Dissolved Organic Carbon, Nitrogen,
and Phosphorous in seawater
Fuels the microbial loop
Sequesters a large amount of carbon,
as well as nitrogen and phosphorus
Complexes trace metals and affects their
concentration and bioavailability
Absorbs UV and PA radiation
Reactivity and the cycling of DOC in seawater
Nonreactive DOC
Semi-reactive DOC
Very reactive DOC
Heterotrophic microbial production ??
0o and 140 oW
Carlson and Ducklow, DSR II v 42; 639-656
Reactivity and the cycling of DOC in seawater
High production in the surface
(high microbial activity & production)
It’s all
Semi-reactive DOC
Low production in the deep
(low microbial activity & production)
Carlson and Ducklow, DSR II v 42; 639-656
Deep sea gradients in [DOC]
D. Hansell and C. Carlson, Nature 1998
Deep sea gradients in [DOC]
D. Hansell and C. Carlson, Nature 1998
Unpublished data
removed
AAIW
NADW
AABW
History of radiocarbon in the
Atmosphere and ocean
14C per mil
Frigate shoals
Figi
Galapagos
Prebomb value of -80 per mil
DOC cycling via DO14C
Williams, Oeschger, and Kinney; Nature v224 (1969)
UV photooxidation
1000L
HCO3- + H+
H2O + CO2
DOC cycling via DO14C
Williams, Oeschger, and Kinney; Nature v224 (1969)
UV photooxidation
1000L
Depth
14C(‰)
1880m
-351 ‰
-3470+330 ybp
1920m
-341 ‰
-3350+300 ybp
Age
How do we measure radiocarbon today ?
LN2 trap
For CO2
100-500 mls
Reduce to graphite
press into a target
Mass spectrometer
Analysis
(>25 µg C needed)
Accelerator Mass Spectrometry (AMS)
NOSAMS at Woods Hole
C-14 PP measurements use 106x more C-14 than natural abundance!!!!!
Radiocarbon in the Atlantic and Pacific Oceans
Peter M. Williams and Ellen Druffel; Nature 1987, JGR 1992
Radiocarbon in the Atlantic and Pacific Oceans
DIC 14C in surface waters
of the Atlantic and Pacific
has the same isotopic value.
Radiocarbon in the Atlantic and Pacific Oceans
DIC 14C in surface waters
of the Atlantic and Pacific
has the same isotopic value.
The deep Pacific DIC is older
than the deep Atlantic DIC
Radiocarbon in the Atlantic and Pacific Oceans
DIC 14C in surface waters
of the Atlantic and Pacific
has the same isotopic value.
DOC is always older than DIC
(by 4 kyrs in surface water)
DIC-> POC -> DOC
Radiocarbon in the Atlantic and Pacific Oceans
DIC 14C in surface waters
of the Atlantic and Pacific
has the same isotopic value.
DOC is always older than DIC
by 4 kyrs in surface water
14C of DIC and DOC
is about the same in the
deep Atlantic and Pacific
Radiocarbon in the Atlantic and Pacific Oceans
DIC 14C in surface waters
of the Atlantic and Pacific
has the same isotopic value.
DOC is older than DIC
by 4 kyrs in surface water
14C of DIC and DOC
is about the same in the
deep Atlantic and Pacific
Deep ocean values of DOC
are equal to a radiocarbon
age of 4000-5000 yrs
Either there is a source of
“old” DOC, or DOC persists
for several ocean mixing
cycles
Why is DOC so old (2000 ybp) in surface water?
DOC
DIC
Why is DOC so old (2000 ybp) in surface water?
“DOC Background”
Pete Williams and Ellen Druffel
“nonreactive” DOC
14C = DOC(deep)
Why is DOC old in surface water?
reactive DOC
14C=DIC
14C= 14C“reactive” DOC + “nonreactive” DOC
Using a simple 2 component mixing model of old “non-reactive” DOC
with deep sea 14C and [DOC] values, and a new “reactive” component with
DIC 14C, and [DOC] = [DOC]total-[DOC]deep,
[DOC]total  14C total = [DOC]deep  14C deep + [DOC]new  14C new
DOC 14C
DOC 14C
Depth
Using a simple 2 component mixing model of old “non-reactive” DOC
with deep sea 14C and [DOC] values, and a new “reactive” component with
DIC 14C, and [DOC] = [DOC]total-[DOC]deep,
[DOC]total  14C total = [DOC]deep  14C deep + [DOC]new  14C new
DOC 14C
DOC 14C
Depth
Modeled and measured DOC 14C values agree pretty well…
14C= “reactive” DOC + “nonreactive” DOC
Atlantic surface water
nonreactive DOC
14C = DOC(deep)
14C
calc = -120
14C
obs = -127
reactive DOC
14C=DIC
‰
‰
Pacific surface water
14C
calc = -147
14C
obs = -148
‰
‰
Nonreactive DOC = 650 GT C
Reactive DOC = 30-50 GT C
What flux of carbon is needed to maintain the
“old” marine DOC reservoir?
