Tina Taitaifono Mareko^1,, Patila Amosa¹, Faainuseimalie Latu¹, Tanuvasa Toetu Leasi²

The ocean plays a crucial role in regulating Earth's climate by absorbing approximately 30% of the carbon dioxide (CO₂) emitted into the atmosphere. This process results in the production of carbonic acid, contributing to the acidification of the ocean and a decrease in seawater pH, which is referred to as ocean acidification. Human activities and natural sources primarily cause this acidification process, and it poses a significant threat to marine ecosystems. One of the key impacts of ocean acidification is the depletion of carbonate ions, which are essential for forming skeletons and shells in many marine organisms, including corals. there is a lack of detailed information regarding the fluctuation of seawater carbonate chemistry in Pacific island coastal regions like Samoa. To bridge this gap in knowledge, a study was conducted to examine the temporal variability of seawater carbonate chemistry at five locations along the North coast of Upolu Island. The mean pH was measured spectrophotometrically using the m-Cresol purple buffer. The total alkalinity (A_T) was measured through titration of seawater with standardized 0.101970 mol/kg HCl. The measured values from the spectrophotometer at three wavelengths: a non-absorbing wavelength (730 nm for m-Cresol purple) and at the wavelengths corresponding to the absorption maxima of the base (I^2–) and acid (HI^–) forms of the dye respectively (578 and 434 nm) and the EMF values from the seawater titration were used to calculate the actual pH and A_T. The results showed that these values varied across 5 sites. The overall distribution of mean pH across 5 sites fell below the mean average pH of 8.1 for open ocean water ranging from 7.944 ± 0.090 to 8.087 ±0.069, while the mean seawater A_T values fell within the normal A_T range of (2100-2500µmol kg^–1). Thus, the variability of these seawater parameters over the study area has indicated healthy coastal waters.

Ocean Acidification, SDG14, Total Alkalinity, climate change, seawater CO₂, ocean monitoring, marine ecosystem