AMSTERDAM — When a 43-foot gray whale was spotted off the Israeli town of Herzliya last year, scientists came to a startling conclusion: it must have wandered across the normally icebound route above Canada, where warm weather had briefly opened a clear channel three years earlier.
Scientists have also found plankton in the North Atlantic where it had not existed for at least 800,000 years.
The odyssey of the whale, whose species lives in the Pacific, and the surprising appearance of the plankton indicates a migration of species through the Northwest Passage, a worrying sign of how global warming is affecting animals and plants in the oceans as well as on land.
“The implications are enormous. It’s a threshold that has been crossed,’’ said Philip C. Reid, of the Alister Hardy Foundation for Ocean Science in Plymouth, England.
“It’s an indication of the speed of change that is taking place in our world in the present day because of climate change,’’ he said in a telephone interview Friday.
Reid said the last time the world witnessed such a major incursion from the Pacific was 2 million years ago, which had “a huge impact on the North Atlantic,’’ driving some species to extinction as the newcomers dominated the competition for food.
Changes in the oceans’ chemistry and temperature could have implications for fisheries, as species migrate northward to cooler waters, said Katja Philippart, of the Royal Netherlands Institute of Sea Research who is coordinating the project funded by the European Union.