Hello aspirant I am here for helping you.
firstly you should know the eligibility criteria for post graduation in oceanography from CU SAT:

B.Sc.degree with Physics / Mathematics as the main subject with 55% marks. Those with Mathematics as the main subject should have studied Physics as one of the subsidiaries and vice-versa.
there is an entrance exam also by which you can have admission in CU sat for post graduation in oceanography.
This test will comprises 150 question, asked for checking your proficiency in your subjects.
if you are going for MSc in oceanography then the subject will be mathematic or physics.
You can appear in any one of the subject test.
Test codes :
Mathematics :612
Physics: 613

I hope you got it.
Feel free to ask any query in comment section.
Best of luck.