5:15 PM - 6:45 PM
[ACG32-P16] Pathways of the North Pacific intermediate circulation estimated by Lagrangian particle tracking based on high-resolution modeling
Keywords:eddy-resolving ocean model, North Pacific Intermediate Water, Lagrangian particle tracking
The North Pacific intermediate circulation which forms and transports North Pacific Intermediate Water is an important circulation that carries the carbon dioxide absorbed from the atmosphere into the ocean interior and transports the nutrients supplied from the deep ocean to the surface. It is thought to play a significant role in climate change and biological production. However, there are still many uncertainties regarding the pathways, transformation processes, and timescale by which the surface water is linked to the intermediate water. It has also been suggested that the intermediate circulation transports heat to the deep ocean through tide-induced vertical mixing and thus has a significant influence on the deep circulation. However, the interaction between the intermediate circulation and the deep circulation, such as the impact of the former on the latter’s pathway and volume transport and the transport processes of deep water to the intermediate layer, has not been fully understood. Previous studies have shown that eddies play an important role in the transport of North Pacific Intermediate Water, so it is necessary to employ an eddy-resolving resolution to properly capture the North Pacific intermediate circulation in ocean models. In this study, we investigate the three-dimensional structure of the North Pacific intermediate circulation using an eddy-resolving ocean model. Based on the high spatiotemporal resolution flow field obtained by the ocean model, we estimate the pathways and timescales of the North Pacific intermediate circulation by using Lagrangian particle tracking.
We employed a nested global ocean model, where a model with 1/12°horizontal resolution for the North Pacific is nested into a global model with 1/4°horizontal resolution. It is initialized by the temperature and salinity of World Ocean Atlas 2018 and forced by the JRA55-do atmospheric reanalysis data. We utilized the velocity and diffusivity fields obtained by integrating the model for 50 years for particle tracking. Virtual particles are initially placed over the entire surface of the North Pacific. After 30 years’ tracking, we extracted the particles that reside in the density layer of North Pacific Intermediate Water.
The positions of the particles that are initially placed north of 40°N, where the subarctic gyre exists, and in the intermediate layer after 30 years are shown in the figure. The colors indicate the depth of particles, and the snapshots at the years 0 (at the start of tracking), 10, 20, and 30 are depicted. From the year 10 and 20, it is found that the particles are transported by the subarctic gyre to the Sea of Okhotsk and the Bering Sea, sink to depths around 400 m, and flow southward and enter deeper layers mainly through the Kuroshio Extension region. These particles spread eastward by the subtropical gyre in mid-latitudes. Some of the particles that are initially placed in the eastern subarctic region are transported by the eastern boundary current into the subtropical region and gradually descend deeper into the layer of North Pacific Intermediate Water in the subtropical gyre. In the presentation, we will discuss the detailed pathways of the North Pacific intermediate circulation, the governing processes for the pathways, and the ventilation timescale of the intermediate layer.
We employed a nested global ocean model, where a model with 1/12°horizontal resolution for the North Pacific is nested into a global model with 1/4°horizontal resolution. It is initialized by the temperature and salinity of World Ocean Atlas 2018 and forced by the JRA55-do atmospheric reanalysis data. We utilized the velocity and diffusivity fields obtained by integrating the model for 50 years for particle tracking. Virtual particles are initially placed over the entire surface of the North Pacific. After 30 years’ tracking, we extracted the particles that reside in the density layer of North Pacific Intermediate Water.
The positions of the particles that are initially placed north of 40°N, where the subarctic gyre exists, and in the intermediate layer after 30 years are shown in the figure. The colors indicate the depth of particles, and the snapshots at the years 0 (at the start of tracking), 10, 20, and 30 are depicted. From the year 10 and 20, it is found that the particles are transported by the subarctic gyre to the Sea of Okhotsk and the Bering Sea, sink to depths around 400 m, and flow southward and enter deeper layers mainly through the Kuroshio Extension region. These particles spread eastward by the subtropical gyre in mid-latitudes. Some of the particles that are initially placed in the eastern subarctic region are transported by the eastern boundary current into the subtropical region and gradually descend deeper into the layer of North Pacific Intermediate Water in the subtropical gyre. In the presentation, we will discuss the detailed pathways of the North Pacific intermediate circulation, the governing processes for the pathways, and the ventilation timescale of the intermediate layer.