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CDOM in the Deep Sea: Distribution and Dynamics from Trans-ocean Sections. Norm Nelson, Dave Siegel, Craig Carlson Chantal Swan, Stu Goldberg UC Santa Barbara Special thanks to : Bill Smethie and Samar Khatiwala, LDEO Dennis Hansell, University of Miami. Ocean Sciences Meeting 2008.

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cdom in the deep sea distribution and dynamics from trans ocean sections

CDOM in the Deep Sea: Distribution and Dynamics from Trans-ocean Sections

Norm Nelson, Dave Siegel, Craig CarlsonChantal Swan, Stu GoldbergUC Santa Barbara

Special thanks to: Bill Smethie and Samar Khatiwala, LDEO

Dennis Hansell, University of Miami

Ocean Sciences Meeting 2008

outline
Outline
  • About the project
  • Distribution and hydrography
  • Global dynamics of CDOM
  • CDOM and DOM diagenesis
  • Ongoing and future activities
what we already know bermuda
What we already know (Bermuda)
  • CDOM is produced and destroyed in the top 250m on an annual basis
  • Sources include microbes and zooplankton
  • Sinks include solar bleaching and possibly consumption by microbes
  • Lab experiments show microbes and zooplankton can produce CDOM faster than observed rates of change in water samples
  • Estimated turnover time scales ~100 days. (we can’t measure these rates very well in the lab)
ucsb global cdom project goals
UCSB Global CDOM Project Goals
  • Quantify global distribution of CDOM Surface, intermediate, and deep water
  • Determine physical and biological factorscontrolling CDOM distribution
  • Apply knowledge gained to problems of ocean circulation and DOM characterization and cycling
  • Collect calibration and validation data for ocean color models
global cdom project sections
Global CDOM Project Sections

EUCFe 2006

AMMA 2006

EqBOX

2005 2006

ucsb global cdom project measurements methods cdom analysis at sea
UCSB Global CDOM Project Measurements & MethodsCDOM Analysis At Sea
  • 200 cm Liquid Waveguide Absorption Cell (UltraPath, WPI Inc)
  • Single-beam spectrophotometer with D2 & Tungsten-halogen light sources, diode-array spectrometer detector
  • Fast, low sample volume (2 min/sample, 30-60 ml)
  • Issues with blanks(refractive index correction)

Nelson et al. [2007] DSR-I

ultrapath precision
UltraPathPrecision
  • Duplicate sampleanalysis (same Niskin)
  • RMS differenceat 325 nm:0.0034 m-1
  • This is ~4% of mean
  • RMS/Mean is between 5 and 10%between 300 and 400 nm
  • Longer wavelengths are not as good
  • Overall project: precision not as good, ca. 0.01 m-1

Nelson et al. [2007] DSR-I

cdom dynamics and hydrography
CDOM Dynamics and Hydrography
  • Distribution of CDOM in the ocean basins
    • Are there spatial gradients in the deep sea?
  • Relationship with AOU and age tracers
    • Is CDOM produced/consumed by microbes at depth?
  • Atlantic vs. Pacific& Indian
slide11

Selected CDOM sections

acdom (443 nm, m-1)

(Global CDOM map from SeaWiFS/GSM, mission mean)

atlantic a22 cdom aou apparent oxygen utilization

GS

STMW

AAIW

Deep

Caribbean

NADW

GS

STMW

AAIW

Deep

Caribbean

NADW

Atlantic A22 CDOM / AOU (Apparent Oxygen Utilization)
atlantic vs pacific indian what s different
Atlantic vs. Pacific/Indian: what’s different?
  • Atlantic: Productivity high but meridional overturning time scales much shorter
  • North Pacific / Indian: Most distant part of the global conveyor, longest time since ventilation, considerable remineralization
  • Southern Ocean / S. Pacific: Massive ventilation and deep water formation, productivity limited (iron?)
  • We can look at this more closely using age tracers -- CFC invasion
atlantic a22 cfc 12 age
Atlantic A22 CFC-12 Age

