Chromophoric signatures of microbial by-products in the dark ocean
Catalá, T. S.; Reche, I.; Ramón, C. L.; López-Sanz, A.; Álvarez, M.; Calvo, E.; Álvarez-Salgado, X. A.
Geophysical Research Letters
Detailed examination of the absorption spectra from dark ocean samples allowed us to
identify and deconvolve two distinct chromophores centered at 302nm (UV) and 415nm (visible) from
the exponential decay curve characteristic of humic substances. The UV chromophore was ubiquitous in
intermediate and deep waters, and it has been proposed as the secondary absorption peak of nitrate. The
visible chromophore was prominent at the central and intermediate water masses of the North Pacific, and it
has been proposed as cytochrome c. Subtraction of the modeled absorption spectra of the two chromophores
from the measured absorption spectrum of the samples leads to a spectral slope overestimation by 13.3 ± 6.0%
for S275–295 and 14.8 ± 10.6% for S350–400. To only consider the chromophoric fraction of DOM, the absorption
spectra of nitrate should be subtracted in samples with a [NO3-]:a302 ratio>70 μMm.