The PMEL automated underway dimethylsulfide (DMS) system is presently on board the NOAA RV Ronald H Brown.
Seawater enters the ship at the bow, 5.6 m below the ship’s waterline, and is pumped to the ship’s laboratory at approximately 30 lpm (water residence time within the ship is < 5 min). Every 30 minutes a 5 ml water sample is valved from the ship’s water line directly into a Teflon gas stripper. The sample is purged with hydrogen at 80 ml/min for 5 min. DMS and other sulfur gases in the hydrogen purge gas are collected on a Tenax filled trap, held at –5 deg C. During the sample trapping period, 6.2 pmoles of methylethyl sulfide (MES) are valved into the hydrogen stream as an internal standard. At the end of the sampling/purge period the trap is rapidly heated to +120 deg C and the sulfur gases are desorbed from the trap, separated on a DB-1 megabore fused silica column held at 70 deg C, and quantified with a sulfur chemiluminesence detector. Between each water sample the system analyzes either a DMS standard or a system blank. The system is calibrated using gravimetrically calibrated DMS and MES permeation tubes. The precision of the analysis has been shown to be ± 2% based on replicate analysis of a single water sample at 3.6 nM DMS. The automated DMS system is described in greater detail in Bates et.al., (J. Geophys. Res., 103, 16369-16383, 1998; Tellus, 52B, 258-272, 2000). The major improvements since these papers are a new automation-data system and a more reliable cold trap consisting of a electically heated stainless steel tube embeded in an aluminum block that is cooled to –5 deg C with a thermoelectric cooling chip.
The chromatographic peak report and auxiliary data (position, seawater temperature and salinity, wind speed, etc.) are compressed into a data file on board ship and sent back to PMEL once per day via email through the ship's satellite communication link. Eight of the 98 daily digital chromatograms are also included in each day’s data transmission to monitor data quality. The data file for the previous day that ends at 2400 UTC is generally received at PMEL by 1700 UTC the next day and placed on this web server. The data on this web server are "raw" data and have not been quality controlled. The quality controlled final data set will be posted on the PMEL Atmospheric Chemistry DMS Data Server
This project is funded by the NASA Office of Earth Science Oceanography Program and the NOAA Office of Oceanic and Atmospheric Research.