| SABSOON : Absorption of CDOM |
Colored components of dissolved organic matter (CDOM) absorb strongly in the near-UV and violet to blue-green visible spectral regions, significantly affecting ocean color, particularly in coastal and shelf regions (Kirk, 1994). Evaluation of the relative contributions of CDOM, phytoplankton and other particulate materials to ocean color is one of the fundamental objectives of bio-optical oceanography. Temporal variability in the absorption of CDOM and UV absorption will be determined continuously at two tower sites; at R2, which is closest to shore and in a location that is likely to be influenced by seasonally varying inputs of CDOM from the coastal zone (e.g., Nelson and Guarda, 1995), and at one of the outer shelf towers where terrestrial sources of CDOM will be minimal. The CDOM fluorescence measurements will provide data which can contribute to the development of robust algorithms for the retrieval of CDOM signals from satellite ocean color and remotely sensed fluorescence (e.g. Hodge et al.,1993).
Hydrographic and bio-optical observations indicate that the winter-spring period is a period of enhanced exchange across the mid-shelf region of the South Atlantic Bight. Lower salinity coastal waters off Georgia are typically turbid with relatively high concentrations of colored dissolved organic matter (CDOM), providing optical tracers of coastal water. SeaWiFS K490 imagery (attenuation in the blue-green) from March 7, 2000 showed a distinct plume-like feature through the tower grid. A week later the feature had dissipated, but a seaward bulge in the coastal turbid zone was still evident (March 14, 2000 image). A plot of temperature, salinity, and CDOM fluorescence at R2 during this period showed that CDOM fluorescence was a sensitive indicator of lower salinity coastal water.
A towed, undulating CTD package was used on a cross-shelf transect past the R2 tower on March 14, 2000. A mid-shelf front was observed in SABSOON domain, where colder mid-shelf water was subducted beneath warm, salty water of Gulf Stream origin.