Autonomous Sensing of Particulate Inorganic Carbon Dynamics

Particulate inorganic carbon (PIC) is produced by coccolithophore phytoplankton and shelled foraminifera and pterpod microzooplankton. These calcite and aragonite particles contribute to excess density of aggregate particles enabling carbon export from surface waters; they are sensitive to the effects of ocean acidification. Concentrations in surface waters range from below 100 nM in oligotrophic waters to 40 uM in the North Atlantic. Very limited ship observations in the Oyashio and subarctic NE Pacific show short term PIC variability of more than one order of magitude over 10 days and 3 months, respectively. At depth concentrations can drop to near zero in waters deeper than the carbonate saturation horizon. Seasonal variations of a factor of two or more at 1000 m depth have been observed. Near surface variability is impossible to follow from ships. We are working on the development of a robust PIC sensor capable of deployment on platforms ranging from CTD's to floats and thus address the gap in observations. The sensor, which uses cross polarized optics, detects the photons that have interacted with birefringent minerals (of which calcite dominates) in the water column. The detection of this very weak signal - which can be 10-6 of the primary beam energy is a daunting task. Here we report results from incomparison deployments of a 'next gen' and prototype sensor during recent expeditions to California coastal and offshore waters (NE Pacific Gyre, Santa Barbara Basin (June 2009); Santa Catalina Basin (October 2010), Santa Cruz Basin (May 2011), California Current and Coastal Waters (July 2011; September 2011). In addition we report calibrations the sensors based on particulate samples filtered from 1L samples and analyzed by HR-ICP-MS.