Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Lebrato, Mario, Garbe-Schönberg, Dieter, Müller, Marius, Blanco-Ameijeiras, Sonia, Feely, Richard A., Lorenzoni, Laura, Molinero, Juan Carlos, Bremer, Karen, Jones, Daniel O.B., Iglesias-Rodríguez, Debora, Greeley, Dana, Lamare, Miles. D., Paulmier, Aurélien, Graco, Michelle I., Cartes, Joan Enric, Barcelos e Ramos, Joana, Lara, Ana de, Sánchez Leal, Ricardo, Jimenez, Paz, Paparazzo, Flavio E., Hartman, Sue E., Westernströer, Ulrike, Küter, Marie, Benavides, Roberto, Silva, Armindo F. da, Bell, Steven, Payne, Chris, Olafsdottir, Solveig, Robinson, Kelly L., Jantunen, Liisa M., Korablev, Alexander, Webster, Richard J., Jones, Elizabeth M., Gilg, Olivier, Bailly du Bois, Pascal, Beldowski, Jacek, Ashjian, Carin, Yahia, Nejib D., Twining, Benjamin S., Chen, Xue-Gang, Tseng, Li-Chun, Hwang, Jiang-Shiou, Dahms, Hans-Uwe, Oschlies, Andreas
• Other Authors: Bundesministerium für Bildung und Forschung, European Commission, Natural Environment Research Council (UK)
• Format: Article in Journal/Newspaper
• Language: English
• Published: National Academy of Sciences (U.S.) 2020
• Subjects: Pacific; Ocean acidification
• Online Access: http://hdl.handle.net/10261/221953; https://doi.org/10.1073/pnas.1918943117

12 pages, 5 figures, supporting information https://doi.org/10.1073/pnas.1918943117.-- Data Availability. Our published databases are publicly accessible for readers, and they are deposited at the NOAA NCEI at https://data.nodc.noaa.gov/cgi-bin/iso?id=gov.noaa.nodc:0171017.-- This is Pacific Marine Environmental Laboratory contribution number 5046 Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth–ocean–atmosphere dynamic exchange of elements. The ratios’ dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios’ variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect This study was developed under a grant from the Federal Ministry of Education and Research to D.G.-S. under contract 03F0722A, by the Kiel Cluster of Excellence “The Future Ocean” (D1067/87) to A.O. and M.L., and by the “European project on Ocean Acidification” (European Community’s Seventh Framework Programme FP7/2007-2013, grant agreement 211384) to A.O. and M.L. Additional funding was provided from project DOSMARES CTM2010-21810-C03-02, by the UK Natural Environment Research Council, to the National Oceanography Centre Peer reviewed