Design, construction, and operation of an actively controlled deep-sea CO2 enrichment experiment using a cabled observatory system

Abstract 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.

[1]  E. Peltzer,et al.  Use of a free ocean CO₂ enrichment (FOCE) system to evaluate the effects of ocean acidification on the foraging behavior of a deep-sea urchin. , 2014, Environmental science & technology.

[2]  D. Wolf-Gladrow,et al.  On the time required to establish chemical and isotopic equilibrium in the carbon dioxide system in seawater , 1999 .

[3]  Finzi,et al.  Net primary production of a forest ecosystem with experimental CO2 enrichment , 1999, Science.

[4]  S. Long,et al.  Food for Thought: Lower-Than-Expected Crop Yield Stimulation with Rising CO2 Concentrations , 2006, Science.

[5]  E. Peltzer,et al.  Deep ocean experiments with fossil fuel carbon dioxide: creation and sensing of a controlled plume at 4 km depth , 2005 .

[6]  Ken Caldeira,et al.  A short-term in situ CO2 enrichment experiment on Heron Island (GBR) , 2012, Scientific Reports.

[7]  E. Peltzer,et al.  First results from a controlled deep sea CO2 perturbation experiment: Evidence for rapid equilibration of the oceanic CO2 system at depth , 2005 .

[8]  N. Crooker,et al.  What is the International Heliophysical Year , 2004 .

[9]  P. Brewer.  A short history of ocean acidification science in the 20th century: a chemist's view , 2013 .

[10]  Izuo Aya,et al.  A field study of the effects of CO2 ocean disposal on mobile deep-sea animals , 2000 .

[11]  W. Kirkwood,et al.  Free-ocean CO2 enrichment (FOCE) systems: present status and future developments , 2014 .

[12]  Christopher B. Field,et al.  Grassland Responses to Global Environmental Changes Suppressed by Elevated CO2 , 2002, Science.

[13]  Paolo Favali,et al.  Seafloor Observatory Science , 2010 .

[14]  G. Wong,et al.  Chemical removal of oxygen with sulfite for the polarographic or voltammetric determination of iodate or iodide in seawater , 1992 .

[15]  E. Peltzer,et al.  Direct experiments on the ocean disposal of fossil fuel CO2 , 1999, Science.

[16]  C. Marchetti.  On geoengineering and the CO2 problem , 1977 .

[17]  Kenneth S. Johnson,et al.  Carbon dioxide hydration and dehydration kinetics in seawater1 , 1982 .

[18]  Robert H. Byrne,et al.  CO2 system hydration and dehydration kinetics and the equilibrium CO2/H2CO3 ratio in aqueous NaCl solution , 2002 .

[19]  J. Barry,et al.  Utility of deep sea CO2 release experiments in understanding the biology of a high-CO2 ocean: Effects of hypercapnia on deep sea meiofauna , 2005 .

[20]  P. Brewer,et al.  Exposure to carbon dioxide-rich seawater is stressful for some deep-sea species: an in situ, behavioral study , 2007 .

[21]  T. Moens,et al.  Resource utilization and trophic position of nematodes and harpacticoid copepods in and adjacent to Zostera noltii beds , 2014 .

[22]  Bert Metz,et al.  Carbon Dioxide Capture and Storage , 2005 .

[23]  Peter G Brewer,et al.  Seeing a deep ocean CO2 enrichment experiment in a new light: laser raman detection of dissolved CO2 in seawater. , 2005, Environmental science & technology.

[24]  Stephen Widdicombe,et al.  Assessing the environmental consequences of CO2 leakage from geological CCS: generating evidence to support environmental risk assessment. , 2013, Marine pollution bulletin.

[25]  P. G. Brewer,et al.  Simulated sequestration of industrial carbon dioxide at a deep-sea site: Effects on species of harpacticoid copepods , 2006 .

[26]  P. Favali,et al.  Seafloor Observatory Science: a review , 2006 .

[27]  E. Peltzer,et al.  Effects of Direct Ocean CO2 Injection on Deep-Sea Meiofauna , 2004 .