SANTA CRUZ -- Clues from ancient Hawaiian coral show a major shift in the subtropic Pacific Ocean's ecosystem around 1850.
A research team from UC Santa Cruz has created a 1,000-year record of how the North Pacific Subtropic Gyre, the world's largest ecosystem, produces organic material, said Owen Sherwood, co-author of the study.
Scientists have long thought global warming affected biological communities mainly at higher latitudes. However, this study, which will be featured on the cover of Nature on Jan. 4, shows a dramatic increase around 1850 in nitrogen-fixing bacteria in the tropics, possibly linked to climate change.
Monthly temperature measurements by University of Hawaii researchers have shown warming Pacific waters since 1988. The bacterial shift, discovered by measuring nitrogen isotopes in coral, may mean the warming trend began around 1850, said Sherwood, research associate at University of Colorado.
"Until now, we haven't had any kind of records for that part of the ocean, at least to decade-level detail," said Sherwood, who was a UCSC post-doctoral fellow at the time of the study. "It helps us distinguish natural climate variability from global warming."
Co-author Matthew McCarthy, a UCSC associate professor, said researchers now understand that ecosystem change started further back than originally thought.
"The fundamental way the system gets nutrients, the basis of the ecosystem, is different, and it's getting more and more different," McCarthy said.
Diving 1,500 feet in Hawaiian waters, researchers collected 1,000-year-old Hawaiian gold coral samples to understand the ecosystem's long-term changes. Co-author Tom Guilderson said this coral grows radially like tree rings, at 30 microns per year, less than the thickness of a human hair.
"Something that would be as thick as your wrist could be about 600 to 1,000 years old," said Guilderson, a scientist affiliated with UCSC and Lawrence Livermore National Laboratory.
This slow growth creates a unique archive of past ocean conditions and environmental change, different from the typical approach, which measures changes in sediment layers.
The layers accumulate on the ocean floor, with the youngest layers on top, Guilderson said.
However, in Hawaiian waters, sediments accumulate so slowly due to crustaceans and worms constantly churning the floor's surface, that scientists can't reconstruct recent history with any resolution, he said.
"The deep sea corals give us an incredible window into past ocean conditions that you can't reconstruct with any other archive," Guilderson said.
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