Cabled observatory technology for ocean acidification research

The burning of fossil fuels for energy production has produced cumulative emissions on the order of 1 trillion tons since the beginning of the industrial revolution. While approximately half of the CO2 has remained in the atmosphere, the ocean is the predominant repository for the remainder of these emissions. This has resulted in a lowering of the surface ocean pH by about 0.1 units and, if society is able to stabilize atmospheric CO2 levels at twice the pre-industrial concentration, will result in a lowering of surface ocean pH by 0.25 units. While some researchers are asking the question of whether we should pursue direct ocean CO2 sequestration, FOCE technology enables scientists to ask what the impact of this pH change will be on ocean biogeochemistry and ecology. In order to address this question, MBARI scientists and engineers have designed apparatus that enable small-scale in situ CO2 enrichment experiments to be carried out, in a manner analogous to the land-based Free Air CO2 Enrichment (FACE) experiments. FOCE is a system that is configured around the science question(s) and is implemented to control pH within a fixed but freely exchanging volume of seawater. The technology uses control feedback and pH sensors to inject CO2 and create the future environment per science requirements. Other aspects of the FOCE design address the inherent time delays and natural background noise of the associated oceanic pH signal. We report recent progress on the design and testing of systems for carrying out controlled CO2 perturbation experiments on the sea floor with the goal of simulating the conditions of our future high CO2 world. Controlled CO2 enrichment (FACE) experiments have long been carried out on land to investigate the effects of elevated atmospheric CO2 levels on vegetation, but only limited work on CO2 enrichment on enclosed systems has yet been carried out in the ocean. With rising concern over the impacts of ocean acidification on marine life there is a n- eed for greatly improved techniques for carrying out in situ experiments, which can create a DeltapH of 0.3 to 0.5 by addition of CO2, on natural ecosystems such as coral reefs, cold water corals, and other sensitive benthic habitats. The FOCE system is now full scale and installed in deep waters in the Monterey Bay Canyon. FOCE is connected to the Monterey Accelerated Research System (MARS) and enables scientists to control a variety of parameters while monitoring in situ ocean acidification experiments. This paper describes the enabling technologies for in situ ocean acidification experimentation. FOCE was originally designed for observatory science and cabled observatories in particular. This paper will discuss the technologies that enable observatory efforts in ocean acidification research. We also discuss the associated technologies that are useful to the greater science community in general. Furthermore the paper will conclude with the next phase of FOCE development and the exportation of the technology to a variety of ocean observatory systems. Details will outlined for a new FOCE system currently in concept design for installation on Heron Island as part of long term studies of the Great Barrier Reef.

Kirkwood, W., Peltzer, E., Walz, P., & Brewer, P., 2009. Cabled observatory technology for ocean acidification research. OCEANS 2009-EUROPE, 2009. OCEANS ’09. 1-6 doi:10.1109/OCEANSE.2009.5278337. Article (subscription required).

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