image: In the autumn of 2010, a La Niña event is formed in the tropical Pacific, characterized by a high Chl concentration. At the same time, tropical instability waves (TIWs) are active, which gives rise to large CHL perturbations as clearly observed in the eastern-central equatorial Pacific. These multiscale CHL perturbations exert effects on penetrative solar radiation in the upper ocean.
Credit: ©Science China Press
This study is led by Prof. Rong-Hua Zhang （School of Marine Sciences, Nanjing University of Information Science and Technology）. Large perturbations in chlorophyll (Chl) are observed to coexist at interannual and tropical instability wave (TIW) scales in the tropical Pacific. “At present, their combined effects on El Niño-Southern Oscillation (ENSO) through ocean biology-induced heating (OBH) feedbacks are not understood well,” Zhang says.
Zhang and his coworkers adopted a hybrid coupled model (HCM) for the atmosphere and ocean physics-biogeochemistry (AOPB) in the tropical Pacific to quantify how ENSO can be modulated by Chl perturbations at interannual and TIW scales, individually or collectively, respectively.
The team found that the HCM-based sensitivity experiments demonstrate a counteracting effect on ENSO: the bio-climate feedback due to large-scale Chl interannual variability acts to damp ENSO through its impact on upper-ocean stratification and vertical mixing, whereas that due to TIW-scale Chl perturbations tends to amplify ENSO.
The researchers also illustrated that because ENSO simulations are sensitively dependent on the ways Chl effects are represented at these different scales, it is necessary to adequately take into account these related differential Chl effects in climate modeling. A bias source for ENSO simulations is illustrated that is related with the Chl effects in the tropical Pacific, adding in a new insight into interactions between the climate system and ocean ecosystem on different scales in the region.
“These new exciting results reveal a level of complexity of ENSO modulations resulting from Chl effects at interannual and TIW scales, which are associated with ocean biogeochemical processes and their interactions with physical processes in the tropical Pacific” Zhang says.
See the article:
Zhang R H, Tian F, Shi Q, Wang X, Wu T. 2024. Counteracting effects on ENSO induced by ocean chlorophyll interannual variability and tropical instability wave-scale perturbations in the tropical Pacific. Science China Earth Sciences, 67(2): 387–404, https://doi.org/10.1007/s11430-023-1217-8
Journal
Science China Earth Sciences