Royal Netherlands Institute for Sea Research
Phone number
+31 (0)222 36 9351
Ocean Systems (OCS)
Senior Scientist
  • Carbon cycle
  • Marine biogeochemistry
  • Anthropogenic carbon dioxide and ocean acidification
  • Seawater carbonate chemistry
  • Alkalinity and chemical buffering
Read the Academic Story of Matthew Humphreys

Dr. Matthew Humphreys

Senior Scientist

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

Linked news

Friday 29 July 2022
How coastal seas help the ocean in absorbing carbon dioxide from the atmosphere
The biologically productive North Sea impacts the global climate through exchange of carbon and nutrients with the Atlantic Ocean. A Dutch consortium of scientists will investigate how big this role of the North Sea really is. Under the leadership of…
Tuesday 09 February 2021
Autonomous measurements of the marine carbon cycle in the North Sea
A consortium of Fugro, NIOZ and two partner companies has been granted EUR 3.3 million by the Netherlands Enterprise Agency (RVO) for the RoboDock project.

Linked blogs

Wednesday 01 May 2024
NIOZ@Sea | 2nd North-Sea Atlantic Exchange (NoSe) expedition
The biologically productive North Sea impacts the global climate through exchange of carbon and nutrients with the Atlantic Ocean. The North Sea is a very productive coastal sea. A lot of carbon dioxide (CO2) can be taken up through physical,…
Monday 22 May 2023
NoSE expedition to the Norwegian Trench 26 May - 14 June 2023
The biologically productive North Sea impacts the global climate through exchange of carbon and nutrients with the Atlantic Ocean. The North Sea is a very productive coastal sea. A lot of carbon dioxide (CO2) can be taken up through physical,…
Monday 13 February 2023
64PE513 NIOZ@Sea blog: The BEYΩND expedition
Many marine plants and animals use carbonate minerals to build their shells and skeletons. The most well-known examples include coral and shellfish, but several important groups of plankton (organisms that spend their lives afloat in the ocean) do…
Wednesday 09 November 2022
BLOG New Research Fleet Equipment | Training and sea acceptance tests Slocum gliders
After the tender procedure, three Slocum gliders have been purchased from Teledyne Webb Research. The first two weeks of November 2022, a team of scientists, electrical engineers and ship technicians went to SOCIB on Mallorca for combined operational…
Wednesday 04 December 2019
NIOZ@SEA | Sinkhole expedition to the Sababank
From 5 to 18 December, NIOZ and Wageningen Marine Research (WMR) are organizing an expedition to the Saba Bank, near the Dutch island of Saba in the Caribbean. Experts on board the research vessel Pelagia hope to gain more knowledge about the…

