providing information on amount of anthropogenic in- 

 puts to the offshore basin, the direction of currents car- 

 rying the materials, and the rate of sedimentation of 

 the materials in the basin. 



In the past 3 years, the program has ac- 

 complished several important objectives. The 

 dynamics of the coastal current systems have been 

 mapped on a temporal basis, describing for the first 

 time details of the northward motion of the easterly 

 current, the surface eddy system, and the anticlock- 

 wise motion of the below sill currents in the basin. 

 Fluxes of dissolved and particulate radionuclides in- 

 volving 239/240 Pu, 137 CS, &4/238 Th, and 210 Pb have al- 

 lowed the quantitative determination of the advective 

 lateral motions and depositional vertical motions in 

 the bight. 



Research biologists have been able to determine 

 with remarkably good precision the productivity 

 within the basin, including new production and the 

 mass balance of carbon imported, exported, and 

 deposited. From the deployment of three different 

 types of sediment traps, the flux of organic particles 

 based on carbon and nitrogen has been very closely re- 

 lated to the production and decomposition flux. It has 

 been shown that the major grazing activity of 

 phytoplankton occurs by micro-(not macro-) 

 zooplankton. These smaller animals repackage far 



more organic material than the large animals do. It has 

 been estimated that bacteria could utilize up to 80 per- 

 cent of the new production of photosynthetic carbon 

 and nitrogen. The sedimenting and dissolved carbon 

 and nitrogen may largely represent micro- 

 zooplankton feces and adsorbed bacterial cells, but 

 not phytoplankton cells. Lastly, C measurements 

 suggest that 5 to 10 percent of sedimenting organic 

 particles maybe derived from fossil carbon. 



The complex sediment deposits in the Santa 

 Monica Basin show evidence of turbidity flows and 

 some re-entrainment of surface sediments. The area of 

 oxygen-free sediment has expanded since 1850 and 

 now covers most of the sea floor of the deep basin. This 

 is partly due to the enrichment of the surface waters by 

 sewage outfalls and nutrient-enriched (agricultural) 

 river runoff. The contribution of sewage particles to 

 the bottom sediments has been estimated at between 1 

 and 5 percent, based on organic or trace metal in- 

 dicators. The contribution of various sources of carbon 

 to the total sediment carbon balance has been quan- 

 tified. At the same time, measurements were obtained 

 on the rates of in situ respiration and nutrient recycling 

 processes occurring in the surface sediments, and 

 these agree with the deposition rates calculated in the 

 studies cited above. 



Coastal Ocean Margins Program 



16 



December 1988 



