carbon-based net primary production and phytoplankton growth rates from ocean color measurements
DESCRIPTION
Carbon-Based Net Primary Production and Phytoplankton Growth Rates from Ocean Color Measurements. Toby K. Westberry 1 , Mike J. Behrenfeld 1 Emmanuel Boss 2 , David A. Siegel 3 1 Department of Botany, Oregon State University 2 School of Marine Sciences, University of Maine - PowerPoint PPT PresentationTRANSCRIPT
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 University2School of Marine Sciences, University of Maine
3Institute for Computational Earth System Science, UCSB
Modelling NPP
NPP ~ [biomass] x physiologic rate
NPP ~ [Chl] x Pbopt
NPP ~ [C] x
Scattering (cp or bbp)
Ratio of Chl to scattering (Chl:C)
General
Chl-based
C-based
C-based approachCh
l:C (m
g m
g-1) Chl:C (m
g mg
-1)
0 1 2 3
0.005
0.020
0.035
0.050
0.065
0.080
0 1 2 3
0.005
0.007
0.009
0.011
0.013
• 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
Laboratory Satellite
Ig (Ein m-2 h-
1)
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 () and NPP given: PAR, Chl, K490, bbp(443), Zeu, MLD
Carbon-Based Production Model (CBPM)
Depth-resolved CBPM
Nutrient-limited &/or light-limited + photoacc.
Uniform (e.g., [Chl/C]sat)
Light-limited + photoacc.
* Iterative such that values at z=zi+1 depend on values at z=zi *
z=zNO3
z=MLD
z=0PAR(z)
Light
-lim
itatio
n In
dex
Ig (Ein m-2 h-1)
~(1-e-3PAR(z))Ik ~0.6
CBPM details (2)1. Let surface values of Chl:C indicate level of nutrient-stress
-nutrient stress falls off as e-z (z=distance from nitracline)
2. Let cells photoacclimate through the water column - Iteratively calculate spectral attenuation
3. Account for light limitation
Ig (Ein m-2 h-1)
Chl :
C
(divisions d-1)
CBPM details (3)
- SeaWiFS: nLw(), PAR, Kd(490)- GSM01: Chl a, bbp(443)- FNMOC: MLD- WOA 2001: ZNO3
- Chl, C, & Chl:C- - NPP
INPUT (surface) OUTPUT ((z))
Run with 1° x1° monthly mean climatologies (1999-2004)
Dept
h (m
)De
pth
(m)
Example profiles
Eastern Pacific (20°N, -110°E, Jan)Eq. upwelling (0°N, -130°E, Aug)
NPP patterns (Jun-Aug)This work
∫NPP (mg C m-2 d-1)VGPM (Chl-based model)
∫NPP (mg C m-2 d-1)
• large spatial & temporal differences in carbon-based NPP from Chl-based results (e.g., > ±50%)
• Chl-based model interprets high Chl areas as high NPP
• differences due to photo- acclimation and nutrient-stress related changes in Chl : C
Seasonal NPP patterns (N. Atl.)
Western N. Atl
Eastern N. Atl
CBPMVGPM
Annual NPP∫NPP (Pg C) VGPM This modelAnnual 45 52Gyres 8 (18%) 13 (26%)High latitudes 15 (34%) 12 (23%)Subtropics? 18 (39%) 25 (48%)Southern Ocean(<-50°S)
2 (4%) 3 (5%)
• 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