The Mediterranean Sea is among the fastest-warming marine regions of the world. As a semi-enclosed basin, it responds rapidly to atmospheric forcing and climate variability, affecting both intermediate and deep waters that are central to ecosystem functioning and biogeochemical cycles.
Hydrochanges is a long-term observational programme dedicated to monitoring temperature and salinity in key areas of the Mediterranean Sea. Supported by CIESM since 2002, it maintains sustained, high-resolution time series at strategically selected sites, including major straits, dense-water formation regions and representative deep basins.
By focusing on fixed, well-chosen locations rather than widespread coverage, Hydrochanges ensures continuity over decadal time scales. These observations allow the scientific community to:
Detect warming and salinification trends
Distinguish long-term change from interannual variability
Track how hydrographic signals propagate between sub-basins
Provide a physical reference framework for ecosystem and biogeochemical research
The programme relies on simple, robust near-bottom moored CTD systems designed to ensure durability and long-term sustainability, a fundamental requirement for detecting climate-scale changes.
Hydrochanges provides essential baseline information for regional climate research, ecosystem assessment and marine policy frameworks.
In the Mediterranean and Black Seas, variability operates simultaneously at multiple time scales, from hours to decades. Short-term campaigns capture variability, but not necessarily long-term change.
In the Mediterranean, deep-water properties are strongly influenced by episodic winter convection events. These events can abruptly modify temperature and salinity at depth, with effects that may persist for years. Without sustained observations before and after such episodes, it is impossible to determine whether they reflect:
natural oscillations
isolated extreme events
or the onset of a structural shift
Long-term time series provide three key advantages:
– Separation of signal from variability
Gradual trends can be distinguished from background fluctuations.
– Tracking of basin-scale propagation
Changes formed in one sub-basin may take years to spread elsewhere. Only fixed, continuous measurements allow this transmission to be followed across the Mediterranean system.
– Understanding system memory
Deep waters integrate atmospheric forcing over long periods. Their evolution reflects accumulated processes rather than instantaneous forcing.
For ecosystem research, this temporal perspective is fundamental. Biological responses often lag behind physical changes, and interpreting variations in oxygen, nutrient supply, or habitat conditions requires knowledge of the hydrographic trajectory over many years. Long-term monitoring transforms isolated observations into process understanding.
Hydrochanges operates as a coordinated regional initiative with clearly defined scientific and operational objectives.
1. Document the evolution of Mediterranean water masses: Maintain sustained hydrographic observations at strategic sites in order to document changes in deep and intermediate waters across different sub-basins.
2. Provide a reference framework for climate-related analyses: Deliver consistent, quality-controlled time series that allow the scientific community to assess hydrographic trends and variability in a climate context.
3. Strengthen regional observational collaboration: Foster coordination among Mediterranean institutions operating long-term moorings, encouraging methodological consistency, data comparability and scientific exchange.
4. Enable integrative scientific research: Support peer-reviewed publications and interdisciplinary studies by providing robust hydrographic baselines that can be combined with ecological, biogeochemical and modelling approaches.
The strength of Hydrochanges lies not only in the sites themselves, but in the continuity of the observations. Sustained time series provide the foundation upon which a more comprehensive and robust Mediterranean monitoring framework can progressively be built.
Network & Sites
The Hydrochanges network consists of a set of fixed mooring stations distributed across the Mediterranean Sea.
The map below shows the current locations of active and historical sites, including exchange passages and open-basin deep stations and the geographic distribution reflects the progressive development of the programme since 2002 and the contribution of participating institutions.
Publications
Partners & Institutions
For more information about the programme