L’acidification des océans en grandeur nature au fond de la Méditerranée (in French)

Villefranche-sur-mer (Alpes-Maritimes) – Sortir du laboratoire pour aller constater in vivo, au fond de la Méditerranée, comment réagissent coquillages et plantes aquatiques face à l’acidification des océans due au CO2: une simulation inédite en Europe est en préparation près de Nice.

Des chercheurs vont déposer au fond de la rade de Villefranche-sur-mer une sorte d’aquarium rectangulaire en plexiglas où ils maintiendront, pendant plusieurs mois, les niveaux d’acidité attendus pour 2050 et pour 2100.

Underwater aquarium

Late last year, after six years of design and testing, California’s Monterey Bay Aquarium Research Institute conducted the first controlled biological experiment on deep-sea animals using a Free-Ocean Carbon Dioxide Enrichment experiment. Ocean chemist Peter Brewer talks to Nature Climate Change about the project.

Benthic invertebrates in a high-CO2 world

Ocean acidification (OA), whereby increases in atmospheric carbon dioxide (cO2) over the past 200 years have led to a decline in the pH and carbonate ion availability of the oceans, has emerged as one of the major drivers of twenty- first century marine scientific research. Here we describe the current understanding of OA effects on benthic marine invertebrates, in particular the calcifiers thought to be most sensitive to altered carbonate chemistry. We describe the responses of benthic invertebrates to OA conditions predicted up to the end of the century, examining individual organism response through to ecosystem- level impacts. Research over the past decade has found great variability in the physiological and functional response of different species and communities to OA, with further variability evident between life stages. Over both geological and recent timescales, the presence and calcification rates of marine calcifiers have been inextricably linked to the carbon chemistry of the oceans. Under short-term experimentally enhanced cO2 conditions, many organisms have shown trade-offs in their physiological responses, such as reductions in calcification rate and reproductive output. In addition, carry-over effects from fertilization, larval and juvenile stages, such as enhanced development time and morphological changes, highlight the need for broad- scale studies over multiple life stages. These organism- level responses may propagate through to altered benthic communities under naturally enhanced cO2 conditions, evident in studies of upwelling regions and at shallow- water volcanic cO2 vents. Only by establishing which benthic invertebrates have the ability to acclimate or adapt, via natural selection, to changes from OA, in combination with other environmental stressors, can we begin to predict the consequences of future climate change for these communities.

Oceanography: plankton in an acidified ocean

The pH of the ocean is expected to drop 0.3 units in the next century. This change is well within the pH range that plankton experience at present, but research suggests that changes in acidity near their cell surface could be larger.

Early developmental gene regulation in Strongylocentrotus purpuratus embryos in response to elevated CO2 seawater conditions

Ocean acidification, or the increased uptake of CO₂ by the ocean due to elevated atmospheric CO₂ concentrations, may variably impact marine early life history stages, as they may be especially susceptible to changes in ocean chemistry. Investigating the regulatory mechanisms of early development in an environmental context, or ecological development, will contribute to increased understanding of potential organismal responses to such rapid, large-scale environmental changes. We examined transcript-level responses to elevated seawater CO₂ during gastrulation and the initiation of spiculogenesis, two crucial developmental processes in the purple sea urchin, Strongylocentrotus purpuratus. Embryos were reared at the current, accepted oceanic CO₂ concentration of 380 microatmospheres (μatm), and at the elevated levels of 1000 and 1350 μatm, simulating predictions for oceans and upwelling regions, respectively. The seven genes of interest comprised a subset of pathways in the primary mesenchyme cell gene regulatory network (PMC GRN) shown to be necessary for the regulation and execution of gastrulation and spiculogenesis. Of the seven genes, qPCR analysis indicated that elevated CO₂ concentrations only had a significant but subtle effect on two genes, one important for early embryo patterning, Wnt8, and the other an integral component in spiculogenesis and biomineralization, SM30b. Protein levels of another spicule matrix component, SM50, demonstrated significant variable responses to elevated CO₂. These data link the regulation of crucial early developmental processes with the environment that these embryos would be developing within, situating the study of organismal responses to ocean acidification in a developmental context.

Decadal changes in the CaCO3 saturation state along 179°E in the Pacific Ocean

To assess degrees of ocean acidification, we mainly investigated decadal changes in the saturation state of seawater with respect to aragonite (Ω_arg), which is a more vulnerable mineral form of CaCO₃, along the 179°E meridian (WOCE P14N) in the Pacific Ocean. We found a maximum decrease of Ω_arg of −0.48 (−0.034 a⁻¹) at 200–300 dbar (isopycnal surfaces of 24.0–25.8 kg m⁻³) at 20°N. Between 1993 and 2007, the saturation horizon rose by 17 dbar (1.2 dbar a⁻¹) at latitudes 10°N–50°N. Although ΔΩ_arg mostly reflected changes in normalized dissolved inorganic carbon (ΔnC_T), it was larger than could be explained by anthropogenic CO₂ storage alone. Decomposition of ΔnC_T revealed that ΔΩ_arg was enhanced by approximately 50% by a non-anthropogenic CO₂ contribution represented by changes in apparent oxygen utilization. Our results suggest that ocean acidification can be temporarily accelerated by temporal changes in oceanic conditions.