Dataset: Underway ALF Data
Deployment: AT21-04

Sampling and Analytical Methodology:
The ALF is a state-of-the-art instrument, that combines high-resolution spectral measurements of blue (405 nm) and green (532 nm) laser-stimulated fluorescence, with spectral deconvolution techniques to estimate CDOM, phytoplankton variable fluorescence (Fv/Fm), Chl a and three types of phycobiliprotein pigments. The fluorescence intensities attributable to each of the variables are normalized to the water Raman and expressed as relative fluorescence units (RFU). The Raman–normalized Chl a (679nm) and CDOM (508nm) fluorescence signals stimulated by the blue laser allow for measurements of Chl a and CDOM, respectively, while the Raman-normalized PE fluorescence signatures stimulated with the green laser allow for detection and quantitative assessment of three PE-containing groups of phytoplankton. These include the:

1) PE-1 peak at 565nm from blue water oligotrophic cyanobacteria with high phycourobilin/phycoerythrobilin (PUB/PEB) ratios,

2) PE-2 peak at 578nm from green water cyanobacteria with low-PUB/PEB ratios that usually thrive in coastal mesohaline waters, and

3) PE-3 peak at 590 nm attributable to eukaryotic photoautotrophic cryptophytes that are rich in phycobiliproteins and often abundant in coastal, and estuarine environments and in enclosed bays (Chekalyuk and Hafez, 2008; Chekalyuk et al., 2012, Goes et al. 2014).

When the instrument is used for underway sampling, the ALF is connected to the ship’s uncontaminated seawater flow-through system allowing for continuous measurements in water drawn from approximately 5m below the surface

Related files and references:
Goes, J.I., Gomes H.R., Chekalyuk A., Carpenter E. J., Montoya J. P., Coles V., Yager P. L., Hafez, M. (2014) Biogeography and ecophysiology of phytoplankton communities of the Amazon River Plume Progress in Oceanography, 120, 29-40.

Chekalyuk, A., and M. Hafez (2008), Advanced laser fluorometry of natural aquatic environments, Limnology and Oceanography-Methods, 6, 591-609.

Chekalyuk, A. M., M. R. Landry, R. Goericke, A. G. Taylor, and M. A. Hafez (2012), Laser fluorescence analysis of phytoplankton across a frontal zone in the California Current ecosystem, Journal of Plankton Research, 34(9), 761-777.