The distribution of salt by ocean currents plays a crucial role in regulating the global climate. This is a finding of a new study published in Science Advances by researchers from Dalhousie University, GEOMAR Helmholtz Centre for Ocean Research Kiel, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), and MARUM Center for Marine Environmental Sciences at the University of Bremen. The study focuses on natural climate anomalies, including the well-known Little Ice Age, to understand the underlying climatic mechanisms and their potential implications for human-induced global warming.
The Little Ice Age, a cold period from the 15th to the mid-19th century, had severe consequences such as poor harvests, famine, and disease in Europe. Despite its significance, the mechanisms behind this climatic phenomenon are still debated. Dr. Anastasia Zhuravleva, lead author of the study, emphasizes the importance of studying recent climate anomalies to gain insights into the processes that human-induced global warming may trigger.
While researchers have often attributed past cold periods to an increase in sea ice extent and desalination in the subpolar North Atlantic, this study highlights the comparable importance of processes in the tropical Atlantic. Dr. Henning Bauch, paleoclimatologist at AWI and GEOMAR, explains that there is limited information on recent climate events in the subtropical-tropical Atlantic and their impact on regions in the Northern Hemisphere. This knowledge gap motivated the research team to investigate the tropical Atlantic’s role during historical climate anomalies and its potential influence on ocean circulation and climate in the north.
To shed light on these questions, the researchers analyzed a sediment profile from the southern Caribbean. By examining the isotopic and elemental composition of plankton shells, they reconstructed the salinity and temperature of the surface water over the past 1700 years. The results revealed a cooling of approximately 1°C during the Little Ice Age, a significant temperature change for the region. Furthermore, the study uncovered another pronounced cooling during the 8th-9th centuries, which coincided with severe droughts in the Yucatan Peninsula and the decline of the Classic Maya culture.
The study also explored the link between cold climate anomalies in the subpolar North Atlantic and Europe and weaker ocean circulation and increased salinity in the Caribbean. Dr. Bauch explains that the movement of tropical salt to high northern latitudes, known as advection, is vital for maintaining high surface densities in the subpolar North Atlantic. This plays a crucial role in stabilizing large-scale ocean circulation and facilitating the transport of warm Gulf Stream water, which, in turn, influences mild temperatures in Europe. The research findings suggest that a decrease in salt movement to high northern latitudes could intensify and prolong climate events associated with cold periods.
The study findings have important implications for understanding and predicting climate change. The slow movement of positive salinity anomalies from the tropics towards the subpolar North Atlantic can increase the surface density and favor the northward transport of heat by ocean currents. This, in turn, can result in milder temperatures over Europe and North America. Dr. Zhuravleva highlights that these assumptions have been previously based on indirect precipitation records, but the data from this study provide more direct evidence for these mechanisms.
There is growing evidence suggesting that the Gulf Stream, an important ocean current system, is weakening, and human-induced warming is likely responsible. The study confirms that the transport of salt from south to north is a critical factor in the complex interactions between different climate mechanisms. Understanding the role of salt distribution in ocean currents is essential for comprehending the global climate system and its potential responses to ongoing climate change.
The research conducted by the interdisciplinary team sheds light on the crucial role of oceanic salt distribution in regulating the global climate. Their findings demonstrate the significance of processes in the tropical Atlantic and emphasize the need for more research in the subtropical-tropical region. By unraveling the mechanisms behind historical climate anomalies, such as the Little Ice Age, scientists can gain valuable insights into potential climate responses to human-induced global warming. Ultimately, understanding the intricate interplay between ocean currents, salt distribution, and climate is essential for predicting and mitigating the impacts of climate change on a global scale.