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Atmospheric Temperature and Humidity:
Air temperature and humidity were measured with an RM Young sensor (SN 30333, calibrated 9/28/93). The sensor was mounted on the railing surrounding the mast on top of Aerovan approximately 14 m above sea level (asl). The sensor was enclosed in an RM Young radiation shield.
Barometric Pressure:
Barometric pressure was measured with the PMEL Qualimetrics sensor. The data were corrected using a linear regression with the ship’s barometer and averaged into 30 minute values. The ship's barometer was calibrated by the National Weather Service.
Corr.PRESS = -1.43331 + 1.00345* PressPMEL
Insolation (sunlight):
Total solar radiation was measured with an Epply radiometer (SN 12946) mounted on the top of AeroVan (14 m asl). There were times when the sampling mast shaded the sensor. Most of these times occurred for about a 30 minute period in the afternoon (when the ship was traveling south, the mast was west of the sensor). These shaded data have not been edited out of the 30 min data record.
Wind:
Winds were measured with the PMEL Weather Measure Skyvane (located on the sampling mast on AeroVan approximately 18 m asl). The wind data were stored as one minute averages. The ship's gyro compass input was used to correct the relative wind to true wind. The wind vector was separated into North and East components and the ship’s velocity vector components (as determined from the GPS record) were subtracted to find the true N and true E components of the wind.
WindD is the true wind direction in compass degrees.
WindS is the true wind speed in m/s.
WindU is the true wind east-west component, wind from the east to the
west is positive.
WindV is the true wind north-south component, wind from the south to
the north is positive.
RelwindS is a 30 min average of the wind speed (in m/s) relative to
the bow of the ship.
RelWindD is a 30 min average of the wind direction relative to the
bow of the ship where:
0 wind is dead ahead
+90, wind is coming from the starboard beam
-90, wind is coming from the port beam
Ship’s position, course and speed:
The ship’s position was recorded from the PMEL Trimbal GPS unit. Latitude and longitude are given here at even 30 minute intervals with no averaging. For those times when there were no data at the 30 minute point, a value was interpolated from the existing data. The course (compass degrees) and speed (knots) were computed from the differences in position.
Aerosol scattering and total number:
Light scattering by aerosol particles (ScatBlue, ScatGreen, ScatRed) was measured with the UW Civil Engineering Department nephelometer (Bodhaine et al., Atmos. Environ., 25A, p2267-2276, 1991). The instrument was calibrated on the cruise using CO2. The scattering values are in units of x10^-6 m^-1 (inverse Megameters, Mm^-1). CN > 12 nm and CN > 3 nm (UFCN) were measured with PMEL TSI CN counters.
Ozone
Two ozone uv analyzers were used, a Dasibi model 1008 AH and a TECO model 49. Both analyzers were calibrated to a NIST traceable analyzer at NOAA-CMDL prior to the project. One minute averages of the output of each analyzer were recorded on the PMEL data system and plots were made of the raw data. A small portion of the data was deleted (consisting mostly of times that the inlet air was passed through a zero filter - usually when the relative wind was well behind the beam of the ship).
After the raw data were cleaned, the calibration function from CMDL (offset and slope) was applied and 30-minute averages were created. The 30-minute averages from each instrument were then averaged together to create the final data file.
Nitrate and Ammonium:
The underway autoanalzyer system was used to measure surface nitrate and ammonium concentrations and pH. The data stream started on JD 327 and ended on JD 370. Data are marked with either a concentration in micromoles per liter, 0 (indicating below detection limit), or -99 when there were no data. The dilutions were adjusted so that the concentrations stayed on scale. The lower limit of detection was generally 0.05 uM but was as low as 0.02 uM at times for both nitrate and ammonium. The ammonium concentrations on the first leg of the cruise were < 0.05 uM. The limit of detection was improved on the second leg. Ammonium was detected from JD 357-370.
Chlorophyll
Continuous underway fluorescence measurements were made with an old Turner fluorometer using a F4T5/BL (400-520 nm) bulb. The data in cold waters were eliminated from the record due to condensation on the cell. The fluoresence readings were converted to mg/L chlorophyll using the calibration data from RITS 93(continuous reading * 0.0185 = ug/L).
Discrete chlorophyll samples were collected four times per day while underway and at each cast (six/day) on the time series station. The fluorometer was not working reliably. The discrete chlorophyll values measured at the equator were extremely low and were not consistent with historical data (Barber/Chavez references or our past data). The uncertainties are extremely high in this data set however it does provide an indication of chlorophyll fronts.
Methane and Carbon Monoxide
Sampling
Gas partial pressures were measured continuously in surface seawater along the cruise tracks using an equilibrator system designed to partition dissolved gases into a vapor phase for sampling. The equilibrator was fed with seawater pumped directly to the laboratory area from an intake located at approximately 5 m depth near the bow of the ship. The equilibrator was constructed from Plexiglass and consisted of a 20 enclosed headspace continuously showered with 15-20 L/min of seawater. Approximately every hour, 2 ml of gas were withdrawn from the headspace for analysis.
Air samples were pulled from the bow of the ship, 10 m above the sea surface, to the oceanographic laboratory (approximately 40 m) through plastic coated aluminum tubing (Dekoron) at a flow rate of 10 L/min. Dekoron tubing was also used to connect the equilibrator to the analytical system.
Analysis
Gas partial pressures were measured with an automated, temperature controlled, gas chromatographic system containing both a flame ionization detector (FID) and a mercury bed detector (MBD). Air samples from the air sampling line, the equilibrator, or a standard stream were dried using phosphorous pentoxide or potassium permanganate and drawn into a 2 ml sample loop connected to an automated sample valve. The gases were separated using a series of five columns with CO valved to the MBD and CH4 valved to the FID. The system was automated with a Carle Series 400 Controller and ran unattended with alternating injections of air, standard, and equilibrated air with the series repeated approximately each hour.
Data Reduction
The raw signals were first visually filtered to eliminate any episodes of ship contamination or instrument malfunction. CO and CH4 mixing ratios in both air and equilibrator samples were then computed based on peak height (CH4) or peak area (CO) and a six-hour running-mean single or dual-point standard. The CH4 data were further smoothed using a 12 hour weighted regression. The dry-air mixing ratios were then binned into hourly values based on the measurements made 30 minutes before and after the hour. The partial pressures measured in the equilibrator samples were corrected for warming during transit from the water intake to the equilibrator using a ratio of the seawater solubilities at sea surface temperature and the equilibrator temperature. The warming values were derived from the regression of hourly warming on sea surface temperature. The seawater phase concentrations were calculated from the measured equilibrator partial pressures and the solubility relations found in Wiesenburg and Guinasso (J. Chem. Eng. Data, 24 p356-360, 1979)
Standards were dried, whole-air mixtures contained in aluminum cylinders and were calibrated by NOAA/CMDL. CO and CH4 mixing ratios are referenced to the CMDL and Rasmussen scales, respectively. The accuracy of the standards, as determined by CMDL is ± 2% and ± 1.5% for CO and CH4, respectively. During these cruises the instrument precision, as determined by the average percent standard deviation of the standard response over a six hour period, was approximately ± 1.5% and ± 1.8% for CO and CH4, respectively.
DMS
DMS was measured with a Gas Chromatograph System. Details can be found
in Bates et al., J. Geophys. Res. 103, 16369-16,383, 1998 and Bates and
Quinn, Geophys. Res. Lett., 24, 861-864, 1997.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry