Articles | Volume 22, issue 18
https://doi.org/10.5194/bg-22-5103-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-22-5103-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
29 Sep 2025
Research article |
| 29 Sep 2025
| 29 Sep 2025
From small-scale variability to mesoscale stability in surface ocean pH: implications for air–sea CO2 equilibration
Louise Delaigue
CORRESPONDING AUTHOR
Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg (Texel), the Netherlands
Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefranche, Villefranche-Sur-Mer, France
Gert-Jan Reichart
Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg (Texel), the Netherlands
Department of Earth Sciences, Utrecht University, 3584 CS Utrecht, the Netherlands
Li Qiu
GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
Eric P. Achterberg
GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
Yasmina Ourradi
Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg (Texel), the Netherlands
Chris Galley
Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL, A1B 3X5, Canada
Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, ON, K1N 6N5, Canada
André Mutzberg
GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
Matthew P. Humphreys
Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg (Texel), the Netherlands
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Joost Frieling, Linda van Roij, Iris Kleij, Gert-Jan Reichart, and Appy Sluijs
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Laura Pacho, Lennart de Nooijer, and Gert-Jan Reichart
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Niels J. de Winter, Daniel Killam, Lukas Fröhlich, Lennart de Nooijer, Wim Boer, Bernd R. Schöne, Julien Thébault, and Gert-Jan Reichart
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Kristian Spilling, Jonna Piiparinen, Eric P. Achterberg, Javier Arístegui, Lennart T. Bach, Maria T. Camarena-Gómez, Elisabeth von der Esch, Martin A. Fischer, Markel Gómez-Letona, Nauzet Hernández-Hernández, Judith Meyer, Ruth A. Schmitz, and Ulf Riebesell
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Siv K. Lauvset, Nico Lange, Toste Tanhua, Henry C. Bittig, Are Olsen, Alex Kozyr, Simone Alin, Marta Álvarez, Kumiko Azetsu-Scott, Leticia Barbero, Susan Becker, Peter J. Brown, Brendan R. Carter, Leticia Cotrim da Cunha, Richard A. Feely, Mario Hoppema, Matthew P. Humphreys, Masao Ishii, Emil Jeansson, Li-Qing Jiang, Steve D. Jones, Claire Lo Monaco, Akihiko Murata, Jens Daniel Müller, Fiz F. Pérez, Benjamin Pfeil, Carsten Schirnick, Reiner Steinfeldt, Toru Suzuki, Bronte Tilbrook, Adam Ulfsbo, Anton Velo, Ryan J. Woosley, and Robert M. Key
Earth Syst. Sci. Data, 14, 5543–5572, https://doi.org/10.5194/essd-14-5543-2022, https://doi.org/10.5194/essd-14-5543-2022, 2022
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Rick Hennekam, Katharine M. Grant, Eelco J. Rohling, Rik Tjallingii, David Heslop, Andrew P. Roberts, Lucas J. Lourens, and Gert-Jan Reichart
Clim. Past, 18, 2509–2521, https://doi.org/10.5194/cp-18-2509-2022, https://doi.org/10.5194/cp-18-2509-2022, 2022
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Carolien M. H. van der Weijst, Koen J. van der Laan, Francien Peterse, Gert-Jan Reichart, Francesca Sangiorgi, Stefan Schouten, Tjerk J. T. Veenstra, and Appy Sluijs
Clim. Past, 18, 1947–1962, https://doi.org/10.5194/cp-18-1947-2022, https://doi.org/10.5194/cp-18-1947-2022, 2022
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Carolien M. H. van der Weijst, Josse Winkelhorst, Wesley de Nooijer, Anna von der Heydt, Gert-Jan Reichart, Francesca Sangiorgi, and Appy Sluijs
Clim. Past, 18, 961–973, https://doi.org/10.5194/cp-18-961-2022, https://doi.org/10.5194/cp-18-961-2022, 2022
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A hypothesized link between Pliocene (5.3–2.5 million years ago) global climate and tropical thermocline depth is currently only backed up by data from the Pacific Ocean. In our paper, we present temperature, salinity, and thermocline records from the tropical Atlantic Ocean. Surprisingly, the Pliocene thermocline evolution was remarkably different in the Atlantic and Pacific. We need to reevaluate the mechanisms that drive thermocline depth, and how these are tied to global climate change.
