Around 13,000 years ago, the Younger Dryas, a climate crisis, caused a significant drop in temperatures in the Northern Hemisphere, leading to severe aridity in the Mediterranean basin, which had a significant impact on terrestrial and marine ecosystems. However, what is less well-known is the impact of this climate change on water circulation in the Mediterranean.
A recent study published in Communications Earth & Environment shows that during the Younger Dryas, the flow of water masses from the eastern Mediterranean to the Atlantic Ocean across the Strait of Gibraltar doubled. The study used the innovative technique of neodymium (Nd) isotopes to reconstruct the conditions in the Mediterranean since the last deglaciation, some 14,000 years ago.
Impact of Younger Dryas
The Younger Dryas was the most intense climate change of the last 13,000 years and the most far-reaching on a planetary scale. It marked the end of the Holocene, the interglacial period in which we find ourselves today. Although there has been climate variability during the Holocene, such as the episodes known as the Little Ice Age, the Medieval Climatic Anomaly or the Roman Warm Period, this climate variability had a lower relative intensity with different regional climatic expressions, without the capacity to generate changes on a global scale.
Role of Mediterranean Waters
The study supports the hypothesis that increased salt input from the Mediterranean into Atlantic waters during the Younger Dryas was key to reactivating the North Atlantic circulation, leading to a rapid warming in Europe and the Mediterranean, which marked the beginning of the Holocene. Mediterranean water masses are one of the primary sources of salt in the North Atlantic. Water salinity is a crucial factor in oceanography, as it determines the density of water masses. Therefore, it is a key process in the formation of deep waters in the Atlantic Ocean and is the driver of global ocean circulation.
In the current context of climate change, studies such as this one are increasingly necessary to better understand the sensitivity of the Mediterranean circulation to different climatic situations. Although the Younger Dryas is not a perfect analogue for future changes, as we are currently facing a much more amplified greenhouse effect, the study reveals that the change in aridity which is expected by the end of the century is capable of inducing an intensification of the Mediterranean circulation, although the projected warming could counteract this effect. Therefore, we need to better understand the relative weight that these two variables—temperature and humidity—have had on the evolution of the Mediterranean circulation.