Surface Geostrophic Circulation of the Mediterranean Sea Derived from Drifter and Satellite Altimeter Data

Abstract

Drifter observations and satellite-derived sea surface height data are used to quantitatively study the surface geostrophic circulation of the entire Mediterranean Sea for the period spanning 1992–2010. After removal of the wind-driven components from the drifter velocities and low-pass filtering in bins of 1° × 1° × 1 week, maps of surface geostrophic circulation (mean flow and kinetic energy levels) are produced using the drifter and/or satellite data. The mean currents and kinetic energy levels derived from the drifter data appear stronger/higher with respect to those obtained from satellite altimeter data. The maps of mean circulation estimated from the drifter data and from a combination of drifter and altimeter data are, however, qualitatively similar. In the western basin they show the main pathways of the surface waters flowing eastward from the Strait of Gibraltar to the Sicily Channel and the current transporting waters back westward along the Italian, French, and Spanish coasts. Intermittent and long-lived subbasin-scale eddies and gyres abound in the Tyrrhenian and Algerian Seas. In the eastern basin, the surface waters are transported eastward by several currents but recirculate in numerous eddies and gyres before reaching the northward coastal current off Israel, Lebanon, and Syria and veering westward off Turkey. In the Ionian Sea, the mean geostrophic velocity maps were also produced separately for the two extended seasons and for multiyear periods. Significant variations are confirmed, with seasonal reversals of the currents in the south and changes of the circulation from anticyclonic (prior to 1 July 2007) to cyclonic and back to anticyclonic after 31 December 2005.

NORTHWARDS RANGE EXPANSION OF Sparisoma cretense (Linnaeus, 1758) IN THE TURKISH AEGEAN SEA

“…Studies based on data including last three decades showed that seawater temperature increased approximately 1-2°C (PancucciPapadopoulou et al, 2012;Bianchi et al, 2014) and warming trend is 0.06°C/year in the south Aegean Sea Skliris et al, 2011, Shaltout andOmstedt, 2014). As it is well known, the SST gradient of whole Aegean subbasin is significantly controlled by water exchange between cold/fresh Black Sea water entering through the Dardanelles Strait and warm/saline Levantine basin water entering through the Cretan Arc Straits (Zervakis et al, 2000;Poulain et al, 2012). Besides, the Aegean SST varies zonary and seasonally, even at the same latitude, due to the Etesian winds and water currents (Kotroni et al, 2001).…”

Dense intermediate water outflow from the Cretan Sea: A salinity driven, recurrent phenomenon, connected to thermohaline circulation changes

“…Theocharis et al, [2002a] observed a few years after the EMT (1997-1999) a reversal of the upper layer circulation in the Central Ionian Sea which returned to the pre-EMT cyclonic pattern, while AW re-established its pre-EMT eastward flow toward the Levantine. Further studies [Borzelli et al, 2009;Gačić et al, 2010Gačić et al, , 2011Poulain et al, 2012] have confirmed that in both 1997 and 2006 the Ionian Sea upper circulation demonstrated reversals and concluded that the changes in the Ionian Sea upper layer circulation pattern is a recurrent phenomenon occurring on an almost decadal time scale. Gačić et al [2010Gačić et al [ , 2011 proposed a feedback mechanism, named the Adriatic-Ionian Bimodal Oscillating System (BiOS), between the observed North Ionian upper layer circulation inversions and the water mass redistributions in the Ionian Sea which relate to variations of the thermohaline properties of waters formed in the Southern Adriatic Sea.…”

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

“…Although the determination of upper wind and wave-driven currents provided by the above equation may not be accurate (see for example Rascle and Ardhuin, 2009), observations do see, in general, differences between different types of drifters (Rio et al, 2014). Interestingly, these differences are very small in the Mediterranean (Poulain et al, 2009(Poulain et al, , 2012. Although the slab model has vertically homogeneous velocities, the inclusion of the Coriolis-Stokes induces vertical variations of the velocity field since, in general d S is smaller than the mixed-layer depth (H in Eq.…”

“…(20) and (23), some approaches to determine the windinduced ageostrophic contribution of the velocity field are physically based statistical models calibrated with independent observations of the velocity field, typically surface drifters (e.g., Lagerloef et al, 1999;Rio and Hernandez, 2003;Poulain et al, 2012). The most widely used model assumes…”