Dataset: Chlorphyll a and pheophytin from two cruises performed as part of the STING project from R/V Atlantic Explorer AE2305 (Sting I cruise) and R/V Endeavor EN704 (Sting II cruise) in the Gulf of Mexico near Florida from February to July 2023

Whole water was collected using three methods: tow-fish, surface pump deployed on a metal-free line, or ctd rosette. There were three "types" of samples: surface (collected from one of the two pumps - towfish or surface stationary), chl max (collected at the chl maximum from one of the two CTDs, conventional or trace-metal clean), and profile.

Whole water (300 - 4300 ml) was filtered onto 25 mm GF/F filters (nominal pore size 0.7 um) using a GAST vacuum pump and and kept frozen (at -20 degrees C) in the dark until analysis. Filters were extracted overnight (16-18 hrs) in 90% acetone before analysis on a Trilogy Fluorometer with the chl a extracted acidification module calibrated using Turner Chl a standards following the extraction protocol of Strickland and Parsons 1972 (Strickland, J. D. H., & Parsons, T. R. (1972). A Practical Handbook of Seawater Analysis, 2nd edition. Fisheries Research Board of Canada.). Following the initial fluorescence reading, 20 ul of 10% HCl was added and another fluorescence reading was recorded.

The surface pump on STING I was a Wilden Pro-Flo Series P100 PTPE pump. The surface pump on STING II and for all tow-fish samples was an Almatec E15TTT pump. All pump samples were pumped through Teflon tubing. The CTD samples were collected via 10 L Niskin bottles. The fluorometer was a Turner Designs Trilogy Fluorometer with the chl a acidification method module. Calibration was done using chl a standards from Turner.