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We describe the design, testing, and performance of an actively controlled deep-sea Free Ocean CO 2 Enrichment (dp-FOCE) system for the execution of seafloor experiments relating to the impacts of ocean acidification on natural ecosystems. We used the 880 m deep MARS (Monterey Accelerated Research System) cable site offshore Monterey Bay, California for this work, but the Free Ocean CO 2 Enrichment (FOCE) system concept is designed to be scalable and can be modified to be used in a wide variety of ocean depths and locations. The main frame is based on a flume design with active thruster control of flow and a central experimental chamber. The unit was allowed to free fall to the seafloor and connected to the cable node by remotely operated vehicle (ROV) manipulation. For operation at depth we designed a liquid CO 2 containment reservoir which provided the CO 2 enriched working fluid as ambient seawater was drawn through the reservoir beneath the more buoyant liquid CO 2 . Our design allowed for the significant lag time associated with the hydration of the dissolved CO 2 molecule, resulting in an e-folding time, τ , of 97 s between fluid injection and pH sensing at the mean local T =4.31±0.14 °C and pH T of 7.625±0.011. The system maintained a pH offset of ~0.4 pH units compared to the surrounding ocean for a period of ~1 month. The unit allows for the emplacement of deep-sea animals for testing. We describe the components and software used for system operation and show examples of each. The demonstrated ability for active control of experimental systems opens new possibilities for deep-sea biogeochemical perturbation experiments of several kinds and our developments in open source control systems software and hardware described here are applicable to this end.

The Monterey Bay Aquarium Research Institute (MBARI) established the Free Ocean Carbon Enrichment (FOCE) experiment to study the long term effects of decreased ocean pH levels by developing in-situ platforms [1]. Deep FOCE (dpFOCE) was the first platform, which was deployed in 890 meters of water in Monterey Bay. After the conclusion of dpFOCE, MBARI developed an open source shallow water FOCE (swFOCE) platform to facilitate worldwide shallow water experiments on FOCE [1][2]. A shallow water platform can be more ubiquitous than a deep-water platform as shallow water instruments are less expensive (as it does not have to be designed to withstand the pressure at deep ocean depths) and more easily deployed (they can be deployed right along the coast). The swFOCE experiment is an open source platform, and MBARI has made the plans available online to anyone interested in studying shallow water carbon enrichment. The Oceanographic instrument simulator (OIS), described in this paper provides the means for MBARI engineers to test the swFOCE platform without attaching the numerous and expensive oceanographic instruments. The Oceanographic Instrument Simulator simulates the various scientific instruments that could be deployed in an actual experiment.

Scientists and engineers at the Monterey Bay Aquarium Research Institute (MBARI) have collaborated to develop SeeStar, a modular, light weight, self-contained, low-cost subsea imaging system for mid- to long-term monitoring of marine ecosystems. SeeStar is composed of separate camera, battery, and LED lighting modules, each rated to 300 meters depth. The system can be deployed in a variety of scenarios utilizing stills and video and can be operated either autonomously or tethered on a range of platforms, including ROVs, AUVs, landers, piers, and moorings. The priorities for implementation included using off-the-shelf and readily available components as much as possible, and providing all designs, schematics and fabrication documents online as open source, so that others can easily build and adapt the camera system for their own uses. The long-term goal of this project is to have a widely distributed marine imaging network across thousands of locations, to develop baselines of biological information.

The Free Ocean CO2 Enrichment (FOCE) concept and systems have been developed by the Monterey Bay Aquarium Research Institute (MBARI) as a way of performing comprehensive in situ ocean acidification (OA) seafloor experiments. MBARI funded an early project to test potential technologies for closed loop control of shifting pH associated with addition of acidified sea water, into a natural flow, stream that would manage the considerable lag times associated with the chemical reactions taking place; thus the protoFOCE was born. Later the full-scale deep water (850m depth) FOCE (dpFOCE) was tested with cabled control. We briefly outline the basic issues with OA experiments and describe why systems like FOCE are needed to better understand the impacts of OA. Early OA studies focused directly on the decreasing ability of some animals to form calcium carbonate shells under more acidic conditions. More recent work has focused on behavioral changes in marine species associated with a high CO2 environment. Each of these science studies can now be addressed by controlled in situ field experiments. Early engineering tests were published and soon external interest in the concept heightened. MBARI transferred FOCE technology to researcher working on the Great Barrier Reef. The resulting collaboration created the Coral-Prototype FOCE (cpFOCE) system. cpFOCE directly demonstrated the significant carbonate losses that may be anticipated in our “High CO2 Ocean” future. We also have the European FOCE (eFOCE), a proposal for Antarctic FOCE (antFOCE), and MBARI's own shallow water FOCE (swFOCE) with local collaborators underway. Interest in FOCE systems continues to grow as we've published and presented this capable in situ technology. To support the interested community MBARI engineering and science has developed a new concept. xFOCE is a project to create a generic FOCE reference design and to build the community support structure enabling FOCE technology to be freely available to the OA science community outside of MBARI. Within this paper we outline the technologies behind the xFOCE project and discuss the various elements of the project including decisions and ultimate goals. We also review how xFOCE can be implemented using alternate technologies if the science user chooses to do so. We outline our heavy focus on building a user group of researchers who ultimately will create and direct FOCE projects much the same as the open source software community has done with the GNU General Public License project. The distinction between “open source” and “free” is clearly articulated and we explain why this is important for building an enduring community with common standards for the execution of FOCE experiments.

The kinetics of the reaction that occurs when CO 2 and seawater are in contact is a complex function of temperature, alkalinity, final pH and TCO 2 which taken together determine the time required for complete equilibrium. This reaction is extremely important to the study of Ocean Acidification (OA) and is the critical technical driver in the Monterey Bay Aquarium Research Institute's (MBARI) Free Ocean CO 2 Enrichment (FOCE) experiments. The deep water FOCE science experiments are conducted at depths beyond scuba diver reach and demand that a valid perturbation experiment operate at a stable yet naturally fluctuating lower pH condition and avoid large or rapid pH variation as well as incomplete reactions, when we expose an experimental region or sample. Therefore, the technical requirement is to create a CO 2 source in situ that is stable and well controlled. After extensive research and experimentation MBARI has developed the ability to create an in situ source of CO 2 enriched seawater (ESW) for distribution and subsequent use in an ocean acidification experiment. The system mates with FOCE, but can be used in conjunction with other CO 2 experimental applications in deep water. The ESW system is completely standalone from FOCE.

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 CO 2 for studies of natural ecosystems such as coral reefs, cold water corals, and other sensitive benthic habitats. Thus controlled CO 2 perturbation experiments in the field rather than in aquaria are quickly becoming an essential ocean science tool. Free Air CO 2 Enrichment (FACE) experiments have long been carried out on land to investigate the effects of elevated atmospheric CO 2 levels on vegetation. However, only limited work on CO 2 enrichment using quasi-open systems has yet been carried out in the ocean. Seawater CO 2 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 CO 2 to seawater is to reduce the concentration of dissolved carbonate ion, and increase bicarbonate ion through the reaction: CO 2 + H 2 O + CO 3 2− → 2HCO 3 − The reaction between CO 2 and H 2 O is slow and is a complex function of temperature, pH, and TCO 2 . 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 CO 2 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.