02.12.2021: Ocean Circulation and Climate Dynamics Colloquium

When?     Thursday, 2. Dezember 2021 at 4 pm
Where?    ZOOM meeting room: https://geomar-de.zoom.us/j/87324779769?pwd=cFNMcFJKOW8xaE1nNGR0ZWc1cVpqdz09

Meeting-ID: 873 2477 9769
Kenncode: 720307

Abstract:
Contrary to surface currents, which have been extensively studied thanks to the large number of observations provided by satellites and other in-situ measurements, currents under the thermocline have so far been observed only sporadically, and this lack of knowledge remains a major obstacle to the improvement of climate models. This is particularly the case at low latitudes, where deep circulation feedbacks on atmospheric variability and ecosystem variability have been demonstrated. Recent observations have shown that at low latitudes, the mean deep circulation is organized in systems of alternating jets. They correspond to narrow currents that flow zonally across the entire width of the oceans and whose direction reverses periodically with latitude off the equator and with depth at the equator. The physical processes involved in the formation of these deep jets, as well as the impact of this circulation on the distribution of water masses on a regional scale are still largely unknown.
In my talk, I will explore these two issues.
The transport and mixing of water masses by deep jets are highlighted from in-situ observations in the equatorial Pacific. It is shown that, on the one hand, the alternating jets contribute to the transport of ventilated water masses from the western boundary to the oxygen minimum zone located at the eastern boundary. On the other hand, these jets are associated with local intensifications of isopycnal mixing, which participate in the erosion of water masses coming from both hemispheres and advected towards the equator by subtropical gyres.
In addition, the physical processes of formation of these jets are studied. An original analysis of deep-drifting float trajectories reveals that intra-annual planetary waves are, at low latitudes, a major source of energy for the deep ocean. From a theoretical approach and idealized numerical simulations, it is shown that such waves are unstable by non-linear interactions and can transfer their energy to jet-like secondary waves, compatible with the scales of the observed jets. 

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