Olivier Sulpis, Matthew P. Humphreys, Monica M. Wilhelmus, Dustin Carroll, William M. Berelson, Dimitris Menemenlis, Jack J. Middelburg, and Jess F. Adkins
Geosci. Model Dev., 15, 2105–2131, https://doi.org/10.5194/gmd-15-2105-2022, https://doi.org/10.5194/gmd-15-2105-2022, 2022
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A quarter of the surface of the Earth is covered by marine sediments rich in calcium carbonates, and their dissolution acts as a giant antacid tablet protecting the ocean against human-made acidification caused by massive CO2 emissions. Here, we present a new model of sediment chemistry that incorporates the latest experimental findings on calcium carbonate dissolution kinetics. This model can be used to predict how marine sediments evolve through time in response to environmental perturbations.
Matthew P. Humphreys, Erik H. Meesters, Henk de Haas, Szabina Karancz, Louise Delaigue, Karel Bakker, Gerard Duineveld, Siham de Goeyse, Andreas F. Haas, Furu Mienis, Sharyn Ossebaar, and Fleur C. van Duyl
Biogeosciences, 19, 347–358, https://doi.org/10.5194/bg-19-347-2022, https://doi.org/10.5194/bg-19-347-2022, 2022
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A series of submarine sinkholes were recently discovered on Luymes Bank, part of Saba Bank, a carbonate platform in the Caribbean Netherlands. Here, we investigate the waters inside these sinkholes for the first time. One of the sinkholes contained a body of dense, low-oxygen and low-pH water, which we call the
acid lake. We use measurements of seawater chemistry to work out what processes were responsible for forming the acid lake and discuss the consequences for the carbonate platform.
Shao-Min Chen, Ulf Riebesell, Kai G. Schulz, Elisabeth von der Esch, Eric P. Achterberg, and Lennart T. Bach
Biogeosciences, 19, 295–312, https://doi.org/10.5194/bg-19-295-2022, https://doi.org/10.5194/bg-19-295-2022, 2022
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Oxygen minimum zones in the ocean are characterized by enhanced carbon dioxide (CO2) levels and are being further acidified by increasing anthropogenic atmospheric CO2. Here we report CO2 system measurements in a mesocosm study offshore Peru during a rare coastal El Niño event to investigate how CO2 dynamics may respond to ongoing ocean deoxygenation. Our observations show that nitrogen limitation, productivity, and plankton community shift play an important role in driving the CO2 dynamics.
Matthew P. Humphreys, Ernie R. Lewis, Jonathan D. Sharp, and Denis Pierrot
Geosci. Model Dev., 15, 15–43, https://doi.org/10.5194/gmd-15-15-2022, https://doi.org/10.5194/gmd-15-15-2022, 2022
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The ocean helps to mitigate our impact on Earth's climate by absorbing about a quarter of the carbon dioxide (CO2) released by human activities each year. However, once absorbed, chemical reactions between CO2 and water reduce seawater pH (
ocean acidification), which may have adverse effects on marine ecosystems. Our Python package, PyCO2SYS, models the chemical reactions of CO2 in seawater, allowing us to quantify the corresponding changes in pH and related chemical properties.
Alice E. Webb, Didier M. de Bakker, Karline Soetaert, Tamara da Costa, Steven M. A. C. van Heuven, Fleur C. van Duyl, Gert-Jan Reichart, and Lennart J. de Nooijer
Biogeosciences, 18, 6501–6516, https://doi.org/10.5194/bg-18-6501-2021, https://doi.org/10.5194/bg-18-6501-2021, 2021
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The biogeochemical behaviour of shallow reef communities is quantified to better understand the impact of habitat degradation and species composition shifts on reef functioning. The reef communities investigated barely support reef functions that are usually ascribed to conventional coral reefs, and the overall biogeochemical behaviour is found to be similar regardless of substrate type. This suggests a decrease in functional diversity which may therefore limit services provided by this reef.
