Characterizing upper ocean CDOM dynamics using integrated laboratory, satellite and global field data Characterizing upper ocean CDOM dynamics using integrated laboratory, satellite and global field data Chantal M. Swan, David A. Siegel, Norman B. Nelson, Tihomir S. Kostadinov, Craig A. Carlson University of California Santa Barbara Ocean Color Research Team Meeting New Orleans, LA May 12, 2010

CDOM (m -1 ) =CDOM (m -1 ) = light-absorbing DOM (≤0.2µm) light-absorbing DOM (≤0.2µm) Open-ocean CDOM << DOMOpen-ocean CDOM << DOM Does not covary with Chl or DOCDoes not covary with Chl or DOC on annual time scales on annual time scales Destroyed by sunlight (photolysis) in surface oceanDestroyed by sunlight (photolysis) in surface ocean Net produced through microbial remin. of DOC & POCNet produced through microbial remin. of DOC & POC These processes modulated by transportThese processes modulated by transport Dominates non-water UV absorption in ocean (up to 90%)Dominates non-water UV absorption in ocean (up to 90%) CDOM causes measurable bias in satellite Chl estimates [S iegel et al. 2005]CDOM causes measurable bias in satellite Chl estimates [S iegel et al. 2005] CDOM in the Open Ocean Absorption coefficient (m -1 ) at 325 nm CDOM Spectrum

CDOM in the Open Ocean UCSB Global CDOM Survey (2003 – present) Cruise transects of U.S. CO 2 /CLIVAR Repeat Hydrography Program 7-yr mean (1997 – 2005) colored dissolved and detrital materials (“CDM” m -1, 443 nm) estimated from GSM algorithm [Siegel et al. 2002] using SeaWiFS P2 I9N I6S I8S A20 P16 A16 A22 P18 P6

Measuring CDOM in the Open Ocean 0.2-μm filtered water samples collected from niskins 1.93 m liquid waveguide spectrophotometer = detection of low CDOM Refractive index correction for salinity of samples Spectral Slope (S) estimation: a CDOM (λ) = a CDOM (λ o ) e – S (λ – λ o ) CDOM Spectra

acdom325 [1/m] P16 r 2 = 0.81,n = 1522 AOU vs. CDOM (z > 100m) 150°W CDOM in the Pacific [Swan et al., DSR-I, 2009] Pacific basin characterized by weak ventilation and strong meridional gradient in CDOM and biogeochemical properties SALINITY [psu] NPIW AABW CDW AAIW

CDOM in the North Atlantic [Nelson et al., DSR-I, 2007] A22 (66°W) Low variability of CDOM in deep waters Rapidly advecting NADW = dominant process for CDOM distribution in N. Atlantic Strong mode water signal (STMW) = photobleached surface waters entrained NADW STMW Deep Caribbean Deep Caribbean NADW STMW acdom325 [1/m] AOU vs. CDOM (z >100m) r 2 = 0.17, n=617

Controls on the open ocean CDOM distribution CDOM distribution is controlled by the relative strengths of: transport (ventilation, advection, upwelling) production (microbial transformations of DOC & POC) loss (photolysis in surface waters)

 = loss of CDOM absorption per unit of light absorbed Determination of the apparent quantum yield (  ) Moderates global surface distribution of CDOM Moderates photochemistry (e.g., CO 2, CO, COS release, DMS photolysis) 15 samples from the major ocean basins Shore-based laboratory incubations using simulated solar irradiation CDOM Photolysis see Swan et al. OCRT POSTER

Experimental Design: = Simulates spectrum and intensity of terrestrial irradiance Solar Light Co. LS1000 Solar Simulator (Dark Control) = 2 days in simulator ≈ 11 days* in surface ocean ≈ 57 days* in mixed layer *estimates based on mean daily insolation at 325nm, MLD, and CDOM/light attenuation in mid- Atlantic in spring [Zafiriou et al. 2008] Time course of CDOM absorption = photolysis rate = da CDOM ( λ o ) /dt CDOM Photolysis in situ T°C

