"lt_DL" indicates that a sample was below the method detection limit

Sample volumes were used to calculate picomolar or femtomolar concentrations of different mercury species.

BCO-DMO added ISO_DateTime_UTC from the original date and time field provided by PI.

Related files and references:
Bloom, N. 1989. Determination of picogram levels of methylmercury by aqueous phase ethylation, followed by cryogenic gas-chromatography with cold vapor atomic fluorescence detection. Can. J. Fish. Aquat. Sci. 46, 1131-1140.

Bloom, N.S., Fitzgerald, W.F. 1988. Determination of volatile mercury species at the picogram level by low-temperature gas chromatography with cold-vapor atomic fluorescence detection. Anal. Chim Acta 208, 151-161.

Bowman, K.L., Hammerschmidt, C.R. 2011. Extraction of monomethylmercury from seawater for low-femtomolar determination. Limnol. Oceanogr.: Methods 9, 121-128.

Cutter, G.A., Bruland, K.W. 2012. Rapid and noncontaminating sampling system for trace elements in global ocean surveys. Limnol. Oceanogr.: Methods 10, 425-436.

Fitzgerald, W.F., Gill, G.A. 1979. Subnanogram determination of mercury by two-stage gold amalgamation applied to atmospheric analysis. Anal. Chem. 51, 1714-1720.

Hammerschmidt, C.R., Bowman, K.L. 2012. Vertical methylmercury distribution in the subtropical North Pacific Ocean. Mar. Chem. 132, 77-82.

Hammerschmidt, C.R., Bowman, K.L., Tabatchnick, M.D., Lamborg, C.H. 2011. Storage bottle material and cleaning for determination of total mercury in seawater. Limnol. Oceanogr.: Methods 9, 426-431.

Lamborg, C.H., Hammerschmidt, C.R., Gill, G.A., Mason, R.P., Gichuki, S. 2012. An intercomparison of procedures for the determination of total mercury in seawater and recommendations regarding mercury speciation during GEOTRACES cruises. Limnol. Oceanogr.: Methods, 10, 90-100.

Tseng, C.-M., Hammerschmidt, C.R., Fitzgerald, W.F. 2004. Determination of methylmercury in environmental matrixes by on-line flow injection and atomic fluorescence spectrometry. Anal. Chem. 76, 7131-7136.

Additional GEOTRACES Processing:
Version 2017-04-11 replaced version 2013-03-05.
Data version 2013-03-05 was revised with corrected sample_GEOTRC and station_GEOTRC values for duplicates of 6963 and 6971:
Changed sample_GEOTRC 6971 to 6871; station_GEOTRC 11 to 10
Changed sample_GEOTRC 6963 to 6991; station_GEOTRC 10 to 11

After 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.

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.

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.

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.

See the dataset parameters documentation for a description of which parameters were supplied by the PI and which were added via the join method.