INTERANNUAL VARIABILITY OF PRIMARY PRODUCTION AND

CARBON FLUXES ALONG THE U.S. EASTERN CONTINENTAL SHELF:

IMPACT OF ATMOSPHERIC FORCING?

INTERANNUAL VARIABILITY OF PRIMARY PRODUCTION AND

CARBON FLUXES ALONG THE U.S. EASTERN CONTINENTAL SHELF:

IMPACT OF ATMOSPHERIC FORCING?Bronwyn Cahill1,2, Katja Fennel3 & John Wilkin2

1Informus GmbH, Berlin, Germany2Institute of Marine and Coastal Science, Rutgers University, USA

3Dept of Oceanography, Dalhousie University, Canada

COASTAL CARBON FLUXES ALONG THE

U.S. EASTERN CONTINENTAL SHELF: U.S. ECOSU.S. ECoS Team

Marjorie Friedrichs (VIMS); Eileen Hofmann (ODU); Bronwyn Cahill (Rutgers University); Cathy Feng (VIMS); Kim Hyde (NOAA NMFS);

Cindy Lee (Stony Brook); Antonio Mannino (NASA GSFC)Ray Najjar (Penn State);Sergio Signorini (NASA GSFC)

Hanqin Tian (Auburn University); Dan Tomaso (Penn State);Yongjin Xiao (VIMS); Jianhong Xue (VIMS);

Qichun Yang (Auburn University); John Wilkin (Rutgers University)

Global distribution of annual sea-air CO2 flux measurements gC m-2 yr-1

(Cai et al, 2006)

Regional differences in continental shelves’ potential to be a source or sink for atmospheric CO2 Important to view regions as distinct provinces (Cai et al

2006, Borges et al, 2005).

1. Evaluate continental shelf carbon cycling processesincluding: biological processes; air sea exchange of CO2; exchange at shelf break; exchange at land-ocean interface; burial

2. Examine sensitivity of these processes to variability in: river discharge, nutrient loadings, freshwater inflow,

precipitation, ocean/air temperature, winds

U.S. ECoS Research Objectives:

evaluation

assimilation

SatelliteSatelliteDataData

In situIn situDataData

CoupledCoupledBGC/CircBGC/Circ

ModelModel

CoastalCoastalCarbonCarbonFluxesFluxes

Climate/Climate/Land-UseLand-UseChangesChanges

LandLandEcosystemEcosystem

ModelModel

evaluationassimilation

OBJECTIVES• Inter-annual variability of primary production

and air-sea CO2 flux in three sub-regions of US east coast continental shelf.

• Investigate sensitivity of air-sea CO2 flux to perturbations in atmospheric forcing.

• Identify the important processes responsible for producing year to year changes in air-sea CO2 flux.

Coupled Biogeochemical Circulation Model: NENA(NorthEast North American shelf)

SAB

MAB

GOM

Spring Chl (mg m-3)

ROMS dx ~10 km horizontal resolution; 30 layers (sigma coord); ~3.7 min time-step

Forcing Bulk formulae (Fairall et al., 2003) applied to sea surface.NCEP NARR 3-h fieldsPAR(0) = 0.43SWRAD; PAR(z)= f(chl(z))

BC & IC 5-day averages HYCOM (Chassignet et al., 2007) output along boundaries for physics; barotropic tides (Egbert & Erofeeva, 2002); NODC climatology for NO3; TIC and ALK based on Lee et al. (2000) and Millero et al. (1998) 30 river inputs based on climatology derived from USGS freshwater gauge data and total nitrogen in nitrate pool (Howarth et al., 1996)

Biology Fasham-type (Fennel et al., 2006; 2008; 2009) nitrogen cycle model with explicit sediment denitrificationOneway coupling

Carbon model

OCMIP standard for carbonate systemWanninkhof (1992) for gas exchange

NENA Model Specifications

Key Biological Model Properties: •Nitrogen dynamics (Fennel et al., 2006); Carbon dynamics (Fennel et al., 2008)•DOM dynamics (Druon et al., 2010; J. Xue)•Multiple P/Z (in development Y. Xiao)•OCMIP standard for carbonate system•Wanninkhof (1992) gas exchange

X X X

X

XX X

X

2 CASE STUDIES“Present” “Future”

Atmospheric Forcing

NCEP-NARR 3-h fields:

TAIR, PAIR, QAIR, RAIN, SWRAD, LWRAD, UWIND, VWIND

Added anomalies to NCEP-NARR fields.

