Towards high-resolution water isotope analysis in ice cores using laser ablation - cavity ring-down spectroscopy

Area of Science:

• Analytical Chemistry
• Geochemistry
• Environmental Science

Background:

• Traditional ice core analysis requires melting, which can introduce errors.
• Direct water isotope analysis of ice is challenging due to sample phase transitions.

Purpose of the Study:

• To present a new micro-destructive laser ablation (LA) technique for high-resolution water isotope analysis of ice.
• To enable direct analysis of ice samples without prior melting or vaporization.
• To develop a method for ice core studies using laser ablation coupled with cavity ring-down spectroscopy (LA-CRDS).

Main Methods:

• Coupling a nanosecond ArF laser ablation system (193 nm) with a cavity ring-down spectrometer (CRDS).
• Utilizing nitrogen as a carrier gas and a two-volume ablation chamber.
• Developing a method for preparing ice standard samples from liquid water standards.
• Performing discrete mode measurements with laser ablation raster scans (4 mm × 4 mm) for 4 mm sampling resolution.

Main Results:

• Successfully coupled LA system with CRDS for direct ice-to-vapor analysis.
• Optimized laser parameters (spot size, repetition rate, fluence, ablation time) and carrier gas flow rates for water vapor formation and isotopic measurements.
• Analyzed ice standards and an ice core section for delta 18O and delta D on the VSMOW-SLAP scale.
• Identified critical parameters influencing precision and accuracy, including isotopic fractionation.

Conclusions:

• The developed LA-CRDS technique offers a promising micro-destructive approach for high-resolution water isotope analysis in ice.
• Optimization of experimental conditions is crucial for accurate and precise isotopic measurements.
• Further investigation into isotopic fractionation phenomena is essential for refining the technique for ice core applications.