d(a CDOM (λ o ))/dt = ∫ Φ(λ o ;λ i ) E o (λ i ) ā CDOM (λ i ) dλ i CDOM Photolysis Analytical Approach: A and B coefficients solved by inversion da CDOM /dt = m -1 s -1 A = m 2 mol photons -1 λ ref = 300nm Φ = m 2 mol photons -1 B = nm -1 E o = mol photons m -2 s -1 nm -1 λ o = observation (nm) ā CDOM = m -1 λ i = irradiation (nm) Φ(λ o ;λ i ) = A(λ o ) e - B(λ o )(λ i – λ ref )

da CDOM /dt (measured) Time E 0 *ā cdom E 0 *ā cdom *  ( o=325nm) Time d(a CDOM (325))/dt E o (λ i )*ā CDOM (λ i )  (325;λ i ) a CDOM (λ o ) Eo(λi)Eo(λi) d(a CDOM (λ o ))/dt = ∫ Φ(λ o ;λ i ) E o (λ i ) ā CDOM (λ i ) dλ i Schematic of inversion terms:  (325;λ i )*E o (λ i )*ā CDOM (λ i ) λ i (nm) λ o (nm) λ i (nm) exposure time (days)

Controls on quantum yield (Φ) variability in the open ocean? Is Φ = f (z, T, salinity, O 2, N, P, Si, Fe 2+, DOC, Chl-a, initial a CDOM, initial S, N:P, Si:N, AOU) ? Φ(325,λ i )

A model for apparent quantum yield (Φ) for CDOM photolysis in the open ocean:  ( o ; i ) =  0 ( o ; i ) +  1 ( o ; i ) (AOU) +  2 ( o ; i ) (N:P) +  3 ( o ; i ) (S)  0 (325;325) = m 2 mol photons -1  1 (325;325) = m 2 mol photons -1  mol -1 kg  2 (325;325) = m 2 mol photons -1  3 (325;325) = m 2 mol photons -1 nm Up to 95% of variability in apparent quantum yield is explained by AOU, N:P and initial S of the samples  i =300 i =310 i =320 i =325 i =330 i =340 i =350 i =360 i =375 i =400 o = NS o =310 NS NS o = NS o = NS o = o =340 NS o = o = o = o = Table of r 2 values (p < 0.04, n = 14) [Swan et al., submitted]  (325;λ i )*E o (λ i )*ā CDOM (λ i ) Action Spectrum

310 – 350 nm wavelengths primarily responsible for CDOM photolysis Need CDOM and E o measurements in the UV Remote-sensed estimates of colored dissolved and detrital materials (‘CDM’) are at 443 nm  d(a CDOM (λ o ))/dt = ∫ Φ(λ o ;λ i ) E o (λ i ) ā CDOM (λ i ) dλ i  (325;λ i )*E o (λ i )*ā CDOM (λ i ) How to apply ocean color data to estimate global CDOM photolysis rate?

Extrapolating satellite-retrieved absorption by colored dissolved and detrital materials, ‘CDM’ (m -1, 443 nm), into the UV Ŝ = *e *CDOM (443) r 2 = 0.73, n = 7611 CLIVAR global field CDOM data Spectral slope (S, nm -1 ) as a function of the CDOM absorption coefficient (m -1, 443 nm)

Estimating CDM UV absorption from satellite: all cruises surf. data (z < 7m) n = 277, p< nm: r 2 = nm: r 2 = nm: r 2 = nm: r 2 = 0.65 Ŝ = *e *a CDM(443) a CDM(λ) = a CDM(443) *e –Ŝ(λ-443) extrapolated CDM vs. measured CDOM SeaWiFS(GSM) a CDM (m -1 ) spectroscopic a CDOM (m -1 )

Estimating CDM absorption in the UV from satellite: Next step: monthly climatologies of CDM(UV)

Estimate depth-resolved CDOM photolysis rates in the global ocean: d(a CDM (λ o ))/dt = ∫ ∫ E s (λ i )e -k d (λ i )z a CDM (λ i ) Φ(λ o ;λ i ;AOU;N:P;S) dλ i dz ( integrated over λ i and z = surf – MLD FUTURE STEPS PROPOSED DATA SOURCES E S (UV-VIS): TOMS, SeaWiFS a CDM (UV-VIS) and S: GSM output (443nm) and Global S Model k d = model (Bonhommeau et al., in prep) z = MLD from FNMOC O 2, N, P = NODC