Transcript Carbon-Based Net Primary Production and Phytoplankton

Carbon-Based Net Primary Production
and Phytoplankton Growth Rates from
Ocean Color Measurements
Toby K. Westberry1, Mike J. Behrenfeld1
Emmanuel Boss2, David A. Siegel3
1Department
of Botany, Oregon State University
2School of Marine Sciences, University of Maine
3Institute for Computational Earth System Science, UCSB
Modelling NPP
General
Chl-based
C-based
NPP ~ [biomass] x physiologic rate
NPP ~ [Chl] x Pbopt
NPP ~ [C] x m
Scattering
(cp or bbp)
Ratio of Chl to
scattering (Chl:C)
C-based approach
• Scattering coefficients covary with particle abundance
(Stramski & Kiefer, 1991; Bishop, 1999; Babin et al., 2003)
• Scattering coefficients covary with phytoplankton carbon
(Behrenfeld & Boss, 2003; Behrenfeld et al., 2005)
• Chlorophyll variations independent of C are an index of
changing cellular pigmentation
Satellite
0.080
0.013
0.065
0.011
0.050
0.009
0.035
0.020
0.007
0.005
0.005
0
1
2
3
0
Ig (Ein m-2 h1)
1
2
3
Chl:C (mg mg-1)
Chl:C (mg mg-1)
Laboratory
CBPM In a nutshell
• Invert ocean color data to estimate [Chl a] & bbp(443)
(Garver & Siegel, 1997; Maritorena et al., 2001)
• Relate bbp(443) to carbon biomass (mg C m-3)
(Behrenfeld et al., 2005)
• Use Chl:C to infer physiology
(photoacclimation & nutrient stress)
• Propagate properties through water column
• Estimate phytoplankton growth rate (m) and NPP given:
PAR, Chl, K490, bbp(443), Zeu, MLD
Carbon-Based Production Model (CBPM)
Depth-resolved CBPM
PAR(z)
z=0
Uniform (e.g., [Chl/C]sat)
z=MLD
Nutrient-limited &/or light-limited
+ photoacc.
z=zNO3
Light-limited + photoacc.
* Iterative such that values at z=zi+1 depend on values at z=zi *
CBPM details (2)
2. Let cells photoacclimate through
the water column
- Iteratively calculate spectral
attenuation
3. Account for light limitation
Chl : C
Ig (Ein m-2 h-1)
Light-limitation Index
-nutrient stress falls off
as e-Dz (Dz=distance from nitracline)
m (divisions d-1)
1. Let surface values of Chl:C
indicate level of nutrient-stress
~(1-e-3PAR(z))
Ik ~0.6
Ig (Ein m-2 h-1)
CBPM details (3)
-
INPUT (surface)
SeaWiFS: nLw(l), PAR, Kd(490)
GSM01: Chl a, bbp(443)
FNMOC: MLD
WOA 2001: ZNO3
OUTPUT ((z))
- Chl, C, &
Chl:C
-m
- NPP
Run with 1° x1° monthly mean climatologies (1999-2004)
Depth (m)
Example profiles
Eq. upwelling (0°N, -130°E, Aug)
Eastern Pacific (20°N, -110°E, Jan)
NPP patterns (Jun-Aug)
This work
• large spatial & temporal
differences in carbon-based
NPP from Chl-based results
(e.g., > ±50%)
VGPM
(Chl-based model)
∫NPP (mg C m-2 d-1)
• Chl-based model interprets high
Chl areas as high NPP
• differences due to photoacclimation and nutrient-stress
related changes in Chl : C
∫NPP (mg C m-2 d-1)
Seasonal NPP patterns (N. Atl.)
Western N. Atl
CBPM
VGPM
Eastern N. Atl
Annual NPP
∫NPP (Pg C)
VGPM
This model
Annual
45
52
Gyres
8 (18%)
13 (26%)
High latitudes
15 (34%)
12 (23%)
Subtropics?
18 (39%)
25 (48%)
2 (4%)
3 (5%)
Southern Ocean
(q<-50°S)
• Although total NPP doesn’t change much (~15%),
where and when it occurs does
Example NPP profiles (HOT)
- Uniform mixed layer (step function) v. in situ incubations
- Discrepancies due to satellite estimates, NOT concept