Louisiana Hypoxia Surveys 1998

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Frequently-anticipated questions:


What does this data set describe?

    Title: Louisiana Hypoxia Surveys 1998
    Abstract:
    Two sets of CTD data were taken during the 1998 surveys of the Louisiana continental shelf. Hydrographic data were obtained with the LUMCON SeaBird 911+ CTD system and a Hydrolab Surveyor 3. Nutrient, pigment, suspended sediment, surface salinity and station information data were also acquired.

  1. How should this data set be cited?

    Rabalais, N., Unknown, Louisiana Hypoxia Surveys 1998.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -93.5
    East_Bounding_Coordinate: -89.4
    North_Bounding_Coordinate: 29.8
    South_Bounding_Coordinate: 28.3
    Description_of_Geographic_Extent: Louisiana coastal waters, Northwestern Gulf of Mexico.

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 13-Jan-1998
    Beginning_Time: Unknown
    Ending_Date: 15-Dec-1998
    Ending_Time: Unknown
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: Database

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • Point (198)

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0001. Longitudes are given to the nearest 0.0001. Latitude and longitude values are specified in Degrees and decimal minutes.

      The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.

  7. How does the data set describe geographic features?

    H98Hydrolab
    The table lists Hydrolab CTD station identification number, record date, station name, record time, record depth, dissolved oxygen, temperature, specific conductance, salinity, pH, percent oxygen saturation and density sigma-t. There are 2685 records. (Source: None.)

    Date
    Date when Hydrolab record was saved. (Date can be different for suspended sediment, Hydrolab CTD cast and SeaBird CTD cast at same station). Station A1 0.3m and 1.5m records are dated 19980722. All other station A1 records are dated 19980721. (Source: Producer defined)

    Range of values
    Minimum:19980113
    Maximum:19981215

    Density
    Density sigma-t (Source: Producer defined)

    Range of values
    Minimum:1.23
    Maximum:26.06
    Units:Density sigma-t

    Depth
    Depth of Hydrolab pressure sensor (Source: Producer Defined)

    Range of values
    Minimum:0.1
    Maximum:68.3
    Units:Meters

    DO
    Dissolved oxygen (Source: Producer defined)

    Range of values
    Minimum:0.05
    Maximum:11.59
    Units:mg/L

    DOPctSat
    Oxygen percent saturation (Source: Producer defined)

    Range of values
    Minimum:0.7
    Maximum:172.9
    Units:Percent

    pH
    pH (Source: Producer defined)

    Range of values
    Minimum:7.33
    Maximum:8.42
    Units:pH units

    Salin
    Salinity (Source: Producer defined)

    Range of values
    Minimum:7.3
    Maximum:36.8
    Units:psu

    SpCond
    Specific conductance (Source: Producer defined)

    Range of values
    Minimum:12.79
    Maximum:55.3
    Units:mS/cm

    Sta
    Station name of location sampled (Source: Producer defined)

    Character field

    StnID
    Station identification number (Source: Producer defined)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    Temp
    Temperature (Source: Producer defined)

    Range of values
    Minimum:14.98
    Maximum:33.26
    Units:Degrees centigrade

    Time
    Time when Hydrolab record was saved (Source: Producer defined.)

    Range of values
    Minimum:00:00:08
    Maximum:23:59:26
    Units:HH:mm:ss

    H98Midas
    Table H98Midas lists sample date, time sample was collected from the ship's MIDAS tap-in, closest MIDAS GPS time, MIDAS GPS latitude and longitude, MIDAS tap-in salinity and weight of suspended sediments. There are 188 records. MIDAS GPS was not functional at all stations. See also Completeness_Report. (Source: Producer defined.)

    Date
    Date when the SPM (suspended sediment) sample was collected from the survey ship's MIDAS. (Source: Producer defined.)

    Range of values
    Minimum:19980113
    Maximum:19981215

    M-Sal
    Salinity as measured by RV Pelican's SeaBird SBE 21 Thermosalinograph in the flow-through seawater component of the ship's MIDAS system. October salinity values reported for stations C8, C7, C6, C6B, C5, C4, C3 and C1 are near-surface Hydrolab values. (Source: Producer defined.)

