I don't find a way to show an expression and the "per-mille" symbol in the same label. I have tried the next four ways:
name1 <- paste(expression(delta^18*O),"(\u{2030})")
name2 <- "\u{1E9F}O18 (\u{2030})"
name3 <- expression(delta^18*O)
name4 <- expression(paste(delta^18*O,"(\u{2030})"))
All of them show errors,

