Levantine Intermediate and Levantine Deep Water Formation: An Argo Float Study from 2001 to 2017

Elisabeth Kubin,Elena Mauri,Pierre-Marie Poulain,Milena Menna,Giulio Notarstefano

doi:10.3390/w11091781

Abstract

Levantine intermediate water (LIW) is formed in the Levantine Sea (Eastern Mediterranean) and spreads throughout the Mediterranean at intermediate depths, following the general circulation. The LIW, characterized by high salinity and relatively high temperatures, is one of the main contributors of the Mediterranean Overturning Circulation and influences the mechanisms of deep water formation in the Western and Eastern Mediterranean sub-basins. In this study, the LIW and Levantine deep water (LDW) formation processes are investigated using Argo float data from 2001 to 2017 in the Northwestern Levantine Sea (NWLS), the larger area around Rhodes Gyre (RG). To find pronounced events of LIW and LDW formation, more than 800 Argo profiles were analyzed visually. Events of LIW and LDW formation captured by the Argo float data are compared to buoyancy, heat and freshwater fluxes, sea surface height (SSH), and sea surface temperature (SST). All pronounced events (with a mixed layer depth (MLD) deeper than 250 m) of dense water formation were characterized by low surface temperatures and strongly negative SSH. The formation of intermediate water with typical LIW characteristics (potential temperature > 15 °C, salinity > 39 psu) occurred mainly along the Northern coastline, while LDW formation (13.7 °C < potential temperature < 14.5 °C, 38.8 psu < salinity < 38.9 psu) occurred during strong convection events within temporary and strongly depressed mesoscale eddies in the center of RG. This study reveals and confirms the important contribution of boundary currents in ventilating the interior ocean and therefore underlines the need to rethink the drivers and contributors of the thermohaline circulation of the Mediterranean Sea.

Highlights

The Mediterranean Sea (Figure 1) is composed of two basins of nearly equal size, the Western and the Eastern Mediterranean Sea, connected by the Sicily Channel
This study reveals and confirms the important contribution of boundary currents in ventilating the interior ocean and underlines the need to rethink the drivers and contributors of the thermohaline circulation of the Mediterranean Sea
This study aims to describe where and when Levantine intermediate water (LIW) and Levantine deep water (LDW) formation take place within the Northwestern Levantine Sea (NWLS), using Lagrangian Argo float data over a period of 16 years

Summary

Introduction

The Mediterranean Sea (Figure 1) is composed of two basins of nearly equal size, the Western and the Eastern Mediterranean Sea, connected by the Sicily Channel. The general circulation of the Mediterranean Sea can be divided into three dominant scales of motion: the basin scale including the thermohaline circulation, the sub-basin scale including permanent and quasipermanent cyclonic and anticyclonic gyres, and the mesoscale with small but energetic temporary eddies [1,2]. The salinity of the AW in the Levantine Sea depends on the circulation patterns during its path, mainly influenced by the variability of the circulation of the North Ionian Gyre (NIG) which varies significantly at seasonal and decadal scales ([3,4,5]; Figure 1a)

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