Dataset: GT11 - As Sb AP - Profiles

Filtered (0.4 microm) water samples from the Geotraces Carousel/GO-FLO bottles were placed into
500 mL Teflon FEP bottles, refrigerated, and analyzed within 24 hours of collection. Arsenic and
antimony speciation determined using selective hydride generation, liquid nitrogen-cooled
trapping, and then revolatilization and determination with gas chromatography/photoionization detection (Cutter et al., 1991; Cutter and Cutter, 2006).

Calibration performed daily via the standard additions method, with a minimum of 4 additions of AsIII, AsV, MMAs, or DMAs depending on the analyses. The slope from the linear fit to these data was then applied to all samples for that day. Detection limits were 25 pmol/L for As(III) and As(III+V), and 50 pmol/L for MMAs and DMAs. Precision was better than 8% (relative standard deviation) for all As species. Alkaline phosphatase samples were taken unfiltered from the ODF rosette bottles (Ra, Th, and pigment hydrocasts) and placed into 500 ml polythylene bottles, then the enzyme activity was measured using the fluorescence method of Ammerman (1993).

Samples analyzed in duplicate or triplicate and means computed.

Related files and references: 
Ammerman, J. W. 1993. Microbial cycling of inorganic and organic phosphorus in the water
column. In: Handbook of Methods in Microbial Ecology (P. Kemp, B. Sherr, E. Sherr, and J. Cole,
Eds.), Lewis, Florida, pp. 649-660.

Cutter, L.S., G.A. Cutter, and M.L.C. San Diego-McGlone. 1991. Simultaneous determination   of
inorganic arsenic and antimony species in natural waters using selective hydride generation
with gas chromatography/photoionization detection. Anal. Chem. 63:1138-1142.

Cutter, G.A. and L.S. Cutter. 2006. The biogeochemistry of arsenic and antimony in the North
Pacific Ocean. Geochem. Geophys. Geosystems (G3), 7, Q05M08, doi:10.1029/2005GC001159.

Additional GEOTRACES Processing:
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.