Dennis Hansell and Craig Carlson

Dissolved Organic Carbon Methodology

Sampling: All samples were gravity filtered through an inline precombusted GF/F filter which was attached directly to a Niskin bottle spigot via silicone tubing. Approximately 30 mls of samples were flushed through the filter prior to collection. Sample was collected into a 40 ml precombusted glass vials with teflon coated cap liners. Samples were stored frozen at -20 degrees C until analysis which took place on board the RVIB N.B. Palmer. HTC analysis: All DOC samples were analyzed by the high temperature combustion (HTC) method using a homemade instrument. We redesigned the HTC systems used previously by Hansell et al. (1993) and Carlson et al. (1994) resulting in a system of high precision (mean standard error +/-0.6 uM Carbon) and increased day-to-day stability. The HTC machine's configuration and operating parameters are as follows: ultra high purity O2 is used as a carrier gas and flows through the machine at 175 ml/min. One hundred microliter of sample was injected manually through a septumless port into the quartz combustion tube (490 mm x 13 mm) packed with Pt gauze (Aldrich), 7% Pt on alumina catalyst (Shimadzu) , Sulfix (Wako Pure Chemical Industries, Inc.) and CuO wire (Leeman Labs). The Pt catalyst, Sulfix and CuO wire are all separated by thin layer of quartz wool. Sulfix was used for the removal of halides and the CuO wire is used to convert CO to CO2. The furnace was divided into two zones with the Pt gauze and Pt beads being heated to 800 degrees C and the remaining packing material was heated to 600 degrees C. After passing through the combustion column, the carrier gas flowed through several water traps and a final copper halide trap before entering the detector. The resulting CO2 was detected with a LiCor 6252 CO2 analyzer and the signal was integrated with chromatographic software (Dynamax Macintegrator I version 1.3; Rainin Inst.). Extensive conditioning of the combustion tube was essential to minimize the machine blank. After conditioning, the system blank was assessed with ampulated low carbon waters (LCW) that have been referenced against blank water provided by Dr. Jonathan Sharp for the 1994 DOC community intercomparison program. The system response was standardized daily with a four point calibration curve of glucose solution in LCW. Deep Sargasso seawater (>2000 m), which has been acidified and ampulated, serves as a reference standard. Analyzing low carbon water and deep seawater reference several times a day allows the detection of the machines stability from run-to-run and day-to-day, ensuring confidence in our analysis. Samples were acidified with 85% H3PO4 (10 ul/10 ml of sample) and immediately prior to injection, sparged with CO2 free oxygen for at least 10 minutes to remove inorganic carbon.