by the TRACMASS Group
October 1996
A research proposal to MAST-III (Marine Science and Technology)
TRACMASS will use a new method that employs Lagrangian trajectories to investigate the North Atlantic and Mediterranean water mass circulation as they result from numerical simulations of the global ocean. Specifically, the major goals of the project are:
We will, above all, provide a new and different perspective on the major circulation features and water mass processes of the North Atlantic ocean and the Mediterrenean and determine the connections between these and other regions of the global ocean.
Simulations from three different general circulation models will be used. One high resolution Cox-Bryan type (OCCAM), one c-grid model with depth or sigma coordintes (OPA) and one isopycnic model (GIM). The project is divided into 4 parallel sub-projects, which are all linked and dependent on each other. The first two are naturally discussed together, although their emphases are logically distinct.
In subprojects A and B we will study qualitatively and quantitatively the formation and transformation of the NADW and its origins. The NADW is probably the most important water mass the ocean produces in terms of impact on the world ocean thermohaline circulation and the climate. The NADW forms the deep part of the World Thermohaline Conveyor Belt that redistributes the heat and salt in the ocean on a global scale.
We are interested in both tracing the conditions of NADW formation and deformation. It is today unclear whether the NADW is transformed into other water masses by ventilation along isopycnals in the Southern Ocean or by diffusion through the thermocline in the tropics and other upwelling areas. We are aiming here to answer these questions by tracing the water masses in some different numerical models.
For the Lagrangian trajectories the full three-dimensional velocity fields from the models are used. The computations are made both with stationary and time varying fields. The obtained results are compared to existing data and theoretical models. We propose to calculate temperature and salinity budgets along trajectories. We will calculate these budgets for representative set of trajectories which constitute the Conveyor Belt in three different models: OCCAM, OPA and GIM. These calculations will enable us to describe the water mass transformation of Conveyor Belt water in the three models and to delineate the different processes which are responsible for this water mass transformation.
Representative subsets of trajectories from the three models are needed which describe the Conveyor Belt. These subsets consist of sets of four-dimensional fields of coordinates as a function of time [x(t),y(t),z(t)], which define the various trajectories.
Project management structure
Project coordinator: Kristofer Döös
Four parallel subprojects:
A The origin and formation of the NADW. Coordinator: Sybren Drijfhout
The NADW is partly formed due to the high salinity of the North Atlantic. The sources of this salt is believed to be either form the Aghulas, the Caribbean or the Mediterranean. We are here going to focus our attention on the Mediterranean Waters possible influence on the NADW.
The NADW is characterised by a deep salinity maximum in a large part of the World Ocean. It is also characterised by relatively high temperatures. The source of the high temperature and salinity is the warm and salty water of the NADW return flow in the thermocline. Up till now it is still unclear whether these high temperature and salinity water mass characteristics are imported into the Atlantic from outside (Indian Ocean/Agulhas Current), or, whether they are acquired by mixing along trajectories in the Atlantic itself (mixing with Caribbean or Mediterranean Water) or, whether they result from air/sea interaction with that part of the NADW return flow which resides in the ocean's mixed layer.
B. The fate and transformation of the NADW. Coordinator: Kristofer Döös
C. The Mediterranean Water (MW) mass circulation. Coordinator: Volfango Rupolo
D. Theoretical studies of the trajectory methods. Coordinator: Bruno Blanke
The Partnership
The contribution of each person in the project is more relevant than each partner since we are all going to be highly nested into each others work. Here is therefore a list of all the participants, their main qualifications for the project and on which sub-projects they are going to be the most active in.
Vincenzo Artale (ENEA): C. He has worked on the Mediterranean.
Email: vincenzo@canaletto.casaccia.enea.it
Bruno Blanke (LODYC): A, B and C. He was the first to calculate Lagrangian trajectories as an exact solution to model output (Blanke and Raynaud, 1996) He will continue to see how the time dependency can be included in the analytical Lagrangian trajectories and it's impact. He has worked on the Analysis of the OPA model. He should be able to deliver to the rest of the project better methods or error bars on the present methods to calculate the mass transport.
Email: blanke@univ-brest.fr
Andrew Coward (SOC): A and B. He is an expert on OCCAM and has worked on the calculation of the Lagrangian trajectories from OCCAM datasets.
Email: Andrew.Coward@soc.soton.ac.uk
Kristofer Döös (SOC): A, B and D. He was the first to use Blanke and Raynaud's (1996) Lagrangian trajectories to calculate mass transports and used them to estimate the Inter-ocean exchange of water masses in the Southern Ocean (Döös, 1996)
Email: Kristofer.Doos@soc.soton.ac.uk
Sybren Drijfhout (KNMI): A. He has worked on the tracing of the Conveyor Belt in the past (Drijfhout et al. 1996).
Email: drijfhou@knmi.nl
Peter Killworth (SOC): D. He is in particular interested in the effects of the eddy-induced bolus transport on Lagrangian trajectories he will also be an invaluable help to the whole project as an "eminence grise".
Email: Peter.D.Killworth@soc.soton.ac.uk
Mei-Man Lee (SOC): D. She has worked on Lagrangian trajectories vs.
passive tracers in a density coordinate model (MICOM).
Email: Mei-Man.Lee@soc.soton.ac.uk
Robert Marsh (SOC): A, B and D. He has been working on the analysis of isopycnic models in the past and is here going to work implement a Lagrangian calculation in the Global Isopycnic Model (GIM).
Email: Robert.Marsh@soc.soton.ac.uk
Volfango Rupolo (ENEA): C. Expert on the Mediterranean circulation
Email: volfango@canaletto.casaccia.enea.it
Sabrina Speich (LPO-UBO): B and C. She has been working on the analysis of OPA from a Lagrangian trajectory aspect in the past and will.
Email: speich@univ-brest.fr
The Laboratories are:
ENEA (Ente per le Nouve technologie, l'Energia et l'Ambiente) - Partner
KNMI (Koninlijk Nederlands Meteorologisch Instituut) - Partner
LODYC (Laboratoire d'Océanographie Dynamique et de Climatologie) - Associated partner
LPO-UBO (Laboratoire de Physique des Océan a l'Université de Bretagne Occidentale) - Partner
SOC (Southampton Oceanography Centre) - Coordinator