Structure and variability of the subtropical gyre
The subtropical gyre is a large system of ocean cur- rents and water masses stretching across each of the oceans at mid-latitudes. Primarily driven by winds, the upper ocean circu- lation tends to accumulate water masses in the center of the gyre. This accumulation drives: a specific stratification,...
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| Format: | Text |
| Language: | English |
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2020
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| Online Access: | https://archimer.ifremer.fr/doc/00721/83302/88317.pdf https://archimer.ifremer.fr/doc/00721/83302/ |
| Summary: | The subtropical gyre is a large system of ocean cur- rents and water masses stretching across each of the oceans at mid-latitudes. Primarily driven by winds, the upper ocean circu- lation tends to accumulate water masses in the center of the gyre. This accumulation drives: a specific stratification, a large scale equatorward circulation in the upper ocean and a compensating intense and narrow current flowing poleward along the western boundary of the ocean (eg: the Gulf Stream in the North At- lantic or the Kuroshio in the North Pacific). The gyre circulation is responsible for redistributing heat taken up by the ocean at low-latitudes to the higher latitudes and to the atmosphere, as well as for storing heat and anthropogenic carbon in its water masses at mid-latitudes. The gyre dynamic furthermore leads to a shallow (1000m) ventilation of the ocean on time scale ranging from 1 to 20 years that plays a role in climate by moderating ocean-atmosphere fluxes on these intermediate timescales. Over 14 years, my work has been centered on subtropical gyres with a focus on the North Atlantic gyre and its water masses. I provide a description of my research contributions to key physical oceanographic questions: what is, and what controls, the ocean stratification structure and variability on seasonal to decadal time-scales ? I answer these questions applied to the most important subtropical gyre water mass of the North Atlantic, the "Eighteen Degree water". I show how I used geophysical fluid dynamic principles of the ocean ventilation. A clear em- phasis is made on the water-mass transformation process. I will furthermore present new analysis and diagnostic techniques I de- veloped to objectively study the ocean stratification from ocean circulation numerical simulations, ocean state estimates based on data assimilation and direct ocean measurements. Last, I conclude with the main research axes I propose to investigate in the upcoming years: the past and future variability of western boundary currents. Le gyre ... |
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