Real-time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy

We demonstrate the ability to obtain accurate estimates of pH and carbonate mineral saturation state (Ω) from an Argo profiling float in the NE subarctic Pacific. Using hydrographic surveys of the NE Pacific region, we develop empirical algorithms to predict pH and Ω using observations of temperature (T) and dissolved O₂. We attain R² values greater than 0.98 and RMS errors of 0.018 (pH), 0.052 (Ω_arag), and 0.087 (Ω_calc) for data between 30–500 m, σ < 27.1. After calibrating optode-based O₂ data, we apply the algorithms to T and O₂ data from an Argo profiling float to produce a 14 month time-series of estimated pH and Ω_arag in the upper water column of the NE subarctic Pacific. Comparison to independent data collected nearby in 2010 indicates pH and Ω_arag estimates are robust. Although the method will not allow detection of anthropogenic trends in pH or Ω_arag, this approach will provide insight into natural variability and the key biogeochemical controls on these parameters. Most importantly, this work demonstrates that an assemblage of well-calibrated regional algorithms and Argo float data can be used as a low-cost, readily-deployable component of a global ocean carbon observing strategy.

Is Panarea Island (Italy) a valid and cost-effective natural laboratory for the development of detection and monitoring techniques for submarine CO2 seepage?

Developing reliable detection and monitoring techniques for underwater CO2 seepage and its effects on the marine environment is important for a wide range of topics; for example: volcanic surveillance, risk assessment of potential leakages from sub-seabed CO2 storage sites, and to forecast the effects of ocean acidification. A novel approach is to use areas where natural release of CO2 is present as ‘field-laboratories’ for validation of CO2 monitoring techniques and procedures. One such area was identified close to the volcanic island of Panarea (Italy). Here, CO2 seeps from the seafloor in shallow water allowing scuba divers to collect the needed data. Moreover, the coastal setting allows use of small boats for the marine operations, thus strongly reducing the costs. The applied study techniques examined are mainly sampling methods for free and dissolved gases, direct measurement of the CO2 fluxes, pH measurement along the water column, and verification of the impact of CO2 on the local environment.

From these first results, the submarine degassing area of Panarea can be realistically considered a natural laboratory where it is possible to test and validate detection methods for the prompt identification of potential seepage from sub-seabed CO2 storage areas. The particularly favorable environment permits the use of simplified logistics, thus reducing the costs of the research to almost negligible values if compared with any high-seas operation.

Interactive comment on “Ocean acidification: setting the record straight” by A. J. Andersson and F. T. Mackenzie

Andersson and Mackenzie (2011) cite our talk on “Carbonate sediments on Antarctic shelves and implications for a mechanism to buffer Ocean Acidification in the Southern Ocean” at the ASLO Aquatic Sciences Meeting in San Juan, Puer to Rico, in February 2011 (Hauck et al., 2011) as an example for investigating possible buffering effects by CaCO3 dissolution of shelf sediments.

We agree with the authors in their recommendations that the points “evidence of a buffer effect“ (when the seawater is already undersaturated with respect to CaCO3 ), “kinetics“, and “physical mixing“ should be considered in studies addressing a possible buffer effect. We would like to add another step (Step Zero), which has to happen even before these considerations: proper quantification of how much CaCO3 is available in the region considered and identification of the mineral composition (aragonite, calcite, magnesium rich calcites). This very first step is what we presented at the ASLO Meeting (Hauck et al., 2011).

New insights from coral growth band studies in an era of rapid environmental change

The rapid formation of calcium carbonate coral skeletons (calcification) fuelled by the coral-algal symbiosis is the backbone of tropical coral reef ecosystems. However, the efficacy of calcification is measurably influenced by the sea’s physico-chemical environment, which is changing rapidly. Warming oceans have already led to increased frequency and severity of coral bleaching, and ocean acidification has a demonstrable potential to cause reduced rates of calcification. There is now general agreement that ocean warming and acidification are attributable to human activities increasing greenhouse gas concentrations in the atmosphere, and the large part of the extra carbon dioxide (the main greenhouse gas) that is absorbed by oceans. Certain massive corals provide historical perspectives on calcification through the presence of dateable annual density banding patterns. Each band is a page in an environmental archive that reveals past responses of growth (linear extension, skeletal density and calcification rate) and provides a basis for prediction of future of coral growth. A second major line of research focuses on the measurement of various geochemical tracers incorporated into the growth bands, allowing the reconstruction of past marine climate conditions (i.e. paleoclimatology). Here, we focus on the structural properties of the annual density bands themselves (viz. density; linear extension), exploring their utility in providing both perspectives on the past and pointers to the future of calcification on coral reefs. We conclude that these types of coral growth records, though relatively neglected in recent years compared to the geochemical studies, remain immensely valuable aids to unravelling the consequences of anthropogenic climate change on coral reefs. Moreover, an understanding of coral growth processes is an essential pre-requisite for proper interpretation of studies of geochemical tracers in corals.

Technical comment on Kroeker et al. (2010) Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters, 13, 1419–1434

Meta-analysis of experimental results has been interpreted to imply that the calcification response of organisms depositing high Mg-calcite is more resilient to ocean acidification than organisms depositing aragonite/calcite. This conclusion might be biased by inadequate recognition and categorisation of high Mg-calcite according to mineral solubility.

