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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.