Tracer transport by a cold-core ring pinched-off from the Kuroshio Extension in an eddy-resolving ocean general circulation model
Abstract
By using an eddy-resolving ocean general circulation model, we examine a cold-core ring pinched-off from the Kuroshio Extension (KE). We try to fill a gap in previous studies, which examine the ensemble effects of rings in realistic simulations and the effects of individual rings in idealized settings and observations. For this purpose, we mostly concentrate on a single cold-core ring in an eddy-resolving OGCM in detail, mainly focusing on its tracer transport. This study has the following specific targets. (1) How does the cold-core ring carry tracers along and north of KE? (2) What are the impacts of the ring's transport on the tracer fields in the ring and the RG region? For the targets of tracers, we consider biogeochemical components as well as temperature and salinity. The modeled ring is pinched off from KE when the first trough of KE extends southward as far as 33N. The cold-core ring is composed of a core water from north of KE wrapped by the KE water. The ring moves westward and rejoins KE four months later. This life history of the ring is comparable that of observed rings in terms of sea surface height (SSH) fields as well as its energetics. Leakage from the ring is directly estimated using passive tracers and Lagrangian particles and is diagnosed using the potential vorticity (PV). High PV water originated from KE at the outer edge of the ring hinders the leakage. The high PV signal diminishes as the density increases from 26.4σ. Then the leakage becomes growing. At densities lower than 26.4σ, the core water is not left in the recirculation gyre to the south of KE because it is not released from the ring until the ring rejoins KE. At these densities, the KE water is transported to the recirculation gyre in the form of disturbances associated with the pinch-off process and wave-like structures along KE, rather than the leakage from the ring. At densities greater than 26.4σ, both the waters are transported through disturbances and the wave-like structures as well as the leakage. Due to the difference in salinity of these waters, their transport contributes to increase vertical gradient of salinity and formation of the North Pacific Intermediate Water. It is found that the bell-shaped high nitrate at 100-500 m at the center of the ring, which is essential for high chlorophyll concentration in the ring, comes from north of KE. Accordingly, the nutrient supply around 100 m, where high chlorophyll maximum appears, is not caused by only the vertical movement due to the isostasy but also directly from the movement of nutrient along the ring.Concentration of the Kuroshio Extension Water at 26.0σ one month after the pinch-off of the cold-core ring.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS32B..03N
- Keywords:
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- 4255 OCEANOGRAPHY: GENERAL / Numerical modeling;
- 4520 OCEANOGRAPHY: PHYSICAL / Eddies and mesoscale processes;
- 4576 OCEANOGRAPHY: PHYSICAL / Western boundary currents;
- 4805 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Biogeochemical cycles;
- processes;
- and modeling