Abstract:
Two sets of CTD data were taken during the 2010 surveys of the Louisiana continental shelf—Transect C off Terrebonne Bay and Transect C off Atchafalaya Bay and the 2010 Shelfwide Hypoxia cruise. Hydrographic data were obtained with the LUMCON SeaBird 911+ CTD system and a YSI 6820. Nutrient, pigment, suspended sediment, surface salinity, secchi depth, Winkler results, and station information data were also acquired.
Suggested Citation:
Nancy Rabalais. 2014. Physical, chemical, and biological data collected in the Gulf of Mexico from 02 Feb 2010 to 28 Oct 2010 (NODC Accession 0117436). Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7W66HP0
Purpose:
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. The size of the hypoxic area is part of the baseline data considered by the Mississippi River/Gulf of Mexico Nutrient/Hypoxia Task Force.
Data Parameters and Units:
• 2010_YSI6820 o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Time (Zulu, HH:mm:ss) o Depth (Meters) o Dissolved Oxygen (mgO2/L) o Temperature (Degrees centigrade) o Specific conductance (mS/cm) o Salinity (psu) o pH (pH units) o pH mV (millivolts) o Percent Oxygen Saturation (%) o Chlorophyll a (µg/L) • 2010_Nutrients o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Depth (Meters) o Vial Number (Integer) o Ammonium concentration (µM/L) o Nitrite + Nitrate concentration (µM/L) o Phosphate concentration (µM/L) o Silicate concentration (µM/L) • 2010_Pigments o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Depth (Meters) o Mean Chlorophyll a (µg/L) o Mean Phaeopigments (µg/L) o Total pigments (µg/L) o Mean F (Mean Fo/Fa ratio) • 2010_Portasal o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Depth (Meters) o Salinity (psu) • 2010_Winkler o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Depth (Meters) o Winkler Dissolved Oxygen (mgO2/L) • 2010_Seabird o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Depth (Meters) o Conductivity (S/m) o In vivo fluorescence (Voltage) o Dissolved Oxygen (mgO2/L) o Percent Oxygen Saturation (%) o Salinity (psu) o Temperature (Degrees centigrade) o Percent light transmission (Percent) o Density (sigma-t, kg m-3) o Seabird scan count (Integer) o Altimeter (Meter) o Irradiance (percent of surface light in the water) • 2010_SPM o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Depth (Meters) o Inorganic suspended particulate material (mg/L) o Organic suspended particulate material (mg/L) o Total suspended sediments (mg/L) • 2010_StationList o Station ID (Integer) o Date (YYYYMMDD) o Station (Character field) o Latitude of sampling station (Decimal degrees) o Longitude of sampling station (Decimal degrees) o Arrival Time at Station (Zulu, HH:mm:ss) o Time of SeaBird CTD cast (Zulu, HH:mm:ss) o Time of YSI CTD cast (Zulu, HH:mm:ss) o Fathometer (Meters) o Secchi disk depth (Meters) o Altimeter (Meters) o Midas Salinity (psu)
Methods:
Field YSI monthly C and F transect surveys Methodology_Description: Deployment: The YSI 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 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 YSI reached 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. Field YSI July shelfwide survey Methodology_Description: Deployment: Due to limitations of time, mid-water depths were generally not sampled with the YSI CTD during the shelfwide cruise. The YSI 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 YSI 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. Field Nutrient Methodology_Description: Care was taken that the collector's hands were clean and avoided touching the sample water. Gloves were worn when two 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. An average of 30 minutes per station and one hour between stations. Working 24 h per d. Lowering rate of the CTD, 1 m/s. YSI 6820, depth not changed until stabilized; not continuous; but hand recorded. 8 hours in transit before first station; 20 hours in transit after last station. Field Pigment Methodology_Description: Water for chlorophyll analysis (10 - 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 AU fluorometer. Field Seabird CTD Methodology_Description: 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 was rapid in order to save time. Field SPM Methodology_Description: Water (approximately 50 to 1500 ml) collected for suspended sediment samples was filtered on board ship through (pre-combusted, pre-weighed) GF/F filters and rinsed with distilled water. The filters were placed in Petri dishes and frozen for later analysis. Field Portasal Methodology_Description: 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. Field Winkler Methodology_Description: Water was collected from Niskin Bottle samples using a 300ml glass BOD bottle. Care was taken so that air bubbles were not introduced into the water sample and titration reagents were added immediately to fix the oxygen Field Station Locations Methodology_Description: Stations along the cross-shelf C and F transect were sampled in March, April, May, June, August, September, and October. The nine C transect stations lie South and East of Terrebonne Bay; the seven F transect stations lie South of the Atchafalaya River. Additional water-column hydrology measurements were made at stations C6C and CSI-9 when other research missions provided opportunities at those locations. During the July shelfwide cruise stations were occupied along 14 generally North-South transects across the Louisiana and Texas coastal shelves. Station depths ranged from 2.40 to 49.10 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, B, C, D, J, and T. Hypoxic oxygen levels were found in transects A’, A, B, C, D, F, G, I, J, K, S, and T. Field water samples Methodology_Description: Water for chlorophyll, nutrient, salinity, and suspended sediment analyses was collected from the surface by twice-rinsed bucket, from mid-water in 5-l Niskin bottles on the SeaBird CTD/rosette system or a messenger triggered 5-l Niskin on the YSI hydrowire. Bottom samples were collected in a 5-l bottom tripping Niskin deployed on the YSI hydrowire. 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 YSI. The SeaBird pressure sensor was located approximately 0.75 meters below the mid-point of the 5-l Niskin. Midwater samples were collected using Niskin bottles on the SeaBird rosette. Lab Nutrient Methodology_Description: Ammonium samples were analyzed according to Lachat Instrument's QuikChem method 31-107-06-1-B. Phosphates are determined by Lachat Instrument's QuikChem Method 31-115-01-1-H. Silicates were measured using Lachat Instrument's Method 31-114-27-1-C. TKN was determined using Lachat Instrument's QuikChem Method 10-107-06-2-H. Nitrates and Nitrites were determined using Lachat Instrument's Method 31-107-04-1-C. Lab SPM Methodology_Description: Suspended sediment filters were dried overnight at 60°C and weighed. The filters were then combusted at 400°C for 12 hours and weighed. The weights of the total suspended, organic and inorganic materials were derived. Lab SeaBird CTD Methodology_Description: Sea-Bird CTD data were acquired using Seasoft and processed using SBE Data Processing-Win32 software. 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. SeaBird data were processed, dissolved oxygen was advanced relative to temperature and conductivity values. 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.
