transmissometry are used to concurrently define scavenging regimes, coagulation rates, and 

 remineralization rates. 



STRENGTHS AND LIMITATIONS OF PROPOSED RESEARCH 



Strengths 



• Collection and measurement of DOC/COC in field: Collection of up to 40% of DOC is 

 possible by crossflow ultrafiltration and lkD cut-off ultrafilters. Colloids are size fractionated 

 using lkD, 3kD and lOkD ultrafilters. 



• Radiochemistry in water column: One can obtain important rate parameters relevant to organic 

 carbon cycling, including rate constants for scavenging, particle cycling and colloidal turnover. 



• Isotopic and elemental composition of colloids from field experiments: Modem 14 C in >10kD 

 fraction. Relationships between 234 Th-derived scavenging and particle cycling rate constants (k s , 

 Xp) and fraction of 234 Th associated with colloids, COC/DOC fraction, and SPM concentrations. 



• Biomarkers from field experiments: Potential of using pigment biomarkers in colloids as dating 

 tools. 



• Benthic resuspension rates of colloids by measurements in lab and field: Development of a 

 colloid flux model including COM/sediment partitioning and the development of shear stresses 

 at the benthic boundary layer. Measurement of COM fluxes from or to sediments as a function 

 of applied shear stress using box core material and a stirred benthic chamber. 



Weaknesses and potential problems : 



• Collection and measurement of DOC/COC in field experiments: Long collection times (8-20 

 hours, but not affecting station time for surface samples; subsurface samples require about 2 

 hours per depth), relatively large concentration factors are necessary to isolate colloids from 

 200-1000 L of seawater. Calibration experiments necessary for evaluating potential for artifacts 

 and blanks (filtration, ultrafiltration) in lab and field. Experiments are currently carried out in the 

 lab, and more will be carried out in the intercomparison experiments ("colloids cook-out") 

 organized by Ken Buesseler in the field. More experiments have been proposed to NSF in a 

 separate proposal. 



• Radiochemistry in water column: Relatively large requirements on wire time (2 hours/depth). 



• Isotopic and elemental composition of colloids from field experiments: Calibration experiments 

 are necessary to evaluate potential for artifacts and blanks. Several experiments have been carried 

 out, and more are planned. 



• Biomarkers from field from field experiments: Black plastic is employed to reduce potential 

 for photochemical degradation, cooling coils to reduce breakdown due to heat during 



98 