Indah Ardiningsih, Kyyas Seyitmuhammedov, Sylvia G. Sander, Claudine H. Stirling, Gert-Jan Reichart, Kevin R. Arrigo, Loes J. A. Gerringa, and Rob Middag
Biogeosciences, 18, 4587–4601, https://doi.org/10.5194/bg-18-4587-2021, https://doi.org/10.5194/bg-18-4587-2021, 2021
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Organic Fe speciation is investigated along a natural gradient of the western Antarctic Peninsula from an ice-covered shelf to the open ocean. The two major fronts in the region affect the distribution of ligands. The excess ligands not bound to dissolved Fe (DFe) comprised up to 80 % of the total ligand concentrations, implying the potential to solubilize additional Fe input. The ligands on the shelf can increase the DFe residence time and fuel local primary production upon ice melt.
Kai G. Schulz, Eric P. Achterberg, Javier Arístegui, Lennart T. Bach, Isabel Baños, Tim Boxhammer, Dirk Erler, Maricarmen Igarza, Verena Kalter, Andrea Ludwig, Carolin Löscher, Jana Meyer, Judith Meyer, Fabrizio Minutolo, Elisabeth von der Esch, Bess B. Ward, and Ulf Riebesell
Biogeosciences, 18, 4305–4320, https://doi.org/10.5194/bg-18-4305-2021, https://doi.org/10.5194/bg-18-4305-2021, 2021
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Upwelling of nutrient-rich deep waters to the surface make eastern boundary upwelling systems hot spots of marine productivity. This leads to subsurface oxygen depletion and the transformation of bioavailable nitrogen into inert N2. Here we quantify nitrogen loss processes following a simulated deep water upwelling. Denitrification was the dominant process, and budget calculations suggest that a significant portion of nitrogen that could be exported to depth is already lost in the surface ocean.
Neil J. Wyatt, Angela Milne, Eric P. Achterberg, Thomas J. Browning, Heather A. Bouman, E. Malcolm S. Woodward, and Maeve C. Lohan
Biogeosciences, 18, 4265–4280, https://doi.org/10.5194/bg-18-4265-2021, https://doi.org/10.5194/bg-18-4265-2021, 2021
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Using data collected during two expeditions to the South Atlantic Ocean, we investigated how the interaction between external sources and biological activity influenced the availability of the trace metals zinc and cobalt. This is important as both metals play essential roles in the metabolism and growth of phytoplankton and thus influence primary productivity of the oceans. We found seasonal changes in both processes that helped explain upper-ocean trace metal cycling.
Luca Possenti, Ingunn Skjelvan, Dariia Atamanchuk, Anders Tengberg, Matthew P. Humphreys, Socratis Loucaides, Liam Fernand, and Jan Kaiser
Ocean Sci., 17, 593–614, https://doi.org/10.5194/os-17-593-2021, https://doi.org/10.5194/os-17-593-2021, 2021
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A Seaglider was deployed for 8 months in the Norwegian Sea mounting an oxygen and, for the first time, a CO2 optode and a chlorophyll fluorescence sensor. The oxygen and CO2 data were used to assess the spatial and temporal variability and calculate the net community production, N(O2) and N(CT). The dataset was used to calculate net community production from inventory changes, air–sea flux, diapycnal mixing and entrainment.
Maximiliano J. Vergara-Jara, Mark J. Hopwood, Thomas J. Browning, Insa Rapp, Rodrigo Torres, Brian Reid, Eric P. Achterberg, and José Luis Iriarte
Ocean Sci., 17, 561–578, https://doi.org/10.5194/os-17-561-2021, https://doi.org/10.5194/os-17-561-2021, 2021
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Ash from the Calbuco 2015 eruption spread across northern Patagonia, the SE Pacific and the SW Atlantic. In the Pacific, a phytoplankton bloom corresponded closely to the volcanic ash plume, suggesting that ash fertilized this region of the ocean. No such fertilization was found in the Atlantic where nutrients plausibly supplied by ash were likely already in excess of phytoplankton demand. In Patagonia, the May bloom was more intense than usual, but the mechanistic link to ash was less clear.
