Work Package IV

Integrated Margin-Exchange Product

The overall objective of OMEX is to understand and to measure the fluxes contributing to ocean margin exchange of the quantities of interest (notably, water, carbon, nutrients, lithogenic and biogenic particulate matter). To achieve this objective, models have important roles to play, firstly in the measurement strategy developed for each WP cruises. Secondly, because understanding is ultimately tested by the ability to form balanced budgets, to formulate and to use models successfully, in both hindcast and predictive mode. Accordingly, the aim of Work Packages IV (WP IV) is to maximise the products of the individual research partners:

• by synthesising the measurements obtained on the complementary cruises as described in WP I, II, III;

• by forming consistent flux and budget estimates from these data;

• by integrating models to form these budgets (hindcast mode);

• by studying the sensitivity to global climate change and anthropogenic inputs (predictive mode).

Key questions that have not been yet addressed, relate to the spatial structure (filaments) and spatial extent (offshore) of upwelling zones and the proportion of the year in which upwelling occurs. Hopefully, the varied and complementary space-time approaches in WP I, II and III provide the means to form budgets and integrated models, even in the presence of three-dimensional filaments and eddies. WP I focuses on time-evolution in a small drogued patch of water, minimising complexities of spatial variation. Its context will be set by WP II, which provides systematic spatial coverage, in both horizontal dimensions and through the water column, on larger scales in space and time. Both consider contrasted seasons and will survey intensively in the locality of filament and eddy structures. Remote sensing provides in-filling temporal and spatial coverage of surface features between the in situ measurements. WP III studies benthic conditions at all time scales, including the sediment record for past millennia back to the last glacial period.

This WP IV is concerned with the several aspects of integrating these approaches to form budgets and models, and with predictive use of the latter. These aspects include:

• extrapolation of relationships found in the "process-study" time-evolution approach (WP I), wherein more detailed process-related measurements are possible, to derive the values of additional variables from the spatially extensive measurements (WP II);

• intercomparison/calibration of the different measurements of comparable quantities made in the different approaches in WP I, II and III, so that all flux estimates are compatible;

• synthesis of the information of varied dimensionality, temporal and spatial resolution and extent, and the use of models, to form optimal views of ocean-margin exchange fluxes and budgets of the quantities of interest: these views may be restricted in dimension (e.g., 2-D cross-slope section) and spatial or temporal resolution (e.g., "summer" and "winter").

Specific objectives in WP IV are to form compatible estimates of fluxes at the Iberian margin, testing consistency and understanding by the formation of budgets, in respect of:

1. Water budget and circulation

2. Carbon sources, cycling and fates

3. Nutrients, trophodynamics and fertility

4. Particle dynamics, scavenging and trapping

5. Sensitivity of upwelling systems to environmental changes, with respect to local consequences of global changes and to their capacity for future anthropogenic inputs.

The final objective in this WP IV is to form an integrated margin exchange model in order to take into account all the results obtained during the fieldwork by each discipline. Even the formation of a consistent budget, for any variable other than temperature and salinity, will be an advance. Indeed, it will be an advance for these physical variables and the water budget itself in the presence of along-shelf variability. The scope of the budgeting is unique in two ways:

1. Embracing a coast with inputs of nutrient and sediment (during winter/spring runoff), of particular significance in the context of a narrow shelf;

2. Extending from air-sea exchange and near-surface primary production to the fate of deposited and buried material, in a highly productive upwelling area.

Specifically, the integration of carbon-cycle elements represents a considerable advance on the present state of the art, involving lateral import/export from river and open ocean, CO₂ exchange between atmospheric and surface waters, pelagic carbon assimilation and recycling, benthic-pelagic coupling, benthic cycling and burial. The scope of the envisaged integration of physics and biological models with benthic-pelagic coupling is correspondingly unique, and enables new estimation of sensitivities in productive upwelling systems.

Updated : 11 September 2003,  Feedback :

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