Global inventory/residence time = annual flux
680 GT C/ 5000-6000 yr = 0.11-0.14 GT C/yr !!!
How does this compare with other C fluxes?
Where does doc come from?
DOC and major carbon reservoirs and fluxes
Terrestrial Plants
900 GT C
Atmosphere 750 GT (CO2)
Terrestrial Primary
Production 75 GT C/yr
River flux
0.5 GT C/yr
Marine Primary
Production 60-75 GT C/yr
Soil 2000 GT C
Burial 0.1-0.2
GT C/yr
Carbonates 60,000,000 GT C
Kerogen
20,000,000 GT C
POC 15 GT C
DOC 700 GT C
150 GT C
The ocean, a global carbon wastebasket?
A small fraction of the DOC added to
the ocean by rivers is colored (colored
dissolved organic matter or CDOM)
that can be tracked by remote sensing.
It is believed that river DOM is
remnant of OM cycling on land, and
represents the material that cannot be
degraded. Is the ocean filling up with
terrestrial DOM?
DOC transport through estuaries and the input of
terrestrial organic carbon to the ocean.
DOC concentrations are nearly always
higher in rivers than in the ocean. Rivers
add C to the ocean.
In general, DOC displays conservative
behavior wrt salinity in estuaries.
Some estuaries add carbon, some
remove it.
Salinity (ppt)
Utilization of DOM by bacteria at different salinities
in the York River
Raymond and Bauer AME v 22 (2000)
What is the source of oceanic DOC ?
Druffel et al., JGR 1992
Stable C isotopes
Marine C
-21‰
Terrestrial C
C3 plants -27‰
C4 plants -15‰
Production of reactive and non reactive DOC by
phytoplankton and bacteria
Microbial diversity is due to
Changes in very reactive DOC
CO2
Reactive DOC
O2
Very reactive DOC
Non reactive DOC ?
Bacterial production is thought to be fuelled by very reactive
DOC (simple, LMW organic compounds) that have half lives
in seawater of hours to days.
….then why isn’t the ocean filled with river DOC,
and where does the non reactive marine DOM come from?
900 m
0
20
40
60
80
DOC (µM)
15 m
100 120
Data from Bob Chen and Jeff Bada
Ken Mopper and his group fwere able to show rapid photoxidation
Of DOM in the presence of sunlight
Filtered SW
DOC + light
C=O + fluorophore
LMW carbonyls (C=O)
HPLC
Whole SW
Filtered SW
Whole SW
Not produced in dark controls,but are produced in sterile controls
Production of LMW highly oxidized DOC with depth in
the ocean
DOC + light
LMW photo-oxidation products
Is photochemical degradation the long term sink for river (terrestrial)
And therefore nonreactive DOM in the ocean ???
H2C=O
HOOCCOOH
Highly oxidized LMW compounds are produced every
day in seawater by photo-oxidation. They serve as a substrate
for bacteria and therefore a sink for non-reactive DOC
CH3C=O
CH3(C=O)CH3
CH3CH2CH2OH
…..then why is the ocean filled with (40 µM) marine DOC, and where does it go?
Unpublished data removed
Dissolved organic nitrogen and phosphorous
Organic C-N-P are connected at the molecular level;
what is true for C is (assumed to be) true for N and P.
We cannot determine the age of DON directly. DOP
residence times in surface water can be measured using
cosmogenic 33P/32P.
DON and DOP concentrations are higher in surface waters
(where production > degradation), than in the deep sea,
so we infer from DOC/DON/DOP ratios that there
are “nonreactive” and “reactive” fractions of DON and DOP.
DON and DOP are even more difficult to measure than DOC,
there is no way to remove inorganic N and P from seawater
prior to DON/DOP analyses, so all measurements of organic N/P
are difference measurements.
What drives microbial diversity in the ocean ?
Karner et al. Nature 2001
What is the relationship between organic matter
composition, microbial diversity & production?
How is microbial metabolism coupled to organic matter
structure?
How does DOM affect microbial adaptation & evolution?
What sets the ocean inventory of organic carbon,
and why is so much organic carbon preserved in seawater?
Why do organic nitrogen and phosphorus accumulate
in nutrient limited regions of the surface ocean where they
are most needed, but disappear in the mesopelagic ocean
where they are not needed?
Karner et al. Nature 2001