M/V Atlantic  Companion cruise:		COM_11_17

This work was supported through EU FP7 project CARBOCHANGE “Changes in carbon uptake and emissions by oceans in a changing climate”  which received funding from the European Community’s Seventh Framework Programme under grant agreement  no. 264879.

Initial submission:		2012
Most recent update:		25. June 2012

Date of cruise (dd/mm/yyyy):	18.10. – 23.10.2012
Geographic coverage: 		48°N, 8°W – 44°N, 63°W
Ports of call: 			Liverpool, UK - Halifax, Canada

Vessel name:	M/V Atlantic Companion
Vessel ID:	SKPE
Country:	Sweden
Owner:		Atlantic Container Lines

PI:		Tobias Steinhoff
		GEOMAR | Helmholtz Centre for Ocean Research
		Duesternbrooker Weg 20
		24105 Kiel
		Germany
		tsteinhoff@geomar.de

Citation: 	Steinhoff, T. and Körtzinger, A. (2011). 
		Underway fCO2 measurements in the North Atlantic Ocean on 
      M/V Atlantic Companion in October 2012.

Reported  variables:
(1-3)	Year|Month|Day		date
(4-6)	Hour|Minute|Second		time (UTC)
(7)	Day of year			decimal year day
(8)	Longitude [deg E]		Longitude in decimal degrees E
(9)	Latitude [deg N]		Latitude in decimal degrees N
(10)	SST [deg C]			Sea surface temperature in deg C
(11)	SSS				Sea surface salinity 
(12) 	Atm. Pressure [mbar]		Atmospheric pressure in mbar
(13)	Equi Temp [deg C]		Water temperature inside the equilibrator in deg C
(14)	Equi Press [mbar]		Pressureinside the equilibrator in mbar
(15)	xCO2 (equi temp, dry) [ppm]	mole fraction of CO2 in the equilibrator 
      headspace (dry) at equilibrator  temperature in ppm	
(16)	pCO2 (SST, 100hum) [uatm]	partial pressure of CO2 in seawater at SST and
      100% humidity in µatm
(17)	fCO2 (SST, 100hum) [uatm]	fugacity of CO2 in seawater at SST and
      100% humidity in µatm
(18)	Atm. xCO2 (dry) [ppm]		mole fraction of CO2 of atmospheric air in ppm
(19)	Atm xCO2 (dry, running mean) [ppm]	same as 18 but with a running mean (700 minutes) to 
						interpolate between measurements.

Instrument information:
- GPS position:
the GPS signal was not recorded during this cruise. The bridge records the position in 6-hour intervals. Thus the position for the measurements was calculated by linear interpolation inbetween the ships position records.

- SST (+- 0.05 deg C):
SST was measured with a thermosalinograph from Seabird (SBE21) with an external SBE38 which was installed approximately 30 cm after the seawater intake. Both instruments were calibrated approximately every 6 months.

SSS (+- 0.3 PSU):
SSS was lower than expected, what might be due to dirt in the salinity cell of the Seabird SBE21 thermosalinograph. The measured data were compared to the data of the World Ocean Atlas (2009). A linear correction was applied to calculate corrected SSS data:
SSS(corr) = 0.99178 * SSS(SBE21) + 1.25

-Atmospheric press. (+- 0.1 mbar):
No atmospheric pressure data were available. During former cruises the relationship between cell pressure (inside the Licor) an dteh atmospheric pressure next to the instrument was estimatedt to be 0.3+-0.05 mbar. Thus 0.3 mbar were subtracted from the cell pressure to calculate the atmospheric pressure.

-Equilibrator temp (0.05 °C):
The temperature probe inside the equilibrator was compared to the SBE38 every 3 months.

-Equilibrator press (+- 0.1 mbar):
Differential measurement. The pressure outside the equilibrator was measured by a SETRA preesure transducer (Model 270), installed next to the equilibrator. Pequ = P(outside) + Pequ(differential).

-pCO2/fCO2 (+- 3µatm):	
	IR sensor:		Licor 7000, calibrated with 3 standard gases.
	Standard gases:		Deuste Steininger (249.3, 350.1, 450.2 ppm), calibrated against 
      NOAA/CMDL standard gases. Resulting uncertainty: +- 0.5 ppm.
	Water flow rate: 	2-3 L min-1
	Gas flow rate:		100 mL min-1

A so-called Neill system was used for pCO2 measurements. The system is described in detail in Pierrot (2009). The instrument is installed next to a sea chest which is used only for the pCO2 instrument.  Directly after the inteake a SBE38 thermometer is installed. The water is pumped continuously (by a torque flow pump) from the intake to the equilibrator passing through a SBE21 thermosalinograph. The equilibrator contains a water spray head, and as the water flows through it the dissolved CO2 equilibrates with the headspace. The headspace is dried and xCO2 is determined by an infrared sensor. Calculations were performed following Pierrot (2009) and are described in detail in Steinhoff (2010). 


References:
Pierrot, D., Neill, C., Sullivan, K., Castle, R., Wanninkhof, R., Lüger, H., Johannessen, T.,
Olsen, A., Feely, R. A., and Cosca, C. E. (2009). Recommendations for autonomous underway
pCO2 measuring systems and data reduction routines. Deep-Sea Res. II , 56, 512_522.

Steinhoff, T. (2010). Carbon and nutrient fluxes in the North Atlantic Ocean. Dissertation. http://eldiss.uni-kiel.de/macau/receive/dissertation_diss_00005704

World Ocean Atlas (2009): http://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html