MEDFLUX: Use of Amino Acid Degradation Indices to Examine Exchange Between Sinking and Suspended Particles Cindy Lee, Zhanfei Liu, Stuart Wakeham & Rob Armstrong w/Jianhong Xue Ocean Sciences 2006

Biological Carbon Pump active vertical migration fixation of C, N by phytoplankton grazing egestion passive sinking of POC, PIC aggregate formation respiration excretion respiration physical mixing of DOC consumption, repackaging CO 2 N2N2 Seabed Base of euphotic zone decomposition break up (bacteria) (zooplankton) Lateral advection (from OCTET Report, 2000)

    R RR R R R R R R R R R      R RR R R R     R RR R R R C C C   Mechanisms of Compositional Change

(Sheridan C.C., C. Lee, S.G. Wakeham, and J.K.B. Bishop Suspended particle organic composition and cycling in surface and midwaters of the equatorial Pacific Ocean. Deep-Sea Res. I 49: ) A little background: Organic Biomarkers as Diagenetic Indices Less degraded More degraded PC1 Site Scores

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 Pumps Pumps Traps Depth (m)

Slide 15 MedFlux Sampling 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

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.

CwCw -k d C s -k a C s - s C s CsCs Average time matter stays in suspended pool is Assuming steady state and 1 st order kinetics:

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 Depth (m)     

Using the equation: And the observed relation between C s 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 CO 2 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.