Development of an in situ fiber optic Raman system to monitor hydrothermal vents

Abstract

The development of a field portable fiber optic Raman system modified from commercially available components that can operate remotely on battery power and withstand the corrosive environment of the hydrothermal vents is discussed. The Raman system is designed for continuous monitoring in the deep-sea environment. A 785 nm diode laser was used in conjunction with a sapphire ball fiber optic Raman probe, single board computer, and a CCD detector. Using the system at ambient conditions the detection limits of SO₄²⁻, CO₃²⁻ and NO₃⁻ were determined to be approximately 0.11, 0.36 and 0.12 g l⁻¹ respectively. Mimicking the cold conditions of the sea floor by placing the equipment in a refrigerator yielded slightly worse detection limits of approximately 0.16 g l⁻¹ for SO₄⁻² and 0.20 g l⁻¹ for NO₃⁻. Addition of minerals commonly found in vent fluid plumes also decreased the detection limits to approximately 0.33 and 0.34 g l⁻¹ respectively for SO₄⁻² and NO₃⁻.