Dataset: Chlorophyll-a: EN532 and EN538

Discrete chlorophyll a (Chla) samples were measured fluorometrically (Holm-Hansen & Riemann 1978) by Nicolas Van Oostende and Jessica Lueders Dumont at 6 depths spanning the surface, the bottom of the euphotic zone, the mixed layer, and Chla maximum depths. Up to 4 liters of seawater, retrieved directly from the Niskin bottles or the surface seawater inflow, were sequentially filtered through a 20 µm pore-size polycarbonate filter, a 2 µm pore-size polycarbonate filter, and a 0.3 µm pore-size glass fiber filter (GF-75; Sterlitech; 47 mm diameter). Filtrations were performed in the dark under low vacuum (<200 mbar). The Chla filters were packaged into aluminium foil (GF filter), or a 5 ml cryovial, and immediately frozen at -80°C until analysis.

Chlorophyll was extracted in 90% acetone at 4°C overnight and measured using a Turner Trilogy fluorometer, calibrated against a pure Chla standard (Anacystis nidulans Chla, Sigma-Aldrich, Saint-Louis, USA). Measurements were corrected for the fluorescence of phaeopigments after acidification with HCl (24 mM final concentration). Limit of quantification was 1 µg per liter in extract, or approximately 1 ng per liter in the sample. The Chlorophyll a concentration of casts 15 to 41 was measured by James L. Pinckney using the HPLC method derived from the Van Heukelem et al. (1992, 1994) and Pinckney et al. (1996) protocols.