Of course natural disasters will add to the problem but i think it would be silly to suggest that thereis not a hell of a lot more rubbish floating about now than say fifty years back.
That part of it caused by natural disasters is to my mind simply suggesting that we as a species generate way too much garbage, much of it non biodegradable and we need to address this issue.
As for the amount in the ocean the damage to marine life alone is enough to cause concern. Only this week a whale calf was seen in Sydney Harbour trailing the remnants of a fishing net. How many more critters die simply because we are thoughtless in the way we generate and dispose of rubbish.
I think everyone should euthanize their children for the sake of 'sustainability'. Apparently not much else seems to be working.