MODELING PHYTOPLANKTON COMMUNITY STRUCTURE:

PIGMENTS AND SCATTERING PROPERTIES

Stephanie Dutkiewicz1

Anna Hickman2, Oliver Jahn1, Watson Gregg3, Mick Follows1

1. Massachusetts Institute of Technology2. University of Essex

3. NASA Goddard Space Flight Center

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

http://darwinproject.mit.edu

modeling the marine ecosystem

nutrients

light

many (100+)phytoplankton

zooplankton

detritus

some sinks out to depthsDarwin Project Model(Follows et al., Science 2007)

PO4NO3

FeSi

randomly assignedgrowth rates

grazing rates

http://darwinproject.mit.edu

modeling the marine ecosystem

nutrients

light

phytoplankton

zooplankton

detritus

some sinks out to depths

PO4NO3

FeSi grazing rates

randomly assignedgrowth rates

Darwin Project Model(Follows et al., Science 2007)

environment 1

http://darwinproject.mit.edu

modeling the marine ecosystem

Darwin Project Model(Follows et al., Science 2007)

nutrients

light

phytoplankton

zooplankton

detritus

some sinks out to depths

PO4NO3

FeSi

grazing rates

environment 2

randomly assignedgrowth rates

http://darwinproject.mit.edu

log10(biomass)

Initial Biomass of 100 phytoplankton types

http://darwinproject.mit.edu

log10(biomass)

Annual Biomass after 10 years simulation

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

EMERGENT COMMUNITY

By putting in appropriate trait trade-offs, environment selects the appropriatecommunity structure:

- K versus r strategies (Dutkiewicz et al, GBC, 2009)

-nitrogen fixing (Monteiro et al, GBC, 2010,2011)

-nitrate assimilation ability (Bragg et al, PlosOne 2010)

-size/grazing pressure (Ward et al. in prep)

-pigments/absorption (Hickman et al, MEPS, 2010)

Phytoplankton Functional Types

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

EMERGENT COMMUNITY

Phytoplankton Functional Types

By putting in appropriate trait trade-offs, environment selects the appropriatecommunity structure:

- K versus r strategies (Dutkiewicz et al, GBC, 2009)

-nitrogen fixing (Monteiro et al, GBC, 2010,2011)

-nitrate assimilation ability (Bragg et al, PlosOne 2010)

-size/grazing pressure (Ward et al. in prep)

-pigments/absorption (Hickman et al, MEPS, 2010)

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

(Data courtesy: M. Zubkov, J. Heywood)

(Hickman et al, MEPS, 2010)

AMT15

Vertical distribution of phytoplankton types

OBSERVATIONS

ONE DIMENSIONAL MODEL

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

Pigments as trait• Different pigment allow absorption of light at different wavebands

wavelength (nm)

Culture date fromL. Moore, D. Suggett

Absorption Spectra: Solid (PS specific); dashed (all pigments)

ONE DIMENSIONAL MODEL

(Hickman et al, MEPS, 2010)

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

(Data courtesy: M. Zubkov, J. Heywood)

(Hickman et al, MEPS, 2010)

AMT15

Vertical distribution of phytoplankton types

OBSERVATIONS MODEL

ONE DIMENSIONAL MODEL

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

more sophisticated treatment of light stream:

- spectral surface input (OASIM – Watson Gregg)

- radiative transfer code: 3 light streams (Iterative solver Oliver Jahn: following Aas, 1987; Ackelson et al 1994, Gregg and Casey, 2009)

- resolve absorption, scattering and backscattering

NEW DEVELOPMENTS

450 475 500 600 625 650 675

a(λ), b(λ), bb(λ)

525 550 575 700400 425

CDOM

water

aw(λ), bw(λ), bbw(λ)

aCDOM(λ)

ap(λ), bp(λ), bbp(λ)

detritus

ad(λ), bd(λ),bbd(λ)

Phytoplankton:diatomscoccolithophoreslarge Eukaryotespico-eukaryotesSynechococcusProchloroccusTrichodesmium

DEVELOPMENTS: RADIATIVE TRANSFER

In collaboration with Anna Hickman, Oliver Jahn, Watson Gregg

Slide modified from Watson Greggexplicit

explicit, under development

function of Chl

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

NEW DEVELOPMENTS

ADDITIONAL FUNCTONAL TYPES

Absorption data fromL. Moore, D. Suggett

In collaboration with Anna Hickman, Oliver Jahn, Watson Gregg

Scattering data fromGregg+Casey, 2009;Morel et al 1993

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

NEW DEVELOPMENTS

Model Output:

• upwelling radiance• water leaving radiance• backscattering (total, detrital, phytoplankton)• absorption (total, CDOM, phytoplankton)• forward scattering• pigments

450nm

500nm

550nm

UPWELLING RADIANCE: July

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

JULY

log10 phytoplankonbiomass (uMP)

log10 backscatterby phytoplankonsum bphym(1/m)

Coccolithophorefraction biomass

NEW DEVELOPMENTS: PRELIMINARY RESULTS

450nm

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

Remote sensing beginning to resolve aspects ofphytoplankton community and functionality:

e.g. PHYSAT (Alvain et al), PHYTODAS (Bracher et al), Aiken et al, Sathyendranath et al, Balch et al, Hirata et al, Uitz et al, Giotti+Bricaud, Mouw+Yoder, Kostadinov et al, etc

Models also resolving community structure:

By resolving optical properties of model ocean can werelate more to the remotely sensed products?

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

SUMMARY

We are currently working to include radiative transfer code (spectral) and explicit absorption and backscattering.

- will provide a closer link with satellite (and other optical) studies- additional remote sensed products could be used

to validate model- potential for data assimilation- model may then help untangle the mechanisms

leading to variability and trend observed in satellite products

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

MODELS HELP WITH OBS DESIGN

Correlation between model variables

Bennington, McKinley, Dutkiewicz, Ullman; GBC, 2009

- pCO2 well correlated with bloom- but year integrated CO2 Flux is not well

correlated with biological variability in subpolar

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

MODELS HELP WITH OBS DESIGN

Number of years for trend to be visible from natural variability

Henson et al, BG, 2010

- 3 models 2000-2100 A2 scenario- average of about 40 years of continuous and consistent measurements needed

stephanie dutkiewiczhttp://ocean.mit.edu/~stephd

O2

air

sea

Ed Es

(1 - ) (1 - )EdEs

Eu

Ed, Es

Lw

OASIM: Ocean-AtmosphereSpectral Irradiance Model

DEVELOPMENTS: RADIATIVE TRANSFER MODEL

Gregg and Casey, 2009

Ed = direct irradianceEs = diffuse downwellingEu = upwelling radianceρ = surface reflectanceLw = water leaving radiance

CO2 W Vaerosols

O3

Three-Stream Ocean Irradiance Modulefollowing Aas(1987), Ackleson et al (1994), Gregg and Casey (2009)

Oliver Jahn

Iterative solver (repeated down/up integration)

Gregg's truncation (downward integration

only)

Downward decaying modes only (à la Aas)

Iterative solver (repeated down/up

integration)

RADTRANS: approximations

Ed

Es

EuEs

Eu

EdEuEs

Ed

Lw

I

I

Oliver Jahn