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Open Ocean CDOM Production and Flux

Open Ocean CDOM Production and Flux. Norm Nelson, Dave Siegel, St é phane Maritorena Chantal Swan, Craig Carlson UC Santa Barbara. ACE Ocean Productivity and Carbon Cycle (OPCC) Workshop UCSB, June 2011. Outline. What is CDOM and why should we care Remote sensing of CDOM

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Open Ocean CDOM Production and Flux

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  1. Open Ocean CDOMProduction and Flux Norm Nelson, Dave Siegel, Stéphane MaritorenaChantal Swan, Craig CarlsonUC Santa Barbara ACE Ocean Productivity and Carbon Cycle (OPCC) Workshop UCSB, June 2011

  2. Outline • What is CDOM and why should we care • Remote sensing of CDOM • CDOM Dynamics in the global ocean

  3. CDOM What and Why • CDOM is dissolved (passes 0.2 m filter) organic matter that absorbs light. • CDOM has a major impact upon ocean color -- influences retrieval of chlorophyll, penetration of PAR and UV to depth. This enables remote sensing of surface CDOM. • CDOM is produced by all kinds of heterotrophic activity and is destroyed primarily by solar radiation. • CDOM is found in measurable (if you’re careful) quantities at all depths everywhere in the ocean. • CDOM is not correlated to DOC abundance in the open sea.

  4. Example spectra for controls vs. plankton Zooplankton CDOM Production

  5. daCDOM/dt (measured) Solar Bleaching of CDOM E0*ācdom Time Time Time Chantal Swan, UCSB E0*ācdom*(o=325nm) E0*ācdom*(o=325nm) Time Time

  6. CDOM What and Why (2) • CDOM is also an primary sensitizer of photochemical reactions involving climate-relevant trace gases (CO2, CO, OCS, DMS) • CDOM is an indicator of terrestrial runoff and riverine input to the ocean • Alas: In the open ocean we can’t ascribe carbon content to CDOM (yet?) nor do we know much about the identities of the chromophores

  7. Photochemical CO production from space

  8. CDOM from Ocean Color

  9. CDOM Optics and Remote Sensing • CDOM absorption spectrum is distinct from phytoplankton absorption • Ocean color reflectance spectra can be inverted to retrieve absorption by CDOM and particles and particulate backscattering CDOM Particles

  10. Mean Global Surface CDOM DistributionFrom SeaWiFS as acdm(443 nm, m-1)Garver-Siegel-Maritorena model acdom (443 nm, m-1) Siegel et al. [2005] JGR -- Nelson et al. [2010] GRL

  11. CDOM from Ocean Color • Matchup with NOMAD data (IOCCG IOP report; Lee et al. 2006) • Model-data fits are pretty good – though not excellent • GSM01 is optimized for all 3 retrievals (CHL, CDM, BBP)

  12. Global Dynamics of CDOM

  13. Example CDOM Profiles

  14. Atlantic • Pacific • Indian CDOM and AOU Distribution [Nelson et al. 2010]

  15. CDOM / AOU Correlation

  16. CDOM Dynamics Summarized • CDOM is produced primarily as a function of remineralization (terrestrial inputs are local, only a few taxa of autotrophs produce CDOM) • CDOM is destroyed primarily by photolysis (we don’t observe labile DOM as it’s consumed too rapidly by microbes) • Time scales for CDOM production / destruction are comparable to time scales for ocean circulation (otherwise the ocean would be yellow) • Observed CDOM distribution results from a balance between source/sink processes and circulation

  17. Biological Physical Bleaching CDOM Dynamics - N. Pacific / Indian Weak ventilation in northern basin Particle flux leads to CDOM accumulation Eq N

  18. Biological Physical Bleaching CDOM Dynamics - N/S Atlantic Strong ventilation in subarctic basin Higher surface CDOM signal transmitted to deep Eq N or S

  19. Biological Physical Bleaching CDOM Dynamics - S Pacific/Indian Strong ventilation in Southern Ocean Lower surface CDOM signal transmitted to deep Eq S

  20. Summary / Conclusions • CDOM is a remotely sensible semiconservative tracer, produced by heterotrophs and destroyed by photolysis • The relationship between CDOM and oxygen (as AOU) in the deep sea is modulated by circulation processes • CDOM assessment is important to do ocean color right, and is useful in its own right

  21. Extra slides

  22. CDOM Optics and Remote Sensing • Remote sensing reflectance spectrum can be inverted to retrieve inherent optical properties (absorption and backscattering spectra) of the surface water (mixed layer to ~ 60m). • Absorption spectra can be deconvolved into particle absorption and CDOM+detritus absorption spectra (which we call CDM) given some assumptions about the shape of the component spectra. • Garver-Siegel-Maritorena model (GSM) uses shape functions determined using a global optimization of available global open ocean field data.

  23. Seasonal CDOM Cycle CDM • Seasonal changes at most latitudes • Lower in summer • Reduced in tropics • Higher towards poles • Hemispheric asymmetry %CDM

  24. Surface CDOM & SeaWiFS r2 = 0.65; N = 111 slope = 1.16 Siegel et al. [2005] JGR A20 A22 A16N

  25. a*cdom(325) a*cdom = CDOM / DOC(units m2g-1) Upper layers bleaching & production signals a*cdom increases w/ depth & age CDOM “abundance” changes less than the DOC decline -- CDOM is refractory DOM New Bleaching Aging Nelson et al. [2007] DSR-I

  26. T ~ 50y T ~ 10y P < 0.025 P < 0.025 T > 200 y P < 0.025 P < 0.025 Regressions between age and CDOM Nelson et al. [2007] DSR-I

  27. Trends in CDOM spectral characteristics - N. Atl. P < 0.025 P < 0.025 P < 0.025 P < 0.025 P < 0.025 P < 0.025 P < 0.025 Nelson et al. [2007] DSR-I

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