Analysis of the timing of phase changes in the chlorophyll concentration in the East/Japan Sea

• Time series of chlorophyll concentration (CHL) are represented by non-linear trends.
• Non-linear trends of CHL are closely related to non-linear Sea Surface Temperature (SST) changes.
• Upward or downward trends of CHL and SST are determined based on non-linear trends.
• General and specific phase changes of CHL are analyzed using the Complex Emprical Orthogonal Function (CEOF) and the Ensemble Empirical Mode Decomposition (EEMD), respectively.
• The timing of phase changes in CHL occurring in 2007 is demonstrated by the cumulative sum of the Multivariate El Nino-Southern Oscillation Index (MEI).

Geographically heterogeneous linear and non-linear chlorophyll-a (CHL) trends in the East Sea/Japan Sea (EJS) region were analyzed based on monthly mean Moderate Resolution Imaging Spectroradiometer (MODIS) CHL data from January 2003 to December 2012. The non-linear trends were derived from the residuals of decomposed CHL time series using ensemble empirical mode decomposition (EEMD). To understand the general spatial and temporal variability of the non-linear CHL trends, a complex empirical orthogonal function (CEOF) was employed. The first two CEOF modes indicate that an upward CHL trend occurred in 2007 with 95.6% variance, whereas a downward CHL trend occurred in 2009 with 4.1% variance. Furthermore, the specific timing of the phase changes in CHL was calculated based on upward or downward non-linear trends of CHL for six major regions of interests.To examine the dominant forces in phase changes in CHL, the Multivariate El Nino-Southern Oscillation (ENSO) Index (MEI) was used. We determined that the local turning patterns of CHL over the last ten years were closely related to changes in ENSO events, which were also associated with changes in the total amount of fish catches off the east coast of the Korean Peninsula. These results also suggest that the short-term total amount of fish catches may be predictable based on the remotely sensed non-linear CHL observations.