Public Research Seminar by Earth, Ocean and Atmospheric Sciences (EOAS) Thrust, HKUST (GZ) - Submarine Groundwater Discharge and Coastal Ocean Acidification

Submarine groundwater discharge (SGD) is well known as an important pathways delivering chemicals such as nutrient and carbon to oceans in addition to river discharge and atmospheric deposition. The biogeochemistry in the intertidal aquifer (the transition zone between the terrestrial and oceanic environment) is the key factor influencing the chemical composition of SGD and subsequently the coastal environment and ecology. In the context of global warming, the increasing atmospheric carbon dioxides (CO2) is regarded as the most important driver for seawater pH decline and ocean acidification in the global scale. However, in coastal oceans, seawater carbonate chemistry that controls the seawater pH is highly sensitive to land-ocean interactions and anthropogenic activities. Other drivers such as river discharge and eutrophication are found to be as important as uptake of atmospheric CO2. However, as the most important chemical loading pathway for coastal ocean, SGD has the great potential to influence carbonate chemistry and ocean acidification, but is usually neglected. In this presentation, the carbonate biogeochemistry in intertidal aquifer will be introduced to understand the sources of carbonates in SGD at first. Then, the carbonates fluxes delivered by SGD will be systematically quantified in 9 coastal zones of Hong Kong coastal waters through catchment water budget analysis. After that, the contribution of the SGD derived carbonate chemical fluxes to the seawater pH will be evaluated. In addition, the contribution of other major processes such as photosynthesis-respiration, mixing with open ocean, air-sea CO2 exchange will be also quantified. After the comparison with all major processes mentioned above, I conclude that SGD is one of the major drivers for coastal ocean acidification in semi-closed bays.