Procedural overview:

- All samples were collected via boat, using 1L square Polycarbonate bottles (surface grabs).
- Bottles were gravity filtered (combusted 47mm GF/F) into glass vials.
- Samples were returned to the on-shore MCR LTER laboratory, acidified and stored at Room Temperature.
- Samples were shipped to Craig Carlson’s Laboratory at UCSB for analysis using the HTCO Method (Carlson, et al. 2010 DSRII).

DOC analysis methodology (from Carlson et al (2010)).

All samples were analyzed via high-temperature combustion on Shimadzu TOC-V analyzers that were slightly modified from the manufacturer’s model system. The condensation coil was removed and the head space of an internal water trap was reduced to minimize system dead space. The combustion tube contained 0.5 cm Pt pillows placed on top of Pt alumina beads to improve peak shape and to reduce alteration of the combustion matrix throughout the analytical run. CO2-free carrier gas was delivered to the TOC-V systems via commercial ultra high purity gas cylinders or a Whatmans gas generator. Three milliliters of sample were drawn into a 5 ml injection syringe, acidified with 2 M HCL (1.5%), and sparged for 1.5 min with CO2-free gas. Three to five replicate 100 ml of sample were injected into the combustion tube heated to 680 1C. A magnesium perchlorate trap was added to the existing water and halide traps to ensure removal of water vapor from the gas line prior to entering a nondispersive infrared detector. The resulting peak area was integrated with Shimadzu chromatographic software.
Extensive conditioning of the combustion tube with repeated injections of low carbon water (LCW) and deep seawater was essential to minimize the machine blanks. The system response was standardized daily with a four-point calibration curve of potassium hydrogen phthalate solution in LCW. Sample and reference swapping and intercalibration exercises were conducted periodically between the UCSB and University of Miami to ensure comparability between sample sets. All samples were systematically referenced against low carbon water, deep Sargasso Sea reference waters (2600 m), and surface Sargasso Sea water every 6-8 analyses (Hansell and Carlson, 1998; Carlson et al., 2004). Daily reference waters were calibrated with DOC Consensus Reference Waters (Hansell, 2005). The standard deviation of the deep and surface references analyzed throughout a run generally had a coefficient of variation ranging between 1-2% over the 3-7 independent analyses (number of references depended on the size of the run), allowing resolution of approximately 1 mmol/kg in the deep waters.