Evaluating Carbonate System Algorithms in a Nearshore System: Does Total Alkalinity Matter?

Area of Science:

• Marine chemistry
• Oceanography
• Environmental science

Background:

• Ocean acidification poses a significant threat to marine organisms, particularly those with calcium carbonate shells and skeletons.
• Accurate measurement of the marine carbonate system is essential for understanding ocean acidification drivers.
• Logistical challenges often limit regular carbonate system sampling in remote or difficult-to-access nearshore environments.

Purpose of the Study:

• To assess the feasibility of estimating total alkalinity from salinity in shallow nearshore waters (<15 m depth).
• To evaluate the accuracy of calculating carbonate system parameters using salinity-derived total alkalinity compared to direct measurements.
• To determine if autonomous measurements of pH and salinity can effectively monitor coastal ocean acidification trends.

Main Methods:

• Routine water sampling at a pier in southern California to measure carbonate system parameters.
• Comparison of carbonate system parameters calculated from measured values versus estimated total alkalinity (TA) derived from salinity.
• Analysis of the predictability of total alkalinity using salinity and temperature data.

Main Results:

• Total alkalinity was not reliably predictable from salinity or temperature at the studied nearshore site.
• Dissolved inorganic carbon (DIC) and calcium carbonate saturation state were estimated within 5% of measured values using measured pH and salinity-derived or regionally averaged TA.
• The study demonstrated that autonomous measurement of pH and salinity can be a viable method for monitoring coastal changes.

Conclusions:

• Estimating total alkalinity from salinity alone is not universally applicable in all nearshore environments.
• Autonomous measurement of pH and salinity provides a cost-effective and high-frequency method for tracking key indicators of ocean acidification in coastal areas.
• This approach can support long-term monitoring of ocean acidification impacts on marine ecosystems.