<div><p><strong>Sampling and Analytical Methodology: </strong><br />
Water samples for CFC and SF6 measurements were collected at all stations, including demi-stations, using the 30-liter Niskin bottle rosette. The CFC/SF6 sample was the first sample drawn from the Niskin bottle. The samples were collected in a 500 cc glass stoppered bottle through a PVC tube connected to the Niskin bottle drain valve. Bubbles were cleared from the tube with water flowing and the tube was inserted to the bottom of the 500 cc glass bottle. The glass bottle was placed in a wide mouth plastic jar that extended above the opening of the glass bottle by 4 cm. The overflow water collected in the jar, filling and overflowing the jar and covering the glass bottle opening. The flow continued for 3 overflow volumes of the glass bottle (1.5 liters) and the glass stopper was then inserted underwater preventing air from being trapped in the sample. The jar was then capped and the sample stored at room temperature until measurement, which was within 8 hours of collection. The measurements were carried out using a dual purge and trap system interfaced to a dual ECD (electron capture detector) HP6890 gas chromatograph. When a water sample is introduced into the system, it is split into two aliquots, a 20 cc aliquot for CFC measurement and a 350 cc aliquot for SF6 measurement. The aliquots are transferred to appropriately sized sparging chambers and stripped with ultra high purity nitrogen, which transports the extracted gases to cold traps (Unibeads-2s for CFCs, Carboxan-1000 for SF6) cooled to -80°C. The traps are then heated to 110°C for CFCs and 165°C for SF6 and flushed into the gas chromatograph where CFCs are separated with a Porasil-B pre-column and a Carbograph 1AC main column and SF6 is separated with a pre-column and main column of Molecular Sieve 5A. The gases are detected by the ECDs. The ECDs are calibrated by running gas standards with known concentrations of CFCs and SF6. Duplicate samples are collected and measured to provide a combined precision for sampling and measurement. The average differences from these duplicate measurements was the larger of 0.006 pmol/kg or 0.6% for CFC-11, 0.004 pmol/kg or 0.8% for CFC-12, 0.002 pmol/kg or 1.6% for CFC-113 and 0.01 fmol/kg or 1.5% for SF6.</p></div>
Concentrations of CFC-11, CFC-12, CFC-113 and SF6 in seawater - GT11
<div><p>Please note that data may not be final, pending intercalibration results and further analysis. If you are interested in following changes to US GEOTRACES data, there is an RSS feed available from the <a href="http://www.bco-dmo.org/project/2066" target="_blank">GEOTRACES-NAT</a> project page.</p>
<p>Concentrations of CFC-11, CFC-12, CFC-113 and SF6 in seawater</p>
<p>CFC-11 CCl3F trichlorofluoromethane pmol/kg (10^-12 moles/kg)<br />
CFC-12 CCl2F2 dichlorodifluoromethane pmol/kg<br />
CFC-113 C2Cl3F3 1,1,2-trichlorotrifluloroethane pmol/kg<br />
SF6 sulfur hexafluoride fmol/kg (10^-15 moles/kg)</p></div>
GT10-11 - CFC and SF6
<div><p><strong>Data Processing: </strong><br />
The gas chromatograph produces a peak for each compound being measured. Each chromatogram is digitally acquired on a PC and the peak areas integrated with software developed specifically for this purpose. Calibration curves relating peak area to concentration are generated using the gas standard data and this information is used to convert peak areas for the samples to concentrations. Blanks and reference standards are run about every 2 hours to provide data to correct for detector drift and blanks. After completion of the cruise, plots of the CFCs and SF6 against each other and against other hydrographic variables are prepared to determine trends in the data and identify questionable data. Questionable data are checked for possible data processing errors, sampling problems, equipment problems, etc. Mistakes are corrected and samples judged to be bad measurements are flagged as such. The WOCE flagging convention is used.</p>
<p><strong>WHP Data Reporting Requirements (Rev. 2, February 1998)</strong><br /><strong>TABLE 4.10: Quality flag definitions for CTD data.</strong><br />
Flag<br />
Value Definition<br />
1 = Not calibrated.<br />
2 = Acceptable measurement.<br />
3 = Questionable measurement.<br />
4 = Bad measurement.<br />
5 = Not reported.<br />
6 = Interpolated over >2 dbar interval.<br />
7 = Despiked.<br />
8 Not assigned for CTD data.<br />
9 = Not sampled.<br />
</p>
<p><strong>BCO-DMO Processing/Edits</strong></p>
<p>- GT11, sta-12, cast-11: corrected the press to 882.9 from submitted 874.1, which matches the depth in the bottle file. - sample_GEOTRC numbers added and dataset joined to the master events data.<br />
- Data generated from original file: gt10_cfcs_sf6_btl.xls contributed by H. Lee on 18 Nov. 2013.<br />
- GT11 data revised Jan. 2013<br />
- Data generated from original file: gt11_cfcs_sf6_btl.xls contributed by Hoyle Lee on 6 Aug. 2012.<br />
- Date column added and formatted as YYYYMMDD from MM,DD,YYYY individual columns<br />
- Cruise_Id column added<br />
- Parameter names modified to conform to BCO-DMO conventions (blanks to underscores, etc.)</p></div>
3692
GT10-11 - CFC and SF6
2012-08-07T11:02:38-04:00
2012-08-07T11:02:38-04:00
2023-07-07T16:10:26-04:00
urn:bcodmo:dataset:3692
Concentrations of CFC-11, CFC-12, CFC-113 and SF6 in seawater from R/V Knorr KN199-04 (GT10), KN204-01 (GT11) in the subtropical northern Atlantic Ocean from 2010-2011 (U.S. GEOTRACES NAT project)
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Smethie Jr., W. M. (2014) Concentrations of CFC-11, CFC-12, CFC-113 and SF6 in seawater from R/V Knorr KN199-04 (GT10), KN204-01 (GT11) in the subtropical northern Atlantic Ocean from 2010-2011 (U.S. GEOTRACES NAT project). Biological and Chemical Oceanography Data Management Office (BCO-DMO). (Version 3) Version Date 2014-06-16 [if applicable, indicate subset used]. http://lod.bco-dmo.org/id/dataset/3692 [access date]
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