There have been many instances of impactful climate changes in our planet’s history. For example, a period of cooling known as the Little Ice Age brought significant turmoil to Europe from the 15th to the mid-19th century.
Understanding the mechanisms behind such anomalies is crucial as it sheds light on the potential impacts of human-induced global warming. A team of researchers led by Dr. Anastasia Zhuravleva has made a breakthrough by examining the role of Caribbean salt in climate regulation.
Although the Little Ice Age is one of the most studied periods in recent history, the underlying climatic mechanisms remain controversial, explained the researchers.
“Looking at recent, natural climate anomalies helps to understand the processes and mechanisms that human-induced global warming may trigger,” said study lead author Dr. Anastasia Zhuravleva, lead author of the study.
“Researchers often consider an increase in sea ice extent and desalination in the subpolar North Atlantic as possible triggers for past cold periods, but processes in the tropical Atlantic appear to be equally important.”
“In fact, in contrast to the northern and mid-latitudes, there is little information on these recent climate events from the subtropical-tropical Atlantic and their impact on regions in the Northern Hemisphere,” added study co-author Dr. Henning Bauch. “This is where our research comes in.”
The interdisciplinary team, including experts from Dalhousie University in Canada and various German research institutes such as GEOMAR, AWI, and MARUM at the University of Bremen, have taken a closer look at the salinity distribution by ocean currents.
The study delves into the lesser-known climatic influences of the tropical Atlantic during historical climate anomalies and presents compelling findings about the Caribbean’s impact on ocean circulation and, consequently, the climate in the Northern Hemisphere.
Through meticulous analysis of sediment profiles and the elemental composition of plankton shells, the researchers discovered a significant 1°C cooling in the tropical Atlantic during the Little Ice Age.
“It is a significant temperature change for this region,” said study co-author Dr. Mahyar Mohtadi. “Particularly noteworthy is the occurrence of another pronounced cooling for the 8th-9th centuries. Colder temperatures in the otherwise warm tropical ocean led to lower regional rainfall, which coincided with severe droughts in the Yucatan Peninsula and the decline of the Classic Maya culture.”
Furthermore, the researchers highlight the importance of advection – the movement of tropical salt to higher northern latitudes. This process contributes to the density of the surface waters in the subpolar North Atlantic, an essential factor for the stability of large-scale ocean circulation.
“Advection, or the movement of tropical salt to high northern latitudes, is essential for maintaining high surface densities in the subpolar North Atlantic. This is a prerequisite for the overall stability of the large-scale ocean circulation, including the transfer of warm Gulf Stream water, which is responsible for our mild temperatures in Europe,” explained Dr. Bauch.
The study’s insights into the historical past enable a reconstruction of the transatlantic connection, proposing that initial cooling could be triggered by factors such as volcanic eruptions, reduced solar activity, and sea ice-ocean feedbacks in the north.
The research suggests that a decrease in salt movement to northern latitudes can amplify and prolong climate anomalies.
By contrast, a slow movement of positive salinity anomalies from the tropics might increase the density at the surface of the subpolar North Atlantic, favoring a northward heat transfer by ocean currents and potentially resulting in milder temperatures over Europe and North America.
“Such a salinity feedback is known from models and has been assumed for the Little Ice Age. However, in the absence of tropical ocean data, these assumptions have been based on less direct precipitation records,” said Dr. Zhuravleva.
In the backdrop of this historical context, the researchers note the present-day weakening of the Gulf Stream, likely influenced by human-induced warming. The study underlines the global implications of such changes and confirms that the transport of salt from south to north is a vital component in the intertwined mechanisms of our climate system.
The research is published in the journal Science Advances.
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