Elemental Uptake by Calcite Slowly Grown From Seawater Solution: An in-situ Study via Depth Profiling

Rinat Gabitov,Chiara Borrelli,Aleksey Sadekov,Kaitlyn Sabourin,Vasiliy Yapaskurt,Alberto Perez-Huerta,Andrey Bychkov

doi:10.3389/feart.2019.00051

Abstract

Crystal growth rate has not been sufficiently explored to understand element partitioning between calcite and seawater solutions. We investigated the uptake of Li, B, Mg, Sr, and Ba by Mg-bearing calcite slowly grown on a calcite cleavage fragment. Experiments were conducted by elevating the alkalinity of an artificial seawater solution. Growth rates were evaluated by addition of lanthanum spike. At the end of each experiment, cleavage fragments were extracted and examined with micro-Raman spectroscopy, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using depth profiling technique. Distribution of Li, B, Mg, Sr, and Ba in calcite overgrowth as well as partition coefficients of those elements were evaluated.

Highlights

Uptake of trace elements by calcite has a variety of applications in climate and environmental sciences
Cleavage fragments of calcite were cleaned with 5% HCl and reverse osmosis (RO) H2O. Those calcite fragments were placed in each container. 100 g of seawater salt mix (Instant Ocean) were dissolved in 3.33 l of RO water. This solution was pumped through 0.2 μm Nalgene filter to remove organic molecules and fluid portions of ∼850 ml was placed in each container (Table 1)
ASW is an artificial seawater mix prior addition of Na2CO3; TA is a total alkalinity; is a saturation state of the fluid with respect to calcite and aragonite (Ar); “No cryst” is a number of calcite cleavage fragments examined via LA-ICP-MS depth profiling technique

Summary

INTRODUCTION

Uptake of trace elements by calcite (one the most abundant marine and terrestrial minerals) has a variety of applications in climate and environmental sciences. Fluid chemistry sometimes affects elemental incorporation into calcite, as shown by the apparent partition coefficient of Mg between calcite and fluid (KMg = (Mg/Ca)calcite/(Mg/Ca)fluid), which decreases with increasing Mg/Ca in the solution (Mucci and Morse, 1983) In this scenario, it appears evident that studies with goals to decouple the effects of growth rate and fluid content on the elemental uptake by calcite, are of fundamental importance to improve our interpretation of palaeoceanographic proxies and our understanding of mineralization processes. Elemental Uptake by Slowly Grown Calcite (ASW) solution at laboratory conditions This slow rate is lower than typical extension rates of coccolithophores and foraminifera, and should represent calcite growth conditions that are closer to equilibrium compared to many marine biominerals. Physiological effect can play an important role in elemental uptake during calcite biomineralization, it is not discussed in this study as we focused on an inorganic system, which is far from being completely understood

MATERIALS AND METHODS

RESULTS

Evaluation of Growth Rate

DISCUSSION

CONCLUSIONS