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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