The last great planetary climate crisis caused a great loss of water from the Mediterranean

Around 13,000 years ago, a climate crisis caused a global drop in temperatures in the Northern Hemisphere.

Oliver Thansan
Oliver Thansan
22 May 2023 Monday 14:38
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The last great planetary climate crisis caused a great loss of water from the Mediterranean

Around 13,000 years ago, a climate crisis caused a global drop in temperatures in the Northern Hemisphere. This episode of intense cold, known as the Younger Dryas or Recent Dryas, also caused great aridity throughout the Mediterranean basin, which had a great impact on terrestrial and marine ecosystems. But what do we know about the impact that this climate change had on the circulation of water in the Mediterranean?

One of the most recently known data regarding this process is that during the Younger Dryas the flow of water masses from the eastern Mediterranean to the Atlantic Ocean through the Strait of Gibraltar doubled, according to a study led by researchers from the University of Barcelona (UB) whose results have been published in the journal Communications Earth

The study is part of the doctoral thesis being developed by Sergio Trias-Navarro, under the direction of Professor Leopoldo Pena and Professor Isabel Cacho, from the Consolidated Research Group (GRC) in Marine Geosciences of the Faculty of Earth Sciences of the UB.

The work presents some of the most relevant results of the TIMED project of the European Research Council (ERC-Consolidator Grant), and has an outstanding participation of members of the GRC in Marine Geosciences, and experts from La Sapienza University of Rome, the University of Palermo (Italy), and the Federal Polytechnic School of Zurich (Switzerland).

The Younger Dryas is the most intense climate change in the last 13,000 years and with the greatest impact on a planetary scale. Its completion marked the end of the Holocene, the interglacial period in which we currently find ourselves. "During the Holocene there has also been climate variability, as now the episodes known as the Little Ice Age, the medieval climate anomaly or the Roman warm period. But this climate variability had a lower relative intensity with different regional climate expressions, without the ability to generate changes on a global scale", details Professor Isabel Cacho, from the Department of Earth and Ocean Dynamics.

The work also analyzes the last sapropel [in marine geology, dark-colored mud that forms on the ocean floor], a Holocene episode after the Younger Dryas linked to an extraordinary increase in rainfall in the Mediterranean region, especially in the north from Africa. The study provides the first quantification of the changes that occurred in the deep circulation of the eastern Mediterranean during this episode, and has estimated that they were four times smaller than the changes produced during the Younger Dryas. As for the impact that this event could have had on the oceanography of the North Atlantic, experts indicate that it is unknown.

The new work supports the hypothesis that the increase in the contribution of salt from the Mediterranean to the Atlantic waters during the Younger Dryas was key to reactivating the North Atlantic circulation: it generated rapid warming in Europe and the Mediterranean, which marked the beginning of the Holocene.

"The Mediterranean water masses are one of the primary sources of salt in the North Atlantic. The salinity of the waters is an important factor in oceanography, since it determines the density of the water masses. Therefore, it is a key process in the formation of deep waters in the Atlantic Ocean and is the motor of global ocean circulation", highlights the researcher Sergio Trias-Navarro.

As in previous GRC work in Marine Geosciences, the team has applied the innovative technique of radiogenic neodymium isotopes as geochemical tracers to reconstruct past oceanographic conditions. This analytical work has been carried out in the LIRA and PANTHALASSA laboratories, unique research support facilities in Catalonia located in spaces of the Faculty of Earth Sciences and the Scientific and Technological Centers of the UB (CCiTUB) and coordinated by the experts Leopoldo Pena and Isabel Cacho.

"Compared to other types of geochemical tracers, neodymium isotopes have the great advantage of being conservative. Therefore, they do not interact or are affected by biological processes, for example, biological productivity or the degradation of organic matter," he highlights. Professor Leopoldo Pena, co-author of the work. "This technique allows us to go beyond time and can be applied to oceanographic reconstructions of the present as well as of the past. Thus, it allows us to know the dynamics of the ocean and reconstruct oceanography long before we could observe or measure it ourselves with other scientific tools. "adds the expert.

There are still many unknowns about the potential impact of Mediterranean waters on the North Atlantic circulation. Despite there being more scientific interest, "many of the oceanographic studies focused on the Atlantic Ocean do not consider the Mediterranean, and perhaps the role of Mediterranean waters in the Atlantic circulation has been minimized", the authors remark.

The latest report from the Intergovernmental Panel on Climate Change (IPCC) presents the Younger Dryas as an example of the foreseeable changes in rainfall that will take place in the Mediterranean as a consequence of an expected reduction in the North Atlantic circulation. "On the other hand, according to the projections for the end of the 21st century, the circulation of the Mediterranean will weaken and, consequently, its contribution to the Atlantic Ocean will also weaken," says Isabel Cacho, coordinator of the TIMED project. In the current context of climate change, studies like this are increasingly necessary to better understand the sensitivity of the Mediterranean circulation to different climatic situations.

"The Younger Dryas is not a perfect analogue for future changes, as we are currently dealing with a much more amplified greenhouse effect. Even so, our work reveals that the change in aridity expected by the end of the century is capable of inducing an intensification of the Mediterranean circulation, although the expected warming could counteract this effect. For this reason, we need to better understand the relative weight that these two variables —temperature and humidity— have had on the evolution of the Mediterranean circulation", concludes the research team.

Reference scientific article:

Trias-Navarro, S.; Pena, L.D.; de la Fuente, M.; Walls, E.; Garcia-Solsona, E.; Frigola, J.; Catala, A.; Caruso, A.; Lirer, F.; Haghipour, N.; Noel Pérez-Asensio, J.; Cacho, I. "Eastern Mediterranean water outflow during the Younger Dryas was twice that of the present day". Communications Earth