Variability of mesoscale features in the Mediterranean Sea from XBT data analysis

G Fusco,G M R Manzella,V Zervakis,C Tziavos,C Millot,A Cruzado,Z R Velasquez,A Walne,G P Gasparini,V Kovačević,M Gačić,G Zodiatis

doi:10.5194/angeo-21-21-2003

Abstract

Abstract. During the period 1998–2000, the Mediterranean Forecasting System Pilot Project, aiming to build a forecasting system for the physical state of the sea, has been carried out. A ship-of-opportunity programme sampled the Mediterranean upper ocean thermal structure by means of eXpendable Bathy-Thermographs (XBTs), along seven tracks, from September 1999 to May 2000. The tracks were designed to detect some of the main circulation features, such as the stream of surface Atlantic water flowing from the Alboran Sea to the Eastern Levantine Basin. The cyclonic gyres in the Liguro-Provenal Basin, the southern Adriatic and Ionian Seas and the anticyclonic gyres in the Levantine Basin were also features to be detected. The monitoring system confirmed a long-term persistence of structures (at least during the entire observing period), which were previously thought to be transient features. In particular, in the Levantine Basin anticyclonic Shikmona and Ierapetra Gyres have been observed during the monitoring period. In order to identify the major changes in the thermal structures and the dynamical implications, the XBT data are compared with historical measurements collected in the 1980s and 1990s. The results indicate that some thermal features are being restored to the situation that existed in the 1980s, after the changes induced by the so-called "Eastern Mediterranean Transient". Key words. Oceanography: physical (eddies and mesoscale processes; general circulation; instruments and techniques)

Highlights

The first circulation schemes of the Mediterranean Sea were provided by Nielsen (1912), Wüst (1961), Ovchinnikov (1966), Lacombe (1973) and other authors
The results indicate that some thermal features are being restored to the situation that existed in the 1980s, after the changes induced by the so-called “Eastern Mediterranean Transient”
The Atlantic Water (AW) flowing into the Eastern Mediterranean was supposed to describe large cyclonic loops in the Ionian Sea and Levantine Basin, and an anticyclonic loop in the Gulf of Syrte

Summary

Introduction

The first circulation schemes of the Mediterranean Sea were provided by Nielsen (1912), Wüst (1961), Ovchinnikov (1966), Lacombe (1973) and other authors. The AW flowing into the Eastern Mediterranean was supposed to describe large cyclonic loops in the Ionian Sea and Levantine Basin, and an anticyclonic loop in the Gulf of Syrte This “horizontal” thermohaline circulation cell was part of two other internal cells of deep circulation, normally known as “Mediterranean Conveyor Belts”, driven by the deep waters formed in the Eastern and Western Mediterranean. The seasonal variability (strength and dimension) of many eddies (having diameters of tens of kilometres) and gyres (diameters of hundred kilometres) has yet to be determined This is an important issue since, inter alia, eddies and gyres influence the transport of properties through the basin (e.g. Malanotte Rizzoli et al, 1999).

Methods and data

Findings

Conclusions