Dataset: Incubation Experiments
Deployment: RR1202

Eight deck-board metal-addition incubation experiments were conducted in total during two cruises across the ‘Great Calcite Belt’, which served as the focal point for this project. All incubations were conducted with water collected from 20 m with a 30-L GO-Flo bottle deployed on non-metal wire (1/4” Aracom Mini-Line). Bottles were immediately transported into a positive-pressure clean van, and water was dispensed gently into 10-L low-density polyethylene cubitainers. A 200µm mesh was placed in-line to remove mesozooplankton grazers. All bottles and plasticware was stringently acid-cleaned prior to use, and trace metal clean techniques were employed for all steps. Cubitainers and polycarbonate incubation bottles were soaked in 1% Micro detergent for several days, then rinsed copiously with ultrapure >18.2 M water and soaked in 1M reagent HCl for several more days before being rinsed again and dried before use.

Cubitainers were spiked with either Fe, Zn, Co, or left unamended. Trace metal solutions were produced from traceable AAS standards diluted into 0.01 M Optima HCl. On MV1101 cruise, the first two incubation experiments involved Fe, Zn and Co additions of 0.02, 0.02 and 0.004 nM, respectively. The third and fourth incubation experiments involved Fe, Zn and Co additions of 2, 2 and 0.4 nM, respectively. Incubations 3 and 4 also involved nitrate additions of approximately 4 μM for the Fe and Zn treatments. On RR1202 cruise, Fe, Zn and Co additions of 2.0, 2.0 and 0.5 nM were used for each experiment, each involving addition of negligible nitrate.

Treatment cubitainers were gently homogenized and water decanted into triplicate 2.5-L polycarbonate bottles. Bottles were filled completely (minimizing headspace) and sealed with Parafilm and vinyl tape, then placed in incubators at 50% surface irradiance. On MV1101 cruise incubator temperature was maintained with surface water circulated through the ship’s through-hull system. On RR1202 cruise a deckboard heater/chiller unit was used to control the temperature of recirculating seawater.

Incubation bottles were sampled several times over the course of each incubation for total chlorophyll and macronutrients (nitrate, phosphate, silicate). Additionally, bottles were sampled at the final timepoint for particulate inorganic carbon (PIC) and biogenic silica (bSi). Chlorophyll samples (100 mL) were filtered through 0.45µm 25-mm Millipore HA filters, frozen, extracted in 90% acetone and quantified fluorometrically. PIC samples (200 mL) were filtered through 0.4 µm 47-mm polycarbonate filters, rinsed with 0.02 M potassium tetraborate, and then dried at 60°C prior to storage. Samples were digested in 0.8 M (5%) nitric acid and analyzed by inductively-coupled plasma optical emission spectrometry. PIC concentrations in filter digests were corrected for contributions of seasalt using Na and a Ca/Na mass ratio of 0.0382. Biogenic silica samples (200 mL) were filtered through 0.4 µm 25-mm PCTE filters and then dried at 60°C prior to storage. Samples were digested in 0.2 M NaOH and quantified spectrophotometrically.

Dissolved nutrients were analyzed by ODF technician on ship using segmented flow injection analysis following the approach of Parsons et al (1984).