Long-lived deep-sea corals preserve evidence of a major shift in the open Pacific Ocean ecosystem since around 1850, according to a study by researchers at the University of California, Santa Cruz. The findings, published December 15 in Nature, indicate that changes at the base of the marine food web observed in recent decades in the North Pacific Subtropical Gyre may have begun more than 150 years ago at the end of the Little Ice Age.
Deep-sea corals are colonial organisms that can live for thousands of years, feeding on organic matter that rains down from the upper levels of the ocean. The corals' branching, tree-like skeletons are composed of a hard protein material that incorporates chemical signatures from their food sources. As a result, changes in the composition of the growth layers in deep-sea corals reflect changes in the organisms that lived in the surface waters at the time each layer formed.
"They're like living sediment traps, recording long-term changes in the open ocean that we can't see any other way," said coauthor Matthew McCarthy, professor of ocean sciences at UC Santa Cruz.
Scientists can study sediment cores taken from the ocean floor for clues to past conditions in the oceans, but that approach is not very useful for the most recent millennia. In the open ocean of the North Pacific, sediment accumulates so slowly that the entire Holocene epoch (the past 12,000 years or so) is represented by less than 10 centimeters (4 inches) of sediment that has been stirred up by organisms living on the seafloor. "Even if there were good sediment records, we would never get the level of detail we can get from the corals," McCarthy said.
To analyze the coral skeletons, the UCSC researchers combined carbon dating with a novel technique for analyzing nitrogen isotopes in proteins. They were able to reconstruct records over the past 1,000 years indicating that a shift occurred around 1850 in the source of nitrog
|Contact: Tim Stephens|
University of California - Santa Cruz