Ocean Freshening and Its Impacts on Seawater Carbonate Chemistry and Ocean Carbon Storage.
Supervisor: Toby Tyrrell (NOCS)
Increasing anthropogenic activities are responsible for the increase of CO2 emission to the atmosphere. This causes the warming trend which leads to many catastrophic events known as part of climate change. The ocean plays a pivotal role in regulating the Earth’s climate through a process known as global carbon cycle. The capacity of marine carbon uptake is supported by total alkalinity (TA) which acts as a buffer, allowing the ocean to absorb atmospheric CO2 without changing its pH. The ongoing climate change imposes risk of weakening the carbon storage capacity of the ocean. The weakening of carbon storage capacity can be observed through decreases in the dissolved inorganic carbon (DIC) concentration. Previous study revealed that the decreases of DIC are due to the decreases of TA. In this research long-term carbonate chemistry observation (DIC and TA) from three regional time series (BATS, HOTS, and ESTOC) and one global spatial dataset (GLODAP) were examined to understand the relationship between DIC and TA over time to determine whether alkalinity is really a strong driver for DIC concentration. The relationship between DIC and TA, as well as with other variables, was analysed using correlation analysis. The results show that TA, salinity, and temperature exhibit moderate to strong association. Through a series of event, temperature influences the CO2 solubility in the water, which lead to disequilibrium between atmospheric and seawater pCO2. The disequilibrium determines whether carbon is absorbed or emitted by the ocean, which means changes in DIC concentration. Regression analysis was used to test which variable drives the changes in DIC. At 95% confidence level, the results show that the effects of TA and salinity are statistically significant on DIC concentration. However, direct impacts of salinity on DIC is very small. The impacts of salinity changes on DIC then can be observed through the changes in TA since they are strongly correlated. Aside from the analysed and discussed variables, the possibilities of other factors controlling DIC concentration cannot be ignored. Therefore, it can be concluded that the changes in DIC concentration is not only controlled by TA, but instead is governed by multiple variables.