Geoscience Reference
In-Depth Information
2.2.1 CDOM as Mixture of Humic and Fulvic Acids
In his work, Hawes (
1992
) assumed that fulvic and humic acids comprise the sum
of total CDOM (although it is not usually true). Hawes (
1992
) isolated humic and
fulvic acids from several samples and measured their absorption and
fl
uorescence;
a
ðk
0
Þ
gðk
0
! kÞ
were
converted into mathematical functions with linear regression in order to use the data
in optical models. He used
and spectral
fl
fluorescence quantum ef
ciency functions
gðk
0
! kÞ
(formulated in numbers of photons), from
which we obtained R
ðk
0
! kÞ
(formulated in terms of energy), according to
Mobley (
1994
). For
uorescence
parameters of samples numbered FA7 (of fulvic acids) and HA6 (of humic acids)
from Hawes (
1992
) were used. Speci
the purpose of our study, absorption and
fl
c absorption spectra and
fl
uorescence
quantum ef
ciency functions for these components are shown in Fig.
1
. For the
investigation of
fluorescence structures in the whole spectral range, concentrations
of fulvic and humic acids were set separately to 1 and 10 g m
−
3
in the 100 m deep
water column. For narrow-band modeling in the spectral region of Fraunhofer line
H
fl
at 486 nm (see Sect.
3
) concentrations of fulvic and humic acids were set
simultaneously to 1, 10, 50 and 100 g m
−
3
.
CDOM abundance is typically quanti
b
cient at a given
wavelength (e.g. 443 or 355 nm). For most of the ocean a(443 nm) is below
0.1 m
−
1
(Morel and Gentili
2009
), but can be much higher for coastal waters. In
European coastal waters a(443 nm) ranges approximately between 0.01 and 1 m
−
1
(Babin,
2003
). In our case, 1 g m
−
3
ed by its absorption coef
of fulvic or humic acids corresponds to
a(443 nm) of 0.075 m
−
1
for FA7 and 0.011 m
−
1
for HA6.
2.2.2 Excitation-Emission Matrices Approach
In the second approach of implementing CDOM
fluorescence into SCIATRAN we
used a PARAFAC (PARAllel FACtor analysis) model. Nowadays, PARAFAC is
fl
Fig. 1 Speci
c absorption spectra and fluorescence quantum ef
ciency functions for samples
numbered FA7 (of fulvic acids) and HA6 (of humic acids). Redrawn from Hawes (
1992
)
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