STMW

AAIW

Deep

Caribbean

NADW

Age calculations by Bill Smethie & Samar Khatiwala [LDEO]

pacific p16 cfc 12
Pacific P16 CFC-12

AAIW

Very Old Water

AABW

slide19

T ~ 50y

T ~ 10y

P < 0.025

P < 0.025

T > 200 y

P < 0.025

P < 0.025

Age vs. CDOM

Nelson et al. [2007] DSR-I

cdom dynamics
CDOM Dynamics
  • Pacific / Indian: Overall correlation with AOU, wide CDOM range
  • Atlantic: Correlation with age & AOU in the main thermocline, subtropical mode water, and upper AAIW, narrow CDOM range
  • Advection obscures CDOM production signal in the Atlantic
slide21

CDOM Atlantic / Pacific sections

Top: (A16N, A20, AMMA, A16S) Bottom: P16N/S

slide22

CDOM Dynamics: Atlantic

Subtropics

EQ

Subtropics

North Atlantic

South Atlantic

Mode Water

Mode Water

Rapid meridional overturning allows little CDOM accumulation

Advection + bleaching balances net production

slide23

CDOM Dynamics: Pacific / Indian

South Pacific

Southern O.

Subtropics

EQ

Subtropics

North Pacific

Mode Water

North: Long residence time allows CDOM accumulation

South: Production limited (iron?) Low surface signal carried to depth by advection / water mass formation

cdom dynamics1
CDOM Dynamics
  • Surface: Rapid turnover, production, consumption, and bleaching balanced, upwelling a minor contributor.
  • Mode waters: Ventilation carries surface signature across wide areas
  • Intermediate + Deep waters: CDOM abundance controlled by advection/net production balance
transformations of cdom dom in the ocean
Transformations of CDOM & DOM in the ocean
  • What chemical transformations of CDOM occur in the ocean?
    • We don’t have many handles to turn on this at the moment, but we have:
  • Changes in the CDOM/DOC relationship(a*cdom)
  • DOM quality indexes(Neutral sugar and carbohydrate content)
  • Changes in the CDOM spectrum(Spectral slope parameter)
a cdom 325
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

dom quality carbohydrates and doc a20
DOM Quality: Carbohydrates and DOC, A20

STMW

LTCL

uAAIW

Sugars decrease

as CDOM increases

Neutral sugar content of

DOC also decreases

AOU increases

STMW

LTCL

spectral slope parameter
Spectral Slope Parameter
  • S (nm-1), 280-400 nm, non linear fit
  • Typical Coastal: 0.015 nm-1
  • Typical Sargasso Surface: > 0.025 nm-1
  • Newly Produced Sargasso: ~ 0.022 nm-1

(Nelson et al. Mar. Chem 2004)

trends in cdom spectral characteristics n atl
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

spectral slope to age
Spectral Slope to Age?

Handwaving age estimate:

Snlf of ≈ 0.014 nm-1 … >50 years mean ventilation age

summary conclusions
Summary / Conclusions
  • CDOM dynamics worldwide reflect a balance between production and bleaching, moderated by the rate of advection.
  • CDOM is also produced (slowly) at depth as a byproduct of remineralization.
  • The CDOM optical signature is more refractory than the bulk DOC pool.
  • DOM undergoes chemical transformations with age that are reflected in the carbohydrate composition and optical properties.
ongoing and future work
Ongoing and future work
  • What is the nature of CDOM in the deep ocean and what transformations occur?
  • We’re tackling this with fluorescence spectroscopy and hopefully more advanced techniques to try and identify key chromophore groups and how they change over time and space
acknowledgments
Acknowledgments
  • NASA Ocean Biology and Biogeochemistry
  • NSF Chemical Oceanography
  • U.S. CLIVAR/CO2 Repeat Hydrography Project(Jim Swift, Lynne Talley, Dick Feely, Rik Wanninkhof, Rana Fine)
  • UCSB Field Teams: Dave Menzies, Jon Klamberg, Meredith Meyers, Ellie Wallner, Meg Murphy, Natasha McDonald
  • Hansell Group: Charlie Farmer, Wenhao Chen
  • Bill Landing (FSU) and Chris Measures (UHI) (Water samples)
  • Ru Morrison & Mike Lesser, UNH (MAA analysis)
  • Wilf Gardner and Team, TAMU (C-Star transmissometer)
  • Mike Behrenfeld and Team, OSU (Equatorial BOX project)
  • Erica Key and Team, U Miami (AMMA-RB 2006)
  • Jim Murray and Team, UW (EUCFe 2006)
  • R/Vs Brown, Knorr, Revelle, Melville, Thompson, Ka’I, Kilo Moana
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