R - how do I change font style and size on my two x-axes which I have moved to the top of the graph?

Question

I am having bother changing the font style and size on my two x-axes, both of which I have moved to the top of the graph.

Here is my code so far:

x1<-Temperature
x2<-Salinity

y<-Depth
par(mar=c(4, 4, 8, 4))

plot(x2,y, type="l",col="darkgrey",ylim=rev(range(0,300)),las=2,xlim=(range(32.5,34.5)),xaxt='n',xlab='',font.axis=2,lwd=3,ylab="Depth [m]",font=2,font.lab=2,cex.lab=1.3,cex.axis=1.2)
axis(side=3, line=4)
par(new=TRUE)
plot(x1,y, type="l",col="black",ylim=rev(range(0,300)),las=2,xaxt='n',xlab='',lwd=3,ylab='Depth [m]',font=2,font.lab=2,cex.lab=1.3,cex.axis=1.2)
axis(side=3, line=0)
par(new=TRUE)

This successfully changes my y-axis but leaves my x-axes unchanged.

Help!

Solution

Reading through the help for axis, ?axis, looking at the documentation for the ... parameters:

 ...: other graphical parameters may also be passed as arguments to
      this function, particularly, ‘cex.axis’, ‘col.axis’ and
      ‘font.axis’ for axis annotation, ‘mgp’ and ‘xaxp’ or ‘yaxp’
      for positioning, ‘tck’ or ‘tcl’ for tick mark length and
      direction, ‘las’ for vertical/horizontal label orientation,
      or ‘fg’ instead of ‘col’, and ‘xpd’ for clipping.  See ‘par’
      on these.

So just pass in your cex.axis etc parameters into the axis call as you did for plot. Here's a reproducible example (Note how I've made up the data, and even though the data is not realistic, at least it makes the example reproducible and still solves your problem):

x1 <- runif(10)
x2 <- runif(10) * 2 + 32.5
y <- runif(10) * 300

par(mar=c(4, 4, 8, 4))    
plot(x2,y, type="l",col="darkgrey",ylim=rev(range(0,300)),las=2,xlim=(range(32.5,34.5)),xaxt='n',xlab='',font.axis=2,lwd=3,ylab="Depth [m]",font=2,font.lab=2,cex.lab=1.3,cex.axis=1.2)

# added in various font/axis labels as in above
axis(side=3, line=4,font.axis=2,font.lab=2,cex.lab=1.3,cex.axis=1.2)

par(new=TRUE)
plot(x1,y, type="l",col="black",ylim=rev(range(0,300)),las=2,xaxt='n',xlab='',lwd=3,ylab='Depth [m]',font=2,font.lab=2,cex.lab=1.3,cex.axis=1.2)
axis(side=3, line=0,font.axis=2,font.lab=2,cex.lab=1.3,cex.axis=1.2)

(Your subsequent calls to axis where replacing the axis from the plot call, so instead of using the axis parameters from plot it uses the axis parameters from axis).