Incubation 1: Chlorophyll and phaeopigment samples were collected from an incubation experiment set up with near-surface waters (35 - 25 meters depth) collected using the TMC CTD at -62.332N, -64.6485E over three casts with each cast homogenized in 50 L carboys. Incubation setup occurred in a TMC van and treatments were incubated in 4L polycarbonate bottles in a temperature controlled (2 °C) lighted incubator van with 24hr light. Sampling occurred in a TMC bubble.Treatment identifiers are as follows:

Cast = Homogenized carboy sample at T0 for individual casts.
A = control
B = +1 nM 57FeCl3
C = +4 nM Fe 57FeCl3
D = +10 nM Fe 57FeCl3
E = +600 pM Vitamin B12
F = +4 nM 57FeCl3/+600 pM Vitamin B12
G = Dark control
H = Dark +1 nM 57FeCl3
I = Dark +4 nM Fe 57FeCl3
J = Dark +10 nM Fe 57FeCl3
K = Dark +600 pM Vitamin B12
L = Dark +4 nM 57FeCl3/+600 pM Vitamin B12

Incubation 2: Chlorophyll and phaeopigment samples were collected from an incubation experiment set up with near-surface waters (35 - 25 meters depth) collected using the TMC CTD at -62.46N, -59.565E over two casts with each cast homogenized in 50 L carboys. Incubation setup occurred in a TMC van, treatments were incubated in 4L polycarbonate bottles in a temperature controlled (2 °C) lighted incubator van with 24hr light. Sampling occurred in a TMC bubble. Treatment identifiers are as follows:

Cast = Homogenized carboy sample at T0 for individual casts.
M = control
N = +4 nM Fe 57FeCl3
O = +600 pM Vitamin B12
S = Dark control
T = Dark +4 nM Fe 57FeCl3
U = Dark +600 pM Vitamin B12

Incubation 3: Chlorophyll and phaeopigment samples were collected from an incubation experiment set up with near-surface waters (35 - 25 meters depth) collected using the TMC CTD at -62.332N, -64.6485E over a single cast where waters were homogenized in 50 L carboys. The only amendment included adding 50% of 0.2 um filtered near surface (35 – 25 meters depth) waters collected at -62.46N, -59.565E. Incubation setup occurred in a TMC van and treatments were incubated in 4L polycarbonate bottles in a temperature controlled (2 °C) lighted incubator van with 24hr light. Sampling occurred in a TMC bubble. Treatment identifiers are as follows:

Cast = Homogenized carboy sample at T0 for individual casts.
Q = control (unfiltered water from -62.332N, -64.6485E)
R = 50% unfiltered water from -62.332,N -64.6485E with 50% 0.2 um filtered waters from -62.46N, -59.565E

For each sampling timepoint, samples of 50-100 mL were filtered onto 25 mm GFF filters and extracted using the protocol of:
Jespersen, A.M. and Christoffersen, K. (1987) Measurements of Chlorophyll-a from phytoplankton using ethanol as extraction solvent. Arch. Hydrobiol. 109 (3) 445-454, as updated in:
Morison, F. and Menden-Deuer, S. (2015) Early spring phytoplankton dynamics in the sub polar North Atlantic: The influence of protistan herbivory. Limnol. Oceanogr. 60(4) 1298-1313.

Analyses were performed by Ms. Zuzanna Abdala (ODU) and Ms. Alexa Sterling (URI).

At the start of the cruise, Turner 10-AU Fluorometer was calibrated using Chla Standard Stock Solution (SSS) from Anacystis nidulans algae (#C-5753) following the protocol by Kirk Ireson & Karen Baker (PDF).

Calibration was performed by Dr. Randelle Bundy (UW) and Dr. Bethany Jenkins (URI).