Ove H. Meisel, Joshua F. Dean, Jorien E. Vonk, Lukas Wacker, Gert-Jan Reichart, and Han Dolman
Biogeosciences, 18, 2241–2258, https://doi.org/10.5194/bg-18-2241-2021, https://doi.org/10.5194/bg-18-2241-2021, 2021
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Arctic permafrost lakes form thaw bulbs of unfrozen soil (taliks) beneath them where carbon degradation and greenhouse gas production are increased. We analyzed the stable carbon isotopes of Alaskan talik sediments and their porewater dissolved organic carbon and found that the top layers of these taliks are likely more actively degraded than the deeper layers. This in turn implies that these top layers are likely also more potent greenhouse gas producers than the underlying deeper layers.
Yu-Te Hsieh, Walter Geibert, E. Malcolm S. Woodward, Neil J. Wyatt, Maeve C. Lohan, Eric P. Achterberg, and Gideon M. Henderson
Biogeosciences, 18, 1645–1671, https://doi.org/10.5194/bg-18-1645-2021, https://doi.org/10.5194/bg-18-1645-2021, 2021
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The South Atlantic near 40° S is one of the high-productivity and most dynamic nutrient regions in the oceans, but the sources and fluxes of trace elements (TEs) to this region remain unclear. This study investigates seawater Ra-228 and provides important constraints on ocean mixing and dissolved TE fluxes to this region. Vertical mixing is a more important source than aeolian or shelf inputs in this region, but particulate or winter deep-mixing inputs may be required to balance the TE budgets.
Delphine Dissard, Gert Jan Reichart, Christophe Menkes, Morgan Mangeas, Stephan Frickenhaus, and Jelle Bijma
Biogeosciences, 18, 423–439, https://doi.org/10.5194/bg-18-423-2021, https://doi.org/10.5194/bg-18-423-2021, 2021
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Results from a data set acquired from living foraminifera T. sacculifer collected from surface waters are presented, allowing us to establish a new Mg/Ca–Sr/Ca–temperature equation improving temperature reconstructions. When combining equations, δ18Ow can be reconstructed with a precision of ± 0.5 ‰, while successive reconstructions involving Mg/Ca and δ18Oc preclude salinity reconstruction with a precision better than ± 1.69. A new direct linear fit to reconstruct salinity could be established.
Siham de Goeyse, Alice E. Webb, Gert-Jan Reichart, and Lennart J. de Nooijer
Biogeosciences, 18, 393–401, https://doi.org/10.5194/bg-18-393-2021, https://doi.org/10.5194/bg-18-393-2021, 2021
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Foraminifera are calcifying organisms that play a role in the marine inorganic-carbon cycle and are widely used to reconstruct paleoclimates. However, the fundamental process by which they calcify remains essentially unknown. Here we use inhibitors to show that an enzyme is speeding up the conversion between bicarbonate and CO2. This helps the foraminifera acquire sufficient carbon for calcification and might aid their tolerance to elevated CO2 level.
Linda K. Dämmer, Lennart de Nooijer, Erik van Sebille, Jan G. Haak, and Gert-Jan Reichart
Clim. Past, 16, 2401–2414, https://doi.org/10.5194/cp-16-2401-2020, https://doi.org/10.5194/cp-16-2401-2020, 2020
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The compositions of foraminifera shells often vary with environmental parameters such as temperature or salinity; thus, they can be used as proxies for these environmental variables. Often a single proxy is influenced by more than one parameter. Here, we show that while salinity impacts shell Na / Ca, temperature has no effect. We also show that the combination of different proxies (Mg / Ca and δ18O) to reconstruct salinity does not seem to work as previously thought.
