Distribution & Dynamics of Colored Dissolved Organic Materials (CDOM) in the Open Ocean

1. Distribution & Dynamics of Colored Dissolved Organic Materials (CDOM)in the Open Ocean Dave Siegel Institute for Computational Earth System Science & Department of Geography University of California, Santa Barbara

2. Thanx ... • Collaborators Norm Nelson, Stéphane Maritorena, Craig Carlson, Chuck McClain, Mike Behrenfeld, Dennis Hansell, Debbie Steinberg, Samar Khatiwala, Pat Hatcher, … • Students Jon Klamberg, Chantal Swan, Stu Goldberg, DeDe Toole, Tiho Kostadinov, Toby Westberry, Eric Brody, Sara Garver, … • Technical Staff Manuela Lorenzi-Kayser, Margaret O’Brien, Erik Fields, Dave Menzies, Liz Caporelli, Nathalie Guilocheau, Ellie Wallner, David Court, Natasha MacDonald, … • Support NASA Ocean Biology & Biogeochemistry Program & NSF OCE

3. Talk Outline • What is CDOM? • Why do wecare? (well … its only me really) Contributions to open ocean optical properties • What is the global CDOM distribution? Ocean color remote sensing & hydrographic observations • What regulates open ocean CDOM cycling? • What is known about CDOM in the deep sea?

4. What is CDOM? • Colored Dissolved Organic Matter • Also called gelbstoff, gilvin, yellow matter, chromophoric DOM, … • Colored portion of the oceanic DOM pool • Probably a small fraction of the total DOM • Don’t really know its composition (like DOM)

5. What is CDOM? • CDOM is defined operationally by filtering Using a 0.2 mm filter Absorption relative to “pure water” standard • Typically, spectrum decreases exponentially ag(l) = ag(lo) exp(-S(l-lo)) S varies from 0.015 to 0.024 nm-1

6. Light Absorption Spectral Shapes water phytoplankton CDOM detritus Wavelength (nm)

7. Why should we care about CDOM? • Dominates light availability for l < 450 nm Huge role in marine photo-processes • CDOM is part of the ocean carbon budget Does CDOM = DOC?? -> NO!!! • Precursor for photochemical rxn’s Emission of trace gas (DMS, COS, CO, CO2) Bioavailability of trace metals (Fe, Mn, Cu, etc.) • A natural tracer of water mass exchange

8. How Important is CDOM? • Assess the light absorption budget: at(l) = aw(l) + aph(l) + ag(l) + ad(l) total water phyto- CDOM detrital plankton particulate • Examine the relative importance of each component using a global dataset

9. Optical Importance of CDOM • Global Data set (N=1044 - pre-NOMAD) • Use Chlorophyll as an ecosystem index • High Chl => more eutrophic ocean • Low Chl => more oligotrophic • Evaluate for 440 nm (peak of the chl-a abs) • Data set is a little “green” (mean Chl ~ 1.5 mg m-3)

10. ag(440)/at(440) adet(440)/at(440) Mean = 9% Mean = 41% aph(440)/at(440) aw(440)/at(440) Mean = 40%

11. Relative Spectral Contributions ag(l)/at(l) aw(l)/at(l) aph(l)/at(l) adet(l)/at(l)

12. Global Data Set • CDOM and Chl equally dominate the at(440) budget • CDOM is more important for l < 440 nm • Phytoplankton dominates from 440 to 490 nm • Water dominates for l > 500 nm & • Detritus is small part of at(l) budget • CDOM importance will increase if data set were less “green” & better represents the global ocean

13. CDOM Total Particles Sargasso Sea (open ocean; summer-time) Nelson & Siegel [2002]

14. How Large is Ocean CDOM?? 6th Floor Ellison Hall – UC Santa Barbara

15. UC Santa Barbara Drinking Water ag() (m-1) Wavelength (nm)

16. UCSB Drinking Water Sargasso Sea

17. Where does ocean CDOM come from? • Lots of places!! • Pelagic ecosystem processes • Inputs from terrestrial biosphere • Benthic environments • Allochthonous or Autochthonous

18. Where does ocean CDOM come from? Historically, only terrestrial discharge sources were considered First optical oceanographers worked on the Baltic Sea There, gelbstoff is obvious component of water clarity & related to land-ocean exchange Results in CDOM = f(Salinity)

19. ?? Observations from the Baltic Sea After Jerlov [1953]

20. Example From Delaware Bay linear mixing line ocean value Does Ocean CDOM = 0?? Vodacek & others, L&O, (1997)

21. Where does ocean CDOM come from? • Simple mixing analyses suggest near zero CDOM at oceanic salinities • What are the oceanic CDOM sources? • Is it simply mixing of terrestrial waters? • Or are autochthonous sources important? • How can we diagnose these sources? • Need to know the time/space CDOM distribution

