small particles and carbon export in the surface ocean chin-chang hung* and gwo-ching gong national...
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Small particles and carbon export in the surface ocean
Chin-Chang Hung* and Gwo-Ching Gong
National Taiwan Ocean University
Acknowledgements
Drs. Hui-Ling Lin, James Liu, David Sheu, Chih-An Huh, Wen-Chen Chou, Chih-Ching Chung
Wang-Chen Chung, Fang-Shi Kuo, Wei-Ting Kuo, Song-Lan Lee, Min-Lan Sheu, Jin-Seng Hsieh, Chin-Wei Tseng, Jin-Min Wu and crews of R/V OR-I and OR-II
Global carbon cycle
7.2 ± 0.3 GtC/yr7.2 ± 0.3 GtC/yr
0.9 ± 0.6 GtC/yr
2.2 ± 0.5 GtC/yr
4.1 ± 0.1 GtC/yr
IPCC, 2007
6CO2 + 6H2O C6H12O6 + 6O2
photosynthesis respiration uptake release
Particulate organic carbon flux, POC flux
Modified from Chung 2008
The Joint Global Ocean Flux Study (JGOFS)
The Operational Goal of JGOFS was to assess more accurately, and understand better the processes controlling, regional to global and seasonal to interannual fluxes of carbon between the atmosphere, surface ocean and ocean interior, and their sensitivity to climate changes.
Methods for measuring POC flux
Sediment traps
Primary production (f ratio)
New production
CO2 & Nutrient budget234Th/238U disequilibrium
Upper ocean carbon flux
A sediment trap directly measures carbon flux in the ocean, but has
problems:1. Hydrodynamics2. Swimmers 3. Solubilization of particles 4. Trapping efficiency
Carbon flux to depth relationship
Cflux(z) = Cpp / (0.0238z +0.212)
Suess (1980)
Cflux(z): carbon flux to depth (z)
Cflux(z) = Cexport x (Z/Zo)-0.858
(Martin et al., 1987)
Comments by Bishop (1989)
Bishop (1989) suggested that if the downward POC flux at 100 m depth is known, then the POC flux to the deep ocean may be predicted more accurately than from the PP-based equation.
1 4 0
1 2 0
1 0 0
8 0
6 0
4 0
2 0
0
dept
h (m
)
0 0 .0 5 0 .1 0 .1 5
P a r. T h -2 3 4 (d p m /L )0 1 2 3
T h -2 3 4 o r U -2 3 8 (d p m /L )
U -2 3 8 T o ta l T h -2 3 4 P articu la te T h -2 3 4 D isso lv ed T h -2 3 4
Deficiency of 234Th = depth integrated 234Th flux
Hung and Gong (2007)
Schematic of the 234Th flux approach (Buesseler et al., 2006)
POC flux = (POC/234Th)p x 234Th flux
POC can be PIC, PAHs, PCB, Biogenic silica & Trace metals etc. 234Th flux: depth integrated 234Th flux.
POC ( at least 50 papers)Particulate inorganic carbon (Bacon et al., 1996 )
Polycyclic aromatic hydrocarbons (Gustafsson et al, 1997)Polychlorinated biphenyles (Gustafsson et al., 1997b)
Biogenic silica (Buesseler et al 2001, Rutgers et al., 2002)Trace metals (Gustafsson et al. 2000, Weinstein et al)
Upper ocean carbon flux
Assumptions of the empirical method
1. Steady state or non steady state conditions
2. POC and 234Th should be carried down by sinking particles
3. Large particles are representative of major carbon flux in the ocean
Previous research review
Smayda, T.J. (1970) documented the trend of larger particles to sink faster (cited # 316).
Fowler and Knauer (1986) proposed that “the rare large particles (>100 m) sinking through the water column are responsible for the majority of the downward vertical mass flux in the ocean (cited# 297)
POC flux = (POC/234Th)p x 234Th fluxHenceforth, the POC/234Th ratio on large particles (e.g.
> 53 or 70 m) has been increasingly adopted to calculate the POC flux through the euphotic zone in different hydrographic settings including many research from the Joint Global Ocean Flux Study
(Buesseler et al., 1995; Bacon et al., 1996; Cochran et al., 2000, and many scientists)
Bacon et al. (1996) pointed out that “the filtered large particles are representative of the sinking particles” has not been proven (cited# 117)
Measuring 234Th and POC on size-fractionated suspended particles
Suspended Particles
>50 m
>10 m
>1 m
Re-filtration through QMA or GF/F filters
Moran et al. (2003) L&O, 48, 1018-1029.
