A recent study that links variations in ocean salinity and circulation to past cooling episodes like the Little Ice Age highlights the crucial role that oceanic salt distribution plays in controlling the global climate. This study highlights the interdependence of tropical and subpolar regions as well as the significance of salt flow for preserving the Northern Hemisphere’s stable climate.
The study examines the connection between ocean salinity, ocean currents, and climate
The distribution of Ocean Salinity by ocean currents is a crucial factor in controlling the global climate, according to research 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 – Centre for Marine Environmental Sciences at the University of Bremen.
Ocean Salinity
Their most recent research has focused on natural climate anomalies, such the Little Ice Age, which occurred between the 15th and the mid-19th century and had severe effects on Europe’s agriculture, starvation, and health. Even though this era has been thoroughly studied, there is still discussion on the underlying climate mechanisms.
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The study’s primary author, Dr. Anastasia Zhuravleva, states that “examining recent, natural climate anomalies helps to understand the processes and mechanisms that human-induced global warming may trigger.” In 2019, while pursuing her PhD at GEOMAR, she was awarded the Annette Barthelt Prize for her dissertation. After the study was over, she worked as a post-doctoral researcher at Dalhousie University and GEOMAR.
Importance of the Tropical Atlantic
“The processes in the tropical Atlantic appear to be equally important, but researchers often consider an increase in sea ice extent and desalination in the subpolar North Atlantic as possible triggers for past cold periods,” explains Dr. Zhuravleva. Dr. Henning Bauch, a paleoclimatologist at AWI and GEOMAR and a co-initiator and co-author of the study, continues, “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.” “Here’s where our research gets useful.”
Ocean Salinity
Thus, what transpired in the tropical Atlantic during past climate anomalies, and how could possible modifications there have impacted climate and ocean circulation far further north? The researchers reproduced the temperature and salinity of the surface water over the last 1700 years using a sediment profile from the southern Caribbean in order to address these problems. Among other things, the researchers ascertained the elemental and isotopic makeup of the plankton’s calcareous shells.
Climate Anomalies and Their Impact
The findings indicate a ±°C cooling during the Little Ice Age. According to Dr. Mahyar Mohtadi, co-author of the paper and leader of MARUM’s Low Latitude Climate Variability section, “it is a significant temperature change for this region.” The occurrence of another notable cooling for the eighth and ninth centuries is particularly significant. Lower regional rainfall caused by colder temperatures in the typically warm tropical water coincided with catastrophic droughts in the Yucatan Peninsula and the downfall of the Classic Maya culture.
Ocean Salinity
Furthermore, the researchers discovered that poorer ocean circulation and higher salinity in the Caribbean were linked to the cold climate anomalies in the subpolar North Atlantic and Europe. In order to keep surface densities high in the subpolar North Atlantic, tropical salt must advect, or travel, to high northern latitudes. This is necessary for the large-scale ocean circulation to remain stable overall and to convey warm Gulf Stream water, which is what gives Europe its pleasant temperatures, according to Dr. Bauch.
Rebuilding the connection across the North Atlantic is thus made possible by the historical data. Volcanic eruptions, low solar activity, and feedbacks between the northern sea ice and the ocean can all contribute to the initial cooling. According to the new study, these climate events will intensify and last longer if salt transport to high northern latitudes decreases. On the other hand, the subpolar North Atlantic’s surface density will gradually rise due to the gradual migration of positive salinity anomalies from the tropics. This could encourage ocean currents to carry heat northward, resulting in milder temperatures over North America and Europe.
Models have demonstrated this kind of salinity feedback, which has been hypothesised for the Little Ice Age. However, these assumptions have been based on less direct precipitation records in the lack of data from the tropical ocean, according to Dr. Zhuravleva.
Ocean Salinity
There is proof that the Gulf Stream is thinning, and the likely culprit is warming brought on by humans. One thing is for sure: this transition will have worldwide effects. It has been unclear how much the various climate mechanisms interact with one another. This study now verifies that a crucial component of the linked processes is the salt’s north-to-south transit.
Reference: “Caribbean salinity anomalies contributed to variable North Atlantic circulation and climate during the Common Era” by Anastasia Zhuravleva, Henning A. Bauch, Mahyar Mohtadi, Kirsten Fahl and Markus Kienast, 3 November 2023, Science Advances.
DOI: 10.1126/sciadv.adg2639
Ocean Salinity
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