Waters in the Gulf of Alaska were unusually warm this fall, up to 5 degrees above normal in the top 300 feet of water. Heat absorbed more than a year ago helped lead to the condition, according to scientists who monitor Alaska marine waters in a program funded by the Alaska Ocean Observing System and other organizations.
"This is the warmest we've seen in 17 years. We believe that to be significant," said Russell Hopcroft, a professor at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences and chief scientist for the long-term monitoring program.
Armed with specialized measuring instruments, Hopcroft and his colleagues cruised the Gulf in September. They found temperatures 1 to 5 degrees warmer than the September average of 55 to 57 degrees Fahrenheit.
A similar cruise in the spring revealed that heat from the summer of 2013 was never entirely lost over the winter, Hopcroft said. That helped magnify the warming that occurred this summer, he said. "By the time it was over, it was much warmer than it used to be," he said.
Though air temperatures are highest in mid-summer, Alaska ocean waters are usually at their warmest in September, Hopcroft said. There is a time lag that causes the waters to retain the summer's warmth, he said. "It takes a long time for the ocean to heat up, and a long time to cool off," he said.
Over the duration of the monitoring program, scientists have seen warm-water years and cold-water years, a pattern influenced by a number of oceanic forces. The early 2000s were warmer, while many of the years from 2007 and later were cold, for example.
But this year's warmth was outside of that pattern, Hopcroft said. Waters were 1 degree warmer than any other year, including 1998, when a powerful El Nino cycle had a pronounced warming effect in Alaska, he said.
Also affecting this year's water temperatures was a relative dearth of storms mixing up the water column, Hopcroft said.
Thriving in the warmer conditions, thanks to oceanic currents that swept north, were several species of marine life that normally dwell farther south, Hopcroft said. Many were tiny copepods, shell-bearing crustaceans eaten by larger fish, he said. There might have been changes to the Gulf's krill population as well, he said.
While some of the warm-water creatures brought north might be too tiny to be noticed by casual observers, others were not.
There were many more jellyfish spread across the water this year, Hopcroft said. "We saw that by just looking over the boat," he said.
Elsewhere in the Gulf region, surprised fishermen netted a skipjack tuna and spotted a massive ocean sunfish, members of species that had swum far north of their normal range.
Real-time measurements of sea-surface temperatures and other factors are available at a web portal maintained by the Alaska Ocean Observing System.