A universal carbonate ion effect on stable oxygen isotope ratios in unicellular planktonic calcifying organisms

The oxygen isotopic composition (δ¹⁸O) of calcium carbonate of planktonic calcifying organisms is a key tool for reconstructing both past seawater temperature and salinity. The calibration of paloeceanographic proxies relies in general on empirical relationships derived from experiments on extant species. Laboratory experiments have more often than not revealed that variables other than the target parameter influence the proxy signal, which makes proxy calibration a challenging task. Understanding these secondary or “vital” effects is crucial for increasing proxy accuracy and possibly for developing new biomarkers. We present data from laboratory experiments showing that oxygen isotope fractionation during calcification in the coccolithophore Calcidiscus leptoporus and the calcareous dinoflagellate Thoracosphaera heimii is dependent on carbonate chemistry of seawater in addition to its dependence on temperature. A similar result has previously been reported for planktonic foraminifera, suggesting that the [CO₃²⁻] effect on δ¹⁸O is universal for unicellular calcifying planktonic organisms. The slopes of the δ¹⁸O/[CO₃²⁻] relationships range between −0.0243 (μmol kg⁻¹)⁻¹ (calcareous dinoflagellate T. heimii) and the previously published 0.0022 (μmol kg⁻¹)⁻¹ (non-symbiotic planktonic foramifera Orbulina universa), while C. leptoporus has a slope of 0.0048 (μmol kg⁻¹)⁻¹. We present a simple conceptual model, based on the contribution of δ¹⁸O-enriched HCO₃⁻ to the CO₃²⁻ pool in the calcifying vesicle, which can explain the [CO₃²⁻] effect on δ¹⁸O for the different unicellular calcifiers. This approach provides a new insight into biological fractionation in calcifying organisms. The large range in δ¹⁸O/[CO₃²⁻] slopes should possibly be explored as a means for paleoreconstruction of surface [CO₃²⁻], particularly through comparison of the response in ecologically similar planktonic organisms.

Response to technical comment on `meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms’

It has been proposed that crustaceans should be excluded from a comparison of biological responses to ocean acidification among organisms with different calcium carbonate (CaCO₃) forms in their calcified structures. We re-analysed our data without crustaceans and found high variation in organismal responses within CaCO₃ categories. We conclude that the CaCO₃ polymorph alone does not predict sensitivity, and a consideration of functional differences among organisms is necessary for predicting variation in response to acidification.

Effects of elevated pCO2 on the early development of the commercially important gastropod, Ezo abalone Haliotis discus hannai

We used an up-to-date, a high accuracy CO₂ manipulation system to investigate the sensitivity of organisms to CO₂ acidification, rearing marine calcifiers under elevated CO₂ in running water. We evaluated the effects of elevated partial pressures of carbon dioxide (pCO₂) in seawater on larvae of the commercially important marine gastropod Ezo abalone Haliotis discus hannai. In larval Ezo abalone, no effect of exposure to <1100 μatm pCO₂ seawater was observed in fertilization, malformation, or mortality rates until 15 h after fertilization. However, compared to control larvae in seawater (450 or 500 μatm pCO₂), the fertilization rate and the hatching rate (15 h after fertilization) decreased with increased pCO₂ exposure (1650 and 2150 μatm pCO₂) and the malformation rate increased significantly, with the larval shell length being smaller 75 h after hatching. These results suggest that ocean acidification will potentially impact the marine population of Ezo abalone as a human food source in the future.

“Bottom up” ocean acidification: A study on the effects of CO2 on the bacterial community in sediments

As atmospheric concentration of CO2 continues to increase, alternatives on how to mitigate and reduce the rate of this development has received much attention. Carbon Capture and Storage (CCS) is doing just this by storing CO2 that ordinarily would have been emitted into the atmosphere. By storing the CO2 in geological storages it is isolated for a long period of time, thousands of years. Even though this type of storage is considered safe and the risk of leakage small, one can never be absolutely sure of it holding. The risk of large leakages is considered negligible, but the risk of relative small leakages is uncertain. If such a small leakage were to occur, what are the consequences and how such a leakage could be detected? These are difficult questions to answer, but the need to be able eventually answer them is important, especially considering that international guidelines (London protocol and OSPAR) has been developed so that these questions can be answered, and they eventually need to be followed. The long term aims of this project are to developing monitoring and detection methods for small leakages and assess the environmental impacts of this type of leakage.

