Interannual variability in a plankton time series

Autor: Murielle M. LeGresley, Jennifer L. Martin, Michael Dowd, Alex Hanke, Fred H. Page
Rok vydání: 2003
Předmět:
Zdroj: Environmetrics. 14:73-86
ISSN: 1099-095X
1180-4009
DOI: 10.1002/env.566
Popis: Temporal changes in a plankton time series are examined, with an emphasis on interannual variability. A stochastic cycle model is used which describes an annual cycle with a fixed frequency, but a randomly varying amplitude and phase. A state space representation is used with the Kalman filter, and associated fixed-interval smoother, to provide estimation of the time-varying state. Parameter estimation relies on maximum likelihood methods. A data set is considered comprised of an irregularly sampled time series of plankton (dinoflagellate) abundance over a 12 year period in the Bay of Fundy, off the east coast of Canada. Analysis of the log10-transformed data indicated timing changes in the seasonal cycle of up to 23 days. Significant variations in abundance relative to the mean cycle were found for some highly sampled summer periods. Case deletion diagnostics identified two influential observations, one of which has a large impact on the estimated system noise. Examination of the sampling protocol, or monitoring design, indicates the need to reduce the observation error variance in order to improve detection of interannual variations in plankton abundance. Copyright © 2003 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.
Databáze: OpenAIRE
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