On calcium-to-alkalinity anomalies in the North Pacific, Red Sea, Indian Ocean and Southern Ocean

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Steiner, Zvi, Sarkar, Amit, Liu, Xuewu, Berelson, William M., Adkins, Jess F., Achterberg, Eric P., Sabu, P., Prakash, Satya, Vinaychandran, P. N., Byrne, Robert H., Turchyn, Alexandra V.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2021
• Subjects: Indian; Pacific; Southern Ocean
• Online Access: https://authors.library.caltech.edu/108637/; https://authors.library.caltech.edu/108637/1/1-s2.0-S0016703721002015-main.pdf; https://authors.library.caltech.edu/108637/6/1-s2.0-S0016703721002015-mmc1.docx; https://authors.library.caltech.edu/108637/7/1-s2.0-S0016703721002015-mmc2.xlsx; https://authors.library.caltech.edu/108637/8/1-s2.0-S0016703721002015-mmc3.xlsx; https://resolver.caltech.edu/CaltechAUTHORS:20210406-143355459

An important factor for predicting the effect of increased CO₂ on future acidification of the ocean is a proper understanding of the interactions controlling production and dissolution of calcium carbonate minerals (CaCO₃). The production and dissolution of CaCO₃ in the ocean can be assessed over large spatial scales by measuring seawater calcium concentrations and total alkalinity (A_T), yet past studies suggest that there could be large discrepancies between calcium and A_T-based balances of the CaCO₃ cycle in the North Pacific and Indian Oceans. Here, we analyse water column samples collected along transects in the North Pacific, Southern Ocean, tropical Indian Ocean and Red Sea for their concentrations of calcium, nutrients, and A_T. We find that there is an excess calcium over A_T anomaly in the top 1000 m of the tropical Indian Ocean water-column. The source of this anomaly is the dissolution of subsurface gypsum deposits in the Red Sea. We find no evidence for calcium-over-A_T anomalies in the North Pacific, in contrast to previous studies. Our results show that, in most cases, calcium and A_T data agree well and can be used to reconstruct the marine CaCO₃ cycle.