Marine Applications of an Autonomous Indicator-Based pH Sensor

• Main Author: Cullison, Sarah E.
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: University of Montana 2010
• Subjects: coral reefs; ocean acidification; pH sensor; Media Luna; Ocean acidification; sami
• Online Access: https://scholarworks.umt.edu/etd/645; https://scholarworks.umt.edu/context/etd/article/1664/viewcontent/Cullison_umt_0136D_10099.pdf

Currently, the lack of accurate in situ pH measurements limits our understanding of natural pH variability. In order to predict future pH changes in the oceans, quality high temporal resolution pH data are needed. This work used the newly developed Submersible Autonomous Moored Instrument for pH (SAMI-pH), a fully autonomous, in situ spectrophotometric pH sensor, to study oceanic pH variability. The three main goals of this research were to: determine the field performance of the new SAMI-pH, establish the utility of combining SAMI-pH data with in situ pCO2 data to characterize the entire inorganic carbon cycle and establish pH variability, and what drives it, in a coral reef. Autonomous pH and pCO2 sensors were deployed in tandem in Monterey Bay, CA from June to August 2007. The results showed that the pH-pCO2 combination can provide information about data quality and can be used to model calcium carbonate (CaCO3) saturation states. The pH and pCO2 can be combined with a salinity-derived AT to model both long and short-term DIC variability. The SAMI-pH was also used to examine pH variability on Media Luna coral reef, Puerto Rico for two month periods over three seasons in 2007 and 2008. pH on the reef was at a minimum of 7.89 pH units during the fall and at a maximum of 8.17 pH units during the winter. Half of this seasonal variability was driven by temperature, with the remaining changes due to organic carbon and CaCO3 production. CO2 gas fluxes showed that the reef was a source of CO2 during the summer and fall, and a sink during the winter. Annually, the reef was a source of CO2, with a flux of 1.19 mol m-2 year-1. Calcium carbonate saturation states were modeled with pH and pCO2 and showed seasonal values between 2.7-5.4 for aragonite and 4.0-7.0 for calcite. Both data sets showed that the SAMI-pHs performed well in extended field tests, including high fouling environments, making it possible to determine combined temporal pH and pCO2 variability in unprecedented breadth and detail.