Instruments:
SeaBird CTD, Optical Spectrometer, YSI – 6820 handheld multi-parameter instrument, 5-L Niskin bottle, conductivity sensor, fluorometer (Turner digital 1-AU), oxygen titrator (Mettler Toldeo DL28), pressure sensors, secchi disk, SeaBird CTD unit with 12 5-l sampling rosette, Sea-Bird Electronics SBE-9+ Underwater Units with Digiquartz Pressure Sensor, 4127 and 6885 meter depth, Sea-Bird Electronics SBE-11 Deck Unit. Temperature Sensors (SBE 3-01/F) 6,800 meter depth, Conductivity Sensors, % transmission sensors, SBE 43 dissolved oxygen sensors (2), in vivo fluorescence sensors.
Error Analysis:
Examination for values +/- 2 SD of mean. Visual inspection for values inconsistent with replicates, and others in a continuous string. Visual inspection for values outside of range of instrument. Comparison with hand-written values. Evaluation of suspected values with station log notes. 2010_YSI6820: The YSI 6820 Conductivity, pH, Oxygen, and Chlorophyll sensors were serviced and calibrated before deployment and maintained in accordance with YSI (http://www.ysi.com/) recommended procedures. The Sonde and Logger are returned to the factory at least annually for inspection and service. Small adjustments based on correlations with Portasal and YSI values were made to YSI salinity data for March, April, July Shelfwide, August, September, and October. Shipboard Winkler titrations during the cruises were used to develop regressions against the YSI data in case it was necessary to correct the oxygen data. YSI oxygen data were corrected for March, May, June, July Shelfwide, August, September, and October using an equation based on the results of the regression. 2010_Nutrients: Nutrient analyses were conducted using a QuikChem 8000 FIA+ (http://www.lachatinstruments.com). Charlie Milan performed the analyses under the supervision of R. E. Turner, LSU. 2010_Pigments: 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. Fluorometry data were corrected based on calibration with a secondary standard. Pigment measurements were supervised by Nancy Rabalais and quality controlled by Nancy Rabalais. 2010_Seabird: 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 WetLabs C Star 10 cm path transmissometer was maintained by RV Pelican Electronic Technical support staff in accordance with Wet Labs recommendations. Small adjustments based on correlations with Portasal and SeaBird values were made to March, April, May, June, July Shelfwide, August, and October salinity data. 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 oxygen value was determined Mettler DL28 Titrator (http://www.mt.com/). Shipboard Winkler titrations during the cruises were used to develop regressions against the SeaBird data in case it was necessary to correct the oxygen data. SeaBird oxygen data were corrected for March, May, June, July Shelfwide, August, September, and October using an equation based on the results of the regression. Winkler titrations were conducted under the supervision of Nancy Rabalais. Post data processing from the SeaBird were generated by Leslie Smith and Lora Pride and quality controlled by Nancy Rabalais. N.B. irradiance values during the end of the July 2010 Shelfwide cruise (transects A’ to E) appear suspect and were given values of zero. During the April cruise, irradiance values for F5 were also deleted because they were suspect. Throughout the dataset, irradiance values greater than 100%, a result of the sensor breaching the sea surface, were removed. Additionally, near bottom high altimeter values (greater than 6.0 m) were deleted throughout, probes were likely within 1 meter of the bottom. 2010_SPM: Suspended sediment concentrations were supervised and quality controlled by Nancy Rabalais. 2010_Portasal: Salinity samples were analyzed in the lab by Guildline Instruments Portasal, using Guildline methods (http://www.guildline.ca/). Salinity analyses were conducted by Lora Pride under the supervision of Nancy Rabalais. 2010_Winkler: Winkler samples were analyzed on board the R/V Pelican with a Mettler Toledo DL28 Titrator using dissolved oxygen determination methods outlined in A Practical Handbook of Seawater Analysis by Strickland and Parsons, 1977. Winkler analyses were conducted by Lora Pride under the supervision of Nancy Rabalais. 2010_StationList: 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. In addition to the monthly surveys, YSI6820 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 2010_YSI6820, 2010_Nutrients, 2010_Pigments, 2010_Seabird, 2010_SPM, 2010_Portasal, 2010_Winkler, and 2010_StationList. Horizontal_Positional_Accuracy: Monthly survey cruise station positions were logged from RV Pelican's manufacturer's accuracy claim is 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, YSI casts were made at stations C6C, and CSI-9 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.
Provenance and Historical References:
Hypoxia surveys in the Northern Gulf of Mexico have been conducted annually since 1985. Data are at the NOAA NODC.
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