Samples for inorganic nutrient analysis were collected in HDPE bottles and frozen (-20ºC) immediately after sample collection. Samples were kept frozen until processing by Joe Jennings at Oregon State University. The analyses for phosphate (PO4), nitrate plus nitrite (NO3_NO2), nitrite (NO2), ammonium (NH4), and silicic acid (silicate) were performed using a hybrid Technicon AutoAnalyzerII and Alpkem RFA300 system following protocols modified from Gordon et al. (see below for reference). The estimated precision for each element was as follows: PO4, ± 0.008 µM; NO3_NO2, ± 0.15 µM; NO2, ± 0.01 µM; silicic acid, ± 0.3 µM.

To obtain the concentration of total organic carbon (TOC) and total nitrogen (TN), a 40 ml aliquot of whole seawater was acidified to pH~3 with concentrated hydrochloric acid (HCl) and stored in combusted glass vials at 4°C until analysis with a Shimadzu TOC-VCSH total organic carbon analyzer coupled to a TNM-1 analyzer. Blanks (MilliQ water) and standard curves with potassium hydrogen phthalate and potassium nitrate were interspersed into the sample runs. The coefficient of variability between replicate injections was <1%. Comparisons to standards provided by Prof. D. Hansell (University of Miami) were made daily.

References:
Gordon, L. I., J. C. Jennings, Jr., A. A. Ross, and J. M. Krest. 1994. A suggested protocol for continuous flow automated analysis of seawater nutrients (phosphate, nitrate, nitrite and silicic acid) in the WOCE Hydrographic Program and the Joint Global Ocean Fluxes Study. In WOCE operations manual. WOCE report no. 68/91, revision 1. WHP Office Report WHPO91-1. Woods Hole Oceanographic Institution, Woods Hole, Mass.