Distinct impacts of the 1997-98 and 2015-16 extreme El Niños on Japanese eel larval catch

Synergistic climatic and anthropogenic effects on marine species turnover in estuarine waters

Climate and anthropogenic stressors are frequent in coastal systems, affecting biological communities in different intensities and directions. When acting synergistically, their effects may be intensified. ENSO strongly affects the climate globally, being responsible for increased rainfall in the Atlantic Southwestern during El Niño and droughts during La Niña phases. Contrasting, human-made breakwaters have static influence in decreasing estuarine salinity. Using a 23-year of fish abundance dataset, we identified that intense El Niño events and breakwater extension decreased the marine fish abundance, with potential additive synergistic effects, whereas La Niña showed no influence. Species composition changes were observed after the breakwater extension, probably related to opportunistic habits of euryhaline species. Anthropogenic and natural climatic disturbances affect habitat use, and their synergic effects must be considered to evaluate ecosystem responses in the current climate change scenario, and constant human modification of coastal zones.

Seasonally-reversed trends in the subtropical Northwestern Pacific linked to asymmetric AMO influences

This study identifies seasonally-reversed trends in Kuroshio strength and sea surface temperatures (SSTs) within the western North Pacific (WNP) since the 1990s, specifically in the 22° N-28° N region. These trends are characterized by increases during summer and decreases during winter. The seasonally-reversed trends are a result of the asymmetric responses of the WNP to a shift towards the positive phase of the Atlantic multidecadal oscillation (AMO) around the same period. The positive AMO induces an anomalous descent over the North Pacific during summer, leading to the direct strengthening of the gyre. However, during winter, it triggers an anomalous descent over the tropical Pacific, which excites a poleward wavetrain impacting the WNP and causing gyre weakening. The associated responses of the East Asian monsoon and China Coastal Current contribute to the observed seasonally-reversed SST trends. It is noteworthy that the seasonally-reversed trends in gyre strength and SSTs are predominantly observed north of 20° N in the WNP. This limitation arises because the anomalous cyclone within the winter poleward wavetrain is located north of this latitude boundary. Specifically, the clearest trends in gyre strength are observed in the northern segment of the Kuroshio, while the manifestation of SST trends in the Taiwan Strait could potentially be attributed to the influence and enhancement of the East Asian monsoon and the China Coastal Current. Due to the limited length of observational data, statistical significance of some of the signals discussed is rather limited. A CESM1 pacemaker experiments is further conducted to confirm the asymmetric responses of the North Pacific to the AMO between the summer and winter seasons.

Remote impacts of 2009 and 2015 El Niño on oceanic and biological processes in a marginal sea of the Northwestern Pacific

The significance of long-term teleconnections derived from the anomalous climatic conditions of El Niño has been a highly debated topic, where the remote response of coastal hydrodynamics and marine ecosystems to El Niño conditions is not completely understood. The 14-year long data from a ship-borne acoustic Doppler current profiler was used to examine the El Niño’s impact, in particular, 2009 and 2015 El Niño events, on oceanic and biological processes in coastal regions across the Korea/Tsushima Strait. Here, it was revealed that the summer volume transport could be decreased by 8.7% (from 2.46 ± 0.39 to 2.24 ± 0.26 Sv) due to the anomalous northerly winds in the developing year of El Niño. Furthermore, the fall mean volume backscattering strength could be decreased by 1.8% (from − 97.09 ± 2.14 to − 98.84 ± 2.10 dB) due to the decreased surface solar radiation after the El Niño events. Overall, 2009 and 2015 El Niño events remotely affected volume transport and zooplankton abundance across the Korea/Tsushima Strait through climatic teleconnections.