A British-led expedition has discovered sizeable chunks of polystyrene lying on remote frozen ice floes in the middle of the Arctic Ocean.

The depressing find, only 1,000 miles from the north pole, is the first made in an area that was previously inaccessible to scientists because of sea ice. It is one of the most northerly sightings of such detritus in the world’s oceans, which are increasingly polluted by plastics.

A team of scientists drawn from the UK, US, Norway and Hong Kong, headed by marine biologist Tim Gordon of Exeter University, said the discovery confirmed just how far plastic pollution has spread. It has prompted fears that plastic waste is flowing into the Arctic as the ice melts because of climate change. The thaw is simultaneously releasing plastic that has long been trapped in the ice.

The scientists, who were on the explorer Pen Hadow’s Arctic Mission attempt to sail to the north pole, were surprised to discover the blocks of polystyrene many hundreds of miles from land in areas that were, until recently, covered by ice all year round. They found two large pieces on the edge of ice floes between 77° and 80° north, in the middle of the international waters of the central Arctic Ocean.

“For the 25 years I have been exploring the Arctic I have never seen such large and very visible items of rubbish,” said Hadow, the only person to have trekked solo, without resupply, from Canada to the geographic north pole. “The blocks of polystyrene were just sitting on top of the ice.”

“Finding pieces of rubbish like this is a worrying sign that melting ice may be allowing high levels of pollution to drift into these areas,” Gordon said. “This is potentially very dangerous for the Arctic’s wildlife.”

The pioneering expedition – using two yachts – sailed further into the international waters of the Central Arctic Ocean than any previous navigation attempt without icebreakers. Rates of ice melt have increased dramatically due to climate change, with 40% of the central Arctic Ocean now navigable in summer.

Estimates suggest that there are more than 5 trillion pieces of plastic floating on the surface of the world’s oceans. It has been claimed that there is now enough plastic to form a permanent layer in the fossil record. Dr Ceri Lewis, scientific adviser to the expedition based at the University of Exeter, has previously warned that people produce around 300 million tons of plastic a year, roughly the same weight as all the humans on the planet. Around half of all plastic produced is used once and then thrown away.

A significant concern is that large plastic pieces can break down into “microplastics” – tiny particles that are accidentally consumed by filter-feeding animals. The particles remain in animals’ bodies and are passed up the food chain, threatening wildlife at all levels from zooplankton to apex predators such as polar bears. In an attempt to gauge the presence of microplastics in Arctic waters, the scientists intend to test samples of seawater they collected in nets with holes smaller than a millimetre across.

“Many rivers that are often a source of plastic pollution lead into the Arctic Ocean, but plastic pollution has been literally trapped into the ice,” Lewis said. “Now the ice is melting we believe microplastics are being released into the Arctic. The Arctic is thought to be a hot spot of microplastics accumulation due to the number of rivers that empty into the Arctic basin, yet we have very little data to support this idea in the more northerly parts of the Arctic Ocean.” He added that the data the expedition was collecting was important because the Arctic supports many fisheries which could be affected by microplastics.

Some projections indicate that the entire Arctic Ocean will be ice-free in summer by 2050. This will allow human exploitation of the newly opened waters and bring a range of fresh threats to Arctic wildlife.

“The Arctic Ocean’s wildlife used to be protected by a layer of sea ice all year round,” Gordon said.

“Now that is melting away, this environment will be exposed to commercial fishing, shipping and industry for the first time in history. We need to seriously consider how best to protect the Arctic’s animals from these new threats. By doing so, we will give them a fighting chance of adapting and responding to their rapidly changing habitat.”

The team is also investigating the impact of human-made noise pollution on Arctic marine life and mammals, using underwater loudspeakers and microphones to understand how sound travels through the polar seas, and how this might be affected by ice loss. Arctic cod, beluga whales, ringed seals and walruses use a range of sounds to communicate in the underwater darkness. Narwhals hunt for fish a mile below the surface using biosonar, emitting 1,000 high-pitched clicks every second and listening to their reflected echoes – much the same way that bats do.

“It is critical that we establish baseline natural recordings in this newly exposed oceanic environment,” said Professor Steve Simpson, an expert in bioacoustics and noise pollution at Exeter University. “These recordings will allow us to understand how human activities are changing the soundscape of the summer Arctic, and assess the success of future noise management in this unique acoustic world.”

On-board wildlife biologist Heather Bauscher said increasing ice melt could have serious consequences for the whole Arctic ecosystem. “Quality research and the development of sound management strategies are necessary to protect the Arctic’s wildlife: this is crucial at a time of such dramatic change,” she said.