Dr. Matthew Humphreys

How do the oceans function as a sponge for CO₂?

Oceanographer Dr Matthew Humphreys investigates the chemistry of the marine carbon cycle and CO₂ exchange between the atmosphere and ocean. ‘The ocean absorbs about a quarter of the CO₂ we emit each year, reducing the rate of human-driven climate change. But there is a drawback: absorbing extra CO₂ changes the chemistry of seawater, for example lowering its pH, which is known as ocean acidification. My research focuses on understanding the balance of the equilibrium chemical reactions involved. How do these equilibria in the ocean control the exchange of CO₂? And what is the role of biological processes, such as the cycle of plankton growing in the sunlit surface ocean and sinking after they die, which can transport carbon down into the deep sea?’

North Sea lends a helping hand

‘Relative to the global ocean, the North Sea is rather small. But from a biological perspective, the North Sea is highly productive, so its role in the marine carbon cycle is greater than expected from it size. The chemical buffering capacity of seawater is also high here, thanks to inputs of alkalinity from rivers and sediments, which allows its waters to absorb more CO₂ and resist the resulting chemical changes. In one project with Rijkswaterstaat, and also through a second project with a consortium led by Fugro, I therefore study how the North Sea punches above its weight in absorbing CO₂ from the atmosphere.’

Solving the marine carbonate system

‘Solving the marine carbonate system is an important computational step in marine carbon cycle research. This means computing the overall balance of all the different chemical reactions in seawater based on a limited set of routinely measurable parameters. I design and develop scientific software (Python packages) to help run these calculations, using both stoichiometric (PyCO2SYS) and thermodynamic (Pytzer) approaches, and my research that aims to improve the parameterisations in these models and understand their inherent uncertainties.’

Chemical buffering and the CaCO₃ cycle

‘Calcium carbonate (CaCO₃) minerals, used by many marine organisms such as coral, oysters and various plankton to create their shells and skeletons, play an important role in the marine carbon cycle. For example, dissolving CaCO₃ raises seawater alkalinity, buffering against the effects of our CO₂ addition. In a joint project with Dr Mariëtte Wolthers at Utrecht University (BEYΩND), I am investigating how seawater chemistry controls the rate and mechanisms of CaCO₃ dissolution in the ocean.’

Academic history

• 2007–2011: MA, MSci in Natural Sciences (Geology), University of Cambridge (Churchill College), UK
• 2011–2015: PhD in Ocean and Earth Science, University of Southampton / National Oceanography Centre Southampton, UK
• 2015–2017: Senior Research Assistant in Marine Biogeochemistry, University of Southampton / National Oceanography Centre Southampton, UK
• 2017–2019: Senior Research Associate in Marine Physical Chemistry, University of East Anglia, UK
• 2019–present: Tenure-Track Scientist, NIOZ Royal Netherlands Insitute for Sea Research, Texel