Jan Lüdke, Marcus Dengler, Stefan Sommer, David Clemens, Sören Thomsen, Gerd Krahmann, Andrew W. Dale, Eric P. Achterberg, and Martin Visbeck
Ocean Sci., 16, 1347–1366, https://doi.org/10.5194/os-16-1347-2020, https://doi.org/10.5194/os-16-1347-2020, 2020
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We analyse the intraseasonal variability of the alongshore circulation off Peru in early 2017, this circulation is very important for the supply of nutrients to the upwelling regime. The causes of this variability and its impact on the biogeochemistry are investigated. The poleward flow is strengthened during the observed time period, likely by a downwelling coastal trapped wave. The stronger current causes an increase in nitrate and reduces the deficit of fixed nitrogen relative to phosphorus.
Ruifang C. Xie, Frédéric A. C. Le Moigne, Insa Rapp, Jan Lüdke, Beat Gasser, Marcus Dengler, Volker Liebetrau, and Eric P. Achterberg
Biogeosciences, 17, 4919–4936, https://doi.org/10.5194/bg-17-4919-2020, https://doi.org/10.5194/bg-17-4919-2020, 2020
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Thorium-234 (234Th) is widely used to study carbon fluxes from the surface ocean to depth. But few studies stress the relevance of oceanic advection and diffusion on the downward 234Th fluxes in nearshore environments. Our study in offshore Peru showed strong temporal variations in both the importance of physical processes on 234Th flux estimates and the oceanic residence time of 234Th, whereas salinity-derived seawater 238U activities accounted for up to 40 % errors in 234Th flux estimates.
Lennart Thomas Bach, Allanah Joy Paul, Tim Boxhammer, Elisabeth von der Esch, Michelle Graco, Kai Georg Schulz, Eric Achterberg, Paulina Aguayo, Javier Arístegui, Patrizia Ayón, Isabel Baños, Avy Bernales, Anne Sophie Boegeholz, Francisco Chavez, Gabriela Chavez, Shao-Min Chen, Kristin Doering, Alba Filella, Martin Fischer, Patricia Grasse, Mathias Haunost, Jan Hennke, Nauzet Hernández-Hernández, Mark Hopwood, Maricarmen Igarza, Verena Kalter, Leila Kittu, Peter Kohnert, Jesus Ledesma, Christian Lieberum, Silke Lischka, Carolin Löscher, Andrea Ludwig, Ursula Mendoza, Jana Meyer, Judith Meyer, Fabrizio Minutolo, Joaquin Ortiz Cortes, Jonna Piiparinen, Claudia Sforna, Kristian Spilling, Sonia Sanchez, Carsten Spisla, Michael Sswat, Mabel Zavala Moreira, and Ulf Riebesell
Biogeosciences, 17, 4831–4852, https://doi.org/10.5194/bg-17-4831-2020, https://doi.org/10.5194/bg-17-4831-2020, 2020
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The eastern boundary upwelling system off Peru is among Earth's most productive ocean ecosystems, but the factors that control its functioning are poorly constrained. Here we used mesocosms, moored ~ 6 km offshore Peru, to investigate how processes in plankton communities drive key biogeochemical processes. We show that nutrient and light co-limitation keep productivity and export at a remarkably constant level while stoichiometry changes strongly with shifts in plankton community structure.
Anne Roepert, Lubos Polerecky, Esmee Geerken, Gert-Jan Reichart, and Jack J. Middelburg
Biogeosciences, 17, 4727–4743, https://doi.org/10.5194/bg-17-4727-2020, https://doi.org/10.5194/bg-17-4727-2020, 2020
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We investigated, for the first time, the spatial distribution of chlorine and fluorine in the shell walls of four benthic foraminifera species: Ammonia tepida, Amphistegina lessonii, Archaias angulatus, and Sorites marginalis. Cross sections of specimens were imaged using nanoSIMS. The distribution of Cl and F was co-located with organics in the rotaliids and rather homogeneously distributed in miliolids. We suggest that the incorporation is governed by the biomineralization pathway.
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Short summary
Our study analysed pH in ocean surface waters to understand how it fluctuates with changes in temperature, salinity, and biological activities. We found that temperature mainly controls daily pH variations, but biological processes also play a role, especially in affecting CO2 levels between the ocean and atmosphere. Our research shows how these factors together maintain the balance of ocean chemistry, which is crucial for predicting changes in marine environments.
Our study analysed pH in ocean surface waters to understand how it fluctuates with changes in...
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