Dataset: SF6 Discrete - Station/Niskin Sort
Deployment: RB-08-02

SF6 Discrete - Station/Niskin Sort

Principal Investigator:

David T. Ho (University of Hawai'i, UH)

Contact:

Burke Hales (Oregon State University, OSU-CEOAS)

BCO-DMO Data Manager:

Stephen R. Gegg (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Project:

Southern Ocean Gas Exchange Experiment (SO_GasEx)

Current State:

Final no updates expected

Version:

16 Feb 2010

Deployment Synonyms:

RB0802, RHB_SO-GasEx

Version Date:

2010-02-16

Data URL:

https://www.bco-dmo.org/dataset-deployment/453013/data

Expand/Collapse All

Description

SF6 Discrete - Station/Niskin Sort
Analysis of discrete samples for SF6
Samples collected from CTD casts, from underway scientific
seawater line, and from submerged water pump

Methods & Sampling

Dataset acquisition description

See: SO-GasEx cruise report, Section 5.3.3 ppgs 19-20

Operation description:
Sampling times and locations:
Sampled all CTD casts where Niskin bottles were tripped.
One deep cast to 4600m, two mid-depth casts to 1500m, four
shallow casts to 100m, and other casts usually to 500m.
See CTD cast logs and bottle files for specific times, locations, and bottles for each cast.
See event log for times and locations when sampled underway seawater line.

Overall sampling strategy:
Normally collected one sample from each depth that might contain
the released SF6, plus three - six samples deeper. All available
depths were sampled on the first four casts and on any later cast
that was shallower than 500m. If multiple Niskins were tripped
at a given depth, hydrography sampled only one of these. Duplicate
samples were drawn from a Niskin, normally in the mixed layer, on
nearly every cast. The first Niskin of a cast that was sampled
was the deepest Helium sample, and the sampling continued in order
to the surface Niskin. The deeper Niskins for SF6 sampling were
done next, starting at the deepest.

Sampling technique:
The discrete samples were collected in 550 ml borosilicate glass bottles
with ground glass stoppers. A sample bottle was shaken with 30-40 ml of
water; then inverted and rinsed with 10-20 ml of water. The bottle was
filled from the bottom with ~800 ml of bubble free water. The stopper
was put in the bottle ensuring that no gas bubble was enclosed. After
all the samples were collected from a cast, a rubber band was slipped
over the stopper. If the samples were not going to be analyzed within
10 hours, the glass bottles were stored in water.

Analytical method:
The samples were analyzed on an instrument patterned after Law et.al. [1998]
and built in 1998 at AOML. About 269 ml of sample water was sucked into an
evacuated chamber through a showerhead. The SF6 that entered the headspace
during filling and the SF6 that remained dissolved in the water were stripped
with ultra high purity nitrogen onto a Carboxen 1000 trap held at -68 C.
After a little more than 3 minutes of purging, the trap was isolated and heated
to 150 C. The trapped gases were swept onto a 1.5 m x 0.3 cm OD molecular sieve
5A column. The SF6 was separated from oxygen and other gases and was measured
with an electron capture detector (ECD).

The detector was calibrated using six standards:
- cyl#CA2071- 5.7 pptrillion (v/v)
- cyl#CA2089- 55.1 pptr
- cyl#CA3452- 112.3 pptr
- cyl#CA2060- 166.6 pptr
- cyl#CA2056- 345.0 pptr
- cyl#CA2093- 1109.0 pptr

The custom software includes a chromatography package from WillStein Software,
which is used for acquisition of the ECD output and to reintegrate peaks.
The SF6 peaks were reintegrated for all blank analyses, water analyses and the
analyses of 5.5 pptr standard. The larger standards had very favorable signal
to noise ratios.

The pattern of analyses include initial and final groups of standards bracketing
groups of water analyses. The water samples from each cast were typically split
into two groups, each covering the entire water column. Within a group, the
deepest water samples were analyzed before the more concentrated surface water
samples.

