No. The items in the Great Pacific Garbage Patch are not bonded together.

1,000 years

87,000 tons, according to the NY Times: See article:

"The 'Great Pacific Garbage Patch' Is Ballooning, 87,000 Tons of Plastic and Counting"

1997 the effect of water pollution on ecosystem

It is located in an area call the North Pacific Gyre, which is a patch of the North Pacific Ocean that covers thousands of square miles roughly between the United States and Japan and reaching toward Alaska and the Aleutian Islands. It's called the Great Pacific Garbage Patch because the prevailing ocean currents tend to swirl around this patch of ocean, causing all manner of floating debris to be concentrated in the gyre.