Recently, Earth system models (ESMs) have begun to consider the marine ecosystem to reduce errors in climate simulations. However, many models are unable to fully represent the ocean-biology-induced climate feedback, which is due in part to significant bias in the simulated biogeochemical properties. Therefore, I developed the Generic Ocean Turbulence Model?Tracers of Phytoplankton with Allometric Zooplankton (GOTM?TOPAZ), a single-column ocean biogeochemistry model that can be used to improve ocean biogeochemical processes in ESMs. This model was developed by combining GOTM, a single-column model that can simulate the physical environment of the ocean, and TOPAZ, a biogeochemical module. Here, the original form of TOPAZ has been modified and modularized to allow easy coupling with other physical ocean models. To demonstrate interactions between ocean physics and biogeochemical processes, the model was designed to allow ocean temperature to change due to absorption of visible light by chlorophyll in phytoplankton. I also added a module to reproduce upwelling and the air?sea gas transfer process for oxygen and carbon dioxide, which are of particular importance for marine ecosystems. The simulated variables (e.g., chlorophyll, oxygen, nitrogen, phosphorus, silicon) of GOTM?TOPAZ were evaluated by comparison against observations. The temporal variability in the observed upper ocean (0?20 m) chlorophyll is well captured by the GOTM?TOPAZ with a correlation coefficient of 0.53 at point 107 in the East Sea. The surface correlation coefficients among GOTM?TOPAZ oxygen, nitrogen, phosphorus, and silicon are 0.47, 0.31, 0.16, and 0.19, respectively. I compared the GOTM?TOPAZ simulations with those from MOM?TOPAZ and found that GOTM?TOPAZ showed relatively lower correlations, which is most likely due to the limitations of the single-column model. Results also indicate that source?sink terms may contribute to the biases in the surface layer ( < 60 m), while initial values are important for realistic simulations in the deep sea (> 250 m). Despite this limitation, I argue that our GOTM?TOPAZ model is a good starting point for further investigation of key biogeochemical processes and is also useful to couple complex biogeochemical processes with various oceanic global circulation models.

Earth System Models (ESMs) simulating the interrelationship between atmospheric chemistry, ocean biogeochemistry, terrestrial ecology and climate processes are widely used to understand current climate and predict future climate change. However, ocean biogeochemical results show wide variability between ESMs, consequently better representation of ocean biogeochemical processes can provide pivotal information to the ESM community. In this regard, we have implemented the Tracers of Phytoplankton with Allometric Zooplankton (TOPAZ) ocean biogeochemistry model into the National Institute of Meteorological Sciences ESM. In this study, the offline version (Nucleus for European Modelling of the Ocean ? Tracers of Ocean Phytoplankton with Allometric Zooplankton v2 (NEMO-TOPAZ) of the coupled global ocean biogeochemistry model has been evaluated compared to both observational data and another biogeochemistry model (NEMO- Pelagic Interactions Scheme for Carbon and Ecosystem Studies volume 2 [PISCES]) with the same ocean physics model. Biogeochemical tracers simulated by these models showed horizontal and vertical spatial distributions similar to observations. However, limitations caused by the shared ocean physical model were found in both models. While NEMO-TOPAZ tended to over-estimate surface chlorophyll and nutrients, surface chlorophyll at the equator correlated well with the El Nino-Southern Oscillation (ENSO) and its spatial variability was better represented overall. NEMO-TOPAZ achieved superior simulation of dissolved inorganic carbon and alkalinity along with vertical distributions of biogeochemical variables in the Pacific and Atlantic Oceans. For nutrients, NEMO-PISCES showed better results overall. This model will improve scientific understanding of ocean biogeochemical processes and can be used in combination with other models for other components of the Earth’s system to develop a new ESM.

Ocean biogeochemical processes play an important role in physical ocean environments and affect the entire Earth’s climate system. Hitherto, multiple studies have been conducted on the feedback processes arising from ocean phytoplankton, which absorbs solar radiations and heat the ocean. However, the wind stress and albedo that appear from phytoplankton floating on the ocean surface have rarely been studied. Herein, a newly developed ocean-biogeochemistry model (NEMO-TOPAZ) was used to investigate the effects of changes in albedo (Alb feedback) and wind stress (Tau feedback) caused by cyanobacteria on the water temperature in the equatorial Pacific. An experiment based on the application of the photosynthetic feedback was set as the control, and a comparative analysis was performed, including the Alb and Tau feedbacks. The Alb feedback caused a slight decrease in water temperature by increasing the solar reflectance in areas where phytoplankton was present. The Tau feedback reduced the El Nino-Southern Oscillation (ENSO) amplitude by reducing the influence of trade winds. Consequently, the errors in the model (cold bias of the equatorial Pacific Sea Surface Temperature (SST) and overestimation of the ENSO amplitude) were reduced. However, it was determined that the effect of Tau feedback was overly applied, and through an additional sensitivity test, information concerning the impact of the feedback and improvement of the model was obtained. The sensitivity test results suggested that the upgrade of the applied feedback equation and determination of the optimal coefficient were required. Finally, this study highlights the importance of considering changes in the albedo and wind stress caused by plankton in climate models.