text: A FOCE system for studies of deep-sea benthic communities (designated dp-FOCE) was developed by Monterey Bay Aquarium Research Institute. The dpFOCE project, deployed at a depth of 900 m, was attached to the MARS cabled seafloor observatory in Monterey Bay, central California. The system used a flume concept for maintaining greater control over the experimental volume while still maintaining access to natural seafloor sediments and suspended particulate material. Time-delay wings attached to either end of the dpFOCE chamber allow for tidally driven changes in near-bottom currents, and provide sufficient time for full hydration of the injected CO enriched seawater before entering into the experiment chamber. Fans are integrated into the dpFOCE design to control flow rates through the experimental chamber and to simulate typical local-scale flow conditions. Multiple sensors (pH, CTD, ADV, and ADCP) used in conjunction with the fans and the enriched seawater injection system allow the control loop software to achieve the desired pH offset. dpFOCE connects to shore via the MARS cabled observatory, which provides power and data bandwidth. Enriched CO seawater is produced from liquid CO held in a small container near the dpFOCE chamber; seawater flowing slowly over the top of the liquid CO dissolves some of the liquid CO producing a CO-rich dissolution plume used for injection into the dpFOCE chamber. The dpFOCE system operated over 17 months and verified the effectiveness of the design hardware and software.