Research suggests that last year's record loss of Arctic sea ice is already causing big changes that scientists are just starting to understand for plants and animals.
German scientists on board a research vessel in the High Arctic last summer found that large clumps of algae that would normally cling to the underside of sea ice were falling and sinking to the ocean floor.
Losing the algae robbed fish and other animals of habitat in which they could feed and hide from predators.
But the sinking algae also radically boosted food supplies for some species on the sea floor.
Bacteria grew so quickly they used all the oxygen over large areas.
Scientists say the results show that Arctic ecosystems can change very quickly.
They urge caution as governments look to develop northern energy and fisheries resources.