WORKSHOP Deep Ocean Exchange with the Shelf Cape Town, 6-8 October 2008 The role of deep eddies in offshore transfers Isabel Ambar and Nuno Serra Instituto de Oceanografia Faculdade de Ciências, Universidade de Lisboa

Chlorophyll pigments (11 July 2002) SST (11 July 2002) Surface filaments and eddies are known as key factors in the transfer processes of mass, heat and momentum between shelf and deep ocean regions.

Do sub-surface eddies, like those detaching from the Mediterranean Undercurrent off Iberia – the meddies - play a role in the transfers from shelf to deep ocean ? Richardson, 2000 Question

Meddies are Mediterranean Water lens-like coherent structures, existing at depths from 600 to 1400 m, in solid body anticyclonic rotation, with typical diameters of about 50 – 100 km. 50 – 100 km 800 m 600 m 1400 m

Floats launched during MEDTOP

Eddy generation at Estremadura Promontory (23 April April 2002)

AMUSE meddies ( ) CANIGO meddies ( ) MEDTOP meddies ( ) float depths: 500 m 800 m 1200 m

dipoles In the last decade, field observations off the southern coast of Iberia were able to detect the presence of cyclones associated with meddies to form vortex pairs - dipoles - at the level of the Mediterranean Water. Serra and Ambar (2002) dipole Generation at the Portimão Canyon region dipole Generation at Cape St. Vincent Serra et al. (2002) meddy cyclone

These cyclones play a role on the detachment of the meddies from the Mediterranean Undercurrent and seem to be fundamental for the translation of meddies away from their generation zone. Cape St Vincent promotes the overshoot and separation of the MW Undercurrent Advection or anticyclone- cyclone coupling provides detachment Serra, Ambar and Käse (2005) Eddy generation at Cape St. Vincent

Eddy generation at the Portimão Canyon region Stretching of the MW layer at the Portimao Canyon induces cyclonic vorticity Serra, Ambar and Käse (2005) Cyclone extracts MW from the slope -> dipole ejection

The dynamical fields associated with the meddies and cyclones extend vertically much farther than the depth range where the thermohaline anomaly is detected, and may reach levels down to 3000 m or up to the sea surface. Oliveira, Serra, Ambar & Fiúza (2000)

Dipole followed by remote sensing (sea surface temperature) and by RAFOS 25 May June 2001 MEDTOP project

SST 12 Jun 98 – 14 Sep 98 Data received and processed at IOFCUL Chlorophyll pigments concentration 17 Jun 98 Serra, Boutov and Ambar (to be submitted)

Vertical structure of the model dipoles Salinity + velocity normal to the section Anticyclones Cyclones

model SST (°C) model MW thickness (m) Serra, 2008

surface temperature and velocitysalinity and velocity at 1200 m Serra, 2008

Model SST In situ Chl-a Serra, 2008

SST 1 Apr 01 – 5 Aug 01 6 Jun 01 Serra, Boutov and Ambar (to be submitted) Chlorophyll pigments concentration

Deep-Sea Research II 52 (2005) 383–408 Observations and numerical modelling of the Mediterranean outflow splitting and eddy generation Nuno Serra, Isabel Ambar, Rolf Kaese Journal of Marine Systems 71 (2008) 195–220 Observations of the Mediterranean Undercurrent and eddies in the Gulf of Cadiz during 2001 I. Ambar, N. Serra, F. Neves, T. Ferreira