A microsensor for carbonate ions suitable for microprofiling in freshwater and saline environments

Abstract

A novel carbonate microsensor, based on the ion-selective ionophore N,N,-dioctyl-3α,12 α-bis(4-trifluoroacetylbenzoxy)-5β-cholan-24-amide, is presented. The sensor chemistry and filling electrolyte, used previously for macrosensors, was improved for use in microsensors, and a simple calibration procedure was designed. The sensor is highly selective for carbonate, having a similar selectivity as the macrosensor, and is so insensitive to Cl -interference that it can be used in seawater. The ability to measure accurate profiles with the carbonate sensor was verified in agar gels with artificial carbonate gradients. Several environmental applications are presented, including photosynthesis and calcification measurements in freshwater stromatolites (tufas) and foraminifera. Carbonate profiles in illuminated and darkened hypersaline microbial mats were qualitatively as expected and aligned with the oxygen and pH profiles. The dissolved inorganic carbon profiles calculated from local pH and carbonate values, however, did not follow the expected trends, both in the foraminifera and the hypersaline mat. Temporal and spatial heterogeneities make perfect alignment of pH and carbonate profiles, needed for DIC calculations, unrealistic. The calculation of dissolved inorganic carbon microprofiles from pH and carbonate microprofiles is not recommended. The microsensor is highly useful in studies on calcification and decalcification, where direct concentrations of carbonate and calcium ions are needed.

Strontium isotope fractionation of planktic foraminifera and inorganic calcite

“…Gradients in the concentrations of O 2 , CO 2 , CO 2À 3 , H + and Ca 2+ have been observed in water around living symbiotic foraminifera (e.g. Kö hler-Rink and Kü hl, 2005;de Beer et al, 2008) and at the surface of corals (Al-Horani et al, 2003). The maximum thickness of these boundary layers is determined by micro eddies in turbulent water (about 1 mm in ocean water), or is in the same order of magnitude as the particle radius (Zeebe and Wolf-Gladrow, 2001 (2007) suggested that the enrichment of heavy calcium isotopes in a diffusive boundary layer around fast growing calcite crystals could explain results of Lemarchand et al (2004).…”

Chemical conditions favoring photosynthesis-induced CaCO3 precipitation and implications for microbial carbonate formation in the ancient ocean

“…In the case of photosynthesis with CCMs, on the other hand, DIC decreases owing to photosynthetic HCO 3 À assimilation and released OH À changes the proportion of carbonate chemistry to increase pH and [CO Chemical profiles of pH, O 2 , CO 2 , Ca 2+ , and CO 3 2À at the substrate surface were measured by microelectrodes, as described by Shiraishi et al (2010). CO 3 2À microelectrode was prepared as described by Meyerhoff et al (1987) andde Beer et al (2008), and CO 2 microelectrode as by de Beer et al (1997). The profiles were measured by moving the electrode tip from the water column (starting from 500 lm above) to the substrate surface in 50 lm intervals.…”

Biosensor for laboratory and lander‐based analysis of benthic nitrate plus nitrite distribution in marine environments

“…Until now, the only chemical parameters being analyzed with marine landers using ion-or gasspecific sensors are O 2 , H 2 S, CO 2 , pH (Reimers and Glud 2000), N 2 O (de Beer unpubl. data), and CO 3 2- (de Beer et al 2008). By use of voltammetry, it is possible to analyze a range of redoxactive species such as Fe 2+ and Mn 4+ for which no satisfactory ion-specific sensors are available (Luther et al 2008).…”