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Title : Meso and submesoscale variability within the Peruvian upwelling regime observed by a fleet of seven gliders
Name of the speaker : S. Thomsen
Affiliation : GEOMAR-Kiel
Laboratory organizer : LOCEAN
Date and time : 10-10-2014 11h00
Location : UPMC - 4 place Jussieu - Paris 5e - Tour 45-55 - 4e étage - LOCEAN - salle de réunion
Summary :

A swarm experiment with seven gliders equipped with sensors measuring pressure, temperature, salinity, oxygen and chlorophyll fluorescence was conducted in early 2013 within the upwelling region off Peru. The goal was to study the role of meso- and submesoscale proccesses for the near-coastal oxygen ventilation of the Peruvian oxygen minimum zone. Each glider carried out about one dive per hour measuring two multi-parameter profiles with a lateral resolution less than 300 m. About 15.000 profiles were recorded during the two-months deployment within a small spatial area to capture both the temporal and spatial variability of the physical and biochemical parameters.

Two main results are presented in the talk:

1) The formation of a low oxygen mode water eddy within the Peru Chile Undercurrent is observed. The near-coastal horizontal circulation off Peru at 12°S changes significantly over the two months of observation. In early January, we observe a pronounced Peru-Chile Undercurrent with maximal poleward velocities of 25 cm/s in
100 - 200 m depth. A week later the circulation start to change and a mode water eddy forms within the glider field. The physical and biogeochemical eddy properties and impacts on the near-coastal salinity and oxygen distribution are described in detail.

2) During an upwelling event the formation and decay of a submesoscale cold water filament is present in the sea surface temperature and glider data. Near the surface, non-density compensated salinity and oxygen intrusions are observed which seem to be associated with this feature. These anomalies reach well below the mixed layer into the thermocline and frontal subduction is suggested as their formation mechanism.

Thomsen S. (1), Kanzow T. (1,2), Krahmann G. (1), Dengler M. (1),
Richard Greatbatch (1) and Gaute Lavik (3)

(1) GEOMAR Helmholz Centre for Ocean Research, Kiel, Germany
(2) The Alfred Wegener Institute, Helmholtz Centre for Polar and Marine
Research, Bremerhaven, Germany
(3) Max Planck Institute for Marine Microbiology, Bremen, Germany