Data Processing:
CDOM absorbance spectra are measured on a multiple pathlength, liquid core waveguide between 370 and 725 nm at 1 nm intervals normalized to the reference spectrum. For seawater samples, an absorbance correction to account for the different refractive indices of Milli-Q water and seawater is applied. The correction is based on previously measured solutions of known salinity devoid of CDOM. The corresponding spectral absorbance correction for a given salinity is subtracted from the observed spectrum of a sample of the same salinity.

The spectral absorption coefficients, a_g(λ) (m-1) are obtained by

a_g(λ) = 2.303A(λ) /L,
where A(λ) is the absorbance at wavelength λ and L is the pathlength in meters. Absorption data are also corrected for baseline offsets by subtracting the average absorption value between 690-700nm.

BCO-DMO Processing Notes:
- One data file sent by Chaves in excel spreadsheet format on 2013.01.31
- Update (v1) sent on 2013.02.01 included station numbers
- Update (v2) sent on 2013.02.01 corrected column/row alignment

Edits made:
- Parameter header names were renamed to BCO-DMO convention
- Blank data fields and data reported as -999 were edited to 'nd'
- Edited time to remove colons and drop unused seconds
- Edited precision of lat/lon to four decimals.
- Edited precision of absorption coefficients to three decimals.
- Transposed rows and columns in file to view values vertically rather than horizontally. Created column for 'wavelength' to accommodate original parameter names and column for absorption coefficient 'absp_coef' to hold values. Removed header information from the file. Where necessary, the information was incorporated into BCO-DMO metadata fields and retained entirely as 'additional information'.

Note: Correspondence with the PI on 2013.01.12, necessitated editing the header note indicating NASA's pump. Therefore, this comment was retained in the header has been edited to the following text:

#samples from station 1 with 0 depth were collected with WHOI's GEOTRACES pump
#sample numbers for stations > 1 with depth = 0 were collected with NASA's
#surface peristaltic pump

Note: Further correspondence with the PI on 2013.03.06, edited sample 5880 (station 3 cast 6) to 5280.

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 name 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.

Absp_CDOM_GT10_joined.csv