How much do we know about the 88-91 regime shift in the southwestern East Sea ecosystem?

Abstract

We investigated the 88-91 regime shift in the southwestern East Sea ecosystem by reconstructing a long-term chlorophyll-a time series from Secchi depth data for 1970-2005. The chlorophyll-a time series showed that a statistically significant shift occurred at 89/90, which is consistent with shifts in a number of climatic, oceanographic, and biological variables with a slight time lag before and after the chlorophyll-a shift. We put forward a hypothesis that several factors, anthropogenic and climate change-related, worked together to induce the jump in the lower trophic level: continuously increasing atmospheric deposition of anthropogenic nitrogen, continuously increasing nitrate loading of the Changjiang river, and sudden increase of Changjiang discharge around 1989. These effects might have been amplified by an increase in the volume transport of Tsushima Warm Current in 1988 leading to nitrogen enrichment in the south East Sea. If such is the case, the 89-91 regime shift in the East Sea ecosystem presents an interesting case where climate change and anthropogenic forcing interacted and produced synergistic effects leading to a step change. We will also discuss further questions such as linkage to large-scale variability and trophic interactions.t shift occurred at 89/90, which is consistent with shifts in a number of climatic, oceanographic, and biological variables with a slight time lag before and after the chlorophyll-a shift. We put forward a hypothesis that several factors, anthropogenic and climate change-related, worked together to induce the jump in the lower trophic level: continuously increasing atmospheric deposition of anthropogenic nitrogen, continuously increasing nitrate loading of the Changjiang river, and sudden increase of Changjiang discharge around 1989. These effects might have been amplified by an increase in the volume transport of Tsushima Warm Current in 1988 leading to nitrogen enrichment in the south East Sea. If such is the case, the 89-91 regime shift in the East Sea ecosystem presents an interesting case where climate change and anthropogenic forcing interacted and produced synergistic effects leading to a step change. We will also discuss further questions such as linkage to large-scale variability and trophic interactions.