Shipboard Winkler titrations during the July shelfwide cruise were used to develop a regression against Hydrolab data in case it was necessary to correct the data. Hydrolab oxygen data were corrected using an equation based on the results of the regression.
H02Nutrients: Nutrient analyses were conducted using a QuikChem 8000 FIA+(<http://www.lachatinstruments.com>). Tom Oswald performed the analyses under the supervision of R. E. Turner.
H02Pigments: The Turner Designs model 10 AU fluorometer was calibrated for chlorophyll a against a chemical supply house chlorophyll a standard measured on a spectrophotometer. Each time the fluorometer was moved, it was tested with a Turner 10-AU solid standard. During cruises, the fluorometer was blanked and calibrated daily in accordance with Turner Designs recommended procedures. Pigment measurements were supervised by Ben Cole or Nancy Rabalais and quality controlled by Nancy Rabalais.
H02PortaSal: Salinity samples were analyzed in the lab by Guildline Instruments PortaSal, using Guildline methods (<http://www.guildline.ca/>). Salinity analyses were conducted by Jim Lee under the supervision of R. E. Turner.
H02Refract: The refractometer was checked with distilled water before each cruise and re-zeroed when necessary.
H02SeaBird: 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 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. Note: WET Labs acquired SEA Tech June 1, 1998, (<http://www.wetlabs.com/>). The Wet Labs C Star 10 cm path transmissometer was maintained by RV Pelican Electronic Technical support staff in accordance with Wet Labs recommendations.
At the beginning of the monthly 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 July shelfwide cruise were used to develop a regression against SeaBird data in case it was necessary to correct the data. SeaBird oxygen data were corrected using an equation based on the results of the regression.
During monthly surveys conducted in other months, shipboard Winkler titrations for regressions were not made due to logistical constraints. Fewer stations were sampled and water columns were often well mixed, making the considerable effort involved in titrating an inefficient allocation of resources, often without a suitable range of data to develop a strong regression.
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.
H02SPM: Suspended sediment concentrations were supervised by Ben Cole or Nancy Rabalais and quality controlled by Nancy Rabalais.
H02Stn: January though October monthly survey SeaBird times and locations of operations were logged 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.
November and December monthly survey station times, locations and depths were logged from RV Acadiana's Garmin GPSMAP 168 Sounder (<http://www.garmin.com/>).
In addition to the monthly surveys, Hydrolab casts were made on a few dates from a small boat. See Horizontal_Positional_Accuracy_Report for details.
Secchi disk depths were measured by hand using standard protocol.
N. Rabalais performed an additional procedure in quality-control/quality-assurance by evaluating relationships between the data in H02Hydrolab, H02Nutrients, H02Pigments, H02PortaSal, H02Refract, H02SeaBird, H02SPM and H02Stn.
The values reported for Dissolved Oxygen: 99.99 and Percent Oxygen Saturation: 999.9 indicate dissolved oxygen concentrations were equal to or higher than 20.0 mg/L and oxygen saturation was equal to or greater than 200.0 percent.
H02SeaBird: 20020814 station C6 at 17.331, 17.469m and 20.188m has negative OxMg/L and OxPS values.
H02SeaBird: 20020902 C6B 0.174m density is negative
NO2+NO3 values are reported for all months. Measuring individual Nitrite and Nitrate values in nutrient samples required additional samples, sample runs and funding. Nitrite and nitrate values were only determined for samples collected during the July shelfwide survey.
The October 2002 cruise was the last cruise when SeaBird CTD data were acquired because RV Pelican, in the shipyard for a midlife re-fit, was out of service through the end of the year.
The Hydrolab CTD sustained weather related damage during the December cruise. No data were acquired on the date 20021212.
Station positions acquired during November and December on RV Acadiana were logged from the ship's Garmin Garmin GPSMAP 168 Sounder with Garmin GBR 21 DGPS. The manufacturer describes the accuracy to be between 1 - 5 meters 95% of the time. Wind, currents and tidal forces may have moved the ship from the beginning position.
In addition to the monthly surveys, Hydrolab casts were made at stations C6B and CST52 on a few dates from a small boat using a Garmin 12XL Personal Navigator. The manufacturer describes the unit as being accurate within 15 meters 95% of the time.
20020827 - 20020829 a series of Hydrolab casts were made at locations in the Ship Shoal and South Timbalier areas in a small boat using a Garmin GPS Map 182. The manufacturer describes the unit as being accurate within 15 meters 95% of the 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 sonde 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.
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 was rapid in order to save time.
During the July shelfwide cruise, stations were occupied along 16 generally North-South transects across the Louisiana and Texas coastal shelves. Station depths ranged from 3.56 to 47.7 meters. The objective was to delimit and describe the area of midsummer bottom dissolved oxygen less than 2 (mg/L). 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 transects A', A, E, F, G, H, I and J. The limit of hypoxia on the Southern end of transect Q was not reached. The limit of hypoxia was not reached at two of four stations on the Western end of the survey. The limit of hypoxia was not reached at two of four stations on the Eastern end of the survey.
Depth values of "0" indicate a bucket sample collected from the surface of the water. Generally, deepest depths of water samples were from the bottom-tripping Niskin and correspond to the deepest depth recorded from the Hydrolab. As noted in the preceding paragraph, bottom water sample-depths at stations K7 and M7 were the depths of the pressure sensor reading for 5-l Niskin bottles on the SeaBird rosette.
The SeaBird pressure sensor was located approximately 0.75 meters below the mid-point of the 5-l Niskin.
Midwater samples at stations on C transect were collected using Niskin bottles on the SeaBird rosette in January through October and by messenger fired Niskin on the Hydrolab hydrowire in November.
January through April data were processed using version 5.25. May data per processed using version 5.25b. June through October data were processed using version 5.26.
All scans were processed without averaging or interpolation with a bin size of one scan.
In order to improve alignment between oxygen sensor values and other CTD sensor values, the Seasoft module ALIGNCTD was used, when possible, to determine which advance best compensated for the delay in oxygen sensor response time. When SeaBird data were processed, dissolved oxygen was advanced relative to temperature and conductivity values as follows: January: 3.3 seconds, February: 3.35 seconds, March: 3.4 seconds, April: 3.25 seconds, May: 3.2 seconds, June: 3.57 seconds, July: 3.45 seconds, September: 4.3 seconds and October: 2.7 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.