The Typical Analyses Sequence:
- 2-3 gas blanks
- 15-20 gas standards spanning the entire range
- gas blank
- 1-2 stripper blanks
- 7-9 water analyses
- stripper blank
- 1 analysis of 166.6 pptr standard
- stripper blank
- 7-9 water analyses
- [repeat analyses of stripper blanks, 166.p pptr std, and water samples two or three times]
- stripper blank
- gas blank
- 5-15 standards
- 2 gas blanks

The stripping chamber was evacuated and flushed with nitrogen before the first use.
If the stripping chamber was not going to used for more than 6 hours, it was rinsed
with fresh water and then evacuated and flushed.

Instrument details:
The ECD gas chromatograph is a Shimadzu Mini 2.
The custom software was written with LabView 5.1 in 1998 and revised in 2002.
The reference for a description of the instrument is: Law, C.S, A.J. Watson,
M.J. Liddicoat, and T. Stanton, Sulphur hexafluoride as a tracer of biogeochemical
and physical processes in an open-ocean iron fertilization experiment,
Deep Sea Research II, 45, 977-994, 1998.

Operation Log - During Cruise
5 - 6 March 2008
Attempts were made to use this discrete instrument to quantitate the amount of
SF6 in water actively being bubbled in the dosing tank. All attempts resulted
in peaks much larger than full scale for the ECD. The excessive amounts of SF6
were easily swept out of the instrument.

Station 3
one sample of a duplicate pair is stored for 23 hours before analyses - precision
of duplicates was good

Station 5
one sample of a duplicate pair is stored for 24 hours before analyses,
another sample of a different duplicate pair is stored for 52 hours.
Precision of the 52-hour duplicates was poorer than normal.

Station 8
These samples were stored overnight before analyses as were some earlier
stations and many later stations. This was the first station for which
some outgassing bubbles in some samples was noticed. These tiny bubbles
(<0.1 ml total volume) were not present when the bottle was sealed and
did not seem to bias the SF6 results.

Station 10
The sampling order was more discontinuous than normal to accommodate noble
gas sampling. For the collection of samples from the underway system after
station 10, the outflow tube of the MicroTSG in the hydro lab sink was put
in the bottom of a sample bottle and left to overfill the bottle for at least
2 minutes (flow at 1.3 liter/min).

13 March 2008
During analysis of sample bottle 15 (stn 9, N 22) the Labview program was in its
'pause and prompt' state longer than usual. The analytical system evacuates the
stripping chamber and then presents a prompt screen until a "start" button is
pushed by the analyst. The analyst has to draw some of the sample through the
inlet tube and solenoid valve before pushing the "start" button. If the 'pause
and prompt' state is long, the chance of outside air leaking into the chamber is
greater (potential higher blank).

15 March 2008
In an effort to have comparable results from the underway and discrete SF6 analytical
systems, the single SF6 gaseous standard for the underway system (58.2 pptr) was run
on the discrete system and three of the discrete standards (166.6, 55.1, and 5.7 pptr)
were run on the underway system.

18 March 2008
Both system and stripper blanks are significantly higher. The second dosing tank is
being bubbled on the afterdeck, and the lab air was enriched in SF6. No leaky fittings
could be found on the analytical system despite a day of searching. After ~48 hrs the
blanks decreased, but remained higher than at the start of the cruise.

22 March 2008
Last night was the first station (16) on the second patch. I took a sample from the
underway system to quickly check the strength of ECD signal. When the sample was run,
the peak went offscale. The ECD was set for 2nAmp standing current through station 14.
I decreased the setting to 1 nAmp. To span the largest peak from the water analyses
of station 16, I had to trap 6 regular gas loops (1.606 ml) of the most concentrated
standard (1109 pptr). I am concerned about peak shape changes while trapping that many
loops sequentially, so I put the second gas sample loop valve back on the system.
[it was taken off during a previous experiment.] I made a large loop (~7 ml) and created
new analytical methods to adequately flush the loop while and after filling it with
standard or blank gas. I will have to determine the exact volume of the new gas loop
back at AOML.

25 March 2008
Try again to locate the source of the elevated blanks, especially the stripper blanks.
Still, could not find any fitting that leaked. At the end of a day of analyses,
the chamber is rinsed with fresh water to reduce the corrosion on the solenoid valves
attached to the drain and vacuum connections. I stripped a sample of the fresh water
on the ship and discovered that it was as concentrated as the surface 'in-patch' water
(>200 fmole/liter). The chamber will continue to be rinsed with fresh water, but it
will go through a couple evacuate-and-purge cycles before being left for the night.
[no reduction in the blanks developed, but the procedure was continued.]

