OS33E-01
The Future of Ocean Chemistry
The oceans have absorbed about 40% of the carbon dioxide emitted by humans over the past two centuries. This equates to nearly 500 billion metric tons of carbon dioxide, equivalent in weight to about 28 inches of water (ca. 70 cm) across the whole State of Texas. As a result, surface ocean pH has already dropped by 0.1 units relative to preindustrial levels and is expected to drop by 0.3 units until year 2100 under business as USual scenarios. This acidification process is expected to have detrimental consequences for a variety of marine organisms. I will present projections of ocean chemistry changes for various CO2 emission scenarios and discuss changes in parameters relevant to marine organisms such as pH and calcium carbonate saturation state. If alterations of ocean chemistry beyond certain threshold values are to be avoided in the future, specific CO2 emission targets will be required. I will suggest values for those emission targets based on results from carbon cycle modeling efforts. I will also address if enhanced weathering of carbonate and silicate rocks in a warmer climate will have the ability to mitigate impacts of anthropogenic CO2 emissions on ocean chemistry. Finally, I will call attention to a surprising and hitherto largely unknown consequence of ocean acidification.
OS33E-02 INVITED
ISFET sensor evaluation and modification for seawater pH measurement
In the future, short-term cycles (daily to subannual) and long-term trends (annual and greater) in the carbonate system will be observed by autonomous sensors operating from a variety of platforms (e.g., moorings, profiling floats, AUVs, etc.). Of the four carbonate parameters, pH measurement has the longest history of development - yet robust autonomous sensing techniques remain elusive due to a catalog of technical challenges. Existing commercial sensor technologies generally do not meet the stringent demands of accuracy, long-term stability, low power, pressure tolerance, resistance to biofouling, and ease of use required by the oceanographic community. We report here on some recent advances in Ion Sensitive Field Effect Transistor (ISFET) technology that may open the door for more widespread autonomous seawater pH measurements. Much of our work has focused on applications of the Honeywell Durafet pH sensor, a product designed for industrial process control. Initial results from laboratory testing and deployments in the MBARI test tank and near shore moorings will be presented. Sensor calibration techniques will be addressed. Applications of now-available off-the-shelf sensors including shipboard underway measurement, shallow water mooring deployment, and a gas controlled seawater aquarium for pH perturbation experiments will be discussed. We hope that an ongoing collaboration between MBARI and Honeywell will result in a commercially available product, designed specifically for oceanographic applications, within the next several years.
OS33E-03
A New Proxy Method for Estimating the Aragonite Saturation State of Coastal Waters Using Chemical and Hydrographic Data
In a recent study (Feely et al., 2008), we determined that the continental shelf of western North America is strongly impacted in the spring and summer months by the upwelling of 'ocean acidified' water. Using the data from this same 2007 North American Carbon Program coastal cruise, we have developed regional algorithms for estimating aragonite saturation state from chemical and hydrographic data. Our approach utilizes a multi-parameter linear regression of aragonite saturation values as a function of temperature, salinity and oxygen so a broader range of cruise data sets can be used to evaluate spatial and temporal variability in saturation state. The calculated saturation states agree well with the measured values. For coastal waters off Oregon we obtained an overall R2 of 0.97 and a standard error 0.1 over a depth range from 30 – 200m. The method is reasonably straightforward and has good resolving power for aragonite saturation. Similar relationships have been developed for coastal waters off Washington and California.
OS33E-04 INVITED
The mineralogical responses of marine calcifiers to CO2-induced ocean acidification
We have conducted 6-month laboratory experiments to investigate the effect of pCO2-induced reductions in
seawater CaCO3 saturation state on biocalcification by 18 aragonitic and calcitic (low-high Mg) taxa
representing eight of the major marine calcifying groups: Chlorophyta; Rhodophyta; Crustacea; Bivalvia;
Gastropoda; Annelida; Cnidaria; and Echinodermata. The CaCO3 saturation states of the experimental
seawaters, constrained by intercalibrated determinations of pH, alkalinity, and DIC, were attained with
bubbled air-CO2 mixtures of 400 (ambient), 600, 900, and 2850 ppm pCO2, yielding Ωarag of 2.5
(ambient), 2.0, 1.5, 0.7, respectively. We previously showed that while rates of net calcification obtained from
buoyant weighing declined with increasing pCO2 for nearly half of the species investigated, a nearly equal
number exhibited constant or, in some cases, increased calcification under moderately (600 ppm) or
extremely (900 or 2850 ppm) elevated pCO2. The organisms' investigated in this study secrete various forms
of CaCO3, which differ in crystallographic structure and therefore solubility: aragonite and high-Mg are
generally more soluble than low-Mg calcite. We have employed powder x-ray diffraction, Raman
spectroscopy, inductively-coupled-plasma mass-spectrometry, and scanning electron microscopy to quantify
changes in the organisms' skeletal mineralogy (aragonite:calcite ratio) and Mg-content (MgCO3:CaCO3
ratio) that occurred in response to the prescribed reductions in seawater CaCO3 saturation state. We will
compare calcification and mineralogical response patterns amongst the organisms to elucidate the role of
mineral lability in driving species-specific responses to CO2-induced ocean acidification.
