An Experimental Approach to Assessing the Roles of Magnesium, Calcium, and Carbonate Ratios in Marine Carbonates

Claire E Reymond,Sönke Hohn

doi:10.3390/oceans2010012

Claire E Reymond, Sönke Hohn

Open Access

https://doi.org/10.3390/oceans2010012

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Abstract

Marine biomineralization is a globally important biological and geochemical process. Understanding the mechanisms controlling the precipitation of calcium carbonate [CaCO3] within the calcifying fluid of marine organisms, such as corals, crustose coralline algae, and foraminifera, presents one of the most elusive, yet relevant areas of biomineralization research, due to the often-impenetrable ability to measure the process in situ. The precipitation of CaCO3 is assumed to be largely controlled by the saturation state [Ω] of the extracellular calcifying fluid. In this study, we mimicked the typical pH and Ω known for the calcifying fluid in corals, while varying the magnesium, calcium, and carbonate concentrations in six chemo-static growth experiments, thereby mimicking various dissolved inorganic carbon concentration mechanisms and ionic movement into the extracellular calcifying fluid. Reduced mineralization and varied CaCO3 morphologies highlight the inhibiting effect of magnesium regardless of pH and Ω and suggests the importance of strong magnesium removal or calcium concentration mechanisms. In respect to ocean acidification studies, this could allow an explanation for why specific marine calcifiers respond differently to lower saturation states.

Highlights

When Mg was included into the aquatic solution, neither a significant weight change of the CaCO3 seed nor a difference between the two Ca:CO3 scenarios were observed (Table 2; Table A1)
Our results show that high calcification rates observed in corals are not possible when the Mg ion concentration in the extracellular calcifying fluid (ECF) is equal to or half that of present day oceanic concentrations (Mg:Ca > 2.5)
To understand the nuances of how coral reef calcifiers can adapt to global change, such as ocean acidification, we need to better understand the ionic composition at the site of calcification

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Calcium carbonate (CaCO3 ) is the most important biogenic mineral, in terms of quantity, global distribution, and diversity [1]. The production of CaCO3 provides a number of ecological goods and services, such as shoreline protection and habitat structures. Coral reefs are one of the most important living bioconstructions of CaCO3 [2]

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