Marine ecological effect of typhoon influenced by the frequency-phases of ENSO and anthropogenic activity: the East China Sea example

In coastal regions, typhoons are one of the most frequent natural disasters, and instrumental data indicate that they can greatly boost marine primary productivity. Typhoons' long-term ecological repercussions, however, are still little understood. To investigate the ecological effects of typhoons since the mid-Holocene, we focused on the sediment cores in the East China Sea, with key parameters of organic CN and Bio-Si to reveal the paleo-productivity variation. Over a millennium, the occurrence of El Ni & ntilde;o-Southern Oscillation (ENSO) has had a substantial impact on primary productivity in the southern East China Sea. The primary productivity in the southern East China Sea was risen by humid climate conditions in similar to 3.0-2.0 ka and frequent typhoons in 1.5-0 ka. With a millennial period, ENSO frequency has been significantly influencing primary productivity in the southern East China Sea since the mid-Holocene. During 1.5-0 ka, frequent ENSO events have led to more frequent typhoons, which caused terrestrial materials input and water vertically mix in the southern East China Sea, ultimately increasing primary productivity. Particularly on a centennial time scale, ENSO phases determined how much primary productivity was increased, and this magnitude was bigger during the La Ni & ntilde;a-like periods than it was during the El Ni & ntilde;o-like periods since La Ni & ntilde;a is when typhoons occur more frequently. During the Little Ice Age, the cold climate hindered the reproduction of phytoplankton, but increased human activities in Taiwan resulted in more soil erosion and the supply of terrestrial-derived nutrients into the sea, then amplified the typhoon-induced increase in primary productivity. As a result, this stage showed the highest primary productivity since the mid-Holocene. This study reveals that frequent typhoons promote marine primary productivity on centennial-millennial timescales and emphasizes that human activities amplify the ecological effect of typhoons in recent centuries.