25 March 2008
During analyses of sample bottles 202 (stn 25, N 3), 206 (stn 25, N 9) and 10
(stn 26, N 18) the Labview program was in its 'pause and prompt' state longer than usual.

26 March 2008
During analysis of sample bottles 203 (stn 27, N 8) the Labview program was in its
'pause and prompt' state longer than usual.

28 March 2008
During analysis of sample bottles 2 (stn 32, submerged pump) the Labview program was
in its 'pause and prompt' state longer than usual.

29 March 2008
During analyses of sample bottles 2 (stn 35, N 7) and 17 (stn 35, underway system)
the Labview program was in its 'pause and prompt' state longer than usual.

30 March 2008
During analysis of sample bottles 202 (stn 37, N 6) the Labview program was in its
'pause and prompt' state longer than usual. During analysis of sample bottles 206
(stn 37, N 10) there seemed to be air in the inlet line and the water level in the
stripping chamber seemed lower than usual. Maybe the inlet tube was not submerged
as low as it should have been [but how would the Pt wire water sensors stop the water
flow automatically - splashes with gas going in?].

31 March 2008
During sampling, the stopper on bottle 203 (stn 41, N 3) was removed ~3 minutes after
sampling so some more a little more water from the niskin was gently added to the very
top of the bottle and the stopper reinserted.

03 April 2008
During sampling, the stopper on bottle 203 (stn 41, N 3) was removed ~3 minutes after
sampling so some more a little more water from the niskin was gently added to the very
top of the bottle and the stopper reinserted.

For Blanks and Cals See: SO-GasEx Discrete SF6 Blanks and Calibration Curves

Data Processing Description

Dataset Processing Description

See: SO-GasEx cruise report, Section 5.3.3 ppgs 19-20

Data Processing Log - Post Cruise
The first step in the data processing is subtracting the appropriate analytical blank
from the raw peak areas: gas blank for standard and air analyses, stripper blank for
the water analyses. The gas and stripper blanks were plotted and appeared to cluster
around different values over separate time periods. This pattern was to be expected
since there was only one analyst, who typically ran the samples from two casts together.
Thus, the analytical system was used for ~1/2 a day and then sat unused for ~1/2 a day.
Nineteen ranges of time were used for blank correction, due primarily to the variability
of the stripper blanks. The same gas blank value was applied in sequentially ranges often.
The applied blank values and a summary of the analytical blank results are provided below.

The analytical blanks showed no systematic trends for all but one range, so a single blank
value was used for the entire range. Within one time period, the stripper blank clearly
increased and then decreased. Rather than use one value, the applied blank for the water
analyses was a time-weighted linear interpolation between bracketing analytical stripper
blanks. For most of the water and gas analyses, the applied blank was significantly less
than 1% of the sample signal.

The blank-corrected peak areas for the standard analyses were plotted versus time. The
response of the ECD was fairly stable within the setting used for a patch (i.e. 2 nA standing
current for patch#1; 1 nA standing current for patch#2). Three time periods were chosen
for each setting. Within each time period, a least-squared regression of the standards
produced a 4th degree polynomial equation relating peak area and femtomole SF6. The peak
areas for the seawater analyses were not larger than for the standards; however, there were
some atypical analyses (e.g. tap water after 26 March) that had peaks larger than the
standards in that time period. Since the detector response was similar in the adjoining
time periods, the data for a couple standard runs were copied to adjoining time periods
to extend the standard curves for some atypical analyses. The 4th degree polynomial
equations were used to convert the blank-corrected peak areas for the water analyses to
aqueous concentrations (femtomole / liter).

The results of the water analyses were examined within the context of the surrounding SF6
analyses, of the titrated oxygen samples, and of the general hydrography. A quality control
flag similar to the WOCE protocol were assigned to each water analysis. There were four
analyses that were deemed 'bad', two of which had observations during analysis to explain
the bad result. There were fifteen analyses that were deemed 'questionable', seven of which
had observations to explain the poor result. The remaining 650 seawater analyses were deemed
'good', though nine analyses had observations that could have explained poor results. The
assignment of a 'bad' quality control flag was conservative so that expected results would
not be excluded from examination by others.

