Satellite Retrieval of Phytoplankton Community Size Structure in the Global Ocean

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Satellite Retrieval of Phytoplankton Community
Size Structure in the Global Ocean
Colleen Mouw University of Wisconsin-Madison In
collaboration with Jim Yoder Woods Hole
Oceanographic Institution
Photo David Doubilet
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Ecological Importance of Cell Size

• Small cells
• recycled within euphotic zone
• utilizing regenerated nutrients
• Prefer stratified high light conditions
• Large cells
• sink out of the euphotic zone
• utilize new nutrients efficiently
• Prefer turbulent, low light conditions

Chisholm, 2000
Many biogeochemical processes are directly
related to the distribution of phytoplankton size
class (Longhurst 1998), and is a major biological
factor that governs the functioning of pelagic
food webs (Legendre and Lefevre 1991).
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Optical Importance of Cell Size

• Despite the physiological and taxonomic
  variability, variation in spectral shape can be
  defined by changes in the dominant size class.

(Ciotti et al. 2002)
aph(?) (1-Sf) ? apico(?) Sf ? amicro(?)
Package effect
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Motivation
Rlog(Rrs443 gt Rrs 490 gt Rrs510)/Rrs555

• Rrs(?) imagery also contains information about
  cell size in addition to chlorophyll and CDM
  concentration.

Chl (mg m-3)

• SeaWiFS standard chlorophyll algorithm (OC4v4).

OReilly et al. 1998
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Effect of Phytoplankton Concentration on Rrs(?)
Effect of Chl on water-leaving radiance
Maximum band shifts from 443 to 490 to 510 nm
with increasing chlorophyll concentration
Spectral shift
OReilly et al. 1998
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Effect of Cell Size on Rrs(?)
Sf varying Constant Chl 0.5 mg m-3 Constant
aCDM/NAP(443) 0.002 m-1
Magnitude shift!
Rrs (sr-1)
Wavelength (nm)
Hydrolight simulations
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Effect of CDM/NAP on Rrs(?)
In addition to the magnitude shift of cell size,
effects of CDM/NAP must be considered.
aCDM/NAP(443) varying Constant Chl 0.5 mg
m-3 Constant Sf 50
Rrs (sr-1)
Wavelength (nm)
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How can phytoplankton cell size be retrieved from
satellite imagery?
Mouw Yoder (2009) Remote Sensing of
Environment, submitted
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HPLC in situ observations
The relative biomass proportions of pico-, nano-,
and microplankton can be estimated from the
concentrations of pigments which have a taxonomic
significance and associated to a size class
(Bricaud et al. 2004 Vidussi et al. 1996).
Percent microplankton
Log10 in situ Chl (mg m-3)
n4,564
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Look-up-table Construction

• Full factorial design
• Independently varied Chl, Sf, aCDM/NAP over
  expected ranges for the global ocean
• For a given combination of IOPs, AOPs are
  calculated via radiative transfer

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Look-up-table Construction
Percent Microplankton
Optical model
Full Factorial Design Chl, Sf, aCDM/NAP(443)
Log10 in situ Chl (mg m-3)
Hydrolight
GSM01 aCDM/NAP(443) m-1
Rrs(?)
Log10 GSM01 Chl (mg m-3)
n 44,343
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Detectable Ranges

• If LUT ?nRrs(443) gt SeaWiFS NE?nRrs(443)
• Beyond detection

Rrs (sr-1)
aCDM/NAP (443) (m-1)
Wavelength (nm)

• SeaWiFS has the sensitivity to retrieve Sf...
• chlorophyll 0.05 - 1.75 mg m-3
• aCDM/NAP(443) lt 0.17 m-1
• Of decadal mean imagery,
• 84 of Chl
• 99.7 of aCDM/NAP(443)
• fall within thresholds

Chlorophyll (mg m-3)
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LUT Retrieval
If Chl above/below threshold lt ? Mask If Chl
within threshold ? Continue
GSM01 Chl
0.05 - 1.75 mg m-3
?
If aCDM(443) gt threshold ? Mask If aCDM(443) lt
threshold ? Continue
GSM01 aCDM/NAP(443)
lt 0.17 m-1
?
Hydrolight Normalized Rrs (443) (Sf range)
Guide search space in LUT
Sf
SeaWiFS Normalized Corrected Rrs(443)
SeaWiFS Rrs(?) imagery
?
(443/555)
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Size Retrieval
Estimated Sf for May 2006
High CDM/Chl
Masked regions that are outside of thresholds for
Sf retrieval.
Low Chl
Land/Cloud
No flag
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Validation

• 85 within 1 standard deviation
• 11, 2 std. dev.
• 4, 3 std. dev.

Sf retrieval
Sf in situ
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Comparison with other functional type retrievals
June 2000

• Uitz et al. 2006

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Sf - SeaWiFS first 10 years
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How do the Sf temporal and spatial patterns
compare with Chl?
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Sf and Chl Decadal Climatology
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Individual EOF Mode 1

• Chl - adjustments to seasonal cycle
• Sf - ENSO relations
• Smaller Sf deviations until until 2002
  (Equatorial Pacific) when deviations become
  negative

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Joint EOF Mode 1

• Amplitude time series
• mirror over zero of individual Sf mode 1
• - Variance driven by Sf

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Summary

• Satellite Sf estimates agree well with previous
  observations
• Regions of the ocean where Sf and Chl are
  decoupled
• ENSO variability more apparent in Sf than Chl
• Non-linear response between Sf Chl points to
  the importance of additional ecological
  information in the interpretation of Chl
  distributions

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Moving Forward

• Much more to investigate with Sf time series
• Further investigation of Sf changes over the
  decadal record
• Flux estimates with assistance from numerical
  models
• Production estimates considering cell size (Mouw
  Yoder 2005)
• Other suggestions/ideas

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Acknowledgements

• Jim Yoder (WHOI)
• Jay OReilly (NOAA, NMFS)
• Tatiana Rynearson (URI, GSO)
• Benjamin Beckmann (MSU)
• Maureen Kennelly (URI, GSO)
• Kim Hyde (NOAA, NMFS)
• Primary Funding
• RI Space Grant/Vetlesen Climate Change Fellowship
• NASA Earth and Space Science Fellowship
• URI GSO Alumni Fellowship

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