Real-time ocean chemical measurement: at-sea ICP-MS experiments

Abstract

We describe the first at-sea deployment and operation of an inductively coupled plasma mass spectrometer (ICP-MS) for continuous measurement of isotopes and trace element concentrations in sea-water. The purpose of these experiments was to demonstrate that an ICP-MS can be operated in a harsh environment with no degradation in performance, and that accurate trace element data can be acquired on rapid analytical time scales. Evaluation at sea involved performance testing, characterization and calibration of a real-time sea-water analytical methodology, and continuous sea-water profiling over an extended three day transect from the Gulf of California to San Diego. We show that mass spectrometers can rapidly, precisely and accurately determine trace element concentrations in sea-water, thus allowing high-resolution mapping of large areas of surface sea-water. This analytical capability represents a significant advance toward real-time observation and characterization of water mass chemistry in dynamic coastal environments. While evaluating the ICP-MS off the coast of Baja California, we discovered barium depletion of 65% in surface waters over tens of kilometres.