Moran et al., 2003
The largest uncertainty of Th-234 method is on POC/Th-234 ratio.
1
10
100
1000
10000
Trap SinkPar 1-10 10-53 >53
Particle size (um)
PO
C f
lux
(mg/
m2/
d)
Hung et al.2004
Hung andGong, 2007
Large
Uncertainty in previous studies
(Hung and Gong, in preparation)
Question
Are the filtered large suspended particles really
representative of major settling particles?
Sinking Particles
Sediment traps
GPS instrument
Satellite
POC, TC, 234Th, TCHO etc.
Measuring POC, acidic polysaccharides
Measuring 234Th in size-fractionated sinking particles
Sinking Particles
>150 m
>50 m
>10 m >1
m
Main
land C
h ina
Y an g tze R iver
11 8 11 9 1 2 0 1 2 1 1 2 2 1 2 3 1 2 4 1 2 5 1 2 6 1 2 7 1 2 8 1 2 9 1 3 0
L o n g itu d e (o E )
2 4
2 5
2 6
2 7
2 8
2 9
3 0
3 1
3 2
3 3L
atit
ude
(oN
)
Main
land C
h ina
2 0 0 m
1 0 0 0 m
O R 1_836 , Ju ly 1 -11 , 2007
C hang jiang
Summer and Winter, 2006~2008.
East China Sea
Taiwan
11 8 1 2 0 1 2 2 1 2 4 1 2 6 1 2 8 1 3 0 1 3 2L o n g itu d e ( oE )
2 0
2 2
2 4
2 6
2 8
3 0
3 2
Lat
itude
(o N
)
2 0
2 2
2 4
2 6
2 8
3 0
3 2
11 8 1 2 0 1 2 2 1 2 4 1 2 6 1 2 8 1 3 0 1 3 2
N o rth w est P a cific O cea n
Ta i
wan
C h in a E a st C h in a S ea
M atsu
K ee lu n g1 0 0 0 m
Status of T7KP Sediment Mooring (July 7-Sept. 11, 2008)
T7KP
Lower trap
y = 3.2x + 64
R2 = 0.76
y = 12.3x + 68
R2 = 0.71
0
50
100
150
200
250
0 10 20 30 40
Th-234 flux
POC fl
ux
Cup #7-8
Cup#9-12
(Cup #7-8)線性 (Cup#9-12)線性
T7KP
Upper trap
Conclusions1. We found that small particles (1-10 and 10-50 m)
likely represent a significant fraction of sinking particles in terms of carbon and 234Th contents in the surface ocean.
2. The results suggest that small sinking particles dominating carbon flux in the surface ocean are beyond current dogma of biological oceanography.
3. Most importantly, our results also show that the previous 234Th-derived carbon export, based on POC/234Th ratios on large filtered particles (>50 m) times 234Th flux, may be significantly biased because plenty of filtered large particles (formed by small particles) may be breakup during sequential filtration process.
B
0
5000
10000
15000
20000
25000
30000
S3 S16 S29
234 T
h fl
ux (
dpm
m -2
d-1
)
sum of fourfractions
no fraction
A
0
20
40
60
80
100
120
140
160
S3 S16 S29P
OC
flu
x (m
mol
m -2
d-1
)
sum of fourfractions
no fraction
0
10
20
30
40
50
60
>150 50-150 10-50 1-10
Size classes (um)
(%)
Vol
POC
Th-234
< 1 1 ~ 1 0 1 0 ~ 2 0 2 0 ~ 5 0 5 0 ~ 1 0 0 1 0 0 ~ 1 5 0 > 1 5 0
P a rtic le S ize (m )
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
Per
cen
tage
(%
)
F a tes_ T 7 K P , b o t to m9 8 ~1 0 0 cm
S28
0 0.2 0.4 0.6
30
40
45
Dep
th (m
)
POC flux (g m-2
d-1
)
S26
0 0.1 0.2 0.3
40
70
100
Dep
th (m
)
POC flux (g m-2
d-1
)
Summer 2007
What kinds of organic compounds are involved in the scavenging of 234Th in different marine environments?
• acidic polysaccharides (APS) and/or protein-sugar?
• Who is responsible for the production of APS (bacteria or phytoplankton)?