of their shells. The biocalcification/dissolution crises may have played a significant role for the low abundance of biogenic calcite in the “impact” layer of the marine boundary clays at Højerup, Agost, Caravaca and El Kef (and elsewhere in the world). Experimental data and observations indicate that the deposition of the “impact” layer probably lasted only a few decades at most.
Continue reading ‘Distal “impact” layers and global acidification of ocean water at the Cretaceous-Paleogene boundary (KPB)’

A biocalcification crisis at the Triassic-Jurassic boundary recorded in the Budva Basin (Dinarides, Montenegro)

Volcanic activity in the Central Atlantic magmatic province, resulting in an increased flux of CO2, SO2, and CH4 into the oceans and atmosphere, has been proposed as one of the mechanisms causing the biotic crisis at the Triassic-Jurassic boundary. Oceanic uptake of CO2 due to extreme greenhouse conditions should have had an impact on ocean chemistry and the position of the calcite compensation depth. In this study, we chose two pelagic sections from the Budva Basin as archives for paleoceanographic change across the Triassic-Jurassic boundary in deep-water settings. Our record represents the first documentation of a sudden termination of carbonate deposition across the Triassic-Jurassic boundary in a pelagic deep-water environment. Based on radiolarian biostratigraphy, the system boundary is placed at the sharp lithological contact between two pelagic formations, the Upper Triassic limestones and Lower Jurassic siliceous limestones alternating with shales. A rapid drop of carbonate content from 90% to less than 10% occurred contemporaneous with a negative anomaly in the stable carbon isotope record measured in both bulk carbonate (1.3) and bulk organic matter (1.1). The abrupt reduction of carbonate content in the Budva Basin was the result of either increased carbonate dissolution causing shoaling of the calcite compensation depth or reduced carbonate input due to biocalcification crisis. Both nonexclusive scenarios support the hypothesis of decreased ocean saturation with respect to calcium carbonate, which could be a direct consequence of increased CO2, SO2, and CH4 fluxes.
Continue reading ‘A biocalcification crisis at the Triassic-Jurassic boundary recorded in the Budva Basin (Dinarides, Montenegro)’

Antarctic echinoids and climate change: a major impact on the brooding forms

Ocean acidification (OA) and the accompanying changes to carbonate concentrations are predicted to have especially negative impacts in the Southern Ocean where, as a result of colder temperatures, there will be shallowing of both the aragonite (ASH) and calcite saturation horizons (CSH). Echinoids are a dominant group of the Antarctic macrofauna which, because of their high-Mg calcite skeleton, are particularly susceptible to changes in the ASH. Using published information on the bathymetric distributions of Antarctic echinoids, we show that the majority of heavily calcified echinoids have their lower bathymetric limit above a depth of ca. 3000 m, approximately the current depth of the CSH. Echinoids whose depth range extends below 3000 m generally have thin, weakly calcified tests and include species from the Order Holasteroida, and the Families Cidaridae and Schizasteridae. Examination of the reproductive mode of Antarctic echinoids shows that brooding, where calcification of the young occurs in the same CaCO3 environment as the mother, is primarily found at a depth above 3000 m. The predicted shallowing of the ASH and CSH under OA conditions is likely to negatively impact growth and reproduction of heavily calcified brooders in the Family Cidaridae, which may result in changes to bathymetric ranges, local population extinction, and associated losses in macrofaunal biodiversity. As with other calcified deep sea invertebrates, echinoids may be particularly vulnerable to the impacts of increased CO2 and OA in the Southern Ocean.
Continue reading ‘Antarctic echinoids and climate change: a major impact on the brooding forms’

Marine methane cycle simulations for the period of early global warming

Geochemical environments, fates, and effects are modeled for methane released into seawater by the decomposition of climate-sensitive clathrates. A contemporary global background cycle is first constructed, within the framework of the Parallel Ocean Program. Input from organics in the upper thermocline is related to oxygen levels, and microbial consumption is parameterized from available rate measurements. Seepage into bottom layers is then superimposed, representing typical seabed fluid flow. The resulting CH4 distribution is validated against surface saturation ratios, vertical sections, and slope plume studies. Injections of clathrate-derived methane are explored by distributing a small number of point sources around the Arctic continental shelf, where stocks are extensive and susceptible to instability during the first few decades of global warming. Isolated bottom cells are assigned dissolved gas fluxes from porous-media simulation. Given the present bulk removal pattern, methane does not penetrate far from emission sites. Accumulated effects, however, spread to the regional scale following the modeled current system. Both hypoxification and acidification are documented. Sensitivity studies illustrate a potential for material restrictions to broaden the perturbations, since methanotrophic consumers require nutrients and trace metals. When such factors are considered, methane buildup within the Arctic basin is enhanced. However, freshened polar surface waters act as a barrier to atmospheric transfer, diverting products into the deep return flow. Uncertainties in the logic and calculations are enumerated including those inherent in high-latitude clathrate abundance, buoyant effluent rise through the column, representation of the general circulation, and bacterial growth kinetics.
Continue reading ‘Marine methane cycle simulations for the period of early global warming’

La acidificacion del Mediterraneo por el CO2, posible causa aumento de medusas (in Spanish)

¿Existe relación entre el aumento de las medusas en el Mediterráneo y la acidificación de sus aguas a consecuencia del incremento del CO2? Ésta es una peliaguda cuestión que busca resolver el proyecto MedSeA, un programa que investiga el impacto ecológico y socioeconómico de este proceso químico reciente.

Las aguas de mares y océanos llevan absorbiendo desde el inicio de la revolución industrial las emisiones de CO2 que el hombre ha emitido a la atmósfera por sus diferentes actividades, proceso que ha retrasado el calentamiento global pero que lleva emparejado esa acidificación que tiene un especial impacto en los organismos marinos, señala a Efe Patrizia Ziveri, coordinadora del proyecto Mediterranean Sea Acidification in a Chanching Climate, liderado por el Instituto de Ciencia y Tecnologías Ambientales de la UAB.
Continue reading ‘La acidificacion del Mediterraneo por el CO2, posible causa aumento de medusas (in Spanish)’

Paleo-ocean acidification WG

The Paleo-Ocean Acidification WG developped from the IGBP-SCOR Fast-Track Initiative “Ocean Acidification”. The current objective of this new group is more centered on exploring evidence for carbon cycle perturbations in the geological record and infer how it can inform our understanding of the response of modern biotic assemblages to ocean acidification.A workshop was held in August 2010 to discuss the state of the science, prepare publications, and discuss potential future course of action.
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