Dave Walsh writes from the Esperanza.

No, this is not a product placement… it’s a real picture of a real coke can lying on the Arctic Ocean sea bed at a depth of 200m, 25km off the north coast of Svalbard, photographed by the Esperanza’s “drop camera”. We don’t know how it got there. Maybe it was thrown overboard from a trawler or cruise ship, or perhaps propelled north by the Gulf Stream.

Every other photograph we’ve made of the sea floor has shown an incredibly diverse and thriving ecosystem once assumed to be devoid of life; yet this one picture symbolises for me the pervasive influence of humans everywhere on the planet – and why we need to clean up our act.

We spent last week lowering the “drop camera”, built by Gavin, housed by a large frame that protects both video and stills cameras, suspended by a reinforced cable, into the Arctic Ocean, sometimes to depths of over 400m. On the Esperanza, crew members have been taking turns to work the winch, or go square-eyed monitoring the live video feed from the sea floor.

They saw all kinds of amazing and beautiful creatures on the screen, but also the gouges left behind by bottom trawling – a highly destructive form of fishing that involves dragging a large net, weighed down with rollers and “trawl doors”, across the ocean floor, demolishing everything in its path.

The Arctic is under pressure from threats from somewhere else; manmade climate change and ocean acidification driven by CO2 emissions; the visible trash like the coke can, and the invisible PCBs and other environmental toxins that come north by sea and by wind, and that find their way into the tissues of top predators, such as polar bears; and then there’s industry itself – the fishing, oil and other extractive industries all clamouring to get a piece of the action.

Climate change is contributing to changes in ocean currents, and warms up high-latitude waters, causing the polar front (or convergence), the delineation between southern warm and northern cold water, to move north. The fish are moving north with this front, as it’s a nutrient rich part of the ocean system, and the fishing fleets are not far behind. We’ve already seen them operating close to the edge of the Arctic sea ice; when this fishery continues to expand into the pristine Arctic Ocean seabed, we can expect a lot more damage to the seabed.

Can you accept the Arctic being turned into a polluted rubbish tip?