A really useful way of visualising the relationship between different aspects of the ocean carbonate system is through plots of alkalinity (ALK) vs. dissolved inorganic carbon (DIC). For instance, the one below made by James Rae clearly shows that pH and CO2 are tightly related - as DIC or ALK (or both) change pH and CO2 change similarly. It is this relationship that largely underpins the utility of the boron isotope pH proxy (see here for e.g.).
I tend to use the R for making plots and analysing data these days and normally if there is something you don't know how to do you can just google it and someone would have uploaded some script somewhere. But after many hours of searching i couldn't find something to make plots like these, so had to make my own using the seacarb package. I have uploaded it here with some annotations so you can make one if you like. I dont think mine is as pretty as James' but its not bad for a first attempt - Let me know if you make it better!