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DETECTION OF ANTHROPOGENIC DIC IN THE OCEAN Keith Rodgers (Princeton) Jorge Sarmiento (Princeton) Anand Gnanadesikan (GFDL) Laurent Bopp (LSCE, France) Olivier Aumont (IRD, France) Yasuhiro Yamanaka (U. Hokkaido, Japan) Akio Ishida (FRCGC, Japan) Bob Key (Princeton) Nicolas Metzl (OCEAN, France) Masao Ishii (MRI, Tsukuba, Japan)

DETECTION OF ANTHROPOGENIC DIC IN THE OCEAN Keith Rodgers (Princeton) Jorge Sarmiento (Princeton) Anand Gnanadesikan (GFDL) Laurent Bopp (LSCE, France)

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DETECTION OF ANTHROPOGENIC DIC IN THE OCEAN

Keith Rodgers (Princeton)Jorge Sarmiento (Princeton)

Anand Gnanadesikan (GFDL)Laurent Bopp (LSCE, France)Olivier Aumont (IRD, France)

Yasuhiro Yamanaka (U. Hokkaido, Japan)Akio Ishida (FRCGC, Japan)

Bob Key (Princeton)Nicolas Metzl (OCEAN, France)

Masao Ishii (MRI, Tsukuba, Japan)

Repeat Hydrography: task would be far simpler if ocean circulation were steady (not time-varying)!

SCIENTIFIC QUESTIONS TO ADDRESS WITH MODELS:

(1) What is amplitude of natural variability on DIC in the ocean (on seasonal, interannual, and decadal timescales), and how does this compare to amplitude of anthropogenic signal?

(2) eMLR method of Friis et al.[2005] for identification of Anthropogenic DIC from Repeat Hydrography,and subsequent variations of that method: Do they account for dynamical component of signal?

C C C

C /t u C' u'C bio mixing...

Consider linear decomposition for tracer into time-mean and perturbation

Can then expand advection/diffusion equation for anomalies of tracer concentration

Questions regarding DIC: (1) Which terms are important where? (2) How large is highlighted term near “fronts”?

Three Models considered: all participated in European NOCES (Northern Ocean Carbon Exchange Study) Project

(1) Japan: FRCGC COCO-NEMURO (~1° res.)(2) Germany: MPI MPIOM1-HAMMOC (~3° res.)(3) France: IPSL ORCA2-PISCES (~2° res.)

All models were forced with NCEP reanalysis fluxes over 1948-2003;

Two runs conducted with each model: “REF” uses anthropogenic transient in atmospheric CO2 as boundary condition, and “CTL” maintains 280ppm boundary condition for atmospheric CO2

Anthropogenic DIC component: ANT = REF-CTL

DIFFERENCE IN INVENTORIES BETWEEN WOCE P17 (May/June 1993) AND CLIVAR P17 (July/August 2001)

For continuous monitoring of DIC along a transect, natural variability (ENSO, PDO, NAO, etc.) component can be larger than anthropogenic perturbation component

Implications: Need to identify mechanisms responsible for this natural variability in order to include correction term in e-MLR or double-MLR

Vertical Inventories of Oceanic DIC(moles/m^2)

Mechanisms? Relationship between variability ofNatural DIC and other variables (SSH, O2) for ORCA2-PISCES

C /t u C' u'C bio mixing...

For sea surface height (vertically integrated quantity), widely known that “highlighted” term for Density variations is dominant:

High correlation between SSH anomalies and natural DIC inventory anomalies strongly suggests that “highlighted” term is making first order contribution to DIC variability

Conclusions(1)Large “natural” variability in DIC introduces

significant aliasing problem over much of global ocean for detection of anthropogenic DIC (signal-to-noise problem) [increases with resolution]

(2)Natural variability in circulation (i.e. 1997/98 El Nino) can give changes in DIC inventories along section which are much larger than anthropogenic component.

(3)Need to use models to test whether skill of eMLR and other related methods can be improved (or errors can be reduced) through use of dynamical information

Implications/future work:

(1) Why can’t models can’t skillfully simulate changes in DIC at 135°W?: Could be due to limitations of NCEP windstress forcing fields, ocean circulation models, or biogeochemistry models?

(2) Test model-based result that DIC/O2 inventories and sea level height (SSH) are correlated

(3) Develop correction to eMLR method of Friis et al. [2005] which includes ocean dynamical component to improve detection skill:

DICssh_eMLR = DICeMLR + f(TOPEX SSH)

Year Period Longitude Latitude ship

Feb 16 - Mar 06 165E 30 N - 04 S RyofuMay 18 - May 24 165E 50 N - 32 N RyofuOct 14 - Nov 10 165E 45 N - 02 S RyofuJun 05 - Jul 11 165E 50 N - 30 N RyofuSep 17 Oct 14 165E 48 N - 02 S RyofuJun 16 - Jun 21 165E 50 N - 30 N RyofuSep 21 - Oct 17 165E 50 N - 03 S RyofuMay 15 - May 20 165E 50 N - 40 N RyofuSep 21 - Oct 17 165E 50 N - 03 S RyofuMay 08 - May 15 165E 48 N - 30 N RyofuSep 28 - Oct 18 165E 30 N - 03 S RyofuJan 27 - Feb 12 165E 20 N - 03 S KeifuMay 15 - May 19 165E 48 N - 35 N RyofuJul 10 - Jul 13 165E 48 N - 35 N RyofuOct 17 - Nov 06 165E 30 N - 03 S RyofuJan 25 - Feb 10 165E 20 N - 03 S KeifuMay 17 - May 22 165E 48 N - 30 N RyofuJul 11 - Jul 16 165E 50 N - 30 N RyofuOct 07 - Oct 30 165E 30 N - 06 S RyofuJan 20 - Feb 10 165E 30 N - 03 S KeifuMay 02 - May 06 165E 48 N - 37 N RyofuJun 27 - Jul 04 165E 50 N - 26 N RyofuJul 03 - Jul 22 165E 28 N _ 5 S KeifuJan 23 - Jan 10 165E 28 N - 05 S RyofuJun 14 - Jun 20 165E 50 N - 28 N RyofuJun 24 - Jul 13 165E 28 N - 05 S KeifuJan 24 - Feb 11 165E 27 N - 05 S RyofuJun 22 - Jun 28 165E 50 N - 28 N RyofuJun 23 - Jul 12 165E 28 N - 05 S Keifu

2004

2005

2000

1996

1997

1998

1999

2001

2002

2003

Japanese Repeat measurements along 165°E:(in collaboration with Ishii Masao)

Modeled DIC on 0=26.6 along 165°E over 1990-2003

Work in Progress: