Photosynthetic properties derived from Fast Repetition Rate (FRR) fluorometry (active fluorescence)
Southern Ocean JGOFS RR KIWI 09 February 13 - March 19, 1998
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Methods:
Measurements were collected with a battery-powered FRR fluorometer with internal
data logging (Chelsea Instruments, Ltd. FASTtracka); the instrument was
attached at the base of the standard CTD/rosette frame during vertical profiles.
All FRR fluorometer data was collected during downward casts; profiles were typically
conducted at 10 m min-1 in the first 100 m of the water column and then
40-60 m min-1 for the remainder of the cast. Excitation conditions in the FRR
fluorometer were set to provide 100 flashlets of light (~1 µs duration)
spaced ~2.8 µs apart, followed by 20 additional flashlets 50 µs apart.
To correct for variations in detector response during the 120-flashlet sequence,
all fluorescence yields (signals divided by reference measurements of the excitation
source) were scaled such that the yield for each flashlet was the same when
analyzing a standard material with constant fluorescence yield, in this case
chlorophyll extracted in methanol. In addition, gain-dependent background
signals (estimated based on measurements in waters deeper than ~100 m where
fluorescence was below detection) were subtracted from all fluorescence
measurements. All reported data are from induction curve measurements in the
instrument's "dark" chamber. Note: Near surface measurements can be contaminated
with surface light effects.
Parameter values (Fo, Fm, Fv/Fm, sigma_PSII, tau_PSII) were determined using
software provided by Chelsea Instruments (FRS v. 1.4). All depth profiles of
fluorescence properties were smoothed using a low-pass filter.
The FASTtracka internal clock was synchronized to UTC several times
during the cruise, and depth values for the profiles were determined by time
synchronization with the CTD data.
Reference:
Sosik, H. M. and R. J. Olson. Phytoplankton and iron limitation of photosynthetic
efficiency in the Southern Ocean during late summer. Deep-Sea Res. Submitted.
Heidi M. Sosik
Biology Department, MS 32
Woods Hole Oceanographic Institution
Woods Hole, MA 02543-1049
phone: 508-289-2311 fax: 508-457-2134
hsosik@whoi.edu