NIOZ publications

  • 2023
    Lodeiro, P.; Rey-Castro, C.; David, C.; Humphreys, M.P.; Gledhill, M. (2023). Proton binding characteristics of dissolved organic matter extracted from the North Atlantic. Environ. Sci. Technol. 57(50): 21136-21144.
  • 2022
    Clegg, S.L.; Humphreys, M.P.; Waters, J.F.; Turner, D.R.; Dickson, A.G. (2022). Chemical speciation models based upon the Pitzer activity coefficient equations, including the propagation of uncertainties. II. Tris buffers in artificial seawater at 25 °C, and an assessment of the seawater ‘Total’ pH scale. Mar. Chem. 244: 104096.
    Humphreys, M.P.; Lewis, E.R.; Sharp, J.D.; Pierrot, D. (2022). PyCO2SYS v1.8: marine carbonate system calculations in Python. Geosci. Model Dev. 15(1): 15-43.
    Humphreys, M.P.; Meesters, E.H.; de Haas, H.; Karancz, S.; Delaigue, L.; Bakker, K.; Duineveld, G.; de Goeyse, S.; Haas, A.F.; Mienis, F.; Ossebaar, S.; van Duyl, F.C. (2022). Dissolution of a submarine carbonate platform by a submerged lake of acidic seawater. Biogeosciences 19(2): 347-358.
    Humphreys, M.P.; Waters, J.F.; Turner, D.R.; Dickson, A.G.; Clegg, S.L. (2022). Chemical speciation models based upon the Pitzer activity coefficient equations, including the propagation of uncertainties: Artificial seawater from 0 to 45 °C. Mar. Chem. 244: 104095.
    Jiang, L.-Q.; Pierrot, D.; Wanninkhof, R.; Feely, R.A.; Tilbrook, B.; Alin, S.; Barbero, L.; Byrne, R.H.; Carter, B.R.; Dickson, A.G.; Gattuso, J.-P.; Greeley, D.; Hoppema, M.; Humphreys, M.P.; Karstensen, J.; Lange, N.; Lauvset, S.K.; Lewis, E.R.; Olsen, A.; Pérez, F.F.; Sabine, C.; Sharp, J.D.; Tanhua, T.; Trull, T.W.; Velo, A.; Allegra, A.J.; Barker, P.; Burger, E.; Cai, W.-J.; Chen, C.-T.A.; Cross, J.; Garcia, H.; Hernandez-Ayon, J.M.; Hu, X.; Kozyr, A.; Langdon, C.; Lee, K.; Salisbury, J.; Wang, Z.A.; Xue, L. (2022). Best practice data standards for discrete chemical oceanographic observations. Front. Mar. Sci. 8: 705638.
    Lauvset, Siv K.; Lange, Nico; Tanhua, Toste; Bittig, Henry C.; Olsen, Are; Kozyr, Alex; Alin, Simone; Álvarez, Marta; Azetsu-Scott, Kumiko; Barbero, Leticia; Becker, Susan; Brown, Peter J.; Carter, Brendan R.; da Cunha, Leticia Cotrim; Feely, Richard A.; Hoppema, Mario; Humphreys, Matthew P.; Ishii, Masao; Jeansson, Emil; Jiang, Li-Qing; Jones, Steve D.; Lo Monaco, Claire; Murata, Akihiko; Müller, Jens Daniel; Pérez, Fiz F.; Pfeil, Benjamin; Schirnick, Carsten; Steinfeldt, Reiner; Suzuki, Toru; Tilbrook, Bronte; Ulfsbo, Adam; Velo, Anton; Woosley, Ryan J.; Key, Robert M. (2022). GLODAPv2.2022: the latest version of the global interior ocean biogeochemical data product. ESSD 14(12): 5543-5572.
    Ouyang, Z.; Collins, A.; Li, Y.; Qi, D.; Arrigo, K.R.; Zhuang, Y.; Nishino, S.; Humphreys, M.P.; Kosugi, N.; Murata, A.; Kirchmann, D.L.; Chen, L.; Chen, J.; Cai, W.-J. (2022). Seasonal water mass evolution and non‐redfield dynamics enhance CO2 uptake in the Chukchi Sea. JGR: Oceans 127(8): e2021JC018326.
    Sulpis, O.; Humphreys, M.P.; Wilhelmus, M.M.; Carroll, D.; Berelson, W.M.; Menemenlis, D.; Middelburg, J.J.; Adkins, J.F. (2022). RADIv1: a non-steady-state early diagenetic model for ocean sediments in Julia and MATLAB/GNU Octave. Geosci. Model Dev. 15(5): 2105-2131.
    Živkovic, I.; Humphreys, M.P.; Achterberg, E.P.; Dumousseaud, C.; Woodward, E.M.S.; Bojanic, N.; Solic, M.; Bratkic, A.; Kotnik, J.; Vahcic, M.; Obu Vazner, K.; Begu, E.; Fajon, V.; Shlyapnikov, Y.; Horvat, M. (2022). Enhanced mercury reduction in the South Atlantic Ocean during carbon remineralization. Mar. Pollut. Bull. 178: 113644.
  • 2021
    Possenti, L.; Humphreys, M.P.; Bakker, D.C.E.; Cobas-García, M.; Fernand, L.; Lee, G.A.; Pallottino, F.; Loucaides, S.; Mowlem, M.C.; Kaiser, J. (2021). Air-Sea Gas fluxes and remineralization from a novel combination of pH and O2 sensors on a glider. Front. Mar. Sci. 8: 696772.
    Possenti, L.; Skjelvan, I.; Atamanchuk, D.; Tengberg, A.; Humphreys, M.P.; Loucaides, S.; Fernand, L.; Kaiser, J. (2021). Norwegian Sea net community production estimated from O2 and prototype CO2 optode measurements on a Seaglider. Ocean Sci. 17(2): 593-614.
    Rahlff, J.; Khodami, S.; Voskuhl, L.; Humphreys, M.; Stolle, C.; Martínez-Arbizu, P.; Wurl, O.; Ribas-Ribas, M. (2021). Short-term responses to ocean acidification: effects on relative abundance of eukaryotic plankton from the tropical Timor Sea. Mar. Ecol. Prog. Ser. 658: 59-74.
    Zhu, K.; Birchill, A.J.; Milne, A.; Ussher, S.; Humphreys, M.P.; Carr, N.; Mahaffey, C.; Lohan, M.C.; Achterberg, E.P.; Gledhill, M. (2021). Equilibrium calculations of iron speciation and apparent iron solubility in the Celtic Sea at ambient seawater pH using the NICA-Donnan model. Mar. Chem. 237: 104038.
  • 2020
    Donald, H.K.; Foster, G.L.; Fröhberg, N.; Swann, G.E.A.; Poulton, A.J.; Moore, C.M.; Humphreys, M.P. (2020). The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii). Biogeosciences 17(10): 2825-2837.

Linked projects

NoSE_North Sea Atlantic Exchange
Matthew Humphreys
Netherlands Organization for Scientific Research
Project duration
1 Oct 2022 - 31 Dec 2027