The standard exponential model for CDOM absorption has been applied to data
from diverse waters. Absorption at 440 nm (ag440) ranged between close to zero
and 10 m−1, and the slope oft he semilogarithmic absorption spectrum over
a minimum range of400 to 440 nm (s440) ranged between <0.01 and 0.04 nm−1. No
relationship was found between ag440 or s440 and salinity. Except in the southern
Baltic, s440 was found to have a broad distribution (0.0165 ± 0.0035), suggesting
that it should be introduced as an additional variable in bio-optical models when
ag440 is large. An alternative model for CDOM absorption was applied to available
high quality UV-visible absorption spectra from the WisGla river (Poland). This
model assumes that the CDOM absorption spectrum comprises distinct Gaussian
absorption bands in the UV, similar to those ofb enzene. Five bands were fit to the
data. The mean central energy ofal l bands was higher in early summer (E ∼7.2,
6.6, 6.4, 6.2 and 5.5 eV or 172, 188, 194, 200 and 226 nm) than in winter. The
higher energy bands were found to decay in both height and width with increasing
salinity, while lower energy bands broadened with increasing salinity. s440 was
found to be correlated with shape parameters of the bands centred at 6.4 and
5.5 eV. While the exponential model is convenient for optical modelling and remote
sensing applications, these results suggest that the Gaussian model offers a deeper
understanding ofc hemical interactions affecting CDOM molecular structure.
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