Protocols for Demonstrating the Performance of In Situ pCO2 Analyzers.

Abstract

There are three important reasons for measuring pCO2 continuously from coastal moorings. The first is to evaluate whether coastal oceans are functioning as a source or a sink of atmospheric CO2. The open ocean and more distal parts of the shelves are reasonably well characterized as either typical CO2 sinks or sources (Takahashi et al., 2009), while the inner shelves are most variable and (with a general predominance of a source function) least well constrained; coastal areas are expected to be rather vulnerable to climate change in the 21st century. This of course has direct consequence of managing CO2 as a pollutant. Near continuous measurements of pCO2 will provide some understanding of the fluxes, their variability and their forcing parameters. The second reason involves the changes in saturation state of the water with respect to carbonate minerals and the impact on calcifying ecosystems. Surface pCO2 measurements in conjunction with direct measurements of one other parameter of the marine CO2 system (pH, TA or total DIC) can be used to calculate saturation state (for calcite and aragonite). The third important use is the direct measurement of net community production in shallow waters, and thus further understanding how the carbon cycle is affected by climate ACT pCO2 Sensor Demonstration Protocols ACT PD09-01 4 changes parameters such as temperature, and pH. Changes in pCO2 can occur on wide range time scales ; from hourly and diel to seasonal and inter-annual. All these parameters are potentially being altered by progressive ocean acidification. Thus it is vital to further promote, develop and improve measurement capabilities for seawater pCO2. The ACT workshop on pCO2 posed the following question: What are the major impediments to transform existing shipboard pCO2 systems for use on cost-efficient autonomous platforms such moorings? Answers were: The measurement of pCO2 is believed by industry to be reliable and ready for use on moorings. The issues of interest follow in order of greatest concern: 1. Reliability (precision and accuracy, long- term stability) and biofouling resistance - the system is designed as a number of components all of which have error and intrinsic limitations. 2. Software should be designed for easy use (e.g. educational use and use by managers), not just experts in the analysis and geochemistry of dissolved inorganic carbon. 3. Supportive financing in terms of supplementing costs, identifying focused markets, and facilitating the movement of technology applications from addressing the questions of individual researchers to broader, regional management issues. These needs could be addressed with the creation of focused RFPs issued by governing agencies. 4. Technologies need to be made relatively compact , portable and of rugged design. 5. Provide venues for training people to not only use the technologies, but on how to understand and interpret the data. Action items regarding pCO2 from the workshop were: 1.More measurements of pCO2 in coastal waters are needed to better quantify CO2 fluxes in coastal environments, not just open- ocean environments. These data need to be coordinated with other spatially dependent physical and biogeochemical information. 2.Verify that in situ pCO2 sensing works within a broad range of environments as prescribed with comparison and availability. Companies working with Euro-ACT should be involved. 3. Objectives and Focus of pCO 2 Analyzer Performance Demonstration The basic objectives of this Performance Demonstration are to: (1) highlight the potential capabilities of in situ pCO2 analyzers by demonstrating their utility in two different coastal environments, a shallow coral reef and a vertically stratified sound; (2) promote the awareness of this emerging technology to the scientific and management community responsible for monitoring coastal environments, and (3) work with manufacturers that are presently developing new or improved sensor systems, by providing a forum for thoroughly testing their products in a scientifically defensible program, at relatively minor costs in time and resources to the companies. At present there are three basic ways to measure CO2 gas with moored instruments, equilibration of a gas phase with seawater and subsequent CO2 measurement by an infrared analyzer, equilibration of a pH sensitive dye with seawater, and fluorescence. We envision that ACT pCO2 Sensor Demonstration Protocols ACT PD09-01 5 in situ pCO2 sensors will be widely deployed to measure patterns in CO2 gas flux in many coastal regions, on relatively small platforms. This includes larger offshore moorings and small shallow water moorings, in time scales of days to months.