Aragonite Li/Mg as an indicator of calcification media saturation state in marine calcifiers
Description
Aragonite precipitations in vitro to test the influence of pH, saturation state, temperature and the presence of amino acids on Li and Mg partitioning in aragonite. In all experiments synthetic aragonite was precipitated from artificial seawater with salinity 35.The seawater DIC/pH conditions were adjusted by addition of Na2CO3 (to increase DIC) and by 2 M HCl or NaOH (to control pH). Seawater [DIC] was measured at the start and end of each experiment using a CO2 differential, non-dispersive, infrared gas analyser (Apollo SciTech; AS-C3) calibrated with a certified reference material (CRM 194, Scripps Institution of Oceanography). ~200 mg of an aragonite seed was added to each titration to provide a surface for aragonite growth. A Metrohm Titrando 902 pH stat titrator dosed equal volumes of 0.45 M CaCl2 and Na2CO3 to maintain constant pH (and Ω) in the reaction vessel during each titration. The pH of the reaction solution was monitored using a combined pH/temperature sensor (Metrohm Aquatrode PT1000). Temperature was maintained by placing the reaction vessel in a water bath equipped with a chiller. The precipitating solution temperature was monitored at 5 s intervals within each titration using the combined pH/temperature sensor. The titration finished when 300 mg of aragonite precipitated onto the seed and the final solid was collected by vacuum filtration onto a 0.2 μm polyether sulfone filter, rinsed with trace element grade ethanol, dried and stored in a desiccator. Samples for solution [Li+], [Mg2+] and [Ca2+] were collected at the start and end of each of the titrations performed over different temperatures. For the remaining titrations, elements were measured for each batch of seawater, at the start of select experiments and at the end of all precipitations. Aragonite precipitation rates were calculated by normalising the rate of titrant addition to the surface area of the seed. All precipitates were confirmed as aragonite by Raman spectroscopy. Solution and solid elements were determined using a Varian ICP-OES and an Agilent 7500ce ICP-MS respectively.
Files
Institutions
- University of St Andrews School of Earth and Environmental Sciences