ultrafiltration, calibration experiments test cell lysis and breakdown during filtration and 

 ultrafiltration procedures. Some of these have been carried out, some more are planned. 



• Benthic resuspension rates of colloids by measurements in lab and field: Long time scales of 

 these experiments, if one wants rigorous approach. 



STATUS OF RESEARCH 



During this funding period, three sampling expeditions to the Gulf of Mexico, and one 

 cruise to the Cape Hatteras region were undertaken. Another one is planned for June 27 -July 13, 

 1994, and a colloids sampling intercomparison experiment ("colloids cookout"), organized by Ken 

 Buesseler, is planned for August 1994. 



During the past two years, we have acquired a unique combination of capabilities and 

 techniques which enabled us to tackle the colloidal puzzle head-on: not only can we extract large 

 volumes of seawater for 234 Th and colloid analysis [described in Baskaran et al., 1992, 1993a,b; 

 Guo et al., 1994a], we can also isolate and characterize large quantities (100-1000 mg) of 

 colloidal matter [Guo et al., 1994a]. Furthermore, we have also established low blanks and 

 excellent mass balances for ultra filtration of DOC, 14 C and 234 Th (as described above). 230 Th and 

 232 Th blanks are satisfactory for MIPS samples, but not yet for all ultrafiltration samples (see 

 above). We also routinely determine the weights of SPM and colloids sampled for radionuclide 

 analyses, which are used in some of our models. We have organized and participated in 3 cruises 

 to the Gulf of Mexico, and one to the Cape Hatteras area. 



Keywords: colloids, isotopes, biomarkers, residence times, thorium, resuspension, benthic 

 boundary layer 



99 



