S797Nutrient: Nutrient analyses were conducted by Tom Oswald under the supervision of R. E. Turner.
S797Pigment: The Turner Designs model 10 fluorometer was calibrated for chlorophyll a against a chemical supply house chlorophyll a standard measured on a spectrophotometer yearly (or more frequently if needed). During the cruise, the Fluorometer was blanked and calibrated daily in accordance with Turner Designs recommended procedures. Pigment measurements were supervised and quality controlled by Nancy Rabalais.
S797SeaBird: Sea-Bird SBE 13-01 dissolved oxygen sensors, the Paroscientific Digiquartz® pressure sensor, the SBE 3-01/F temperature sensors , SBE 5-01 pumps, and the SBE 4-01/0 Conductivity sensors were factory tested and calibrated at Sea-Bird recommended intervals and maintained and serviced by RV Pelican Electronic Technical support staff in accordance with Sea-Bird procedures. The Sea Tech 5.0 cm Transmissometer was factory tested and calibrated at Sea Tech recommended intervals and maintained and serviced by RV Pelican Electronic Technical support staff in accordance with Sea Tech procedures. The Chelsea AQUATRAKA III Fluorometer was factory tested and calibrated at Chelsea Instruments recommended intervals and maintained and serviced by RV Pelican Electronic Technical support staff in accordance with Chelsea procedures.
Oxygen sensors were calibrated using the procedures described in Seabird APPLICATION NOTE NO. 13-1, Rev. D. The Winkler Titration (OXFITW) oxygen value was determined chemically from replicate samples processed using a Mettler DL21 Titrator. Shipboard Winkler titrations during the cruise were used to develop a regression against CTD data, which were corrected if necessary. A correction was not needed for the July 1997 CTD oxygen data because there was good agreement of SeaBird CTD values with Winkler values and bottom values obtained from the HydroLab CTD.
Winkler titrations were conducted under the supervision of Nancy Rabalais. Data reductions from the SeaBird were generated by Ben Cole and quality controlled by Nancy Rabalais.
S797-Stn: Times and locations of operations were acquired from RV Pelican's Multiple Instrument Data Acquisition System (MIDAS) which was maintained by the ship's electronic staff. Navigational data were acquired from a Starlink differential GPS or a Trimble GPS with a Micronet Receiver Station with sub 5-meter accuracy. Station depths were logged from the ship’s Odom Echotrac II fathometer. The Secchi disk depths were measured by hand using standard protocol.
S797PortaSal: The samples were analyzed in the lab by Guildline Instruments PortaSal, using Guildine methods. Salinity analyses were conducted by Jim Lee under the supervision of R. E. Turner.
S797SuspSed: Suspended sediment concentrations were supervised and quality controlled by Nancy Rabalais.
N.B. There may have been a problem with samples collected with the bottom tripping Niskin. Surface PortaSal samples were collected at each station in order to get precise salinity values for the bucket samples. On transect C in addition to surface salinity samples; bottom salinity samples were collected from the Niskin. The salinity samples were read after the cruise in the laboratory using both the HydroLab and the PortaSal.
PortaSal salinity readings matched those taken in the lab with the Hydrolab. Surface salinity data recorded in the field also corresponded well with the PortaSal data. Bottom salinities recorded in the field with the Hydrolab and CTD, however, were an average of 4 ppt higher than those recorded in the lab with the Hydrolab and PortaSal using water taken from the horizontally mounted bottom-tripping Niskin. Lab values ranged between 1.0 and 6.7 ppt lower than field samples.
Since the proper functioning of the Hydrolab was supported by the PortaSal and the CTD, the water from the horizontal Niskin does not appear to have been collected at the bottom. Smaller discrepancies (< 1 ppt) could be expected due to the Niskin not sampling at exactly the same location as the other instruments. Differences of
3 ppt, however, are highly unlikely. Water column data suggestthat the horizontally mounted Niskin sample salinities would have been encountered above the bottom.
The horizontal Niskin was used to collect bottom water samples at all stations, but bottom salinity samples were collected only for transect C. The possibility exists that other bottom samples also had salinities that differed from those recorded by the Hydrolab or CTD. The "bottom" samples may not represent bottom water.
N. Rabalais performed an additional procedure in quality-control/quality-assurance by evaluating relationships between the data in S797PortaSal, S797HydroLab, S797Nutrient, S797Pigment, S797-Stn and S797SuspSed.
In order to minimize the effect of delays in oxygen sensor response time caused by temperature, sensor condition and plumbing configuration, the CTD package was lowered as close to dead slow as possible. The sensor packages were located below the Niskin bottles and rosette.
At stations where the watch chief deemed the structure of the oxygen profile contained features useful in post-processing the oxygen data (AlignCTD), the CTD package was raised at the same speed it was lowered. At all other stations, the upcast is rapid in order to save time.
Depth values of 0 indicate a bucket sample collected from the surface of the water. Deepest depths of water samples were from the bottom-tripping Niskin and correspond to the deepest depth recorded from the Hydrolab. Other depths indicate the p-sensor reading for 5-l Niskin bottles on the Seabird rosette. The Seabird p-sensor was located approx. 1 meter below the mid-point of the 5-l Niskin.
Data values reported are from downcasts. Downcast scans selected for each CTD station were chosen to illustrate: 1) data values as near to the surface as possible, 2) data values at whole meter increments, and 3) data values as close to the bottom as the CTD was lowered. In certain cases where data values of a parameter changed significantly between whole meter increments, 0.1- or 0.2-meter scans were selected.