For explanation and units of acronyms such as dC13_POM used below, please refer to the "Parameters" section.

Water column samples for TCO2 and TA were collected in 250 mL BOD bottles following the protocols of Dickson et al. (2007) and poisoned immediately with 50 uL saturated mercuric chloride.

TCO2:

Samples were allowed to warm to room temperature prior to analysis, which was typically performed within 4 hours of collection. A volume of 1.25 mL of sample was acidified using an automated custom-built injection and bubble stripping system coupled to an infrared gas analyzer (LICOR LI7000). Integrating the infrared absorbance signal with respect to time for each stripped gas sample yields the total amount of CO2 evolved from the sample. TCO2 measurements were calibrated using certified reference materials (CRMs) obtained from Andrew Dickson at UCSD (Batch 122). CRM’s were run periodically as unknowns over the course of a run to constrain instrument drift. All unknowns were run in triplicate. Precision estimated on the basis of triplicate analysis of unknown seawater samples (>3500 runs) and CRM replicates (n=855) for NBP 1302 is ±3 umol kg-1.

Total Alkalinity (TA):

Samples were prefiltered through 0.45 um polyvinylidene fluoride filter and were typically analyzed within 12 hours of collection with a potentiometric titrator (Metrohm 855 Robotic Titrosampler). TA calculations follow Dickson et al. (2003). Measurements were calibrated using CRMs (Batch 122) and precision estimated on the basis of CRM replicates (n=108) is ±1.5 umol kg-1.

POC, PON, dC13_POM, dN15_POM:

POM was collected by filtering between 0.5 and 4 liters of seawater through precombusted (450C for 4.5 hours) Whatman GFC filters following the protocols of Knap et al. (1996). Filters were rinsed immediately after filtration with 10 mL of 0.1N HCl to remove calcium carbonate. The filters were air dried and analyzed shore-based using a Carlo Erba NA1500 Series 2 elemental analyzer coupled to a Finnigan Delta+ mass spectrometer with a ConFloII open split interface.

References:

Dickson, A. G., Afghan, J. D., and Anderson, G. C.: Reference materials for oceanic CO2 analysis: a method for the certification of total alkalinity, Mar. Chem., 80, 185–197, doi:10.1016/S0304-4203(02)00133-0, 2003.

Dickson, A. G., Sabine, C. L., and Christian, J. R.: Guide to best practices for ocean CO2 measurements, PICES Spec. Publ., 3, p. 191, doi:10.1159/000331784, 2007.

Knap, A., Michaels A., Close A., Ducklow, H., and A. Dickson: Protocols for the Joint Global Ocean Flux Study (JGOFS) Core Measurements, JGOFS Rep., 19, 1–170, 1996.