The distribution and movement of salt by ocean currents plays a crucial role in regulating global climate. This is what an international team of researchers led by the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany, found 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, a cold period from the 15th to the mid-19th century that led to poor crop production, famine, and disease in Europe. Although this era is one of the most studied periods in modern history, the basic climate mechanisms for its occurrence are still a matter of controversy.
“Looking at recent natural climate anomalies helps us understand the processes and mechanisms that human-caused global warming may be driving,” says Dr. Anastasia Zhuravleva, lead author of the study.
She adds that researchers often see that the increase in the extent of sea ice and the decrease in water salinity in the Arctic region and the North Atlantic Ocean were the catalysts for the occurrence of previous cold periods, but processes in the tropical Atlantic Ocean appear to be equally important. This is what called on the team to focus on… Their search in that area.
Tropical Atlantic Ocean
So, what happened in the tropical Atlantic during historical climate events, and how might potential changes affect Atlantic currents and climate in the north?
To answer these questions, the team studied sediments in the southern Caribbean Sea and reconstructed their view of the salinity and temperature of surface waters over the past 1,700 years.
The results showed a cooling of about 1 degree Celsius during the Little Ice Age. Cold temperatures in the warm tropical ocean led to regionally low precipitation, which coincided with severe drought in the Yucatan Peninsula and the decline of Classic Maya culture.
In addition, the researchers found that cold climate anomalies in the subarctic North Atlantic and Europe were accompanied by weaker ocean circulation and increased salinity in the Caribbean.
Tropical salt movement
As the researchers say in the press release published on the GEOMAR Center website, “Advection, or the movement of tropical salt, to high northern latitudes, is essential for maintaining high surface densities in the subarctic North Atlantic, and this is a prerequisite for the overall stability of large-scale ocean movement.” , including the transport of the warm Gulf Stream.
The new study provides evidence that reduced salt movement to high northern latitudes will amplify and prolong these climate events.
Conversely, the slow movement of positive salinity anomalies from the tropics will eventually lead to increased density at the subarctic North Atlantic surface. This may cause heat to be transported northward by ocean currents, resulting in milder temperatures over Europe and North America.
Finally, there is evidence that the Gulf Stream is currently weakening, and that human-induced global warming is the likely cause. What is certain is that the consequences of this change will be global.
This study confirms the extent to which different climate mechanisms interact and that the transfer of salt from south to north – as one of these mechanisms – is a major factor in the effects of climate change.