Dataset: Series 2A: POC, PON, Chl-a

Experiments were conducted in the lab at the University of California Santa Barbara.

Experimental setup:

The experiments were designed to test the combined effects of four temperatures, and eight light intensities on growth and photophysiology of the diatom T. pseudonana CCMP1014 in a multifactorial design. Six temperatures were tested: 13.5°C, 20°C, 25°C, 29°C, 31°C, and 32.5°C. Within each temperature, eight light levels were tested: 25, 50, 80, 115,190, 300, 450 and 600 µmol photons · m-2 · s-1. All lights were set at a 12 h day: 12 h dark cycle. For logistical reasons, experiments were partially conducted in series.

Experiments were conducted in Multicultivator MC-1000 OD units (Photon Systems Instruments, Drasov, Czech Republic). Each unit consists of eight 85 ml test-tubes immersed in a thermostated water bath, each independently illuminated by an array of cool white LEDs set at specific intensity and timing. A 0.2µm filtered ambient air was bubbled through sterile artificial seawater, and the humidified air was supplied to each tube.  Each experiment was split into two phases: An acclimation phase spanning 3 days, was used to acclimate cultures to their new environment. Pre-acclimated, exponentially-growing cultures were then inoculated into fresh media and incubated through a 4-day experimental phase during which assessments of growth, photophysiology, and nutrient cycling were carried out daily. All sampling started 6 hours into the daily light cycle to minimize effects of diurnal cycles.

Experiments were conducted with artificial seawater (ASW) prepared using previously described methods (Kester et. al 1967), and enriched with 50mL per liter of UV sterilized natural seawater and nitrate (NO3), phosphate (PO4), silicic acid (Si[OH]4), at levels ensuring that the cultures would remain nutrient-replete over the course of the experiment. Trace metals and vitamins were added as in f/2 (Guillard 1975). The pH of the growth media was measured spectrophometrically using the m-cresol purple method (Dickson 1993), and adjusted using 0.1N HCl or 0.1M NaOH.

Organic Carbon and Nitrogen concentrations

Samples were filtered onto pre-combusted GF/F filters, dried at 60°C, and stored at room temperature until analyses of particulate organic carbon (POC), and particulate organic nitrogen (PON).  Samples were analyzed using an elemental analyzer (CEC 44OHA; Control Equipment). Samples where C or N concentrations were below instrument detection limits (columns J and K) were flagged (column I).

Chlorophyll

Daily subsamples from each treatment were filtered onto 0.45 µm polycarbonate filters and stored at -20°C. Filters were placed in 90% acetone (v/v) overnight at -20°C, and the extracted chlorophyll was measured fluorometrically on a Turner 700 fluorometer (Strickland 1972). Chlorophyll-a liquid standards in 90% acetone (Turner Designs Inc.), and adjustable solid secondary standards (Turner Designs Inc. P/N 8000-952) were used for calibrations, and to calculate the chlorophyll content of the samples (Column M)

Problem report: No data was collected from treatments grown at 32.5°C as this extreme temperature inhibited growth. Growth rate was zero.