北赤道逆流影响的热带西太平洋秋冬转换期海表叶绿素浓度与ENSO循环

Response mechanism of the surface chlorophyll concentration to ENSO cycle influenced by North Equatorial Countercurrent during autumn and winter transition period in the tropical western Pacific

在厄尔尼诺-南方涛动(El Nino-Southern Oscillation, ENSO)的发生、发展中,北赤道逆流也有明显的年际变化,但北赤道逆流的变化如何影响海洋水文生态条件的变化过程尚不清楚。本文以位于热带西太平洋的北赤道逆流影响区为研究海区,分析了2006-2022年ENSO循环期间研究区不同阶段秋冬转换期水文生态气候条件的变化特征。结果表明,北赤道逆流源区及其路径上存在海表叶绿素浓度高值条带,这是由北赤道逆流从其源区携带的和新几内亚海岸潜流携带的营养物质共同影响下形成的,棉兰老冷穹上升流也会对其营养盐供给产生较大影响。厄尔尼诺事件发生时,热带西太平洋西风事件增多,北赤道逆流增强,大量表层水东移,研究区海平面降低,深水向浅层补给增加,深层冷水上抬,共同增强的北赤道逆流、新几内亚海岸流、新几内亚海岸潜流和棉兰老冷穹上升流将更多的养分从水平和垂直层面输送到海面,导致海面叶绿素浓度和原位有机碳总量显著增加。拉尼娜事件发生时,北赤道逆流影响区生态水文气候条件变化与厄尔尼诺事件发生时的变化特征几乎相反,但其变化程度弱于厄尔尼诺时期,共同减弱的北赤道逆流、新几内亚海岸潜流和棉兰老冷穹上升流使从水平和垂直层面输送到海面的养分显著减少,导致海面叶绿素浓度和原位有机碳总量显著降低。本文提出了北赤道逆流影响区水文生态气候条件演化对厄尔尼诺事件和拉尼娜事件的响应机制模型,这有利于进一步分析ENSO循环在局地生态效应和水文气候演化中的作用,对认识全球气候变化对物质循环的影响具有重要意义。

There are also obvious inter-annual variations of the North Equatorial Countercurrent(NECC)during the occurrence and development of the El Niño-Southern Oscillation(ENSO),but its changing process in hydroecolo-gical conditions and response mechanism influenced by ENSO cycle are still unclear.Taking the NECC affected area in the tropical western Pacific as the study area,this paper analyzes the characteristics of the changes of hy-droecoclimatic conditions at different stages during the ENSO cycle during autumn and winter transition period from 2006 to 2022.Results reveal that there are high chlorophyll concentration bands in the NECC source area and its path,which are formed by the combined influence of nutrients carried by the NECC from its source area and the New Guinea Coastal Undercurrent.The upwelling of the Mindanao Dome also has a great influence on the nutrient supply.When El Niño events occurred,the westerly wind events in the tropical western Pacific increased,the NECC strengthened,a large amount of surface water moved eastward,the sea level in the study area decreased,the deep water recharge to the shallow layer increased,and the deep cold water rose.The jointly enhanced NECC,New Guinea Coastal Current,New Guinea Coastal Undercurrent and Mindanao Dome upwelling transport more nutri-ents to the sea surface from both horizontal and vertical levels,resulting in significant increases in surface chloro-phyll concentration and primary organic carbon production by all types of phytoplankton.When La Niña events oc-curred,the changes of ecohydroclimatic conditions in the NECC affected area are almost opposite to those during El Niño events,but the degree of change is weaker than that during El Nino events.The combined weakening of the NECC,the New Guinea Coastal Undercurrent and the Mindanao Dome upwelling significantly reduce the nutrients delivered to the sea surface from the horizontal and vertical levels.The chlorophyll concentration and primary or-ganic carbon production by all types of phytoplankton decreased significantly.This paper proposes a model of the response mechanism of the evolution of hydroecoclimatic conditions in the NECC affected area to El Niño and La Niña events,which is conducive to further analysis of the role of ENSO cycle in local ecological effects and hydro-climatic evolution.It has important significance for understanding the impact of global climate change on the mater-ial cycle.