    Range of values
    Minimum:1.73
    Maximum:34.9
    Units:parts per thousand

    SS-Lat
    MIDAS GPS latitude of sampling station. (Source: Producer defined.)

    Range of values
    Minimum:28.3916
    Maximum:29.6937
    Units:Decimal degrees

    SS-Lon
    MIDAS GPS longitude of sampling station. (Source: Producer defined.)

    Range of values
    Minimum:-93.417
    Maximum:-89.4246
    Units:Decimal degrees

    Sta
    Station name of location sampled. (Source: Producer defined.)

    Character field

    StnID
    Station identification number. (Source: Producer defined)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    SuspSed
    Total suspended sediments collected by tapping into the flow-through seawater component of the ship's MIDAS system. October 1998 suspended sediment samples were collected from twice-rinsed buckets of surface water. (Source: Producer defined)

    Range of values
    Minimum:1.9
    Maximum:84.4
    Units:mg/L

    TimeM
    Time when SPM sample was collected (Source: Producer defined)

    Range of values
    Minimum:0:23:42
    Maximum:23:40:02
    Units:Hours:minutes:seconds

    H98Nutrients
    The table lists station NH4, NO2, NO2+NO3, NO3, PO4 and SiO3 values at depths. There are 393 records. (Source: Producer defined.)

    Depth
    Depth of Hydrolab p sensor, 0.0 depth = bucket sample. 6.5m and 14m samples were collected using Niskin bottles on the Seabird rosette. Bottom samples were collected using a bottom-tripping Niskin bottle on the Hydrolab Hydrowire. (Source: Producer defined)

    Range of values
    Minimum:0
    Maximum:68.3
    Units:Meters

    NH4
    Ammonium (Source: Producer defined)

    Range of values
    Minimum:0.1
    Maximum:27.9
    Units:µg-at/L

    NO2
    Nitrite (Source: Producer defined)

    Range of values
    Minimum:0.1
    Maximum:16.3
    Units:µg-at/L

    NO2+NO3
    Nitrite + Nitrate (Source: Producer defined)

    Range of values
    Minimum:0.1
    Maximum:150.5
    Units:µg-at/L

    NO3
    Nitrate (Source: Producer defined)

    Range of values
    Minimum:0
    Maximum:149.9
    Units:µg-at/L

    PO4
    Phosphate (Source: Producer defined)

    Range of values
    Minimum:0.1
    Maximum:4.1
    Units:µg-at/L

    SiO3
    Silicate (Source: Producer defined)

    Range of values
    Minimum:0.3
    Maximum:128.6
    Units:µg-at/L

    Sta
    Station name of location sampled (Source: Producer defined)

    Character field

    StnID
    Station identification number (Source: Producer defined)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    H98Pigments
    The table lists sample depth, mean chlorophyll a, Fo/Fa ratio, mean phaeopigments, mean total pigments, station name and station identification number. There are 393 records. (Source: Producer defined.)

    Date
    Date station was sampled. (Source: Producer defined.)

    Range of values
    Minimum:19980113
    Maximum:19981215

    Depth
    Depth of Hydrolab p sensor, 0.0 depth = bucket sample. 6.5m and 14m samples were collected using Niskin bottles on the Seabird rosette. Bottom samples were collected using a bottom-tripping Niskin bottle on the Hydrolab Hydrowire. (Source: Producer defined)

    Range of values
    Minimum:0
    Maximum:68.3
    Units:Meters

    MeanC
    Mean Chlorophyll a (Source: Producer defined)

    Range of values
    Minimum:0
    Maximum:38.75
    Units:µg/L

    MeanF
    Mean Fo/Fa ratio. F(original), F(acidified). (Source: Producer defined)

    Range of values
    Minimum:0.51
    Maximum:4.61
    Units:Fo/Fa ratio

    MeanP
    Mean Phaeopigments (Source: Producer defined)

    Range of values
    Minimum:0
    Maximum:49.76
    Units:µg/L

    Sta
    Station name of location sampled (Source: Producer defined)

    Character field

    StnID
    Station identification number (Source: Producer defined)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    Total
    Total pigments (Source: Producer defined)

    Range of values
    Minimum:0.2
    Maximum:59.23
    Units:µg/L

    H98PortaSal
    The table lists sample depth and sample salinity (psu), station name and station identification number of values measured using a Guildline Instruments PortaSal. There are 248 records. (Source: Producer defined.)

