Filtered (0.4 \u00b5m) water samples from the Geotraces surface tow-fish and water from the upper 200 m water column (GEOTRACES Carousel/GoFlo system) were analyzed on an Astoria Pacific 300 series gas-segmented continuous flow nutrient auto-analyzer modified with 200 cm liquid waveguide capillary cells (LWCC; World Precision Instruments). Nitrate was reduced to nitrite using a Cd-column, then determined spectrophotometrically following formation of a highly colored dye, but slightly modified for use with a liquid core waveguide (see references below). Nitrite is measured separately without the Cd column and then subtracted from the combined nitrate+nitrite sample. The molybdenum blue method modified for use with liquid core wave guide was used for phosphate (references below).
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Recovery for phosphate measurements for LWCC relative to the MAGIC method is 100 \u00b1 15 % for concentrations below 100 nmol/L. The relative standard deviation for nine measurements of 5 nmol/L phosphate was 1.6 %. The relative standard deviation for nine measurements of 60 nM phosphate was 0.9 %. LWCC detection limit (3 x \u03c3 of blank) for phosphate was 0.5 nmol/L, 1.5 nmol/L for nitrate and 0.6 nmol/L for nitrite.
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Upper working limit for LWCC:
\nPhosphate 100 nmol/L
\nNitrate 200 nmol/L
\nNitrite 200 nmol/L
Data Processing:
\nNitrate = (Nitrate+nitrite) \u2013 nitrite
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Samples were measured in triplicate (flag =6)
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Samples out of linear calibration range for LWCC (flag = 10)
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BCO-DMO Processing Notes:
\n- Generated from original spreadsheet file \"GEOTRACES Knorr199-4 and -5 nanomolar nutrients.xls\", sheet: \"surface\" contributed by Greg Cutter
\n- Parameter names modified to conform to BCO-DMO convention
\n- cruise_id added
\n- date/time reformatted to date as YYYYMMDD
\n- date/time reformatted to time as HHMM
\n- longitude values converted to negative (West)
\n- \"nd\" (no data flag) inserted into blank cell
\n- added ISO_DateTime_UTC based on the original date and time fields
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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.