22. So, What is the Global CDOM Distribution?? • Field observations are too scarce (& uncertain) • If CDOM dominates optics of the sea, it should be part of the ocean color signal • Fortunately, there are excellent ocean color sensors in orbit

23. The GSM Ocean Color Model • Relationship between LwN(l) & ocean optical properties is known • Component spectral shapes are constant – only their magnitudes vary • Solve least-squares problem for 3 components • Water properties are known • Nonlinear processes are ignored • Detrital absorption is small

24. The GSM Ocean Color Model Parameters (aph*(l), S, etc.) • Problems • Only first order understanding • Parameterizations are imperfect Garver & Siegel, JGR [1997] GSM Model Products (Chl, CDM & bbp) LwN(l)

25. Optimizing the GSM Model Compiled a global LwN(l) & validation data set Used it to “tune” the parameters in the model Maritorena et al. [2002] AO(… the GSM01 model) Validation Data “Tuned” Parameters Optimization UCSB Ocean Color Model LwN(l) Products

26. Does this all work?? • Algorithm alone… • 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

27. Does this all work?? • Independent global match-up data set of SeaWiFS & CDM observations • Regression is pretty good (r2 = 71%) Siegel et al. [2005] JGR

28. Comparison of Patterns r2 = 0.65; N = 111 slope = 1.16 Siegel et al. [2005] JGR A20 A22 A16N

29. Global CDOM Distribution Siegel et al. [2005] JGR

30. Global CDOM Distribution % non-water absorption(440) due to CDM

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

32. Role of Rivers Large River Outflows… Maximum annual change due to global rivers is 0.005 m-1 River inputs are just not important on a global scale

33. Global CDOM & DOC • CDOM ¹ DOC • Completely different Tropics vs. high latitudes Subtropical gyres • Different processes driving CDOM & DOC CDM DOC Siegel et al. [2002] JGR

34. Summary of Satellite CDOM • Large latitudinal trends (low in tropics) • Large seasonal trends (low in summer) • Ocean circulation structures are apparent • CDOM follows basin-scale upwelling patterns • Rivers are small, proximate sources • CDOM is not related to DOC simply These are global surface CDOM values … what are the roles of vertical processes??

35. Seasonal Cycles of CDOM at BATS BATS - Sargasso Sea (after Nelson et al. 1998) Seasonal cycle CDOM ¹ DOC CDOM ¹ POC CDOM ¹ Chl Temperature DOC CDOM

36. Seasonal Cycle of CDOM at BATS Fall Mixing Deep Mixing Depth (m) Summer Stratification Month

37. Net Production of CDOM Summer – Spring CDOM BATS data Sargasso Sea (Nelson et al. 1998) Production max at 40-60 m Similar to the bacterial production

38. Seasonal CDOM Cycle at BATS Links mixing, photolysis & production • Low summer ML CDOM due to bleaching • Shallow summer max of CDOM production • Mixing homogenizes the system • Again, not related to DOC [CDOM] << [DOM]

39. Photobleaching of CDOM Laboratory incubations of filtered Delaware Bay water Blough & Del Vecchio [2002] time

40. Microbial Production of CDOM Bacteria Microbes produce long-lived CDOM Experiments from BATS 60m water by Nelson & Carlson After Nelson et al. [2005] CDOM

41. Example spectra for controls vs. plankton Zooplankton & CDOM 8 hour excretion experiments from Sargasso Sea Steinberg et al. [2005] - MEPS

42. The Open Ocean CDOM Cycle • Losses due to photobleaching • Mixed layer climate & UV dose • There is a net biological source • Likely microbial activity on organic carbon • Zooplankton too, BUT this material seems to be labile (and back to microbes…) • Likely biological sinks too…

43. The Open Ocean CDOM Cycle Siegel et al. [2002] JGR

44. The Hydrography of CDOM Nelson, Carlson & Siegel - Support by NSF & NASA

45. The Global CDOM Project CLIVAR - Repeat Hydrography Survey Full hydrographic suite T,S,O2,Nuts,CFC’s,CO2,... CDOM measured using WPI Ultrapath CDOM reported as ag(325) Nelson et al., DSR-I [2007] & more in review… www.icess.ucsb.edu/GlobalCDOM Just North of Hawaii

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

47. Atlantic A22 Temperature GS STMW AAIW Deep Caribbean NADW Nelson et al. [2007] - DSR-I

48. Atlantic A22 CDOM Grand Banks Orinoco GS STMW AAIW Deep Caribbean NADW

49. CDOM in Subtropical Mode Water Potential Temperature CDOM ag(325) BATS observations Nov 11, 2001 Low CDOM in 18o water mass 18o water ventilates north of BATS bringing low CDOM surface waters to south low CDOM 18o water

50. Atlantic A22 CDOM Grand Banks Orinoco GS STMW AAIW Deep Caribbean NADW How do DOC distributions look??