How much garbage goes into the Pacific Ocean every year? In this article, they mention that:


  More than 4.8 million metric tons [of] plastic waste gets dumped into the world’s oceans from land each year. And this number is just a conservative estimate. Researchers believe the real amount could be as high as 12.7 million metric tons.


How much total garbage is going into the Pacific Ocean every year? and what fraction of the garbage is "biodegradable".

In this other article, they point out that the size of the Great Pacific Garbage Patch is much larger than previously thought.  They go on to say that they are developing a technology that will clean up some of the garbage:


  The organization hopes to deploy its Pacific array in 2020 and says it could remove almost half of the Great Pacific Garbage Patch ― more than 150 million pounds of trash ― in a decade.


This is great news if it actually works out.  However, how much garbage will still be retained at the sea floor (or suspended below the level at which the garbage can be removed)?
I've been looking for information on non-plastic garbage, and haven't had much luck. Plastic waste is an extensively researched topic. I don't have access to  Jambeck et al., Science 2015, but I did find a graphic and summary. The numbers are all year-long totals for 2010.



The study's estimated range of plastic entering the ocean is 4.8 million to 12.7 million metric tons (MMT). 

For the United States we can find some other figures to try to complete the picture. According to the EPA, in 2012, the US generated 251 MMT of municipal solid waste (MSW). Of that, 11.7% was burned, 34.5% was recovered by some sort of recycling, and 53.8% was discarded (Fig. 4). Plastics compose 12.7% of pre-recycling waste but 17.6% of post-recycling waste. Biodegradables (here I'm using food, paper, yard trimmings, and wood, but not textiles) consist of 61.7% of trash before recycling and 52.8% after.

So if we assume those ratios can be applied to the plastics sent to the ocean (8 MMT) you get the following:


Assuming global ocean waste has a similar composition as US
non-recycled waste, there are 63 MMT garbage entering the sea, of
which 39 MMT are biodegradable. 
Assuming global ocean waste has a similar composition as US recycled
waste, there are 45 MMT garbage entering the sea of which 24 MMT are
biodegradable.