PhD ceremony Ms. L.A. Salt: Process studies of the carbonate system in coastal and ocean environments of the Atlantic Ocean

PhD ceremony: Ms. L.A. Salt

Dissertation: Process studies of the carbonate system in coastal and ocean environments of the Atlantic Ocean

Promotor(s): prof. H.J.W. de Baar, prof. H. Thomas

Faculty: Mathematics and Natural Sciences

The increase in anthropogenic, atmospheric carbon dioxide (CO₂) has been largely mitigated by ocean uptake since the start of the Industrial Revolution, with the Atlantic Ocean providing the largest store of anthropogenic carbon. The thesis of Lesley Salt examines how the uptake of CO₂ varies in different regions of the Atlantic Ocean, from diel scales to decadal scales. The difference in partial pressure of CO₂ (pCO₂) between the ocean and atmosphere is what drives the fluxes of this gas. Three of the main controls on pCO₂ expression are biology, temperature and total alkalinity (A_T). On diel scales, in the shelf waters of the Atlantic, Salt shows that biology dominates this signal, however, only when stratification of the water column exists. On a seasonal scale, data from the Marsdiep basin shows that a combination of biology and A_T control the pCO₂ signal, with fluxes in A_T being largely controlled by the nitrogen cycle. Contrastingly, in the adjacent North Sea, he finds that inter-annual changes to the carbonate system in later summer are driven by large-scale climate forcing, which impact biology, temperature and A_T. This affects the stratification, water mass end member properties and circulation patterns. In the southwest Atlantic Ocean, the migration of this anthropogenic CO₂ into the ocean interior is studied. Salt has found that mode and intermediate waters are the most sensitive to CO₂ increases, due to the low A_T values. As such, ocean acidification will have the greatest impact on these water masses.