Design of autonomous in-situ spectrophotometric systems for measurement of nutrients and CO2-system parameters

A compact spectrophotometric analysis system (SEAS) has been developed for autonomous analyses of the upper ocean. SEAS is capable of spectral analysis from 400 to 750nm in both absorbance and fluorescence modes. The sample cell is configured to use long pathlength liquid core waveguides (10500cm) whereby analyte detection limits are on the order of one nanomolar or better. Internal memory of SEAS is sufficient to store 1000 complete measurements. A serial port or LonWorks interface can be used to access stored data and/or control the instrument’s operation. Field deployments have measured in-situ nitrite profiles to 200 meters and surface seawater pH on a long-term mooring. SEAS is currently being configured for measurements of ferric and ferrous iron in rainwater. Demonstrated measurement capabilities using our liquid core waveguide systems in absorbance and fluorescence modes include ammonia, nitrate, nitrite, iron, copper, chromate, molybdate, hydrogen sulfide, pH, pCO2, total inorganic carbon, total alkalinity and fluorescence of natural organics. In this work we present an overview of SEAS, discuss applications for our sensor and present calibration and field data.