Global trends in air-sea CO2 fluxes based on in situ and satellite

products

Rik Wanninkhof, NOAA/AOMLACE Ocean Productivity and Carbon Cycle (OPCC)

Workshop - June 6-8,UC Santa Barbara

Sea surface temperature(SST) Wind speed

CCMP (Cross-Calibrated Multi-Platform wind product)

[Atlas et al., 2011]

Sea-air CO2 Flux = K0 × k × ΔpCO2

Sea-air CO2 Flux = K0 × k × ΔpCO2

[Takahashi et al., 2009]

OPCCOPCC Global Ocean Sea-Air CO2 FluxesMethods:

ΔpCO2 climatologyk660 = 0.251 <u2>

Wind

k pCO2

Air-Sea CO2Flux

SST

Transport

BiologyWindWaves

BubblesSurfaceFilm

Near SurfaceTurbulence

Bock et al. (1999)

OPCCOPCC Global Ocean Sea-Air CO2 FluxesFactors influencing CO2 flux estimates

OPCCOPCC Global Ocean Sea-Air CO2 FluxesData coverage T-09 climatology

A Multi-national Effort:

EnglandUSAFranceNetherlandsGermanySpainChina JapanTasmaniaNorway

And more…

Complete Data Set: 1968–200810M points

Our contribution: 3M points

OPCCOPCC Global Ocean Sea-Air CO2 FluxesSurface Ocean Carbon Atlas (SOCAT)Surface Ocean Carbon Atlas (SOCAT)

OPCC OPCC Global Ocean Sea-Air CO2 FluxesRemote sensing

Wind: CCMP 6-hr ¼˚

k660 = 0.251 <u2> based on global 14C constraint

Gas transfer velocity

OPCC Global Ocean Sea-Air CO2 FluxesGlobal 14C constraint

Broecker and Peng (1994)

Transfer velocitykav = 17.5 cm/hru2 = 69.3 (m/s) 2

umean ≈ 7.4 m/s

Semi-infiniteHalf space

Bomb 14C inventory constraintGlobally: a <u2> = Constant

€

a = kav /∑[P(u)un ]

k = aun (Sc /660)−1 2

OPCC Global Ocean Sea-Air CO2 FluxesRelationship of k and U10

Good agreement with global bomb 14C constraint and local studies

Ho et al. 2011

Uncertainty in different components of the flux estimate (adapted from section 6, T-09)

Takahashi et al. (2009) RECCAP (2011)Pg C yr-1 % Pg C yr-1 % Pg C yr-1

Net flux -1.4 -1.2 ∆pCO2 ±0.18 ±13% ±0.18 k ±0.42 ± 30% ±0.2Wind (U) ±0.28 ± 20% ±0.2 <pCO2w/dt>a ±0.5 ± 35% ±0.5 Total ±0.7 ± 53%. ±0.6 Under-sampling bias -0.2 -0.2Pre-industrial sea-air flux 0.4 ± 0.2 0.4 ± 0.2Anthropogenic CO2 flux -2.0 ± 1.0 -1.8 ± 0.8

OPPCOPPC Sea-Air CO2 FluxesClimatological Magnitude and Uncertainty

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dpCO2 =∂pCO2

∂T

⎛

⎝ ⎜

⎞

⎠ ⎟dT +

∂pCO2

∂TCO2

⎛

⎝ ⎜

⎞

⎠ ⎟dTCO2 +

∂pCO2

∂TALK

⎛

⎝ ⎜

⎞

⎠ ⎟dTALK +

∂pCO2

∂S

⎛

⎝ ⎜

⎞

⎠ ⎟dS

Temperature (C) -2 –30 (ln pCO2/T) = 0.0423oC-1 400%

Variable Range Relation Effect

TCO2(mol kg-1) 1900-2200 (ln pCO2/Tln TCO2) = 10 400%

Alkalinity(mol kg-1)* 2150-2350 (ln pCO2/Tln TALK) = -9.4 -200%

Salinity(mol kg-1)* 33.5-37 (ln pCO2/Tln S) = 0.94 ~10%

*Alkalinity and salinity are proportional and can be accounted for

OPCC Global Ocean Sea-Air CO2 FluxesFactors influencing surface water pCO2

Annual uptake of anthropogenic CO2 since 1960 from models. The absolute uptake (solid line, left axis) has increased over time while the fraction of uptake (=ocean uptake/fossil fuel CO2 release *100) (dashed line, right axis) has decreased. Data are obtained from http://lgmacweb.env.uea.ac.uk/lequere/co2/carbon_budget.htm (Le Quéré et al., 2009).

OPPCOPPC Sea-Air CO2 Fluxes: Model and atm. based estimates of trends

OPCCOPCC Sea-Air CO2: Flux variabilityTrends

Fym = kym K0 ym {[ΔpCO2 2000m + (δpCO2SW / δSST)2000m × ΔSSTym – 2000m] },

(δpCO2SW / δSST)2000m : Optimal subannual relationships for each 4˚ by 5˚ grid box

Park et al. Tellus B 2010:Variability of global net sea-air CO2 fluxes over the last three decades using empirical relationships

The linear regressions (solid line) for the flux are 0.009± 0.005 Pg C yr-1, respectively. The 20-years mean values for the flux is -1.12± 0.13 Pg C, respectively.

Decrease in uptake due to winds and SST feedbacks

OPCCOPCC Sea-Air CO2 Fluxes Trends 1980-1999

Sea-air CO2 Flux = K0 × k × ΔpCO2

OPCC OPCC Global Ocean Sea-Air CO2 FluxesRemote sensing

How can we quantify the impact of [remotely measured] biological processes on ∆pCO2?

Regional approach Multi-sensor Melding in situ and remotely sensed information

Annual uptake of anthropogenic CO2 since 1960 from models. The absolute uptake (solid line, left axis) has increased over time while the fraction of uptake (=ocean uptake/fossil fuel CO2 release *100) (dashed line, right axis) has decreased. Data are obtained from http://lgmacweb.env.uea.ac.uk/lequere/co2/carbon_budget.htm (Le Quéré et al., 2009).

OPCCOPCC Sea-Air CO2 Fluxes: IPCC estimates

Figure 4. Zonal wind comparison of several global wind products for the year 2000. The differences of up to 2 m/s are observed but the biases are not always consistent between high and low latitudes. (Figure courtesy of C. Sweeney) .CCMP = Cross Calibrated Multi-Platform winds (Atlas et al., 2011); ECWMF =European Center for Medium Weather Forecasting; NCEP = National Center for Environmental Prediction; QSCAT = QuikSCAT polar orbiting satellite with an 1800 km wide measurement swath on the earth's surface equipped with the microwave scatterometer SeaWinds

OPCCOPCC Sea-Air CO2: Global Winds