    Depth
    Depth of Hydrolab p sensor, 0.0 depth = bucket sample. Bottom samples were collected using a bottom-tripping Niskin bottle on the Hydrolab Hydrowire. (Source: Producer defined)

    Range of values
    Minimum:0
    Maximum:30.5
    Units:Meters

    PortaSal
    Salinity (Source: Producer defined.)

    Range of values
    Minimum:0.001
    Maximum:35.853
    Units:psu

    Sta
    Station name of location sampled (Source: Producer defined)

    Character field

    StnID
    Station identification number. (Source: Producer defined)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    H98Refract
    The table lists sample salinity, station name and station identification number of values measured using a refractometer. There are 4 records. (Source: Producer defined)

    Refracto
    Salinity measured with a refractometer. (Source: Producer defined.)

    Range of values
    Minimum:1
    Maximum:15
    Units:Parts per thousand.

    Sta
    Name of station sampled. (Source: Producer defined.)

    Character field.

    StnID
    Station identification number. (Source: Producer defined.)

    Range of values
    Minimum:86
    Maximum:89
    Units:Integer.

    Time
    Time of refractometer sample. (Source: Producer defined.)

    Range of values
    Minimum:6:23
    Maximum:6:44
    Units:HH:MM

    H98SeaBird
    The table lists SeaBird CTD conductivity, depth, FlC (Chelsea fluorometer voltage), FlS (SeaTech fluorometer voltage), dissolved oxygen, oxygen percent saturation, salinity, density sigma-t, station name, station identification number, temperature and light transmissivity. There are 2825 records. (Source: Producer defined.)

    COS/m
    Conductivity (Source: Producer defined.)

    Range of values
    Minimum:1.482476
    Maximum:5.940581
    Units:S/m

    DepS
    Depth of SeaBird pressure sensor. (Source: Producer defined.)

    Range of values
    Minimum:0.742
    Maximum:67.604
    Units:Meters

    FlC
    in vivo fluorescence. Chelsea fluorometer voltage. (Source: Producer defined.)

    Range of values
    Minimum:0.07499
    Maximum:7.285
    Units:Voltage

    FlS
    in vivo fluorescence. SeaTech fluorometer voltage. N.B. 30 is the maximum value for the instrument. Values of 30 indicate in vivo fluorescence was equal to or greater than what the instrument measured. (Source: Producer defined.)

    Range of values
    Minimum:0.5275
    Maximum:30
    Units:Voltage

    OxMg/L
    Dissolved oxygen (Source: Producer defined.)

    Range of values
    Minimum:0.00042
    Maximum:8.86001
    Units:mg/L

    OxPS
    Percent oxygen saturation. (Source: Producer defined.)

    Range of values
    Minimum:0
    Maximum:128.6
    Units:Percent

    Sal00
    Salinity (Source: Producer defined.)

    Range of values
    Minimum:7.9114
    Maximum:36.3431
    Units:psu

    Sigma-t00
    Density sigma-t (Source: Producer defined.)

    Range of values
    Minimum:1.885
    Maximum:26.1714
    Units:sigma-t

    Sta
    Station name of location sampled. (Source: Producer defined.)

    Character field

    StnID
    Station identification number. (Source: Producer defined.)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    T068
    Water Temperature (Source: Producer defined.)

    Range of values
    Minimum:14.9617
    Maximum:32.0635
    Units:Degrees centigrade

    Xmiss
    Percent light transmission (Source: Producer defined.)

    Range of values
    Minimum:1.46
    Maximum:102.06
    Units:Percent

    H98Stn
    The table lists altimeter height, date, fathometer depth, latitude, longitude, secchi disk depth, station name, station identification number, time of Hydrolab CTD cast and time of SeaBird CTD cast. There are 198 records. (Source: Producer defined.)

