WORKSHOPWORKSHOP

Deep Ocean Exchange with the ShelfDeep Ocean Exchange with the Shelf Cape Town, 6-8 October 2008Cape Town, 6-8 October 2008

The role of deep eddies in offshore The role of deep eddies in offshore transferstransfers

Isabel Ambar and Nuno SerraIsabel Ambar and Nuno Serra

Instituto de OceanografiaInstituto de Oceanografia

Faculdade de Ciências, Universidade de LisboaFaculdade 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 2001 - 18 April 2002)

AMUSE meddies

(1993-1995)

CANIGO meddies

(1997-1999)

MEDTOP meddies

(2001-2003)

float depths:

500 m

800 m

1200 m

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 dipoles - at the level of the Mediterranean Water.

Serra and Ambar (2002)

dipoleGeneration at the Portimão Canyon region

dipole

Generation at Cape St. VincentSerra 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 2001 18 June 2001

MEDTOP project

SST

12 Jun 98 – 14 Sep 9812 Jun 98 – 14 Sep 98

Data received and processed at IOFCUL

Chlorophyll pigments concentration

17 Jun 9817 Jun 98

Serra, Boutov and Ambar (to be submitted)

Vertical structure of the model dipoles

Salinity + velocity normal to the section

AnticyclonesCyclones

model SST (°C) model MW thickness (m)

Serra, 2008

surface temperature and velocity salinity and velocity at 1200 m

Serra, 2008

Model SST In situ Chl-a

Serra, 2008

SST

1 Apr 01 – 5 Aug 011 Apr 01 – 5 Aug 01 6 Jun 016 Jun 01

Serra, Boutov and Ambar (to be submitted)

Chlorophyll pigments concentration

Deep-Sea Research II 52 (2005) 383–408Observations and numerical modelling of the Mediterraneanoutflow splitting and eddy generationNuno Serra, Isabel Ambar, Rolf Kaese

Journal of Marine Systems 71 (2008) 195–220Observations of the Mediterranean Undercurrent and eddiesin the Gulf of Cadiz during 2001I. Ambar, N. Serra, F. Neves, T. Ferreira