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Ocean’s deep-water may be corroding Byron Bay’s coastal ecosystems

Cold ocean waters, the sort that gives relief to beachgoers in the heat of summer, may in fact be corroding coastal ecosystems according to new research from Southern Cross University.

This is because upwelling events – when cold water is forced up from the deep ocean floor – along the East Australian coast (caused by the East Australian Current (EAC)) are accompanied by increasing levels of carbon dioxide which leads to ocean acidification.

On the other side of the Pacific Ocean, in the Californian and Peruvian systems, such upwelling events are accompanied by significant drops in seawater oxygen saturation and pH. Lower pH levels lead to conditions where upwelling waters become corrosive to the mineral aragonite, a vital building block of a number of marine organisms, including corals, snails, mussels and oysters. So, what’s the situation back home in Australia?

Continue reading ‘Ocean’s deep-water may be corroding Byron Bay’s coastal ecosystems’

Sensitivities to global change drivers may correlate positively or negatively in a foundational marine macroalga

Ecological impact of global change is generated by multiple synchronous or asynchronous drivers which interact with each other and with intraspecific variability of sensitivities. In three near-natural experiments, we explored response correlations of full-sibling germling families of the seaweed Fucus vesiculosus towards four global change drivers: elevated CO2 (ocean acidification, OA), ocean warming (OW), combined OA and warming (OAW), nutrient enrichment and hypoxic upwelling. Among families, performance responses to OA and OW as well as to OAW and nutrient enrichment correlated positively whereas performance responses to OAW and hypoxia anti-correlated. This indicates (i) that families robust to one of the three drivers (OA, OW, nutrients) will also not suffer from the two other shifts, and vice versa and (ii) families benefitting from OAW will more easily succumb to hypoxia. Our results may imply that selection under either OA, OW or eutrophication would enhance performance under the other two drivers but simultaneously render the population more susceptible to hypoxia. We conclude that intraspecific response correlations have a high potential to boost or hinder adaptation to multifactorial global change scenarios.

Continue reading ‘Sensitivities to global change drivers may correlate positively or negatively in a foundational marine macroalga’

Job opportunity: ocean acidification project at Universita Di’ Bologna, Italy

Project title: Anthropogenic impacts on calcification of Mediterranean benthic invertebrates as bio-indicators of marine ecosystem health: consequences of ocean acidification

Project description: The research project aims to investigate the effects of seawater acidification in calcifying marine organisms along a natural pH gradient, created by constant carbon dioxide emissions from the underwater crater of Panarea (Eolian Island). This site in the Mediterranean Sea is an ideal natural laboratory for studying acidification because there are acidity levels predicted for the current century by the IPCC. In particular, this project wants to study the effects of acidification on calcification (skeletal density, porosity, linear extension, calcification rates) and skeletal properties (structure and morphology of crystal domains, mineral phase, mechanical properties) of benthic invertebrates like corals, gastropods, bivalves and vermetides. Moreover, during the project the environmental characterization of the site will be carry out with measurements of the environmental parameters along the pCO2 gradient (temperature, pH, alkalinity, nutrients concentrations).

Application deadline: 28/10/2019

Continue reading ‘Job opportunity: ocean acidification project at Universita Di’ Bologna, Italy’

Upwelling amplifies ocean acidification on the East Australian shelf: implications for marine ecosystems

Frequent upwelling of deep, cold water, rich in dissolved inorganic nutrients and carbon dioxide but low in oxygen concentrations and pH, is well documented in eastern boundary systems. As a consequence, waters in vast areas of the continental shelf can turn corrosive to the mineral aragonite, vital to a number of marine organisms. This phenomenon is projected to become more severe with ongoing ocean acidification. Although upwelling is also known to occur in western boundary systems, the impact on present day aragonite saturation state (Ωarag) is virtually unknown, let alone for the decades to come. Here we identified 32 events during 18 weeks of continuous measurements in Cape Byron Marine Park, Australia, with prolonged drops in ocean temperature of up to 5°C, oxygen concentrations by 34%, pH by 0.12 and Ωarag by 0.9 in a matter of hours. Temperature, salinity and oxygen saturation during these events hint at a water mass from 200 to 250 m depth off the Central East Australian shelf. Extrapolating present day upwelling to a preindustrial setting shows that ongoing ocean acidification has already lead to the crossing of a number of biological and geochemical Ωarag thresholds. The future intensity of these events critically depends on carbon dioxide emission scenario, and might be even more pronounced in the Great Barrier Reef where current day shelf associated waters carry a stronger deep water signal (based on oxygen levels) than at the study location. Finally, the proposed use of artificially upwelled water to cool increasingly temperature-stressed coral reef communities will need to take its unique carbonate chemistry properties into account.

