Using Giovanni with Tri-Plot to Create a Simple Ternary Optical Classification System for Ocean Surface Waters

We have devised a simple optical parameter classification system using the three apparent optical property (AOP) parameters available in the NASA Geospatial Interactive Online Visualization and Analysis Infrastructure (Giovanni). These parameters are produced by the NASA Ocean Biology Processing Group (OBPG). The three AOP parameters are: a_dg, the absorption coefficient of dissolved and detrital matter; a_ph, the absorption coefficient of phytoplankton, and b_bp, the backscatter coefficient. The Microsoft Excel ternary diagram plotting spreadsheet Tri-Plot (Graham and Midgely 2000) was used for visualization of the three-parameter ocean optical parameter classification scheme. This simple analysis method can be utilized by researchers, continuous water quality monitoring campaigns, citizen scientists, and students.

In this paper we demonstrate the use of this ternary optical classification system by applying it to an examination of the seasonal outflow of the Orinoco River into the eastern Caribbean Sea. End-member optical regimes consist of the river mouth waters during the rainy season, and high clarity Caribbean Sea waters which are not influenced by the optically active constituents in the Orinoco River plume. The variability of the optical characteristics of the surface waters between the rainy and dry seasons is clearly distinguishable in the ternary plots, particularly in the coastal region adjacent to the northern coast of South America.