University of New Hampshire- Coastal Ocean Observing Center

Underway Carbon Dioxide Data description

Investigators: Doug Vandemark, Joe Salisbury, Chris Hunt

Vessel:Commercial Vessel Seafarer

Temporal coverage of data:20171005

Contact: Doug Vandemark (doug.vandemark@unh.edu)

PLEASE NOTE: Users of data will be required to provide proper credit and acknowledgment of the 
provider.  Users of data are encouraged to discuss relevant findings with the provider early in the research.
The user is required to give all providers of the data being used a copy of any manuscript resulting from use
of the data prior to the initial submission for publication, thus giving the data provider an opportunity to
comment on the paper. The provider(s) shall have the right to be named as a co-author.

List of variables included in this dataset:
COLUMN	HEADER			EXPLANATION
=======	=======			============
1.	year			Year measurements were taken
2.	day_of_year		Sequential day of year measurements were taken
3.	secDay			Sequential seconds of day of measurement (e.g. 60,000 secDay=16:40:00)
4.	lat                 Latitude in decimal degrees (negative values are in the Southern Hemisphere)
5.	lon                 Longitude in decimal degrees (negative values are in the Western Hemisphere)
6.	speed			Ship speed in meters per second
7.	Water_temp		Sea surface temperature measured by a SBE-45 thermosalinograph, in degrees Celcius
8.	salinity		Sea surface salinity measured by a SBE-45 thermosalinograph, on the Practical Salinity Scale
9.	pressure_atm        Barometric pressure from either onboard barometer, in hectopascals.  Average daily pressure was used to fill missing measurements.
10.	xCO2_w			Mole fraction of CO2 (dry) in equilibrator headspace at equilibrator temperature, in parts per million
11.	fCO2_w			Fugacity of CO2 in seawater, in microatmospheres
12.	xCO2_a			Mole fraction of CO2 (dry) in air, in parts per million
13.	fCO2_a			Fugacity of CO2 in air, in microatmospheres
14.	air_temp		Air temperature in degrees Celcius

The following fields have been Quality Controlled by the UNH Coastal Ocean Observing Center:
year
day_of_year
secDay
lat
lon
speed
Water_temp
Salinity
xCO2_w
fCO2_w
xCO2_a
fCO2_a

The following fields came at least partly from National Buoy Data Center data, and cannot be verified:
pressure_atm
air_temp

CO2 Analyzer: LI-840 (Li-cor Biosciences Inc, Lincoln NE).

Drying method:  Nafion selectively permeable membrane drying loop (Perma Pure, Toms River NJ) with
counter-flowing nitrogen stream.

Equilibrator type:  Three-chamber fast-rate equilibrator similar to that of Wanninkhof and Thoning (1993,
reference below), flow rate 1.5 l/min.  Note that equilibrator pressure was not measured.

CO2 calibration standards:  Two-point calibration using ultrapure nitrogen and a mixture of CO2 in
nitrogen.  Mixtures of CO2 in nitrogen, analyzed to within +/- 1%, were
obtained from Scott-Marrin Inc (Riverside, CA).  These standards are then adjusted based on comparison to
a series of standards ranging from 378-2584 ppmv obtained from NOAA/ESRL (http://www.esrl.noaa.gov/).

CO2 span concentration: 2588.9 ppm

Seawater temperature and salinity were measured using a SBE-45 thermosalinograph, pumped at 1.5 l/min.
The temperature offset listed in the header of the data file is the difference between the water 
temperature measured by the continuous-flow system (SBE-45, intake depth =~0.5m) and 
profiler package (SBE-49) water temperature at 0.5m.  This offset has been subtracted 
from the water temperature data in this file, and corrections to in-situ
temperature have been applied to the pCO2 data in this file.
Accuracy of the SBE-45 is verified to less than 0.005 degC.
Accuracy of the SBE-45 is verified to less than 0.005 salinity.
Accuracy of the SBE-49 is verified to less than 0.0003 degC.

CO2 data calculation: Corrections of the data for water vapor pressure and sea surface temperature and
conversion from pCO2 to the fugacity of carbon dioxide (fCO2) were carried out according to the DOE
handbook (2007).

CO2 data quality: all data, excepting those from 20040721, have been verified to an accuracy of +/- 2
mmol/mol or uatm.

References:

DOE (2007) Guide to Best Practices for Ocean CO2 Measurements, A.G. Dickson, C.L. Sabine and J.R.
Christian, eds.  PICES Special Publication, 191 pp.

Wanninkhof, R. and Thoning, K.  1993.  Measurement of fugacity of CO2 in surface water using
continuous and discrete sampling methods.  Marine Chemistry 44: 189-204.