ASSESSING BIODIVERSITY OF PHYTOPLANKTON COMMUNITIES FROM

OPTICAL REMOTE SENSING

Julia Uitz, Dariusz Stramski, and Rick A. ReynoldsScripps Institution of OceanographyUniversity of California San Diego

NASA Biodiversity Team Meeting – May 2010 – Washington DC

WHY STUDYING PHYTOPLANKTON DIVERSITY?

•Phytoplankton diversity influences many important biogeochemical processes▫Photosynthetic efficiency▫Fate of carbon fixed via photosynthesis▫Marine biological pump of carbon

•Key questions to be addressed▫Understanding of marine biogeochemical

cycles and modeling capabilities▫Distribution and variability on scales relevant

to environment and climate changes

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PROJECT OBJECTIVES AND STRATEGY

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OCEAN-COLOR BASED DISCRIMINATION OF DIFFERENT

PHYTOPLANKTON GROUPS•Satellite measurements of ocean color

▫Surface Chla concentration▫Quasi-global spatial scale▫Daily to decade

•New generation of algorithms for discriminating different phytoplankton groups from ocean color▫Dominance (Alvain et al. 2005)▫Surface Chla (Devred et al. 2006; Hirata et al.

2008)▫Vertical profile of Chla (Uitz et al. 2006)

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Conversion to CAbsorbed light energy

OCEAN COLOR-BASED PRIMARY PRODUCTION MODEL

P(t,z) = Chla(z,t) a*(z,t) PAR(z,t) Φc(z,t)

▫ P: Primary production (g C m-3 d-1)

▫ PAR: Irradiance available for photosynthesis (mol quanta m-2 s-1)

▫ Chla: Concentration of chlorophyll a (mg m-3)

▫ a*: Chla-specific absorption coefficient of phytoplankton [m2 (mg Chla)-1]

▫ Φc: Quantum yield of carbon fixation [mol C (mol quanta)-1]

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PRIMARY PRODUCTION AT THE PHYTOPLANTKON GROUP LEVEL

Ppg(t,z) = Chlapg(z,t) apg*(z,t) PAR(z,t) Φc,pg(z,t)

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Pmicro Pnano Ppico

3. Computation of group-specific primary production rates

(Uitz et al. GBC in press)

2. Bio-optical model of Morel (1991) + photophysiological properties of

Uitz et al. (2008)φmicro φnano φpico

Chlamicro Chlanano

1. Computation of Chla vertical profiles from surface Chla (Uitz et al.

2006)Chlapico

METHODOLOGY

Ppg(t,z) = Chlapg(z,t) apg*(z,t) PAR(z,t) Φc,pg(z,t)

(mg m-3)10-year time series of SeaWiFS

surface Chl (1997-2007)

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GLOBAL ANNUAL PRIMARY PRODUCTION

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CLIMATOLOGY OF MICROPHYTOPLANKTON PRODUCTION

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• Boreal winter/Austral summer(Dec-Jan-Feb)

• Boreal summer/Austral winter(Jun-Jul-Aug)

• Temp/subpolar latitudes in summer: high contribution (e.g. Atl Nord >50%)• Near-coastal upwelling systems: 70% (1 g C m-2 d-1)• South Pacific Subtropical Gyre: Minimum contribution (0.02 g C m-2 d-1)

CLIMATOLOGY OF PICOPHYTOPLANKTON PRODUCTION

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• Boreal winter/Austral summer(Dec-Jan-Feb)

• Boreal summer/Austral winter(Jun-Jul-Aug)

• Maximum contribution in oligotrophic subtropical gyres (40-45%)• Contribution reduced to ~15% at high latitudes

CLIMATOLOGY OF NANOPHYTOPLANKTON PRODUCTION

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• Boreal winter/Austral summer(Dec-Jan-Feb)

• Boreal summer/Austral winter(Jun-Jul-Aug)

• Substantial contribution on global scale: 0.07-1 g C m-2 d-1 (30-60%)• Can be found in extremely diverse environmental conditions (subtropical gyres vs. winter subantarctic waters Biodiversity? (see Liu et al. PNAS 2009)

CONCLUSIONS AND PERSPECTIVES

• First climatology of phytoplankton group-specific primary production on global scale over seasonal to interannual scales▫ Significant contribution to our ability to understand

and quantify marine carbon cycle with implications for carbon export

▫ Key elements required to calibrate/validate new biogeochemical models (e.g. Le Quéré et al. 2005)

▫ Benchmark for monitoring responses of marine pelagic ecosystems to climate change

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• Chla-based approaches▫ Describe general trends across various trophic regimes▫ But do not necessarily account for specific local conditions

• New complementary approaches need to be developed• Explore the potential of hyperspectral optical

measurement for discriminating different phytoplankton groups▫ Hyperspectral optical measurements have matured into

powerful technologies in the field of remote sensing▫ Yet remain largely unexplored for open ocean applications

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CONCLUSIONS AND PERSPECTIVES

HYPERSPECTRAL OPTICAL APPROACH

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Evaluation of performance

(Torecilla et al. in prep.)

• “Pilot” study• Small set of stations from Eastern Atlantic open ocean

▫ HPLC pigments▫ Optical data

• Encouraging results▫ Best classification with hyperspectral derivative spectra

• 2nd cruise in the Atlantic Ocean almost completed!

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HYPERSPECTRAL OPTICAL APPROACH

THANK YOU FOR YOUR ATTENTION

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