”] 
Comparing estimates from different Lagrangian investigations 
one notes sometimes a wide span of residence-times calcula- 
ted for given areas. So natural tracers as fish-eggs yield 
travel-times for certain distances differing an order of 
magnitude with estimates from Cs 137 data. 
Such discrepancies could be explained by sampling and inter- 
pretation problems. These surveys may take place in a time 
and space domain that might not be well suited to estimate 
drift of "water bodies"”, Further there are problems with 
the interaction of the radionuclides with the sea water 
and particularly the sediment, where re-suspension processes 
could deteriorate simple decay and diffusion argumentation. 
Further developments, especially the use of an "internal 
clock" based on the different decay of different isotopes 
are likely to add substantially to our understanding of 
travel times, (Jefferies, Preston and Steele, 1973; 
McKinley et al. 1981; Livingston, Bowen and Kupferman, 
1982; Jefferies, Steele and Preston, 1982). 
Dye tracers, on the other hand, have recently led to large- 
scale interpretation problems, because it could not be well 
astablished if one monitors, after some time, the same 
"cloud", It also seems possible, that under certain hydro- 
graphic conditions dye is locked to small-scale hydrographic 
features with higher concentrations, which in turn either 
escape future surveys and damage the cöoncentration balance 
or, if found, lead to unrealistically high concentrations 
and derived assumptions On the transport processes involved. 
It therefore seems necessary as these tools present a strong 
case for assessing the circulation magnitude and pattern of 
an area, to compare in depth the suggested and applied 
techniques for sampling and interpretation. This is 
especially important as this may further indicate the im- 
sortance of variability versus average pictures.