Abstract:
Present-day expeditionary oceanography is beginning to shift from a focus on short-
term ship and submersible deployments to an ocean observatory mode where long-
term temporally-focused studies are feasible. As a result, a critical need for in situ
chemical sensors is evolving. New sensors take a significant amount of time to develop;
thus, the evaluation of techniques in the laboratory for use in the ocean environment
is becoming increasingly important. Laser-induced breakdown spectroscopy (LIBS)
possesses many of the characteristics required for such in situ chemical sensing, and
is a promising technique for field measurements in extreme environments. Although
many LIBS researchers have focused their work on liquid jets or surfaces, little at-
tention has been paid to bulk liquid analysis, and especially to the effect of oceanic
pressures on LIBS signals. In this work, laboratory experiments validate the LIBS
technique in a simulated deep ocean environment to pressures up to 2.76 × 107 Pa. A
key focus of this work is the validation that select elements important for understand-
ing hydrothermal vent fluid chemistry (Na, Ca, Mn, Mg, K, and Li) are detectable
using LIBS. A data processing scheme that accurately deals with the extreme nature
of laser-induced plasma formation was developed that allows for statistically accu-
rate comparisons of spectra. The use of both single and double pulse LIBS for high
pressure bulk aqueous solutions is explored and the system parameters needed for
the detection of the key analytes are optimized. Using both single and double pulse
LIBS, the limits of detection were found to be higher than expected as a result of the
spectrometer used in this experimentation. However, the results of this validation
show that LIBS possesses the characteristics to be a viable chemical sensing method
for in situ analyte detection in high pressure environments like the deep ocean.
