期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：37
页码：11496-11501
DOI：10.1073/pnas.1501781112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceSea surface temperature (SST) variations in the North Pacific have triggered past abrupt changes in fisheries and other ecosystems. We have discovered that over the last century, fluctuations of North Pacific SSTs have become less frequent and longer-lived. This "reddening" behavior can also be seen in the dominant pattern of climate variability in the region, known as the Pacific Decadal Oscillation index. This fundamental change in climate variability has important implications for ecosystems in the region. It implies that over the last century, ecosystems have become prone to undergoing larger climate-triggered abrupt shifts. Hence our discovery of changing climate variability could have contributed to the large magnitude of well-known abrupt changes in North Pacific ecosystems in 1977 and 1989. Marine ecosystems are sensitive to stochastic environmental variability, with higher-amplitude, lower-frequency--i.e., "redder"--variability posing a greater threat of triggering large ecosystem changes. Here we show that fluctuations in the Pacific Decadal Oscillation (PDO) index have slowed down markedly over the observational record (1900-present), as indicated by a robust increase in autocorrelation. This "reddening" of the spectrum of climate variability is also found in regionally averaged North Pacific sea surface temperatures (SSTs), and can be at least partly explained by observed deepening of the ocean mixed layer. The progressive reddening of North Pacific climate variability has important implications for marine ecosystems. Ecosystem variables that respond linearly to climate forcing will have become prone to much larger variations over the observational record, whereas ecosystem variables that respond nonlinearly to climate forcing will have become prone to more frequent "regime shifts." Thus, slowing down of North Pacific climate variability can help explain the large magnitude and potentially the quick succession of well-known abrupt changes in North Pacific ecosystems in 1977 and 1989. When looking ahead, despite model limitations in simulating mixed layer depth (MLD) in the North Pacific, global warming is robustly expected to decrease MLD. This could potentially reverse the observed trend of slowing down of North Pacific climate variability and its effects on marine ecosystems.
