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Fluorescence Data

The Field Data path of our website is intended to serve as a repository for productivity- related measurements that will contribute to an advanced understanding of phytoplankton physiology and photosynthesis. We encourage researchers collecting relevant data to contribute their results to this website (to make a contribution, please contact Robert O'Malley at: omalleyr_at_science_dot_oregonstate_dot_edu). Currently, the two categories of field data we're supporting are variable fluorescence data and carbon-14 based productivity measurements. You can access these data by selecting the appropriate tab above.

Currently, you are viewing the Fluorescence field data page. Here you can access variable fluorescence data collected in the tropical Pacific ocean with a Fast Repetition Rate fluorometer (FRRf). Measurements were conducted on flow-through seawater, and therefore correspond to physiological properties of phytoplankton within the surface mixed layer. Our field work in the tropical Pacific began in 1994 and continues to this day (see Behrenfeld et al. 2006a for details). New data will continue to be posted as final quality control assessments are completed. Currently, you can download data collected between 1995 and 2006.

To access fluorescence data, go to the "Online Data" tab above. Each data set is identified by the year of collection and then a lower case letter if multiple field studies were conducted in a single year. To view the location of the field studies, go to the "Location Map" tab above.

Variable fluorescence parameters derived with an FRRf are based on single turnover excitation flash sequences, as described by Kolber & Falkowski (1993) and Falkowski & Kolber (1995). During these measurements, fluorescence levels increase from an intial low value to a saturated value. The difference between these fluorescence yields is referred to as "variable fluorescence" and it is typically normalized to the maximum saturated value to account for spatial variability in phytoplankton biomass. In addition, the rate at which fluorescence saturates is related to the functional "antennae size" of the oxygen-evolving photosynthetic reaction centers. Thus, the variable fluorescence parameters you will find in our online data are:

  • initial fluorescence (Fo),
  • maximum fluorescence (Fm),
  • variable fluorescence (Fv/Fm = (Fm-Fo)/Fm), and
  • photosystem II functional absorption cross sections (sigma PSII).

Some of the notable features you will see in the data when viewed over diel cycle are:

  • midday decreases in variable fluorescence associated with (reversible) photoinhibition of PSII,
  • strong midday decreases in Fo and Fm from nonphotochemical quenching, and
  • large nocturnal decreases in Fv/Fm in the equatorial upwellnig zone that are occassionally accompanied by significant decreases in sigma PSII.

The large nocturnal changes in Fv/Fm and sigma_PSII are repercussions of iron limiting growth conditions (see Behrenfeld et al. 2006a). The regularly expressed diurnal nonphotochemical quenching features that you will see throughout each transect data set severely limit the utility of daytime fluorescence values (Fo or Fm) as indices of phytoplankton pigment concentration (e.g., chlorophyll). Night-time fluorescence values (particularly Fm) provide a better proxy of chlorophyll biomass, but it is important to recognize that the relationship between Fm and chlorophyll is not a constant and is particularly different between regions where phytoplantkon are iron limited in the presence of high macronutrient concentrations (i.e., HNLC waters) and waters where phytoplankton are growing under conditions of very low macronutrient levels. It should also be noted that Fo and Fm data retain some effect of cuvette fouling. This fouling issue is seen each night around midnight when the cuvette was cleaned. The effect is largely in the upwelling region and, although it affects Fo and Fm, it does not impact Fv/Fm or sigma_PSII.

Note: when looking at the fluorescence data set, you will find periods during each transect with no data. The missing data periods are due to instrument failures or various other problems.

The 2003 file also includes coincident data for particulate beam attenuation at 532 nm and 660 nm, and discrete measurements of particle abundance (Coulter counter) and particulate organic material (POC). For details on all these measurements, see Behrenfeld and Boss (2006b).

For more detailed information on the TAO cruises (e.g., sea state, CTD data, etc), please see the TAO web site at http://www.pmel.noaa.gov/tao/ and match up cruises by date and location.

Last modified: 13 March 2007
by:  Robert O'Malley

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