U.S. Geological Survey Data Series 741
Sampling of water included both underway continuous and discrete water samples. These samples were analyzed either shipboard, onshore, or both, as noted in the descriptions.
Continuous measurements of pH, pCO2, TCO2, salinity, and temperature were collected from 22:35 UTC on August 3, 2010 to 20:55 UTC on September 5, 2010 using a flow-through Multiparameter Inorganic Carbon Analyzer (MICA) and Sea-Bird SBE49 CTD attached to the flow-through system of the USCGC Healy. Geographic, salinity, temperature, and fluorometric data were also collected using a shipboard Ashtech ADU5 GPS system, a Sea-Bird SBE45 Thermosalinograph, and a Seapoint Chlorophyll Fluorometer (SCF). A complete description of these can be found in Chayes and others (2010). The intake of the shipboard flow-through system was located approximately 8 meters (m) below the sea surface on the port side of the vessel. Water entered the sampling baffles at depth, was pumped to an ice chest for separation of ice, and was then pumped to a de-bubbler and a multiport sampling manifold located in the ship's laboratory. Filtered seawater was then fed to a custom made PVC de-bubbler containing a Sea-Bird SBE49, prior to being transported to the intake port of the MICA. Measurements were taken and logged approximately every 60 seconds except during a MICA flushing cycle, which occurred for approximately 10 min each hour. The MICA was calibrated using Certified Reference Material from Professor Andrew Dickson of the University of California at San Diego. Precision and accuracy for each channel were 0.002 for pH, 2 parts per million (ppm) pCO2, and 2 micromoles per kilogram (μmol/kg) for TCO2. Quality of the data as determined by Xuewu Liu (USF) are reported on the HLY1002_MICA.csv spreadsheet.
Discrete water samples were collected while underway following protocols outlined in Dickson and others (2007). Surface water samples were collected every 2 hours (h) for measurement of pH and carbonate ion concentration. Additional discrete samples were collected three times per day for post-cruise laboratory analysis of total alkalinity and total carbon, nutrients (NH4, silica, PO4, and NO2+N), carbon and oxygen isotopes, and elemental analysis. Water samples were removed from the manifold sampling port of the vessel's flow-through seawater system downstream from the de-bubbler, thermosalinograph, and fluorometer.
Approximately 30 milliliters (mL) of seawater was collected directly into cylindrical optical glass cells for pH on the total scale (pHT) measurements on the total hydrogen ion scale following the procedure of SOP6b (Dickson and others, 2007). Once filled, cuvettes for pH were rinsed with distilled (DI) water, then placed into an aluminum cell warmer attached to a water bath at 25°C for approximately 30 min. Shipboard pH measurements were performed using an Agilent 8453 spectrophotometer, purified metacresol purple indicator dye, and equations modified by Liu and others (2011).
pCO2 of air was measured using a Li-Cor LI-7000 infrared gas analyzer affixed to the jack staff at the bow of the vessel approximately 10 m above the sea surface. The gas analyzer was calibrated daily using standardized gases of concentration 402 ppm. Data were logged every 2 min. The precision of air pCO2 measurements is ±1 ppm.
Discrete samples from vertical profile casts were collected at 10 locations (see Maps section). For 6 of these casts, a 24-bottle Niskin rosette (12-L bottle volume) with an electronic trigger was fitted with a Sea-Bird SBE 911plus CTD and altimeter. The CTD provided salinity, temperature, depth, fluorescence, and dissolved oxygen data. The rosette was lowered to just above the sea floor, and bottles were filled at select depths as the rosette was brought to the surface. During two deployments, a 12-bottle rosette (30-L bottles) was fitted with a CTD and an altimeter. Water samples were collected from the Niskin bottles for the full suite of discrete analyses shipboard and ashore as described above for surface samples. Shipboard TA was measured spectrophotometrically using a method under development by Dr. Xuewu Liu of USF. These TA values were derived from an experimental procedure and are thus not definitive. Detailed procedures will be published.
Geographic data was collected using the vessel's Ashtech ADU5 global positioning system. Latitude, longitude, date, and time were recorded at 1-min intervals and reconciled with underway and discrete data after the research expedition. Wind speed was acquired from the Healy yardarm ultrasonic anemometer (or the jackstaff ultrasonic anemometer).
