The Mediterranean Sea is one of the foremost areas of the world where interannual and long term climatic variability is predominant. It is a complex basin with high levels of ocean-atmosphere-land interactions, and evidently plays a role disproportionate to its size within the global climate system. For instance, the outflow of deep water from the Gibraltar Strait preconditions the climatically important North Atlantic Deep Water. The long-range transport of dust from Sahara influences the entire European region as well as parts of North Atlantic and Red Sea region. The aerosols in turn determine the atmospheric fluxes of heat and materials into these regions, and could play a major role in the marine ecosystems.
On the other hand, the Mediterranean itself is a delicate system sensitive to the effects of global change. Because its deep waters have a relatively short mean residence time (~100 years), The Mediterranean Sea is fundamentally very sensitive to climate variability, and possibly to climate change. The elements of the system are basin, sub-basin and mesoscale circulation features, and characteristic subdomains (broad shelf regions and river dominated areas, narrow continental margins, and deep ocean oligotrophic areas). The elements of the system are interconnected cells or subdomains (ecological microcosms) which can be studied separately to develop an understanding of the response to change.
Two main forms of thermohaline circulations determine the intermediate and deep water properties of the Mediterranean Sea. One of these is the closed thermohaline cell renewing the bottom waters in each of the main (eastern and western) basins. The other is the open cell starting at the Gibraltar Straits, and extending to the eastern basin, where Lewantine Intermediate Water is formed, and ending again at the Gibraltar Straits. The circulation and water properties in either of these cells have recently been subjected to significant changes.
Land-ocean interactions in coastal regions lead to eutrophication problems linked to human activity and hydrological changes. Lessepsian migration of organisms and introduction of foreign species are also very important in modifying the ecosystem structure, which is already undergoing recent change, even in the absence of migration.
The priority of future research, to evaluate Global Change impact
or forcing in the region, can be proposed as follows:
- effects of temperature and fertilization changes on the productivity
of characteristic subdomains (river driven systems, shelf areas and oligotrophic
deep ocean);
- continued monitoring to include new types of measurements covering
long term, extreme events, and extending to previously unexplored regions
including the open ocean and some parts of the southern and eastern Mediterranean
Sea,
- better understanding of convection and thermohaline circulation leading
to deep and intermediate water renewal, and determining the residence time
and productivity of waters in the system,
- role of atmospheric transport of aerosols in the radiative budget
of the region, role of atmospheric aerosols and nutrients in photoreactive
kinetics of the atmospheric constituents, and resultant supplies to the
ecosystem,
- development of modeling technique to accommodate sufficiently high
resolution air-sea fluxes and to provide a better representation of the
effects of land topography; development of data assimilation methodology,
and calibration of models based on measurements of physical and biological
state variables,
- investigation of the atmospheric teleconnections of Mediterranean
climate system with other global systems (such as the Indian monsoon and
ENSO events).
Needs for Monitoring
The following parameters are considered to have priority for studies
evaluating global change impacts / forcing in the region: SST, sea level,
temperature and salinity in the water column, precipitation, evaporation,
and riverine fluxes, fluxes of nutrients and biogenic materials from rivers
and coastal sources, fluxes between the shelf and open ocean regions, biomass
and community structure of marine organisms, fluorometric measurements
of chlorophyll in surface and intermediate waters, solar radiation and
heat budgets, air-sea interaction parameters, chemistry, concentrations
and surface deposition rates of atmospheric aerosols and nutrients, as
well as satellite derived information, including altimetry, SST and pigments.
These measurements are especially needed in the open ocean; but better
resolution and continued monitoring of coastal areas are also needed. It
is noted that this set of measurements are compatible with the overall
requirements of the GOOS (Global Ocean Observing System) context, in planning
for the future.
- strategic, long-term monitoring of straits are needed to determine
changes in the fluxes of mass, and chemical, biogenic matter between the
various basins of the Mediterranean Sea (e.g. Gibraltar, Otranto, Sicily,
Bosphorus and Dardanelles Straits).
Other recommendations
- the creation of common, intercalibrated and quality controlled data
sets are urgently needed, and have to be made available to the community
for process and climate change studies.
- stronger cooperation among entire boundaries of the Mediterranean,
including capacity building and training, should be encouraged and supported
to increase scientific productivity in the near future.
- interdisciplinary interactions with other groups studying climate
effects in relation to desertification, atmospheric chemistry, paleogeography
and paleoecology are highly needed.