MEDFLUX: Use of Amino Acid Degradation Indices to Examine Exchange Between Sinking and

Suspended Particles

Cindy Lee, Zhanfei Liu, Stuart Wakeham & Rob Armstrongw/Jianhong Xue

Ocean Sciences 2006

Biological Carbon PumpBiological Carbon Pump

activevertical migration

fixation of C, Nby phytoplankton grazing

egestion

passivesinking ofPOC, PIC

aggregate formation

respiration

excretion

excretion

respiration

physical mixingof DOC

consumption,repackaging

CO2

N2

Seabed

Base of euphotic zone

decomposition

break up

(bacteria) (zooplankton)

Lateraladvection

(from OCTET Report, 2000)

RR R

R

RR

R

RR

R

R

R

RR R

R

RR

RR R

R

RR

C

CC

Mechanisms of Compositional Change

(Sheridan C.C., C. Lee, S.G. Wakeham, and J.K.B. Bishop. 2002. Suspended particle organic composition and cycling in surface and midwaters of the equatorial Pacific Ocean. Deep-Sea Res. I 49: 1983-2008)

A little background: Organic Biomarkers as Diagenetic Indices

Les

s de

grad

edM

ore

degr

adedP

C1

Site

Sc o

res

EqPac trap and pump data suggest that in the upper water column, suspended particles are similar or fresher than sinking particles.

We did not have deeper pump samples.

Amino Acid Degradation Index

Eq PumpsPumpsTraps

Dep

th (

m)

Slide 15

MedFluxSampling

site

MONACO

We collected suspended and sinking particles using in-situ pumps and sediment traps at the French JGOFS DYFAMED site in the western Mediterranean. For more information, see http://www.msrc.sunysb.edu/MedFlux/.

According to Hill (1988), slowly sinking particles collide with other particles to form larger aggregates, but when they get too large and start sinking too quickly, they fall apart because of the high shear.

Basically, particle size and sinking velocity adjust to changes in particle density, always yielding the same sinking velocity spectrum.

How can we measure the extent of equilibration between suspended and sinking particles.

The relationship of particle compositions of suspended and sinking particles should be determined by the ratio of remineralization rate R to exchange rate E. In the case of little or no exchange between fast- and slow-sinking particle pools (E<<R), we expect the difference in DI and POC/Th between slow and fast pools to increase with

depth.

Cw

-kdCs

-kaCs

-sCsCs

Average time matter stays in suspended pool is

Assuming steady state and 1st order kinetics:

€

1

λ s + ka

€

kdCw = (ka + λ s)Cs

In surface waters, the suspended particles are slightly fresher than sinking particles.

DI of sinking particles shows no trend with depth. Suspended particles are more degraded than sinking particles at depth.

Amino Acid DI-5 -3 -1 1 3 5

Dep

th (

m)

Using the equation:

€

kdCw = (ka + λ s)Cs

€

1

ka + λ s

= 5.31

kd

And the observed relation between Cs and depth, we calculate:

NEXT:

Use other indicators of degradation, including POC/Th, so that we can calculate the residence time of the suspended particles.

Include in the model second order aggregation kinetics and depth-varying values of k and

Experimentally relate DI to CO2 lost on a site-specific basis.

Compare suspended, slow and fast sinking particles from our 2005 cruise.

The addition of Th may give us the time constant necessary to independently determine sinking rates as well.