Development of Seawater Dissolved Gas Extraction and Laser-based DIC and δ13C-DIC Analysis System

The ocean plays a critical role in the global carbon cycle and it is especially important to improve our understanding of how marine carbon uptake and storage may respond to climate change. The ¹³C/¹²C ratio of dissolved inorganic carbon (δ¹³C-DIC) in seawater is a powerful tool for quantifying important aspects of the marine carbon cycle, especially when combined with measurements of total DIC and Alkalinity (ALK). Currently, high precision measurements of δ¹³C-DIC ratios are made using isotope ratio mass spectrometers (IRMS) which have significant limitations in terms of reliability, analytical costs, and complexity. Here I present the development of a seawater gas extraction system to interface with a new laser-based isotope measurement instrument offering a simplified method and streamlined sample introduction that will reduce sample size and run-time while optimizing precision, cost, and reliability. The new analyzer uses a continuous-wave quantum cascade laser (QCL) and multi-pass optical absorption cells. Bypassing the need for additional analytical steps such as CO₂ vacuum-based extractions, the QCL and seawater gas extraction system will facilitate high precision measurements of δ¹³C-DIC and DIC that can be made directly on seawater samples. Pioneering the use of QCL for discrete seawater samples, this project will upgrade the current isotopic seawater carbon analysis capabilities at Scripps, making it more feasible to continue to maintain the Scripps seawater δ¹³C-DIC time series records while also providing the opportunity to significantly broaden the application of these important biogeochemical values and this technology.