H99Nutrient: Nutrient analyses were conducted using a Technicon (<http://www.techniconinstruments.com/>) autoanalyzer by Tom Oswald under the supervision of R. E. Turner.
H99Pigment: The Turner Designs model 10 and model 10 AU fluorometers were calibrated for chlorophyll a against a chemical supply house chlorophyll a standard measured on a spectrophotometer yearly. During cruises, the fluorometer was blanked and calibrated daily in accordance with Turner Designs recommended procedures. Beginning in June 1999, a Turner Designs model 10 AU replaced the model 10. Each time the model 10 AU was moved, it was tested with a Turner 10-AU solid standard. Pigment measurements were supervised and quality controlled by Nancy Rabalais.
H99SeaBird: Sea-Bird SBE 13-01 dissolved oxygen sensors, the Paroscientific Digiquartz(r) 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 (<http://www.seabird.com/>) recommended intervals and maintained and serviced by RV Pelican Electronic Technical support staff in accordance with Sea-Bird procedures. The Sea Tech 500m Fluorometer and Sea Tech 5.0 cm Transmissometer were 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. Note: WET Labs acquired SEA Tech June 1, 1998, (<http://www.wetlabs.com/>). The Wet Labs WetStar fluorometer was maintained in accordance with Wet Labs recommendations by RV Pelican Electronic Technical support staff. The Chelsea Fluorometer was also maintained by RV Pelican Electronic Technical support staff in accordance with Chelsea recommended procedures (<http://www.chelsea.co.uk/>).
For the months January - June and August, the calibration of the SeaBird oxygen sensors was accomplished as follows. A large tub of clean seawater was mixed and aerated for 24 hours. The Sea-Bird CTD package was placed in the oxygen-saturated water bath for the next hour. The Hydrolab CTD, freshly calibrated, was also placed in the bath. Both CTD systems were powered up. The SeaBird Deck unit and Hydrolab logger were observed. Time for sensor equilibration was allowed.
The manufacturers stated +/- 0.2mg/L as the error allowance for both SeaBird and Hydrolab oxygen sensors. SeaBird and Hydrolab oxygen values were compared.
If the sensors agreed within 0.4mg/L, no further action was taken. If sensor values were more than 0.4mg/L apart, The Hydrolab value was used for the "W" value and the SeaBird oxygen sensor was calibrated using the procedure described in Seabird APPLICATION NOTE NO. 13-1, Rev. D.
At the beginning of the July shelfwide cruise, 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 (<http://www.mt.com/>). Shipboard Winkler titrations during the cruise were used to develop a regression against CTD data.
Winkler titrations and the OXFITW procedure were used to check the SeaBird oxygen sensors at the beginning of the September - December cruises.
The September and October cruises were made on RV Acadiana. On those cruises, the General Oceanics CTD rosette was not used and a SeaBird SeaCat CTD was used instead of the SeaBird 911+ CTD used on Pelican cruises. A pumped Sea-Bird SBE 13-01 dissolved oxygen sensor was employed on each of the September and October cruises. The September configuration file was used during the October cruise because it gave better post-calibration results than an October calibration adjustment attempt.
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.
H99Stn: 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 (<http://www.starlinkdgps.com/>) differential GPS or a Trimble (<http://www.trimble.com/>)GPS with a Micronet Receiver Station with sub 5-meter accuracy. Station depths were logged from the ship's Odom Echotrac II (<http://www.odomhydrographic.com/>) fathometer. The Secchi disk depths were measured by hand using standard protocol.
During the September and October cruises on the RV Acadiana, RV Pelican's Starlink and Trimble GPS units were transferred to Acadiana. Position data were logged from the Starlink and Trimble GPS units. Station depths were logged from Acadiana's fathometer.
H99PortaSal: The samples were analyzed in the lab by Guildline Instruments PortaSal, using Guildine methods (<http://www.guildline.ca/>). Salinity analyses were conducted by Jim Lee under the supervision of R. E. Turner.
