Dataset: Concentration of inorganic nutrients, primary productivity measurements and phytoplankton cell concentration in seawater samples from the Malaspina 2010 Circumnavigation Expedition (VitaMaps project)

All sampling and analytical procedures are reported in [Estrada M, Delgado M, Blasco D, Latasa M, Cabello AM, Benítez-Barrios V, et al. (2016) Phytoplankton across Tropical and Subtropical Regions of the Atlantic, Indian and Pacific Oceans. PLoS ONE 11(3): e0151699. doi:10.1371/journal. pone.0151699] and are detailed below.

Hydrography and sampling details
In general, two vertical profiles of Conductivity-Temperature-Depth (CTD) were carried out at a fixed position every day, a first one down to 4000 m depth at 5:00 and a second one, starting around 10:00 local time, down to 200 m depth. The CTD, a SeaBird 9/11-plus, was equipped with dual conductivity and temperature sensors, calibrated at the SeaBird laboratory before the cruise. Water samples were obtained using a rosette of 24 10-liter Niskin bottles. Profiles of underwater photosynthetically active radiation (PAR) were obtained with a 4π Biospherical QCP2300-HP sensor attached to the CTD. The mixed layer depth (MLD) was defined [Monterey G, Levitus S (1997) Seasonal variability of mixed layer depth for the world ocean. Washington D. C.: U. S. Government Printing Office. 96 p] as the first depth (z) where σθ(z)- σθ(10)> 0.125 kg m-3, where σθ(z) and σθ(10) are, respectively, the potential density anomalies at depths z and 10 m. The Ocean Data View software [Schlitzer R (2013) Ocean Data View. http://odv.awi.de] was used to present the distribution of hydrographical variables.

Water samples for nutrient and total Chl a determination were collected from about 10 depths between surface and 200 m, including those selected for phytoplankton sampling. Water for fractionated Chl a analyses and for phytoplankton examination was taken from the Niskin bottles of the second cast of the rosette, at the depth of the 20% light level and at the depth of the subsurface chlorophyll a (Chl a) maximum (SCM). Additional surface seawater samples (3 m depth) were collected with a 30 L Niskin bottle.

Phytoplankton analysis
Approximately 250 cm3 of water were placed in a glass bottle and fixed with hexamine-buffered formaldehyde solution (4% final formalin concentration). A 100 cm3 composite chamber was filled with sample water and its content was allowed to settle for 48 hours. At least two transects of the chamber bottom were observed with an inverted microscope [Utermöhl H (1958) Zur Vervollkommung der quantitativen Phytoplankton-Methodik. Mitt Int Verein Limnol 9: 1–38.] at 312 X magnification to enumerate the most frequent, generally smaller, phytoplankton forms. Additionally, the whole chamber bottom was examined at 125 X magnification to count the larger, less frequent cells. In both cases, all cells encountered were tallied. Classification was done at the genus or species level when possible, but many taxa could not be identified and were pooled in categories such as “small flagellates” or “small dinoflagellates”.

Chlorophyll a, inorganic nutrient determinations and metal determination
To determine total Chl a concentration [Estrada M (2012) Determinación fluorimétrica de la clorofila a. In: Moreno-Ostos E, editor. Expedición de circunnavegación Malaspina 2010: Cambio global y exploración de la biodiversidad del océano Libro blanco de métodos y técnicas de trabajo oceanográfico. Madrid: CSIC. pp. 399–405], a volume of water ranging between 200 and 500 cm3 was filtered through GF/F glass fiber filters that were subsequently frozen at -20°C and, after a minimum of 6 hours, introduced in acetone 90% and left for 24 hours in a refrigerator, in the dark. The fluorescence of the acetonic extracts was determined with a Turner Designs fluorimeter calibrated with a Chl a standard (Sigma-Aldrich); no phaeopigment correction was applied. Chl a concentration for different size fractions was obtained by sequential filtering of
an additional 500 cm3 water sample through Poretics (polycarbonate) membrane filters of pore sizes 20 μm, 2 μm and 0.2 μm. Total Chl a values are those of the GF/F filters; however, as these filters tended systematically to collect more Chl a than 0.2 μm membrane filters, the proportion of Chl a in a particular size fraction was referred to the total obtained by adding up the Chl a collected in the three consecutive membrane filters. Dissolved inorganic nutrients were analyzed with a Skalar AutoAnalyzer, using the procedures of Grasshoff et al. [Grasshoff K, Kremling K, Erhardt M (1999) Methods of Seawater Analysis. Weinheim: Wiley-VCH. 632 p], as described in [Blasco D, De la Fuente Gamero P, Galindo M (2012) Muestreo y análisis de nutrientes inorgánicos disueltos en agua de mar. In: Moreno-Ostos E, editor. Expedición de circunnavegación Malaspina 2010: Cambio global y exploración de la biodiversidad del océano Libro blanco de métodos y técnicas de trabajo oceanográfico Madrid: CSIC. pp. 103–121]. Metal concentrations were analyzed as described in [Pinedo-González, P., et al. (2015), Surface distribution of dissolved trace metals in the oligotrophic ocean and their influence on phytoplankton biomass and productivity, Global Biogeochem. Cycles, 29, 1763–1781, doi:10.1002/ 2015GB005149] using a Thermo Element 2 HR-ICP-MS.