Evaluation of Autonomously Measured Alkalinity, pH, and pCO2 Variability on a Coral Reef

Author

Brittany PetersonFollow

Year of Award

2018

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Chemistry (Analytical/Environmental Option)

Department or School/College

Chemistry and Biochemistry

Committee Chair

Michael D. DeGrandpre

Commitee Members

Christopher Palmer, Maury Valett

Keywords

coral, reef, ocean, acidification

Subject Categories

Analytical Chemistry | Environmental Chemistry

Abstract

Currently, our understanding of alkalinity (A_T) variability in highly dynamic environments such as coral reefs is limited by the dearth of A_T measurements. In order to better characterize these environments, high temporal resolution A_T data are needed. This work employed the newly developed Submersible Autonomous Moored Instrument for Alkalinity (SAMI-alk), a fully autonomous in situ A_T analyzer, to study seawater A_T variability. The main goals of this research were to evaluate the utility of combining the SAMI-alk data with currently available in situ measurements of pH and partial pressure of carbon dioxide (pCO₂) to characterize the inorganic carbon cycle, and to measure A_T variability and determine what drives it on a coral reef.

Autonomous A_T and pH sensors (SAMI-alk and SAMI-pH) were deployed along with existing pCO₂ (MAPCO2) and pH (SeaFET) sensors in Kanoehe Bay, HI from June 4 – 21, 2013. The results show that the pH – A_T combination can provide important information about autonomously measured in situ data quality, and that it can be used to fully characterize the inorganic CO₂ system in seawater. The SAMI-alk data were also used to examine A_T variability and thereby calcification rates on coral reefs in Kaneohe Bay. A_T varied by more than 100 µmol kg^-1 on a diel basis due to CaCO₃ production and dissolution. Dissolved inorganic carbon (DIC), calculated from the pH – A_T sensor pair, varied by more than 200 µmol kg^-1, due primarily to biological metabolism on the reef. Reef calcification and metabolism dramatically alter the seawater chemistry from the open ocean source water and drive the large diel changes in all measured inorganic carbon parameters (i.e. aragonite saturation state (Ω_arag), pH, pCO₂, A_T, DIC). This data set demonstrates the value of a high-quality in situ A_T analyzer in a coral reef environment; making it possible to determine combined CO₂ system variability with unprecedented temporal resolution. These data show that NEC can be consistently sustained (net CaCO₃ production) until a threshold level of net respiration (NEP) is reached, around -50 (mmol m^-2 h^-1), which corresponds to an A_T : DIC ratio of about 1:1.

Recommended Citation

Peterson, Brittany, "Evaluation of Autonomously Measured Alkalinity, pH, and pCO2 Variability on a Coral Reef" (2018). Graduate Student Theses, Dissertations, & Professional Papers. 11305.
https://scholarworks.umt.edu/etd/11305