2:30 PM - 2:45 PM
[AOS13-04] Refining Modeled Steady-State Ocean Circulations Using Constraints of Observed Tracers
Keywords:Optimization of circulation fields, Biogeochemical cycles, Inverse modeling, Global overturning circulation, Dissolved phosphorus , Dissolved silicon
The deep North Pacific is the endpoint of the global ocean circulation, which begins with the subduction of surface waters in the North Atlantic. The water mass age in the North Pacific is estimated to be the oldest in the ocean. This area serves as a massive reservoir of regenerated nutrients and carbon, with high concentrations. When these deep waters return to the surface, the large nutrient concentration enhances biological productivity and stored carbon is released into the atmosphere. Therefore, the circulation from the deep Pacific to the surface plays a crucial role in biogeochemical cycles and the climate system.
In recent years, advances in high-precision observational data and modeling studies have improved our understanding of deep Pacific circulation. However, key aspects remain under debate, including where deep waters from the Southern Ocean upwell in the North Pacific, the intensity of their southward return flow, and their interactions with the nutrient-rich pool in the mid-depth of the North Pacific.
Studies with biogeochemical models have shown that differences in the prescribed ocean circulation fields lead to variations in the reproducibility of regenerated nutrients in the North Pacific. The variations in turn affect the interpretation of biogeochemical processes. This study aims to construct an ocean circulation field that accurately reproduces realistic tracer distributions in the North Pacific by applying an inverse approach to refine the circulation fields.
In this inversion approach, we systematically varied both the kinds of tracers used and the initial circulation fields being adjusted. We compared the resulting differences in ocean circulation patterns. Specifically, we incorporated dissolved phosphorus (P) and dissolved silicon (Si) as additional tracers alongside commonly used ones such as temperature, salinity, and water mass age (Δ14C). As initial circulation fields, we utilized two different circulation fields: one from the coupled atmosphere-ocean model MIROC and another from the OCIM circulation field, which had already been optimized using temperature, salinity, Δ14C, CFC-11, CFC-12, and δ3He.
Among the obtained circulation fields, the one that best reproduced observed tracer distributions suggested characteristics such as diffusion-dominated mixing in the mid-depth North Pacific and a vertically suppressed southward return flow of deep waters originating from the Southern Ocean. In future, applying the circulation fields that accurately reproduces tracer distributions to a biogeochemical model is expected to provide tighter constraints on quantitatively assessing biogeochemical processes.
In recent years, advances in high-precision observational data and modeling studies have improved our understanding of deep Pacific circulation. However, key aspects remain under debate, including where deep waters from the Southern Ocean upwell in the North Pacific, the intensity of their southward return flow, and their interactions with the nutrient-rich pool in the mid-depth of the North Pacific.
Studies with biogeochemical models have shown that differences in the prescribed ocean circulation fields lead to variations in the reproducibility of regenerated nutrients in the North Pacific. The variations in turn affect the interpretation of biogeochemical processes. This study aims to construct an ocean circulation field that accurately reproduces realistic tracer distributions in the North Pacific by applying an inverse approach to refine the circulation fields.
In this inversion approach, we systematically varied both the kinds of tracers used and the initial circulation fields being adjusted. We compared the resulting differences in ocean circulation patterns. Specifically, we incorporated dissolved phosphorus (P) and dissolved silicon (Si) as additional tracers alongside commonly used ones such as temperature, salinity, and water mass age (Δ14C). As initial circulation fields, we utilized two different circulation fields: one from the coupled atmosphere-ocean model MIROC and another from the OCIM circulation field, which had already been optimized using temperature, salinity, Δ14C, CFC-11, CFC-12, and δ3He.
Among the obtained circulation fields, the one that best reproduced observed tracer distributions suggested characteristics such as diffusion-dominated mixing in the mid-depth North Pacific and a vertically suppressed southward return flow of deep waters originating from the Southern Ocean. In future, applying the circulation fields that accurately reproduces tracer distributions to a biogeochemical model is expected to provide tighter constraints on quantitatively assessing biogeochemical processes.