The ARGO array of free-drifting, profiling floats provides a unique opportunity to improve our understanding of global carbon, particularly at subsurface depths inaccessible to satellite observations. These floats are parked at a depth of 1,000 to 2,000 meters for several days, then surface to transmit a profile of physical measurements to national data centers via the satellite-based ARGOS system. By the end of 2006, the ARGO array should approach 3,000 floats, a level that will be sustained as long as national commitments provide about 800 floats per year (ARGO, 2006).

Optical sensors for scattering plus chlorophyll fluorescence were added to APEX Float 0005 to demonstrate the complementary information such instruments could provide to future deployments and other ARGO-like programs. Float 0005 was released in the North Atlantic at the mouth of the Labrador Sea in 2004. To date, we have received 140 profiles, one every five days, each including 50 discrete measurements from 1,000 meters to the surface. Initial observations indicate that the optical and physical data correlate well with similarly located data obtained from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS), NOAA’s World Ocean Database 2001, and a bio-optical mooring. The success of this mission implies that optical sensors could be added to the floats without compromising the quality of their physical measurements. In addition, no significant instrumental drift has been observed to date, suggesting instrument stability and lack of fouling.

This pilot deployment demonstrates the possibility for year-round collection of chlorophyll fluorescence and backscattering data from profiling floats for systematic delineation and tracking of POC distribution in time and space, particularly in areas generally inaccessible by ship. The floats also permit measurements under cloudy conditions when satellite imagery is unavailable (thus expanding global coverage), while affording a means for validating data obtained from remote sensing platforms such as MODIS.