Atmospheric anomalies derived from two 10-year

simulations of RegCM3 model (Chen et al., 2003)

representing present and end of century (doubled) CO2 levels, forced by 100 year

transient run of NCAR climate system model

Time Period 2004 to 2007 2004 to 2007

Future scenario characterized by ~ 2oC air temperature increase

Higher Precipitation and SWRAD in Spring / Summer

FUTURE - PRESENT

2004 2005

2006 2007

S N alongshore decrease in wind speed

WINTER SPRING

SUMMER FALL

Model vs. Satellite SST

Subregions:

Satellite-model statistical comparisons

Hofmann et al., 2011

satellite SST

NENA1

NENA2

satellite

NE

NA

diffce

diffce

Taylor/Target diagrams evaluation

(Jolliff et al., 2008)

Hofmann et al., 2008, 2011, Druon et al., 2010

Model evaluation with satellite data

But how do we evaluate carbon fluxes?

Model shows reasonable comparison to in situ PP data, considering variability involved

NENA annualprimary

productivitygC m-2 yr-1

in situ dataNENA

PresentNENA Future

GOM 220 (Balch et al., 2008) 355±36 399±32

MAB 310 (O’Reilly et al., 1987) 245±21 238±21

SAB 320 (Menzel et al. 1993) 217±21 214±16

annual PPgC m-2 yr-1

We generally need to examine in situ data

“PRESENT”

“FUTURE”

Positive ocean is a sink of CO2

Negative ocean is a source of CO2

AIR-SEA CO2 FLUXES

SOME CHARACTERISTICS:• Generally acts as a sink• Clear alongshelf gradient• Interannual variability• Regional differences• “Future” – shift in position of alongshore gradient

GOM NENA 1.4 sea-air CO2 fluxes 2004 to 2007 & VDK et al., 2011

2004

2006

2005

2007

NENA NET ANNUAL FLUX: -1.77 MOL C M-2 Y-1; VDK ET AL., 2008 NET ANNUAL FLUX: 0.34 MOL C M-

2 Y-1

VDK et al., 2011, observations from

2004 to 2008

CAHILL ET AL., IN PREP

GOM NENA 1.4 pCO2 2004 to 2007 & VDK et al., 2011

2004

2006

2005

2007

VDK et al., 2011, observations from

2004 to 2008

SPRING AUTUMNCAHILL ET AL., IN PREP

GOM NENA 1.4 & NENA 4.1 Sea-Air CO2 Flux & pCO2 2004 to 2007

PRESENT NET ANNUAL FLUX: -1.77 MOL C M-1 Y-

1

FUTURE NET ANNUAL FLUX: -1.74 MOL C M-2 Y-1

SPRING AUTUMNCAHILL ET AL., IN PREP

MAB NENA 1.4 sea-air CO2 fluxes 2004 to 2007 & Takahashi et al., 2009

2004

2006

2005

2007

NENA NET ANNUAL FLUX: -1.2 MOL C M-2 Y-1; TAKAHASHI ET AL., 2009: -1.84 MOL C M-2 Y-1

Takahashi et al., 2009

“VARIOUS” OTHER ESTIMATES: -0.6 to -1.7 MOL C M-2 Y-1 (Fennel et al., 2008, Previdi et al., 2008, DeGrandpre et al., 2002)

