Codes in the data:
* ND: not determined
* BDL: below detection limit
* DNP: Data not presented

Water column sample collection and in-situ measurements:

Water-column samples for analysis of Chl a, nitrate, nitrite, phosphate, urea, ammonium and net primary productivity, and continuous profiles of temperature and salinity were collected using a conductivity-temperature-depth sensor (SBE 911 plus) with a 12 Bottle Frame & Carousel (SBE 32) consisting of 12 niskin bottles. Nutrient samples were collected from the niskin bottles using acid cleaned tubing and were filtered through a 0.2 µm filter. Whole water samples to measure net primary production were collected directly from CTD bottles using acid cleaned tubing and drained into acid cleaned 10L carboys. Measurement of net primary production was done using stable isotopes. Whole water samples were taken with a niskin bottle from the surface, mix layer, and chlorophyll maximum and transferred into acid-cleaned 250 mL, 500mL, 1000ml or 2000ml PETG incubation bottles in triplicate. Primary productivity was measured by adding tracer additions (<10% of the ambient dissolved inorganic carbon) of NaH13CO2 and incubating for 12-24 hours in flow-through seawater incubators under neutral density screening. Dark bottles were also incubated. After 12-24 hours, incubations were terminated by filtration through pre-combusted (450 degree C for 2 h) GF/F filters. Filters were stored at -20 degree C until analysis in the laboratory. Filters were analyzed on a Europa 20/20 isotope ratio mass spectrometer equipped with an automated nitrogen and carbon analysis for gas, solids, and liquids (ANCA-GSL) preparation module. Analysis also resulted in particulate nitrogen (PN) and particulate carbon (PC) values.

NO3 & NO2: Dissolved nitrate and nitrite was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with a detection limit of 0.14 µM (Parsons et al., 1984; Price and Harrison, 1987). In surface waters, nitrate and nitrite were determined using the same autoanalyzer equipped with a liquid waveguide capillary cell (World Precision Instruments) (Zhang, 2000) to achieve a detection limit of 0.02 µM.

PO4: Dissolved phosphate was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with a detection limit of 0.03 µM (Parsons et al., 1984; Price and Harrison, 1987).

NH4: Dissolved ammonium was determined at sea using the manual orthophthaldialdehyde method (Holmes et al., 1999).

Urea: Dissolved urea was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with a detection limit of 0.08 µM (Parsons et al., 1984; Price and Harrison, 1987).

Temperature: In-situ temperature was measured using a conductivity-temperature-depth sensor (SBE 911 plus).

Salinity: Salinity was calculated from in-situ conductivity, as measured using a conductivity-temperature-depth (CTD) sensor (SBE 911 plus).

Chl: Chlorophyll a was determined at sea using the non-acidification method with a Turner 10-AU fluorometer (Welschmeyer et al., 1994).

NPP: Net primary production was measured using stable isotopes (Mulholland et al., 2006).

PNPC: Particulate nitrogen and carbon samples were collected by filtering whole water samples through pre-combusted (450 degree C for 2 h) GF/F filters. Filters were stored at -20 degree C until analysis in the laboratory. Filters were analyzed on a Europa 20/20 isotope ratio mass spectrometer equipped with an automated nitrogen and carbon analysis for gas, solids, and liquids (ANCA-GSL) preparation module.