Anyone done a Marine Science A level?

I’m a mature student looking to self study A levels (I completed my Biology degree with the Open University without A levels and feel insecure about my unconventional path).
I’m going to do biology and chemistry international A levels, which I’ll be able to do without too much effort.
My third choice will require much more study. I’m considering doing marine science for my third but it seems quite rare and I would like to know what past/current students think of it? How hard is it and what’s the workload? The syllabus looks very interesting to me.
My other third choice is geography. I never did this for GCSE but my uni modules have covered some amount of earth science, weather etc. Again it seems interesting but worried about the workload.
Really I’d like my third to be environmental science (again I could do this with minimal effort) but it’s not available as an international A level.

I did A Level Marine Science. Very fun, no regrets, the books are great to dip in and out of after the course. Quite easy going and easy to manage, most of the time is revising instead of studying. It's a great choice as there are no practicals requried for the examination like A Level Environmental Science. Hope this helps