    Alt
    Height of SeaBird CTD package above the bottom. (Source: Producer defined.)

    Range of values
    Minimum:1.5
    Maximum:7
    Units:feet

    Date
    Date samples were collected at station. (Date may be different for suspended sediment sample, Hydrolab CTD cast and SeaBird CTD cast at same station). (Source: Producer defined.)

    Range of values
    Minimum:19980113
    Maximum:19981215

    Depth
    Depth of Station as measured by ship's fathometer, corrected for hull depth. (Source: Producer defined.)

    Range of values
    Minimum:5.3
    Maximum:68.3
    Units:Meters

    Lat
    Latitude of sampling station. (Source: Producer defined.)

    Range of values
    Minimum:28.3911
    Maximum:29.7077
    Units:Decimal degrees.

    Lon
    Longitude of sampling station. (Source: Producer defined.)

    Range of values
    Minimum:-93.4167
    Maximum:-89.4246
    Units:Decimal degrees.

    Secc
    Secchi disk depth. N.B. Secchi disk depths at stations G3 and G4 on the date 19980724 were greater than 17 meters. (Source: Producer defined.)

    Range of values
    Minimum:0.4
    Maximum:17
    Units:Meters

    Sta
    Station name of location sampled. (Source: Producer defined.)

    Character field

    StnID
    Station identification number. (Source: Producer defined.)

    Range of values
    Minimum:1
    Maximum:242
    Units:Integer

    TimeHL
    Time of beginning of Hydrolab CTD cast as well as time of Pigment, PortaSal and Nutrient samples. (Source: Producer defined.)

    Range of values
    Minimum:00:06:18
    Maximum:23:56:09
    Units:HH:mm:ss

    TimeSB
    Time of beginning of Seabird CTD cast. (Source: Producer defined.)

    Range of values
    Minimum:00:27
    Maximum:23:48
    Units:HH:mm

    Entity_and_Attribute_Overview:
    The related data tables H98Hydrolab, H98Midas, H98Nutrients, H98Pigments, H98PortaSal, H98Refract, H98SeaBird, and H98Stn contain spatial, temporal, physical and biological water quality data acquired during the 1998 Hypoxia Surveys of the Louisiana coastal waters. Each table contains a StnID field that can be used to key joins with other tables.
    Entity_and_Attribute_Detail_Citation: For detailed attribute information contact N. Rabalais.


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    N.N., Turner, R.E. and Wiseman, Jr., W.J. Funding: Funds for the research were provided by the National Oceanic and Atmospheric Administration, Coastal Ocean Program, Grant Nos. NA86RG0341 and NA960P0112. Funds for rental of the R/V PELICAN were provided by National Science Foundation Grant No. OCE-9818985 to Q. Dortch, Louisiana Universities Marine Consortium, and by NOAA for the July shelfwide cruise.

  3. To whom should users address questions about the data?

    Nancy N. Rabalais
    Louisiana Universities Marine Consortium
    Louisiana Universities Marine Consortium, 8124 Hwy 56
    Chauvin, LA 70344
    USA

    985 851 2800 (voice)
    985 851 2874 (FAX)
    Unknown


Why was the data set created?

The physical, biological and chemical data collected are part of a long-term coastal Louisiana dataset. The goal is to understand physical and biological processes that contribute to the causes of hypoxia and use the data to support environmental models for use by resource managers.


How was the data set created?

  1. What methods were used to collect the data?

    Method 0 of 12
    Type: Field SeaBird

    The SeaBird CTD number of scans to average in the deck unit was set to one. At the beginning of each hydrocast the entire CTD/Rosette package was soaked while submerged 0.5m to 1.0m below the surface until pump flow and oxygen values observed via the Sea-Bird deck unit indicated the system was operating correctly.

    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.

    Method 0 of 12
    Type: Field Hydrolab C Transect

    Deployment: 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 1.0-meter increments, after D.O. sensor stabilization, data records were stored. When the Hydrolab was raised a depth of two to three meters from the surface, 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.

