Dataset: phytoplankton chl-a
Deployment: PE08-54

At each hydrographic station, The R/V Pelican’s SeaBird CTD provided profiles for light attenuation, pressure, temperature, salinity, dissolved oxygen, chlorophyll fluorescence and turbidity during the first downcast. Beam-t measurements obtained from the CTD transmissometer were used to approximate potential PAR attenuation based on the sequential application of the percent transmission through successive 1 m layers of the water column. A Secchi disc was attached to the top of the CTD (2009). 

A SeaBird Rosette on the CTD was configured with eleven 5 L Niskin bottles that were triggered during the first upcast near the sediment interface and then at 2 m intervals (~9 bottles) as well as mid-depth in the remaining water column to the surface (1 bottle) and at the surface (1 bottle).

The seawater collected by the Rosette was used for nitrate-nitrite (NO3- + NO2-) analyses and HPLC pigment determinations. In May 2008, phosphate (PO4) and silicate (SiO4) were also measured.  For nutrient samples, 10 ml of the filtered seawater were frozen immediately after collection and returned to NCSU for laboratory analyses. In the laboratory, these samples were thawed and analyzed against a standard of natural seawater with low nitrate concentrations. NO3- + NO2-  were determined colorimetrically at NCSU using an automated QuAAtro Continuous-Flow Analysis system. Precision of the NO3- + NO2- analysis was 0.1 µM with a detection limit of 1.4 µM.

For High-Performance Liquid Chromatography (HPLC) analysis, approximately 1000 ml of water from selected sample depths were filtered through a 2.5 cm diameter GF-F filters under a low pressure vacuum (< 200 mmHg). The filters were frozen with liquid nitrogen and stored for 6-9 months. In the laboratory of Dr. J. L. Pinckney (USC), excess water was removed and the filters for HPLC analysis were analyzed in the dark on a Shimadzu dual LC10-AT vp and Controller SCL-10A vs binary gradient pump. Pigments on the filters were extracted after they were allowed to incubate for 18-24 hours in an acetone solution. The supernatant separated from the filter was extracted and inserted into smaller amber vials. The HPLC analysis was run with solvent A of 80% methanol and 20% ammonium acetate and a solvent B of 80% methanol and 20% acetone. Spectra measurements between 380-700 nm were taken every 2 seconds and peaks were identified based on retention time. CHEMTAX, a matrix factorization program, was used to optimize the contribution of the selected groups to total Chl a. The taxonomic groups, dinoflagellates (both gyroxanthin and peridinin types), and diatoms in May 2008, plus chlorophytes, cyanobacteria, cryptophytes, chrysophytes, and prymnesiophytes in Oct. 2008 and 2009, were selected according to the 'hierarchical guide to interpreting pigment data'.  Initial pigment ratios were selected from the literature and regional studies. The initial pigment ratio was optimized using multiple randomly generated starting points as seed values.  Output ratios from the previous runs were used as input values for successive runs. Values are reported here as absolute chlorophyll units.