Scientists study deep waters of western Mediterranean

Scientists from Oceanographic Centres in the Balearic Islands, the Spanish Institute of Oceanography in Gijón and the University of Oviedo have published a study in the 'Journal of Geophysical Research: Oceans', evaluating the characteristics of the deep waters of the Western Mediterranean between 2005 and 2017 after an event in the winter of 2005 that caused a series of drastic changes in its deep layers.

The work analyses the role that successive deep water renewals have played in its evolution and the mixture of its properties with other water bodies present in the basin.

During the severe winter of 2005, there were five episodes of Arctic and Siberian winds and significant snowfalls throughout the Western Mediterranean and IEO scientists detected the appearance of an anomaly in the temperature and salinity of deep waters in the area.

The exceptional production of deep waters with infrequent temperatures and salinities induced a series of drastic changes in the deep layers of the western Mediterranean.

This event was at the beginning of a period called the Western Mediterranean Transition, or WMT, which led to important changes throughout the Mediterranean basin. Its evolution has been studied thanks to ocean observation programs at the Spanish Institute of Oceanography.

The study results show that the deep waters of the western Mediterranean in 2017 were substantially hotter, saltier and denser than they were prior to 2005, mainly because of those formed between 2005 and 2006 and between 2011 and 2013, which injected a large amount of heat and salt to the deep layers of the basin.

In the period analysed, the waters present in abyssal depths suffered considerable heating and salination, registering an increase in temperature and salinity of 0.059 ° C and 0.021, respectively.

These waters are formed in certain years in the northwest of the basin during the winter months when the intermittent action of the northern component continental winds in the Gulf of León cools the surface layers of the sea while increasing evaporation and salinity, making them denser.

When these surface layers become sufficiently dense they sink to the bottom of the basin. This is the main mechanism for the renewal and ventilation of the waters present in the deepest parts of the western Mediterranean.

The Mediterranean is a continuous source of warm saline water and plays an important role in the processes of deep water formation in the North Atlantic and the global circulation of the ocean.

The deep water of the western Mediterranean contributes to the characteristics of this water, which leaves the basin through the Strait of Gibraltar, so these types of studies and the observation systems that support them are important for evaluating heat transfer to the ocean.

Global Depth

"The warming rate in the Western Mediterranean is proportionally higher than estimates for the first 2000 metres of depth of the global ocean in recent decades," says Study Author, Safo Piñeiro.

“Another relevant conclusion is that, as the bottom density and stratification increase, the waters that form in the Gulf of León currently need to reach a higher density to sink to the bottom of the basin than those prior to 2005. This has a very important implication in the renovation and ventilation of deep waters and for the biological communities that inhabit them,” says co-Author, Rosa Balbín.

The study was carried out within the framework of the project 'Study of the thermohaline anomaly in the deep waters of the western Mediterranean and its relation to climatic oscillations', or ATHAPOC, whose objective is to study the WMT and its relation to climatic oscillations.

The project was funded by the State Plan for Scientific & Technical Research & Innovation 2013-2016, coordinated by the Researcher of the IEO Oceanographic Centre of the Balearic Islands, or COB, Rosa Balbín and Director of the doctoral thesis of Safo Piñeiro, hired predoctoral at the COB through the 2015 call in the framework of the State Program for the Promotion of Talent and its Employability of the State Plan for Scientific and Technical Research and Innovation 2013-2016.