Water samples were collected from CTD Niskin bottles. Water samples for HPLC analyses were taken from one Niskin bottle per cast-depth combination included in the dataset. Note that the niskin_sampled column indicates which Niskin bottle the HPLC sample was taken from. The niskins_fired column indicates all Niskin bottle numbers fired at the specified depth, though the HPLC sample was taken from only one of those bottles.

Chlorophyll and accessory pigment composition was analyzed by high performance liquid chromatography (HPLC; Agilent 1100). Culture aliquots were filtered on Whatmann GF/F filters, flash frozen in liquid nitrogen, and stored at -80°C until analysis. Just prior to analysis, pigments were extracted overnight in acetone at -20°C. The following day extracted pigments were centrifuged and measured using a gradient elution method (DiTullio and Geesey, 2003), a modification of the Zapata et al 2000 method. Chromatographic separation was performed using a Waters C8 symmetry column, photodiode array and fluorescence detectors. The internal standard, β-Apo-8-carotenal-trans standard (Fluka Chemical Corp., USA) was added to extracted pigments as a peak reference. Individual pigment peaks were quantified with Chemstation software (revision B.03.01, Agilent) and our pigment action spectra library calibrated using pigment standards from DHI LABS (Hoersholm, Denmark) and in-house purifications of non-commercially available pigments. Coefficient of variation among replicate HPLC injections is < 3% and our limit of detection is approximately 1 ng L-1.