From satellite-based primary productionto export production

Toby K. Westberry1 Mike J. Behrenfeld1

David A. Siegel2

1Department of Botany & Plant Pathology, Oregon State University2Institute for Computational Earth System Science,

University of California Santa Barbara

What is the fate of net primary production (NPP)? (i.e., export v. recycling)

Motivation

In situ observational studies

Eppley & Peterson (1979)

Suess et al. (1980)Buesseler et al. (1998)

Ecosystem models

Fasham et al. (1990)Laws et al. (2000)

Dunne et al. (2005)

Satellite based

Falkowski et al. (1998)Iverson et al. (2000)Goes et al. (2000),

(2004)

NPP

Export

pro

duct

ion

CbPM (1) - Overview

1. Invert ocean color data to estimate Chl a & bbp(443)

(Garver & Siegel, 1997; Maritorena et al., 2001)

2. Relate bbp(443) to phytoplankton carbon biomass, C

3. Use Chl:C to infer physiology (photoacclimation & nutrient stress)

4. Estimate phytoplankton growth rate () and NPP

Carbon-based Production Model (CbPM)

(Behrenfeld et al., 2005; Westberry et al., submitted to GBC)

CbPM (2) – Details

We can push model verticallythrough the water column:

• Spectral accounting for underwater light field

• Cells photoacclimate through the water column

• Nutrient-stress decays as nitracline is neared (using climatological nutrient fields)

**Westberry et al., (submitted to GBC)

Chl NPP

Depth

(m

)mg Chl m-3 d-1 mg C m-3 d-1

CbPM (3) – Results & Validation

Surface patterns

Data from Winn et al. (1995); Durand et al. (2001)

**Westberry et al., (submitted to GBC)

HOT

BATS

CbPM (4) – Results & Validation

**Westberry et al., (submitted to GBC)

Depth patterns

BATS

BATS

summer winter

wintersummer

CbPM (5) – ∫NPP Patterns

NPP (mg C m-2 d-1)

Onset and peak of blooms can be delayed (~1-2 months)

Spatial (and temporal) patterns of NPP are different compared to Chl-based model (VGPM, Behrenfeld & Falkowski,

1997)VGPM – CbPM (Jun – Aug)

NPP to Export – empirical (1)

• Annual particle export predicted from Laws et al. (2000)

Zonal regions as in Yoder et al. (1993)

CbPM = 11.2 Gt C yr-1

VGPM = 10.6 Gt C yr-1

NPP to Export – mechanistic (1)

][ recyclingexportdilutionadvection Cdt

dC

Biomassaccumulation

NPP Losses

Apr biomass

mg C m-3

Aug biomass

mg C m-3 % of “expected biomass”

Aug biomass

NPP to Export – Dilution

• Change (%) in ML phytoplankton C due to ML deepening

% phyto C

lost

NPP to Export – mechanistic (2)

][ recyclingexportdilutionadvection Cdt

dC

Biomassaccumulation

NPP Losses

• Ad hoc approach -- look at dC/dt, d/dt, dNO3/dt to constrain one of the processes

NPP to Export – mechanistic (3)

dC/dt ~ EXPORT

Example 1Export under oligotrophic conditions

% M

L phyto. C lost

t1 t2

[NO3]1 = [NO3]2

1 = 2

C1 > C2

NPP to Export – mechanistic (4)

Export from seasonal nutrient drawdown

% M

L phyto. C lost

t1 t2

[NO3]1 > [NO3]2

1 = 2

C1 ≥ C2

Example 2

dNO3/dt - dC/dt ~ EXPORT

NPP to Export – END

• CbPM provides critical pieces of information for diagnosing export from satellite (, C, NPP)

• Haven’t solved the whole problem … yet

• Can estimate time varying fields of export (and recycling)

toby.westberry@science.oregonstate.eduwww.science.oregonstate.edu/ocean.productivity

www.science.oregonstate.edu/ecophysiology

NPP to export – Export

Map?

