Submarine carbon dioxide (CO2) seeps as natural laboratories to study coral reef acclimatization to ocean acidification

• Applicant: Professor Dr. Thomas Pichler
• Subject Area: Oceanography ; Mineralogy, Petrology and Geochemistry
• Term: from 2016 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321738094

• Final Report Year: 2018

Final Report Abstract

Ocean acidification (OA) due to the oceanic uptake of anthropogenic CO2 could have far reaching ramifications for coral reefs due to a fundamental alteration in seawater carbonate chemistry. Thus far, the majority of research to assess the impact of OA on coral reefs was conducted under laboratory conditions. While informative, those studies had limitations with respect to natural variability, multispecies interaction and their ability to adapt. A possible solution is the study of coral reefs in the vicinity of volcanic submarine CO2 seeps, mimicking future conditions (i.e., what would be expected by 2100). Previous studies, however, were lacking a detailed analysis of the potentially toxic compounds (e.g., arsenic), which are often emitted in addition to CO2. With this in mind, we put together a team with expertise in aqueous chemistry and coral physiology to carry out chemical and biological characterizations of corals, hydrothermal fluids and CO2 seeps in Tutum Bay, Papua New Guinea. There venting occurs in shallow water in a patchy distribution of coralalgal reefs. Two types of venting are present: (1) “vents”, focused discharge of clear, twophase fluids occurring at discrete ports, with phase separation (boiling) at the sea floor and (2) “seeps”, dispersed or diffuse discharge consisting of gas bubble streams (> 95% CO2) emerging directly through the sandy to pebbly unconsolidated sediment. As a result, several areas inside Tutum Bay have lower pH and locally temperature 1 to 2 °C higher than ambient seawater, providing exactly those conditions expected to occur by 2100 with OA. During the research cruise with the French R/V Alis we measured the physicochemical conditions, seawater carbonate chemistry and trace elements in Tutum Bay, Papua New Guinea. There, intense emission of hydrothermal fluids and CO2 expose the coral reef to a seawater pHT between 7.6 and 7.7. Arsenic and silica were enriched by up to six times in surface seawater, while bottom concentrations were lower and thus similar to coral reefs worldwide. Manganese, cesium, iron and zinc concentrations fell into the range of other coastal environments. Our measurements suggest that Tutum Bay is a suitable site to study the response of coral reefs to high pCO2. Considering that arsenic is a common metal in hydrothermal fluids, its characterization should be included in any study that uses volcanic CO2 seeps as natural laboratories for ocean acidification.

Publications

• (2017) Understanding coral reef acclimatization to ocean acidification at submarine CO2 seeps, Tutum Bay, Ambitle Island, Papua New Guinea, 3rd European Conference on Scientific Diving, Funchal, Madeira
  T. Pichler, T. Biscéré, J. Kinch, M. Zampighi, F. Houlbréque and R. Rodolfo-Metalpa
  
• (2018). Evidence for mitigation of coral bleaching by manganese, Scientific Reports
  Biscéré, T., Ferrier-Pagès, C., Gilbert, A., Pichler, T. and Houlbrèque, F.
  
• (2018). Suitability of the shallow water hydrothermal system at Ambitle Island (Papua New Guinea) to study the effect of high pCO2 on coral reefs, Marine Pollution Bulletin
  Pichler, T., T. Biscéré, J. Kinch, M. Zampighi, F. Houlbréque and R. Rodolfo-Metalpa