Dave Siegel Institute for Computational Earth System Science &

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

Thanx ... Collaborators Students Technical Staff Support
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

Talk Outline What is CDOM? Why do we care? (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?

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)

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 to nm-1

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

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

at(l) = aw(l) + aph(l) + ag(l) + ad(l)
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

Optical Importance of CDOM
Global Data set (N= 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)

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

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

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

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

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

UC Santa Barbara Drinking Water
ag() (m-1) S = 0.04 nm-1 Wavelength (nm)

UCSB Drinking Water Sargasso Sea

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

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)

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

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

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

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

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

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

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

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

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

Comparison of Patterns
slope = 1.16 Siegel et al. [2005] JGR A20 A22 Overall, there was good correspondence between the GSM01 estimated CDM and the in situ CDOM absorption coefficient at 443 nm (r2 = 0.65; N = 111). The linear regression slope was 1.16, with an intercept of m-1, indicating approximately a 15% overestimation of CDOM absorption by the GSM algorithm. A16N

Global CDOM Distribution
Siegel et al. [2005] JGR

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

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

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

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

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??

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

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

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

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]

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

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

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

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…

The Open Ocean CDOM Cycle
Deep CDOM lead in… Siegel et al. [2002] JGR

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

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… Just North of Hawaii

Surface CDOM & SeaWiFS r2 = 0.65; N = 111 slope = 1.16
Siegel et al. [2005] JGR A20 A22 Overall, there was good correspondence between the GSM01 estimated CDM and the in situ CDOM absorption coefficient at 443 nm (r2 = 0.65; N = 111). The linear regression slope was 1.16, with an intercept of m-1, indicating approximately a 15% overestimation of CDOM absorption by the GSM algorithm. A16N

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

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

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

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

A22 DOC Distribution CDOM ¹ DOC
Data from Dennis Hansell [UM] & Craig Carlson [UCSB]

How to diagnose the spatial patterns in CDOM??

Mankind to the rescue!!!

CFC’s as Transient Tracers
Mixing with ocean imprints ventilated waters w/ CFC levels Provides a ventilation “age” for water mass Atmospheric CFC’s are now dropping Good for O3 hole Bad for tracer work…

A22 CFC-12 Concentrations High CFC’s – recently ventilated waters
GS STMW AAIW Deep Caribbean NADW High CFC’s – recently ventilated waters Low CFC’s – old water

Atlantic A22 CFC-12 Age STMW AAIW NADW Deep Caribbean
Age calculations by Bill Smethie & Samar Khatiwala [LDEO]

Definitions follow Joyce et al. [2001]
Layer Abbreviation gn range (kg m-3) Surface SURF 18.00 – 25.00 Upper Thermocline UTCL 25.00 – 26.40 Subtropical Mode Water STMW 26.40 – 26.60 Lower Thermocline LTCL Upper Antarctic Intermediate Water uAAIW 27.00 – 27.50 Lower Antarctic Intermediate Water lAAIW 27.50 – 27.80 Labrador Sea Water LSW 27.80 – Iceland-Scotland Overflow Water ISOW – 28.05 Denmark Strait Overflow Water DSOW 28.05 – 28.14 Antarctic Bottom Water AABW 28.14 – 29.00 Definitions follow Joyce et al. [2001]

Regressions between age and CDOM
T ~ 10y T ~ 50y T > 200 y P < 0.025

a*cdom(325) a*cdom = CDOM / DOC
Upper layers bleaching & production signals a*cdom increases w/ depth & age CDOM is largely recalcitrant Nelson et al. [2007] DSR-I

Atlantic CDOM CDOM follows hydrographic & transient tracer patterns
Ventilation & advection appear to be the dominant processes (CDOM is set at surface) Evidence of a remineralization source (CDOM vs. age relationship decreases w/ depth) CDOM ¹ DOC (it is also recalcitrant) Nelson et al. [2008]

Pacific P16 Temperature AAIW AA Front Along 150oW done in 4 legs over 2 campaigns (2005/06) Swan et al. [ in prep]

Pacific P16 Salinity NPIW AAIW AA Front AABW

Pacific P16 CDOM SH Subtropical CDOM low extends thru upper 1000 m
High CDOM in NH thermocline

Pacific P16 CDOM AAIW NPIW AA Front Low CDOM in SH subtropical gyre
Very high in NH thermocline Some subducting water mass signature are seen in CDOM

Pacific P16 CFC-12 AAIW Very Old Water AABW
CFC concentrations at or below detection levels -> can’t calculate ages using CFC’s - too old

Pacific P16 AOU Apparent Oxygen Utilization = O2sat – O2
Measure of past remineralization of organic carbon

Pacific P16 CDOM SH Subtropical CDOM low extends thru upper 1000 m
High CDOM in NH thermocline

Pacific AOU vs. CDOM Z > 700 m Swan et al. [in prep] Satellite
ag(325) (m-1) Water-leaving Z > 700 m Swan et al. [in prep] AOU (mmol/kg)

