Officials leading the search for the missing Malaysia Airlines plane are now focused on deep-sea signals that could be coming from the passenger jet's black box. But five weeks into the search, there is still no trace of the plane's wreckage. Instead, the search keeps turning up practically everything but the plane: hundreds of large objects shown in blurry satellite images, and pieces of fishing equipment and other flotsam examined by ships sailing in the area. If nothing else can be learned from this bizarre hunt, one thing has become clear: There's a ton of trash in the Indian Ocean.

But what is it exactly and how did it get there? Marcus Eriksen, executive director of the advocacy group 5 Gyres, has sailed from Perth, Australia, to the island of Mauritius, covering the same area of ocean that the search team has been scouring for the last few weeks. In 2010, Eriksen was looking for trash -- in particular the vast amounts of plastic that get dumped in the water and then take years to disintegrate into tiny salt-and-pepper flakes in the water.

"If you're out there when you're on the deck, it's pretty frequent that you're going to look down and see something," said Eriksen, whose group aims to reduce plastics pollution and tracks garbage in the world's oceans. "A small piece of netting, a piece of rope just goes by. Every hour or two, you'll see something on the horizon. An oil drum, a bucket."

The most famous area of trash in the world's oceans is the Great Pacific Garbage Patch, stumbled upon by Charles Moore in 1997 on his way back from a sailing race. Since then, at least four more of these garbage patches have been documented around the planet, including in the Indian Ocean. "It's a nonstop soup of plastic waste from one continent to another," said Eriksen, who added that the Malaysia Airlines search team is on the eastern edge of the Indian Ocean Garbage Patch.

The vast majority of the pollution is smaller than a grain of rice: particles of plastic broken down by sunlight and waves until they are so small they can no longer be seen by the naked eye. Environmental groups are concerned that as these particles move through the oceans, pesticides and other chemicals glom onto them. When marine animals then ingest the particles, the chemicals can kill the animals or enter the human food supply. Eriksen remembers once watching a turtle investigate a large tangled ball of fishing netting.

Other pieces of debris can be enormous. Two weeks ago, French and Thai satellites picked up objects that measured as long as 75 feet. When asked what kind of debris could be that large, Eriksen said that the item could have been the fiberglass hull of a lost ship. The largest item he has ever seen was a 50-foot sailboat lost by someone in Bermuda. Large ocean shipping containers, frequently lost in the ocean, typically top out at 40 feet in length. There are also massive buoys used by cruise ships. "If you have ever seen an Oscar Meyer Wienermobile, there are buoys as big as that," said Eriksen.

The trash in the Indian Ocean comes from a number of sources, including shipping lanes and populations that live along bodies of water that pour into the Bay of Bengal and then into the ocean. Catastrophic events such as hurricanes and tsunamis also contribute to the pollution. But Eriksen said one of the biggest causes is the use of plastic for items that are designed for only one use but that take years to break down. "Why do we have to use plastic for a straw that we use for ten minutes?"

As for whether the search team will ever find debris associated with the plane, Eriksen suggests it all depends on how the plane hit the water. If it largely didn't break up, then much of it will have sunk together, making it that much harder to find. If it did break apart, Eriksen said you would at least expect to find items such as the carts that roll down the aisle; those are often made with a honeycomb material that should float. You would also expect to see life jackets, drink bottles and suitcases. "Then again, if you get a few waves, you get a few weeks, things get dispersed and are hard to see," he said.

It takes six to 10 years for debris to make one full loop around the large system of currents known as the Indian Ocean gyre. Whatever ends up in the soup tends to stay there, meaning that the mysterious debris of the plane - -if in fact it ended up in the Indian Ocean -- isn't going anywhere.