Climate Change and the European Water Dimension - Agri ...

the processes controlling, regional to global and seasonal to inter-annual fluxes of
carbon between the atmosphere and the ocean, and their sensitivity to climate
changes. The role and the complexity of the continental margins on the marine
biogeochemical cycles was quickly highlighted, calling for the launch of two other
IGBP core projects, the Global Ocean Ecosystem Dynamics (GLOBEC) in 1995, and
the Land-Ocean Interactions in the Coastal Zone (LOICZ) in 1993. Both projects
consider global change in the broad sense, encompassing the gradual processes of
climate change, as well as shorter-term changes resulting from anthropogenic
pressures. The numerous studies conducted thus far in the frame of LOICZ and its
European counterpart, the ELOISE cluster (Murray et al. 2001), have contributed to
substantial knowledge on climate change science, addressing both coastal
ecosystems and coastal hydrology and their complex interplay between atmosphere,
ocean, and land systems.
In this chapter, the contribution of recent scientific results to our increasing
knowledge and understanding of the coastal system are presented and to what
extent changes in the various compartments of that system could reflect or be
indicative of a climate change. The chapter is divided into sections addressing
climate impact on the hydrography and chemistry of the coastal system, the carbon
pool and budget, potential shifts in the coastal ecosystem, and changes in coastal
habitats.
IV.C.2. Hydrography
Coastal systems encompass a wide range of environmental conditions over short
spatial gradients, particularly with respect to salinity content and chemical speciation
controlled in many ways by the hydrologic cycle. Hence, any climatic disturbances
affecting the sea level, the rate of precipitation, freshwater runoff, and evaporation,
will have direct consequences on the geochemistry of coastal waters.
Global warming is responsible for a general increase in sea level due to thermal
expansion of the water on the one hand, and melting of glaciers and polar ice caps,
on the other hand. According to IPCC (2001), the sea level is rising at 1 to 2mm/yr
on average, threatening most coastal regions and causing major problems just at the
time when rapid coastal development is taking place. Sea level, however, appears to
be rising at different rate depending on the oceanic regions (Figure IV.C.1),
interfering with other processes such as tides, evaporation, or even various tectonic
processes (e.g. seismic disturbance and volcanic action) that may lead to crustal
motions along the coastline.
During the last 2 centuries, sea level has increased significantly in the Baltic with a
clear shift in the rate of change at the end of the 19 th century from 1.8 cm/century to
9.9 cm/100 yrs (Omstedt et al. 2004). This is correlated with a decrease in the
probability of ice occurrence, particularly in the southern Baltic, and a tendency for
shorter ice periods (Jevrejeva et al. 2004).
The progression of sea level is different for the Mediterranean Sea where a shift is
observed at several tide gauge stations from an increasing trend (ca. 1.2-1.5 mm.yr -1 )
before 1960 to a decreasing trend (ca. -1.3 mm.yr -1 ) after 1960 (Tsimplis and Baker
2000). Recent data indicate another trend reversal around 1995 with a rapid rising of
sea level, up to 20 mm.yr -1 in the eastern Mediterranean (Figure IV.C.2.), as
observed from field measurements as well as satellite altimetry (Cazenave et al.
2001;Tsimplis and Rixen 2002). Whether the sudden rise in sea level since the mid-
1990’s represents a long-term trend or an inter-annual/decadal fluctuation is still an
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