    Method 0 of 12
    Type: Field Hydrolab shelfwide

    Deployment: Due to limitations of time, mid-water depths were generally not sampled with the Hydrolab CTD during the shelfwide cruise.

    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.

    Method 0 of 12
    Type: Field Pigment

    Water for chlorophyll analysis (30 - 100 ml) was filtered on board ship through GF/F (0.7 micron) filters, which were then fixed in 5 ml of DMSO/90% acetone (40/60) solution, allowed to extract for at least two hours in the dark, then measured pre- and post-acidification on a Turner Model 10 fluorometer.

    Method 0 of 12
    Type: Field PortaSal

    Water was collected in an acid-washed, triple-rinsed 500ml Nalgene jar from a twice-rinsed bucket of surface water. The jar lid was secured tightly to minimize evaporation.

    Method 0 of 12
    Type: Field Station Locations

    C transect lies South and East of Terrebonne Bay. Nine cross-shelf stations on C transect were sampled monthly. Additional water-column hydrology measurements were made at station C6B when other research missions provided opportunities at that location.

    During the July shelfwide cruise, stations were occupied along 13 generally North-South transects across the Louisiana coastal shelf. Station depths ranged from 5.3 to 68.3 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 four transects: A', A, C and F. 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 was reached. The limit of hypoxia was reached at all stations on the western end of the survey. The limit of hypoxia was only reached at station A'6 on the eastern end of the survey. Bottom waters at stations A'1, A'2, A'3 A'4 and A'5 were hypoxic.

    Method 0 of 12
    Type: Field Nutrient

    Care was taken that the collector's hands were clean and avoided touching the sample water. Gloves were worn when three replicate sample vials and caps were triple rinsed with sample before vial filling and closing. Samples were not filtered. The sample vials were frozen for later analysis in the laboratory.

    Method 0 of 12
    Type: Field suspended sediments

    Water (approximately 300 to 1000 ml) collected for suspended sediment samples was filtered on board ship through pre-weighed GF/F filters, rinsed with distilled water. The filters were placed in Petri dishes and frozen for later analysis.

    Method 0 of 12
    Type: Field water samples

    Water for chlorophyll, nutrient analyses and PortaSal salinity was collected from the surface by twice-rinsed bucket, from mid-water in 5-l Niskin bottles on the Seabird CTD/rosette system and from bottom in a 5-l bottom tripping Niskin deployed on the Hydrolab hydrowire.

    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 approximately 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.

    Method 0 of 12
    Type: Lab SPM

    Suspended sediment filters were dried at 40 - 60 degrees centigrade for 24 hours. Filters were weighed. Total suspended sediments were derived from volume filtered, pre-weight and post weight values.

    Method 0 of 12
    Type: Lab Nutrient

    Nitrogen and phosphorus are analyzed according to methods described in EPA publication EPA 600/4-79-020 (1979), method 350.1 for ammonia-N, method 353.2 for nitrate/nitrite-N, and method 365.1 for phosphate-P. Silicate is analyzed according to Technicon Industrial method 186-72 W/B (1977).

    Method 0 of 12
    Type: Lab SeaBird

    Sea-Bird CTD data were acquired using Seasoft version 4.225 in all months. Data were post processed using Seasoft version 4.3 January through March. Data for other months were post processed with Seasoft version 4.225. 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 post-processed, dissolved oxygen was advanced relative to temperature and conductivity values as follows: January +3.75 seconds; February, March and August +4.0 seconds; July +4.055 seconds; April, September, November and December +4.25 seconds; May 5.5 seconds; and June +6 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.

  2. From what previous works were the data drawn?

  3. How were the data generated, processed, and modified?

    Date: Unknown (process 1 of 1)
    Unknown


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    H98Hydrolab: The Hydrolab Surveyor 3 Conductivity, pH and Oxygen sensors were serviced and calibrated before deployment and maintained in accordance with Hydrolab (<http://www.hydrolab.com/>) recommended procedures. The Sonde and Logger were returned to the factory at least annually for inspection and service.

