An international research team comprising scientists from Dalhousie University in Canada, GEOMAR Helmholtz Centre for Ocean Research Kiel, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), and MARUM at the University of Bremen has uncovered the pivotal role of salt distribution by ocean currents in regulating the global climate. Their study, focusing on natural climate anomalies, sheds light on the Little Ice Age, a cold period from the 15th to the mid-19th century, which had significant societal impacts, including poor harvests, famine, and disease in Europe.
The Little Ice Age is one of the most studied periods in recent history, yet the underlying climatic mechanisms responsible for it remain a subject of debate. “Looking at recent, natural climate anomalies helps to understand the processes and mechanisms that human-induced global warming may trigger,” says Dr. Anastasia Zhuravleva, lead author of the study.
While researchers have previously considered increased sea ice extent and desalination in the subpolar North Atlantic as possible triggers for past cold periods, this study emphasizes the importance of processes in the tropical Atlantic. To explore these tropical processes, the team studied a sediment profile from the southern Caribbean, reconstructing salinity and temperature in the surface water over the last 1700 years.
The results of the study reveal a cooling of approximately 1°C during the Little Ice Age in the tropical Atlantic—a significant temperature change for the region. Notably, a pronounced cooling occurred during the 8th-9th centuries, leading to lower regional rainfall and severe droughts in the Yucatan Peninsula, contributing to the decline of the Classic Maya culture.
Moreover, the research indicates that cold climate anomalies in the subpolar North Atlantic and Europe coincide with weaker ocean circulation and increased salinity in the Caribbean. This is essential for maintaining high surface densities in the subpolar North Atlantic and overall stability in large-scale ocean circulation, including the transfer of warm Gulf Stream water that influences Europe’s climate.
The study provides evidence that a decrease in salt movement to high northern latitudes amplifies and prolongs climate events such as the Little Ice Age. Conversely, the slow movement of positive salinity anomalies from the tropics increases surface density in the subpolar North Atlantic, favoring the northward transport of heat by ocean currents and resulting in milder temperatures over Europe and North America.
The research highlights the importance of the south-north transport of salt in the Earth’s climate system and its role in climate regulation. With evidence of the weakening Gulf Stream, attributed to human-induced warming, the study underlines the global consequences of this change. The interaction between different climate mechanisms and the role of salt transport in these processes have been key questions, and this study confirms the significance of south-north salt transport as a fundamental factor.
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Reference: https://www.sciencedaily.com/releases/2023/11/231103170642.htm