Continue reading ‘Upwelling amplifies ocean acidification on the East Australian shelf: implications for marine ecosystems’

PhD Scholarship in coral reef biogeochemistry in Australia

Project title: The contribution of sediment dissolution to whole coral reef dissolution

Description: A number of coral reefs around the globe are already net dissolving (i.e. negative net ecosystem calcification) for periods of the year due to ongoing global change (e.g. ocean acidification, warming, eutrophication). Our recent work has shown how shallow water coral reef carbonate sediments will dissolve due to ocean acidification (e.g. Eyre et al., 2018. Science). However, little is known about the contribution of carbonate sediment dissolution to negative net ecosystem calcification on coral reefs. This fully funded project will study a number coral reefs that are already showing negative net ecosystem calcification for periods of the year. Measurements of net ecosystem calcification and sediment dissolution will be made simultaneously to estimate the contribution of sediment dissolution to negative net ecosystem calcification.

This project involves collaboration with Dr. Tyler Cyronak at Nova Southeastern University, Florida and there may be opportunity to undertake field work in Florida, as well as Australia.

Continue reading ‘PhD Scholarship in coral reef biogeochemistry in Australia’

Webinar recording: Community of Ocean Action on Ocean Acidification

The Community of Ocean Action on Ocean Acidification held its fourth webinar on 25 September 2019. The webinar included presentations from Dr Peter Thor from the Swedish Meteorological and Hydrological Institute (SMHI) on Sweden’s plans to address and support SDG14.3, including through a national ocean acidification monitoring programme, and from Dr Dorothee Bakker, University of East Anglia, UK, who presented on the Surface Ocean CO2 Atlas (SOCAT).

The webinar recording can be found here.

Continue reading ‘Webinar recording: Community of Ocean Action on Ocean Acidification’

Control of CaCO3 dissolution at the deep seafloor and its consequences

Prediction of the neutralization of anthropogenic CO2 in the oceans and the interpretation of the calcite record preserved in deep-sea sediments requires the use of the correct kinetics for calcite dissolution. Dissolution rate information from suspended calcite-grain experiments consistently indicates a high-order nonlinear dependence on undersaturation, with a well-defined rate constant. Conversely, stirred-chamber and rotating-disc dissolution experiments consistently indicate linear kinetics of dissolution and a strong dependence on the fluid flow velocity. Here, we resolve these seeming incongruities and establish reliably the kinetic controls on deep-sea calcite dissolution. By equating the carbonate-ion flux from a dissolving calcite bed, governed by laboratory-based nonlinear kinetics, to the flux across typical diffusive boundary layers (DBL) at the seafloor, we show that the net flux is influenced both by boundary layer and bed processes, but that flux is strongly dominated by the rate of diffusion through the DBL. Furthermore, coupling that calculation to an equation for the calcite content of the seafloor, we show that a DBL-transport dominated model adeptly lysoclines adeptly, i.e., CaCO3 vs ocean depth profiles, observed across the oceans. Conversely, a model with only sediment-side processes fails to predict lysoclines in all tested regions. Consequently, the past practice of arbitrarily altering the calcite-dissolution rate constant to allow sediment-only models to fit calcite profiles constitutes confirmation bias. From these results, we hypothesize that the reason suspended-grain experiments and bed experiments yield different reaction orders is that dissolution rates of individual grains in a bed are fast enough to maintain porewaters at or close to saturation, so that the exact reaction order cannot be measured and dissolution appears to be linear. Finally, we provide a further test of DBL-transport dominated calcite dissolution by successfully predicting, not fitting, the in-situ pH profiles observed at four stations reported in the literature.

Continue reading ‘Control of CaCO3 dissolution at the deep seafloor and its consequences’

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Ocean acidification in the IPCC AR5 WG II

OUP book