    December 1998 Transect C Hydrolab CTD conductivity sensor problems were indicated by many salinity values that were considered too high (greater than 37ppt).

    Seawater samples were collected at the same times and depths the Hydrolab values were recorded. The seawater samples were later measured in the laboratory with a PortaSal salinometer. The salinometer values were used to develop an equation to correct the Hydrolab Salinity values:

    (Hydrolab Salinity - 1.5156)/1.0376 = Corrected Hydrolab Salinity

    2180 pairs of Hydrolab spCond-Salinity values (considered good) which had been acquired on Transect C cruises in 1985 through 1997 were used to develop a multiple regression model of the form spCond =f(S). The result of this nonlinear regression exercise was a fourth order polynomial with a high correlation coefficient (R^2 = 0.99992).

    December 1998 Transect C specific conductance was derived as follows. Derived spCond = -0.50203+1.92169*(CorrectedHydrolabSalinity)-0.02105*(CorrectedHydrolabSalinity)^2+0.000381377*(CorrectedHydrolabSalinity)^3-0.00000290903*(CorrectedHydrolabSalinity)^4

    December 1998 Transect C Density sigma-t values were derived using methods described in Montgomery, R. B., and Wooster, Warren S., "Thermosteric Anomaly and the Analysis of Serial Oceanographic Data', Deep-Sea Research, Vol. 2, 1954 and values from Knudsen, Martin, Hydrographical tables, 1901. Formulas available upon request.

    December 1998 Transect C Dissolved Oxygen and Percent Oxygen Saturation values logged by the Hydrolab were not corrected. Values reported for December 1998 Transect C Dissolved Oxygen and Percent Oxygen Saturation should be considered suspect.

    H98Nutrients: Nutrient analyses were conducted using a Technicon (<http://www.techniconinstruments.com/>) autoanalyzer by Tom Oswald under the supervision of R. E. Turner.

    H98Pigments: The Turner Designs model 10 was 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. Pigment measurements were supervised and quality controlled by Nancy Rabalais.

    H98PortaSal: 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.

    H98Refract: The refractometer was checked with distilled water before each cruise and re-zeroed when necessary.

    H98SeaBird: 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 Chelsea Fluorometer was also maintained by RV Pelican Electronic Technical support staff in accordance with Chelsea recommended procedures (<http://www.chelsea.co.uk/>).

    Use of a more compact CTD carousel and extension was adopted beginning with the May 1998 cruise. The SeaBird CTD package was re-oriented from vertical to horizontal and plumbing was re-configured. The distance from the center of Niskin sample bottles and the pressure sensor decreased from 1.0 meter to 0.75 meters.

    Before the start 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 in case it was necessary to correct the data. The July SeaBird data agreed with the Winkler values and no correction was necessary.

    Winkler titrations and the OXFITW procedure were used to check the SeaBird oxygen sensors at the beginning of the September - December cruises.

    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.

    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. A suitable range of data could not be acquired to develop a strong regression.

    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.

    Jan SeaBird ~ 1mg/L lower than Hydrolab Feb SeaBird ~ 0.8mg/L lower than Hydrolab Mar SeaBird ~ 0.6-1.0mg/L lower than Hydrolab Apr SeaBird ~ 1.5-2.0mg/L too low, Note in log book not to trust May SeaBird ~ 0.5-1.0mg/L lower than Hydrolab except C6B higher than Hydrolab Jun SeaBird C9 no good, delete Jun SeaBird C6B a bit off Jun SeaBird C1 pump out, no cast Aug SeaBird is similar to Hydrolab Sep SeaBird is similar to Hydrolab Oct Acadiana Nov SeaBird is off from Hydrolab plus or minus 0.5 Dec SeaBird is similar to Hydrolab

    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.

    H98Stn: 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 using either a StarLink Invicta 210S Differential GPS System with dual output with Gyro interface (<http://www.starlinkdgps.com/>) or a Northstar 800x Differential GPS System (<http://www.northstarcmc.com>). During April and May 1998 while the Northstar was being repaired a Garmin GPS 45 with GBR 21 was used. 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 October cruise on the RV Acadiana, position data were logged from the ship's NorthStar 800 Loran C. Station depths were logged from Acadiana's fathometer.

