Long-term monitoring programme of the hydrological variability in the Mediterranean Sea: a first overview of the HYDROCHANGES network

Abstract

Abstract. The long-term monitoring of basic hydrological parameters (temperature and salinity), collected as time series with adequate temporal resolution (i.e. with a sampling interval allowing the resolution of all important timescales) in key places of the Mediterranean Sea (straits and channels, zones of dense water formation, deep parts of the basins), constitute a priority in the context of global changes. This led CIESM (The Mediterranean Science Commission) to support, since 2002, the HYDROCHANGES programme (www. ciesm.org/marine/programs/hydrochanges.htm), a network of autonomous conductivity, temperature, and depth (CTD) sensors, deployed on mainly short and easily manageable subsurface moorings, within the core of a certain water mass. The HYDROCHANGES strategy is twofold and develops on different scales. To get information about long-term changes of hydrological characteristics, long time series are needed.Published by Copernicus Publications on behalf of the European Geosciences Union. K. Schroeder et al.: Long-term monitoring programme of hydrological variabilityBut before these series are long enough they allow the detection of links between them at shorter timescales that may provide extremely valuable information about the functioning of the Mediterranean Sea. The aim of this paper is to present the history of the programme and the current set-up of the network (monitored sites, involved groups) as well as to provide for the first time an overview of all the time series collected under the HYDROCHANGES umbrella, discussing the results obtained thanks to the programme.

Characterizing, modelling and understanding the climate variability of the deep water formation in the North-Western Mediterranean Sea

“…• data from one of the HYDROCHANGES deep moorings (Schroeder et al 2013). Initiated in 2003, the HYDROCHANGES programme aims at recording time series of the hydrological characteristics of the water masses and of their variability in key places (straits, DWF areas, trenches, .…”

“…Long-term and continuous monitoring of the phenomenon started only recently thanks to the HYDROCHANGES programme with deep moorings (Schroeder et al 2013) and to the integrated observing system MOOSE (Mediterranean Ocean Observing System for the Environment, www.moose-network.fr) since 2010 with annual and monthly CTD cruises and continuous recording by surface buoys and deep moorings (Testor et al 2012;Durrieu de Madron et al 2013). Therefore, our current knowledge of the long-term variability of the phenomenon before 2007 mainly comes from yearly case studies and sparse field campaigns (Leaman and Schott 1991;Schott et al 1996;Schroeder et al 2008;Durrieu de Madron et al 2013) or from satellite-derived reconstructions .…”

Comparison of high resolution hydrodynamic model outputs with in-situ Argo profiles in the Ionian Sea

“…Furthermore, at the south-eastern part of the basin, dense water outflow has been recorded during 2009 from the Aegean Sea, that followed a northward path along the Hellenic Trench giving a signal of increased salinity in the intermediate layers . This outflow was the result of the preconditioned for dense water formation status of the Aegean that has been reported for the period 2007-2012 (Schroeder et al, 2013;Krokos et al, 2014;Cardin et al, 2015;Kassis et al, 2015) and resulted in the alternation of the southeastern Ionian upper and intermediate waters. The aforementioned short term inter-annual changes in the area's hydrography create a challenging field for the performance of numerical hydrodynamic simulations.…”

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

“…Data collected in the framework of the HYDROCHANGES program [Schroeder et al, 2013] from a permanently moored CTD station at the bottom (850 m) of the Antikythira strait, showed that there were episodic According to Kontoyiannis et al [1999b], water masses denser than LIW with densities up to 29.16-29.18 kg/m 3 were formed during 1986, 1992, and 1995 in the Rhodes Gyre area, reaching depths of 1000 m in 1986 and 1995 and even deeper ( 2000 m) during the peak-EMT period in 1992. To investigate the possible existence of similar water masses being formed in the same area during the period examined in this work, deep ARGO profiles at the wide area of the Rhodes Gyre between 2005 and 2012 were examined.…”