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)?