Emiliania huxleyi shows identical responses to elevated pCO2 in TA and DIC manipulations

With respect to their sensitivity to ocean acidification, calcifiers such as the coccolithophore Emiliania huxleyi have received special attention, as the process of calcification seems to be particularly sensitive to changes in the marine carbonate system. For E. huxleyi, apparently conflicting results regarding its sensitivity to ocean acidification have been published (Iglesias-Rodriguez et al., 2008a; Riebesell et al., 2000). As possible causes for discrepancies, intra-specific variability and different effects of CO2 manipulation methods, i.e. the manipulation of total alkalinity (TA) or total dissolved inorganic carbon (DIC), have been discussed. While Langer et al. (2009) demonstrate a high degree of intra-specific variability between strains of E. huxleyi, the question whether different CO2 manipulation methods influence the cellular responses has not been resolved yet. In this study, closed TA as well as open and closed DIC manipulation methods were compared with respect to E. huxleyi’s CO2-dependence in growth rate, POC- and PIC-production. The differences in the carbonate chemistry between TA and DIC manipulations were shown not to cause any differences in response patterns, while the latter differed between open and closed DIC manipulation. The two strains investigated showed different sensitivities to acidification of seawater, RCC1256 being more negatively affected in growth rates and PIC production than NZEH.

Ocean acidification: setting the record straight

In recent years, ocean acidification has gained continuously increasing attention from scientists and a number of stakeholders and has raised serious concerns about its effects on marine organisms and ecosystems. With the increase in interest and the number of scientific investigations of this environmental problem, the number of opinions, often emotional, and misinterpretations of the issue have also increased. Regrettably, this is not necessarily helping to advance scientific understanding of the problem. In this article, we revisit a number of issues relevant to ocean acidification that we think require thoughtful consideration including: (1) surface seawater CO2 chemistry in shallow water coastal areas, (2) experimental manipulation of marine systems using CO2 gas or by acid addition, (3) net versus gross calcification and dissolution, and (4) CaCO3 mineral dissolution and seawater buffering.

Cabled instrument technologies for ocean acidification research — FOCE (free ocean CO2 enrichment)

With rising concern over the impacts of ocean acidification on marine life there is a need for greatly improved techniques for carrying out in situ experiments. These must be able to create a ΔpH of 0.3 to 0.5 by addition of CO2 for studies of natural ecosystems such as coral reefs, cold water corals, and other sensitive benthic habitats. Thus controlled CO2 perturbation experiments in the field rather than in aquaria are quickly becoming an essential ocean science tool. Free Air CO2 Enrichment (FACE) experiments have long been carried out on land to investigate the effects of elevated atmospheric CO2 levels on vegetation. However, only limited work on CO2 enrichment using quasi-open systems has yet been carried out in the ocean. Seawater CO2 has complex chemistry with significantly slow reaction kinetics, unlike land-air experiments where simple mixing is the major concern. Ocean experimental designs must to take these reaction rates into account. The net result of adding a small quantity of CO2 to seawater is to reduce the concentration of dissolved carbonate ion, and increase bicarbonate ion through the reaction: CO2 + H2O + CO3²⁻ → 2HCO3⁻ The reaction between CO2 and H2O is slow and is a complex function of temperature, pH, and TCO2. The reaction proceeds more rapidly at lower pH and higher temperatures. Marine animals in the natural ocean will typically experience only small and temporary shifts from environmental CO2 equilibrium. Valid perturbation experiments must try to expose an experimental region to a near stable lower pH condition, and avoid large and rapid pH variability to the extent possible. This paper describes the design, development and testing of an in situ pH perturbation experiment deployed on a subsea cable for control. The paper addresses the differences between the deep-sea and shallow water versions of the experiments and addresses the pH sensor developments that enable long deployments.

Novel methodology for in situ carbon dioxide enrichment of benthic ecosystems

Future climate change will likely represent a major stress to shallow aquatic and coastal marine communities around the world. Most climate change research, particularly in regards to increased pCO₂ and ocean acidification, relies on ex situ mesocosm experimentation, isolating target organisms from their environment. Such mesocosms allow for greater experimental control of some variables, but can often cause unrealistic changes in a variety of environmental factors, leading to “bottle effects.” Here we present an in situ technique of altering dissolved pCO₂ within nearshore benthic communities (e.g., macrophytes, algae, and/or corals) using submerged clear, open-top chambers. Our technique utilizes a flow-through design that replicates natural water flow conditions and minimizes caging effects. The clear, open-top design additionally ensures that adequate light reaches the benthic community. Our results show that CO₂ concentrations and pH can be successfully manipulated for long durations within the open-top chambers, continuously replicating forecasts for the year 2100. Enriched chambers displayed an average 0.46 unit reduction in pH as compared with ambient chambers over a 6-month period. Additionally, CO₂ and HCO₃^– concentrations were all significantly higher within the enriched chambers. We discuss the advantages and disadvantages of this technique in comparison to other ex situ mesocosm designs used for climate change research.

United States integrated ocean observing system and the shellfish growers partnership

This scientific note provides a summary of a new partnership developing between two groups who have found a common area of interest focused on the value of building a better network for real-time coastal ocean observing data and information and how such a network may inform research on ocean acidification. The note examines the development of the partnership over the past year, which is providing mutually beneficial opportunities for interaction. Shellfish growers are able to learn about a federal and regional framework providing integrated data along our coasts, and the Integrated Ocean Observing System program is able to learn directly from one of its stakeholders who demonstrates the clear economic and scientific value of coastal, ocean, and Great Lakes observing systems. By working together, the two are finding ways to improve our coastal observing networks and to support research on ocean acidification.