Cahill

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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, Germany
2Institute 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. ECOS
U.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)
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).
Global distribution of annual sea-air CO2 flux measurements gC m-2 yr-1
(Cai et al, 2006)
U.S. ECoS Research Objectives:
1. Evaluate continental shelf
carbon cycling processes
including: 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
Land
Ecosystem
Model
Coupled
BGC/Circ
Model
Satellite
Data
In situ
Data
Coastal
Carbon
Fluxes
Climate/
Land-Use
Changes
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)
NENA Model Specifications
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 fields
PAR(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
denitrification
Oneway coupling
Carbon
model
OCMIP standard for carbonate system
Wanninkhof (1992) for gas exchange
GOM
MAB
SAB
Spring Chl (mg m-3)
X
X
X
X
X
X
X
X
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
2 CASE STUDIES
Atmospheric
Forcing
Time Period
“Present”
“Future”
NCEP-NARR 3-h fields:
Added anomalies to NCEPNARR 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
TAIR, PAIR, QAIR, RAIN, SWRAD,
LWRAD, UWIND, VWIND
2004 to 2007
2004 to 2007
Future scenario characterized by ~ 2oC air temperature increase
Higher Precipitation and SWRAD in Spring / Summer
S  N alongshore decrease in wind speed
2004
2005
FUTURE - PRESENT
2006
2007
WINTER
SPRING
SUMMER
FALL
Model evaluation with satellite data
Satellite-model statistical
comparisons
NENA1
satellite
SST
Taylor/Target diagrams
evaluation
(Jolliff et al., 2008)
Model vs. Satellite SST
NENA2
diffce
diffce
NENA
Subregions:
satellite
Hofmann et al., 2011
Hofmann et al., 2008, 2011, Druon et al., 2010
But how do we evaluate carbon fluxes?
We generally need to examine in situ data
NENA annual
primary
productivity
gC m-2 yr-1
annual PP
gC m-2 yr-1
Model shows reasonable comparison to in situ PP data,
considering variability involved
in situ data
NENA
Present
NENA
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
“PRESENT”
AIR-SEA CO2
FLUXES
SOME CHARACTERISTICS:
• Generally acts as a sink
“FUTURE”
•
•
•
•
Clear alongshelf gradient
Interannual variability
Regional differences
“Future” – shift in
position of alongshore
gradient
Positive  ocean is a sink of CO2
Negative  ocean is a source of CO2
GOM NENA 1.4 sea-air CO2 fluxes 2004 to 2007 & VDK et al., 2011
VDK et al., 2011,
observations from
2004 to 2008
2004
2005
2006
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
CAHILL ET AL., IN PREP
GOM NENA 1.4 pCO2 2004 to 2007 & VDK et al., 2011
VDK et al., 2011,
observations from
2004 to 2008
2004
2005
2006
2007
SPRING
AUTUMN
CAHILL ET AL., IN PREP
GOM NENA 1.4 & NENA 4.1 Sea-Air CO2 Flux & pCO2 2004 to 2007
SPRING
PRESENT NET ANNUAL FLUX: -1.77 MOL C M-1 Y-1
AUTUMN
FUTURE NET ANNUAL FLUX: -1.74 MOL C M-2 Y-1
CAHILL ET AL., IN PREP
MAB NENA 1.4 sea-air CO2 fluxes 2004 to 2007 & Takahashi et al., 2009
Takahashi et al.,
2009
2004
2005
2006
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
“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
Takahashi et al.,
2009
2004
2005
2006
2007
SPRING
AUTUMN
CAHILL ET AL., IN PREP
MAB NENA 1.4 & NENA 4.1 Sea-Air CO2 Flux & pCO2 2004 to 2007
SPRING
PRESENT NET ANNUAL FLUX: -1.2 MOL C M-1 Y-1
AUTUMN
FUTURE NET ANNUAL FLUX: -1.21 MOL C M-2 Y-1
CAHILL ET AL., IN PREP
SAB NENA 1.4 sea-air CO2 fluxes 2004 to 2007 & Jiang et al., 2008
Jiang et al., 2008,
observations from
2005/2006
2004
2005
2006
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
CAHILL ET AL., IN PREP
SAB NENA 1.4 pCO2 2004 to 2007 & Jiang et al., 2008
Jiang et al., 2008,
observations from
2005/2006
2004
2005
2006
2007
SPRING
AUTUMN
CAHILL ET AL., IN PREP
SAB NENA 1.4 & NENA 4.1 Sea-Air CO2 Flux & pCO2 2004 to 2007
SPRING
PRESENT NET ANNUAL FLUX: -0.51 MOL C M-1 Y-1
AUTUMN
FUTURE NET ANNUAL FLUX: +0.2 MOL C M-2 Y-1
CAHILL ET AL., IN PREP
DISSOLVED INORGANIC CARBON (DIC)
2


DIC
Phy
 CNPhy  m Phy  
lBM  lE
b CNZoo  Zoo ...
2 

t
k p  Phy 

... CNDet  rSD  SDet  CNDet  rLD  LDet  ...
...
kw 2
SOL
2
CO
1
Sc 2 z
CO2 solubility
Gas- transfer velocity
parameterization
pCO
air
2
 pCO
SW
2

 DIC  V  DDIC
Airsea CO2 partial
pressure difference
F
1 n n  2F
F  
Xi  
XiX j
Xi
2 i1 j1 XiX j
i1
n

Approximate difference in annually integrated flux using a secondorder Taylor series expansion
PROCESS IDENTIFICATION USING TAYLOR SERIES
DECOMPOSITION
FUTURE – PRESENT
∆CO2 FLUX ALL TERMS
CO2 FLUX
Schmidt Number = f(T)
Solubility = f(T,S)
Winds = f(U,V)
pCO2 = f(TA, TIC, T,S)
pCO2 Temperature
Salinity
Biological Effects, NEP
TIC/TA mixing
(Adapted from Previdi et al., 2009; Colman et al., 1997; Wetherald & Manabe, 1988)
∆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
Net Ecosystem Production
NEP=f(PP,Rem)
Rate of organic carbon accumulation
(mol C m-3yr-1)
NEP=f(PP, Rem)
∆CO2 FLUX VS ∆NEP
∆CO2 FLUX
2004
2005
2004
2005
∆NEP
∆CO2 FLUX VS ∆NEP
∆CO2 FLUX
2006
2007
2006
2007
∆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!
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