CDOM in the Deep Sea: Distribution and Dynamics from Trans-ocean Sections Norm Nelson, Dave Siegel,...
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Transcript of CDOM in the Deep Sea: Distribution and Dynamics from Trans-ocean Sections Norm Nelson, Dave Siegel,...
CDOM in the Deep Sea: CDOM in the Deep Sea: Distribution and Dynamics from Distribution and Dynamics from
Trans-ocean SectionsTrans-ocean Sections
CDOM in the Deep Sea: CDOM in the Deep Sea: Distribution and Dynamics from Distribution and Dynamics from
Trans-ocean SectionsTrans-ocean Sections
Norm Nelson, Dave Siegel, Craig CarlsonChantal Swan, Stu Goldberg
UC Santa BarbaraSpecial thanks to: Bill Smethie and Samar Khatiwala, LDEO
Dennis Hansell, University of Miami
Norm Nelson, Dave Siegel, Craig CarlsonChantal Swan, Stu Goldberg
UC Santa BarbaraSpecial thanks to: Bill Smethie and Samar Khatiwala, LDEO
Dennis Hansell, University of Miami
Ocean Sciences Meeting 2008
OutlineOutline
• About the project
• Distribution and hydrography
• Global dynamics of CDOM
• CDOM and DOM diagenesis
• Ongoing and future activities
• 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)
• 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)
Global Surface CDOM Distribution
(From SeaWiFS)
Global Surface CDOM Distribution
(From SeaWiFS)
Siegel et al. [2005] JGR
UCSB Global CDOM Project GoalsUCSB Global CDOM Project Goals
• Quantify global distribution of CDOM Surface, intermediate, and deep water
• Determine physical and biological factors controlling CDOM distribution
• Apply knowledge gained to problems of ocean circulation and DOM characterization and cycling
• Collect calibration and validation data for ocean color models
• Quantify global distribution of CDOM Surface, intermediate, and deep water
• Determine physical and biological factors controlling CDOM distribution
• Apply knowledge gained to problems of ocean circulation and DOM characterization and cycling
• Collect calibration and validation data for ocean color models
UCSB Global CDOM Project Measurements & MethodsCDOM 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)
• 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
UltraPathPrecisionUltraPathPrecision
• 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
• 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 HydrographyCDOM 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
• 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
Selected CDOM sectionsSelected CDOM sections
(Global CDOM map from SeaWiFS/GSM, mission mean)
acd
om (443 nm
, m-1)
Atlantic A22 CDOM / AOU (Apparent Oxygen Utilization)Atlantic A22 CDOM / AOU (Apparent Oxygen Utilization)
STMW
DeepCaribbean
AAIW
NAD
W
GS
STMW
DeepCaribbean
AAIW
NAD
W
GS
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: 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
Age calculations by Bill Smethie & Samar Khatiwala [LDEO]
STMW
DeepCaribbean
AAIW
NAD
W
P < 0.025 P < 0.025
P < 0.025
P < 0.025
T ~ 10y
T ~ 50y
T > 200 y
Age
vs.
CD
OM
Nel
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007]
DS
R-I
CDOM DynamicsCDOM 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
• 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
CDOM Atlantic / Pacific sectionsCDOM Atlantic / Pacific sectionsTop: (A16N, A20, AMMA, A16S) Bottom: P16N/STop: (A16N, A20, AMMA, A16S) Bottom: P16N/S
CDOM Dynamics: Atlantic
North Atlantic EQSubtropics Subtropics
Mode Water Mode Water
South Atlantic
Rapid meridional overturning allows little CDOM accumulationAdvection + bleaching balances net production
CDOM Dynamics: Pacific / Indian
North Pacific EQSubtropics Subtropics
Mode Water
South PacificSouthern O.
North: Long residence time allows CDOM accumulation
South: Production limited (iron?) Low surface signal carried to depth by advection / water mass formation
CDOM DynamicsCDOM 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
• 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 oceanTransformations 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)
• 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)
aa**cdom cdom = CDOM / DOC= CDOM / DOC
(units m(units m22gg-1-1))
Upper layers bleaching Upper layers bleaching & production signals& production signals
aa**cdomcdom increases w/ increases w/
depth & agedepth & age
CDOM “abundance” CDOM “abundance” changes less than the changes less than the DOC decline -- CDOM is DOC decline -- CDOM is refractory DOMrefractory DOM
Aging
NewNew
Ble
ach
ing
Nelson et al. [2007] DSR-I
DOM Quality: Carbohydrates and DOC, A20DOM Quality: Carbohydrates and DOC, A20
STMW
STMW
LTCL
LTCL
uAAIW
Sugars decreaseas CDOM increases
Neutral sugar content of DOC also decreases
AOU increases
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)
• 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 < 0.025P < 0.025 P < 0.025
P < 0.025P < 0.025
P < 0.025 P < 0.025
Nel
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DS
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Spectral Slope to Age?Spectral Slope to Age?
Handwaving age estimate:Handwaving age estimate:
SSnlfnlf of ≈ 0.014 nm of ≈ 0.014 nm-1-1 … >50 years mean ventilation age … >50 years mean ventilation age
Summary / ConclusionsSummary / 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.
• 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 workOngoing 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
• 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
AcknowledgmentsAcknowledgments
• 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
• 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