Mean Annual fraction of phyto. C exported

EXTRA

What is the fate of net primary production (NPP)? (i.e., export v. recycling)

Motivation

In situ observational studies

- 15N incubations - Sediment traps - Geochemical balances - 234Th inventories

Eppley & Peterson (1979)

Suess et al. (1980)Buesseler et al. (1998)

Ecosystem models

Fasham et al. (1990)

Laws et al. (2000)Dunne et al. (2005)

Satellite based

- Applications of empirical results

- [Chl], NPP, and SST are not sufficient

Falkowski et al. (1998)Iverson et al. (2000)

CbPM (2) – Details

• Spectral accounting for underwater light field

• Cells photoacclimate through the water column

• Nutrient-stress decays as nitracline is neared

Mixed layer

Photoacclimation +Relaxation from nut. stress

Photoacclimation

Particle loss

**Westberry et al., (in review GBC)

Realistic profiles with noassumptions about shape

CbPM (3) – Results & Validation

Chl NPP

Depth

(m

)

mg Chl m-3 d-1 mg C m-3 d-1

**Westberry et al., (in review GBC)

Surface patterns

Depth patterns

HOT

BATS

BATS

BATS

CbPM (4) - Patterns

• Both spatial AND temporal patterns of NPP are different wrt Chl-based model (VGPM)

• ~30% more NPP in open ocean (and ~30% less in northern high latitudes)

• Onset and peak of blooms can be delayed (~1-2 months)

VGPM - CbPM (Jun-Aug)

mg C m-2 d-1

Export – empirical (2)

VGPM CBPM

> 60°N 46% 22%

30°N - 60°N 22% 19%

0° - 30°N 10% 11%

0° - 30°S 8% 12%

30°S - 60°S 6% 14%

> 60°S 8% 23%

Total (Gt C yr-1) 10.6 11.2

Fraction of total export

• CbPM suggests much more production in open ocean and So. Ocean and less in N. hemisphere high latitudes and upwelling regions

Export – empirical (2)

VGPM CBPM

Oligotrophic 1.9 (18%) 3.1 (28%)

Mesotrophic 3.6 (34%) 4.4 (39%)

Eutrophic 5.1 (48%) 3.7 (33%)

Total 10.6 11.2

> 60°N 46% 22%

30°N - 60°N 22% 19%

0° - 30°N 10% 11%

0° - 30°S 8% 12%

30°S - 60°S 6% 14%

> 60°S 8% 23%

Total (Gt C yr-1)

Fraction of total export

Total Export (Gt C yr-1)

How to assess export?

1. Apply **new** CbPM patterns to existing empirical export algorithms (i.e., Laws et al., 2000; Dunne et al., 2005)

2. Use biomass (C) and growth rate () in addition to NPP to construct a mass balance for phytoplankton C in the mixed layer

NPP to Export – nutrient constraints

• surface NO3 (SSN) ~ 0

- dC/dt < 0 ---- (export)

• SSN ~ 0 & dNO3/dt > 0

- dC/dt > 0

- dC/dt ~ 0 & d/dt > 0 ----(recycling)

- dC/dt ~ 0 & d/dt ~ 0 ---- (export)

• SSN > 0 & dNO3/dt < 0

- similar to above

• SSN > 0 & dNO3/dt ≥ 0 - light or Fe limitation ….??

NPP to Export – mechanistic (2)

Considerations

1. Are there nutrients IN the mixed layer?

2. Were nutrients entrained into the mixed layer? Drawn down?

4. Was there an increase in biomass? Decrease?

5. Was there an increase in growth rate? Decrease?

[C] NPP

NO3-

1 2

3

OR

NPP to Export – mechanistic (2)

Considerations

1. Are there nutrients IN the mixed layer?

2. Were nutrients entrained into the mixed layer?

4. Was there an increase in biomass? Decrease?

5. Was there an increase in growth rate? Decrease?

[C1] NPP1 [NO3-]

t1

t2

[NO3-]

[C2] > [C1]

NPP1