Liquid climate archives: a study on tide levels in the straits

New European achievements in research for Ca' Foscari University: a new study published by the prestigious scientific journal "Scientific Reports" reveals how tidal measurements can tell us something about the masses of ocean water – and therefore the climate – of the past, and act as "liquid climate archives".

The currents and water masses of the deepest part of the ocean play a fundamental role in the evolution of the planet’s climate, because they affect the interactions between ocean and atmosphere and thus contribute to determining the local, regional and global climate. It is thus extremely important that they be described and understood. Unfortunately, hardly any information in this regard is available from the past; very few deep measurements were taken until recent decades.

The study, co-authored by Angelo Rubino, professor of Oceanography at Ca' Foscari University of Venice, along with the researcher Davide Zanchettin, demonstrates that it is possible to obtain the lacking data, at least partially, via the study of strait dynamics. In such areas, in fact, there are often a number of different stations for tide measurement which have been operational for over a century. The main discovery gleaned by this new research is that, surprisingly, variations in the position of the sea’s surface measured by these stations contain information that may also affect many phenomena occurring under the surface of the adjacent basins. It is precisely the morphology of the straits that enables researchers to amplify these signals and transmit them up to the surface.

The discovery began, as often happens in science, with an empirical observation: the team, composed of researchers hailing from Ca' Foscari University of Venice, the Alfred-Wegener Institute of Bremerhaven (Germany), and the P. P. Shirshov Institute of Oceanology of St Petersburg (Russia), noted that the sea level measured at Messina did not correspond to that of Catania, merely tens of kilometers away, and that the trend representing the variation in this difference over time overlapped with the periodic alternation in water circulation of the nearby Ionian Sea basin.

With the use of a numerical model for describing strait dynamics, the scholars were able to demonstrate that the empirical relationship is supported by a physical explanation: the clockwise rather than counter-clockwise movement in the Ionian Sea pushes water masses of different densities into the vicinity of the Strait of Messina and the different densities affect the strait dynamics.

"What we have concluded,” explain Angelo Rubino and Davide Zanchettin, two of the study’s co-authors, “is that the differences between the sea levels of Messina and Catania measured in the early 1900s are similar to those of today; therefore we hypothesize that variations in the circulation of the Ionian Sea similar to those observed recently may have taken place in the past."

The study demonstrates that some “lost” data pertaining to local deep sea variability can be recovered. As the team explains, "It can thus be confirmed that regions such as straits, where different water masses are coming into contact, constitute a sort of "magnifying lens" to highlight the dynamics of the deep sea and make it possible to put together some "liquid archives" for climate research.”