296
w. Roether, B. Klein
has moved nearer to the euphotic zone compared to the classical situation (Klein et
aI., 1999).
The changes were presumably initiated by a change in the near-surface
circulation that diverted high-salinity waters from the Levantine Sea into the Aegean
Sea and blocked the intrusion of less saline surface waters from the Ionian Sea
(Malanotte-Rizzoli et aI., 1999). In combination with enhanced cooling during a
particularly cold winter, this led to the formation of very dense waters (Lascaratos
et aI., 1999; Wu et aI, 2000). The situation was self-sustaining in that the dense
waters overflowing the sills of the Aegean Sea were replaced by more saline nearsurface and intermediate waters from the Levantine Sea. A contributing factor has
been that the LIW, rather than taking its classical westward route south of Crete,
took a path through the southern Aegean Sea. More recently the Aegean outflow has
become less dense so that it reached to intermediate depths only, by which it was
enabled to intrude the South Adriatic Basin. As the resulting salt import into the
Adriatic preconditions dense water production in the classical deep water formation
region, the THZ of the sea may in fact move back toward the classical situation
(Klein et aI., 2001).
The transient effected a net deposition of salt in the deep waters of the Eastern
Mediterranean. While part of this salt originated from shallower strata in which
salinity was lowered, and a further part can be ascribed to increased net evaporation
during the past decade, it appears that a substantial fraction originated from the
Western Mediterranean. This means that the entire Mediterranean has been involved
in the salt deposition in the Eastern Mediterranean deep waters, pointing to a
complex interaction. The westward outflow through the Strait of Sicily has been
lowered in salinity, and a similar, albeit smaller salinity decrease may occur in the
Mediterranean outflow into the Atlantic, with the faint possibility of affecting the
formation of North Atlantic Deep Water. The development of the deep oxygen field
(Fig. 3) indicates that deep water oxygen consumption, which was rather high
already in the classical situation (Roether and Well, 2001) has become still larger.
A possible explanation is that the transient effected a fast downward transfer of
dissolved organic carbon from the euphotic zone. The increase is indication that the
changes have severly disturbed the entire biogeomechistry of the deeper waters of
the sea.
The future will see continued changes in the hydrography and biogeochemistry
of the Eastern Mediterranean waters. Considering that the turnover time of the deep
waters is on the order of 100 years (Roether and Schlitzer, 1991; Roether and Well,
2001), the Eastern Mediterranean deep waters evidently will remain in a transient
state for many decades to come. Should the system move close to its previous,
classical situation, this will be accompanied by a higher salt and a lower nutrient
supply to the upper waters as the deep waters return toward the surface.
The present and future implication of the ongoing Eastern Mediterranean
Transient can be summarized as follows:
1. Textbooks may mislead one: The Eastern Mediterranean has become a different
ocean and is now in a transient state.
w. Roether, B. Klein
has moved nearer to the euphotic zone compared to the classical situation (Klein et
aI., 1999).
The changes were presumably initiated by a change in the near-surface
circulation that diverted high-salinity waters from the Levantine Sea into the Aegean
Sea and blocked the intrusion of less saline surface waters from the Ionian Sea
(Malanotte-Rizzoli et aI., 1999). In combination with enhanced cooling during a
particularly cold winter, this led to the formation of very dense waters (Lascaratos
et aI., 1999; Wu et aI, 2000). The situation was self-sustaining in that the dense
waters overflowing the sills of the Aegean Sea were replaced by more saline nearsurface and intermediate waters from the Levantine Sea. A contributing factor has
been that the LIW, rather than taking its classical westward route south of Crete,
took a path through the southern Aegean Sea. More recently the Aegean outflow has
become less dense so that it reached to intermediate depths only, by which it was
enabled to intrude the South Adriatic Basin. As the resulting salt import into the
Adriatic preconditions dense water production in the classical deep water formation
region, the THZ of the sea may in fact move back toward the classical situation
(Klein et aI., 2001).
The transient effected a net deposition of salt in the deep waters of the Eastern
Mediterranean. While part of this salt originated from shallower strata in which
salinity was lowered, and a further part can be ascribed to increased net evaporation
during the past decade, it appears that a substantial fraction originated from the
Western Mediterranean. This means that the entire Mediterranean has been involved
in the salt deposition in the Eastern Mediterranean deep waters, pointing to a
complex interaction. The westward outflow through the Strait of Sicily has been
lowered in salinity, and a similar, albeit smaller salinity decrease may occur in the
Mediterranean outflow into the Atlantic, with the faint possibility of affecting the
formation of North Atlantic Deep Water. The development of the deep oxygen field
(Fig. 3) indicates that deep water oxygen consumption, which was rather high
already in the classical situation (Roether and Well, 2001) has become still larger.
A possible explanation is that the transient effected a fast downward transfer of
dissolved organic carbon from the euphotic zone. The increase is indication that the
changes have severly disturbed the entire biogeomechistry of the deeper waters of
the sea.
The future will see continued changes in the hydrography and biogeochemistry
of the Eastern Mediterranean waters. Considering that the turnover time of the deep
waters is on the order of 100 years (Roether and Schlitzer, 1991; Roether and Well,
2001), the Eastern Mediterranean deep waters evidently will remain in a transient
state for many decades to come. Should the system move close to its previous,
classical situation, this will be accompanied by a higher salt and a lower nutrient
supply to the upper waters as the deep waters return toward the surface.
The present and future implication of the ongoing Eastern Mediterranean
Transient can be summarized as follows:
1. Textbooks may mislead one: The Eastern Mediterranean has become a different
ocean and is now in a transient state.