Core Theme 1: surface fluxes

• WP 4: The North Atlantic observing system

• WP5: The Southern Ocean

• WP6: modelling and synthesis

• (WP7: mooring development; discontinued)

WP4: North Atlantic observing system

Ongoing data collection and synthesis of fluxes

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Jul-Aug Nov-DecSep-Oct

Data coverage in two-month intervals, 2005

Constructing basin-wide fluxes

• For each pCO2 measurement, assign SST, mixed layer depth, (chlorophyll, position)

• Find pCO2 as a function of these variables using – multiple linear regression– Neural network

• Interpolate to generate a pCO2 map for the whole area

• Calculate fluxes

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MLR estimates of pCO2 field for each month usingindependent variables SST, MLD and longitude, in 20° latitude bands

Jan Jan Mar Apr

JunMay Jul Aug

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50 to 65 N

JFMAMJ

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lux

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2005 fluxes by season and latitude band

CO2 fluxes into the North Atlantic

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CO2 fluxes into the North Atlantic – 1994/5 to 2005(Wanninkhof 1992 gas exchange)CO2 fluxes into the North Atlantic

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Takahashi 1995 climatology

Carbo-ocean 2005

Cavassoo – era (approx)

What is the uncertainty on pCO2sw?

• Calculate semi-variograms of the residuals from the multiple linear regressions

• Where – r are the residuals from the model – N(h) is the set of pairs of observations i, j, that are a

separated by a distance h.

2

,

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( ) i ji j h

h r rN h

Omni-directional Variograms of residuals

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model

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model

171(1-exp(-x/6.6))

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pCO

2 va

rianc

e (μ

atm

2 )Uncertainty continued…

Separation (Degrees of latitude)

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orre

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ngth

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Variance of decorrelated data

Uncertainty continued….

• The number of degrees of freedom in the estimation problem is n ~A/x2

where A is the area of the North Atlantic and x is the decorrelation length obtained from the semi-variograms.

• An upper limit on the variance, σ2, of pCO2 about the regressions is given by the sill (amplitude) of the variograms.

• The 1-σ uncertainties on mean pCO2 for the region as a whole is given by

= ~0.8 μatm using the summer variogram, or 1.5 μatm using the winter variogram. These represent ~6% or ~10% errors on ΔpCO2 (air-sea difference).

• A more careful calculation gives overall 1-σ uncertainty of 6% on fluxes from this source.

2

n

N.Atlantic air-sea fluxes with unprecedented accuracy and

resolution• We obtain pCO2 for the entire region (10°-65°N) by

relating CO2 to SST, mixed layer depth, using regressions and/or neural nets

• Fluxes are derived with ~10° spatial resolution and seasonal-to-monthly time resolution.

• The precision is 6% (1-σ) for the NA annual flux – (calculated using geostats theory or data gap analysis) -- much better than for any other comparable region in the world.

• In combination with atmospheric inversions should enable greatly improved estimates for adjacent land sinks.

WP5: Southern Ocean air-sea CO2 fluxes:From Weddel sea to open ocean areas

N. Metzl, OISO10, Jan 2003

CARIOCA measurements

Synthesis of 65 months of CARIOCA measurements:

- SAZ strong sink (-0.8PgC yr-1) contrary to PZ (-0.1PgC yr-1)–Seasonal variation of DIC in SAZ (~30mol kg-1)–North-South increase of DIC and fCO2 in winter between Subtropical front and Subantarctic front

Boutin et al, submitted, 2007

Trend atmosphere: + 1.72 µatm/yrTrend ocean: + 2.11 µatm/yr

Ocean sink decreases ?

(Metzl, 2007 sub.)0,0

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Ocean pCO2 trend between 1991 and 2007

Atm. trend

Summer Winter

(December 2002-January 2003)

AWBAntarctic ice shelf

Ridge

Rapid transition from ice covered CO2–rich waters to a biologically mediated sink

in the eastern Weddell Gyre

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24 December 2002

Ice Cover (blue=open water)

(Bakker and Hoppema, in prep.)

Neural nets: Poster, Maciek Telszewski and colleagues

IFM-GEOMAR

COCO22 Gas Exchange Rates from Gas Exchange Rates from

Inversion of Water Column DataInversion of Water Column DataR. Schlitzer, J. Schneider, Alfred Wegener Institute, Bremerhaven

1. Pre-industrial, annual mean CO1. Pre-industrial, annual mean CO22 Fluxes Fluxes

2. Seasonal CO2. Seasonal CO22 Fluxes Fluxes

Approach:Approach:•Use tracer calibrated model (CFC, radiocarbon, etc.; Schlitzer, 2007)Use tracer calibrated model (CFC, radiocarbon, etc.; Schlitzer, 2007)

•Determine CODetermine CO22 fluxes by fitting to ocean interior DIC data fluxes by fitting to ocean interior DIC data

Results:Results:•Outgasing in tropics, ingassing in subtropics. As in Takahashi Outgasing in tropics, ingassing in subtropics. As in Takahashi (1999) and other studies.(1999) and other studies.

•Net outgasing in Southern Ocean (not seen in Takahashi, 1999 or Net outgasing in Southern Ocean (not seen in Takahashi, 1999 or OCMIP II models): 0.6 PgC yrOCMIP II models): 0.6 PgC yr -1 -1 south of 50°S.south of 50°S.

•Near-zero pre-industrial interhemispheric C transport by ocean.Near-zero pre-industrial interhemispheric C transport by ocean.

Takahashi 1999Takahashi 1999

Investigation of the effect of varying strength and timing of Investigation of the effect of varying strength and timing of biological production on monthly CObiological production on monthly CO22 fluxes fluxes

See poster of Judit Schneider.See poster of Judit Schneider.

Assimilation of pCO2 data into an obgc model: progress

• Assimilation of pCO2 surface data into Met office FOAM model using Hadley centre OBGCM is ongoing.

• Operational system assimilates SST, SSH, ARGO… • Assimilation of ocean colour with biogeochemical code• Additional nudge of DIC/ALK using ocean pCO2 data.• The system in testing phase but work delayed by other

priorities in 2007. It is planned to re-start the work in the first few months of 2008.

Surface fluxes: progress

• High precision estimates of North Atlantic flux.• Progress in characterizing the Southern Ocean

using measurements and models: observations of a decreasing flux?

• New techniques for constraining fluxes: neural nets, ocean inversions

• Progress in assimilating carbon measurements into ocean biogeochemical models.