For the duplicate water samples drawn from niskin bottles, the relative precision was 3.3%
for all 38 duplicate pairs and was 1.4% for the 31 duplicate pairs definitely above background
SF6 concentrations (i.e. >8 fmole SF6/Liter). For the nineteen sets of multiple samples
collected from the underway sea water line the average precision was 5.3%, which reflects
analytical variability as well as changes in the water being sampled. A restrip of a
concentrated water sample was done on nearly every day. All 27 restrips of a water sample
contained 2% or less of the total SF6 extracted from a water sample, so no correction for
stripping efficiency was done.

For Blanks and Cals See: SO-GasEx Discrete SF6 Blanks and Calibration Curves

BCO-DMO Processing Notes
- Generated from original file SO-GasEx08_Disc-SF6_Final.xls, Sheet: stn-nsk

BCO-DMO Edits
- parameter names modified to conform to BCO-DMO convention
- event, station, date, time, lon, lat inserted from CTD headers file
- blank cells changed to 'nd'

More information about this dataset deployment

Funding

Award Number	Funding Source
unknown SO_GasEx NASA	National Aeronautics & Space Administration
unknown SO_GasEx NOAA	National Oceanic and Atmospheric Administration
unknown SO_GasEx NSF	National Science Foundation

Instruments

CTD Sea-Bird SBE 911plus

Supplied Name: CTD Seabird 911plus

Supplied Description:

Instrument Configuration File for SO-GasEx:

PSA file: C:GasExacqSeasave.psa
Date: 02/23/2008
Instrument configuration file: C:GasExconssec_24_1.con
Configuration report for SBE 911plus/917plus CTD
------------------------------------------------
Frequency channels suppressed : 0
Voltage words suppressed      : 0
Computer interface            : RS-232C
Scans to average              : 1
Surface PAR voltage added     : No
NMEA position data added      : No
Scan time added               : Yes

1) Frequency 0, Temperature
   Serial number : 4211
   Calibrated on : 08-Nov-07
   G             : 4.38706278e-003
   H             : 6.46536683e-004
   I             : 2.23272060e-005
   J             : 1.77872902e-006
   F0            : 1000.000
   Slope         : 1.00000000
   Offset        : 0.0000

2) Frequency 1, Conductivity
   Serial number : 2887
   Calibrated on : 18-Oct-07
   G             : -1.00439325e+001
   H             : 1.36330343e+000
   I             : -2.56289727e-003
   J             : 2.54823008e-004
   CTcor         : 3.2500e-006
   CPcor         : -9.57000000e-008
   Slope         : 1.00000000
   Offset        : 0.00000

3) Frequency 2, Pressure, Digiquartz with TC
   Serial number : 209
   Calibrated on : 09-Jul-07
   C1            : -3.920451e+004
   C2            : 6.234560e-001
   C3            : 1.350570e-002
   D1            : 3.894300e-002
   D2            : 0.000000e+000
   T1            : 3.046303e+001
   T2            : -9.018862e-005
   T3            : 4.528890e-006
   T4            : 3.309590e-009
   T5            : 0.000000e+000
   Slope         : 0.99985000
   Offset        : 1.00090
   AD590M        : 1.144000e-002
   AD590B        : -8.805040e+000

4) Frequency 3, Temperature, 2
   Serial number : 1455
   Calibrated on : 13-Nov-07
   G             : 4.84617647e-003
   H             : 6.77841857e-004
   I             : 2.60561588e-005
   J             : 2.02936086e-006
   F0            : 1000.000
   Slope         : 1.00000000
   Offset        : 0.0000

5) Frequency 4, Conductivity, 2
   Serial number : 2882
   Calibrated on : 18-Oct-07
   G             : -1.02006582e+001
   H             : 1.39961765e+000
   I             : 7.01158866e-004
   J             : 2.20787100e-005
   CTcor         : 3.2500e-006
   CPcor         : -9.57000000e-008
   Slope         : 1.00000000
   Offset        : 0.00000

6) A/D voltage 0, Oxygen, SBE 43
   Serial number : 315
   Calibrated on : 16-Oct-07p
   Equation      : Owens-Millard
   Coefficients for Owens-Millard: 
   Soc           : 3.6150e-001
   Boc           : 0.0000
   Offset        : -0.5838
   Tcor          : -0.0001
   Pcor          : 1.35e-004
   Tau           : 0.0
   Coefficients for Murphy-Larson: 
   Soc           : 0.00000e+000
   Offset        : 0.00000e+000
   A             : 0.00000e+000
   B             : 0.00000e+000
   C             : 0.00000e+000
   E             : 0.00000e+000
   Tau           : 2.00000e+000

7) A/D voltage 1, Free

8) A/D voltage 2, Free

9) A/D voltage 3, User Polynomial
   Serial number : 8756
   Calibrated on : 
   Sensor name   : Metrox
   A0            : 12.00000000
   A1            : 445.60000000
   A2            : 0.00000000
   A3            : 0.00000000

10) A/D voltage 4, Free

11) A/D voltage 5, Free

12) A/D voltage 6, Free

13) A/D voltage 7, Free
---------------------------------------------
Pump Control
   This setting is only applicable to a custom build of the SBE 9plus.
   Enable pump on / pump off commands: NO
---------------------------------------------
Data Acquisition:
   Archive data:                    YES
   Delay archiving:                 NO
   Data archive:                    C:P18_07data
h21731.hex
   Timeout (seconds) at startup:    20
   Timeout (seconds) between scans: 20
---------------------------------------------
Instrument port configuration:
   Port      = COM1
   Baud rate = 19200
   Parity    = N
   Data bits = 8
   Stop bits = 1
---------------------------------------------
Water Sampler Data:
   Water Sampler Type:   SBE Carousel
   Number of bottles:    24
   Port:                 COM2
   Enable remote firing: NO
   Firing sequence:      Sequential
---------------------------------------------
Header information:
   Header Choice = Prompt for Header Information
      prompt 0 = Cruise:  CLIVAR P18 2007
      prompt 1 = Ship:  NOAA RONALD H. BROWN
      prompt 2 = Station/Cast Number:
      prompt 3 = Nominal Latitude:
      prompt 4 = Nominal Longitude:
---------------------------------------------
TCP/IP - port numbers:
   Data acquisition:
      Data port:            49163
      Status port:          49165
      Command port:         49164
   Remote bottle firing:
      Command port:         49167
      Status port:          49168
   Remote data publishing: 
      Converted data port:  49161
      Raw data port:        49160
---------------------------------------------
Miscellaneous data for calculations
   Depth and Average Sound Velocity
      Latitude when NMEA is not available: 0.00000000
   Average Sound Velocity
      Minimum pressure [db]:               20.00000000
      Minimum salinity [psu]:              20.00000000
      Pressure window size [db]:           20.00000000
      Time window size [s]:                60.00000000
   Descent and Acceleration
      Window size [s]:                     2.00000000
   Plume Anomaly
      Theta-B:                             0.00000000
      Salinity-B                           0.00000000
      Theta-Z / Salinity-Z                 0.00000000
      Reference pressure [db]              0.00000000
   Oxygen
      Window size [s]:                     2.00000000
   Potential Temperature Anomaly
      A0:                                  0.00000000
      A1:                                  0.00000000
      A1 Multiplier:                       Salinity
---------------------------------------------
Serial Data Output:
   Output data to serial port: NO
---------------------------------------------
Mark Variables:
   Variables:
   Digits   Variable Name [units]
   ------   ---------------------
   0        Scan Count
   4        Pressure, Digiquartz [db]
   5        Temperature [ITS-90, deg C]
   5        Salinity [PSU]
   4        Oxygen, SBE 43 [umol/Kg]
   5        Density [sigma-theta, Kg/m^3]
---------------------------------------------
Shared File Output:
   Output data to shared file: NO
---------------------------------------------
TCP/IP Output:
   Raw data:
      Output raw data to socket:              NO
      XML wrapper and settings:               NO
      Seconds between raw data updates:       0.00000000
   Converted data:
      Output converted data to socket:        NO
      XML format:                             NO
---------------------------------------------
SBE 11plus Deck Unit Alarms
   Enable minimum pressure alarm:    NO
   Enable maximum pressure alarm:    NO
   Enable altimeter alarm:           NO
---------------------------------------------
SBE 14 Remote Display
   Enable SBE 14 Remote Display:     NO
---------------------------------------------
Options:
   Prompt to save program setup changes: YES
   Automatically save program setup changes on exit: NO
   Confirm instrument configuration change: YES
   Confirm display setup changes: YES
   Confirm output file overwrite: YES
   Check scan length: YES
   Compare serial numbers: YES
   Maximized plot may cover Seasave: NO