H99MIDAS: Suspended sediment concentrations were supervised and quality controlled by Nancy Rabalais. Times and locations of operations were acquired from the ships MIDAS system (described above in H99Stn).
N. Rabalais performed an additional procedure in quality-control/quality-assurance by evaluating relationships between the data in H99PortaSal, H99Hydrolab, H99Nutrient, H99Pigment, H99Stn and H99MIDAS.
Hydrolab data were derived from a pre- and post-calibrated instrument. Therefore, there is often disagreement between SeaBird and Hydrolab oxygen values. It is the opinion of the PI, Nancy Rabalais, that the Hydrolab data for the monthly cruises are the more reliable data.
For the July SeaBird data, Winkler titrations were used to develop a regression which was used to correct the SeaBird oxygen data if necessary. The data for the SeaBird and the Hydrolab compare better for the shelfwide July cruise.
August 24th Hydrolab data were not acquired due to a battery problem.
SeaBird FlC (fluorescence Chelsea), FlS (Fluorescence Sea-Tech) and Xmiss (transmission percent) data were not acquired during the September 14th and October 12th surveys on RV Acadiana because of the reduced number of instruments in the SeaCat CTD package.
November 4th station C9 Seabird oxygen data were not included because the oxygen sensor failed.
Station positions acquired during the September and October cruises on RV Acadiana were logged from the ship's NorthStar 800 LORANC. The manufacturer describes the accuracy to be within 30 meters 90% of the time.
On the following dates hydrocasts were made from a small boat tied to the oilfield platform at station C6B: 19990301, 19990322, 19990428, 19990513, 19990520, 19990603, 19990624, 19990712, 19990730, 19990818 and 19990907.
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.
The Hydrolab CTD was attached by chain to a lead weight. The weight was lowered to the bottom by hydrowire. With the weight on the bottom, the Hydrolab sonde was positioned just above the bottom. When the oxygen sensor stabilized, a data record of all the sensor values was stored electronically. The sonde was raised in approximately 0.5-meter increments, after D.O. sensor stabilization, data records were stored. After storing data for the few meters closest to the bottom, the Hydrolab was raised to two to three meters from the surface and a data record was saved. The sonde was raised, and records stored, in approximately 0.5-meter increments until finally a record was stored with the sonde submerged but as close as possible to the surface.
During the July shelfwide cruise, stations were occupied along 14 generally North-South transects across the Louisiana coastal shelf. Station depths ranged from 4.6 to 61.8 meters. The objective was to delimit and describe the area of midsummer bottom dissolved oxygen less than 2 (mg/L). Due to limitations of equipment, time and funding, this was not always possible. Northern end stations of transects were chosen based on the survey vessel's minimum depth limits for each longitude. The northern extent of hypoxia was not reached on nine transects. Optimally, one or two stations south of the southern most station with bottom dissolved oxygen less than 2 (mg/L) were sampled. The limit of hypoxia on the southern ends of all transects, except transect J, was reached. The limit of hypoxia was not reached at station M3 on the western end of the survey. The limit of hypoxia was not reached at stations A'1, A'2 and A'3 on the eastern end of the survey.
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.
Water for Suspended Sediment samples was collected by tapping into discharge of the shipâ€(tm)s seawater flow through system MIDAS. MIDAS intake was 2 -3 meters below the surface. The watch chief observed MIDAS navigational data, when distance to station was 0.3 miles, a triple-rinsed jar (1000ml) was collected from the silicon MIDAS discharge tube in the ship's bottle lab. Finally, collection time was logged.
When Seabird data were processed, dissolved oxygen was advanced relative to temperature and conductivity values as follows: January, November and December +4.25 seconds; March, April, May, June and August +4.5 seconds; July +4.333 seconds.
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.
Latitude and Longitude values listed in table H99MIDAS are more precise positions for suspended sediment samples. See also: suspended sediment section of field water sample Methodology.