New Development of Eastern Mediterranean Circulation based on Hydrological Observations and Current Measurements

Abstract

A number of recent studies based on hydrographic observations and modelling simulations have dealt with the major climatic shift that occurred in the deep circulation of the Eastern Mediterranean. This work presents hydrographic observations and current measurements conducted from 1997 to 1999, which reveal strong modifications in the dynamics of the upper, intermediate and deep layers, as well as an evolution of the thermohaline characteristics of the deep Aegean outflow since 1995. The reversal of the circulation in the upper layer of the north/central Ionian is worthy of note. The observations indicate a reduction of Atlantic Water in the northern Ionian with an increase on the eastern side of the basin. In the intermediate layer, the dispersal path of the Levantine Intermediate Water (LIW) is altered. Highly saline (> 39.0) and well-oxygenated intermediate waters were found near the Western Cretan Arc Straits. They flow out from the Aegean, thus interrupting the traditional path of the LIW, and spread prevalently northwards into the Adriatic Sea. In the deep layer, dense waters, exiting from the Adriatic (s q~2 9.18 kg´m ±3 ), flow against the western continental margin in the Ionian Sea at a depth of between 1000±1500 m. Dense waters of Aegean origin (> 29.20 kg´m ±3 ), discharged into the central region of the Eastern Mediterranean during the early stages of the transient, propagate prevalently to the east in the Levantine basin and to the west in the northern Ionian Sea. Near-bottom current measurements conducted in the Ionian Sea reveal unforeseen aspects of deep dynamics, suggesting a new configuration of the internal thermohaline conveyor belt of the Eastern Mediterranean. U. S.

Abyssal undular vortices in the Eastern Mediterranean basin

“…We note that Manca et al 15,20 observed the arrival of deep water of Adriatic origin at the base of the Sicily escarpment during 1991 that was possibly able to produce some reversals in the main bottom flow, which, at the time, was dominated by an anticyclonic motion. However, these authors also pointed out that during 1999 the region was still occupied by waters of Aegean origin, as confirmed by other studies 14,30 .…”

“…Also as a consequence of such a complexity, in the Ionian basin, deep waters can differ considerably in their characteristics, dynamics and routes, which are partly determined by the underlying bathymetry 5 . Note also that the beginning of the new millennium can be considered as a period of large variability for water mass formation and stratification in the EM 5,6,[12][13][14][15][16] .…”

The circulation pattern in the Mediterranean Sea: issues for modeller consideration

“…Intensive field experiments conducted from the early 1980s within the international co-operative research POEM programme (Physical Oceanography of the Eastern Mediterranean) demonstrated that a single homogeneous water body filled the entire Eastern Mediterranean below a depth of about 1200m. 42 They mentioned that the deep water column is characterised by potential temperature and salinity slowly decreasing with depth, which implies a very low static stability.…”

Exploring Relationships between Demersal Resources and Environmental Factors in the Ionian Sea (Central Mediterranean)

“…This flux interrupted the traditional path of Levantine Intermediate Waters (LIW) spreading northwards into the Ionian Sea and eastwards into the Levantine basin and affecting the dynamics of the upper, intermediate, and deep layers. During the EMT an uprising of the nutrients close to the euphotic zone occurred in the northern and eastern Ionian [12,15]. This large modification in the eastern Mediterranean circulation lasted approximately 10 years, until 1997 when the general Ionian cyclonic circulation was restored [15,16].…”

“…The most important and evident phenomenon that involved the change in circulation and thermo-haline properties of the water masses is the so-called Eastern Mediterranean Transient (EMT), corresponding to the shift in deep water formation in the eastern basin from its usual source in the southern Adriatic to a new source in the Aegean Sea [12][13][14][15]. Even though such a change included the whole Mediterranean, some basins such as the Ionian, Adriatic, and Levantine basin were primarily involved.…”