Instrument Type

Generic Name: CTD Sea-Bird SBE 911plus

Acronym: CTD SBE 911plus

Community Identifier: http://vocab.nerc.ac.uk/collection/L22/current/TOOL0058/

Generic Description:

The Sea-Bird SBE 911 plus is a type of CTD instrument package for continuous measurement of conductivity, temperature and pressure. The SBE 911 plus includes the SBE 9plus Underwater Unit and the SBE 11plus Deck Unit (for real-time readout using conductive wire) for deployment from a vessel. The combination of the SBE 9 plus and SBE 11 plus is called a SBE 911 plus. The SBE 9 plus uses Sea-Bird's standard modular temperature and conductivity sensors (SBE 3 plus and SBE 4). The SBE 9 plus CTD can be configured with up to eight auxiliary sensors to measure other parameters including dissolved oxygen, pH, turbidity, fluorescence, light (PAR), light transmission, etc.). more information from Sea-Bird Electronics

Parameters

Supplied Name	Supplied description	Supplied Units	Standard Name
event	Unique event number	YDAHHMM	event
date	Date (UTC)	YYYYMMDD	date
time	Time (UTC)	HHMM	time
lon	Station longitude in decimal degrees (West is negative)	decimal degrees	lon
lat	Station latitude in decimal degrees (South is negative)	decimal degrees	lat
stn_nskn	The CTD station number followed by a 0; followed by the niskin number. e.g. stn_nskn 1001 is CTD station 1; niskin 1.	integer	station
smpl_btl_num	Sample bottle number	integer	bottle
Helium_Flag	Helium Flag (0=yes)	integer	flag
WOCE_QC	2 = good analysis. 3 = questionable analysis - the result does not seem to fit into the context of surrounding results whether or not any unusual conditions were observed during sampling or analysis. 4 = bad analysis - the result does not fit into the context of surrounding results and an unusual condition was observed.	integer	flag
comments	data collection comments	text	comment
year_day_analyzed	year day analyzed	decimal day	julian_day_yr0
WS_area	WS area	integer	no_bcodmo_term
SF6	SF6	fmole/Liter	no_bcodmo_term
precision	Precision percentage: For 2 analyses percentage is difference divided by average; For >2 analyses percentage is standard deviation divided by average	percentage	no_bcodmo_term
station	SO-GasEx CTD Station Id	integer	station
niskin	niskin bottle number	integer	bottle
year_day_collected	year day collected	decimal day	julian_day_yr0
pres	pressure from CTD	decibars	press
temp	temperature from CTD	degrees celcius	temp
sal	salinity from CTD	dimensionless	sal
sigma_t	sigma_t (density) from CTD	kilograms/meter^3	sigma_t
o2	dissolved Oxygen	umol/kg	O2
lon_collection	Collection longitude in decimal degrees (West is negative)	decimal degrees	lon
lat_collection	Collection latitude in decimal degrees (South is negative)	decimal degrees	lat
DrawT_minus_C	DrawT-C	(tbd)	no_bcodmo_term
O2_discrete	Oxygen discrete	umol/kg	O2
O2_satur	Oxygen saturated	milliliters/liter	O2sat

Database

Contribute Data

Dataset: SF6 Discrete - Station/Niskin Sort
Deployment: RB-08-02

Dataset acquisition description

Dataset Processing Description

Database

Contribute Data

Dataset: SF6 Discrete - Station/Niskin SortDeployment: RB-08-02

Dataset acquisition description

Dataset Processing Description

Dataset: SF6 Discrete - Station/Niskin Sort
Deployment: RB-08-02