Laboratory and mesocosm studies are only part of the tool set for ocean acidification (OA) studies. In situ experiments over months and longer can provide inference concerning the response of natural communities to ocean acidification not possible with laboratory studies. Drawing on the long experience of terrestrial Free Air CO2 Enrichment (FACE) experiments, MBARI has developed Free Ocean CO2 Enrichment experiments (FOCE), among its experimental methods and technologies for in situ ocean acidification studies. xFOCE is an open source package created to transfer FOCE technology to interested researchers. xFOCE is a modular system design intended to support a wide variety of OA studies, and to be extensible and adaptable to new requirements for OA research. The ocean science community can use xFOCE to develop cost effective FOCE experiments in diverse marine environments lasting weeks to months.



Ocean Acidification (OA) is happening quickly and will be a concern for centuries. The Intergovernmental Panel on Climate Change (IPCC) has strongly encouraged research into the potential effects of ocean acidification. In addition, recent meetings between scientists on this topic have indicated that in situ experiments are a top priority in studying OA impacts. The Monterey Bay Aquarium Research Institute (MBARI) has developed the Free Ocean CO2 Enrichment system (FOCE) as a tool to help the science user community address the current and future OA research needs. Ocean acidification is expected to be a large and very rapid change in ocean chemistry as atmospheric CO2 levels rise through this century and beyond. The IPCC has strongly encouraged research concerning the potential consequences of OA for marine organisms, and funding for OA studies have increased dramatically in the past 5 years. MBARI has developed the FOCE system as a tool to address the current and future requirements of the research community. In situ perturbation experiments with high CO2/low pH treatments over long periods are a key to evaluating the biological responses of future OA. The objectives of these experiments vary, but most focus on the biology and ecology of organisms and communities to increasing CO2 levels (reduced pH) over long periods, under relatively natural conditions. FOCE systems aim to allow researchers to perform experiments with specified (and perhaps variable) levels of CO2 enrichment for extended periods while other environmental parameters vary naturally. Atmospheric CO2 levels are expected to rise rapidly through this century due to continued (or perhaps elevated) use of fossil fuels for global energy needs. Rising CO2 levels in the atmosphere will increase the flux of CO2 to ocean surface waters. Ocean mixing processes are now moving the signal of ocean acidification to deeper ocean depths, and eventually the oceans will store most (ca. 85%) of fossil fuel CO2 emitted to the atmosphere. Thus, ocean acidification will eventually alter the carbonate chemistry of the entire world ocean. FOCE experimental approaches can be used in various marine environments to increase our understanding of the potential consequences of ocean acidification for marine ecosystems.



The goal of FOCE is to provide precise control of pH within in situ experimental chambers with minimal effect on other environmental conditions, to support experiments evaluating the consequences of ocean acidification on marine organisms and communities. CO2 enrichment in a FOCE system is achieved by controlling the addition of CO2 enriched (low pH) seawater (ESW) into experimental chambers on the seabed. The ESW is made by mixing seawater from the site with CO2. The FOCE system continually adjusts the delivery of ESW to maintain a constant pH offset relative to the surrounding area, or to maintain a specified constant pH level in experimental chambers. Thus, experiments using constant pH levels or specified offsets around natural pH variability can be performed. The key elements of a FOCE experiment include the CO2 mixing system, sensors to continuously monitor ambient and chamber pH, and a control loop to regulate the flow of ESW to each experimental chamber. The best configuration for generating ESW, power and for data collection depends upon the experiment site and existing infrastructure. The chemical and physical techniques for controlling CO2 chemistry are well understood, but depend on the marine environments of interest. The technologies and application techniques used to execute FOCE required considerable time and expertise to develop. MBARI is now putting FOCE technology and expertise in an open source package called xFOCE. xFOCE makes FOCE techniques cost-effective and adaptable, reducing the learning curve and making it a useful tool for multi-disciplinary OA studies in any marine environment. Like other open technology projects, xFOCE includes the idea of community building, to enable more researchers to use FOCE tools and techniques by contributing expertise and technical support.