Nutrients: run fresh, unfiltered on a Seal QuAAtro nutrient analyzer. Standards were made daily in artificial seawater, baseline was artificial seawater. Samples were corrected for residual contamination in the baseline. Values are the mean of two samples (±10%). Level of detection is -0.1 µM N and P. Si is 0.5µM.
chl: filtered onto either 0.4 or 10 µm pore size polycarbonate filters, extracted in MeOH overnight in the freezer and then run on a Turner TD-700 with the Welschmeyer (1994) non-acidification filters. The instrument was calibrated prior to each batch with a solid standard calibrated against pure chlorophyll a. Results are the average of two duplicates, variation is ±10%.
Cell counts: preserved in 1% hexamine buffered formalin. 25-50 ml of sample was settled overnight in a Utermohl settling chamber and then counted on a Zeiss ICM-405 inverted microscope. A single sample from each depth was counted.
Related files and references:
Welschmeyer NA (1994) Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnology and Oceanography 39: 1985-1992.
Knapke, E. (2012) Influence of Mississippi River Plume on Distributions of Diazotrophs in the Northern Gulf of Mexico During Summer 201. M.S., University of Texas at Austin. http://hdl.handle.net/2152/ETD-UT-2012-08-6107