Methane and other trace gases: NIWA measurements

Keith Lassey

NIWA, Wellington, New Zealand.(k.lassey@niwa.co.nz)

Asia-Pacific Workshop on Carbon-Cycle ObservationsNIES, Tsukuba, Japan, 17–19 March 2008

on behalf of: Tony Bromley, Ross Martin, Gordon Brailsford, Rowena Moss, Kim Currie, Bill Allan, Dave Lowe

Trace gas sampling programme

• Baseline levels of trace gases at Baring Head, Wellington:

CO2 (since 1972), CH4 (since 1989), CO (since 1989), N2O (since 1996), O2/N2 (since 1999)13C, 14C in above, and 18O in some of above

• Baseline levels of some gases/isotopes at Scott Base, Antarctica

• Trace gases/isotopes in shipboard air samples (NZ to Japan), since May 2004

• pCO2 , etc, in sub-Antarctic surface water

41°S

Baring Head

Baring Head

Wellington

Nelson

Baring Head CO2

• monitoring commenced in Dec 1972 in cooperation with C.D. Keeling, Scripps

• measured continuously in situ by NDIR

• longest-running continuous station in SH, next longest in world after Mauna Loa

• inter-calibrated with Scripps & NOAA

• complemented in 1998 by δ13C measurements (continuous flow: D. F. Ferretti)

• complemented in 1999 by O2 measurements (paramagnetic analyser: A. C. Manning)

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

310

320

330

340

350

360

370

380

390

CO

2 (p

pm)

Mauna LoaBaring Head

Baring Head & Mauna Loa CO2

Acknowledgement: Scripps Institution of Oceanography

Features (SH vs NH):• Much smaller seasonal amplitude

(more demands on precision) due to less biosphere in SH

• Lower [CO2 ] due to NH-dominated anthropogenic sources

Baring Head CO2

• Dataset largely under-utilised in global carbon-cycle studies

• Data (not just CO2 ) submitted to World Data Centre for Greenhouse Gases (Tokyo)

• Reported strongly in IPCC 4th Assessment Report (Dave Lowe, Lead Author, Chapter 2)

• Data used in recent study of the Southern Ocean as a CO2 sink [Le Quéré et al., 2007]

Le Quéré, C. et al. (2007). Science 316: 1735–1738.

Baring Head 14CO2

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

-100

010

020

030

040

050

060

070

0

Δ14C

O2

(pm

C)

“Bomb-14C pulse”

Baring Head Δ14CO2

• Visionary commencement of measurements, pre-dating the “bomb-14C pulse”

• Near-unique and valuable dataset:long-term evolution of Δ14CO2 critical to carbon-dating calibration [eg, Hua & Barbetti, 2004]

response of C reservoirs to bomb-14C injection pivotal to understanding C-cycling [eg, Lassey et al., 1996; Peacock, 2004]

Hua, Q.; Barbetti, M. (2004). Radiocarbon 46: 1273–1298.Lassey, K.R. et al. (1996). Tellus 48B: 487–501.Peacock, S. (2004). GBC 18: GB2022,

pCO2 time series along a sub-Antarctic surface transect

STF

SAF

SASW

Subtropical water

SASWMay SSTs

Attribution: Work of Kim Currie et al.transect

pCO2 time series along a sub-Antarctic surface transect

SASW

‘Munida’ time series since 1998, led by Kim Currie

Measurements of:• temperature• salinity• pCO2• pH• alkalinity• etcbi-monthly since 1998

RV Polaris (Munida replacement)

⎟⎠⎞

⎜⎝⎛ −

+=365

3172sin1.23.10 tT π

SASW Seasonal Cycles

⎟⎠⎞

⎜⎝⎛ −

+=365

1562sin103552tpCO π

⎟⎠⎞

⎜⎝⎛ −

+=365

1382sin9.12.123tNO π

6

8

10

12

14

16

1998 1999 2000 2001 2002 2003 2004 2005

Tsw

/ oC

3 20

3 30

3 40

3 50

3 60

3 70

3 80

19 9 8 19 9 9 2 0 0 0 2 0 0 1 2 00 2 20 0 3 20 0 4 2 0 0 5

pCO

2 / Η

atm

7.75

7.8

7.85

7.9

7.95

8

1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

pH (2

5 oC

)

02468

101214161820

1998 1999 2000 2001 2002 2003 2004 2005

[NO

3] /

mm

ol m

-3

⎟⎠⎞

⎜⎝⎛ −

+=365

1622sin05.0869.7 tpH π

No

indi

catio

n of

a tr

end!

