Shipboard Sample Collection Methods
\nSamples are collected in pre-washed and baked 250 ml ground glass stoppered bottles that were poisoned with 100\u00b5l of a saturated HgCl2 solution. The stored sealed samples were returned to the Stable Isotope Laboratory at the University of Washington for extraction and measurement.
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Laboratory Methods
\nCO2 is extracted from the DIC seawater sample using a modification of the helium stripping technique described in Quay et al (1992). The del13C is measured on a Thermo Delta Plus XL mass spectrometer.
delta 13C measurements made on dissolved inorganic carbon (DIC) samples collected at stations during the GT10 and GT11 (KN199-04 and KN204-01) cruises as part of the U.S. GEOTRACES North Atlantic Transect project.
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Version History:
\n17 June 2014\u00a0(current version) = data updated/corrections made; several bottle numbers, cast numbers, and depth values that were previously erroneous have been corrected;
\n04 April 2013 = original data submitted.
Data Processing
\nSurface samples collected at stations through sample clean seawater feed have no cast and sample numbers.
\nQuality flags here include:
\n2 = good data;
\n3 = questionable data;
\n9 = no data.
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BCO-DMO Processing Notes:
\n- Modified parameter names to conform with BCO-DMO naming conventions.
\n- Separated original date field into month, day, and year.
\n- Replaced blanks with 'nd'.
\n- Added 'cruise_id' based on the 'cruise_name' provided.
\n- lat_nom and lon_nom were added from station waypoints provided by the cruise Chief Scientists.
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Additional GEOTRACES Processing:
\nAfter the data were submitted to the International Data Management Office, BODC, the office noticed that important identifying information was missing in many datasets. With the agreement of BODC and the US GEOTRACES lead PIs, BCO-DMO added standard US GEOTRACES information, such as the US GEOTRACES event number, to each submitted dataset lacking this information. To accomplish this, BCO-DMO compiled a 'master' dataset composed of the following parameters: station_GEOTRC, cast_GEOTRC (bottle and pump data only), event_GEOTRC, sample_GEOTRC, sample_bottle_GEOTRC (bottle data only), bottle_GEOTRC (bottle data only), depth_GEOTRC_CTD (bottle data only), depth_GEOTRC_CTD_rounded (bottle data only), BTL_ISO_DateTime_UTC (bottle data only), and GeoFish_id (GeoFish data only). This added information will facilitate subsequent analysis and inter comparison of the datasets.
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Bottle parameters in the master file were taken from the GT-C_Bottle_GT10, GT-C_Bottle_GT11, ODF_Bottle_GT10, and ODF_Bottle_GT11 datasets. Non-bottle parameters, including those from GeoFish tows, Aerosol sampling, and McLane Pumps, were taken from the Event_Log_GT10 and Event_Log_GT11 datasets. McLane pump cast numbers missing in event logs were taken from the Particulate Th-234 dataset submitted by Ken Buesseler.
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A standardized BCO-DMO method (called \"join\") was then used to merge the missing parameters to each US GEOTRACES dataset, most often by matching on sample_GEOTRC or on some unique combination of other parameters.
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If the master parameters were included in the original data file and the values did not differ from the master file, the original data columns were retained and the names of the parameters were changed from the PI-submitted names to the standardized master names. If there were differences between the PI-supplied parameter values and those in the master file, both columns were retained. If the original data submission included all of the master parameters, no additional columns were added, but parameter names were modified to match the naming conventions of the master file.
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See the dataset parameters documentation for a description of which parameters were supplied by the PI and which were added via the join method.