Satellite Retrieval of Phytoplankton Community Size Structure in the Global Ocean

1. 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

2. 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).

3. 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) a*ph()= [(1-Sf) a*pico()] + [Sf a*micro()] Package effect

4. Motivation R=log{(Rrs443 > Rrs 490 > 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). O’Reilly et al. 1998

5. 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 O’Reilly et al. 1998

6. 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

7. 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)

8. How can phytoplankton cell size be retrieved from satellite imagery? Mouw & Yoder (2009) Remote Sensing of Environment, submitted

9. 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 Log10in situ [Chl] (mg m-3) n=4,564

10. 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

11. Look-up-table Construction Percent Microplankton Optical model Full Factorial Design: Chl, Sf, aCDM/NAP(443) Log10in situ [Chl] (mg m-3) Hydrolight GSM01 aCDM/NAP(443) m-1 Rrs() Log10 GSM01 [Chl] (mg m-3) n = 44,343

12. Detectable Ranges If LUT ∆nRrs(443) > 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) < 0.17 m-1 • Of decadal mean imagery, • 84% of [Chl] • 99.7% of aCDM/NAP(443) • fall within thresholds Chlorophyll (mg m-3)

13. LUT Retrieval If [Chl] above/below threshold <  Mask If [Chl] within threshold  Continue GSM01 Chl 0.05 - 1.75 mg m-3  If aCDM(443) > threshold  Mask If aCDM(443) < threshold  Continue GSM01 aCDM/NAP(443) < 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)

14. 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

15. Validation • 85% within 1 standard deviation • 11%, 2 std. dev. • 4%, 3 std. dev. Sf retrieval Sf in situ

16. Comparison with other functional type retrievals Uitz et al. 2006 June 2000

17. Sf - SeaWiFS first 10 years

18. How do the Sf temporal and spatial patterns compare with [Chl]?

19. Sf and [Chl] Decadal Climatology

20. Individual EOF – Mode 1 • [Chl] - adjustments to seasonal cycle • Sf - ENSO relations • Smaller Sf deviations until until 2002 (Equatorial Pacific) when deviations become negative

21. Joint EOF – Mode 1 • Amplitude time series • – mirror over zero of individual Sf mode 1 • - Variance driven by Sf

22. 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

23. 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…

24. Acknowledgements • Jim Yoder (WHOI) • Jay O’Reilly (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