The Spectrophotometric Analysis of Lead Carbonate Complexation and Carbonate Saturation States in Seawater

• Main Author: Easley, Regina Anita
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: Digital Commons @ University of South Florida 2013
• Subjects: carbon dioxide; marine carbon cycle; metal speciation; ocean acidification; pH; Analytical Chemistry; Other Oceanography and Atmospheric Sciences and Meteorology; Ocean acidification
• Online Access: https://digitalcommons.usf.edu/etd/4668; https://digitalcommons.usf.edu/context/etd/article/5865/viewcontent/Easley_usf_0206D_11790.pdf

The carbon dioxide (CO2) system is the primary buffer in seawater which controls oceanic pH. Changes in the marine CO2 system affect a number of processes such as metal speciation, mineral saturation states, auditory responses in fish, and primary productivity rates. Increased atmospheric concentrations of CO2 from human activities (e.g. burning of fossil fuels, deforestation, and cement production) has led to a global decrease in surface ocean pH termed anthropogenic ocean acidification. One particular concern in response to increased oceanic CO2 is a substantial decrease in the calcium carbonate (CaCO3) saturation states, ΩCaCO3. The long-term physiological effects of ocean acidification and decreased ΩCaCO3 on marine biota are currently subjects of intensive global investigation. Consequently improved methods are needed to facilitate evaluations of the evolving CO2 system chemistry and the responses of marine organisms to those changes. Currently two of four measureable chemical parameters (pH, dissolved inorganic carbon, fugacity of CO2, and total alkalinity) are required for full characterization of the inorganic CO2 system; carbonate ion concentrations ([CO3 2-]) can, for example, be calculated from paired measurements of pH-DIC and pH-TA. The primary objective of this dissertation is to refine a method for directly determining [CO3 2-] using a single measurement, the distinctive ultraviolet absorbance spectra of Pb(II) species in seawater. The technique is fast, methodologically simple, and suitable for routine use in laboratory and shipboard studies. It is, as well, suitable for analyses using autonomous instrumentation. My studies began with an investigation of lead carbonate (PbCO3 0) complexation in synthetic media (at 25 °C between 0.001 to 5.0 molal ionic strength) to evaluate factors that control Pb(II) speciation, and thereby Pb(II) spectra, in seawater. Since laboratory investigations of Pb(II) speciation in seawater require potentiometric measurements of seawater pH, my dissertation includes ...