Analytical challenges and the development of biomarkers to measure and to monitor the effects of ocean acidification

Changing ocean-carbonate chemistry caused by oceanic uptake of anthropogenic atmospheric carbon dioxide leads to the formation of carbonic acid, thus lowering the pH of the sea with predictions of a decrease from current levels at 8.15 to 7.82 by the end of the century. The exact measurement of subtle pH changes in seawater over time presents significant analytical challenges, as the equilibrium constants are governed by water temperature and pressure, salinity effects, and the existence of other ionic species in seawater.

Here, we review these challenges and how pH also affects dissolved inorganic and organic chemicals that affect biological systems. This includes toxic compounds (xenobiotics) as well as chemicals that are beneficial for marine organisms, such as the chemical signals (i.e. pheromones) that are utilized to coordinate animal behavior. We review how combining analytical, molecular and biochemical tools can lead to the development of biosensors to detect pH effects to enable predictive modeling of the ecological consequences of ocean acidification.

Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes

Calcium-isotope ratios (δ^44/42Ca) were measured in carbonate-rich sedimentary sections deposited during Oceanic Anoxic Events 1a (Early Aptian) and 2 (Cenomanian–Turonian). In sections from Resolution Guyot, Mid-Pacific Mountains; Coppitella, Italy; and the English Chalk at Eastbourne and South Ferriby, UK, a negative excursion in δ^44/42Ca of ~ 0.20‰ and ~ 0.10‰ is observed for the two events. These δ^44/42Ca excursions occur at the same stratigraphic level as the carbon-isotope excursions that define the events, but do not correlate with evidence for carbonate dissolution or lithological changes. Diagenetic and temperature effects on the calcium-isotope ratios can be discounted, leaving changes in global seawater composition as the most probable explanation for δ^44/42Ca changes in four different carbonate sections. An oceanic box model with coupled strontium- and calcium-isotope systems indicates that a global weathering increase is likely to be the dominant driver of transient excursions in calcium-isotope ratios. The model suggests that contributions from hydrothermal activity and carbonate dissolution are too small and short-lived to affect the oceanic calcium reservoir measurably. A modelled increase in weathering flux, on the order of three times the modern flux, combined with increased hydrothermal activity due to formation of the Ontong-Java Plateau (OAE1a) and Caribbean Plateau (OAE2), can produce trends in both calcium and strontium isotopes that match the signals recorded in the carbonate sections. This study presents the first major-element record of a weathering response to Oceanic Anoxic Events.

Aquarius reef base—A living laboratory for ocean acidification (video)

Over the past 15 years, scientists have been documenting increases in acidity in waters of the global ocean. This summer, two groups of scientists will be researching the very local aspect of ocean acidification on coral reefs in the Florida Keys.

Ocean acidification, a phenomenon scientists call “the other carbon problem,” hinders the ability of marine creatures to build shells – and already is presenting challenges to oyster harvesters on the U.S. West Coast. Over many decades, emissions of carbon dioxide into Earth’s atmosphere have significantly increased, mainly due to burning of fossil fuels. The oceans have been absorbing some (about 25 percent) of these emissions. While this may help delay atmospheric warming and climate change, scientists have discovered that carbon dioxide in the ocean is making the waters more acidic.

Research scientist – ARC super science fellowship

Interactive effects of changing climate, seawater carbonate chemistry and nutrient availability on corals and coral reefs

The Australian Institute of Marine Science (AIMS) is the leading national organisation researching tropical marine ecosystems. As part of the Australian Government’s Super Science Initiative (Marine and Climate), AIMS has received competitive funding from the Australian Research Council to support an exceptional early-career researcher. The successful applicant will conduct original research within a Project entitled “A Changing Climate on the Great Barrier Reef: Present and Future Implications”, with a focus on the topic “Interactive effects of changing climate, seawater carbonate chemistry and nutrient availability on corals and coral reefs.”