Quantifying the Mechanisms Governing Interannual Variability in Air-sea CO2

FluxS. Doney & Ivan Lima (WHOI), K. Lindsay & N. Mahowald (NCAR), K. Moore (UCI) & Matt Maltrud

(LANL)Global Ocean Hindcast Simulations (1958-

2004)-Upper ocean multi-functional group, multi-nutrient ecosystem model (Moore et al., 2004) -Coupled to full-depth ocean BGC model (CCSM-POP)-Surface forcing (1957-2004) from NCEP reanalysis and satellite products-Fixed pre-industrial atmospheric CO2 (~280 ppm) & transient anthropogenic CO2 simulations

Physical & Biological Controls

pCO2 = f(Temp., Salinity, DIC, Alkalinity) + (+) + -

Net Community Prod.

Winter mixed layer

Circulation

Light

Nutrient/DIC Supply

Export

Winds, Heat & Freshwater Fluxes Dust/iron CO2 O2

Remineralization

Regenerated Prod.

Biology only one factor on surface pCO2 & air-sea CO2 flux;

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Ocean Model Hindcast (1957-2004)

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′ F CO2 = ′ k < ΔpCO2 > + < k > ΔpC ′ O 2

Factors driving interannual pCO2 anomalies: Wind Speed

Alk

TempnDIC

Freshwater

W. Eq. Pacific

1:1

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pC ′ O 2 =∂pCO2

∂T′ T +

∂pCO2

∂DICnDI ′ C +

∂pCO2

∂AlknAl ′ k +

∂pCO2

∂S(DIC ,ALK ,s)

′ S

Regression of surface pCO2 anomalies on forcing terms

~1 driving term 0 minor term<0 compensating term

Masked in areas of low pCO2’ and low correlation

Dissolved Inorganic Carbon

Temperature

Alkalinity

Freshwater

Regression of surface pCO2 anomalies on forcing terms

~1 driving term 0 minor term<0 compensating term

Masked in areas of low pCO2’ and low correlation

Q’

I

A’

V’

E’

0

100

Annual inventory change & flux anomalies X’:I/t = Q’ srf. flux + A’ horz. advection + E’ eddies + V’ vert. adv. + P’ net comm. prod. + other P’

Dust Only

Dust Only

Physics Only

Physics Only

Dust & Physicsr=0.48

SeaWiFS

Physicsr=0.11

Dustr=0.82

Smoothed w/annual filter

Monthly

Annual

-Models as tools for identifying ocean biogeochemical mechanisms-Regional partitioning of factors driving air-sea CO2 flux

•Southern Ocean wind speed variability •Subtropics thermal•Tropics/high latitude biology and circulation on nDIC•Tropical Indo-Pacific freshwater

-Non-linear interactions of dust and climate variability

Is low dust deposition downwind of Australia in 1997/1998 realistic? Tentative answer: yes

Chen et al. precip slightly above average for 1997 and 1998

All values are anomalies from climatological mean (1979-2004): black monthly: Yellow line: 0: blue line: annual mean

Two met stations close to source area: 946720 and 944820 have fewer dust events than average in 1997 and 1998

Low dep due to low source

Low dep due to high precip

Model Obs

Dust & Physicsr=0.60

SeaWiFS

Physicsr=0.56

Dustr=0.71

Monthly anomalies