Seawater samples were collected from the sampling manifold of the shipboard flow-through seawater system in 300-mL borosilicate glass biochemical oxygen demand (BOD) bottles. Samples were preserved by adding 100 microliters (μL) of a saturated solution of mercuric chloride (HgCl2) and were sealed with a ground glass stopper lightly coated with Apiezon grease. Samples were transported to the USGS Carbon Chemistry Lab in St. Petersburg, Fla. Total alkalinity samples were analyzed using an Ocean Optics USB 2000 spectrophotometer, bromol cresol purple indicator dye, and the methods of Yao and Byrne (1998). Total carbon was analyzed using coulometric methods of Dickson and others (2007). Precision and accuracy for these methods was 1 μmol/kg for TA and TCO2.
A syringe that was pre-rinsed with sample water was used to collect approximately 60 mL of seawater. A Sterivex filter cartridge (pore size 0.22 micrometer, μm) was attached to the Luer-Lock fitting of the syringe and was rinsed with approximately 40 mL of sample. The remaining 20 mL of sample was then collected in a 20-mL glass scintillation vile and frozen. Samples were analyzed for NH4, silica, PO4, and NO2+N at the Woods Hole Oceanographic Institution (WHOI) Nutrient Analytical Facility.
Seawater samples were collected for stable isotopic analysis by rinsing, then filling 125-mL serum bottles such that no headspace remained. Samples were fixed with 50 microliters (µL) of saturated mercuric chloride and sealed with Teflon crimp caps containing a thin coating of Apiezon grease. Samples were refrigerated continuously prior to analysis. Analyses were completed at the USF Department of Geology Stable Isotope Laboratory using a Thermo-Finnigan Delta V 3-kiloelectron volt (keV) Isotope Ratio Mass Spectrometer coupled to a Finnigan GasBench II preparation device. Separate analyses of δD and δ18O of H2O were completed by equilibrating 200 µL of sample with approximately 12 mL headspace of H2 (approximately 1% in balance He for δD) and CO2 (approximately 0.3% in balance He for δ18O) in septum-capped vials. After equilibration, the isotopic composition of the headspace gas was measured (methods following Epstein and Mayeda, 1953; Prosser and Scrimgeour, 1995). Analyses of δ13C of dissolved inorganic carbon (DIC) was completed by injecting 1 mL of sample into an approximately 12-mL vial that was pre-flushed with He and pre-filled with 1 mL of 85 percent H3PO4 (methods following Assayag and others, 2006). The CO2 produced by this acid-stripping of the DIC was then measured after 24 h of equilibration. All stable isotope data are expressed in the conventional delta (δ) notation:
δ = [(Rsample-Rstandard)/Rstandard] × 1000‰
where Rsample and Rstandard are the 18O/16O, D/H 13C/12C ratios of the sample and standard, respectively for δ18O, δD and δ13C. The standards used as a reference for the δ-scale are VSMOW for H2O and VPDB for DIC. Internal standards were used in the calibration to the VSMOW and VPDB scales (VEEN and HTAMP waters with δ18O = -13.17 per mil (‰) and +15.05‰; δD = -96.8 and +40.5‰; Carrara Marble and NBS-18 calcites with δ13C = +2.01‰ and -5.04‰). Analytical precision (2σ) on these standards was better than 0.15, 1.0 and 0.2‰ for δ18O, δD, and δ13C, respectively. Analytical precision (2σ) on the samples was better than 0.2‰ for δ18O and 1‰ for δD and δ13C.
Other carbonate system parameters including seawater calcite and aragonite saturation states were calculated using the carbonate speciation program called CO2Calc (Robbins and others, 2010). Equilibrium constants used for these calculations included those created or modified by Dickson (1990), Lueker and others (2000),and Ho and others (2006).
Table 1 indicates number of samples taken, field preparation, and location of analysis. Table 2 describes the sensors on the sampling Rosette.Table 1. Sample overview, field activity H-03-10-AR.
|Number of Samples||Amount||Sample Container Type||Type of Analysis||Preparation in field||Where Analyzed|
|240||300 mL||Borosilicate Bottles||DIC/TA||HgCl2, not filtered||USGS St. Petersburg|
|220||125 mL||Serum Bottles||Isotopes||HgCl2, not filtered, refrigerated||USF Stable Isotope Lab|
|220||60 mL||Glass||TOC||Not filtered, frozen||USGS Denver|
|220||20 mL||Scintillation Vials||Nutrients||Filtered, frozen||WHOI|
|Sensor||Description||Serial No.||Calibration Date|
|TSG||Sea-Bird SBE 45||0228||02/20/2010|
|Sea surface water intake sea temperature||Sea-Bird SBE3S||4063||02/18/2010|
|Flowmeter at TSG||Flocat ES45B003C||09061005||01/07/2008|
|Fluorometer at TSG||Seapoint SCF||SCF2957||12/15/2007|
|Oxygen sensor at TSG||Sea-Bird SBE-43||431333||09/09/2010|