[R] x axis problems

[Ener Borg]

I have been searching for the R manual, unable to solve my problem.

Questions

1) How can I put the x axis at the top of the plot?

2) I am plotting data from a CTD. I want to add series sal, obs and fluo
at  the same plot by using points(sal,deepth) ets. The data have
different values so I want to use multiple x axis (4) with different
scaling. How can I do that?

plot(sal,depth,ylim=c(100,0),xlim=c(-0.0120,62),type="l",col.axis="",xaxt="s",xlab="")
points(temp,depth,type="l",col="red")
points(obs,depth,type="l",col="green")
points(fluo,depth,type="l",col="blue")

Thank you for any help!

Ener Borg