A Coupled Ocean Physics‐Biology Modeling Study on Tropical Instability Wave‐Induced Chlorophyll Impacts in the Pacific

Abstract

Tropical instability waves (TIWs) play an important role in modulating the physical variability (e.g., sea surface temperature [SST] and heat flux) and biological activity (e.g., phytoplankton and chlorophyll (Chl)) in the eastern tropical Pacific. The impacts of TIW‐induced Chl perturbations (ChlTIW) are examined using a coupled ocean physics‐biology model in the tropical Pacific. TIW‐scale biological and physical perturbations are extracted using a zonal high‐passed filter. The TIW‐induced perturbations of biological and physical fields (e.g., Chl, nitrate, iron, and SST.) exhibit their close relationships, with negative correlation between SST and Chl at TIW scale. Processes responsible for the impacts of ChlTIW are diagnosed. ChlTIW acts to modulate the incoming solar radiation that penetrates the bottom of the mixed layer (Qpen). In addition, two experiments are conducted with the impacts of ChlTIW on the ocean included or not. The results show that the ChlTIW effects tend to substantially increase seasonal variability of eddy kinetic energy (EKE) and slightly decrease SST in the eastern equatorial Pacific. At large scale, ChlTIW leads to an increase in mean Chl concentration, which induces a SST cooling and an increase in EKE in the boreal winter. At TIW scale, ChlTIW leads to the change in Qpen and a decrease in baroclinic conversion term and eventually decreases the EKE in the boreal spring and summer. So the ChlTIW acts to have influences both on the intensity of TIW and large‐scale SST in the tropical Pacific, involving multiscale interactions and feedbacks between ocean physics and biology.

A Positive Feedback Onto ENSO Due to Tropical Instability Wave (TIW)‐Induced Chlorophyll Effects in the Pacific

“…Compared with FILT (Figure S8), the SST is cooling by 0.1–0.2 °C in CTRL during La Niña event, demonstrating the Chl TIW effect induces a cooling during La Niña event. This result is also consistent with previous ocean general circulation model study (Tian et al, ).…”

“…Additionally, the HCM can well simulate coherent structure of SST and Chl at TIW scale (Figures a–d); that is, high Chl concentration corresponds to cold SST phase, whereas low Chl concentration corresponds to warm SST phase (Figures c–d). The amplitude of Chl TIW is 0.05–0.1 mg/m 3 , which is in good agreement with estimates from observations (Tian et al, ).…”

“…High and low chlorophyll concentrations are associated with cold and warm phases of TIWs‐induced perturbations in SST ( SST TIW ), with the amplitude of Chl TIW reaching 0.05 mg/m 3 (Evans et al, ; Gorgues et al, ; Legeckis et al, ; Menkes et al, ; Strutton et al, ; Yoder et al, ). Furthermore, presence of Chl TIW influences the redistribution of solar radiation in the upper ocean and consequently weakens the intensity of TIW itself (Tian et al, ). In particular, penetrative solar radiation induced by Chl TIW changes ocean stratification, with the reduced baroclinic conversion rate between eddy available potential and eddy kinetic energy (EKE).…”

Effects on Ocean Biology Induced by El Niño‐Accompanied Positive Freshwater Flux Anomalies in the Tropical Pacific

“…The model used in this study is a coupled ocean physics‐biogeochemistry model (Tian et al, ; Wang et al, ; Wang, Le Borgne, et al, ; Zhang et al, ), which consists of an ocean general circulation model (OGCM) and a biogeochemistry model. It is also the ocean component of the hybrid‐coupled model for atmosphere‐ocean and biogeochemistry (HCM‐AOPB), which is employed in ZH19.…”

“…Previous studies documented basic performances of the coupled ocean physics‐biogeochemistry model, which shown that the model could well simulate mean state, seasonal cycle, and interannual variability in the physical and biological fields (Tian et al, ; Wang et al, , ; Zhang et al, ). Figure shows the response of chlorophyll to ENSO for the observations and model forced by observed and reanalysis atmospheric forcing.…”