    H98Midas: Suspended sediment concentrations were supervised by Ben Cole or Nancy Rabalais and quality controlled by Nancy Rabalais. Times and locations of operations were acquired from the GPS component of the ship's MIDAS system (when available).

    N. Rabalais performed an additional procedure in quality-control/quality-assurance by evaluating relationships between the data in H98Hydrolab, H98Midas, H98Nutrients, H98Pigments, H98PortaSal, H98Refract, and H98Stn.

  2. How accurate are the geographic locations?

    All station positions, except those acquired during the October cruise on RV Acadiana, were logged from RV Pelican's differential GPS at the beginning of sampling operations. GPS manufacturer's accuracy claim is 1-5 meters 95% of the time. Wind, currents and tidal forces may move the ship from the beginning position.

    Station positions acquired during the October cruise 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: 19980402, 19980420, 19980619, 19980716, 19980811 and 19981012.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    On 19980113, the 5.0 meter Niskin sample at station C1 was muddy. Nutrient and Pigment samples were considered compromised and were deleted.

    SeaBird Dissolved oxygen (OxMg/L) and percent oxygen saturation data acquired 19980610 at station C9 were deleted because the data were considered unreliable.

    During the July shelfwide 1998 survey the SeaBird CTD package was configured with a single fluorometer. No Chelsea Fluorometer (FlC) data were collected during the July cruise.

    Suspended sediment values (SuspSed) that did not meet quality control criteria were deleted.

    The navigation component of the ship's MIDAS system was not always functional. thirty-two suspended sediment latitude and longitude values (SS-Lat and SS-Lon) are missing from table H98Midas. The station latitude and longitude (Lat and Lon) values reported in table H98stn were within 0.3 nautical miles of the suspended sediment sample location.

  5. How consistent are the relationships among the observations, including topology?

    Table H98SeaBird lists Sea Tech fluorometer voltage values (FlS) of 30 for one or more depths at eleven stations in 1998. A value of 30 indicates that fluorescence was high enough to maximize the sensor.

    Table H98SeaBird percent light transmission (Xmiss) values exceeded 100 percent at six stations: 19980414 station C9, 19980512 stations C9 and C6B, 19980610 station C6BN, C9N and C9.


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:
1. Dataset credit required. 2. Experience with similar datasets has shown that when data are plotted or used in further analysis, outlying values may occasionally be discovered. Please report any possible problems with the data to N. Rabalais.

  1. Who distributes the data set? (Distributor 1 of 1)

    Nancy N. Rabalais
    Louisiana Universities Marine Consortium
    Louisiana Universities Marine Consortium, 8124 Hwy 56
    Chauvin, LA 70344
    USA

    985 851 2800 (voice)
    985 851 2874 (FAX)
    Unknown

  2. What's the catalog number I need to order this data set?

  3. What legal disclaimers am I supposed to read?

    I, the data requestor, agree to credit the data originators in any publications, reports or presentations generated from this data. I also accept that although these data have been processed successfully on a computer system at the Louisiana Universities Marine Consortium, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. I recognize that these data are best acquired from the originator and not from a secondary source. I recognize that careful attention must be paid to the contents of the metadata file associated with these data. I will not hold Louisiana Universities Marine Consortium liable for improper or incorrect use of the data described and/or contained herein. This disclaimer applies both to individual use of the data and aggregate use with other data.

  4. How can I download or order the data?

  5. Is there some other way to get the data?

    Contact distributor


Who wrote the metadata?

Dates:
Last modified: 05-Jun-2003
Last Reviewed: 15-Jun-2003
To be reviewed: 15-Jun-2013

Metadata author:
Ben Cole or Adam Sapp
Louisiana Universities Marine Consortium
LUMCON, 8124 Hwy 56
Chauvin, LA 70344
USA

985 851 2800 (voice)
985 851 2874 (FAX)
Unknown

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)


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