Hydrography of Chromophoric Hydrography of Chromophoric Dissolved Organic Matter (CDOM) Dissolved Organic Matter (CDOM)

in the Pacific Oceanin the Pacific Ocean

Chantal SwanChantal Swan, David Siegel, Norm Nelson, Craig Carlson, David Siegel, Norm Nelson, Craig CarlsonInstitute for Computational Earth System ScienceInstitute for Computational Earth System Science

University of California Santa BarbaraUniversity of California Santa Barbara

ASLO Aquatic Sciences, Santa Fe, NM 2007ASLO Aquatic Sciences, Santa Fe, NM 2007

Open-ocean CDOM: quick factsOpen-ocean CDOM: quick facts

• CDOM (mCDOM (m-1-1) = light-absorbing fraction ) = light-absorbing fraction of DOM (of DOM (≤≤0.2µm)0.2µm)

• Open-ocean CDOM Open-ocean CDOM ≠≠ DOC DOC

• Net produced through microbial processing of DOC & POCNet produced through microbial processing of DOC & POC• Destroyed by sunlight (photobleaching) in surface oceanDestroyed by sunlight (photobleaching) in surface ocean• Modulated by transport processes Modulated by transport processes

• Dominates UVR absorption in oceanDominates UVR absorption in ocean

• CDOM causes measurable bias in satellite Chl estimates CDOM causes measurable bias in satellite Chl estimates Siegel et al. [2005] GRLSiegel et al. [2005] GRL

300 350 400 450 5000

0.05

0.1

0.15

0.2

0.25

Wavelength (nm)

a cdom

(m-1

)

CDOM absorption spectrum

m-1 at 325nm

Global surface distribution of CDOMGlobal surface distribution of CDOM

7-yr. mean CDOM (440nm) from GSM algorithm (SeaWiFS-derived) 7-yr. mean CDOM (440nm) from GSM algorithm (SeaWiFS-derived) Siegel et al. [2005] GRLSiegel et al. [2005] GRL

UCSB Global CDOM Distribution and Dynamics SurveyUCSB Global CDOM Distribution and Dynamics Surveyhttp://www.icess.ucsb.edu/GlobalCDOM/http://www.icess.ucsb.edu/GlobalCDOM/

9 cruises 2003-present: 9 cruises 2003-present: NSFNSF CO CO22/CLIVAR Repeat Hydrography Program/CLIVAR Repeat Hydrography Program

& & NASANASA (D. Siegel, N. Nelson, C. Carlson) (D. Siegel, N. Nelson, C. Carlson)

4 cruises 2005-present: Equatorial BOX Project (M. Behrenfeld et al.)4 cruises 2005-present: Equatorial BOX Project (M. Behrenfeld et al.)

Eq. BOX

A

A F

ront

AAIWNPIW

AA

Front

AAIWNPIW

Pacific CDOM along 150Pacific CDOM along 150°°WW

• Meridional gradient in CDOM upper 3000m• Subtropical S. Pac. CDOM ‘low’ extends to 1000m• Characteristic features of water masses & equatorial upwelling

P16

Pacific CDOM vs. AOU (150Pacific CDOM vs. AOU (150°°W)W)

SALINITY [psu]

Pacific CDOM vs. AOU (150°W)Pacific CDOM vs. AOU (150°W)

r2 = 0.88, n=863

(z > 700m)

AOU (μmol/kg)

CD

OM

(m

-1)

P2

Pacific CDOM (zonal 30°N)Pacific CDOM (zonal 30°N)

NPIW

STMW

NPIWCDOM vs. AOU at 30°N

z > 0mr2 = 0.59, n=636

North Atlantic CDOM North Atlantic CDOM 66°W66°WA22

(Nelson et al. in press DSR-I)

• Low variability in CDOM in deep waters• Relatively rapid advection (NADW) = dominant process in N. Atlantic basin • Strong STMW signal – photobleached surface waters entrained

NADW

STMW

AAIW

DeepCaribbean

DeepCaribbean

NADW

STMW

STMW

North Atlantic CDOM vs. AOUNorth Atlantic CDOM vs. AOU

r2 = 0.01, n=613

(Pooled data: A16N, A20 & A22)

(z > 700m)

AOU (μmol/kg)

CD

OM

(m

-1)

SummarySummary

• The relative importance of net CDOM production vs. ventilation determines the CDOM-AOU relationship.

• The ratio of CDOM production rate to ventilation rate controls the basin-scale CDOM patterns observed.

Thank You:Thank You:• Funding Programs: NSF Chemical Oceanography

NASA Ocean Biology and Biogeochemistry

• NASA Earth System Science Fellowship Program

• Repeat Hydrography chief scientists & field teams

• A. Mishonov (TAMU)

• D. Hansell, S. Brown, W. Chen (RSMAS)

• D. Menzies, E. Wallner, M. Meyers, S. Goldberg,

J. Klamberg, K. Ireson, T. Westberry (UCSB)

Global CDOM ≠ DOC

CDM

DOC

Siegel et al. [2002] JGR

Surface CDOM & SeaWiFS

A16N

A20

A22

r2 = 0.65; N = 111slope = 1.16

Siegel et al. [2005] JGR