Wenzhe Zhang ^1,2 Chuan Gao ^1,3* Feng Tian ^1,3 Yang Yu ¹ Hongna Wang ^1,3 Rong-Hua Zhang ^3,4*

• ¹ Institute of Oceanology, Chinese Academy of Sciences (CAS), Qingdao, China
• ² University of Chinese Academy of Sciences, Beijing, Beijing, China
• ³ Laoshan Laboratory, Qingdao, China
• ⁴ Nanjing University of Information Science and Technology, Nanjing, Jiangsu Province, China

Incident shortwave radiation can penetrate and heat the upper ocean water column, acting to modulate the stratification, vertical mixing and sea surface temperature. As a light-absorbing constituent, ocean chlorophyll (CHL) plays an important role in regulating these processes; however, its heating effect on the ocean state remains controversial and exhibits strong model dependence on ways the solar radiation transmission and the related CHL-induced heating are represented. In this study, we implement a chlorophyll-based two-way coupling between physical and ecological processes within the Regional Ocean Modeling System (ROMS). The bio-physics coupled model performs well in simulating the structure and variability of oceanic physical and ecological fields in the tropical Indo-Pacific region. Three CHL-related heating terms are analyzed based on the model output to diagnose the ocean biology-induced heating effects, namely the shortwave radiation part penetrating out of the base of the mixed layer (ML; Qpen), the portion absorbed within the ML (Qabs), and the rate of temperature change of the ML resulting from the Qabs effects (Rsr). Results show that the spatio-temporal distributions of the three heating terms are mainly determined by the ML depth (MLD). However, Qpen can also be regulated by the euphotic depth (ED), especially in the western-central equatorial Pacific. This moderating effect is particularly evident during El Niño when the ED tends to be greater than the MLD; positive ED anomalies act to enhance the positive Qpen anomalies caused by negative MLD anomalies. For the first time, the bio-heating effects are quantified within the ROMS-based two-way coupling context between the physical submodel and ecological submodel over the tropical Indo-Pacific Ocean, providing a basis for further understanding of the bio-effects and mechanisms. It is expected that the methodology and understanding developed in this study can help explore the chlorophyll-related processes in the ocean and the interactions with the atmosphere.