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

Atlantic A22 AOU GS STMW AAIW Deep Caribbean NADW

North Atlantic AOU vs. CDOM
Z > 700 m

Deep Open CDOM Cycling Ratio of time scales Þ Tphys/Tbio
Large Tphys/Tbio Slow ventilation & Fast biology Þ Biogeochemical control Þ Pacific Small Tphys/Tbio Fast ventilation & Slow biology Þ Ventilation control Þ North Atlantic

Open Ocean CDOM CDOM distributions are consistent with hydrographic & transient tracer patterns Ventilation & net BGC production are the two dominant processes Their relative importance determines the observed patterns for each ocean CDOM ¹ DOC

Talk Outline What is CDOM? Why do we care?
Contributions to biogeochemistry & optical properties What is the global sea surface CDOM distribution? Ocean color remote sensing What regulates open ocean CDOM cycling? What is known about CDOM in the deep sea?

Thank You!!

Regressions between age and CDOM
Layer CDOM vs. Age (m-1yr-1) R2 n t-test SURF 0.005 0.031 80 N.S. UTCL -0.002 0.019 48 STMW 0.0100 0.028 20 P < 0.025 LTCL 0.0030 0.197 113 uAAIW 0.0006 0.064 144 lAAIW 8 E-5 0.003 83 LSW 0.010 131 ISOW 0.0002 0.016 58 DSOW 0.042 138 AABW 0.002 0.107 37

Table 1: Water mass layer definitions in terms of neutral density intervals (based on Joyce et al. 2001) and estimated CFC-12 saturation at formation (this study) Layer Abbreviation gn range (kg m-3) CFC-12 Saturation Surface SURF 18.00 – 25.00 100% Upper Thermocline UTCL 25.00 – 26.40 Subtropical Mode Water STMW 26.40 – 26.60 94% Lower Thermocline LTCL 90% Upper Antarctic Intermediate Water uAAIW 27.00 – 27.50 70% Lower Antarctic Intermediate Water lAAIW 27.50 – 27.80 Labrador Sea Water LSW 27.80 – Iceland-Scotland Overflow Water ISOW – 28.05 43% Denmark Strait Overflow Water DSOW 28.05 – 28.14 75% Antarctic Bottom Water AABW 28.14 – 29.00

CDOM As A Geochemical Tracer?
CDOM cycle and water mass ventilations Subducted waters should be “imprinted” with a net photobleaching signal Obducted waters should see the effects of higher micobial production on CDOM Would CDOM be a useful age tracer?

CDOM As A Geochemical Tracer?
BATS data Temp/TOC/CDOM CDOM low from Related to water mass renewal? Temperature High TOC TOC low CDOM CDOM

Modeling the CDOM Cycle
Are these simple concepts useful for the quantitative modeling of the CDOM cycle? Cycle links mixing, photolysis & production Model Components … CDOM Photolysis = f(solar radiation) CDOM Production = f(microbial production) PWP mixed layer model seasonal cycle

Modeling the CDOM Cycle
__________ = a(z) [CDOM] - b _______ [CDOM] exp(-cz) a(z) = production rate by microbial activity b = photobleaching rate c = extinction coefficient Parameter values chosen from BATS data Sol(t) Solo

Zooplankton & CDOM Copepods
Debbie Steinberg, Norm Nelson & Craig Carlson (unpubl. data)

Trichodesmium & CDOM Trichodesmium (cyanobacteria)
Debbie Steinberg, Norm Nelson & Craig Carlson (unpubl. data)

How to Quantify Ocean Color?
Ocean color is quantified by the normalized water-leaving radiance, LwN(l) LwN(l) = Fo(l) Lw(l) / Ed(l) where Lw(l) is the nadir upwelling radiance Ed(l) is the downwelling irradiance Fo(l) is the ET irradiance spectrum

Ocean Color Remote Sensing
Simple in concept green water is productive, blue water is not, brown is turbid, yellow is CDOM-rich, etc. The bio-optical link can be quantified Water-leaving radiance = LwN(l) can be modeled as a f(in-water constituents) Step is called a bio-optical algorithm

But, Ocean Color Remote Sensing is Difficult…
The ocean is a dark target Atmosphere path radiance is >90% of satellite signal Correcting for the atmospheric signal is still difficult Satellites are delicate optical instruments launched from rockets (on-board calibration)

Modeling Ocean Color Theory … Ocean Color = LwN(l) = ________________
Optical properties can vary independently Three components of ocean color CDOM, phytoplankton & particulate scattering backscattering absorption

What is Ocean Color? Light backscattered from the ocean
Quantified by water-leaving radiance LwN(l) atmosphere ocean

GSM01 Chlorophyll SeaWiFS chlorophyll distribution

Lots of places!! Washed to sea or formed in situ Allochthonous or Autochthonous Land vs. Ocean Not all CDOM is equal Different reactivities by region

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