SASW Air-Sea flux of CO2SASW C O 2

330

340

350

360

370

380

Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05

pC O 2swpC O 2air

SASW Flux and �pCO2

-10-8-6-4-2024

Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05-60

-40

-20

0

20

40

60fluxDpCO2

ΔpCO2

Baring Head CH4 and δ13C(CH4 )

• monitoring of δ13C(CH4 ) commenced in 1987; [CH4 ] commenced in 1989

• [CH4 ] measured by GC/FID, δ13C(CH4 ) by IRMS, on grab samples

• inter-calibrated with recognised standards

• [CH4 ] complements NOAA record; δ13C(CH4 ) arguably the best record globally

Baring Head CH4

1989 1991 1993 1995 1997 1999 2001 2003 2005 2007

Year

1650

1670

1690

1710

1730

1750

1770

CH

4 (p

pb)

CH4 plateaued?

CH4 rising again?

CH4 mini-plateau?

Baring Head δ13C(CH4 )

1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007

Year

-47.

5-4

7.4

-47.

3-4

7.2

-47.

1-4

7-4

6.9

-46.

8-4

6.7

δ13C

H4

(‰)

what happened here?

CH4 “stable”?

An important chlorine sink for CH4 ?

• Upper plot:composite seasonality of [CH4]

• Centre plotcomposite seasonality of δ13CH4

• Lower plot:[CH4] vs δ13CH4: “phase ellipse”Slope of ellipse axis determined by isotope fractionation in sinkDash-dot line corresponds to ‘accepted’ fractionation of 5.4‰Actual slope ⇒ fraction’n ~13‰

Allan, W. et al. (2001). GBC 15: 467-481.Allan, W. et al. (2007). JGR 112: D04306.

Source: Allan et al. (2001)

An important chlorine sink for CH4 ?

• Why is sink fractionation as high as ~13‰? (OH sink has fractionation ~5.4‰ or less)

• Likely answer: role by active Cl (fractionation ~60‰)

• Allan et al. (2007) argue that a Cl sink that removes 13–37 TgCH4 /yr globally can account for observations

• Cl sink absent from current global budgets

Allan, W. et al. (2001). GBC 15: 467-481.Allan, W. et al. (2007). JGR 112: D04306.

Source: Allan et al. (2001)

Ship voyages, Nelson (NZ) to Osaka

Shipboard measurements

• transect: 41.3°S, 174.3°E to 34.7°N, 135.5°E • 8 voyages on two bulk-carrier vessels*, May

2004 to May 2007• collect dried air samples every 2.5° between

latitudes –20° to +20°, every 5° elsewhere• record meteorology at time of sampling• analyse samples in NIWA laboratory for:

CH4, 13CH4, CO, 13CO, 14CO, C18O

• measure real-time CN densities• 24-hr particulate aerosols (hi-vol filtration)

* Vessels Fujitrans World then Transfuture 5, Toyofuji Shipping Company Ltd, Nagoya

Shipboard CO• Inter-comparisons of CO:

3 voyages, Dec – early Jan4 voyages in May (but CO unavailable for May 2007)

• approx. NH seasonality:peak ~150ppb in Martrough ~90 ppb in Aug

• approx. SH seasonality:peak ~60ppb in Septrough ~40 ppb in Feb

• Note inter-annual variability north of ~10°S

CO Dec Jan

0

50

100

150

200

-32 -24 -16 -8 0 8 16 24 32

Dec 04 Dec 05 Jan 07

CO May

0

50

100

150

200

-32 -24 -16 -8 0 8 16 24 32

May 04 May 05 May 06

Shipboard CH4 and δ13C(CH4 )

CH4 Dec Jan

1700

1720

1740

1760

1780

1800

1820

1840

1860

1880

1900

-32 -24 -16 -8 0 8 16 24 32

Dec 04 Dec 05 Jan 07

CH4 May

1700

1720

1740

1760

1780

1800

1820

1840

1860

1880

1900

-32 -24 -16 -8 0 8 16 24 32

May04 May05 May 06 May07

13CH4 Dec Jan

-47.5

-47.4

-47.3

-47.2

-47.1

-47

-46.9

-32 -24 -16 -8 0 8 16 24 32

Dec 04 Dec 05 Jan 07

13CH4 May

-47.5

-47.4

-47.3

-47.2

-47.1

-47

-46.9

-32 -24 -16 -8 0 8 16 24 32

May04 May05 May 06 May 07

Why the NZ focus on CH4 ?The NZ GHG emission inventory (shown for 2004):• approx 50% CO2 , 50% agricultural GHGs

— highest ag. component of all developed countries• 2/3 of ag. GHGs are CH4 from ruminant livestock• ruminant CH4 has no known abatement prospects

SF60.03%

PFCs0.12%

HFCs0.80%N2O

17.2%

CO245.6%

CH436.2%

Acknowledgements

• NIWA colleagues, both past and present, for their foresight and skill

• Logistical and technical support from NIES (Prof. Yukihiro Nojiri et al.)

• Opportunities, facilities and hospitality aboard vessels of Toyofuji Shipping Company Ltd

• Funding: NZ Foundation for Research, Science & Technology

• Co-funding: NOAA GCOS programme

Thank you