The distribution and movement of salt by ocean currents plays a crucial role in regulating the global climate. That's what an international team of researchers led by the Geomar Helmholtz Ocean Research Center in Kiel, Germany, finds in a new study published in the journal Science Advances.
Little Ice Age
To reach that conclusion, the team studied natural climate anomalies, including the so-called Little Ice Age, the cold period from the 15th century to the mid-19th century that led to poor crop production, famine and disease in Europe. Although this is one of the most studied periods in modern history, the underlying climatic mechanisms of its occurrence are still controversial.
Dr Anastasia Juravleva, lead author of the study, said: "Looking at recent natural climate anomalies helps us understand the processes and mechanisms that human-induced global warming may lead to.
"Researchers often see increased sea ice volumes and reduced water salinity in the North Atlantic as catalysts for previous cold periods, but operations in the tropical Atlantic seem to be equally important," she says, prompting the team to focus their research in that region.
Atlantic currents that distribute heat are affected by changing salinity in tropical and subtropical parts of it (geomar)
Equatorial Atlantic Ocean
So, what happened in the equatorial Atlantic during historical weather events, and how could potential changes affect Atlantic currents and climate in the North?
To answer these questions, the team studied sediments in the southern Caribbean and reconstructed their perception of the salinity and temperature of surface water over the past 1700,<> years.
The results showed cooling of about one degree Celsius during the Little Ice Age. Cold temperatures in the warm tropical ocean led to lower regional rainfall, which coincided with severe drought on the Yucatán Peninsula and the decline of classical Mayan culture.
In addition, the researchers found that cold climate anomalies in the North Atlantic subarctic and Europe were accompanied by poor ocean circulation and increased salinity in the Caribbean.
Tropical salt movement
As the researchers say in a press release published on the Geomar Center website, "Horizontalism, or the movement of tropical salt, to high northern latitudes, is necessary to maintain high surface densities in the North Atlantic subarctic, and this is a prerequisite for the overall stability of large-scale ocean movement, including the transfer of the Warm Gulf Stream.
The core of a sample of Caribbean sediments where the research team studied salinity changes (Geomar)
The new study provides evidence that reduced salt movement to upper northern latitudes will amplify and prolong these weather events.
Conversely, the slow movement of positive salinity anomalies from the tropics will eventually lead to increased density on the surface of the North Atlantic subarctic. This could cause heat to move north via ocean currents, leading to milder temperatures over Europe and North America.
Finally, there is evidence to suggest that the Gulf Stream is currently weakening, that human-induced global warming is the likely cause, and what is certain is that the consequences of this change will be global.
This study emphasizes the interplay of different climate mechanisms and that the transition of salt from south to north, as one of them, is a major factor in the effects of climate change.