http://www.whoi.edu/page.do?pid=10616&tid=282&cid=35329
OS33E-05
A Function for Representing the Biological Challenge to Respiration Posed by Ocean Acidification and the Geochemical Consequences Inferred
Increasing levels of dissolved total CO2 in the ocean from the invasion of fossil fuel CO2 via the atmosphere are widely believed to pose challenges to marine life on several fronts. This is most often expressed as a concern from the resulting lower pH, and the impact of this on calcification in marine organisms (coral reefs, calcareous phytoplankton etc.). These concerns are real, but calcification is by no means the only process affected, nor is the fossil fuel CO2 signal the only geochemical driver of the rapidly emerging deep-sea biological stress. Physical climate change is reducing deep-sea ventilation rates, and thereby leading to increasing oxygen deficits and concomitant increased respiratory CO2. We seek to understand the combined effects of the downward penetration of the fossil fuel signal, and the emergence of the depleted O2/increased respiratory CO2 signal at depth. As a first step, we seek to provide a simple function to capture the changing oceanic state. The most basic thermodynamic equation for the functioning of marine animals can be written as Corg + O2 → CO2 , and this results in the simple Gibbs free energy equation: ΔG° = - RT * ln [fCO2]/[Corg]*[fO2], in which the ratio of pO2 to pCO2 emerges as the dominant factor. From this we construct a simple Respiration Index: RI = log10 (pO2/pCO2), which is linear in energy and map this function for key oceanic regions illustrating the expansion of oceanic dead zones. The formal thermodynamic limit for aerobic life is RI = 0; in practice field data shows that at RI ~ 0.7 microbes turn to electron acceptors other than O2, and denitrification begins to occur. This likely represents the lowest limit for the long-term functioning of higher animals, and the zone RI = 0.7 to 1 appears to present challenges to basic functioning of many marine species. In addition, there are large regions of the ocean where denitrification already occurs, and these zones will expand greatly in size as the combined effects of higher pCO2 and lower pO2 emerge. We show from simple ROV controlled short-term field experiments the impacts of low RI on marine animals. More complex predictions wait to be tested, but the function presented here leads to the prediction that even absent changes in pO2 several critical microbially mediated redox reactions (IO3 → I-; production of N2O) will occur at higher pO2 levels than at present, and that their oceanic signature will increase.
OS33E-06
Effect of Ocean Acidification on the Speciation of Metals in Seawater
The continued production of CO2 from the burning of fossil fuel is estimated to increase the pCO2 in the atmosphere to 2000 μatm by the year ~2300. The equilibration of the CO2 in the atmosphere with surface ocean waters will decrease the pH from the present value 8.1 to 7.4. Although a number of workers have examined how this decrease in pH can affect the production and dissolution of calcareous organisms in ocean waters, studies on the effect this has on the speciation of metals have not been examined. This decrease in the pH of seawater will decrease the concentrations of OH- and CO32- in the surface ocean, respectively by as much as 82 and 77%. Since these anions form strong complexes with divalent and trivalent metals, their decrease will increase the concentration of the free or uncomplexed metals in seawater. This will also increase the thermodynamic and kinetic activity of these ions. Since the ionic form of Cu2+ is toxic to some organisms, the lower pH may affect the productivity of phytoplankton in the oceans. A decrease in the concentrations of OH- and CO32- will also slow down the rate of oxidation of Fe(II) with O2 and H2O2 and increase the solubility of Fe(III). These two effects will make iron more available to phytoplankton.
OS33E-07
A Calcium Isotope Record Across the Permian-Triassic Boundary From an Isolated Carbonate Platform in South China
We measured the calcium isotope composition (δ44Ca) of marine carbonate sediments spanning the Permian-Triassic boundary on a carbonate platform in the Nanpanjiang Basin of southern China. The δ44Ca of the sediments exhibits a transient negative excursion of approximately 0.3‰ across the end-Permian extinction horizon. Isotopically light values persist through the basal Triassic Hindeodus parvus conodont zone. Strata within the overlying Isarcicella isarcica zone exhibit heavier values, similar to those observed in pre-extinction strata. The excursion could reflect either a change in the local fractionation between seawater Ca and carbonate minerals or a shift in the δ44Ca composition of seawater. Because the dominant mode of carbonate deposition shifted from skeletal to microbial across the boundary, a local change in fractionation is difficult to rule out. However, δ44Ca values return to pre-extinction values within strata still lacking any significant skeletal contribution, suggesting that the isotope excursion may instead record a global shift in δ44Ca of seawater. If the values measured do reflect an excursion in the isotope composition of calcium in the oceans, they imply an increase of 25 to 30% in the marine calcium concentration over a few hundred thousand years or less. Such an increase could result from ocean acidification via the addition of CO2 (and possibly SO2) to the ocean and atmosphere. Such a scenario could also account for the coeval negative excursion in δ13C and the preferential extinction of heavily calcified marine invertebrates.
OS33E-08 INVITED
Geobiological Responses to Ocean Acidification
During 240Ma of evolution, scleractinian corals survived major changes in ocean chemistry, yet recent concerns with rapid acidification after ca. 40Ma of almost constant oceanic pH have tended to distract attention from natural pH variation in coastal waters, where most corals and reefs occur. Unaltered skeletal environmental proxies reflect conditions experienced by individual organisms, with any variation on micro- habitat and micro-time scales appropriate for that individual's ecology, behavior and physiology, but proxy interpretation usually extrapolates to larger spatial (habitat, region to global) and temporal (seasonal, annual, interannual) scales. Therefore, predicting consequences of acidification for both corals and reefs requires greater understanding of: 1. Many potential indirect consequences of pH change that may affect calcification and/or carbonate accretion: e.g. an individual's developmental rates, growth, final size, general physiology and reproductive success; its population's distribution and abundance, symbionts, food availability, predators and pathogens; and its community and ecosystem services. 2. Potentially diverse responses to declining pH, ranging from non-evolutionary, rapid physiological changes (acclimation) or long term (seasonal to interannual) plasticity (acclimatization) of individuals, through genetic adaptation in local populations, and up to directional changes in species" characteristics and/or radiations/extinctions. 3. The evolutionary and environmental history of an organism's lineage, its ecological (own lifetime) exposure to environmental variation, and "pre-adaptation" via other factors acting on correlated characters.