MIRAI MR07-06 Leg1 Partial Pressure of CO2 (pCO2)

Vessel Name: Mirai

Vessel ID: JNSR

Country: Japan

Vessel Owner: JAMSTEC

Equilibrator type: Shower-head type equilibrator

Equilibrator volume (L): 1.2

Water_Flow_Rate (L/min): 5-8

Headspace_Gas_Flow_Rate (L/min): 0.6-0.8

Vented: During equilibrium, closed circulation of air. When measured by NDIR, vented to ambient air.

   Continuous underway measurements of atmospheric and surface seawater pCO₂ were made with the CO₂ measuring system (Nippon ANS, Ltd) installed in the R/V Mirai of JAMSTEC. The system comprises of a non-dispersive infrared gas analyzer (NDIR; BINOSR model 4.1, Fisher-Rosemount) or the variations, an air-circulation module and a showerhead-type equilibrator. To measure concentrations (mole fraction) of CO₂ in dry air (xCO₂a), air sampled from the bow of the ship (approx. 30 m above the sea level) was introduced into the NDIR through a dehydrating route with an electric dehumidifier (kept at ~ 2 °C), a Perma Pure dryer (GL Sciences Inc.), and a chemical desiccant (Mg(ClO4)2). The flow rate of the air was 500 ml min-1. To measure surface seawater concentrations of CO₂ in dry air (xCO₂s), the air equilibrated with seawater within the equilibrator was introduced into the NDIR through the same flow route as the dehydrated air used in measuring xCO₂a. The flow rate of the equilibrated air was 600 - 800 ml min-1. The seawater was taken by a pump from the intake placed at the approx. 4.5 m below the sea surface. The flow rate of seawater in the equilibrator was 500 - 800 ml min-1.

   The CO₂ measuring system was set to repeat the measurement cycle such as 4 kinds of CO₂ standard gases (Table 1), xCO₂a (twice), xCO₂s (7 times). This measuring system was run automatically throughout cruises by a PC control. Effects of water temperature increased between the inlet of surface seawater and the equilibrator on xCO₂s were adjusted based on Gordon and Jones (1973), although the temperature increases were slight, being ~ 0.5 °C at maximum.

Gordon, L. I. and L. B. Jones (1973), The effect of temperature on carbon dioxide partial pressure in seawater. Mar. Chem., 1, 317 - 322.

   Concentrations of CO₂ of the standard gases are listed in Table 1, which were calibrated by the JAMSTEC primary standard gases after 2000 (MR00-K01 and later). Before that time, the standard gases were calibrated against the scale of the Meteorological Research Institute, Tsukuba, Japan, and fitted to the 1985 World Meteorological Organization scale by using the equation of Inoue et al. (1995). The CO₂ concentrations of the primary standard gases were calibrated by C. D. Keeling of the Scripps Institution of Oceanography, La Jolla, CA, USA. The values are 230.33 ppm (Cyl. No. 11325), 259.74 (11326), 279.67 (11327), 308.93 (11328), 328.25 (11329), 348.79 (11330), 369.55 (11331), 389.54 (11333), 411.60 (11334), 440.94 (11335), 460.42 (11336), and 478.54 (11337).

   Since differences of concentrations of the standard gases between before and after the cruise were all allowable (< 0.1 ppmv), the averaged concentrations (Table 1) were adopted for the subsequent calculations.

Table 1. Concentrations of standard gases used in individual cruises.

Cruise #	STD1	STD2	STD3	STD4	Remark
MR98-06	-	-	-	-	No records left
MR98-K01	270.28	330.95	360.48	410.85
MR99-K02	270.28	330.95	360.48	410.85
MR99-K04	270.26	330.98	360.43	410.85
MR99-K05	247.74	304.98	333.32	382.57
MR00-K01	329.71	359.17	409.39	439.94
MR00-K03	269.60	329.71	359.17	439.94
	269.60	329.71	359.17	409.39
MR00-K06	246.95	305.13	333.44	382.74
	305.13	333.44	382.74	409.40
MR01-K02	269.60	329.74	359.22	409.39
MR01-K03	269.60	329.74	359.22	409.39
MR01-K04 Leg1	298.56	321.17	370.75	439.95
MR01-K04 Leg2	298.56	321.17	370.75	439.95
MR01-K05 Leg1-2	247.99	298.56	321.17	370.75
MR01-K05 Leg3-4	247.99	298.56	321.17	370.75
MR02-K03	269.20	329.52	359.11	408.76
MR02-K05 Leg1	246.69	297.83	320.05	391.66
MR03-K01	270.16	340.21	371.39	389.97
MR03-K02	270.08	328.87	359.10	409.23
MR03-K04 Leg1	270.08	328.87	359.10	409.23
MR03-K04 Leg2	270.08	328.87	359.10	409.23
MR03-K04 Leg4	270.08	328.87	359.10	409.23
MR03-K04 Leg5	268.84	330.16	369.37	414.39
MR04-04	268.85	328.87	369.39	414.43
MR04-05	268.84	330.16	369.37	414.39
MR05-02	262.94	320.42	381.04	420.76
MR05-05 Leg1	262.94	320.42	381.04	420.76
MR05-05 Leg2	262.94	320.42	381.04	420.76
MR05-05 Leg3	262.94	320.42	381.04	420.76
MR06-04 Leg1	289.76	349.00	393.75	439.72
MR06-04 Leg2	289.76	349.00	393.75	439.72
MR07-04	289.77	349.02	393.77	439.75
MR07-05	289.77	349.02	393.77	439.75
MR07-06 Leg1	270.02	330.40	369.28	419.68
MR07-06 Leg2	270.02	330.40	369.28	419.68
MR09-01 Leg1	270.22	330.43	360.04	420.32
MR09-01 Leg2	270.22	330.43	360.04	420.32

Inoue, H. Y., H. Matsueda, M. Ishii, K. Fushimi, M. Hirota, I. Asanuma, and Y. Takasugi (1995), Long-term trend of the partial pressure of carbon dioxide (pCO₂) in surface waters of the western North Pacific 1984 - 1993. Tellus 47B, 391 - 413.

Manufacturer: Rosemount Analytical

Model: BINOS 4.1

Resolution: -

Uncertainty: -