CAHILL ET AL., IN PREP

MAB NENA 1.4 pCO2 2004 to 2007 & Takahashi et al., 2009

2004

2006

2005

2007

SPRING AUTUMN

Takahashi et al., 2009

CAHILL ET AL., IN PREP

MAB NENA 1.4 & NENA 4.1 Sea-Air CO2 Flux & pCO2 2004 to 2007

PRESENT NET ANNUAL FLUX: -1.2 MOL C M-1 Y-1 FUTURE NET ANNUAL FLUX: -1.21 MOL C M-2 Y-1

SPRING AUTUMNCAHILL ET AL., IN PREP

SAB NENA 1.4 sea-air CO2 fluxes 2004 to 2007 & Jiang et al., 2008

2004

2006

2005

2007

NENA NET ANNUAL FLUX: -0.51 MOL C M-2 Y-1; JIANG ET AL., 2008 NET ANNUAL FLUX: -0.48 MOL C M-2 Y-1

Jiang et al., 2008, observations from

2005/2006

CAHILL ET AL., IN PREP

SAB NENA 1.4 pCO2 2004 to 2007 & Jiang et al., 2008

2004

2006

2005

2007

Jiang et al., 2008, observations from

2005/2006

SPRING AUTUMNCAHILL ET AL., IN PREP

SAB NENA 1.4 & NENA 4.1 Sea-Air CO2 Flux & pCO2 2004 to 2007

PRESENT NET ANNUAL FLUX: -0.51 MOL C M-1 Y-

1

FUTURE NET ANNUAL FLUX: +0.2 MOL C M-2 Y-1SPRING AUTUMN

CAHILL ET AL., IN PREP

€

∂DIC∂t

=−CNPhy• m• Phy+ lBM+ lEPhy2

kp+Phy2b

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟• CNZoo• Zoo+ ...

... CNDet• rSD• SDet+CNDet• rLD• LDet+ ...

... kw2

Sc12Δz

Gas- transfer velocityparameterization

1 2 3 CO2

SOL

CO2solubility1 2 3 pCO2

air−pCO2SW( )

Air− sea CO2 partial pressure difference

1 2 4 4 3 4 4 +∇DIC• V+ DDIC

€

δF ≈∂F∂Xi

δXi +12

∂2F∂Xi∂X j

δXiδX jj=1

n

∑i=1

n

∑i=1

n

∑

DISSOLVED INORGANIC CARBON (DIC)

Approximate difference in annually integrated flux using a second-order Taylor series expansion

PROCESS IDENTIFICATION USING TAYLOR SERIES DECOMPOSITION

CO2 FLUXSchmidt Number = f(T)

Solubility = f(T,S)Winds = f(U,V)

pCO2 = f(TA, TIC, T,S)

pCO2 TemperatureSalinity

Biological Effects, NEPTIC/TA mixing

(Adapted from Previdi et al., 2009; Colman et al., 1997; Wetherald & Manabe, 1988)

FUTURE – PRESENT∆CO2 FLUX ALL TERMS

Schmidt=f(T)

Solubility=f(T,S)

∆CO2 FLUX ALL TERMS

Winds=f(U,V)

pCO2=f(TA, TIC, T,S)

∆CO2 FLUX ALL TERMS

NEP=f(PP, Rem)

Net Ecosystem ProductionNEP=f(PP,Rem)

Rate of organic carbon accumulation(mol C m-3yr-1)

∆CO2 FLUX ALL TERMS

∆CO2 FLUX VS ∆NEP

2004 2005

2004 2005

∆CO2 FLUX

∆NEP

∆CO2 FLUX VS ∆NEP

2006 2007

2006 2007

∆CO2 FLUX

∆NEP

CONCLUSIONS• U.S. East Coast Continental Shelf is an overall sink of

atmospheric CO2

• Alongshelf gradient (S-N) in magnitude of flux, regional differences.

• Potentially important inter-annual variability in air-sea CO2 fluxes in all sub regions of U.S. East Coast Continental Shelf.

• Winds and pCO2 dominate the response of sub-regions to variability in atmospheric forcing.

• Regime shifts (sink source) occur in response to “future” perturbations in atmospheric forcing.

• Complex picture of sink / source regimes along US East Coast Continental Shelf!