Abstract
Abstract. 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, we 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. We 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 Sea of Japan. The surface correlation coefficients among GOTM–TOPAZ oxygen, nitrogen, phosphorus, and silicon are 0.47, 0.31, 0.16, and 0.19, respectively. We 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, we 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.
Highlights
Over several decades, climate researchers have accumulated significant knowledge on atmosphere–land–ocean feedback processes through various studies related to climate systems (Friedlingstein et al, 2006; Soden and Held, 2006; Dirmeyer et al, 2012; Randerson et al, 2015)
Tracers of Phytoplankton with Allometric Zooplankton (TOPAZ) was initially coupled with Modular Ocean Model 5 (MOM5), an ocean general circulation models (OGCMs) developed by the Geophysical Fluid Dynamics Laboratory (GFDL)
Observational results showed that the water temperature was affected by the East Sea Intermediate Water (ESIW), a finding that did not appear in the General Ocean Turbulence Model (GOTM)–TOPAZ results
Summary
Climate researchers have accumulated significant knowledge on atmosphere–land–ocean feedback processes through various studies related to climate systems (Friedlingstein et al, 2006; Soden and Held, 2006; Dirmeyer et al, 2012; Randerson et al, 2015). A single-column form of a biogeochemistry model might be a useful tool to meet the ongoing demand for improvements in biogeochemistry models in ESMs. The oceanic biogeochemical cycle affects the physical environment of the upper ocean and that of the entire climate system, and such changes produce feedback that, in turn, alters the ocean ecosystem (Hense et al, 2017; Lim et al, 2017; Park et al, 2018). SCMs are crucial for applying and testing new climate–ocean biogeochemistry feedbacks in existing ESMs. In this study, we developed the Generic Ocean Turbulence Model–Tracers of Phytoplankton with Allometric Zooplankton (GOTM–TOPAZ), which is a single-column ocean biogeochemistry model. The results produced by the model were compared to observed data and results from OGCMs to verify the reliability of GOTM-TOPAZ
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