Marine humic and fulvic acids: Their effects on remote sensing of ocean chlorophyll

TLDR

Marine humic and fulvic acids have low molecular weights that align with soil‑derived absorption coefficient curves, indicating their relevance in marine optical properties. The study concentrated humic and fulvic acids from ~1,400 L Gulf of Mexico seawater, measured their absorption coefficients from 240–675 nm, and used these data to calculate spectral absorption coefficients for stations with known concentrations. The acids largely explain offshore Gulf of Mexico water color and the elevated Gelbstoff:chlorophyll ratio in productive waters, which accounts for much of the deviation from the Coastal Zone Color Scanner’s global chlorophyll algorithm.

Abstract

Marine humic and fulvic acids were concentrated from about 1,400 liters of seawater from the Gulf of Mexico, and specific absorption coefficients were measured for each from 240 to 675 nm. Spectral absorption coefficients were then calculated for Gulf of Mexico stations where earlier data on humic and fulvic acid concentrations were available. Marine humic and fulvic acid values have low molecular weights consistent with extrapolations from soil#x2010;derived curves of their specific absorption coefficients vs. molecular weight. Marine fulvic and humic acids appear to account for most if not all water color or Gelbstoff in the offshore regions of the Gulf of Mexico. Based on a remote#x2010;sensing reflectance model, it appears that the increase in the Gelbstoff: chlorophyll ratio for waters adjacent to and downstream from regions of high primary productivity accounts for much of the deviation found for such waters from the global chlorophyll algorithm of the Coastal Zone Color Scanner.