Geoscience Reference
In-Depth Information
Relative Fluorescence
20
0
40
60
80
0
50
100
150
200
CDOM
Flavin
250
CHL*3
300
Figure 6.3. First published
in situ
DOM fluorescence profile from the Black Sea. DOM measured
at ex/em = 320-390/475-530 nm, flavins at ex/em = 420-470/527 nm, and chlorophyll ex/em =
420-470/660 nm. (Redrawn from Coble et al.,
1991
.)
respectively. Meter output was in volts and was observed to be linear (using quinine sulfate
dihydrate [QS] standards) over a wide range of concentrations due to operator selection
among three gain settings. This sensor was tested and utilized by a number of researchers
(Chen and Bada,
1992
; Coble et al.,
1998
; Chen,
1999
; and others) and demonstrated that it
was a robust tool for tracking DOM optical properties in aquatic environments. The optical
design is still used today and is discussed later in this chapter.
The following years gave rise to a number of instrument design types for various applica-
tions. In 1992, Lieberman et al. developed a fiber optic-based system to measure petroleum
hydrocarbons in the San Diego Bay. It utilized a pulsed N
2
laser source (ex = 337 nm), mea-
sured fluorescence at 360 nm (50 nm bandpass), and possessed a sheath on the optic probe
to protect the sensor from seaweed and provide constant viewing volume. Strong agree-
ment was found between this design and flow-through measurements (
Figure 6.4A
), but
with the advantage of rapid response times of measurements to align CDOM fluorescence
data with CTD measurements. Another fiber optic design was introduced by Klinkhammer
in
1994
. The submersible profiling zero angle photon spectrometer (ZAPS) probe offered
the sensitivity of PMT detection and utilized a xenon flash lamp and the versatility of fiber
optics. It measured ex/em = 320/420 nm down to 6000 m. Data were calibrated using QS
standards at several temperatures. Good agreement between a Sea Tech
in situ
CDOM
